Lack of GABAergic modulation of acetylcholine turnover in the rat thalamus

,~euros~eme Letters 87 (1988) 293 296 Elsevier Sc~enufic Publishers Ireland Lid

2~

NSL 05282

Lack of GABAergic modulation of acetylcholine turnover m the rat thalamus C Cos~ a n d P L W o o d R¢ ~eat~h Dept

Pharma~eutt¢al~ Dtvtston Ctha-Getg~ (orp

~ummtt ~¢J 07001 ( ~ S 4

(Rccc~ed 9 No~ember 1987 Revised ~ers~on r~.ce~ed 2l December 1987 Accepted 15 Januar,~ It)88~ Acctylcholine turnover Gas chromatography mass lragmentograph,~ Thalamus ( o r t e \ , - 4 m m o b u t 3 r l c acid (GABA), 4 5 6 7-Tetrah'~dro~soxazoln[5 4-c]p,,Ndm-3-ol (THIP) Daa7epam

In order to ln~eshgate the GABAerg~c m o d u l a h o n of the chohnerg~c mldbram-thalamus pathua~ the ~.ffccts ol the G A B A a agomst 4 5 6 7-tetrah)drolsoxa7olo[5 4-c]p~ndm-3-ol (THIP) and of the bcn/odlazcpme dla/epam on acetylchohne (ACh) turnover m the thalamus have been studied TR x~h ~ a s also measured m the lrontal and parietal cortices ol the same animals Our data confirm an mhlbJtc~r,~ GABAerglc m o d u l a h o n of the chohnergJc nucleus basalis-corte~ projechon but suggest a lack ol GABAerglc modulation of the chohnerg~c m~dbram-thalamus pathway

Chohnesterase-hlstochemlcal studies by Shute and Lewis [12] first suggested the presence of chohnerglc projections originating m the nucleus cunelformls region of the mldbram reticular formation and terminating m ~anous thalamtc nuclei The eMstence of th~s chohnergic mldbram-thalamus projection system has since been confirmed by neurochemlcal [7]. electrophyslologtcal [5] and chohne acet~ltransferase (ChAT)-tmmunohtstochemlcal [i 3] studies The neurophyslologlcal results of Dmgledlne and Kelley [5] first indicated that electrical stimulation of the midbram reticular formation lnh~b~ted the umt actt~ lty of neurons m the reticular thalamus by a mechanism that was partially antagomzed by atropine Next. Hoover and Jacobowltz [7] demonstrated that electrol~uc lesions of the nucleus cunelformls were followed by a decrease in ChAT acttwty m ,~aNous thalamlc nuclei Sofromew et al [13]. by detection of retrogradely transported horseradish peroxtdase (HRP) and tmmunohlstochemlcal demonstration of ChAT m the same neurons, demonstrated that the anteroventral, rostral m t r a l a m m a r and reticular thalamlc nuclei receive a direct lpsdateral lnnervation from two cholmerglc nuclei located m the nucleus cunelformis region the lateral dorsal tegmental nucleus (LTD) and the parabrachlal nucleus (orrt spomh'nt~ ¢ 07901 U S A

Cos1 Research DepI

Pharmaceuticals Division, (lba-Gelgy ¢ o r p

0~04-~940,88 $ 0~ 50 © 1988 Elsevier Sclentlhc Pubhshers Ireland Ltd

Summit NJ

294

The modulation of these chohnergic projections by other neurotransmltter system, has not been described A GABAerglc mnervaUon of thalamlc nuclei has been described [3, 4] as well as intrinsic G A B A neurons in the reticular nucleus [8] Since a GABAerglc inodulatlon of other central chohnerglc systems, including the septohippocampal [14, 15] and nucleus basahs-cortlcal pathways [I 14 16, 18] is known, the present study investigated the effects of GABAerglc drugs on the actlvlt) of chohnerglc neuron~ in the thalamus, by measuring the regional acetylchohnc (ACh) turnover rate (TR~,¢ h), m ~=vo Male Sprague Dawley rats (180 200 g, M b f (SD), Marland Farms, Hewltt, NJ) were Injected intraperltoneally with e,ther 4,5,6,7-tetrahydrolsoxazolo[5,4-c]pyrldln3-ol (THIP, 20 mg/kg, i p ). a GABAA agonist, or with the benzodlazepme receptor agonlst, dlazepam (5 mg/kg, l p ) and the animals sacrtficed 30 mln after the mjecuon of the drugs [14] At 21 mm after the administration of the drug, rats were refused ,~la the lateral tall vein w,th deuterated phosphorylchohne (15/Jmol/kg/mm) lot mm at the rate of 0 ! ml/mln They were then sacrificed by focused mlcrowa,,ed irradiation of the brain using a Thermex Metabostat focused microwave generator ( ~ 5 kW 2450 M H z Thermex New York, NY) The thalamus, frontal cortex and parietal cortex were dtssected and were processed as previously described [18] The percentage of deuterium mcorporated into regional brain choline and ACh, was monitored by gas c h r o m a t o g r a p h y - m a s s spectrometry in postUve chemtcal Ionization mode with methane as the reagent gas [17] Turno,,er calculations were performed according to Racagnl et al [11] and Cheney et al [2] Tissue protein was assayed by the method of Lowry et al [10] Statistical analysis of data was performed using Dunnett s multiple t-test subsequent to a one-way ANOVA 35 CONTROL

A

~30

THIP (20mg/kg)

"25 ~

E

DIAZEPAM(5mg/kg)

2o

c

ne > 0

15

~o :1:05

oo

THALAMUS

FRONTAL C

PARIETAL C

Fig 1 A c t i o n s o f T H I P a n d d l a z e p a m on A C h t u r n o v e r m the rat frontal cortex, parietal cortex a n d thalamus P < 0 0 5 ( n = 5 7)

29~

THIP (20 mg,'kg) reduced TRAch in the frontal and pametal corttces to 53 and 48% of controls ( P < 0 05), respecttvely (F~g 1) It dtd not affect the ACh turnover rate m the thalamus of the same ammals Slmtlarly, &azepam (5 mg/kg) decreased TR,x¢ m the frontal and pametal cortices to 65 and 48% of controls ( P < 0 05), but agam d~d not affect the ACh turnover rate in the thalamus of the same annnals (Ftg I) ACh levels were unaltered by all drug treatments (data not shown) These data confirm prewous studies [1, 14, 16]. demonstrating an mhtbttory GA BAergtc modulation of the chollnerg~c projection from the nucleus basahs to the cortex However our current data would suggest that the chohnerg~c projections of the laterodorsal tegmental nucleus do not possess an lnhlb~tor~ GABAergtc input Th~s conclus~on ~s strengthened by the expertmental destgn m which the rcgtonal drug effects under stud.~ uere measured m the same ammals m which pos~t~,~e drug effects on the nucleus basahs-cortlcal chohnerg~c pathway were mon,tored m the presence of no drug effects on the mtdbram-thalamus projectton Howe~er, since the bramstem cholmerg~c input to the thalamus ts wtdespread [6], and the basal forebram choltnerg~_ input ts rcstrtcted to the reticular thalamus [9], our data for ACh turnover ~n the whole thalamus cannot exclude a small effect of GABAerg~c agents on the cholmerg~c input to the rettcular thalamus I Blakcr Vv D GABAerglc control of the chollnerglc proJections to the lrontal cortex is not tom~. Brain Re', :~25 (1985) ~89 z;90 2 (h enc~ D L Trabucchl M Racagm, G Wang C a n d ( o s t a E E f l e c t s o l a c u t e a n d c h r o n l c r n o r phmc on regional rat brain acet~lchohne turno,~cr rate Lile Scl 15 (1974) 1977 1990 ~, ( urtl', D R and Tebecls A k Blcuculhne and thalamlc inhibition hxp Brain Res 16 (1972) 210 21~: 4 1)1 ( h l t r a G Porccddu M L Morelh M Mulas M L and Gessa G L Strlo-mgral and mgrothalam~e G&B,S,-erglc neurons as output pathwa,rs for stmatal responses In P Krogsgaard-Larsen I qchcel-kruger and H Kolod CEde, ) GABA-ncurotransm~tters Alfredo BenTon S~mposlum 12 Mu nksg aard Academic, New York, pp 1978 4,55 481 s Dmglcdme R and Kell'y J G Brain ,,t~.m ~tlmulatlon and the acetylchohne-e,,oked mhlbfllon ol n,.urtme,, m the lehnc nucleus retlcularls thalami J Ph~'qol ( L o n d ) 271 (1977) 1~,5 1":,4 6 Hallangcr ,~ L Lc~e'r A I Lee H J R)e D B and Warner, B H , The origins ot the chohnerglc md other subcortlcal affcrents to the thalamus In the rat J C omp Neurol 262 (1987) 11)5 124 7 l loo,,cl D B and Jacobowltz D M Neurochemlcal and hJstochernlcal studies of the ellect ol a lesion ol the nucleus euneflorm s on the chohnerg~c mner'~at~on of dr, crete areas of the rat br nn Brain Re,, 15~(1979) I1~ 122 8 Housel ( R ',/aughn J Barber, R P and Roberts, F G A B A neurones are the major cell l~,pt_ ol the nucleus rctlculans thalami Brain Res 200 (1980) ~,41 354 9 Lc',_', a. I Hallanger A E and Warner B H Chohnerglc nucleus basahs neurons rna,, retire_nee the cortex ~la the thalamus Neuroscl L e t t , 7 4 ( 1 9 8 7 ) 7 13 111 Lowr', O H Roscbrough N J Farr A L and Randall R J Protein measurcm~.nt x~lth the bohn phenol reagent J Blol ( h e m , 1 9 3 1 1 9 5 1 ) 2 6 5 275 II Racagm G ¢hene~ D L Trabuechl, M , Wang (~ and Costa E Measurement o[ acct~lchohne turnoxer rate In discrete areas o f t h e rat brain Lfle Sol 15 (1974) 1961 1975 12 Shule ( ( D lnd Lewis P R The asccndmg chohnerglc reticular s',stem neocortlcal ollactor'~ and subcortlcal prolectlons Brain 91) (1967) 497 520 1:~ bofromew M V Prlestlev J V (~onsolaz~one A Eckenstem F and ( u c l l o & C (_ hohnerglc proj,.ctlon lrona the m~dbram and pont to the thalamus m the rat ~dcntlhed by combined retrograde tracing and ehohne acetvllransferase nnmunoh~stochem~str) Brain Res ~29 (1985) 21~ 2~,3

296 14 Wood, P L, Pharmacological evaluation of GABAerglc and glutamaterglc inputs to the nucleus ba~,~hs-cortlcal and the septal-hlppocampal chohnerglc projections, Can J Physlol Pharmacol 64 [1986) 325-328 15 Wood, P L, Cheney, D L and Costa, E , An mvest~gatlon of whether septal ~-ammobutyrate-contammg mterneurons are revolved m the reduction m the turnover rate ofacetylchohne ehc~ted by substant.L P and fl-endorphln in the hlppocampus Neurosc~ence, 4 (1979) 1479 1484 16 Wood, P L , McQuade, P S and Nalr, N P V GABAerglc and oplold regulation ot the substantla mnommata-cort~cal chohnerglc pathway Jn the rat Proc Neuro-Psychopharmacol Blol Psychmtr~ 8 (1984) 789- 792 17 Wood, P L and Peloqum, A , Increases m chohne levels m rat brain ehclted by meclolenate, Neuropharmacology, 18 (1982) 519 523 18 Wood P L and Richard, J GABAerg~c regulation of the substantm mnommata-cort~cal chohnerg~t. pathway, Neuropharmacologv, 21 I 1982) 969-972