Differential behavioural effects after subtotal depletions of dopamine or noradrenaline in the ventral striatum.

Open-field behaviour was investigated in rats subjected to neurotoxic lesions of the ventral striatum. The neurotoxin 6-hydroxydopamine was used to produce depletions of dopamine or noradrenaline. Lesions which decreased dopamine content of the ventral striatum decreased rearing behaviour in the two postoperative weeks. Depletions of noradrenaline, on the other hand, increased both locomotion and rearing behaviour. When rats were tested following injections with the direct acting dopamine agonist apomorphine (0.1, 0.5 and 1.0 mg/kg) all animals exhibited a dose dependent decrease in activity. At the 0.1 mg/kg dose, however, the dopamine denervated group exhibited increased activity. These results indicate that both dopamine and noradrenaline in the ventral striatum can influence motor behaviour. Further, the direction of effects of noradrenaline and dopamine on behaviour suggests that these transmitters may have opposing influences on motor function.