Murine strain differences in beta-endorphin immunoreactivity

The murine strains BALB and C57 differ in behavioral sensitivity to opioid alkaloids, beta-endorphin, and met-/leu-enkephalin. Possible differences in levels of endogenous "opioid peptides" have not been evaluated in the BALB and C57 murine genotypes by the use of immunohistochemical procedures. Antisera to synthetic ovine beta-endorphin was used to examine neuropil and somatic immunoreactivity in various diencephalic and telencephalic areas within three strains of inbred mice, BALB/c, C57BL and the heterogenous strain (CF1). Results indicate that quantitative differences exist between these strains in the number of immunoreactive cells present in the arcuate nucleus of the hypothalamus and in neuropil straining. These observations indicate that behavioral differences in opioid responsivity may relate to differences in either the number of parent somata in the arcuate nucleus and/or the organization and/or trajectory of efferent projections arising from arcuate nucleus neurons.