Multiple Molecular Forms of Enkephalins in the Guinea Pig Hippocampus

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Abstract
Combined HPLC [high performance liquid chromatography] and radioimmunoassay were used to identify and quantitate enkephalin-related peptides in the guinea pig hippocampus. Both Met- and Leu-enkephalin were identified, in approximately a 2:1 ratio, as well as a 3rd enkephalin-like molecule that is neither Met- nor Leu-enkephalin. The 3rd enkephalin elutes ealier than Met- or Leu-enkephalin from a reversed-phase column, has a MW similar to the other enkephalins, and is as active as these enkephalins are in inhibiting binding of labeled opiates to rat brain membranes. All regions of the hippocampus (dentate gyrus, CA1-2, CA3-4 and subiculum) contain all 3 immunoreactive peptides. Immunocytochemical techniques, using antisera raised against Met-enkephalin, show with one antiserum immunoreactivity in the granule cell-mossy fiber system, and with the other scattered immunoreactive cells mostly in the CA2 region. Enkephalins are not confined to the mossy fiber system, as previously suggested, but may be a component of another hippocampal innervation.