SELECTIVE EFFECTS OF ENKEPHALIN ON ELECTRICAL-ACTIVITY OF THE INVITRO HIPPOCAMPAL SLICE

The effect of infusion of small concentrations of d-Ala-d-Leu-enkephalin on electrical responses to stimulation of the in vitro hippocampal slice preparation was investigated. Concentrations of enkephalin as low as 10 nM dramatically increased the magnitude of the population spike response of pyramidal cell neurons to stimulation of their Schaffer-commissural afferents. This effect had a rapid onset and was quickly eliminated when the peptide was removed from the perfusion medium. Enhancement of the population spike was blocked by the opiate receptor antagonist naloxone, which, by itself, did not affect either synaptic potentials or the population response. In contrast even relatively high concentrations of the enkephalin produced no detectable effect on either the synaptic potentials recorded in the dendrites or the antidromic response of the pyramidal cells to stimulation of their axons. These findings suggest that enkephalin attenuates the effect of either a feedback or feed-forward inhibitory system which is usually activated by stimulation of the Schaffer-commissural pathways. © 1979 Academic Press, Inc.