Regional distribution of endorphin,met5-enkephalin and leu5-enkephalin in the pigeon brain

The distribution of β-endorphin and enkephalin in the pigeon forebrain by immunohistochemistry and radioimmunoassay is essentially analogous to mammals. Both endorphin- and enkephalin-reactive fibers have a similar periventricular distribution, but the enkephalin fibers are more extensive and are also found in the paleostriatum, limbic regions and brain stem, pituitary stalk and notably, penetrating the organum vasculosum hypothalami. There was poor correlation between endorphin and enkephalin regional contents by radioimmunoassay. In contrast, a highly significant correlation was observed between Met⁵-enkephalin and Leu⁵-enkephalin regional distribution. These data support the view that enkephalin neurons and endorphin neurons are independent central neuronal systems.