Aging in an androgen-sensitive rat neuromuscular system: A light and electron microscopy study

An androgen sensitive system can be used as a model system to study aging. The lumbar spinal cord of the rat contains a steroid-sensitive motoneuron nucleus, the spinal nucleus of the bulbocavernosus (SNB) which is part of this simple neuromuscular system. The SNB innervates the perineal muscles, the bulbocavernosus (BC) and the levator ani (LA) which are necessary for successful copulation. The SNB neuromuscular system is sensitive to androgens throughout life, and alterations in androgen result in dramatic changes in both the structure and the function of this system. Androgen levels decline normally with advancing age in male rats, providing an opportunity to study the interaction of normal aging and hormone sensitivity. There are regressive changes in the morphology of the SNB at the light and electron microscope levels with advancing age which seem to parallel the declines in the testosterone (T) titers. With advancing age, the perineal target muscle weight declines along with several features of cellular morphology, such as, dendritic length, motoneuron soma size, and synaptic number and density. Synapse size does not change with advancing age.; Pronounced changes can be seen in the structure and function of this neuromuscular system in old animals, and regressive changes can be reversed by androgen treatment which restores testosterone to levels similar in a young adult. While some of the age-related changes in this system are restored with T replacement, ultrastructural changes are not reversed with acute androgen treatment. It may be possible that the ultrastructural changes seen in this system may be restored under conditions not examined in this dissertation. The retention of the hormone-mediated plasticity in this system has important implications for restoration after functional loss or prevention of that loss.