[Role of opioid and adrenergic mechanisms in the analgesic action of GABA-positive drugs].

The experiments on rats have shown that repeated administration of depakin and baclofen induced the development of tolerance to their antinociceptive effect. The animals tolerant to depakin and baclofen were supersensitive to the analgetic effect of morphine and clonidine in tail-flick test. In vocalization test the analgetic effect of clonidine in baclofen- and depakin-tolerant animals was not altered. The antinociceptive effect of morphine under these conditions was reduced significantly in depakin-tolerant rats and was unchanged in baclofen-tolerant animals. The role of opioid and adrenergic mechanisms in GABA-ergic analgesia and in the development of tolerance is discussed.