Castration reduces the dendritic length of androgen-sensitive motoneurons in the lumbar spinal cord of adult male rats. Androgen treatment reverses this effect. The proposal is to inject horseradish peroxidase intracellularly into these motoneurons and measure the size and shape of the dendritic tree under high and low levels of androgen. We will also measure various electrophysological characteristics of the neurons as a function of androgen level. These studies will clarify the cellular basis of androgen-induced neural plasticity in adult mammals.