Journal of NeurochemistryLippincott—Raven Publishers, Philadelphia© 1997 International Society for Neurochemistry

Rapid Communication

Effect of Cocaine on the Histaminergic Neuron Systemin the Rat Brain

Chihiro Ito, lKenji Onodera, *Ejko Sakurai, Mitsumoto Sato, and *Takehiko Watanabe

Departments of Psychiatry and * Pharmacology I, Tohoku University School of Medicine, andt Department of Pharmacology, Tohoku University School of Dentistry, Sendai, Japan

Abstract: To examine the effect of cocaine on the brain hista-mine neuron system, histamine levels and histamine N-methyl-transferase activity in the rat brain were measured after the ad-ministration of cocaine. Moreover, we examined the effect of L-histidine on cocaine-induced wheel-running behavior. The ad-ministration of cocaine (20 mg/kg) increased histamine levelsand histamine N-methyltransferase activity in the striatum, nu-cleus accumbens, and amygdala 1 h later. The pretreatment withL-histidine (350 and 700 mg/kg) inhibited the cocaine (20 mg/kg)-induced increase of wheel-running activity in a dose-depen-dent manner. These findings suggest that cocaine activates thebrain histamine neuron system, which may play the role of inhib-iting the cocaine-induced wheel-running behavior. Key Words:Cocaine— Histamine level— HistamineN-methyltransferase—L-Histidine—Wheel-running behavior—Rat brain.J. Neurochem. 69, 875—878 (1997).

A biogenic amine, histamine (HA), has been suggestedrecently to be a neurotransmitter or neuromodulator in themammalian brain. Cell bodies ofHAneurons are localized inthe tuberomammillary nucleus in the posterior hypothalamicregion, whereas their varicose fibers are found in almost allregions of the brain. In the mammalian brain, HA is synthe-sized from L-hïstidine (L-His) by histidirie decarboxylaseand is inactivated by histamine N-methyltransferase (HMT)to N~-methylhistamine(Prell and Green, 1986; Schwartz etal., 1991; Watanabe andWada, 1991; Onodera et al., 1994).

Theinvolvement of thebrain HAneuron system in diversebrain functions and behaviors has been reviewed (Prell andGreen, 1986; Schwartz et al., 1991; Watanabe and Wada,1991; Onodera et al., 1994). But the effect of cocaine (Coc)on the brain HA neuron system is still unclear, although itseffects on other biogenic amine systems have been studiedextensively (Lakoski et al., 1992). H1 antagonists enhancedCoc-induced self-administration or place preference (Berg-mann and Spealman, 1986; Masukawa et al., 1993). How-ever, there have been no reports on the neurochemicalchanges in the brain HA neuron system resulting from theadministration of Coc. Recently, we reported that the admin-istration, of methamphetamine increased the HA level andrelease in the rat striatum (Ito et al., 1996a,b).

In this study, we first examinedwhether theadministrationof Coc influenced HA levels and HMT activity as markers

of HA turnover in the rat cortex, striatum, nucleus accum-hens, amygdala, hippocampus, diencephalon, midbrain, ponsmedulla, and cerebellum. Moreover, we studied the effectof L-His on Coc-induced wheel-running behavior to deter-mine the functional role of the neurochemical change inthe brain HA neuron system caused by the administrationof Coc.

MATERIALS AND METHODS

AnimalsWistar ratsweighing 220—240 g at thebeginning of exper-

iments were group-housed (two rats per cage) with freeaccess to food and water in aroom maintained at 22 ±2°Cand 65 ±5% humidity under a 12-h light/l2-h dark cycle(lights on at 6:00 am.). This study was conducted in accordwith a guide for the care and use of laboratory animalsregulated by Tohoku University School of Medicine andNIH guidelines on animal care.

Measurements of HA levelsRats were killed by decapitation 1 h after the intraperito-

neal injection of saline (1 ml/kg) or Coc (10 and 20 mg/kg). Coc (Shionogi Pharmaceutical Co., Osaka, Japan) wasdissolved in 0.9% (wt/vol) NaC1 solution. The brains wererapidly removed anddissected on ice into nine regional partsof thecortex, striatum, nucleus accumbens, amygdala, hippo-campus, diencephalon, midbrain, pons medulla, and cerebel-lum by the method of Glowinski and Iversen (1966). Thebrain parts were homogenized in 10 volumes of 3% perchlo-rie acidcontaining 5 mM Na2-EDTA with aPolytron homog-enizer (Kinematica, Lucerne, Switzerland) at a maximumsetting for 10 s in an ice bath, and then the homogenateswere centrifuged at 10,000 g for 30 min at 4°C.The superna-tants were stored at —80°Cuntil HA analyses.

HA was measured by a sensitive HPLC—fluorometric

Received April 18, 1997; accepted April 28, 1997.Address correspondence andreprint requests to Dr. C. Ito at De-

partment of Psychiatry, Tohoku University School of Medicine, I -

1 Seiryo-machi, Aoba-ku, Sendai, 980-77, Japan.Abbreviations used: Coc, cocaine; HA, histamine; HMT, hista-

mine N-methyltransferase; L-His, L-histidine.

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method as described by Yamatodani et al. (1985). In brief,HA was separated on a cation exchanger, TSK gel SP2SW(Tosoh, Tokyo, Japan; particle size 5 tim), and eluted with0.25 M KH2PO4 as the mobile phase at a flow rate of 0.6mi/mm using aconstant flow pump (model CCPM, Tosoh).HA eluate was derivatized using an on-line automated o-phthalaldehyde method (Shore et al., 1959), and the fluo-rescence intensity was measured at 450 nm with excitationat 360 nm in a spectrofluorometer equipped with a flow cell(model C-R3A, Shimadzu, Kyoto, Japan) and a chromato-graphic data processor (model C-R3A, Shimadzu).

Measurements of HMT activityRats were killed by decapitation I h after the injection of

saline (1 mI/kg i.p.) or Coc (20 mg/kg i.p.). The parts ofthe brain (striatum, nucleus accumbens, and amygdala) thathad been removed and combined were homogenized in 4volumes of HMT solution (100 mM sodium phosphatebuffer, pH 7.4, 10 mM dithiothreitol, 1% polyethylene gly-col) in a Polytron homogenizer (Kinematica) at a maximumsetting for 10 s in an ice bath. The homogenates were centri-fuged at 10,000 g for 30 mm, and the supernatants weredialyzed against an HMT solution at 4°Cfor 3 h. The HMTreaction was carried out at 37°Cwith 0.25 ml of a mixturecontaining 0.1 mM HA, 30 mM sodium phosphate buffer,0.25 mM S-adenosyl-L-methionine, and 0.2 mM aminogua-nidine and the supernatants. Three hours later, the reactionwas stopped by adding 0.03 ml of 60% perchloric acid. Themixtures were centrifuged briefly, and the supernatants werestored at —80°Cuntil Nr~methylhistamineanalyses. Proteinswere determined by the method of Lowry et al. (1951) withbovine serum albumin as the standard.

N~-Methylhistaminewas separated from HA by the sensi-tive HPLC—fluorometric method as mentioned above, exceptwith 37.5 mM citric acid, 1.25% imidazole, and 20% metha-nol, pH 6.8, as the mobile phase.

Measurements of wheel-running activityRats were injected with saline (1 mi/kg i.p.) or Coc (20

mg/kg i.p.). In some experiments, they were also pretreatedwith saline (1 mi/kg i.p.) or L-His (350 and 700 mg/kgi.p.) 30 min before. The total wheel-running activity wasmeasured with the wheel-running meter (Muramachi KikaiCo., Japan) 60 min after the last injection.

DrugsCoc hydrochloride (Shionogi) and L-His hydrochloride

(GIBCO, Grand Island, NY, U.S.A.) were dissolved in sa-line.

StatisticsStatistical analyses of data were carried out using one-

way ANOVA, followed by Duncan‘s test. In all cases, pvalues of <0.05 were considered statistically significant.

RESULTS

Effect of Coc on HA levels in various regions ofthe rat brain

The administration of Coc (20 mg/kg) significantly in-creased HA levels in the striatum, nucleus accumbens, andamygdala 1 h later (Table 1). There were no significantchanges in the HA levels of other regions alter the adminis-tration of Coc (Table 1). The administration of Coc (10mg/kg) did not change HA levels.

Effect of Coc on HMT activity in the rat brainThe administration of Coc (20 mg/kg) significantly in-

creased HMT activity in the brain (the striatum, nucleusaccumbens, and amygdala) 1 h later (Fig. 1).

Effect of pretreatment with L-His on Coc-inducedwheel-running behavior

The administration of Coc (20 mg/kg) increased wheel-running activity to about sevenfold (Fig. 2). The pretreat-ment with L-His (350 and700 mg/kg) significantly inhibitedthe Coc-induced increase of wheel-running activity in adose-dependent manner (Fig. 2).

DISCUSSION

It is well known that Coc acts on dopamine, norepineph-rine, and serotonin neuron systems (Lakoski et al., 1992).In the present study, we first found that Coc also acts on thebrain HA neuron system. The administration of Coc in-creased HA levels in the striatum, nucleus accumbens, andamygdala. The administration of Coc also increased the ac-tivity of an HA-inactivating enzyme, HMT, in these regionsof the brain. The doses of Coc in the present study are

TABLE 1. The effect of Coc on HA levels in the rat brain

Brain part Saline Coc (10 mg/kg) Coc (20 mg/kg)

Cortex 128.3 ±5.1 179.5 ±55.4 147.6 ±9.2Striatum 273.8 ±30.2 285.1 ±29.7 381.7 ±43.3°Nucleus accumbens 422.6 ±64.1 447.0 ±52.7 686.0 ±105.7°Amygdala 239.0 ±20.8 276.0 ±39.0 383.3 ±54.5°Hippocampus 229.3 ±27.4 220.4 ±29.1 243.5 ±25.3Diencephalon 1,378.3 ±185.0 1,290.5 ±92.9 1,516.1 ±223.3Midbrain 187.9 ±38.1 166.4 ±13.2 222.5 ±12.2Pons medulla 87.1 ±9.5 106.2 ±22.2 92.4 ±7.9Cerebellum 78.0 ±8.6 81.0 ±7.9 97.6 ±17.0

Rats were killed I h after the administration of saline (1 mi/kg i.p.) or Coc (10 and20 mg/kg i.p.). Each value represents the mean ±SEM (pmol/g) of six rats.

Statistical anslysis was performed by means of one-way ANOVA, followed by Dun-can‘s test (“p < 0.05).

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COCAINE AND HISTAMINERGIC NEURONS 877

relevant to those used to increase locomotor activity, andthey neither cause convulsions nor are toxic to neurons (La-koski et al., 1992). These findings suggest that Coc activatesthe brain HA neuron system. Coc acts through monoamine-uptake transporters, but the uptake system of HA was notinfluenced by Coc (Smits et al., 1988). We recently foundthat the administration of methamphetamine increased HAlevels and release in the rat striatum and cortex, includingthe nucleus accumbens and amygdala (Ito et al., 1996a,b).Moreover, we recently showed that dopamine D2 receptorantagonists, sulpiride and haloperidol, blocked the metham-phetamine-induced increase of HA release in the striatum,whereas a D1 receptor antagonist, SCH23390, did not (Itoet al., 1996b). Therefore, the activation of the brain HAneuron system by Coc may result from the activation of theDA neuron system, because the effect of Coc on the dopa-mine neuron system is assumed to be similar to that ofmethamphetamine (Seiden et al., 1993).

The effect of Coc on the brain HA neuron system maybe associated with various functions, such as motor activity,because the brain HA neuron system has an important rolein all these functions (Prell and Green, 1986; Schwartz etal., 1991; Watanabe and Wada, 1991; Onodera et al., 1994).In the present study, we found that L-His inhibited the Coc-induced increase of wheel-running activity in rats. HA pro-duced from L-His in the peripheral system is unlikely toaffect the CNS, because HA cannot cross the blood—brainbarrier (Prell and Green, 1986; Schwartz et al., 1991; Wata-nabe and Wada, 1991; Onodera et al., 1994). The dose ofL-His used in our experiment increased the brain HA level30 min later (Yokoyama et al., 1992). Thus, the inhibitoryeffect of L-His on the Coc-induced wheel-running behavioris dependent on HA in the CNS. Treatments with agents thatactivate the brain HA neuron system, such as the intracere-broventricular injection of HA and the intraperitoneal injec-tion of L-His, an inhibitor of HMT (metoprine), or an H3receptor antagonist (thioperamide), also inhibited metham-phetamine-induced locomotor and stereotyped behavior inmice and rats (Joshi et al., 1981; Onodera and Ogura, 1982;Itoh et al., 1986; Clapham and Kilpatrick, 1994). Therefore,the activating effect of Coc on the brain HA neuron systemmay have the important role of inhibiting the Coc-inducedwheel-running behavior.

In conclusion, our study suggests that Coc activates the

FIG. 1. The effect of Coc on HMT activity in the rat brain. Ratswere killed by decapitation 1 h after the administration of saline(1 mI/kg p.) or Coc (20 mg/kg p.). Results are mean ±SEM(bars) values (n = 6). Statistical analysis was performed bymeans of ANOVA, followed by Duncan‘s test (°p< 0.05).

FIG. 2. The effect of L-His on Coc-induced wheel-running be-havior. Rats were injected with saline (1 mI/kg i.p.) or Coc (20mg/kg p.). They were also pretreated with saline (1 mI/kg i.p.)or L-His (350 and 700 mg/kg p.) 30 min before. The total wheel-running activity was measured with the wheel-running meter 60min after the last injection. Results are mean ±SEM (bars) val-ues (n = 6). Statistical analysis was performed by means ofANOVA followed by Duncan‘s test (**p < 0.01, vs. the groupinjected with saline; #p <0.05, ##p <0.01, vs. the group injectedwith Coc).

brain HAneuron system in the striatum, nucleus accumbens,and amygdala, and that the pretreatment with L-His inhibitedthe Coc-induced wheel-running behavior.

Acknowledgment: This study was partly supported bygrants from the Ministry of Health and Welfare and Grants-in-Aid from the Ministry of Education, Science, Sports andCulture of Japan.

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