Endogenous Opioid Regulation of Synaptic Transmission in the Dentate Gyrus An important role of endogenous neuropeptide transmitters in brain function is suggested by their prevalence and diversity. Understanding how these molecules may normally function as potential neurotransmitters requires that we know what controls their release, where they act, and what effects they have. We have made substantial progress in answering these questions for endogenous opioid peptides in the hippocampus by characterizing the molecular forms of the peptides present, the distribution of the receptor sites, and the pharmacological effects of opioids in each of the principal regions of the hippocampus. Further work is required to define the effects of endogenously- released opioids on hippocampal neurons. Information obtained from this study will allow us to construct a detailed description of the role of endogenous opioid peptides in the hippocampal neural network and provide a model of neuropeptide action in normal hippocampal physiology associated with learning and memory processes.
