title: Breeding status affects motoneuron number and muscle size in naked mole-rats: recruitment of perineal motoneurons?
abstract: 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.
authors.affiliation: Department of Psychology and Center for Neuroendocrine Studies, University of Massachusetts, Amherst, Massachusetts 01003, USA. mlseney@cns.umass.edu
authors.forename: Marianne
authors.initials: M
authors.lastname: Seney
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Goldman
authors.forename: Nancy G
authors.initials: NG
authors.lastname: Forger
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002452:Cell Count; D002467:Cell Nucleus / Q000502:physiology / Q000648:ultrastructure; D048429:Cell Size; D003307:Copulation / Q000502:physiology*; D005260:Female; D006608:Hierarchy, Social; D008297:Male; D019577:Mole Rats / Q000033:anatomy & histology / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D010413:Penis / Q000294:innervation / Q000502:physiology; D010502:Perineum / Q000294:innervation / Q000502:physiology; D012726:Sexual Behavior, Animal / Q000502:physiology*; D014844:Vulva / Q000294:innervation / Q000502:physiology
chemical_list: D015415:Biomarkers