The effect of castration on calcitonin gene-related peptide in spinal motor neurons

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic nucleus of about 200 androgen-accumulating motor neurons in lumbar segments 5 and 6 of the rat spinal cord. In the present work we have used immunohistochemistry to investigate the change in calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) in these motor neurons induced by long-term castration. CGRP-LI was found in the cell bodies of the SNB motor neurons and in thin varicose fibers coursing through the nucleus. In the intact animals 48.4 +/- 3.9% (n = 8) of the SNB neurons were CGRP-LI positive while in the castrates this ratio increased to 80.0 +/- 1.7% (n = 9, p less than 0.001). Animals castrated for 4 weeks and then implanted with testosterone-containing Silastic capsules for an additional 4 weeks had the same percentage of CGRP-LI-containing SNB motor neurons as intact animals. These results demonstrate that a reduction in circulating testosterone levels increases the number of SNB motor neurons that express CGRP-LI implying that androgen stimulation inhibits the expression of CGRP-LI in SNB motor neurons.