Opioid enhancement of perforant path transmission: effect of an enkephalin analog on inhibition and facilitation in the dentate gyrus.

The enkephalin analogue [D-Ala2,D-Leu5]enkephalin, applied locally in vivo, enhanced the responsiveness of dentate granule cells of the hippocampus to perforant path stimulation. The facilitatory effect included a decrease in the inhibition and increase in the facilitation induced by sequential stimuli. The results indicate that opioids, acting at opioid receptors, can enhance responsiveness of the dentate gyrus to perforant path transmission, possibly via a disinhibitory mechanism.