Analysis of the properties specific for sex hormone-dependent motoneurons

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The spinal nucleus of the bulbocavernosus (SNB) in the rat innervates perineal striated muscles, including the bulbocavernosus, levator ani and external anal sphincter. These motoneurons are sexually dimorphic and responsive to the male hormone, testosterone. In female rats, the majority of SNB motoneurons die at early postnatal stages. In adult male rats, the size of SNB neurons is reduced by castration and increases by treatment with testosterone. The principal question posed in this research proposal is twofold : first, are the electrophysiological properties of the sex hormone-dependent SNB neurons are distinct from those of the motoneurons innervating skeletal muscles? ; second, is the effect of testosterone on neuronal size exerted directly on the SNB motoneurons or mediated by their target perineal muscles?Intracellular potentials and membrane currents were recorded from SNB motoneurons in male and female rats by the whole-cell configuration of patch-clamp techniques in thin sli … More ces of the lumbar spinal cord. The electrophysiological properties differed only quantitatively between the SNB motoneurons and the motoneurons innervating the hiridlimb muscles. It is concluded that the sex hormone-dependent SNB motoneurons and the motoneurons innervating the skeletal muscles cannot be classified into two distinct neuron types.The effects of castration and testosterone on neuronal size were compared between the SNB motoneurons reinnervating the original, hormone-sensitive perineal muscles and the SNB motoneurons reinnervating a skeletal muscle, the soleus muscle which lacks androgen sensitivity. The size of the SNB motoneurons reinnervating the original perineal muscles was reduced by castration and increased by testosterone manipulation. In contrast, the size of the SNB motoneurons reinnervating the grafted soleus muicle remained unchanged by castration or by treatment with testosterone. It is concluded that hormonal regulation of the size of SNB motoneurons is mediated by their target muscles. Less