GABA receptor alterations after chronic lithium administration. Comparison with carbamazepine and sodium valproate

prcg. NouroPs~,~hophnd Printed In Cheat Brttatn.

& Btol Psychti All ii&s rcsemed

1992.

Vol.

16.

pp.

571-579 0

0278 - 5846/92 1992 Per&amcm

GABA RECEPTOR ALTERATIONS AFTER CHRONIC LITHIUIb!lADMINISTRATION. COMPARISON WITH URBAMAZEPINEAND SODIUM VALPROATE NOBUTAKA MOTOHASHI' Department of Neuropsychiatry, Yamanashi Medical College Tamaho, Yamanashi, JAPAN (Final form, November 1991)

Motohashi, Nobutaka: GABA Receptor Alterations After Chronic Lithium Administration. Comparison With Carbamazepine And Sodium Valproate. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1992, 16(4):571-579. 1. Effects of lithium, carbamazepine, sodium valproate and baclofen on GABA receptors were examined in several regions of the rat brain. 2. [3HlMuscimol (MUS) and [3H](-)baclofen (BAC) were used to label GABA, and GABA, receptors, respectively, in synaptic membranes from rat brain. 3. Single treatment with lithium chloride, carbamazepine or sodium valproate did not change [3H1MUS or 13HlBAC binding in the frontal cortex, hippocampus and thalamus. 4. Following chronic treatment with lithium, carbamazepine or sodium valproate, [3H]BAC binding was significantly increased in the hippocampus but not in the frontal cortex, thalamus or striatum. 5. [3HlMuscimol binding did not change in any region examined after chronic treatment with lithium, carbamazepine or sodium valproate. 6. Single and chronic administration of baclofen did not change [3H]MUS or 13H]BAC binding. 7. One common mechanism of action of mood stabilizers may be mediated by GABA, receptors in the hippocampus. Z

: baclofen, carbamazepine, GABA, receptor, hippocampus, , sodium valproate.

v: baclofen (BAC), y-aminobutyric acid (GABA), cerebrospinal fluid (CSF), muscimol (MUS).

GABA is one of the major inhibitory neurotransmitters

in the

mammalian central nervous system and is thought to be involved in lPresent address: Department of Neurology and Psychiatry, Hiroshima University School of Medicine, Kasumi, Hiroshima, JAPAN

571

$15.00 Press Ltd

572

N. Motohashl

the pathophysiology

of many neuropsychiatric

disorders. The GABA

hypothesis of affective disorders has been proposed for several reasons. First, the concentration of GABA plasma of depression 1981; 1984).

Gold et

al.,

was

decreased in CSF and

(Berrettini et al., 1983; Gerner and Hare,

1980;

Kasa et

al.,

Second, some GABA agonists such

1982; Petty as

and

Coffman,

sodium valproate and

progabide were effective in the treatment of affective disorders (Calabrese and Delucchi, 1990; Emrich et al., 1980; Pope et al., 1991; Weiss et al., 1986 . Lastly, many classes of antidepresant drugs and electroconvuls ive shock, when applied repeatedly, upregulated GABA, receptors in the frontal cortex of the rat (Gray and Green, 1987; Lloyd et al., 1985), although conflicting reports have been published

(Cross and Horton, 1987; Szekely et al., 1987).

Lithium and carbamazepine have been widely used for the acute and prophylactic treatment of affective disorders 1986). Recently, sodium valpropate has been

(Post, 1990: Schou,

introduced

as

an

alternative in the treatment of bipolar disorders, especially rapidcycling ones (Calabrese and Dellucchi, 1990; Emrich et al., 1980; Pope et al., 1991). Although chronic treatment with lithium, carbamazepine or sodium valproate increased the concentration of GABA and decreased the turnover of GABA in some regions of the rat or mouse brain (Bernasconi, 1982; Gottesfeld et al., 1971; Marcus et al., 1986; Mitsushio et al., 1988; Nagaki et al., 1990; Patsalos and Lascelles, 19811, the effects of these drugs on GABA receptors have rarely been examined

(Lloyd et al., 1985; Maggi and Enna, 1980; Slevin and

Ferrara, 1985). In this study, the author have examined the effects of lithium, carbamazepine and sodium valproate on GABA, and GABA, receptors in the rat brain. Moreover, the results were compared to those obtained with a GABA, receptor agonist, baclofen.

[3H]Muscimoi

and ['HI(-lbaclofen were used to label GABA, and GABA, receptors, respectively. Part of this work has been published elsewhere (Motohashi et al., 1989).

Male Wistar-Kyoto

rats (Shizuoka Laboratory Animal Center, Japan)

LIthlum. carbamazepine,valproate and GABAreceptors

573

weighing between 200 and 250 g were used. The rats were housed at 23f2'C under a 12 hr light/dark cycle and given free access to food and water.

Carbamazepine,

sodium valproate and baclofen were kindly donated

by Ciba-Geigy, Kanebo Pharmaceuticals and Daiichi Pharmaceuticals, Japan, respectively.

[3H]Muscimol and [3H](-)baclofen were purchased

from New England Nuclear. Other chemical compounds were obtained from commercial sources. Prow

. .

Druo admlnlstration. valproate

Lithium chloride

(150 mg/kg) and baclofen

(1.5 mEq/kg), sodium

(10 mg/kg) were dissolved in 0.9%

saline. Carbamazepine was suspended in 0.9% saline containing 0.1% (v/v) Tween 80. All drugs were injected i-p. The Control rats received 0.9% saline. For chronic treatment, the drugs were injected i.p. once daily for 14 days. The rats were decapitated 24 hr after the last (or single) injection, and brain regions rapidly dissected, frozen on dry ice and stored at -80°C up to the time of the binding experiment. In one experiment, the rats were decapitated 72 hr after the last injection of lithium, carbamazepine or 0.9% saline.

* . vAssavs.

Synaptic membranes were prepared according to

Herschel and Baldessarini

(1979). The membranes were frozen

overnight at -20°C prior to use in binding assays. GABA, and GABA, receptor binding assays were performed by the.methods of Herschel and Baldessarini

(1979) and Motohashi et al. (1989), respectively.

Synaptic membranes were not treated with Triton X-100. The final concentration of [3H]muscimol was 4 nM and that of [3H](-)baclofen, 10 nM. The incubation for both binding assays was stopped by rapid filtration on GF/B glass fiber filters under reduced pressure. The filters were washed three times with ice-cold Tris-HCl buffer and the radioactivity was measured in a liquid scintillation counter. Protein was quantified according to Lowry et al. (1951).

Statistical analysis of the data was performed by one-way analysis of variance

(ANOVA) followed by the multiple comparison test

N.Motohashi

574

(Duncan's method).

Single treatment with lithium, carbamazepine,

sodium valproate or

baclofen did not change either [3H]muscimol or [%I(-_)baclofen binding in the frontal cortex, hippocampus or thalamus

(data not

shown).

.

Trek

.

Following chronic treatment with lithium or carbamazepine, [3H]muscimol binding did not change in any of the brain regions examined

(Fig 1A). f3H](-)Baclofen binding, however, was

significantly increased in the hippocampus, but not in the frontal cortex, thalamus or striatum

(Fig 1B). The increase in [3H](-)

baclofen binding in the hippocampus remained 12 hr after the last injection of lithium or carbamazepine

(data not shown).

Thalemur

l. 1

200

100

specific Mndlng (% of control)

1 0

i 0

, loo

1

200

Spe&fic binding (% of control)

Fig 1 Effects of chronic treatment with carbamazepine or lithium on GABA, (A) and GABAs (B) receptors in the rat brain. Control values for GABA, and GABA, receptors, respectively, are as follows (fmollmg protein) : 487f12 and 219f12 in the frontal cortex; 239k20 and 2823 in the hippocampus; 971545 and lOlf5 in the thalamus; 310f24 and 29f4 in the striatum. The results are expressed as the mean* S.E.M. for six rats. **p
Llthlum. carbamazepine.

valproate and GABA receptors

575

Tr$ [3HIMuscimol binding did not change in any of the regions examined after chronic treatment with sodium valproate or baclofen f3Hl (-jbaclofen binding was significantly

hippocampus

(Fig ZA).

increased in the

(35%) and tended to increase in the frontal cortex

following chronic administration of sodium valproate

(20%)

(Fig 2B).

Chronic baclofen, however, did not change [3H](-)baclofen binding in any

of

the brain regions (Fig 2B).

B Strlatum

1;3 Baclofen W 0

Valproate Control

Hippocampus

Frontal cortex r 200

100

Specific binding (SCof control)

0

;

Id0

2tiQ

Speclflc blnding (% of control)

Fig 2 Effects of chronic treatment with valproate or baclofen on GABA, (A) and GABAs (B) receptors in the rat brain. Control values for GABA,,and GABAs receptors, respectively, are as follows (fmol/mg protein): 490f19 and 232fll in the frontal cortex; 256f9 and 27f2 in the hippocampus; 1020f33 and llOf5 in the thalamus; 342f20 and 2lf2 in the striatum. The results are expressed as the mean* S.E.M. for eight rats. *p
The present findings have demonstrated that chronic treatment with lithium, carbamazepine or sodium valproate increases GABA, receptors in the rat hippocampus. Moreover, since chronic valproate tended to increase frontal GABA, receptors, the results are almost in accord with those of Lloyd et al. (1985) showing a small but significant increase

(20%) in GABA, receptors in the frontal cortex. However,

GABA, receptors did not change in any of the regions examined

N.Motohashi

516

following chronic administration of baclofen, which is thought to be devoid of a mood-stabilizing

effect. It is interesting in this

regard that chronic treatment with lithium, carbamazepine or sodium valproate has been shown to increase the concentration of GABA and decrease the turnover rate of GABA in some brain regions of rodents (Bernasconi, 1982; Gottesfeld et al., 1971; Marcus et al., 1986; Nagaki et al., 1990; Patsalos and Lascelles, 1981). One common mechanism of action of mood stabilizers may be mediated by the GABAergic system, especially GABA, receptors. wInJQ==Q-= In contrast to GA3A, receptors, the present study failed to show any change in GABA, receptors following chronic treatment with lithium, carbamazepine or sodium valpraate. Part of our results are in accordance with those of Slevin and Ferrara

(1985) demonstrating

that [3H]muscimol binding did not change in the frontal cortex or hippocampus after chronic administration of sodium valproate. Although

[3H]GABA binding was decreased in the striatum and

hypothalamus following chronic lithium treatment, the same treatment did not change the binding in the [Maggi and Enna, 1980) I Because

cerebral

t3H]GA3A

cortex or hippocampus labels primarily the GABA,

site, our data accord with these results except in the striatum. This discrepancy may be due to the difference in the method of drug administration.

GABA, receptors were increased only in the hippocampus

in the

present study. Chronic lithium treatment increased serotonin release and decreased serotonin receptors in the hippacanpus but not in the cerebral cortex

(Treiser et al., 1981). Moreover, somatostatin level

was decreased only in the hippocampus following chronic treatment with carbamazepine

fNagaki et al., 1990). From

these studies,

the

hippocampus may be the major anatomical site at which mood stabilisers act. Nore neuroanatomical

information would be needed to

clarify the mechanisms of action of mood stabilizers.

Ltthium.carbamasepine,valproateandGABA receptors

577

The present study has demonstrated that GABA, receptors were upregulated in the hippocampus following chronic treatment with carbamazepine, valproate or lithium. One common mechanism of action of mood stabilizers may be related to GABA, receptors in the hippocampus.

The author thanks Prof. T. Kariya, Dr. K. Ikawa and Dr. K. Shioe for helpful suggestions and discussions. Part of this study was supported by grants from the Ministry of Education, Science and Culture and from the National Center of Neurology and Psychiatry (NCNP) of the Ministry of Health and Welfare, Japan.

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LIthium,carbamazepine.valproate andGABAreccptors

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Ther., w: 155-159. TREISER, S.L., CASCIO, C.S., O'DONOHUE, T.L., THOA, N.B. JACOBOWITZ, D.M. and KELLAR, X.J. (1981) Lithium increases serotonin release and decreases serotonin receptors in the hippocampus. Science, 211: 1529-1531. WEISS, E., BRUNNER, G., CLERC, G., GUIBERT, M., DROFIAMMA, B., PAGOT, R., ROBERT, G., THILLIEZ, D. and MUSCH, 8. (1986) Multicenter double-blind study of progabide in depressed patients. In: GABA and Mood Disorders: Animal and Clinical Studies, Bartholini, G., Lloyd, K.G. and Morselli, P.L. (Eds.), pp 127-133, Raven Press, New York. Inquiries and reprint requests should be addressed to: Nobutaka Motohashi, M.D., D.M.Sc. Department of Neurology and Psychiatry Hiroshima University School of Medicine l-2-3 Xasumi, Minami-ku, Hiroshima 734 JAPAN