Effects of dopaminergic and cholinergic interactions on rat behavior.

The present work studied the effects of dopaminergic and muscarinic receptor agonists and antagonists on rat locomotor activity and catalepsy. Results showed that carbachol at the highest dose used (10 mg/kg, p.o.) decreased and pimozide at the dose used abolished locomotor activity. Atropine at a low dose (1 mg/kg, p.o.) increased and at a high dose decreased this parameter. Mazindol at a high dose also increased locomotor activity. A significant and dose-dependent increase in the time on the bar was observed in animals treated with carbachol or pimozide as compared to controls. The increase observed with pimozide was greater than 60 s. Effects of carbachol on locomotor activity were observed already after the first drug exposure, but the increased time on bar produced by this drug in the test of catalepsy was observed only after repeated exposure (7th day). The effect of the highest dose (10 mg/kg, p.o.) of atropine (decreased activity) as related to the lowest one was evident at the 7th day, but the increased locomotor activity seen at the low dose was detected already at the first day. There was a predominance of the effect of pimozide on the open field as well as on catalepsy after its association with each one of the three doses of carbachol. The association of atropine and mazindol did not seem to alter locomotor activity and catalepsy as related to each drug alone. Our results indicate that interactions between dopaminergic and cholinergic systems play an important role on behavior and motor functions.