Amphetamine and chick behavior. A role for monoamines in the causation of vocalizations and emotions

The effects of amphetamine (AMP) on the behaviour of domestic chicks were studied by methods of direct observation of behaviour. 7.5 mg/kg d-amphetamine sulphate injected into 5-day-old chicks characteristically facilitated vocalization-a period of peeps followed by short calls (twitters and short peeps), head shakes, forced locomotion and wing drooping; and decreased the duration of eye closure. AMP also increased the responsiveness of chicks to external stimuli. Bilateral lesions in the midbrain inhibited primarily the vocalizations but not the other behavioural changes produced by AMP. Evidence is presented to explain the neurochemical basis of the AMP-induced behaviour: namely, that peeping depends on 5-hydroxytryptamine-dependent mechanisms, which may also influence the postural changes, and head shakes, whereas short calls may be mediated by an interaction between dopaminergic and tryptaminergic mechanisms. It is suggested that the monoamines may also be involved in the attentional changes associated with the vocalizations.