مرکزی صفحہ European Journal of Pharmacology Effect of a novel cognition enhancer NS-105 on learned helplessness in rats: Possible involvement...
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European Journal of Pharmacology 338 Ž1997. 225–232 Effect of a novel cognition enhancer NS-105 on learned helplessness in rats: Possible involvement of GABA B receptor up-regulation after repeated treatment Takako Shimidzu, Yoshinori Itoh ) , Michiko Oka, Tsuyoshi Ishima, Yojiro Ukai, Yoshiaki Yoshikuni, Kiyoshi Kimura Research Laboratories, Nippon Shinyaku Co., Ltd., Nishiohji Hachijo Minami-ku, Kyoto 601, Japan Received 10 April 1997; revised 5 September 1997; accepted 9 September 1997 Abstract We have previously found that a cognition enhancer wŽq.-5-oxo-D-prolinepiperidinamide monohydratex ŽNS-105. reversed the inhibition of cyclic AMP formation induced by the GABA B receptor agonist baclofen. The GABA B receptor has been implicated in the pathophysiology of depressive illness. The present experiment was designed to evaluate the antidepressant activity of NS-105 in the forced swimming and learned helplessness tests in rats. NS-105 Ž1–100 mgrkg, p.o.. significantly decreased immobility time in the forced swimming test, an effect similar to that of desipramine. Repeated administration of NS-105 also reversed the failure to escape in the shuttle-box test of rats previously exposed to inescapable footshock. Biochemical data showed that repeated administration of NS-105 increased the number of GABA B receptors in rat cerebral cortex without affecting the binding properties of b-adrenoceptors and 5-HT2 receptors. In contrast to other antidepressants, NS-105 did not inhibit monoamine uptake in vitro, nor did it change monoamine concentrations in brain tissues or extracellular fluids. These findings suggest that NS-105, which lacks an effect on monoaminergic systems, has potent antidepressant activity, which may involve up-regulation of GABA B receptors after repeated administration. q 1997 Elsevier Science B.V. Keywords: Antidepressant; Forced swimming; Learned helplessness; GABA B receptor 1. Introduction wŽq.-5-oxo-D-prolinepiperidinamide monohydratex ŽNS105. has been developed as a cognition enhancer th; at reverses learning and memory deficits caused by dysfunction of central cholinergic neurons ŽNakagawa et al., 1988, 1990; Ukai et al., 1990.. It reverses the decrease in highaffinity choline uptake in rat cerebral cortex induced by electrolytic lesion of the basal forebrain or pentobarbital anesthesia ŽUkai et al., 1990.. We have recently found that NS-105 also reverses the memory impairment caused by baclofen, a potent GABA B receptor agonist ŽBowery et al., 1980., in rats. This action was not mimicked by another structurally related cognition enhancer aniracetam ŽOka et al., 1995a.. In addition, NS- ) Corresponding author. Tel.: Ž81-75. 321-9112; Fax: Ž81-75. 314-3269. 0014-2999r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved. PII S 0 0 1 4 - 2 9 9 9 Ž 9 7 . 0 1 3 3 9 - 3 105 inhibited baclofen-induced suppression of cyclic AMP formation in rat cerebral cortex ŽOka et al., 1995a,b, 1997.. Therefore, it is possible that NS-105 has a functional GABA B receptor antagonistic action. Recent biochemical evidence has indicated that the GABA B receptors are involved in the pathophysiology of affective disorders such as depression: chronic administration of a variety of antidepressant drugs or repeated exposure to electroconvulsive shock causes up-regulation of GABA B receptors in rat cerebral cortex and hippocampus ŽLloyd et al., 1985; Gray and Green, 1987; Wojcik and Holopainen, 1992; Pratt and Bowery, 1993.. Conversely, down-regulation of GABA B receptors is observed in the cerebral cortex of olfactory-bulbectomized rats, a possible animal model of depression ŽLloyd, 1990.. Therefore, in the present experiment, we tested whether NS-105 possesses antidepressant activity in two representative animal models of depression, namely, forced swimming and learned helplessness in rats. 226 T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 2. Materials and methods 2.1. Animals Male Wistar rats Ž5–6 weeks old, Charles River Japan, Kanagawa. were used. They were housed in groups of 5–6 in a room kept at 21–258C with 45–65% humidity and maintained under an alternating 12 h lightrdark cycle Žlights automatically on at 8.00 a.m... Food and water were freely available. Experiments were all carried out in accordance with the Guide for the Care and Use of Laboratory Animals of the Japanese Pharmacological Society. 2.2. Chemicals and drugs The chemicals used in the present experiment were as follows: NS-105 wŽq .-5-oxo-D-prolinepiperidinamide monohydratex was synthesized in our laboratories. Maprotiline hydrochloride, fluoxetine hydrochloride, dopamine hydrobromide and 5-hydroxytryptamine Ž5-HT. hydrochloride were purchased from Sigma ŽSt. Louis, MO, USA.. Noradrenaline bitartrate was obtained from Wako Pure Chemicals ŽKyoto, Japan.. Ž".-Baclofen, nomifensine maleate, isoguvacine hydrochloride, GABA and nipecotic acid were from Funakoshi ŽTokyo, Japan.. w3 HxGABA, w3 Hxdihydroalprenolol, w3 Hxspiperone, w3 Hxnoradrenaline hydrochloride, w3 Hx5-HT binoxalate and w3 Hxdopamine hydrochloride were obtained from DuPontrNEN Research ŽBoston, MA, USA.. Other chemicals were reagent grade. 2.3. Forced swimming The forced swimming test was performed according to the method of Porsolt et al. Ž1977, 1978.. Briefly, a Plexiglas cylinder Ž18 cm, diameter= 40 cm, height. was filled with water warmed at 258C to the height of 25 cm, and rats were placed in the water for 15 min Žfirst session.. On the next day, rats were again forced to swim in the same cylinder for 5 min Žsecond session.. The total duration that rats showed a posture of immobility in the second session was measured. Drugs were administered orally immediately after the first session and 1 h before the second session. 2.4. Learned helplessness in the shuttle-box test Learned helplessness in the shuttle-box test was used as another model of behavioral despair ŽMurua and Molina, 1991.. Briefly, rats were individually exposed to a train of inescapable footshocks Ž0.5 mA, 10 s duration and 5 s interstimulation interval, 100 times. once a day for 3 days in a Plexiglas chamber Ž30 = 30 = 30 cm., the floor of which consisted of stainless steel grids spaced 1 cm apart Žshuttle-box.. On the 4th day, rats were trained, in 40-trials, to perform an active avoidance task in a shuttle-box and the number of escape failures was counted. Drugs were administered orally once daily for 10 days Žfrom 7 days before to the third day of exposure to inescapable shocks.. 2.5. Receptor binding assays after repeated oral administration Rats were repeatedly administered either NS-105 Ž100 mgrkg per day, p.o.. or desipramine Ž10 mgrkg per day, p.o.. for 14 days and were killed by cervical dislocation on the day following the last treatment. The brain was quickly removed and the cerebral cortex was dissected on ice. The membrane fractions were obtained as follows: brain tissues were homogenized with 10 vol of 50 mM Tris–HCl buffer ŽpH 7.4. and centrifuged at 39 000 = g for 20 min. The above procedure was repeated twice and the resultant pellets were re-suspended in the same buffer, then stored at y608C until assayed. For the GABA B binding assay, frozen membranes were further treated to avoid the influence of endogenous GABA on binding: stored membranes were re-suspended in 10 volumes of 50 mM Tris–HCl buffer and centrifuged at 39 000 = g for 20 min. This procedure was repeated twice and the final pellets were re-suspended in 50 mM Tris–HCl buffer containing 2.5 mM CaCl 2 and 40 mM isoguvacine. b-Adrenoceptors and 5-HT2 receptors were labeled by 0.1–2 nM w3 Hxdihydroalprenolol ŽYamada et al., 1983. and 0.1–2 nM w3 Hxspiperone ŽLeysen et al., 1978., respectively. GABA B receptor binding was assayed according to the method of Bowery et al. Ž1983. with 10–300 nM w3 HxGABA in the presence of 40 mM isoguvacine to prevent binding to GABA A receptors. The non-specific binding to b-adrenoceptors, 5-HT2 and GABA B receptors was determined in the presence of 1 mM DL-propranolol, 10 mM methysergide and 100 mM Ž".-baclofen, respectively. Protein content was measured by the method of Bradford Ž1976., using bovine serum albumin as the standard. The K d and Bmax values were evaluated by Scatchard analysis. Data were obtained from 8–10 separate experiments determined in duplicate. 2.6. Uptake of monoamines into rat brain membrane preparations The rat cerebral cortex or striatum was homogenized with 10 vol of 0.32 M sucrose, using a teflon homogenizer. After centrifugation at 1000 = g for 10 min, the supernatant was centrifuged at 17 000 = g for 15 min and the resultant pellet was re-suspended in 10–20 volumes of 0.32 M sucrose and used for the measurement of monoamine uptake. w3 HxNoradrenaline uptake was determined according to the method of Gehlert et al. Ž1995., while w3 Hx5-HT or w3 Hxdopamine uptake was assayed by the method of Bennett et al. Ž1995.. Briefly, Krebs bicarbonate solution ŽNaCl, 110 mM; KCl, 5.9 mM; MgCl 2 , 1.2 mM; NaH 2 PO4 , 1.2 mM; CaCl 2 , 2.5 mM; D-glucose 11.5 mM; NaHCO 3 , 25 mM, pH 7.4. containing 10 mM T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 pargyline, 1 mM ascorbic acid and 0.17 mM ethylenediamine tetraacetic acid disodium salt was added to the membrane preparations and incubated at 378C for 5 min under continuous gassing with 95% O 2r5% CO 2 . After this incubation, radiolabeled ligands were added and the mixture was incubated at 378C for 10 min. After incubation, the medium was aspirated through a Whatman GFrB filter, and the filter was washed 3 times with ice-cold Krebs bicarbonate solution. The radioactivity associated with the filter was counted. The non-specific uptake of noradrenaline, 5-HT or dopamine was measured in the presence of 10 mM each of maprotiline, fluoxetine or nomifensine, respectively. Specific uptake was calculated as the difference in the radioactivity counts between total and non-specific uptake. The experiments were carried out in duplicate and data were obtained from 4 independent experiments. 2.7. Intracerebral microdialysis 227 assay. containing 10 mM ethylenediamine tetraacetic acid disodium salt and 1.85 mM sodium 1-octanesulfonate. The flow rate was 0.21 mlrmin. For the measurement of monoamines and their metabolites in rat brain tissues, brains were dissected on ice into six regions, namely the cerebral cortex, hippocampus, striatum, hypothalamus, midbrain and pons–medulla oblongata, according to the method of Glowinski and Iversen Ž1966.. The tissues were homogenized with more than 10 vol of 0.4 M perchloric acid containing an appropriate amount of 3,4-dihydroxybenzylamine, as an internal standard. Monoamines and their metabolites in supernatants were determined according to the method of Warnhoff Ž1984. with modifications ŽItoh et al., 1996.. 2.9. Statistical analyses Statistical analyses were performed using SAS program ŽSASrSTAT, Ver. 6, fourth edition, 1990, SAS Institute The extracellular concentrations of noradrenaline and 5-HT were measured by intracerebral microdialysis in urethane-anesthetized rats, as described previously ŽItoh et al., 1994, 1996.. Briefly, a microdialysis probe ŽI-shaped: BDP-I-4-03, Eicom, Kyoto, Japan. was inserted into the cerebral cortex Ž3.7 mm anterior to the bregma, 3.0 mm lateral and 3.8 mm below the dura mater. and Ringer’s solution ŽNaCl, 147 mM; KCl, 4 mM; CaCl 2 , 2.3 mM. was perfused at a flow rate of 2 mlrmin. Microdialysates were collected into polyethylene tubes containing 10 ml of 0.1 M formic acid, 2–3 h after the start of perfusion. NS-105 was dissolved in Ringer’s solution. Rats were wrapped in a blanket to maintain constant body temperature throughout the experiment. At the end of the experiment, brains were perfused with 50 ml of 10% formalin saline solution via a carotid artery, and serial 50 mm thick coronal brain sections were made to verify the location of the tip of the dialysis probe. 2.8. Determination of monoamines and their metabolites in rat brain regions The concentrations of noradrenaline and 5-HT in microdialysates were determined by high-performance liquid chromatography ŽHPLC. with electrochemical detection. The HPLC system consisted of a pump ŽEP-300, Eicom. equipped with a damper ŽDG-300, Eicom., a guard column Ž4.0 = 2.1 mm inside diameter. packed with Nucleosil 5C18 ŽChemco., a reversed-phase separation column ŽCA50 DS: 150 = 2.1 mm inside diameter, Eicom., an electrochemical detector ŽECD-300, Eicom. and a recorder ŽChromatopac C-R4A.. The potential of the working electrode was set at 0.45 V vs. an AgrAgCl reference electrode. The mobile phase was a mixture of 0.1 M sodium phosphate buffer ŽpH 6.0. and methanol Ž95:5 Žvrv. for the measurement of noradrenaline; 84:16 Žvrv. for 5-HT Fig. 1. Effects of NS-105 and desipramine on immobility of rats in the forced swimming test. Rats were forced to swim for 15 min in warmed water Ž258C. Žfirst session. and were then exposed to the same situation for 5 min on the second day Žsecond session.. The total duration of immobility during the second session was measured. Drugs were administered p.o. immediately after the first session and 1 h before the second session. Each column represents the mean"S.E.M. for 10 animals. ) P - 0.01 vs. Control. 228 T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 Ins., Cary, NC.. Data for forced swimming were compared between control and drug-treated groups and analyzed by Dunnett’s test. Data obtained for learned helplessness in the shuttle-box test were evaluated by comparing the values of drug-treated groups with those of the saline-treated group. Biochemical data were analyzed by one-way analysis of variance followed by Dunnett’s test. 3. Results 3.1. BehaÕioral actions of NS-105 In the forced swimming test, NS-105 Ž0.3–100 mgrkg, p.o.. produced a dose-dependent decrease in the duration Fig. 3. Effects of repeated administration of NS-105 and desipramine ŽDMI. on binding properties of GABA B receptors, b-adrenoceptors and 5-HT2 receptors in rat cerebral cortex. NS-105 Ž100 mgrkg. or desipramine Ž10 mgrkg. was administered p.o. once daily for 14 days. Animals were killed 24 h after the last administration, and crude synaptosomal membranes were prepared. GABA B receptors were labelled with w3 HxGABA in the presence of 40 mM isoguvacine to prevent binding to GABA A receptors. b-adrenoceptors and 5-HT2 receptors were labelled with w3 Hxdihydroalprenolol and w3 Hxspiperone, respectively. The K d and Bma x values were estimated by Scatchard analysis. Each column represents the mean"S.E.M. of 8 to 10 experiments. ) P - 0.05, ) ) P - 0.01 vs. Control. Fig. 2. Effects of NS-105 ŽA. and desipramine ŽB. on escape failures in the learned helplessness test in rats. Rats were exposed to inescapable footshock for 3 days and were then subjected to 40-trials of an active avoidance task in a shuttle-box on the following day. The total number of escape failures during the 40 trials was counted. Drugs were administered p.o. once daily for 10 days Žfrom 7 days before to the third day of the exposure to inescapable footshock.. Each column represents the mean" S.E.M. for 10 animals. ) P - 0.01 vs. Saline treated group. of immobility, and significant effects were observed at doses higher than 1 mgrkg ŽFig. 1.. Desipramine Ž1–50 mgrkg, p.o.. also decreased the duration of immobility in a dose-dependent manner, significant actions being observed at ) 3 mgrkg. When rats were previously exposed to inescapable footshock, they failed to escape in the subsequent active avoidance task in the shuttle-box test ŽMurua and Molina, 1991.. As shown in Fig. 2, repeated administration of either NS-105 Ž1–30 mgrkg, p.o.. or desipramine Ž1–10 mgrkg, p.o.. for 10 days reduced the number of escape failures in a dose-dependent manner, and significant effects were observed at doses higher than 10 mgrkg of NS-105 and at 10 mgrkg of desipramine. NS-105 at the doses tested in the present experiment T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 229 Fig. 4. Effects of NS-105 and various antidepressants on the uptake of w3 Hxnoradrenaline ŽA., w3 Hx5-HT ŽB. and w3 Hxdopamine ŽC. into rat brain synaptosomal membranes. The uptake of w3 Hxnoradrenaline and w3 Hx5-HT was measured in the cerebral cortex, while that of w3 Hxdopamine was determined in the striatum. Each point represents the mean " S.E.M. of 4 experiments. caused no obvious behavioral changes. Locomotor activity was slightly and not significantly lowered after administration of 100 mgrkg of this compound, although a significant Ž P - 0.05. reduction in locomotor activity was observed at 300 mgrkg Žthe activity counts during 60 min measured by photocell counting were 368 " 46 in control group, 282 " 28 in 100 mgrkg NS-105 Ž100 mgrkg.treated group, and 225 " 36 in NS-105 Ž300 mgrkg.treated group Žmean " S.E.M. of 6 animals... 3.2. Effects of repeated administration of NS-105 on binding properties of GABA B receptors, b-adrenoceptors and 5-HT2 receptors in rat cerebral cortex To determine the possible mechanisms underlying the antidepressant action of NS-105, we examined the effect of repeated administration of NS-105 on the binding properties of GABA B receptors, b-adrenoceptors and 5-HT2 receptors in rat cortical membranes. As shown in Fig. 3, NS-105 Ž100 mgrkg, p.o., once daily for 14 days. caused a significant increase in the number Ž Bmax . but not the affinity Ž K d . of GABA B receptor without affecting the binding properties of either b-adrenoceptors or 5-HT2 receptors. Repeated administration of desipramine Ž10 mgrkg, p.o., once daily for 14 days. also significantly increased the number of GABA B receptors, although it decreased the number of b-adrenoceptors and 5-HT2 receptors. 3.3. Effects of NS-105 on monoamine dynamics in rat brain Unlike other antidepressant drugs, NS-105 Ž1 nM–1 mM. had no influence on the uptake of w3 Hxnoradrenaline ŽFig. 4A., w3 Hx5-HT ŽFig. 4B. and w3 Hxdopamine ŽFig. 4C. into crude synaptosomal membranes. In contrast, desipramine and maprotiline potently inhibited w3 Hxnoradrenaline uptake with IC 50 values of 3.6 " 0.6 and 41.0 " 2.9 nM, respectively Žmean " S.E.M., N s 4. ŽFig. 4A.. w3 Hx5-HT uptake was strongly inhibited by imipramine and fluoxetine with IC 50 values of 85.3 " 7.9 and 35.4 " 5.5 nM, respectively ŽFig. 4B.. Both imipramine and nomifensine, a selective dopamine uptake inhibitor, inhibited w3 Hxdopamine uptake, the IC 50 values of which were 5.4 " 0.6 mM and 0.750.13 mM, respectively ŽFig. 4C.. Also in the in vivo microdialysis experiment, perfusion of NS-105 Ž0.1–100 mM. into the cerebral cortex did not affect the extracellular concentrations of noradrenaline ŽFig. 5A. and 5-HT ŽFig. 5B. in the same brain area, whereas desipramine Ž0.1–1 mM. and imipramine Ž1 mM. markedly increased the extracellular concentrations of noradrenaline and 5-HT, respectively. In addition, single oral administration of NS-105 Ž10–100 mgrkg. did not significantly change tissue concentrations of noradrenaline, dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid, 5-HT and 5-hydroxyindoleacetic acid determined 1 h after injection in the cerebral cortex, 230 T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 Fig. 5. Effects of NS-105 and tricyclic antidepressants on the extracellular concentrations of noradrenaline ŽNA. ŽA. and 5-HT ŽB. in rat cerebral cortex, as measured by intracerebral microdialysis. Rats were anesthetized with urethane Ž1.1 grkg, i.p.. and Ringer’s solution was perfused at a flow rate of 2 mlrmin. Two to three hours after the start of perfusion, microdialysates were collected every 20 min Žin case of noradrenaline. or 30 min Žin case of 5-HT.. NS-105, desipramine ŽDMI. or imipramine ŽIMP. was perfused into the cerebral cortex through the microdialysis probe. Each column represents the mean " S.E.M. of 5 experiments. ) P - 0.05, ) ) P - 0.01 vs. average of three consecutive pre-drug infusion values. hippocampus, striatum, hypothalamus, midbrain and pons–medulla oblongata in rats Ždata not shown.. 4. Discussion The forced swimming test, which was originally developed by Porsolt et al. Ž1977. as an animal model of behavioral despair, is currently used as a screening model for antidepressants, since several antidepressant drugs reduce the immobility in this behavioral paradigm. However, forced swimming is especially sensitive to antidepressant drugs which activate central catecholaminergic neurons, and drugs which selectively inhibit 5-HT uptake such as fluoxetine and chlorimipramine were less active in this behavioral model ŽPorsolt et al., 1979.. Conversely, several compounds which stimulate locomotor activity, such as amphetamine, apomorphine and caffeine ŽPorsolt et al., 1978., or those that disrupt learning and memory, such as anticholinergic agents ŽHerman et al., 1981., have been reported to act as false positives in this behavioral test. Murua and Molina Ž1991. have reported in another learned helplessness model, in which escape failure in a shuttle-box test is measured in rats with previous exposure to inescapable footshock, that chronic administration of a variety of antidepressants reduces the number of escape failures. In the present experiment, NS-105 was as potent and as effective as desipramine in the two representative screening models for antidepressant drugs. NS-105 at the doses used in the present experiment had no significant influence on locomotor activity. In addition, this compound did not cause amnesia, but it rather reversed the impairment of learning and memory induced by the dysfunction of central cholinergic systems ŽNakagawa et al., 1988, 1990; Ukai et al., 1990.. Therefore, it is suggested that NS-105 possesses potent antidepressant activity. In the present experiment, repeated administration of NS-105 significantly increased the number of GABA B receptors in the rat cerebral cortex. A similar result was obtained after repeated administration of desipramine. Although the precise mechanisms underlying the therapeutic action of antidepressant drugs remain to be clarified, an involvement of GABA B receptor up-regulation in the antidepressant action has been postulated by several investigators: the Bmax but not K i value for GABA B receptor binding increased in rat cerebral cortex and hippocampus after repeated administration of a variety of antidepressant drugs ŽLloyd et al., 1985; Suzdak and Gianutsos, 1986; Motohashi et al., 1989; Pratt and Bowery, 1993. or chronic exposure to electroconvulsive shocks ŽLloyd et al., 1985.. Therefore, the up-regulation of GABA B receptors after repeated administration may at least in part contribute to the antidepressant action of NS-105. However, we do not know the precise reason for the GABA B receptor up-regulation after chronic treatment with NS-105, since this compound did not affect the binding of various neurotransmitters to GABA B receptors, a- and b-adrenoceptors, dopamine receptors, 5-HT2 receptors, muscarinic acetylcholine and GABA A receptors in rat brain in vitro ŽOka et al., 1997.. We have recently found that NS-105 reverses baclofen-induced inhibition of adenylate cyclase activity in slices of the rat cerebral cortex via an interaction with GTP-binding proteins ŽOka et al., 1997.. Pratt and Bowery Ž1993. have demonstrated in an autoradiographic study that GABA B receptors are up-regulated after repeated administration of a selective GABA B receptor antagonist CGP 36742. Conversely, down-regulation of GABA B receptors is reported to occur after T. Shimidzu et al.r European Journal of Pharmacology 338 (1997) 225–232 long-term treatment with baclofen ŽSuzdak and Gianutsos, 1986.. Therefore, it is likely that the functional antagonism by NS-105 against GABA B receptor-mediated responses, such as inhibition of adenylate cyclase activity, is involved in GABA B receptor up-regulation after its long-term treatment. Most antidepressant drugs are known to interact with monoaminergic systems. It has been demonstrated that b-adrenoceptors and 5-HT2 receptors are down-regulated in the cerebral cortex after chronic treatment with a variety of antidepressant drugs ŽPeroutka and Snyder, 1980; Friedhoff and Miller, 1983; Green et al., 1983; Sulser, 1984; Vetulani et al., 1984; Okada et al., 1986.. Also, in the present experiment, repeated administration of desipramine Ž10 mgrkg, p.o., once a day for 14 days. caused significant decreases in the number of b-adrenoceptors and 5-HT2 receptors. However, repeated administration of NS105 did not affect the binding properties of either b-adrenoceptors or 5-HT2 receptors. In addition, unlike other antidepressant drugs, NS-105 had no influence on monoamine uptake in vitro and central monoaminergic transmission Žrelease and turnover. in vivo. Therefore, it is unlikely that the antidepressant action of NS-105 is mediated by central monoaminergic neurons. In conclusion, a pyroglutaminamide derivative NS-105 had potent antidepressant activity in rats in the forced swimming and learned helplessness tests. Repeated treatment with NS-105 caused up-regulation of GABA B receptors without affecting the dynamics of b-adrenoceptors and 5-HT2 receptors in rat cerebral cortex. Unlike other antidepressants, NS-105 had no influence on either monoamine uptake or central monoaminergic transmission, and thus the compound may have potential in the therapy of depressive illness. References Bennett, B.A., Wichems, C.H., Hollingsworth, K., Davies, H.M.L., Thornley, C., Childers, S.R., 1995. 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