Effects of Response Contingent and Noncontingent CocaineInjection on Hypothalamic-Pituitary-Adrenal Activity in RhesusMonkeys1

JILLIAN H. BROADBEAR, GAIL WINGER, THEODORE J. CICERO, and JAMES H. WOODS

Departments of Psychology (J.H.B., J.H.W.) and Pharmacology (G.W., J.H.W.), University of Michigan Medical School, Ann Arbor, Michigan;and Department of Psychiatry, Washington University, St. Louis, Missouri (T.J.C.)

Accepted for publication March 24, 1999 This paper is available online at http://www.jpet.org

ABSTRACTEarlier studies of cocaine’s effects on the hypothalamic-pitu-itary-adrenal (HPA) axis used nonresponse-contingent designsin which the investigator determined dose, timing, and route ofadministration. It is important to evaluate whether “control”over cocaine delivery is a significant determinant of cocaine’sHPA axis effect. This study measured cocaine’s effects onplasma adrenocorticotropic hormone and cortisol, using non-response-contingent injections followed later by response-con-tingent cocaine delivery. In addition, the effects of cocainehistory on the HPA response to a noncontingent injection of 1mg/kg of cocaine were measured. HPA effects of corticotropin-releasing hormone (CRF) were also measured. Male and femalerhesus monkeys, with surgically placed venous catheters, weretested in their home cages. Up to 13 injections of saline and

cocaine (0.01-, 0.03-, 0.1-, and 0.3-mg/kg/injection) were ad-ministered at 10-min intervals (nonresponse-contingent condi-tion) and on a fixed ratio 30, time out 10-min schedule ofreinforcement. Overall, cocaine delivered response contin-gently produced larger, more dose-dependent HPA responsesthan did noncontingent delivery. The HPA response to a 1mg/kg cocaine infusion in cocaine-naive monkeys was notpredictive of the HPA effect of this dose subsequent to acqui-sition of cocaine self-administration. Overall, male monkeyshad larger HPA responses to cocaine than did female monkeys.Finally, the HPA effects of CRF were significantly correlatedwith those of large cocaine doses delivered nonresponse con-tingently, but not with response-contingent administration.

Cocaine administration activates the hypothalamic-pitu-itary-adrenal (HPA) axis in rats (Rivier and Vale, 1987; Sa-phier et al., 1993), rhesus monkeys (Broadbear et al., 1999;Sarnyai et al., 1996) and humans (Vescovi et al., 1992;Heesch et al., 1995; Ward et al., 1998), increasing the releaseof plasma adrenocorticotropic hormone (ACTH) and the glu-cocorticoids cortisol or corticosterone. In most of the studiesthat have examined the relationship between cocaine andHPA axis activation, the dose, route, and frequency of co-caine’s administration were controlled by the investigator(e.g., Sarnyai et al., 1996; Spangler et al., 1997) using proce-dures that may have incorporated restraint, hypodermic in-jection, and anesthesia, each of which may itself have ele-vated HPA axis activity (Setchell et al. 1975; Elvidge et al.,1976; Puri et al., 1981; Reinhardt et al., 1990; Piazza et al.,1991). This can be problematic, because an increase in stress

hormones before drug administration may blunt the effectproduced by the drug (Dallman and Jones, 1973; Sarnyai etal., 1996). Therefore, it may be difficult to separate the con-tribution of cocaine to HPA activation from that of the exper-imental procedure. Procedural confounds may be problematiceven for subjects apparently familiarized with the procedurebefore testing, because the elevation in HPA response mayremain despite repeated presentation of a stressful handlingprocedure (Coe et al., 1983; Hattingh et al., 1988; Higley etal., 1992; Kirschbaum et al., 1995).

Does the method by which cocaine is administered affectthe degree to which the HPA axis is activated? The issue of“control” over stimulus delivery, and how this may affectphysiological and behavioral responses to the stimulus, hasbeen addressed in a number of studies. Studies of this naturemay employ a yoked-control design, where subjects in the“control” group respond to present, postpone, or terminatestimulus delivery, whereas those in the “yoked” group receiveidentical stimulus deliveries as their matched controls butare unable to alter their delivery. The HPA axis response toaversive stimuli has been found to vary between subjects in

Received for publication December 7, 1998.1 This work was supported by the United States Public Health Service

Grant DA 09161. Results from this study were originally presented at theannual meeting of the International Society of Psychoneuroendocrinology inAugust, 1998.

ABBREVIATIONS: HPA axis, hypothalamic-pituitary-adrenal axis; ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone;FR, fixed ratio; TO: time out.

0022-3565/99/2901-0393$03.00/0THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 290, No. 1Copyright © 1999 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A.JPET 290:393–402, 1999

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yoked-control designs. For example, rhesus monkeys thatlearned to press a lever to terminate high-intensity noise hadlower cortisol levels than their yoked counterparts (Hansonet al., 1976), even though they were exposed to the samesound intensity and duration. Monkeys trained in the “con-trol” group and then transferred to the “yoked” group had thehighest cortisol levels. Similar findings were reported in ratsin a yoked-control shock postponement paradigm (Herrmannet al., 1984). In the case of rewarding stimuli, two studieshave examined the conditions under which animals will workto terminate the delivery of a formerly reinforcing stimulus.In the first, rats rapidly learned to terminate the delivery ofi.c. self-stimulation when it was delivered in a pattern iden-tical with what had been self-administered on an earlieroccasion (Steiner et al., 1969). Similarly, squirrel monkeysworked simultaneously to obtain and terminate cocaine ad-ministration when drug delivery was controlled by two dif-ferent, concurrent contingencies (Spealman, 1979). Bothstudies demonstrate that there are circumstances underwhich the same stimulus can maintain behavior that leads toboth its delivery and its avoidance, and highlight how areinforcer may be aversive under conditions where the sub-ject does not instigate its delivery.

Previously, we demonstrated that self-administered co-caine produces dose-dependent increases in plasma ACTHand cortisol in male rhesus monkeys (Broadbear et al., 1999)and, in a pilot to the present study, that automatic infusionsof cocaine using the same doses and pattern of delivery gen-erated by each monkey the previous day led to identicalcortisol levels (Broadbear et al., 1997). It was unclearwhether the extensive cocaine self-administration history ofthese subjects may have influenced the results. The presentstudy was designed in part to address this issue.

There were three purposes to this study. The first was todetermine whether the effects of cocaine on the HPA axiswere different when cocaine delivery was either responsedependent or response independent. The second was to de-termine whether the effects of cocaine on the HPA axis weremodified by a history of cocaine self-administration. Thethird was to determine whether parallels existed betweenHPA responsiveness to an infusion of corticotropin-releasinghormone (CRF) and to infusions to cocaine under the differ-ent contingencies.

Experimental ProceduresSubjects

Five adult male rhesus monkeys (Macaca mulatta), four intact,and one castrated (monkey 1583), weighing between 9.0 and 14 kg,and five intact adult females, weighing between 4.0 and 7.4 kg, wereused in this study. One of the males (2900) had a cocaine self-administration history. This monkey only took part in the CRFinfusion experiment. Of the remaining nine monkeys, three malesand four females had no prior experience with cocaine (ketamine,used for sedation, was the only psychoactive drug noted in thehistories of these monkeys) and eight had no previous history of drugself-administration. One female monkey (2490) had a history of drugdiscrimination testing in another laboratory (involving mainly opi-oids), and the other, a male (1583), had scarring consistent withjugular vein catheterization before purchase, but there were norecords available to indicate his drug history. The presence of jugularveins in this monkey has not yet been determined.

The monkeys were individually housed in stainless steel cagesmeasuring 83.3 3 76.2 3 91.4-cm deep (Bryan Research EquipmentCorporation, Bryan, TX) located in a laboratory that contained atotal of 24 similarly housed monkeys. The monkeys were fed 8 to 12Purina Monkey Chow biscuits twice daily to maintain normal adultweight and water was available ad libitum. Each monkey had anindwelling venous catheter in a femoral, internal, or external jugularvein. Catheters were inserted during aseptic surgery under ket-amine (10 mg/kg) and xylazine (2 mg/kg) anesthesia. Followingplacement in the vein, the catheter was guided s.c. to the midscapu-lar region where it exited the monkey. The external portion of thecatheter was protected inside the cage by a flexible stainless steelarm, with one end attached to the polyester jacket (Lomir, New York)worn by the monkey and the other bolted to the rear of the cage.

Animals used in these studies were maintained in accordance withthe University of Michigan Committee on Animal Care and Guide-lines of the Committee on the Care and Use of Laboratory AnimalResources, National Health Council (Department of Health, Educa-tion and Welfare, ISBN 0–309-05377–3, revised 1996).

Apparatus

Each cage had a 15 3 20-cm panel fixed to its right wall. Eachpanel had three stimulus lights, two red and one central green light,placed above two response levers. The red stimulus light over theright lever signaled drug availability. Drug delivery was contingenton the monkey emitting the required response (30 lever presses). Thegreen center light was illuminated for the duration of the druginfusion, 1 ml over 5 s. During each 10-min time out (TO), allstimulus lights were extinguished and responding had no pro-grammed consequences.

The experiment was controlled by IBM/PS2 computers located inan adjacent room. The computers were programmed using Med As-sociates software (Georgia, VT).

Procedure

The temporal sequence of the experiments was as follows.1. An i.v. injection of 1 mg/kg of cocaine was administered to the

nine monkeys with no cocaine history, and blood was sampled fromthe i.v. catheter at various times before and following the injection.

2. The nine monkeys with no history of response-contingent co-caine administration received either no injections or nonsignaled,noncontingent injections of saline or cocaine every 10 min for a totalof 13 injections of the same dose of cocaine or saline. Each dose waspresented on successive days in the following sequence: No injection;saline; 0.01, 0.03, 0.1, 0.3, 0.3, 0.1, 0.03, and 0.01 mg/kg/injection ofcocaine; saline; and no injection.

3. The nine monkeys with no history of cocaine self- administra-tion were trained to self-administer 0.03 or 0.1 mg/kg/injection ofcocaine. Initially, a fixed ratio (FR) 1, TO 10-s schedule was used,with 0.01 mg/kg/injection of cocaine as the reinforcer. Once a monkeyhad learned to lever press on this schedule, which took one session(n 5 7), 1 week (monkey 2087), or 5 weeks (monkey 2490), the FR andTO were gradually increased to 30 and 10 min, respectively, over 1 to3 weeks. During this time, the dose of cocaine was increased to 0.03or 0.1 mg/kg/injection. Seven monkeys were maintained on 0.03mg/kg/injection of cocaine, and 2 monkeys (2087 and 2490) weremaintained on 0.1 mg/kg/injection of cocaine.

4. Following the acquisition of stable cocaine-maintained behavior(criteria listed below), the experiments described in section 2 wererepeated, only this time cocaine delivery was contingent upon themonkey fulfilling the FR 30 (FR 20 for monkey 2490, because thissubject was older and less mobile that the other subjects) responserequirement.

5. An i.v. injection of 1 mg/kg of cocaine was administered to thepreviously cocaine-naive monkeys (n 5 9) exactly as described insection 1 above, and blood was sampled in an identical fashion.

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6. Intravenous injections of 1 and 10 mg/kg of CRF were adminis-tered to eight monkeys (7/9 of the monkeys that took part in sections1–5 of this protocol, and 1 monkey that had an extensive drugself-administration history that predated this study), all of whomhad experience with cocaine self-administration at the time of CRFadministration. Blood was sampled before and after each CRF infu-sion. CRF infusion experiments took place at least 1 week apart.

Effect of Cocaine History on HPA Response to a SingleCocaine Infusion. Nine cocaine-naive monkeys (5 female and 4male) took part in this study. Monkeys were given a single infu-sion of 1 mg/kg of cocaine on two occasions. These experimentscommenced between 9 and 10 AM, and although the self-admin-istration session normally scheduled in the room took place asusual, the monkeys in this study did not participate during themorning that this test was done. Blood was sampled at 215, 210,and 25 min before the infusion of cocaine, and then at 5-minintervals for the first hour and 10-min intervals for the secondhour postinfusion. Details of the blood collection are describedbelow.

Data were normalized before statistical analysis by averaging thecortisol and ACTH values obtained from samples taken before co-caine administration and then subtracting these mean values frompostcocaine infusion levels. The plasma cortisol (mg/dl) and ACTH(pg/ml) levels over the 2-h, 15-min sampling period were analyzed forgender, cocaine history. and sampling time differences.

Effect of Response-Contingent versus Noncontingent Co-caine Delivery on HPA Activation. The subjects for this studywere four male and five female monkeys, none of whom had a priorhistory of drug self-administration. In experiments where noncon-tingent cocaine or saline was administered, neither the levers northe stimulus lights were present, and cocaine (0.01, 0.03, 0.1, or 0.3mg/kg/injection) or saline was injected at 10-min intervals, one dose/session, beginning at approximately 10 AM, for a total of 13 infusionsin the sequence described above.

For the response-contingent part of the study, drug self-adminis-tration sessions were scheduled for these monkeys twice daily for 130min starting at approximately 10 AM and 4 PM. Saline or 0.01, 0.03,0.1, or 0.3 mg/kg/injection of cocaine was made available, and thetesting sequence was the same as for the nonresponse-contingenttests. There was a maximum of 13 infusions available in each ses-sion. A stable baseline of self-administration behavior in this studywas defined as response rates that were greater than 1 response/s for0.03 mg/kg/injection of cocaine (0.1 mg/kg/injection of cocaine forsubjects 2490 and 2087), and delivery of the maximum number ofinjections available during the session (13 injections). In addition,when saline was available for self-administration, response rateswere required to be less than 20% of the rates for 0.03 (or 0.1)mg/kg/injection of cocaine, with total saline injections numbering lessthan 13. Each monkey had several days’ experience with each dosebefore each blood drawing session. Each monkey had blood samplestaken on two to four occasions (three on average) at each dose ofcocaine or saline.

Blood was sampled during morning sessions for both noncon-tingent- and response-contingent tests, as frequently as threetimes per week. A sample of venous blood was drawn via thecatheter 5 to 30 min before the session, and then again after the1st, 4th, 8th and 13th infusions (or at approximately 5, 30, 70, and130 min after the session began if the monkey’s response andinfusion rate slowed under self-administration conditions, such asduring self-administration of 0.01 mg/kg/injection of cocaine orsaline). Blood samples continued to be drawn at 15 min postses-sion, and at hourly intervals for the next 3 h, making a total ofnine blood draws.

Data were normalized before statistical analysis by subtractingthe cortisol or ACTH value obtained from the presession sample fromthe cortisol or ACTH levels measured during and after the session.Area under curve (AUC) values for ACTH (pg z min/ml) and cortisol(mg z min/dl) were used as an estimate of ACTH and cortisol release

relative to basal (presession sample) levels during the session inwhich cocaine or saline was either passively injected every 10 min orself-administered as described above. AUC values were calculatedaccording to the trapezoidal rule (e.g., Tallarida and Murray, 1987).The AUC was calculated from the six samples taken before, during,and 15 min after the session. Normalized data were analyzed forgender, contingency, and treatment (dose of cocaine) differences asdescribed below.

Comparison of Effect of CRF and Cocaine on HPA AxisActivity. Five male and four female monkeys were the subjects forthis study. At the time the CRF study was conducted, each subjecthad at least several months’ experience with cocaine self-adminis-tration.

Each monkey received i.v. CRF (1 and 10 mg/kg of human/rat CRF;Calbiochem, La Jolla, CA). Blood sampling took place at 220, 210min, and immediately before CRF infusion. Samples were drawn at10-min intervals for 90 min postinfusion, and at 2, 2.5, 3, and 4 husing the procedure described below.

Data were normalized before statistical analysis by averaging thecortisol and ACTH values from samples taken before CRF adminis-tration and then subtracting these mean values from post-CRF in-fusion levels. AUC values for cortisol (mg z min/dl) and ACTH(pg z min/ml) were calculated as described above. The plasma cortisoland ACTH data were analyzed for gender, CRF dose, and samplingtime differences.

Blood Collection and Handling

Each blood sample (1.1–1.4 ml) was placed in a 2-ml Vacutainer(Becton Dickinson and Company, Franklin Lakes, NJ) containing0.04 ml of 7.5% EDTA and immediately placed on ice. After drawingeach blood sample, 1.5 to 3 ml of 30 U/ml heparin saline solution wasinfused into the catheter and, when sampling was done during ses-sions in which cocaine was available, a volume of the cocaine solutionequal to the catheter volume (0.6–1.5 ml) was injected after theheparin saline solution.

Blood samples were centrifuged at 5000 rpm for 5 min and thenthe plasma (0.7 ml) was pipetted into 2-ml Cryovials (Corning) andstored at 280°C until assay. Samples were sent on dry ice to Wash-ington University (St. Louis, MO) where ACTH and cortisol levelswere determined using radioimmunoassay kits (cortisol: DiagnosticProducts Corporation, Los Angeles, CA; ACTH: Nichols InstituteDiagnostics, San Juan Capistrano, CA).

Statistical Analyses

Data are presented as mean 6 S.E.M. and also as AUC 6 S.E.M.Both forms of data presentation were used because each highlightsdifferent aspects of the study. Presentation of data averaged for eachsampling time provides the actual plasma measurements of cortisoland ACTH and shows the onset and duration of HPA changes fol-lowing cocaine or CRF infusion. AUC data summarizes the overallchanges in HPA activity, and normalizes the HPA response bothbetween and within subjects for easier comparison. One- or two-wayANOVA and multiple ANOVA were conducted on normalized data,and where appropriate, post hoc pairwise comparisons using theTukey honest significant difference (HSD) test of significance (p ,.05) were carried out (Statistica v.5.0, Statsoft, Tulsa, OK). Whereexperiments were replicated within subjects, the mean response foreach subject was used to calculate treatment effects across subjects.One subject (monkey 2087) showed no discernible HPA response tothe 1-mg/kg cocaine infusions relative to his HPA response followinga saline infusion (data not shown). His results were not included inthe analysis of those data.

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ResultsEffect of Response-Contingent versus NoncontingentCocaine Delivery Studies on HPA Activation

One male monkey (2087) had an ACTH response to nonre-sponse contingent infusions of cocaine or saline that was thereverse of that observed for the other three male monkeys.The ACTH response for monkey 2087 was greatest at thelowest cocaine dose (0.01 mg/kg/injection) and saline-like atthe highest cocaine dose (0.3 mg/kg/injection). His ACTHdata were excluded from subsequent analyses.

Data Analysis Across Sampling Times. Rates of re-sponding for saline and cocaine as well as the number ofinfusions earned during the response-contingent part of thisstudy are shown in Table 1. Increases in cocaine dose arepositively correlated with increases in rates of responding.Infusion number and rates of responding both peaked at acocaine dose of 0.1 mg/kg/injection. Response rates and infu-sion numbers increased relative to saline responding for 0.01mg/kg/injection of cocaine in most monkeys, and increasedfor all monkeys for 0.03 mg/kg/injection of cocaine. Theseincreases in the levels of cocaine-maintained behavior oc-curred with or without any concomitant increase in HPA axisactivity. There were no gender differences in either the ratesof responding or the number of infusions of saline or cocainethat were earned (Table 1).

Nonresponse-contingent and response-contingent cocaineadministration resulted in a dose-dependent increase in cor-tisol levels that was significant for 0.1 and 0.3 mg/kg/injec-tion of cocaine relative to the no injection and saline condi-tions (p , .05; Fig. 1, upper panels). Overall, the contingencyof cocaine or saline delivery, whether it was nonresponse-contingent or response-contingent, did not have any signifi-cant effect on the cocaine-induced increases in cortisol. How-ever, there was a significant interaction between the contin-gency of cocaine administration and sampling time (df 5 7,F 5 2.04, p , .05), due mainly to the cocaine-induced eleva-tion in cortisol levels after response-contingent delivery ofthe 4th infusion relative to noncontingent delivery (Fig. 1,upper panels). Male monkeys had a larger cortisol responsethan did females to cocaine administration (p 5 .05; Fig. 2,upper and middle panels). There was a significant interac-tion between gender and sampling time (df 5 7, F 5 3.67, p ,.001), that reflected the larger cortisol response of male mon-keys to cocaine over the course of the experiment. There wasalso a significant interaction between cocaine dose and sam-pling time (df 5 35, F 5 3.62, p , .001), because increasingthe number of infusions (and hence cocaine intake) led to acumulative increase in cortisol.

Nonresponse-contingent and response-contingent cocaineadministration also resulted in a dose-dependent increase inACTH levels, but only response-contingent delivery of 0.1and 0.3 mg/kg/injection of cocaine led to increases in ACTHthat were significantly larger than the ACTH response to theno injection and saline conditions (p , .05; Fig. 1, lowerpanels). Despite this difference, the contingency of cocaine orsaline delivery, whether it was nonresponse-contingent orresponse-contingent, did not have significant effects overallon the cocaine-induced increases in ACTH. There was a sig-nificant interaction between gender and sampling time (df 57, F 5 4.82, p , .001), that reflected the larger ACTH re-sponse of male monkeys, particularly in the no injection T

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condition. There was also a significant interaction betweencocaine dose and sampling time (df 5 35, F 5 2.87, p , .001),because increasing the number of infusions (and hence co-caine intake) led to a cumulative increase in ACTH (Fig. 2,lower panel).

AUC Data Analysis. Cocaine administration had a sig-nificant effect on cortisol AUC (df 5 5, F 5 15.19, p , .001),with 0.1 and 0.3 mg/kg/injection of cocaine (n 5 9) eachproducing a larger cortisol AUC than the no injection, saline,and 0.01 and 0.03 mg/kg/injection of cocaine conditions (p ,.05; Fig. 3, top and center panels). There was a near-signifi-cant effect of contingency (p 5 .08), because response-contin-gent cocaine was associated with a larger cortisol responserelative to noncontingent cocaine administration, particu-larly in male monkeys. There was a significant gender dif-ference in the cortisol AUC data (df 5 1, F 5 5.30, p , .05),because male monkeys had a larger cortisol response to re-sponse-contingent cocaine administration than did femalemonkeys (Fig. 3, top and center panels).

Cocaine administration had a significant effect on ACTHAUC (df 5 5, F 5 6.92, p , .001), with cocaine producinglarger ACTH AUC than the no injection or saline conditions(p , .05; Fig. 3, bottom panel). There was a significant effectof contingency (df 5 1, F 5 4.83, p , .05), because response-contingent cocaine was associated with a larger ACTH re-sponse, which was significant for 0.1 mg/kg/injection of co-caine (p , .05; Fig. 3, bottom panel). The dose-effect functionfor ACTH AUC differed between response-contingent andnoncontingent cocaine delivery. The effect of noncontingentcocaine on ACTH AUC was independent of dose, whereascontingent cocaine administration (0.1 and 0.3 mg/kg/injec-tion of cocaine) resulted in larger, more dose-dependent in-creases in the ACTH AUC (Fig. 3, bottom panel). There wasno gender difference in the ACTH AUC for cocaine undereither contingency.

Individual AUC data for three subjects, comparing theirHPA responses with noncontingent- and response-contingentdelivery of cocaine and saline, highlights the variability ofthe responses of the nine subjects in this study (Fig. 4 andTable 1). The example on the left (male: 2087) is illustrativeof monkeys (male: 2087 and RN23, female: 4393) that did notshow a dose-dependent HPA response to cocaine under eithercontingency. The center example (male: 2484) representsmonkeys (male: 2484 and 1583, female: 2083) that did nothave a dose-dependent HPA response to cocaine under thenoncontingent condition, but did when cocaine was self-ad-ministered. The example on the right (female: 2487) repre-sents monkeys (female: 2487, 2490, and 4394) that showed adose-dependent response to cocaine and saline under boththe noncontingent- and response-contingent conditions. De-spite these differences in HPA sensitivity to cocaine, therewere no differences in either response rates or infusion num-ber for saline and cocaine among the monkeys in each ofthese HPA-response subgroups (Table 1).

Effect of Cocaine History on HPA Response to a SingleCocaine Infusion

One male monkey (2087) had no increase in HPA activityfollowing infusions of 1 mg/kg of cocaine relative to saline(data not shown) unlike the other monkeys in this study. Hisdata were excluded from subsequent analyses.

There was a modest increase in plasma cortisol levels

following i.v. cocaine administration (1 mg/kg) in male (n 53) and female (n 5 5) monkeys (Fig. 5, top panels). Plasmacortisol levels obtained from samples taken from 20 until 60min after the cocaine infusion were significantly higher thanthe cortisol levels from earlier sampling times (n 5 8; p ,.05). There was no difference in the cortisol response to aninfusion of 1 mg/kg of cocaine depending on whether themonkeys were cocaine-naive or -experienced. Males tended tohave a larger cortisol response to the cocaine infusion, andthis difference was significant in the cocaine-experiencedmales at a few sampling times (Fig. 5, top right panel).

There was also an increase in plasma ACTH levels follow-ing i.v. cocaine administration (1 mg/kg) in male (n 5 3) andfemale (n 5 5) monkeys (Fig. 5, bottom panel). Plasma ACTHlevels obtained from samples taken from 30 until 60 minafter the cocaine infusion were significantly higher than theACTH levels from earlier sampling times (n 5 8; p , .05).There was no difference in the ACTH response to an infusionof 1 mg/kg cocaine depending on whether the monkeys werecocaine-naive or -experienced. Males tended to have a largerACTH response than did females to the cocaine infusion, andthis difference was significant in the cocaine-experiencedmales at several sampling times (Fig. 5, bottom right panel).

Comparison of Effects of CRF and Cocaine on HPA AxisActivity

Intravenous administration of CRF (1 and 10 mg/kg) re-sulted in significantly increased release of cortisol relative topreinfusion levels, from 30 to 80 min (1 mg/kg of CRF) and atall postinfusion sampling times (10 mg/kg of CRF; Fig. 6, toppanel). The 10 mg/kg dose of CRF produced a 1.97 6 0.29-foldgreater release of cortisol than did 1 mg/kg of CRF (df 5 1,F 5 8.90, p , .01). There was a near-significant genderdifference (p 5 .07), with male monkeys tending toward alarger cortisol response to CRF than female monkeys.

Intravenous administration of CRF (1 and 10 mg/kg) alsoresulted in significantly increased release of ACTH relativeto preinfusion levels, from 10 to 50 min (1 mg/kg of CRF) andat all postinfusion sampling times up to 120 min (10 mg/kg ofCRF; Fig. 6, center and bottom panels). The 10 mg/kg dose ofCRF produced a 5.45 6 1.01-fold greater release of ACTHthan did 1 mg/kg of CRF (df 5 1, F 5 29.26, p , .001). Therewas a significant gender difference (df 5 1, F 5 6.36, p , .05),with male monkeys having a larger ACTH response to 10mg/kg of CRF than did female monkeys. The difference in theACTH response of female monkeys to 1 and 10 mg/kg of CRFwas not significant at any time point.

DiscussionThe primary goal of this study was to investigate whether

the ACTH and cortisol response to cocaine would differ whenthe cocaine delivery was controlled either by the investigatoror by the monkey. It should be noted that response-contin-gent cocaine can function as a reinforcer without elevatingplasma ACTH or cortisol, in confirmation of earlier findings(Broadbear et al., 1999). Nevertheless, we found that cortisoland ACTH levels were higher and more dose dependentfollowing response-contingent cocaine administration thanthey were after noncontingent cocaine at higher cocainedoses. The secondary goal was to determine whether cocainehistory had a significant impact on cocaine’s effects on HPA

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axis activity. A single infusion of 1 mg/kg cocaine, adminis-tered when the monkeys were cocaine-naive and then againsubsequent to the noncontingent and response-contingentexperiments, did not differ in its effects on ACTH and corti-sol. In addition, distinct gender differences were found dur-ing the course of this study, with male monkeys showinghigher cortisol levels following noncontingent and response-contingent cocaine administration, and higher ACTH levelsfollowing administration of 1 mg/kg cocaine and 10 mg/kg ofCRF infusions.

Although there were no overall differences in the HPAresponses to the first and subsequent exposures to a single 1mg/kg cocaine infusion for male or female monkeys, therewas a distinct lack of correlation between both the ACTH andcortisol responses to cocaine on the two occasions that thisdose was given (data not shown). This lack of correlationsuggests that the HPA response of a cocaine-naive subject toa large noncontingent cocaine infusion is not at all predictiveof that subject’s HPA response to the same dose of cocaineonce he has acquired extensive experience with cocaine. Itwas correctly anticipated that the first exposure to cocaine

would increase HPA activity as it did in a study done inhumans, where first-time administration of cocaine to malesubjects produced an increase in plasma cortisol levels (Hee-sch et al., 1995). Similar results to ours were also found in astudy by Sarnyai et al. (1996), in which male rhesus monkeyswere infused with saline or 0.4 or 0.8 mg/kg of cocaine.Significant correlations were found between the behavioralresponse to cocaine and the cortisol and ACTH changes inthese monkeys. One notable difference with this earlier studywas that the baseline cortisol and ACTH values obtained inthe hour before the cocaine infusion were considerably higherin some monkeys than those that were measured in thepresent study, particularly in monkeys that showed little orno HPA response to the cocaine infusion (ACTH . 40 pg/ml,cortisol $ 18 mg/dl). These high levels may have been aconsequence of ketamine anesthesia (Elvidge et al., 1976;Puri et al., 1981), and the fact that testing took place inrestraint chairs. Indeed, a negative correlation was foundbetween baseline cortisol and subsequent changes in ACTHfollowing infusion of 0.8 mg/kg of cocaine, possibly because ofdown-regulation of HPA axis activity via a negative feedback

Fig. 1. Mean (6S.E.M.) plasma cortisol (mg/dl) and ACTH levels (pg/ml) determined from blood sampled before, during, and after noncontingent andresponse-contingent administration of saline or of cocaine (mg/kg/injection). Upper panels, cortisol data following noncontingent (upper left) andresponse-contingent administration (upper right) for male (n 5 4) and female (n 5 5) monkeys. Lower panels, ACTH data following noncontingent(lower left) and response-contingent administration (lower right) for male (n 5 3) and female (n 5 5) monkeys. In the nonresponse contingentcondition, an unsignaled infusion of saline or cocaine was injected every 10 min for a total of 13 infusions. In the response-contingent condition, cocaine(or saline) availability was signaled by a red stimulus light, which remained illuminated until the requisite number of lever presses had been emitted(FR 30, TO 600 s); drug or saline delivery was signaled by a green stimulus light. Each session lasted 130 min and a maximum of 13 infusions waspossible. a, versus no infusion, saline, and 0.01 and 0.03 mg/kg/injection of cocaine (p , .05); b versus no infusion, saline, and 0.01 mg/kg/injection ofcocaine (p , .05); c versus no infusion (p , .05); d versus 0.03 mg/kg/injection of cocaine (p , .05); e versus saline (p , .05); f versus no infusion andsaline (p , .05).

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mechanism (Dallman and Jones, 1973). An earlier studyusing ovariectomized female rhesus monkeys (Sarnyai et al.,1995), found that acute infusions of 0.4 and 0.8 mg/kg ofcocaine changed neither pulsatile ACTH nor cortisol release.CRF infusions given to these monkeys showed that theirHPA axes were intact and responsive. This lack of effect ofcocaine was attributed to the absence of normal levels ofgonadal steroids. This may indeed be the case, because thefive intact female monkeys in the present study each showedincreased HPA activity in response to cocaine. The present

Fig. 2. Mean (6S.E.M.) plasma cortisol (mg/dl) and ACTH levels (pg/ml)determined from blood sampled before, during, and after noncontingentand response-contingent administration of saline or cocaine (mg/kg/injec-tion). Upper and middle panels, cortisol data following noncontingent andresponse-contingent administration was combined for male (n 5 4, upperpanel) and female (n 5 5, center panel) monkeys as contingency ofadministration was not a significant determinant of cortisol levels. Lowerpanel, data for male (n 5 3) and female (n 5 5) monkeys were combinedas there were no statistically significant differences in ACTH levels foreither male and female monkeys or for noncontingent and response-contingent administration of cocaine or saline. a versus no infusion (p ,.05); b versus no infusion and saline (p , .05); c versus no infusion, saline,and 0.03 mg/kg/injection of cocaine (p , .05); d versus no infusion and0.03 mg/kg/injection of cocaine (p , .05); e versus no infusion, saline, and0.01 and 0.03 mg/kg/injection of cocaine (p , .05). Details as for Fig. 1.

Fig. 3. Mean (6S.E.M.) cumulative release (AUC) of plasma cortisol(mg z min/dl) and ACTH (pg z min/ml) above basal (presession) levels dur-ing saline or cocaine (mg/kg/injection) administration. There was a gen-der difference in cortisol levels, and a near-significant difference due tocontingency (p 5 .08). Upper panel, cortisol AUC for female monkeys (n 55) for nonresponse contingent (hatched bars) and response contingent(solid bars) cocaine administration. Center panel, cortisol AUC for malemonkeys (n 5 4) for nonresponse contingent (hatched bars) and responsecontingent (solid bars) cocaine administration. *versus no infusion (p 5.05), **versus saline (p , .05), ***versus no infusion and saline (p 5 .01),****versus no infusion, saline, and 0.01 and 0.03 mg/kg/injection of co-caine (p , .001). Lower panel, ACTH AUC for male and female monkeys(n 5 8) following nonresponse contingent (hatched bars) and response-contingent (solid bars) administration of cocaine. There was no genderdifference in the ACTH response to cocaine. Response-contingent admin-istration of 0.1 and 0.3 mg/kg/injection cocaine resulted in larger in-creases in ACTH levels than did noncontingent administration, attainingsignificance for 0.1 mg/kg/injection of cocaine (p , .05). In addition, theACTH response to cocaine was more dose dependent under the response-contingent administration condition. a, ACTH for 0.3 coc (response con-tingent) greater than no infusion, saline, and 0.01 and 0.1 mg/kg/injectionof cocaine (noncont.; p , .05). b, ACTH for 0.3 coc (noncont.) greater thanno infusion (noncont.; p 5 .06). c, ACTH for 0.1 coc (resp. cont.) greaterthan for no infusion and 0.1 mg/kg/injection of cocaine (noncontingent;p , .05). d, ACTH for 0.3 and 0.1 coc (resp. cont.) greater than for noinfusion and saline (resp. cont.; p , .05). Other details as for Fig. 1.

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study constitutes the first demonstration of cocaine’s effectson HPA activity in intact, female rhesus monkeys.

Studies done in humans, comparing the pharmacokineticsand subjective effects of cocaine in males and females, havedemonstrated that overall, phase of the menstrual cycle doesnot have any significant effect on these measures (Mendelsonet al., 1998). The effect of 0.4 mg/kg of cocaine on ACTH wasthe same in male subjects as it was in 6/13 female subjects,and there was a sex difference in the cortisol response, with

women having higher peak plasma levels (Sholar et al.,1998). The remaining seven women had elevated cortisollevels before the cocaine infusion, which once again may havecontributed to the lack of effect of cocaine on HPA activity.

In the experiments that evaluated the effects of repeatednoncontingent or response-contingent infusions of cocaine orsaline, it was found that ACTH responses were similar formale and female monkeys. When combined, their datashowed a distinctly dose-related response to cocaine over the

Fig. 4. Cortisol (mg z min/dl) and ACTH AUC (pg z min/ml) for three subjects illustrating the individual variability of the HPA response tononcontingent and response-contingent cocaine administration (mg/kg/injection) or saline. The three upper panels represent the HPA response underthe noncontingent infusion condition, and the lower three panels show the corresponding data for the response-contingent administration condition.Other details as for Fig. 1.

Fig. 5. Mean (6S.E.M.) plasma corti-sol (mg/dl) and ACTH (pg/ml) subse-quent to i.v. administration of 1 mg/kgof cocaine in male (n 5 3) and female(n 5 5) monkeys. The monkeys re-ceived 1 mg/kg of cocaine on two occa-sions: first as cocaine-naive subjects(left panels) and then as monkeyswith a history of cocaine self-adminis-tration (right panels). Male (M) andfemale (f) cortisol and ACTH re-sponses to a single injection of 1mg/kg of cocaine are compared in eachpanel. There were no differences inthe cortisol or ACTH response to co-caine between cocaine-naive and -ex-perienced monkeys. *p , .05, **p ,.01.

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course of the session. This is in agreement with our earlierfindings in male monkeys with years of experience with co-caine self-administration (Broadbear et al., 1999). There wasalso an overall difference in the cortisol and ACTH responsesto noncontingent versus response-contingent cocaine, whichwas particularly apparent with the higher doses of cocaine(AUC data). Overall, it appears that under the response-contingent condition, cocaine produced larger, more dose-dependent changes in cortisol and ACTH release. These dif-ferences may indicate that response-contingency and/orcocaine history “fine tunes” the HPA response to cocaine,from a more generalized “cocaine response” (as was seen inthe non-dose-dependent nature of the ACTH AUC data fol-

lowing noncontingent administration) to a response that bet-ter reflects a high-dose cocaine response-contingent effect.

Unlike the ACTH data, there was a gender difference inthe cortisol response to noncontingent and response-contin-gent cocaine administration, with male monkeys having alarger response to saline and cocaine over the entire doserange. When comparing these data with our earlier findings(Broadbear et al., 1999), the cortisol AUC for the male mon-keys in the present study are only one-half the size of thoseoriginally reported, although the ACTH data are comparable.This difference could be due to the inclusion of monkeys inthe present study that did not show a dose-dependent re-sponse to cocaine, or they could reflect the comparative lackof cocaine history of subjects in the present study. This raisesthe possibility that some of the differences in HPA responseobserved between noncontingent and response-contingent co-caine administration in the present study were due more tothe extent of the monkeys’ experience with cocaine than tothe contingency of its administration, and that repeatingthese observations after a period of prolonged cocaine self-administration would result in an enhanced, more dose-de-pendent HPA response. In an earlier study, when cocainewas administered noncontingently to monkeys with an ex-tensive self-administration history, their cortisol responseswere no different from earlier occasions when cocaine wasdelivered response contingently (Broadbear et al., 1997).

It was surprising that some of the monkeys (2 males and 1female) lacked a dose-dependent HPA response to cocaineunder both noncontingent and response-contingent condi-tions. These monkeys were no different from the others withrespect to response rate and cocaine intake. The CRF infu-sion also highlighted individual variability in ACTH andcortisol responses, revealing some interesting similarities inthe monkeys’ HPA responses to CRF and cocaine. Althoughregression analysis showed a significant positive correlationfor both the cortisol and ACTH AUCs following nonresponse-contingent administration of 0.3-mg/kg/injection of cocaineand 1 or 10 mg/kg of CRF, there were no correlations betweenthe HPA responses to CRF and/or cocaine when cocaine wasadministered as either a single injection or as repeated, non-response-contingent infusions (data not shown). This is per-haps an indication that differences exist in the sensitivity ofeach monkey to stimulation of the HPA axis directly by CRF,or indirectly, by cocaine. There was no gender difference inthe cortisol response to a single infusion of cocaine or CRF,but male monkeys had a substantially larger ACTH responsethan females to 10 mg/kg of CRF, as was the case for anoncontingent infusion of a large (1 mg/kg) dose of cocaine.Past studies have demonstrated that plasma levels of ACTHare not always correlated with corticosteroid levels (Kriegerand Allen, 1975). The fact that the larger dose of CRF stim-ulated a proportionally larger increase in ACTH relative tocortisol (as did cocaine) indicates that there may be a “ceilingeffect” for the sensitivity of the adrenal cortex to ACTH (seealso Cador et al., 1992).

In summary, both male and female rhesus monkeysshowed an increased secretion of ACTH and cortisol follow-ing cocaine administration. This HPA response was largerand more dose dependent when cocaine was administeredresponse-contingently then when it was delivered nonre-sponse-contingently to monkeys before acquisition of self-administration behavior. Male monkeys tended to have a

Fig. 6. Mean (6S.E.M.) plasma cortisol (mg/dl) and ACTH (pg/ml) subse-quent to i.v. infusion of human/rat CRF (1 and 10 mg/kg) in male (n 5 5)and female (n 5 4) rhesus monkeys. Upper panel, cortisol levels beforeand after 1 and 10 mg/kg of CRF for all monkeys (n 5 9); **p , .01, ***p ,.001. Middle panel, ACTH levels before and after 1 and 10 mg/kg of CRFin male monkeys (n 5 5); ***p , .001. Lower panel, ACTH levels beforeand after 1 and 10 mg/kg of CRF in female monkeys (n 5 4); there was anoverall increase in cortisol levels subsequent to 10 mg/kg of CRF relativeto 1 mg/kg (p 5 .05).

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larger HPA response to both cocaine and CRF infusions thandid female monkeys. It is possible that the differences in thecharacteristics of the ACTH and cortisol release to cocaineunder the two contingencies are due to the relative amount ofexperience with cocaine as well as to whether the delivery ofcocaine is under the control of the monkey.

Acknowledgments

We thank Myrtle Barrett, Jana Weinberger, Deborah Huntzinger,Amy Foster, Georghe Pusta, Karen Wiesenhauer and Laurie Mc-Dowell for their expert technical assistance.

ReferencesBroadbear J, Winger G, Cicero T and Woods J (1997) ACTH and cortisol in cocaine

self administration in Rhesus monkeys. NIDA Res Monogr 178:212.Broadbear JH, Winger G, Cicero TJ and Woods JH (1999) The effects of self-

administered cocaine on plasma ACTH, and cortisol in male rhesus monkeys.J Pharmacol Exp Ther 289:1641–1647.

Cador M, Ahmed S, Koob G, Le Moal M and Stinus L (1992) Corticotropin-releasingfactor induces a place aversion independent of its neuroendocrine role. Brain Res597:304–309.

Coe C, Glass J, Wiener S and Levine S (1983) Behavioral, but not physiological,adaptation to repeated separation in mother and infant primates. Psychoneuroen-docrinology 8:401–409.

Dallman, MF and Jones, MT (1973) Corticosteroid feedback control of ACTH secre-tion: Effect of stress-induced corticosterone secretion on subsequent stress re-sponses in the rat. Endocrinology 92:1367–1375.

Elvidge H, Challis J, Robinson J, Roper C and Thorburn G (1976) Influence ofhandling and sedation on plasma cortisol in rhesus monkeys (Macaca mulatta).J Endocrinol 70:325–326.

Hanson J, Larson M and Snowdon C (1976) The effects of control over high intensitynoise on plasma cortisol levels in rhesus monkeys. Behav Biol 16:333–340.

Hattingh J, Pitts N and Ganhao M (1988) Immediate response to repeated captureand handling of wild impala. J Exp Zool 248:109–112.

Heesch C, Negus B, Keffer J, Snyder R, Risser R and Eichhorn E (1995) Effects ofcocaine on cortisol secretion in humans. Am J Med Sci 310:61–64.

Herrmann T, Hurwitz H and Levine S (1984) Behavioral control, aversive stimulusfrequency, and pituitary-adrenal response. Behav Neurosci 98:1094–1099.

Higley J, Suomi S and Linnoila M (1992) A longitudinal assessment of CSF mono-amine metabolite and plasma cortisol concentrations in young rhesus monkeys.Biol Psychiatry 32:127–145.

Kirschbaum C, Prussner J, Stone A, Federenko I, Gaab J, Lintz D, Schommer N andHellhammer D (1995) Persistent high cortisol responses to repeated psychologicalstress in a subpopulation of healthy men. Psychosom Med 57:468–474.

Krieger DT and Allen W (1975) Relationship of bioassayable and immunoassayableplasma ACTH and cortisol in normal subjects and in patients with Cushing’sDisease. J Clin Endocrinol Metab 10:675–687.

Mendelson JH, Sholar MB, Mello NK, Siegel AJ and Halpern J (1998) Cocainepharmacokinetics in mean and in women during two phases of the menstrualcycle. NIDA Res Monogr 179, 149.

Piazza P, Maccari S, Deminiere J, le Moal M, Mormede P and Simon H (1991)Corticosterone levels determine individual vulnerability to amphetamine self-administration. Proc Natl Acad Sci 88:2088–2092.

Puri C, Puri V and Anand Kumar T (1981) Serum levels of testosterone, cortisol,prolactin and bioactive luteinizing hormone in adult male rhesus monkeys follow-ing cage-restraint or anaesthetizing with ketamine hydrochloride. Acta Endocri-nologica 97:118–124.

Reinhardt B, Cowley D, Scheffler J, Vertein R and Wegner F (1990) Cortisol responseof female rhesus monkeys to venipuncture in homecage versus venipuncture inrestraint apparatus. J Med Primatol 19:601–606.

Rivier C and Vale W (1987) Cocaine stimulates adrenocorticotropin (ACTH) secre-tion through a corticotropin-releasing factor (CRF)-mediated mechanism. BrainRes 422:403–406.

Saphier D, Welch J, Farrar G and Goeders N (1993) Effects of intracerebroventric-ular and intrahypothalamic cocaine administration on adrenocortical secretion.Neuroendocrinology 57:54–62.

Sarnyai Z, Mello N, Mendelson J, Eros-Sarnyai M and Mercer G (1996) Effects ofcocaine on pulsatile activity of the hypothalamic-pituitary-adrenal axis in malerhesus monkeys: Neuroendocrine and behavioral correlates. J Pharmacol ExpTher 277:225–234.

Sarnyai Z, Mello N, Mendelson J, Nguyen P and Eros-Sarnyai M (1995) Effects ofcocaine and corticotropin-releasing factor on pulsatile ACTH and cortisol releasein ovariectomized rhesus monkeys. J Clin Endocrinol Metab 80:2745–2751.

Setchell K, Shackleton C and Himsworth R (1975) Studies on plasma corticosteroidsin the rhesus monkey (Macaca mulatta). J Endocrinol 67:241–250.

Sholar M, Mendelson J, Mello N, Siegel A, Kaufman M, Levin J, Renshaw P andCohen B (1998) Concurrent pharmacokinetic analysis of plasma cocaine and ad-renocorticotropic hormone in men. J Clin Endocrinol Metab 83:966–998.

Spangler R, Zhou Y, Schlussman S, Ho A and Kreek MJ (1997) Behavioral stereo-typies induced by ’binge’ cocaine administration are independent of drug-inducedincreases in corticosterone levels. Behav Brain Res 86:201–204.

Spealman R (1979) Behavior maintained by termination of a schedule of self-administered cocaine. Science 204:1231–1233.

Steiner S, Beer B and Shaffer M (1969) Escape from self-produced rates of brainstimulation. Science 163:90–91.

Tallarida RJ and Murray RB (1987) Manual or Pharmacologic Calculations withComputer Programs. Springer-Verlag, New York.

Vescovi P, Coiro V, Volpi R and Passeri M (1992) Diurnal variations in plasmaACTH, cortisol and beta-endorphin levels in cocaine addicts. Horm Res 37:221–224.

Ward AS, Collins ED, Haney M, Foltin RW, Fischman MW (1998) Ketoconazoleattenuates the cortisol response but not the subjective effects of smoked cocaine inhumans. Behav Pharmacol 9:577–586.

Send reprint requests to: Jillian Broadbear, University of Michigan, De-partment of Pharmacology, 1301 Medical Sciences Research Building 3, AnnArbor, MI 48109-0632. E-mail: jillianb@umich.edu

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