The role of serotonergic mechanisms on amphetamine-induced stereotyped behaviour.

The effects of 5-hydroxytryptophan (5-HTP) and p-chlorophenylalanine (PCPA) on amphetamine-induced stereotyped behaviour (ASB) and on the behavioural and EEG effects of caudate nucleus stimulation have been studied in the cat. After a pretreatment with 5-HTP (10--30 mg/kg) the threshold dose of amphetamine to induce ASB remained the same, but its pattern assumed a more organized character with reduced amplitude of stereotyped movements. On the contrary, after PCPA (200 mg/kg) a disorganized pattern of ASB was observed. 5-HTP increased and PCPA decreased the threshold of the arrest reaction induced by low frequency stimulation of ventro-lateral parts of the head of caudate nucleus. 5-HTP and PCPA also influenced in the opposite direction caudate-induced spindle waves in the neocortex. The effects of amphetamine on behavioural and EEG pattern of arrest reaction due to stimulation of the caudate nucleus were antagonized by 5-HTP and potentiated by PCPA. It is supposed that serotonergic mechanisms present in the ventro-lateral regions of the caudate nucleus can modulate stereotyped behaviour triggered by amphetamine.