SEXUAL DIMORPHISM IN THE DISTRIBUTION OF ALPHA-NEOENDORPHIN-LIKE IMMUNOREACTIVITY IN THE ANTERIOR-PITUITARY OF THE RAT

The localization of the opioid peptide alpha-neoendorphin (alpha-Neo-E ) was studied in the anterior pituitary of normal and castrated male a nd normal female rats. Immunoreactive (ir) cells were noted in both se xes. These alpha-Neo-E-ir cells were further characterized using doubl e immunostaining with an elution-restaining procedure. It was seen tha t in males, alpha-Neo-E-ir cells corresponded mainly to luteinizing ho rmone/follicle-stimulating hormone cells and a few thyroid-stimulating hormone (TSH) cells, whereas in females, virtually all alpha-Neo-E-ir cells corresponded to TSH cells. Castration of male rats caused, with in 3 to 5 days, a dramatic decrease in the number of alpha-Neo-E-ir go nadotrophs, whereas the number of alpha-Neo-E-ir TSH cells tended to i ncrease. Two weeks after castration, however, most alpha-Neo-E-ir cell s were also follicle-stimulating hormone-ir. This study demonstrates t hat in the anterior lobe of the rat, alpha-Neo-E-ir is located within gonadotrophs and/or thyrotrophs, depending on the sex. In addition, re sults obtained following castration suggest that the expression of thi s peptide in the anterior pituitary depends upon the steroid environme nt, possibly indicating that alpha-Neo-E is implicated in the regulati on of the pituitary-gonadal axis.