Relative contents and concomitant release of prodynorphin/neoendorphin-derived peptides in rat hippocampus.

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Abstract
The contents and molecular forms of 5 different prodynorphin-derived opioid peptides were compared in extracts of rat hippocampus by radioimmunoassay after C18-HPLC [high pressure liquid chromatography] resolution. Dynorphin (Dyn) A(1-17) immunoreactivity (ir) and Dyn B-ir were heterogeneous in form; Dyn A(1-8)-ir, .alpha.-neoendorphin (.alpha.neo)-ir and .beta.-neoendorphin (.beta.neo)-ir each eluted as single homogeneous peaks of immunoreactivity. The fraction of immunoreactivity having the same retention as the appropriate synthetic standard was used to estimate the actual hippocampal content of each peptide. Comparison of these values showed that the concentrations of Dyn B, .alpha.neo and Dyn A(1-8) were nearly equal while both Dyn A(1-17) and .beta.neo were 1/5th to 1/10th the value of the other 3. Ca-dependent K+-stimulated release of these prodynorphin-derived opioids from hippocampal slices was detected. The sitmulated rates of release were highest for Dyn B-ir followed by .alpha.neo-ir, then .beta.neo-ir and Dyn A(1-8)-ir with Dyn A(1-17)-ir lowest. The relative rates of stimulated release were in agreement with the relative proportions of peptide present within the tissue. This evidence of the presence and release of these opioid peptides considerably strengthens the hypothesis that this family of endogenous opioids plays a neurotransmitter role in the hippocampus.