[Effects of bifemelane on central dopaminergic and cholinergic systems in rats]

Abstract

The study served to examine the effects of bifemelane on central dopaminergic-cholinergic neuronal mechanisms in rats. Bifemelane (5-20 mg/kg) evoked yawning responses, the frequency being low. Bifemelane (10 mg/kg) as well as bromocriptine (2.5 mg/kg) potentiated physostigmine (0.2 mg/kg)-, bromocriptine (2.5 mg/kg)- or apomorphine (0.1 and 0.5 mg/kg)-induced yawning but completely inhibited pilocarpine-induced yawning. Pretreatment with sulpiride (20 mg/kg) and a low dose of haloperidol (0.02 mg/kg) reversed the stimulatory effect of bifemelane on physostigmine-induced yawning and the inhibitory effect of the drug on pilocarpine-induced yawning, whereas atropine (5 mg/kg) diminished these yawning responses. SK&38393 (2.0 mg/kg), a dopamine D-1 receptor agonist, markedly potentiated bifemelane- and bromocriptine-induced yawning but inhibited physostigmine-induced yawning, and did not affect pilocarpine-induced yawning. The increased yawning responses were blocked by atropine and a low dose of haloperidol. Bifemelane (10 mg/kg) and bromocriptine (2.5 mg/kg) tended to increase apomorphine (5 mg/kg)-induced oral stereotypy, such as licking and biting, but the increase was not significant. These results suggest that the effects of bifemelane on central dopaminergic and cholinergic neurons may be similar to those of bromocriptine.