[Effect of enkephalins on the reactivity of 2 hippocampal synaptic systems]

The effects of leu- and metenkephalin administration into the perfusion medium on CA-1 and CA-3 pyramidal cell reactivity to electric stimulation of Shaffer collaterals and mossy fibers, respectively, were investigated on mice hippocampal slice preparations. The reactivity changes were measured by amplitude changes in focal potential, which reflected a synchronous pyramidal cell discharge (population spike, PS). Infusion of 10(-6) M leu- or metenkephalin resulted in a rapid and reversible 200-300% increase in the PS amplitude in CA-1 field of the hippocamp, that was blocked by preliminary administration of 10(-5) M naloxone. An increase in the PS amplitude in CA-3 region was observed as a result of the infusion of much higher enkephalin concentrations (10(-4) M) and did not exceed 50%. The data obtained allow the conclusion that enkephalins enhance the reactivity in the two main intrahippocampal synaptic systems but have a more pronounced effect on CA-1 pyramids.