Roles of dopamine and 5-hydroxytryptamine in stereotyped and non-stereotyped behaviour.

The roles of dopamine (DA) and 5-hydroxytryptamine (5-HT) in stereotyped and non-stereotyped components of the classical behavioural syndromes induced by 5-HT and DA were investigated by studying (a) behavioural interactions between the DA agonist apomorphine and the 5-HT agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) and (b) the effects of depletion of 5-HT on the behavioural responses to amphetamine and p-chloroamphetamine. In agreement with evidence [Andrews, Fernando and Curzon (1982) Neuropharmacology 21:63-68] that non-stereotyped (i.e. body shakes and hind limb abduction) and stereotyped (i.e. head weaving and reciprocal forepaw treading) behaviour induced by d-amphetamine (25 mg/kg, i.p.) were inhibited and enhanced respectively by DA, apomorphine inhibited two non-stereotyped behavioural responses induced by 5-MeODMT (hind limb abduction and Straub tail) but enhanced reciprocal forepaw treading. However, head weaving was inhibited. Evidence indicated that behaviour induced by DA (whether stereotyped or not) was inhibited by 5-HT. Thus, the induction by apomorphine of sniffing and mouth movements was enhanced when the synthesis of 5-HT was inhibited. Also, p-chloroamphetamine caused sniffing and mouth movements only when 5-HT synthesis was inhibited. Under the latter conditions, while most classical behavioural responses associated with 5-HT did not occur, hind limb abduction persisted. Similarly, amphetamine (25 mg/kg) caused hind limb abduction and forepaw treading even when 5-HT was almost completely depleted. These results may indicate that the amine releasers have some direct 5-HT agonist properties. Results in general indicate the multiplicity of behavioural interactions between DA and 5-HT.