Captodiamine, a putative antidepressant, enhances hypothalamic BDNF expression in vivo by synergistic 5-HT2c receptor antagonism and sigma-1 receptor agonism

The putative antidepressant captodiamine is a 5-HT2c receptor antagonist and agonist at sigma-1 and D3 dopamine receptors, exerts an anti-immobility action in the forced swim paradigm, and enhances dopamine turnover in the frontal cortex. Captodiamine has also been found to ameliorate stress-induced anhedonia, reduce the associated elevations of hypothalamic corticotrophin-releasing factor (CRF) and restore the reductions in hypothalamic BDNF expression. Here we demonstrate chronic administration of captodiamine to have no significant effect on hypothalamic CRF expression through sigma-1 receptor agonism; however, both sigma-1 receptor agonism or 5-HT2c receptor antagonism were necessary to enhance BDNF expression. Regulation of BDNF expression by captodiamine was associated with increased phosphorylation of transcription factor CREB and mediated through sigma-1 receptor agonism but blocked by 5-HT2c receptor antagonism. The existence of two separate signalling pathways was confirmed by immunolocalisation of each receptor to distinct cell populations in the paraventricular nucleus of the hypothalamus. Increased BDNF induced by captodiamine was also associated with enhanced expression of synapsin, but not PSD-95, suggesting induction of long-term structural plasticity between hypothalamic synapses. These unique features of captodiamine may contribute to its ability to ameliorate stress-induced anhedonia as the hypothalamus plays a prominent role in regulating HPA axis activity.

Nicotine receptors and depression: revisiting and revising the cholinergic hypothesis

There is a well-established connection between smoking and depression. Depressed individuals are over-represented among smokers, and ex-smokers often experience increased depressive symptoms immediately after stopping smoking. Nicotine in tobacco binds, activates and desensitizes nicotinic acetylcholine receptors (nAChRs), but it is not known whether activation or desensitization is more important for the effects of nicotine on depressive symptoms. Here we review, based on clinical and preclinical studies of nicotinic drugs, the hypothesis that blockade (rather than activation) of neuronal nAChRs might be important for the effects of nicotinic agents on depressive symptoms. The endogenous neurotransmitter for nAChRs is acetylcholine, and the effects of nicotine on depression-like behaviors support the idea that dysregulation of the cholinergic system might contribute to the etiology of major depressive disorder. Thus, pharmacological agents that limit acetylcholine signaling through neuronal nAChRs might be promising for the development of novel antidepressant medications.

Prevention of pro-depressant effect of l-arginine in the forced swim test by NG-nitro-l-arginine and [1H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one]

Previous studies have shown that l-arginine, the precursor of nitric oxide, has a dual effect (antidepressant and pro-depressant) in the forced swim test. The aim of the present study was to investigate whether nitric oxide-cGMP pathway was involved in this dual effect. Porsolt swim test was conducted to resemble the symptomatology of major depressive disorder. An open field locomotor activity test was also used. L-arginine exerted a U-shape effect in the forced swim test: doses of 30, 100, 300, and 1000 mg/kg caused no alteration, statistically significant reduction, no alteration, and non-significant enhancement, respectively. Neither N(G)-nitro-L-arginine (NNA) nor [1H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one] (ODQ) at doses of 3 mg/kg was found to be effective in the forced swim test, whereas 10 mg/kg ODQ significantly reduced the immobility time. In the presence of NNA, the antidepressant and pro-depressant effects of L-arginine disappeared, however, only the pro-depressant component of l-arginine effect was prevented by ODQ (3 and 10 mg/kg). Saline, the solvent of L-arginine and NNA, and dimethyl sulfoxide (15% in saline), the solvent of ODQ, had no effect on the duration of immobility. None of the drugs or solvents used in the present study had any effect on locomotor activity over the dose range applied. The results show that L-arginine exerts its paradoxical effects by producing nitric oxide and that cGMP seems to have a role only in the pro-depressant component.

Biphasic Effects of Losartan Potassium on Immobility in Mice

The effects of losartan potassium, an angiotensin AT(1) receptor blocker on immobility in forced swim test have been studied. Effect of losartan potassium, nortriptyline HCl, fluoxetine HCl and reserpine per se and in combination on forced swimming-induced immobility in mice have also been studied. In mice, losartan potassium elicits biphasic responses i.e. positive responses at lower doses (0.1, 1.0 and 5 mg/kg, i.p.) in the forced swim test, a test of potential antidepressant activity and vice versa at higher dose (20 and 100 mg/kg, i.p.). In chronic studies, enhancement in immobility was observed for losartan potassium (3 and 30 mg/kg, p.o., 21 days). In acute combination studies, losartan potassium (1 and 5 mg/kg) significantly reversed the reserpine-induced immobility, but vice versa at 100 mg/kg. Losartan potassium (0.1 and 5 mg/kg) potentiate antidepressant activity of nortriptyline (30 mg/kg, i.p.) in mice, but vice versa at 100 mg/kg. Likewise, Losartan potassium (100 mg/kg), significantly reversed antidepressant activity of fluoxetine HCl, but at 0.1 and 5 mg/kg, failed to modify fluoxetine HCl induced immobility. The obtained biphasic effect of losartan potassium on immobility in mice might be due to inhibitory effect on AT(1) receptor at lower dose and pronounced effect on AT(2) receptor at higher dose (large concentrations of losartan potassium can displace Angiotensin II (Ang II) from its AT(1) receptor to AT(2) receptor.

Gender differences in clinical presentation and response to sertraline treatment of generalized anxiety disorder

OBJECTIVE

To evaluate gender differences in the clinical presentation of generalized anxiety disorder (GAD) and response to sertraline treatment.

METHODS

Adult outpatients who met DSM-IV criteria for GAD with a minimum Hamilton rating scale for anxiety (HAM-A) total score>or=18 were randomized to 12 weeks of double-blind treatment with flexible doses (50-150 mg) of sertraline (n=182; female, 59%) or placebo (n=188; female, 51%).

RESULTS

Clinical presentation of GAD was very similar in men and women in terms of the severity of the HAM-A psychic factor, severity of concomitant depression symptoms, duration of GAD, quality of life and impairment in physical health. Women had an earlier age of onset and higher HAM-A somatic factor scores compared with men. For both men and women, treatment with sertraline resulted in greater change from baseline to endpoint on the HAM-A compared with placebo (adjusted change+/-SE: men:-12.1+/-0.9 vs -8.8+/-0.9; women: -11.4+/-0.8 vs -7.1+/-0.9, p<0.001); the interaction between gender and treatment group was not significant, nor was there a significant difference between the average change from baseline for men compared with women. Similarly, responder rates based upon clinical global impression-improvement (CGI-I) scores at endpoint showed no significant interaction between gender and treatment, nor was there a significant difference in the response rates by gender; however, the response rate of sertraline compared with placebo was significantly different (p<0.0001) (men: 64% vs 40%; women: 62% vs 34%). Similar findings were evident at week 4 assessment and for completers (week 12). Overall, sertraline was well tolerated by both men and women.

DISCUSSION

Women and men with GAD showed similar clinical presentations, with the exception that women had an earlier age of onset and reported more somatic anxiety symptoms. Sertraline was an effective and well tolerated treatment for GAD in both men and women.

Corticosterone attenuates the antidepressant-like effects elicited by melatonin in the forced swim test in both male and female rats

Melatonin has been demonstrated to increase activity in the forced swim test (FST), a putative model of antidepressant efficacy, indicating that it may possess antidepressant-like qualities. It has been suggested that corticosterone can interfere with the efficacy of antidepressants, an effect that has previously been demonstrated in the FST. This experiment examined the effects of melatonin and corticosterone, independently and in combination, on the behaviours of both male and female rats in the FST. Corticosterone, melatonin, combined vehicles or a combined melatonin/corticosterone regimen were administered for 20 days, after which the animals were observed in the FST. As seen in previous research, melatonin elicited an antidepressant-like effect in the FST by reducing immobile behaviour (P<.01) and increasing active behaviour (P<.01). Corticosterone was found to reduce activity (P<.01) and increase immobility (P<.01), as well as attenuate the anti-immobility effects of melatonin (P=.03). These findings suggest that while melatonin may possess antidepressant-like qualities, high levels of corticosterone seem capable of attenuating these effects.

Galanin attenuates basal and antidepressant drug-induced increase of extracellular serotonin and noradrenaline levels in the rat hippocampus

Galanin is co-localized with classical neurotransmitters, such as acetylcholine, serotonin (5-HT) and noradrenaline (NA) in neurons or in brain regions implicated in cognitive and affective behaviour. In the present study, the effects of galanin on extracellular 5-HT and NA levels in the rat hippocampus were measured by in vivo microdialysis under basal conditions and following systemic administration of antidepressant drugs. Galanin (1.5 nmol i.c.v.) reduced basal 5-HT and NA levels to 65% and 86% of controls, respectively. Galanin (0.5 and 1.5 nmol i.c.v.) dose-dependently attenuated the elevation of 5-HT concentrations induced by imipramine and citalopram (10 mg/kg i.p., each) from 350% to 312% and from 230% to 160%, respectively. Galanin at 1.5 nmol transiently attenuated the effect of desipramine-induced (10 mg/kg i.p.) increase in extracellular NA levels from a maximal increase of 389-296% of the predrug levels. It is concluded that intraventricularly administered galanin attenuated both basal 5-HT and NA release and antidepressant drug-induced accumulation of extracellular 5-HT and NA levels most likely via a predominant inhibitory action on serotonergic and noradrenergic neurons in the raphe and locus coeruleus, respectively. These results further emphasize a possible role of galanin in regulation of 5-HT and NA neurotransmission in depressive states and during the course of antidepressant therapy.

An investigation of monoamine receptors involved in antinociceptive effects of antidepressants

We attempted to determine which monoamine receptor subtypes are predominantly involved in antidepressant-induced antinociception. Antinociceptive effects were evaluated by using formalin tests with rats. Antidepressants acting as potent inhibitors of norepinephrine reuptake (nisoxetine, nortriptyline, and maprotiline) or inhibiting reuptake of both norepinephrine and serotonin (5-HT) (imipramine and milnacipran) induced dose-dependent antinociception. Simultaneous intraperitoneal administration of antidepressants and either prazosin (alpha(1) antagonist) or ketanserin (5-HT(2) antagonist) significantly antagonized antinociceptive effects. Fluvoxamine (selective serotonin reuptake inhibitor) induced antinociception less potently than other antidepressants and was significantly antagonized by ketanserin, but not prazosin. Ondansetron (5-HT(3) antagonist) significantly antagonized antinociception by 10 mg/kg of imipramine. In contrast, SDZ-205,557 (5-HT(4) antagonist) markedly enhanced antinociception by small-dose (2.5 mg/kg) imipramine. Imipramine-induced antinociception was significantly antagonized by intracerebroventricular administration of prazosin or ketanserin, but not by yohimbine (alpha(2) antagonist) or ondansetron, and was significantly enhanced by intracerebroventricularly administered SDZ-205,557. These findings suggest that alpha(1) adrenoceptors and 5-HT(2) receptors in the brain are involved in antidepressant-induced antinociception. In addition, the results suggested functional interactions between noradrenergic and serotonergic neurons as mechanisms for antidepressant-induced antinociception.

IMPLICATIONS

Formalin tests of rats treated with antidepressants and antagonists of monoamine receptors indicate that alpha(1) adrenoceptors, serotonin (5-HT)(2) receptors, and 5-HT(3) receptors are involved in antidepressant-induced antinociception, suggesting functional interactions between noradrenergic and serotonergic neurons as mechanisms of antidepressant-induced antinociception.

The 5-HT3 receptor agonist attenuates the action of antidepressants in the forced swim test in rats

Involvement of 5-hydroxytryptamine (5-HT)3 receptors in action of antidepressants was examined in the forced swim test in rats. Rats were forced to swim in a cylinder for 15 min on day 1 and for 5 min on day 2. Imipramine, desipramine and mianserin, administered after the 15-min swim session on day 1 and before the 5-min swim test on day 2, dose-dependently decreased the duration of immobility in the swim test on day 2. 1-(m-Chlorophenyl)-biguanide (mCPBG) attenuated the decreased duration of immobility induced by imipramine, desipramine and mianserin, although mCPBG did not affect the duration of immobility when it was given alone. ICS205-930 dose-dependently decreased the duration of immobility in the swim test on day 2, and the effect of ICS205-930 was attenuated by mCPBG. These results suggest that the suppression of 5-HT3 receptor activity may contribute to the action of antidepressants.

Antidepressant-like effects of p-synephrine in mouse models of immobility tests

We studied the effects of p-synephrine on the immobility behaviors and on the spontaneous motor activity in mice. p-Synephrine at oral doses from 1 to 10 mg/kg significantly decreased the duration of immobility in the tail suspension test and the forced swimming test in mice. At 30 mg/kg, the duration of immobility was returned to control values in both tests. Subcutaneous administration of prazosin hydrochloride (62.5 micrograms/kg), an alpha 1 adrenoceptor antagonist, blocked the p-synephrine (3 mg/kg)-induced decrease in immobility in the tail suspension test. p-Synephrine did not change the spontaneous motor activity at oral doses from 0.3 to 10 mg/kg. These results suggest that p-synephrine elicits an antidepressant-like activity in mouse models of immobility tests, through the stimulation of alpha 1 adrenoceptors.

Involvement of GABA(B) receptor systems in action of antidepressants: baclofen but not bicuculline attenuates the effects of antidepressants on the forced swim test in rats

Involvement of GABAergic systems in action of antidepressants was examined in the forced swim test in rats. Rats were forced to swim in a cylinder for 15 min on day 1 and for 5 min on day 2. Desipramine, mianserin and buspirone, administered after the 15-min swim session on day 1 and before the 5-min swim test on day 2, dose-dependently decreased the duration of immobility in the swim test on day 2. Baclofen attenuated the decreased duration of immobility induced by desipramine, mianserin and buspirone in the swim test, although baclofen did not affect the duration of immobility when it was injected alone. Muscimol dose-dependently decreased the duration of immobility in the swim test on day 2. Bicuculline antagonized the decreased duration of immobility induced by muscimol. However, bicuculline failed to antagonize the decreased duration of immobility induced by desipramine, mianserin and buspirone. These results suggest that GABA(B) but not GABA(A) receptor systems may be involved in action of antidepressants.

The central effects of moxonidine on intraocular pressure and its antagonism by L-659, 066 and L-657, 743 in the rabbit

1) The imidazoline, moxonidine (MOX), injected icvt into the anterior lateral ventricle of NZW rabbits induced ocular hypotension (> 7.0 mmHg) that persisted for two hrs. 2) L-659, 066 injected i.v. or icvt inhibited MOX-induced ocular hypotension, significantly. 3) L-657, 743, injected icvt at 100-fold lower concentration than icvt L-659, 066, significantly inhibited MOX-induced ocular hypotension. 4) Alpha-2-adrenoceptors, located in the CNS, play a role in MOX-induced ocular hypotension, as evidenced by the ability of the relatively selective alpha-2 antagonists, L-659, 066 and L-657, 743 to inhibit icvt MOX-induced ocular hypotension.

Effect of milnacipran and desipramine on noradrenergic alpha 2-autoreceptor sensitivity

1. The effects of chronic administration with milnacipran and desipramine on the noradrenergic alpha 2-autoreceptor sensitivity in the rat hypothalamus were compared. 2. Rats were administered, in their diet, milnacipran (50 mg/kg/day for 21 days, 24 h wash-out), desipramine (35 mg/kg/day for 21 days, 24 h wash out) or desipramine (14 mg/kg/day for 21 days, 41 h wash-out). Hypothalamic slices were incubated with [3H]noradrenaline, superfused and stimulated electrically. 3. Chronic administration with milnacipran did not modify basal or electrically induced release of [3H]noradrenaline, tissue incorporation of [3H]noradrenaline or the sensitivity of the alpha 2-autoreceptor assessed by the inhibition of the stimulation-evoked release of [3H]noradrenaline by the alpha 2-adrenoceptor agonist, guanabenz, in comparison to controls. After chronic desipramine (35 mg/kg), basal and evoked release of [3H]noradrenaline were increased, tissue incorporation of [3H]noradrenaline decreased and the inhibitory effect of guanabenz was diminished. At the lower dose (14 mg/kg), chronic desipramine increased only the evoked release of noradrenaline but did not modify the sensitivity of the alpha 2-autoreceptor. 4. Desipramine at 35 mg/kg remains in the tissue after 24 h wash out, causing a reduction of uptake and complicating the interpretation of the data.

Antidepressant-like effects of CCKB antagonists in mice: antagonism by naltrindole

1. The effects of selective CCKB agonists, BC 264 and BC 197 were investigated in the conditioned suppression of motility test in mice, an animal model used to select antidepressant drugs. The results showed that both CCKB agonists at doses of 3 and 30 micrograms kg-1, accentuated the suppression of motility in shocked mice and did not modify the behaviour of non-shocked mice. The effects of BC 264 were suppressed by L-365,260. 2. L-365,260 alone, at doses of 0.2 and 2 mg kg-1 decreased motor inhibition in shocked mice and had no effect in non-shocked mice. 3. The effects of L-365,260 observed in shocked mice were suppressed by naltrindole, a selective antagonist for delta-opioid receptors, suggesting the occurrence of physiological adverse interactions between CCK and opioid systems. 4. Together, these results suggest that CCKB antagonists could block centrally located CCKB receptors to produce antidepressant-like effects which could indirectly involve delta-opioid receptor stimulation.

Inhibition of uptake 1 by (+)-oxaprotiline reveals a differential central regulation of noradrenaline and adrenaline release

Inhibition of uptake 1 in the central nervous system leads to a decrease of sympathetic outflow to many tissues; central alpha 2-adrenoceptors are involved in this decrease. The aim of the present study was to compare the effects of the selective uptake 1 inhibitor (+)-oxaprotiline on the plasma kinetics of noradrenaline and adrenaline in anaesthetized and in conscious rabbits. [3H]Noradrenaline and [3H]adrenaline were infused i.v. The arterial plasma concentrations of endogenous and radiolabelled noradrenaline and adrenaline were measured, and the clearance from and spillover into the plasma of noradrenaline and adrenaline were calculated. Results obtained in conscious and anaesthetized rabbits were similar. (+)-Oxaprotiline 0.2, 0.6 and 1.8 mg kg-1 i.v. dose-dependently reduced the clearance of [3H]noradrenaline from the plasma. The clearance of [3H]adrenaline was reduced less. The spillover of endogenous noradrenaline was decreased by up to 35%. In contrast, the spillover of adrenaline tended to be enhanced. Prazosin 0.1 and 1 mg kg-1 was injected i.v. in a second part of each experiment. It lowered the blood pressure and caused a marked increase in noradrenaline spillover but no increase or even a decrease in adrenaline spillover. The results are compatible with the following hypothesis. The sympathetic outflow from the central nervous system is subject to a twofold alpha-adrenoceptor-mediated modulation: alpha 2-adrenoceptor-mediated inhibition and alpha 1-adrenoceptor-mediated excitation. In the control of the sympathetic outflow to many extra-adrenal tissues, the alpha 2-adrenergic inhibition prevails. Uptake 1 inhibitors depress sympathetic outflow to such tissues by enhancing the alpha 2-adrenergic inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Flumazenil prevents the anxiolytic effects of diazepam, alprazolam and adinazolam on the early acquisition of two-way active avoidance

The effects of diazepam (DZ, 4 mg/kg), alprazolam (ALP, 1.25 mg/kg) and adinazolam (ADIN, 6 mg/kg), as well as their interaction with the benzodiazepine receptor antagonist flumazenil (Ro15-1788), were studied on the early acquisition of two-way active (shuttlebox) avoidance in male Sprague-Dawley rats. The three benzodiazepines increased shuttlebox avoidance acquisition, and their effects were prevented (antagonized) by flumazenil (10 mg/kg). The present results indicate that central benzodiazepine (BZ) receptors are involved in the anxiolytic effects of diazepam and triazolobenzodiazepines on the early acquisition of two-way active avoidance.

Benzodiazepines reverse the anti-immobility effect of antidepressants in the forced swimming test in mice

The present study provides evidence that, in mice subjected to the forced swimming test, the anti-immobility effect of the tricyclic antidepressants, desipramine and imipramine (16-32 mg/kg) was antagonized by the acute co-administration of a benzodiazepine, diazepam (0.25-2 mg/kg) and lorazepam (0.125 mg/kg). This effect cannot be accounted for by variations in plasma and/or brain levels of each compound since brain and plasma concentrations of desipramine and plasma levels of diazepam and desmethyldiazepam, measured immediately after the swimming test, were not significantly modified by the co-administration. Diazepam (2 mg/kg) also counteracted the reduction of time spent immobile induced by the MAO inhibitors, toloxatone (256 mg/kg) and selegiline (4 mg/kg) and the 5-HT1A receptor agonist, 8-OH-DPAT (1 mg/kg), but not by the psychostimulant, caffeine (32 mg/kg). The sedative neuroleptic, thioridazine (4 mg/kg) was also found to reverse the anti-immobility effect of desipramine whereas the non-benzodiazepine anxiolytics, alpidem (8 mg/kg) and buspirone (0.5 mg/kg) did not. These results indicate that the observed interactions were unlikely to be accounted for by a reduction of the stressful aspect of the situation whereas the participation of some motor or sedative component could not be totally ruled out.

Antidepressant profile in rodents of SR 58611A, a new selective agonist for atypical beta-adrenoceptors

beta 2-Adrenoceptor agonists possess antidepressant-like activity in animals and man, but their peripheral side-effects prevent their therapeutic use. Atypical beta-adrenoceptors have not been demonstrated in the central nervous system, but are known to exist in peripheral tissues such as the rat colon. We have now studied the antidepressant-like effects in rodents of a new selective atypical beta-adrenoceptor agonist, SR 58611A. SR 58611A was active with minimal effective doses of 0.1-0.3 mg kg-1 i.p. in several models (antagonism of the hypothermia induced by apomorphine and reserpine; potentiation of the toxicity produced by yohimbine; reversal of learned helplessness), but was inactive in the tests of reserpine-induced ptosis and behavioural despair. The antidepressant-like effect of SR 58611A was not antagonised by selective beta 1- or beta 2-adrenoceptor antagonists, but was blocked by high doses of the non-selective beta-adrenoceptor antagonists, propranolol and alprenolol. Unlike beta 2-adrenoceptor agonists, SR 58611A did not reduce locomotor activity or increase water intake at doses up to 10 mg kg-1. Therefore, SR 58611A may represent the prototype of a new class of antidepressant compounds.

[Sidnofen-dependent pre- and postsynaptic activation of peripheral adrenergic transmission]

The psychostimulant sydnophen causes a spontaneous activity and increases contractile responses evoked by noradrenaline (NA) and field stimulation in rat vas deferens. The effects of the agent are independent of its ability to inhibit MAO activity. The sydnophen-induced spontaneous activity is blocked not only by alpha-adrenoceptor antagonists such as phentolamine and prazosin, but by guanethidine that blocks presynaptic neuronal NA release. Analysis of dose-response NA action has indicated that sydnophen enhances adrenoceptor sensitivity (the dissociation constant changes from 10.10(-6) M to 2.7.10(-6) M). Experimental findings suggest that sydnophen has activating presynaptic and postsynaptic action.

Antidepressant-like activity of the melatonin receptor antagonist, luzindole (N-0774), in the mouse behavioral despair test

The anti-immobility effect of the selective melatonin receptor antagonist, luzindole, was investigated in the behavioral despair test using three different strains (C3H/HeN, C57BL/6J and albino ND/4) of mice. The time of immobility of the C3H/HeN during the 240 s swimming period measured at noon (12:00 to 14:00 h) was 47.8 +/- 3.0 s (n = 63) and at midnight (00:00 to 02:00 h) was 67.7 +/- 2.8 s (n = 68) (P less than 0.001, when compared with the noon value), when the levels of endogenous melatonin are presumably low and high, respectively. Melatonin (30 mg/kg) given i.p. did not modify the time of immobility at either time of measurement. Luzindole (30 mg/kg i.p.) reduced the time of immobility in a dose-dependent manner, the effect being more pronounced at midnight (60% reduction) than at noon (39% reduction). The effect of luzindole was time-dependent, showing a maximal effect at 60 min. The anti-immobility effect of luzindole (10 mg/kg i.p.) was prevented by the administration of melatonin (30 mg/kg i.p.). Luzindole (30 mg/kg i.p.) did not modify the time of immobility either at noon or midnight in the albino ND/4 mouse, or in the C57BL/6J mouse, which does not produce melatonin. Our results suggest that endogenous melatonin plays a role during swimming in the C3H/HeN mouse behavioral despair test. We conclude that luzindole may exert antidepressant-like activity in the C3H/HeN mouse by antagonizing the action of endogenous hormone.

Blockade of brain dopamine receptors antagonizes the anti-immobility effect of MIF-1 and Tyr-MIF-1 in rats

Previous studies have shown effects of MIF-1 (prolyl-leucyl-glycinamide) and Tyr-MIF-1 (tyrosyl-prolyl-leucyl-glycinamide) in animal models of depression and also effects on dopaminergic function. These observations prompted us to examine whether the effects of the two peptides in the behavioral 'despair' test were modulated by dopamine antagonists. MIF-1 and Tyr-MIF-1, at the small dose of 0.01 mg/kg i.p. (24, 5 and 1 h before the test), produced a significant anti-immobility effect. This effect was antagonized by a single injection of either haloperidol or sulpiride, two dopamine receptor blockers. The same low dose of the tricyclic antidepressant desipramine was without significant effect in this test. The results indicate that Tyr-MIF-1, like MIF-1, is active in the behavioral despair test for antidepressants and that at least some of the CNS actions of these peptides are mediated by dopamine receptors.

Influence of naloxone on the antinociceptive effects of some antidepressant drugs

The antinociceptive effects of tricyclic and atypical antidepressants were studied using the rat tail mechanical method. Clomipramine produced analgesia at the doses of 30 and 40 mg/kg, desimipramine at 10, 20 and 40 mg/kg, maprotiline at 20 and 30 mg/kg, mianserin at 30 mg/kg, nomifensine at 1, 2.5 and 5 mg/kg, indalpine at 10, 20 and 40 mg/kg, viloxazine at 60 and 80 mg/kg. Naloxone (0.8 mg/kg) abolished the antinociceptive action of these antidepressant drugs. These results suggest that the antinociceptive activity of these six antidepressant drugs in acute experimental pain could involve opiate mechanisms.

[Effects of 4-(o-benzylphenoxy)-N-methylbutylamine hydrochloride (MCI-2016) on monamine metabolism in the brain]

Effects of MCI-2016 on the uptake, contents and turnover rate of monoamines were studied in the rat brain. MCI-2016 exhibited more potent inhibitory effect on the noradrenaline (NA) uptake than on dopamine (DA) and serotonin (5-HT) uptake. Especially, the inhibitory effect of MCI-2016 on the NA uptake in the hypothalamus was comparable to that of imipramine with the IC50 value of 4 X 10(-8) M. The levels of NA and its metabolite, MHPG-SO4, in the whole brain were significantly increased by 30 mg/kg, i.p. of MCI-2016. The peak effects were reached between two to 4 hrs after administration. The increase in 5-HT contents at the cortex were also observed by MCI-2016 (30 mg/kg, i.p.), with little changes in 5-HIAA contents. The levels of DA, HVA and DOPAC in the whole brain were not significantly influenced by MCI-2016. The turnover rate of NA was facilitated by 61.1% by 15 mg/kg, i.p. of MCI-2016. DA and 5-HT turnover rates were little affected by the same dosage of MCI-2016. In the case of imipramine (15 mg/kg, i.p.), however, it didn't increase the NA turnover, and in addition, it inhibited the 5-HT turnover. The increase in NA turnover rate induced by MCI-2016 was antagonized by 54.5% by 30 mg/kg, i.p. of atropine. Physostigmine (1 mg/kg, i.p.) also increased NA turnover rate which was also partially (62.6%) inhibited by atropine. These results may suggest that the effects of MCI-2016 on noradrenergic mechanisms were qualitatively different from those of tricyclic antidepressants. In addition, the results with atropine on the turnover rate may in part suggest a possible participation of the cholinergic mechanism on the turnover increasing effect of MCI-2016.

[Anti-anoxic effect of 4-(o-benzlphenoxy)-N-methylbutylamine hydrochloride (MCI-2016)]

Anti-anoxic effects of MCI-2016 were compared with those of drugs for cerebrovascular diseases, tricyclic antidepressants and physostigmine in mice. Minimal effective doses of MCI-2016 which significantly increased the survival time or gasping duration were 12.5 mg/kg, p.o. for hypoxia, 50 mg/kg, p.o. for KCN-induced anoxia, and 100 mg/kg, p.o. for decapitation-induced gasping. As a whole, these effects of MCI-2016 were superior to those of reference drugs for cerebrovascular diseases. MCI-2016 was also shown to be effective under a consecutive administration schedule. In marked contrast to the effect of MCI-2016, tricyclic antidepressants significantly shortened the survival time under hypoxia. Considering that atropine shortened and physostigmine markedly increased the survival time under hypoxia, involvement of anti-cholinergic action may be postulated for the shortening effect of tricyclic antidepressants. The anti-hypoxic effect of MCI-2016 as well as physostigmine was diminished by atropine treatment. Furthermore, MCI-2016 exhibited a combination effect with physostigmine at optimal doses. Although the influence of norepinephrine uptake inhibitory action on the hypoxic condition are not clear in the present study, these results may suggest that activation of CNS cholinergic system is involved as one of the causative mechanisms for anti-anoxic effect of MCI-2016.

Biochemical differentiation of amphetamine vs methylphenidate and nomifensine in rats

Amphetamine-like stimulants were divided into two groups, one in which the stereotyped behaviour was not antagonized by reserpine [(+)-amphetamine, (-)-amphetamine, methamphetamine, phenmetrazine and phenethylamine] and another group in which the behavioural effects were blocked by reserpine (methylphenidate, nomifensine, pipradrol and amfonelic acid (NCA; Win 25978)). Both groups increased homovanillic acid (HVA) in whole brain 2 h after administration. The 'methylphenidate group' also increased brain 3,4-dihydroxyphenylacetic acid (DOPAC) in naive rats; whereas the '(+)-amphetamine group' decreased DOPAC in naive rats, as well as in reserpinized rats, alpha-methyl-p-tyrosine-treated rats and after acute hemisection. The reserpine antagonism of the 'methylphenidate group'-induced stereotyped behaviour was partially reversed by type A monoamine oxidase inhibition. The '(+)-amphetamine group'-induced stereotyped behaviour was not blocked by short time pretreatment with alpha-methyltyrosine, only by longer pretreatment intervals. The mechanisms by which the two groups are differentiated biochemically is discussed with special attention to possible intra-neuronal inhibition of dopamine oxidation by the '(+)-amphetamine group'.

Methylphenidate-like effects of the new antidepressant drug nomifensine (HOE 984)

Nomifensine (HOE 984) belongs to a chemically new class of drugs with reported antidepressant properties. Nomifensine, like methylphemidate, d-amphetamine and apomorphine, induces strong, intense stereotypes behaviour in the rat. The nomifensine-induced stereotyped behaviour was completely antagonized by pretreatment with reserpine (7.5 mg/kg, 18 h) but not by short-time pretreatment with alpha-methyltyrosine (250 mg/kg, 2 h.) Nomifensine thus differs from d-amphetamine and apomorphine but resembles methylphenidate on stereotyped behaviour. Nominfensine, M1 (8-amino-2-methyl-4-(4-hydroxyphenyl)-1,2,3,4-tetrahydroisoquinoline fumarate) (Hoechst), methylphenidate and d-amphetamine induced a strong increase in the brain level of homovanillec acid (HVA), whereas the dopamine uptake inhibitor benztropine induced no changes in HVA and cocaine induced only a small increase. Nomifensine and the M1 metabolite, like methylphenidate, also increased 3,4-dihydroxyphenylacetic acid (DOPAC) whereas amphetamine, apomorphine, benztropine and cocaine decreased this dopamine metabolite. This suggests that the stereotyped licking and/or biting activities in the rat are related to dopamine releasing properties of nomifensine, methylphenidate and amphetamine. This is further supported by an inverse relationship between the in vitro dopamine uptake inhibitory concentrations and the sterotypy-inducing dose levels of nomifensine and d-amphetamine. Amphetamine caused a strong, and nomifensine and apormorphine a week increase in brain 3-methoxy-4-hydroxyphenylglycol (MOPEG).

Comparative pharmacological studies on butriptyline and some related standard tricyclic antidepressants

Butriptyline was compared with imipramine and other tricyclic antidepressants for its ability to modify: (a) contractions of the cat nictitating membrane induced by noradrenaline (NA) and 5-hydroxytryptamine (5-HT), (b) the adrenergic neuron blocking action of guanethidine in the guinea pig vas deferns, (c) the rabbit's electroencephalogram (EEG) and physostigmine arousal, and (d) the sleep pattern of the rat. Imipramine and amitriptyline potentiated the NA and 5-HT effects on the nictitating membrane and antagonized the inhibitory actions of guanethidine in the guinea pig vas deferens, whereas iprindole and butriptyline were ineffective. These results are consistent with the ability of these drugs to block the neuronal uptake of catecholamines. Butriptyline was a potent blocker of the arousal reaction induced by physostigmine. Butriptyline (20--30 mg/kg) and amitriptyline (10--20 mg/kg) reduced rapid eye movement sleep with a conmitant increase in non-rapid eye movement sleep. This may be a reflection of the dual activity observed in the clinic with these compounds, namely, antidepressant and antianxiety effects.