Ž .Brain Research 834 1999 152–154www.elsevier.comrlocaterbres

Short communication

Intra-periaqueductal grey injection of galanin increases the nociceptiveresponse latency in rats, an effect reversed by naloxone

Duo Wang a, Hai-Hong Ye a, Long-Chuan Yu a,b,), Thomas Lundeberg b

a Department of Physiology, College of Life Sciences, Peking UniÕersity, Beijing 100871, Chinab Department of Physiology and Pharmacology, and Department of Surgery and Rehabilitation, Karolinska Institutet, 171 77 Stockholm, Sweden

Accepted 13 April 1999

Abstract

Ž .The nociceptive response latencies were increased significantly after intra-periaqueductal grey PAG administration of 1.0 or 3.0nmol of galanin, but not 0.3 nmol, in rats. The effect of galanin was attenuated by following injection of 5.5 nmol of naloxone into PAG.These results indicate an anti-nociceptive role of galanin, and a possible interaction between galanin and opioid peptides in PAG in rats.q 1999 Elsevier Science B.V. All rights reserved.

Keywords: Periaqueductal grey; Nociceptive response latency; Galanin; Opioid peptide; Naloxone

Many studies have shown that the neuropeptide galaninmay be involved in the transmission of nociceptive infor-

w xmation in the spinal cord 2–4,9,11 . Previous studies inour laboratory also demonstrated that intrathecal adminis-tration of galanin resulted in dose-dependent antinocicep-

w xtive effects in the mononeuropathic rats 14 . Nevertheless,the mechanisms of the various actions of galanin, espe-cially in antinociception in the brain, is not yet clearlyknown. Galanin immunoreactive substance, galanin-im-munoreactive fibers and galanin receptors are shown to

Ž . w xexist in the rat periaqueductal grey PAG 5 . Endogenousopioid peptides are also found in PAG and are demon-strated to contribute significantly to the pain modulationw x1,4,8,10 . The present study was performed to investigatethe role of intra-PAG injection of galanin, and the possibleinteraction between galanin and opioid system in rat’sPAG.

Experiments were performed on freely moving maleŽSprague–Dawley rats 200–300 g; Experimental Animal

.Center of Beijing Medical University, Beijing, China . Allexperiments were conducted according to the guideline ofthe animal ethical committee of Karolinska Institutet andevery effort was made to minimize animal suffering. Theanimals were anaesthetized by intraperitoneal pentobarbitalŽ .40 mgrkg and were mounted on a stereotaxic instru-

) Corresponding author. Fax: q86-10-62751850; E-mail:yulc@pku.edu.cn

ment. A stainless steel guide cannula of 0.8 mm out-diam-Žeter was directed to PAG AP 5.5, L 0.5, H 6.0 mm from

.the surface of the skull according to Paxinos and Watsonw x6 , and was fixed to the skull by dental acrylic. All ratswere accustomed to the nociceptive tests for 5 days beforethe surgery. At 2 days after the surgery, intra-PAG injec-tions were performed. On the experimental day, a stainlesssteel needle with 0.4 mm diameter was directly insertedinto the guide cannula, with 1 mm beyond the tip of thelatter. One ml of solution was thereafter infused into PAGover 1 min.

The latencies to hindpaw withdrawal during thermalw xand mechanical stimulation were measured 14–16 .

Briefly, the entire ventral surface of the rat’s hindpaw wasplaced manually on the hot-plate which was maintained at

Ž . w xa temperature of 528C 51.8–52.48C 14 . The time toŽ .hindpaw withdrawal was measured in seconds s to be

Ž .referred to as the hindpaw withdrawal latency HWL . TheŽ .Randall Selitto Test Ugo Basile, Type 7200, Italy was

used to assess the HWL to mechanical stimulation. Awedge-shaped pusher at a loading rate of 30 grs wasapplied to the dorsal surface of the manually handledhindpaw and the latency required to initiate the struggleresponse was assessed and expressed in seconds. Theaverage values obtained before intra-PAG injection wereregarded as the basal HWL. The HWLs recorded duringsubsequent experiments were expressed as percentage

Žchanges of the basal level for each rat % change of.HWL , with a cutoff limit of 15 s to avoid the skin

0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0006-8993 99 01513-9

( )D. Wang et al.rBrain Research 834 1999 152–154 153

Table 1Effects of galanin administrated into periaqueductal grey on the hindpaw withdrawal latency to thermal and mechanical stimulation in rats

Ž .Treatments n Before s % Change of HWL after intra-periaqueductal grey injection

5 10 20 30 min

Hot-plate test 0.9% Saline 1 ml 10 3.7"0.2 4.3"6.5 3.6"2.9 3.2"4.5 4.6"5.4Galanin 0.3 nmol 6 3.6"0.1 0.7"12.5 y4.5"6.9 12.2"8.0 y11.8"6.0

UGalanin 1 nmol 6 3.9"0.4 25.9"11.4 24.2"13.4 12.6"8.5 3.1"5.6UUUGalanin 3 nmol 8 3.4"0.2 12.8"11.0 66.9"16.0 45.3"12.8 17.2"6.1

Randall–Selitto test 0.9% Saline 1 ml 10 5.9"0.2 3.8"3.6 1.4"4.7 y0.3"4.5 2.2"1.9Galanin 0.3 nmol 6 4.9"0.2 15.5"10.3 10.6"5.6 9.1"10.2 0.4"10.4

UUUGalanin 1 nmol 6 5.6"0.4 23.0"7.5 30.7"7.3 23.7"9.2 17.7"4.0UUUGalanin 3 nmol 8 5.2"0.2 27.2"9.4 55.1"12.5 27.7"9.8 29.0"9.5

Ž .Control group: 1 ml of 0.9% saline ns10 ; HWL: hindpaw withdrawal latency.U UU UUU Ž .The data are presented as means"S.E.M., P-0.05, P-0.01 and P-0.001 compared with the control group two-way ANOVA .

damage. Each rat was tested with both types of stimula-tion. At the conclusion of the experiments, the location ofthe tip of the injecting tube was verified and only theresults from nociceptive tests with the tips of the injectingtubes placed within PAG area were used for statisticalanalysis. Data from nociceptive tests were presented asmeans"S.E.M. The difference between groups was deter-

Ž . Umined by two-way analysis of variance ANOVA , P-

0.05, UUP-0.01 and UUUP-0.001 were considered assignificant differences.

Solutions for intra-PAG administration were preparedŽ .with sterilized saline, each with a volume of 1 ml: 1 0.3,

Ž1.0 or 3.0 nmol of galanin galanin, Bachem, Fein-. Ž . Žchemikalien, Switzerland , respectively; 2 5.5 nmol 2

. Žmg of naloxone naloxone hydrochloride, Sigma, St. Louis,.MO . Control groups were given 1 ml of 0.9% saline.

A total of 30 rats received intra-PAG injection of 0.3Ž . Ž . Ž .nmol ns6 , 1.0 nmol ns6 or 3.0 nmol ns8 of

Ž .galanin, or 1 ml of 0.9% saline ns10 as control group.The results are shown in Table 1. The HWLs to thermaland mechanical stimulation increased significantly after

Žintra-PAG injection of 1.0 nmol Thermal test: F s1r14.6.23, P-0.05; Mechanical test: F s35.04, P-0.0011r14

Žor 3.0 nmol of galanin Thermal test: F s27.51, P-1r16.0.001; Mechanical test: F s42.23, P-0.001 com-1r16

pared with the control group. In the group receiving intra-PAG injection of 0.3 nmol of galanin, there were nosignificant changes in HWLs in comparison with the con-

Žtrol group Thermal test: F s1.06, Ps0.31; Mechan-1r14.ical test: F s2.71, Ps0.11 . The effects of intra-PAG1r14

administration of 3.0 nmol of galanin reached the peakbetween 5–10 min, then began to recovery from 20 min.

Two groups of rats received intra-PAG injection of 3.0nmol of galanin, followed 5 min later, by 5.5 nmol of

Žnaloxone ns10; basal HWLs were 4.8"0.3 s for of.thermal tests and 6.1"0.2 s for mechanical tests or 1 ml

Žof 0.9% saline ns10; basal HWLs were 4.6"0.3 s for.of thermal tests and 6.7"0.4 s for mechanical tests . In

our experiments, 5 min after intra-PAG injection of 5.5nmol of naloxone, the increased HWL was attenuated

Žpartially in both tests Fig. 1A, Thermal test: F s43.67,1r18

P-0.001; Fig. 1B, Mechanical test: F s34.39, P-1r18.0.001 in comparison with the control group, in which the

HWLs to both noxious stimulation increased for about 30Ž .min, as shown in Fig. 1. Another group of rats ns5 ,

received intra-PAG administration of 1 ml of saline, fol-

Fig. 1. Effects of intra-PAG injection of naloxone on the galanin-inducedincrease in HWLs in rats. Times0 min: 3 nmol of galanin was injectedinto PAG; Times5 min: intra-PAG administration of 5.5 nmol of

Ž .naloxone ns10 . Control group: 3 nmol of galaninq1 ml of 0.9%Ž .saline ns10 . HWL: hindpaw withdrawal latency, vertical bars indicate

S.E.M., two-way ANOVA, UUU P -0.001 compared with control group.

( )D. Wang et al.rBrain Research 834 1999 152–154154

lowed 5 min later by 5.5 nmol of naloxone, showed nosignificant changes of HWLs to either stimulation.

w xYaksh et al. 13 reported that the antinociceptive ef-fects induced by intra-PAG injection of morphine werereversed by following intra-PAG administration of nalox-one. The results of the present study showed clearly thatthe nociceptive response latencies were increased signifi-cantly after intra-PAG administration of 1.0 or 3.0 nmol ofgalanin, but not 0.3 nmol in rats, indicating that in PAGgalanin may be involved in the endogenous antinociceptivesystem. Studies suggested that in the spinal cord galaninand opioids played synergic effects in the transmission of

w xpresumed antinociceptive information 7,12 . In the presentstudy, we demonstrated that the increase in HWLs inducedby intra-PAG administration of galanin could be attenuatedby the opioid antagonist naloxone, indicating a possibleinteraction of antinociception between galanin and opioidin PAG.

Acknowledgements

This study was supported by funds from the KarolinskaInstitutet Foundation, the Foundation for Acupuncture andAlternative Treatment Methods, the National Natural Sci-

Ž .ence Foundation of China NSFC and the Natural SciencePre-Research Foundation of Peking University.

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