The effect of fasting on the stereotyped behaviour induced by amphetamine and by apomorphine in the albino rat.

Fasting increases the synthesis and metabolism of cerebral 5-hydroxytryptamine and modifies dopamine turnover in the striatum. We studied the effect of a 24 h fast on the motor hyperactivity induced by amphetamine or by apomorphine. Locomotion was evaluated in photocell cages and stereotypy by direct observation and the use of rating scales. Amphetamine, 2.0 mg/kg, induced and increase in locomotion with a maximum between 20 and 30 min of its injection. After 40 min there was a decay in the amphetamine effect but the reduction was significantly smaller in the fasted than in the fed rats. Haloperidol, 0.025 mg/kg, abolished the decay of the amphetamine effect mentioned above and also eliminated the difference between fasted and fed rats. The stereotypy effect of amphetamine was of similar intensity in both groups during the first 30 min after the injection. After 40 min however, fasted rats developed a less intense stereotypy effect than did fed rats. Haloperidol induced a pronounced reduction of stereotypy in both groups and abolished the difference between fasted and fed rats. The stereotypy effect of apomorphine was unaffected by fasting. We suggest that food deprivation reduces the stereotypy effect of amphetamine by acting at a presynaptic dopaminergic level in the striatum.