Increase in motoneurons in the spinal nucleus of the bulbocavernosus of prepubertally castrated male Mongolian gerbils following delayed treatment with testosterone

Breeding status affects motoneuron number and muscle size in naked mole-rats: recruitment of perineal motoneurons?

Naked mole-rats live in large colonies and exhibit a strict reproductive hierarchy. Each colony has one breeding female and one to three breeding males; all other individuals are nonreproductive subordinates. Subordinates show a remarkable lack of sex differences in behavior and anatomy, but can become reproductive if removed from the colony. We recently reported that the striated perineal muscles and their innervating motoneurons, which are sexually dimorphic in all other mammals examined to date, are not dimorphic in subordinate naked mole-rats. Here we asked whether sexual differentiation of this neuromuscular system occurs when a subordinate becomes a breeder. The size and number of cells within Onuf's nucleus (homologue of the rat spinal nucleus of the bulbocavernosus) as well as perineal muscle volume were examined in subordinate and breeding naked mole-rats of both sexes. Sex differences in perineal motoneurons were not observed, regardless of social status. To our surprise, however, counts of motoneurons in Onuf's nucleus were increased approximately 30% in breeders of both sexes. This was accompanied by a reciprocal decrease in cells in Onuf's nucleus that were characterized by small soma size, and lacked a clear nucleus or nucleolus. Although not exhibiting typical motoneuron morphology, some of these small cells were positive for the motoneuron marker, SMI-32. The neuronal changes correlate with increased perineal muscle volumes in breeders. We propose that small, relatively undifferentiated cells are recruited to the pool of large Onuf's nucleus motoneurons when subordinate naked mole-rats become breeders.

Age-related alteration of neurturin receptor GFRa2 and nNOS in pelvic ganglia

Neurturin is a neurotrophic factor that is widely expressed in cavernous tissue and retrogradely transported to penis-projecting neurons via its receptor, glial cell line derived neurotrophic factor family receptor alpha-2 (GFRa2). To investigate the influence of aging on neural function on the penis, we examined the expression of GFRa2 mRNA in the major pelvic ganglion and its relationship to neuronal nitric oxide synthase (nNOS)- and tyrosine hydroxylase (TH)-positive neurons. GFRa2 and nNOS mRNA expression levels in RT-PCR showed age-related decreases in 1-, 3-, 6-, 12-, 18- and 24-month-old rats. In situ hybridization also revealed that the number of GFRa2-positive neurons in pelvic ganglia decreased with aging. A double-labeling study revealed the co-expression of GFRa2 and nNOS, which simultaneously decreased in old adult (24 months) and young castrated rats compared with young adult rats (3 months). These results suggest that aging and castration influence the numbers of nNOS- and GFRa2-positive neurons. Higher age might affect not only cavernous tissue but also the neural plasticity of the cavernous nerve related to erectile function.