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The effects of enantiomers of nomifensine were compared in five psychopharmacological tests in which (+/-)-nomifensine is active. In mice, (+)-nomifensine increased motor activity at 16 mg/kg, 8 mg/kg reduced the hypothermia and ptosis induced by reserpine and antagonized the hypothermia induced by 16 mg/kg of apomorphine. (+)-Nomifensine 4 mg/kg potentiated yohimbine toxicity. (-)-Nomifensine 4,8, or 16 mg/kg was inactive in all these tests. In rats, (+)-nomifensine 8 mg/kg induced stereotyped movements whereas (-)-nomifensine 64 mg/kg did not produce stereotypies.

Rats with a history of daily (21 days) amphetamine (2.5 mg/kg) treatment showed enhanced activity when under placebo in their amphetamine-associated environment. We found that this conditioned effect was reduced by haloperidol (0.06; 0.125; 0.25 mg/kg), pimozide (0.25; 0.5 mg/kg) and sulpiride (8; 16; 32 mg/kg) but only at doses similar to or, in the case of pimozide, higher than those required to antagonize the unconditioned stimulant effects of amphetamine (2.5 mg/kg). Conversely, we observed that clonidine (7; 15; 30; 60 micrograms/kg) or lithium regimen (between days 15 and 21) leading to lithium plasma levels of 1.3 +/- 0.1 mEq/l, abolished amphetamine-conditioned hyperactivity but did not affect the unconditioned stimulation of amphetamine or locomotor activity in control rats. Moreover, we found that hyperactivity induced by the daily anticipation of food delivery shared identical pharmacological sensitivity with the behavioural excitation produced by a conditioning history with amphetamine. In light of the antimanic properties of lithium and clonidine and the ability of this latter drug to reduce noradrenergic transmission, our findings raise the possibility that incentive activity may model noradrenergic-dependent aspects of mania.

Several studies have indicated that alpha-adrenergic systems are implicated in the anticonvulsant activity of diphenylhydantoin. We now report that in mice prazosin (0.125 mg/kg), a blocker of alpha 1-adrenoceptors, reverses the effects exerted by diphenylhydantoin (256 mg/kg) in tests which are predictive of antidepressant activity: reserpine-induced ptosis and immobility which are caused by inescapable, aversive situations. These date indicate that alpha-adrenoceptors are not only involved in the anticonvulsant action of diphenylhydantoin, but also in its antidepressant-like effects.

Four effects of nomifensine were studied in interaction with a dopamine receptor blocker (pimozide) and a beta-adrenergic receptor blocker (propranolol). The effects of nomifensine were divided into two categories: 1. Psychomotor stimulant effect a) Stimulation of locomotor activity in mice b) Stereotyped behavior in rats 2. Antidepressant effect a) Antagonism of hypothermia caused by reserpine in mice b) Potentiation of yohimbine-induced toxicity in mice. The psychomotor stimulant effects were antagonized by pimozide but not by propranolol. The antidepressant effects were antagonized by propranolol but not by pimozide. Our results support the hypothesis that nomifensine acts via both dopaminergic and noradrenergic mechanisms subserving distinct behavioral effects, psychomotor stimulant and antidepressant, respectively.