Opioid receptor activity in the dentate region of the rat hippocampus.

The electrophysiological actions of normorphine and dynorphin-A were compared in the dentate gyrus and CA1 regions of the rat hippocampus. In both regions, these opioids increased cell excitability and induced afterpotentials following electrical stimulation of synaptic afferents. Based upon apparent naloxone dissociation constants, we conclude that normorphine activated mu receptors in both regions. However, dynorphin-A appears to act via mu receptors in CA1, but kappa receptors in the dentate gyrus.