Antipodal central effects of apomorphine and dopamine in chickens

Abstract

Dopamine, infused into the hypothalamus or injected into the 3rd cerebral ventricle of chickens pretreated with mebanazine, induced behavioural and electrocortical sleep, suppressed motor activity and lowered body temperature and CO 2 elimination, effects prevented by phenoxybenzamine but not spiperone. The hypothermic effects of dopamine were intensified by testing chicks below thermoneutrality. Ampomorphine, infused into the hypothalamus, injected into the 3rd cerebral ventricle or given intravenously, evoked behavioural and electrocortical arousal in the intact chicken and in the enc'ephale isolé preparation. Additionally, pecking, vocalization, increased motor activity and CO 2 elimination were elicited; body temperature was elevated in about half the chickens but lowered in the remainder. Chicks tested below thermoneutrality responded with a fall in body temperature to apomorphine, the fall being greatest for those in which apomorphine had hypothermic actions at thermoneutrality. The actions of apomorphine, except on body temperature, were antagonized by spiperone. The effects of apomorphine resembled those of dexamphetamine, but whereas those of the latter were antagonized by less than equimolar dosage of methysergide, the effects of apomorphine were not; spiperone, effective against apomorphine, in equimolar dosage did not prevent the effects of dexamphetamine in 3 of 4 chickens tested.