Involvement of the locus coeruleus in the potentiation of the quipazine-induced head-twitch response by diazepam and beta-adrenoceptor agonists.

Head-twitching in rats induced by quipazine was reduced by bilateral lesions of the locus coeruleus (LC) produced by 6-hydroxydopamine. Both beta 1-and beta 2-adrenoceptor agonists potentiated the head-twitch induced by quipazine in sham-operated controls. Lesions of the locus coeruleus increased the responses to the beta 1-adrenoceptor agonists, prenalterol and dobutamine, but reduced the response to the beta 2-adrenoceptor agonists, salbutamol and procaterol. Diazepam (0.25 mg/kg) also potentiated the response to quipazine and this was reversed to inhibition by lesions of the locus coeruleus. These results suggest that the beta 1-adrenoceptors involved are postsynaptic and the beta 2-adrenoceptors are presynaptic to neurones of the locus coeruleus and indicate a dual action of diazepam on the head-twitch induced by quipazine. Possible mechanisms for these effects are discussed.