Characterization and Location of Met5‐Enkephalin‐Arg6‐Phe7 Stored in Various Rat Brain Regions

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Abstract
A specific antiserum against met5‐enkepha‐lin‐arg6‐phe7 was raised and used to study the distribution and characterization of met5‐enkephalin‐arg6‐phe7‐like immunoreactive material in rat brains by radioimmunoassay and immunohistochemical procedures. The antiserum appears to be directed to the COOH‐terminus of the peptide, as it fails to cross‐react with met5‐enkeph‐alin, met3‐enkephalin‐arg6, met5‐enkephalin‐arg6‐arg7, met6‐enkephalin‐lys6, and leu‐enkephalin. However, it cross‐reacts with phe‐met‐arg‐phe by about 10% and with phe‐met‐arg‐phe‐NH2 to an insignificant degree. The highest content of met5‐enkephalin‐arg6‐phe7 was found in the striatum, which contains a dense network of immunoreactive varicose fibers and terminals, as well as immunoreac tive cell bodies. The met5‐enkephalin‐arg6‐phe7 in striatum can be released in a Ca2+‐dependent manner by a depolarizing concentration of KC1, raising the possibility of a neu‐roregulatory role for met5‐enkephalin‐arg6‐phe7. Characterization of the immunoreactive material by gel filtration and high pressure liquid chromatography revealed the presence of multiple forms of immunoreactive material in some brain regions.