Different role of opiate mu-, delta-, kappa- and sigma-receptors in modification of habituation of orthodromic evoked potential in the turtle's visual cortex.

The ability of specific agonists of opiate mu-, delta-, kappa- and sigma-receptors: morphine, D-Ala2, D- Ley5 -enkephalin (DADL), bremazocine, SKF 10,047 used separately and jointly as well as of Met-enkephalin and naloxone, to modify habituation of orthodromic evoked potential (EP) in the turtle's visual cortex was studied. Though the agonists mentioned above inhibited orthodromic EP in a similar manner they had a different ability to modify habituation: morphine, bremazocine and SKF 10,047 were highly effective in contrast to the low efficacy of DADL. Joint activation of different opiate receptors proved the existence of their interaction which led to changes in the modulating effect of receptors on the habituation dynamics.