Lesion of locus coeruleus: the effect on pethidine and pentazocine analgesia.

Analgesic activity of pethidine and pentazocine in the locus coeruleus lesioned rats was evaluated. Bilateral destruction of locus coeruleus resulted in a marked decrease in noradrenaline content in forebrain but did not change significantly the levels of dopamine. Lesioned animals showed a marked decrease of predrug pain threshold. However, pethidine increased more effectively the nociceptive threshold in lesioned rats. The effect observed after pentazocine was generally similar but the maximal increase in pain threshold in lesioned animals did not differ significantly from the values observed in sham lesioned rats. The action of both analgesics was markedly prolonged after the lesion of the locus coeruleus.