Differential effects of enkephalin within hippocampal areas.

The synthetic opiate D-Alanine-methionine enkephalin (D-Ala) affects neuronal activity of the fascia dentata (FD). D-Ala causes a depression of the population spike evoked by stimulation of the perforant path, which is antagonized by naloxone. In so called "Tandem" experiments it was shown that D-Ala had opposite effects on the CA1 pyramidal and FD granule cells. It is likely that in the FD the site of action of D-Ala is at the afferent synapses.