Biogenic amine and neuropeptide inputs to identified pelvic floor motoneurons that also express SRC-1

In the rat, the neurochemical phenotypes of neurons that are presynaptic to motoneurons innervating the levator ani are poorly defined. In this study, motoneurons within the spinal nucleus of the bulbospongiosus (SNB) were revealed, using retrograde labelling, following injection of cholera toxin B subunit into the levator ani muscle. Different classes of neuron making substantial inputs onto these labelled neurons were revealed by using immunocytochemistry for dopamine beta hydroxylase, serotonin and substance P. Appositions (sites of presumptive synapses) between immunoreactive terminals and both the somata and dendrites of labelled SNB motoneurons were commonly seen suggesting that substance P, noradrenaline and serotonin are likely to exert a significant influence on the activity of perineal motoneurons and thus on sexual reflexes. Additionally, steroid receptor coactivator-1 was found to be present in the nuclei of 96% of SNB neurons retrogradely labelled from the levator ani. This suggests that practically all of the neurons that innervate the levator ani are likely to be modulated by circulating steroid hormones.