CALCITONIN-GENE-RELATED PEPTIDE-LIKE IMMUNOREACTIVITY IN SPINAL MOTONEURONS OF THE MALE-MOUSE IS AFFECTED BY CASTRATION AND GENOTYPE

Calcitonin gene-related peptide (CGRP) is found in motoneurons of the mammalian spinal cord, including motoneurons of the androgen-dependent spinal nucleus of the bulbocavernosus (SNB) of the mouse. Motoneurons of the SNB innervate the bulbocavernosus (BC), a striated muscle invo lved in penile reflexes. CGRP is thought to be a trophic factor produc ed by motoneurons to regulate the expression of the acetylcholine rece ptor at the neuromuscular junction. ln rats, the number of SNB motoneu rons containing CGRP is increased by gonadal steroids. This regulation appears to rely on an activity-dependent factor produced by the BC mu scle. The purpose of the present study was to examine, using immunohis tochemistry, the steroid dependence of CGRP in the SNB of male house m ice. Genotypic differences in the steroid regulation of CGRP immunorea ctivity were examined in three strains of mice that differ in their be havioral sensitivity to castration. The results demonstrate that castr ation reduces the number of CGRP-positive SNB motoneurons in mice. The magnitude of the change in CGRP in response to castration and the len gth of time required following castration to alter CGRP were dependent on genotype. Interestingly, the effect of castration in mice, to redu ce the number of CGRP-immunoreactive SNB motoneurons, is opposite in d irection from the increase in CGRP SNB motoneurons observed in rats ob served following castration. These experiments suggest that androgens may alter neuromuscular junction function of mouse SNB by regulating t he production of CGRP in a species-specific, genotypically dependent f ashion.