Actions of opiates upon single unit activity in the cortex of naive and tolerant XXXX .

@entity8854 @entity2227 @entity14887 @entity1510 @entity1286 @entity3982 @entity35 @entity3575 @entity934
The effect of microelectrophoretically and systemically applied opiates on neuronal discharge activity in the sensorimotor cortex of naive and @entity1286 tolerant/dependent @entity35 has been studied. In naive @entity35 depression of spontaneous discharge activity was the predominant effect of low doses of phoretically applied @entity1286 . Higher doses and repeated application frequently converted this effect into excitation. Only the depressant effect was antagonised by @entity1510 . @entity1510 itself had no effect on spontaneous discharge activity when applied at dose-levels sufficient to antagonise the depressant effect of @entity1286 . @entity14887 mimicked the action of @entity1286 whereas @entity3982 was inactive. @entity1286 depressed the excitatory action of @entity8854 and of @entity934 by a @entity1510 -antagonisable mechanism. Systemic application of @entity3575 mimicked the inhibitory effect of phoretically applied @entity1286 upon transcallosally evoked discharge activity. The late response was markedly depressed whereas the primary response was little affected. Phoretically applied @entity1510 antagonised the effects of systemically applied @entity3575 . In chronically morphinised @entity35 the depressant effect of microelectrophoretically administered @entity1286 was almost lacking and a @entity1510 -resistant excitation became the predominant effect. In these animals the excitant effect of @entity1510 was also increased and the anti- @entity2227 effect and the anti- @entity934 effect of @entity1286 was abolished. The present data speak in favour of a postsynaptically located stereospecific receptor which mediates the inhibitory effects of opiates and which may be involved in the development of acute and chronic tolerance to these drugs.
