Effect of morphine on aluminium fluoride and dibutyryl-cyclic AMP induced reduction of field potentials in hippocampal slices

Effects of morphine and aluminum fluoride on field potentials evoked in hippocampal pyramidal cells were investigated revealing the physiological significance of adenylate cyclase in morphine action. Dibutyryl-cyclic AMP (db-cAMP) reduces the amplitude of potentials, while morphine enhances it. Morphine was without effects on db-cAMP induced reduction of potentials. Aluminum fluoride, known to activate GTP binding proteins, also reduced potentials and this was antagonized by morphine. Furthermore, N-[2-(methylamino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-8), a protein kinase A inhibitor, enhanced potentials. When GABA synthesis was inhibited by 3-mercaptopropinoic acid, both morphine and db-cAMP was without effect. These results suggested the inhibition of adenylate cyclase by morphine which might be related with the reduction of GABA release in hippocampal slices.