Repeated administration of antidepressant drugs reduces regional somatostatin concentrations in rat brain

hatrnal of AJfecctir*eDisorders, 25 \ I992) 2 15-220 c, 1992 Elsevier Science Publishers B.V. All rights reserved 016.50327/32/$05.00

215

ces

T. Kakigi ‘, K.

aeda ‘, H. Kaneda a and K. Chihara ’

Depcwmaems of MPsychimy and “ Medicine, Kobe hirersi& School of Medicine, Kobe, Japan artd ’ h)ogo ?mtirarreof Clinica! Research, Himeji, Japan (Received 17 December I991 ) (Revision received 17 March 1992) (Accepted 31 March 1992)

A possible role for somatostatin in affective dic_prders is suggested by its low concentration in cerebrospinal fluid of patients with depression. Therefore, we studied the regional effects of antidepressant drugs and antimanic agents on somatostatin concentrations in rat brain. Repeated, but not acute, administration of clomipramine, a specific serotonin uptake inhibitor, caused a highly significant, widespread reduction in somatostatin levels. Somatostatin content was similarly reduced in the hypothalamus, and midbrain and thalamus following repeated administration of zimelidine, another specific serotonin uptake inhibitor. Repeated administration of either imipramine, maprotiline, mianserin, carbamazepine or zotepine were without effect on somatostatin levels. These results suggest that somatostatin in the brain might be involved in therapeutic effects of some of antidepressant drugs.

Key words: Somatostatin;

Antidepressant;

Clomipramine;

Zimelidine;

Carbamazepine;

Zotepine

._

Introduction Somatostatin, originally isolated from porcine hypothalam,, has subsequently been demonstrated ts occur in neurons of the cerebral cortex, basal ganglia, hippocampus and amygdala in high concentrations (Brownstein et al., 1975; Kobayashi et al., 1977). Reduction in the CNS

Correspondence to: Kiyoshi Maeda, Hyogo Institute of Clinical Research, 520 Saisho-kou, Hirneji 670, Japan.

and/or cerebrospinal fluid (CSF) concentrations of the neuropeptide has been described in several neuro-psychiatric disorders. A low level of CSF somatostatin has been demon;trzted in patients with depression by many investigators (Agren et al., 1984; Doran et al., 1986; Widerlijv et al., 1988; Davis et al., 1988), although no reduction in somatostatin levels was shown in postmortem cortical tissue from depressed patients (Charlton et al., 1988). Furthermore, a disturbed growth hormone secretion occurs in patients with depression (Maeda et al., 1975). Growth hormone secretion

is regulated in part by somatostatin in the hy pot halamus. This indicates that a disturbcd metabolism in somatostatin regulation in the brain may exist in patients with depression. The present study was designed to define the effect of repeated administration of various antidepressam drugs or antimanic agents on somatostatin metabolism in rat brain.

ra/Iale Wister rats, weighing 250400 g. were used in all experiments. Five antidepressant drugs, clomipramine, zimeiidine, imipramine, maprotiline and mianserin, and two antimanic agents, carbamazepine ?nd zotepine, were administered to rats twice daiiy for 10 days, intraperitoneally. The antidepressants and zotepine were given at a

dosage of 5 mg/kg and carbamaze ministered at 20 mg/kg. Drugs were obtained from Ciba-Caigy Co. (clomipramine, imipramine, maprotiline and carbamazepine), from Fujisawa Pharm. Co. (zimelidine and zotepine) an Organon-Sankyo Co. (mianserin). Contr mals were administered the same regimen physiologic saline. Six rats were used for eat group. tiour hours after t e last injection, all ha y their brains dissecte were killed by decapitati on ice into samples of five regions according to the method of Glowinski and Iversen : 31966)with a slight modification; hypothaIa turn (ST), hippocampus GIG), cere CCC), and midbrain and thalam Extraction and measurement statin were performed as reported previously (Maeda and Frohman, 1980). Briefly, each

TABLE 1 Effects of antidepressants

on bomatostatin in discrete brain regions in rats

Acute Clomipramine Region Hypot h,kImus Hippocampus Striatum Cerebral Cortex Midbrain and Thaiamus

Control c._ a__ .- _ 477 77’53+ 54.1 f 4.x X3.4+ 3.9 99.5 + 7.4 56.1 _t 7.7

CLomipramine __ ‘35_.ot_ 49.5 SS.Yt_ 6.1 57.2 * 9.6 133.1 * 23.0 62.9& 9.1

Chronic Imipramine Region Hypothalamus 1iltppocdmpus StiiatUm Cerebral Cortex Midbrain and Thalamus

Control 275.4 + 22.4 55.1; 3.3 2:X$4 1.8 92.7 * ,! 7 S7.6 &- 3.0

Imipramine 30h.l 5 4.4 S6.7+ 6.2 28.6+ 4.2 84.4* 7.4 06.L -+ 4.1

Chroiiic Maprotiline Region Hypothalamus Hippocampus Striatum Cerebral Cortex Midbrain and Thalamus

Control 397.7 f 163.7 77.7* 8.X 35.6k 2.7 66.1 + 1.8 97.0 * 18.6

Maprotiline 31 I.9& 178.6 42.5 _F 29.0 6.7 29.1 f 111.6& 36.8 71.h-t t(.ip

Chronic Mianserin Region Hypothalamus I Iippocampus Striatum Cerebral Cortex Midbrain and Thalamus

Control 257.4 + 24.2 si.st_ 4.2 29.0+ 8.1 97.2 * 7.4 56.7-t 2.3

Mianserin 276.2 + 10.4, 5X4+ 5.0 22.s+ 1.5 x1.7+ 3.6 54.3* 4.1

Values are Pg/mg wet weight

and expressedmeant_ SE. Antidepressants were given 5 mg/kg, i.p.

ed, homogenized in 2 ml of ice cold ,?N acetic a d. The homogenate was boiled water bath to * ctivate degrading supernatant was reconstituted with the assay

q

chrontc ** **L

tostatin and synthetic somatostatin( I - ‘!4) were purchased from Amersham (Japan) ar d Sigma USA), respectively. least of somatostatin was tube. The inter-assay and intra-assay variance were 8.1% and 5.6%, respectively. Controls and experitaa? SIZ pie;; vQe1c ru i:r a sir& cessay 00 eliminate inter-assay variations. Differences between sample eans were determined by nonpaired Student”s t-test.

Somatostatin concentrationS were highest in the HT (225.3 + 43.3 pg/mg wet wt) and lowest in the cerebellum (17.4 + 2.6 pg,/mg wet wt) in the control rat. The levels of somatostatin in various discrete brain regions examined in the present study were consistent with previously reported values (Brownstein et al., 1975; Kobayashi administration of et al., 1977). Repeated clomipramine resulted in a significant reduction

control Clomlpramine

pco 02 PC0 005

Fig. 1. Effect on rat regional brain somatostatin concentrations of repeated administration of clomipramine (5 mg/k,. ip, twice a day for 10 days). Abbreviations used are following: i i i, iiypornaiamus, HC; hippocanrpus, ST, sir ialurll, CC. cttiebra1 cortex, MB and TH; midbrain and thalamus. The vertica: bars are mean + SE.

in somatostatin concentrations in all regions examined except HT and MB and TH with reductions from 30 to 50% (Fig. 1). In HT and MB and TH, clokprclmine tended to reduce somatostatin, although the differences did not reach the significant level CO.05< P < 0,l). After acute administration of clomipramine, somatostatin levels were not changed in any region, compared with control rats (Table I). In HT and MB and TI-I, somatostatin levels were decreased following chronic treatment with zimelidine (Fig. 2) but no

TABLE 2 Effects of carbamazepine

and zotepine on somatostatin

in discrete brain regions in rats

Chronic Carbamazepine Region Hypothalamus Hippocampus Striatum Cerebral Cortex Midbrain and Thalamus

Control 413.0f33.1 139.2f 8.7 101.6 + 13.3 107-l+ 16.3 118.7f 8.4

Carbamazepine 453.6 f 56.0 135.4f s.0 76.8 f 12.7 101.3f 4.6 127.3 &-15.2

Chronic Zotepine Region Hypothalamus Hippocampus Striatum Cerebral Cortex Midbrain and Thalamus

Control 3 15.3 k 80.4* 66.5 f 94.1+ lOO.4f

Zotepine 278.4 + 23.2 79.3 + 2.7 57.5 f 5.5 105.4f 4.9 100.5 f. 4.4

Values are pg/mg respectively.

wet weight and expressed

36.5 2.2 7.9 9.6 4.7

mean &SE. Carbamazepine

and zotepine

were given 20 and 5 mg/kg,

i.Psl

q

contrcl chront Zimelldlne

*

HT

HC

ST

CCMB

p
&TH

Fig. 2. Effect on rat regional brain somatostatin concentrations of repeated administration of zimelidine (5 mg/kg. ip. twice ti day for 10 days). Abbreviations used are following: HT; hypothalamus. HC: hippocampus. ST; striatum, CC: cerebral cortex, MB and TH; midbrain and thalamus. The vertical bars are mean rt SE.

changes occurred in other brain areas. Following neither imipramine, mianserin nor maprotiline administration, did any significant change in somatostatin levels occur in the regions examined (Table 1). Administration of neither carbamazepine nor zotepine caused a significant change in peptide levels (Table 2). iscussion We found that chronic administration of either clomipramine or zimelidine caused a significant reduction in brain somatostatin levels in rats. An acute injection of clomipramine did not alter somatostatin levels in any brain region of the rat. The other antidepressant drugs examined m the present study were without effect. The dosage we used in this study (5 mg/kg) for the antidepressants was similar to that used by the other investigator (Charney et al., 1981) and we administered 20 mgjkg of carbamazepine to compare results to those of the previous report (Weiss et al., 1980), in which the same dosage of carbamazepine was used. Both clomipramine and zimelidine are considered relatively selective serotonin uptake inhibitors. Imipramine is an uptake inhibitor for both noradrenaline and serotonin (Goodwin et al., 1978). Maprotiline and mianserin are a selec-

tivc: noradrenaline uptake inhibitor and a presyndptic qadrenergic receptor blocker, respectively (Goodwin et al., 1978; Baumann and Maitre 1977). Recently, neurochemical changes includi terations in neurotransmitter receptors folio long-term, not short-term, treatment with a pressants have been focussed to investigate mechanisms by which these drugs exert in treatment for dep?ession. Since Banerjee et al. (1 reported that long-term tricyclic antidepressa administration reduces the density of ,@adreuergic receptors in rat brain homogenates, a large number of studies have replicated this findi This effect seems to be specific to treatment a large variety of clinically effective antide sants with exception that mianserin and zi dine fail to induce down-regulation of P-adrcnergic receptors (Mishra et al., 1980). SHT, receptors appear to be consistently creased in density, although not always to a significant degree, by long-term administration of Chronic administration of antidepressants. imipramine results in subsensitivity of 5-HTz receptors (Peroutka and Snyder, 1980). bgren et al. (1985) have observed that proionged treatment of rats with zimelidine, a more selective inhibitor of 5-HT uptake than clomipramine (Ross and Renyi, 1977), caused a decrease in t e density of high affinity binding sites Car 5-HT, in the cerebral cortex. Following chronic treatment with clomipramine, however, no alteration demonstrated in the SHT, receptor bi (Blackshear et al., 1980). Although mian caused a marked decrease in the density of sites after repeated doses (Blackshear et al., 1986 chronic administration with maprotiline cause no reduction of the number of 5-HT, r (Ggren et al., 1985). We have demons reduced concentration of somatostati long-term administration of 5-HTP, a serotoni precursor, in the rat (Kakigi et al., 199 term administration of trifluoromet piperazine (TFPP), a 5-HT agonist, r number of 5-HT, receptor binding in the brain (Blackshear et al., 1986). Thus, it is unlikely that a decreased concentration in brain somatostatin relates with a reduction in either P-adrenergic receptors or 5-HT, receptor binding.

Somatostatin metabolism in the brain is influenced by various neurotransmitters. Somatostatin secretion is modified by dopamine, norepinephrbne, acetylcholine, histamine, GABA and some e rat (Chihara et al., 19’?9). There been few studies on effects of serotonergic agents on brain somatostatin. Inhibition by serotonin of matostatin release from the in vivo (Chihara et al., 1979) hardson et al., 1981) has been he rat. Decreased somatostatin concentrations following 5-HTP administration have been found in rat brain (Kakigi et al., 1990). Rubinow et all. (1983) have found a negative correlation of CSF somatostatin with CSF 5-hydroxyindole acetic acid (5HIAAI in depressed patients. Thus, it might be concluded that a reduction in regional brain somdtostatin related with a disturbed serotonin turnover in the brain. After long-term administration with either clomipramine or zimelidine, a decreased 5-HT turnover has been observed (Fuxe et al., 1979; Sugrue, 1980). A pathophysidlogic role of somatostatin in affective disorders remains to be investigated. Qur results that no change in somatostatin concentrations following long-term administration of carbamazepine in the brain regions was consistent with the previous report (Weiss et al., 1980). A potent antimanic agent, zotepine, did not affect somatostatin metabolism in the rat brain regions. Chronic treatment with zotepine elicited a reduction in serotonin receptors in the rat (Harada et al., 1986). We have recently revealed that administration with a dopamine receptor antagonist into the rat reduces tissue somatostatin levels in the brain (Kawata et a!., 1990). No significant effects on somatostatin levels following administration with zotepine may result from antagonistic effects for dopamine and serotonin receptors (Lai et al., 198Ol Acknowledgements

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