Relative role of catecholamines in head-shaking of infant rats.

The relative contribution of catecholaminergic mechanisms in head-shaking (H-S) of infant rats was explored by comparing the H-S inducing effects of apomorphine and amphetamine in rats from 4-14 days old, and the blocking effect of neuroleptic drugs (chlorpromazine and haloperidol) and more specific alpha- and beta-adrenergic receptor antagonists (phenoxybenzamine and propranolol), on amphetamine induced head-shaking. As apomorphine, but not amphetamine, may induce H-S in four-day-old rats, and the latter drug potentiates apomorphine induced H-S, even in days in which, if injected alone it has no effect, it is suggested that both dopaminergic and noradrenergic mechanisms are involved in H-S, thus differentiating this motor item from other motor patterns included in stereotyped behaviour. This suggestion is further supported by the demonstration that while D-amphetamine induced H-S is blocked by phenoxybenzamine, other stereotyped motor patterns continue unimpaired.