ABSTRACTS

A199

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A202

DECREASE IN THE AFFINITY OF NIGRAL BENZODIAZEPINE

RECEPTORS FOLLOWING GABAergic DENERVATION OF SUB-

STANTIA NIGRA (S.N.). Biggio G., Corda M.G.,Gessa

G.L. Institute of Pharmacology, University of

Cagliari, Italy.

In rat=, the degeneration of the striatonigral

GABAergic pathway after intrastriatal injectionof

kainic acid (K.A.) causee an increaseinthe "amber

of GABA receptors in the S.N. without change= in

the affinity for the ligand (NatureZJ$ 618; 197tTJ.

Since a functional link between GABA and benzodie-

zepine receptore exists (Nature Z_Q, 553; 1978)we

studied the effect of the GABAergic denervationof

S.N. oo the 'H-di=~ep=m (3H-DZ) binding.Th= high

affinity 3H-DZ receptor binding wa= found lover in

the S.N. ipsilateral to K.A. injectedcaudatenu-

cleua than in S.N. of the intact side. The decrea-

=e of DZ bindi”g resulted from an increase in the

dissociation constant (KD) rather than a change i”

the “umber of available binding sites; the KD in

the lesioned and intact S.N. were 3.1 nMand8.7 n&l,

respectively. The results demonstrate forthe first

time that degeneration of a GABAergic afferent fi-

bers produces changes in the sensitivity of benro- diazcpine receptors.

A200

PWLOCENETIC AND PNAnnAcOLOGICAL C8AnACTERI8TIC8 OF WSCI- NOI. ACTIVATED BENZODIAZEPWE RECEPTOR BINDING. A. M.as,ti, J. Satinover. n. Oberdorfer. E. Plan” and S.J. E”“a. ““iv. *exa* “ed. School. “oo8C.m. Texas 77cl25

TO better charicterire the relationship between CABA and benzodiaepine recqtors. the Phylogeneric and Pharm- scolo&ical properties of muacinol-activated benzodiarepine rec=Ptor bindin cimol enhsnced f

in "ertebrste brain "ere examined. tius- H-diazepam binding to brain membranes of

all vertebratea studied, except the hagfish, (L apefies know” to possess GABA receptors, but where neither bs=al, nor =cLi"at=d 3H-dl=zep=m binding were observed. In re- spending ti8sue.v. the magnitude of the increase varied with the relative density of benrodiarepine rece

s tars.

Furthermore, the potency of muscinol to enhance H-dia-

repam binding appean to be subatsntially greater in h-n brain than in ocher species. Theme findIngs suggest that benrodiazepine and GABA receptors developed independently and that vat, if not all. benrodiarepine receptors are coupled to CAEA receptors with the coupling being most efficient in human brain.

This interaction W.L) also examined in the cerebral cortex of rats treated chronicall” with either v-acetvl- enic GABA (GAG), a GABA tra”sa.i”;.e inhibitor, or THIP, a direct acting GABA receptor agonist. Treatment with these agent8 caused a shift in the se”szitivity of bcnro- dimepine bind+"8 to muscimol =cti"=tion, "ith GAG de- creasin8, sod THIP increasing the response. suggesting that this receptor intersction can be pharmacolo8icelly manipulated in "ivo.

A201

EvIofNcE ED* Ih""OLvEMwrOFACNS G4eAExIC MEclwiISM IN 8ARXKEPIORINiXCED-AND SYNPA'D,ElXACl'IVA'iYON. Daniel J. Williford and Richard A. Gillis, Dept. of RI=- cology, Georgetarn UniMcsity. Washington, D.C. 20007.

Previw studies have demx&_cated that CNS GABAergic tianisns exert an influence on tonic autannic outflw fran the OvS (nntonaccio et al., Mucqbarmaml. 17: 597, 1978; DiMicco et al., 8&i&-204: 1106, 1979). 'It, deter- mine tfle plysiZic&=l iqrt=ii& of ulis Gneneqic system, the effects of drugs tiat rr0aify OJS wLBAer9ic synaptic transmission we= tested on reflex-itioced "qal brady- cxdia produCea by activation Of baroceazptors with i.". talus injections Of *enyle*cine, ard on reflerirduced pressor res&zonses produced by bilateral carotid occlusion. ~localose anesthetized cats were used and all drugs were administered into the fourth cecebroventricle. Pdministra- tion of GA8A as Well =s the GABR receptor agoniat, nwscinol, munteracted both reflex-induced changes in cat= xd pees- SUIX. Cnc= blockade Of reflerindwed vagal bradycardia wa8 present, administration of the GABR ceceptor anmist bicuculline restored the resp3ns.e to near normal. Pmnini- stration of bicwulline alone ahaxed ceflerirduced "agal bcadycxdia. These results suqqzstthata cNs_qic syrwse carprises part of the reflex vagal and smtietic pathways in the cat. (Supported by Gcants NS-12566 frcm the U.S.P.H.8. and 79-985 fmm the &wcican Heart Assaiation).

GAB* *No GLUTANATE: POSSIBl,E METABOLIC lNTLwlEDIARIE8 1NVOLVED IN THE 8YPOT8ALAMIC REGULATION OF FOOD INTAKE. R. B. Xeeker and R. D. Myers. Deparcmepta of Psychiatry and Pharmacology, University of North Carolina School of Medicine. Chapel “ill, North Carolina 27514

Pbarmacolo8i==lly-induced increases and decrease= in GABA activity in the "entromedial hypothalamus cau=e reciorocal chances in food intake in the rat. Condi- tions which ..,e”t GABA reduce &3 feeding whereas e decrease in GABA activity is associated with an in- crease in food intake. These chan8es are mo=t prominent within a discrete region of the hypothalamus which has low basal metabolic activity but a~relatively high yield of 14c-WA from a (U-14C)elucose DIeCUrSor. Both CABA

and glutamate are released into push-pull perfusates collected from this circumscribed region as the rat ~on=umes food. Thus far, the release of GABA appears to be tri88ered by nutrients arri"in8 at the gut and does not specifically parallel the entry of intraduo- denally infused 8lucose into the brain. Sites "hich release GA8A appear to be neuroaoatomically distinct from site= "hich release norepinephrine during feedin8. The data support the existence of a” independent and metabolically dietinet GABA-miner@c system within the basal hypothalamus which exert= inhibitory control over feeding behavior. (Supported by NlNCDS Po.fdoctor=l Fellowship F 32 N8 05395-02 to R.D.M. and NSF grant BMS-18441 to R.D.M.)

A203

VOLTA-.x CWLW ANALYSIS OY ANTIomwLSILNT FoTEmT.4TIoN OF GABA HESFONSEY OF CnAYPmR SW R8cNPmH NWROHBS.

Adams, P. R. and Banks, P. II. oept. Of Ph@Ol. b

Biophys., UlXB, Galveston, vex== 77550. wyala. Johnston=, Lin Md Dichtsr ,sr. Res. 121:259)

=nd Deisz and Lox (Nsurosci. Letters 5:199) h="e shown that the anticonvul~ant diphenylhydantoin (DPB) drauti- cslly enhances postsynaptic inhibition and GAW, respaues in the crayfish stretch receptor neuro"c. He have further inveatiyated the meohanimn of thi8 effect in stretch re- oeptnr "e"ro"es "oltayed clam@ "ith 2 KCC1-filled micro- electrodes. The inhibitory postsynaptic current (ipso) was elicited by setting up M axon reflex with a third, extracellular pipette. Tha do==-conduota,ce c"r"e for

bath apelied GABA "a= Obtain& by appLyin step hyp.rpc- larizing -=Dds in the abscncc and pre=enc= of G&B& The WA-induced ourrent ==9gs during hyp=rpolariz=tion, probably beoausc of intr=callular chloride depletion. The initial amplitude of the ==99in9 corr=nt ,,== taken to be proportional to the GABA conductance. Control ipsc's peaked in 1.5 IPS~C, and abowed exponantial dK=ya 1~ = 4 m9=o =t -100 m"). The dec=y rate decreased with membranc depolarization, the =-folding voltage being about 300 mV. Addition of 50 !JM DW sliyhtly increased the ipsc ampli- tude, and decreased the decay rate by 5 to 6 fold. The decay remained a single exponential and retained normal voltaoe sensitivitv. 50 u" DPI( also oroduoed a leftward parallel shift in the GABi doser=sp&s= cur"eL m*po- tency increased about I-fold, with no change in the Ipaxi- mum response. Our d=ta su99est that DPR prolongs the open time of _-operated channels. Supported by NS-14546 and NS-lr1920.

A204

EVIDENCE FOR GAr&',-ASSOCIATED AliD GADA-IFIDEPEADENT BEN7,ODIAZR:PINE(BZ) RECEPTOR COI:PLXXES IN BRAIN. Richard F. Squires. Lederle Laboratories, Pearl River, aerr York 10965.

One population of BZ receotors in rat brain IS SeAectiVely ppotected against heat inactivation at 60 C in dilute Tris HCl buffer b" GADA. muscimol and beta-Ruanidinopropionic acid. but not by Certain other GASA-nimetics (e.g. THIP, isoguvacine). Time CoUPSes Of BZ receptor inactivation reveal three populations of receptors: one which is not protected by GABA, another with is slightly protected and a third which is strongly protected. Dose-response C"="eS for GACA (30 min, 60%) reveal that two GABA receptors. with high and low affinities for GmA, reepectively, are in"olVed in the protective effects. UsipR ""washed P2 fmotions, the GABP.-minetics THIP end isoguvacine selectively inhibit 60:: and 4C$;, r=SpeCtiVely, of the total 8H-flunitrazepan binding sites, probably by antap.onizing endozenous CAEA. since both inhibitory effects are fully reversed by adding GACA. It is concluded that different kinds of GAM mimetics produce different kinds of confor- mational changes in associated BZ receptors. There are multiple BZ-GABA-ion receptor complexes.