Distribution of immunoreactive alpha-neo-endorphin in the rat brain.

The distribution of immunoreactive alpha-neo-endorphin (alpha-Neo) in the rat brain was demonstrated by means of highly specific radioimmunoassay (RIA). The highest concentrations of immunoreactive (ir) alpha-Neo (100 pmol/g tissue) were found in the substantia nigra, the hypothalamic supraoptic nucleus (86 pmol/g) and the preoptic area (63 pmol/g); medium levels were found in the basal ganglia, mesencephalic reticular formation, nucleus accumbens and hippocampus. Other structures contained less alpha-Neo-ir. The possible anatomical interaction between alpha-Neo and monoaminergic nerve terminals or cell bodies in some structures is discussed.