Brain distributions of α-neo-endorphin and β-neo-endorphin: Evidence for regional processing differences

The leu-enkephalin containing opioid peptides α-neo-endorphin and β-neo-endorphin i.e., α-neo-endorphin(1–9)] were measured in rat brain region extracts with two highly specific radioimmunoassays. The molar ratio of α-neo-endorphin to β-neo-endorphin was extremely variable among brain regions. In hypothalamus and posterior pituitary β-neo-endorphin levels were almost as high as α-neo-endorphin levels. In contrast, in the striatum α-neo-endorphin was 30-fold more concentrated than β-neo-endorphin. In all other brain regions α-neo-endorphin was present in 3 to 20-fold higher concentrations than β-neo-endorphin. The β-neo-endorphin immunoreactive material was found to comigrate with authentic β-neo-endorphin on reverse phase HPLC. These findings suggest that in certain brain regions but not in others processing mechanisms exist which can generate β-neo-endorphin through processing of α-neo-endorphin or its precursors.