CILIARY NEUROTROPHIC FACTOR-RECEPTOR-ALPHA IN SPINAL MOTONEURONS IS REGULATED BY GONADAL-HORMONES

Ciliary neurotrophic factor receptor ac (CNTFR alpha) is the ligand-bi nding component of the CNTF receptor. CNTFR alpha expression is essent ial for the normal development of spinal motoneurons and is required f or the development of a sex difference in motoneuron number in androge n-sensitive perineal motoneurons. We used immunocytochemistry to exami ne the expression and hormone regulation of CNTFR alpha protein in the spinal nucleus of the bulbocavernosus (SNB), dorsolateral nucleus and retrodorsolateral nucleus of the lower lumbar spinal cord of adult ra ts. CNTFR alpha immunoreactivity (CNTFR alpha-IR) was observed in the somata and dendrites of virtually all motoneurons. In all three motor pools, the intensity of motoneuron soma labeling was greatest among go nadally intact males and was reduced in females and gonadectomized mal es. The density of CNTFR alpha-IR in neuropil also tended to be highes t in intact males. Short-term (2 d) testosterone propionate treatment reversed the decline in the density of soma labeling in the SNB of cas trated males but did not reverse any other effects of castration. Long -term hormone treatment, achieved by implanting males with testosteron e capsules at the time of gonadectomy, prevented the decline in soma l abeling in all motor pools and partially prevented the decline in neur opil label caused by castration. We conclude that expression of CNTFR alpha protein is androgen-regulated in spinal motoneurons.