Differential involvement of dopamine-containing tracts in 5-hydroxytryptamine-dependent behaviours caused by amphetamine in large doses

Abstract

Dopamine (DA) concentrations in the rat striatum and/or nucleus accumbens were decreased by lesions in the nigra, ventral tegmentum, striatum and accumbens induced by 6-hydroxydopamine. These affected a range of DA- and 5-hydroxytryptamine-(5HT) dependent behaviours induced by 25 mg/kg of D-amphetamine as follows. Changes in DA-dependent behaviour (forward locomotion, head bobbing) occurred which were consistent with DA terminals in the accumbens and striatum being required for locomotor and stereotypical behaviour, respectively. A repetitive 5HT-dependent behaviour (head weaving) was decreased by lesions which depleted striatal DA. A 5HT-dependent behaviour with repetitive and locomotor elements (reciprocal forepaw treading) was only decreased by the nigral and tegmental lesions which depleted DA in both the striatum and the accumbens (and presumably also in other regions). These results suggest that 5HT-dependent behaviours of stereotypical character also require DA. Conversely, two 5HT-dependent behaviours, without obvious stereotypical or locomotor elements (body shakes, hind limb abduction), were not decreased by any of the lesions (and increased by some). Backward walking was markedly inhibited by lesions which decreased striatal DA. The above evidence for different relationships between each of the 5HT-dependent behaviours studied and DA-containing systems implies that these behaviours are separately mediated. It may clarify previous disagreement on the role of DA in these behaviours.