Sexual dimorphism in the number and size of SNB motoneurons: delayed development during normal ontogeny

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic poo l of motoneurons that innervates the perineal musculature. In the Mongolian gerbil, the SNB lies dorsolateral to the central canal within the lumbosac ral spinal cord. Previously, no information was available on the normal dev elopment of the sexual dimorphism of this structure in the Mongolian gerbil , although evidence exists for a peripubertal development of the SNB in the gerbil. At each age from postnatal day I (PND1) through PND15 and at PND25 , male and female gerbils were aldehyde perfused. Spinal cords were gelatin -embedded, cryoprotected. frozen and sectioned coronally through the lumbos acral transition zone and stained for Nissl substance with thionin. Examina tion by light microscopy revealed that the number of visible male and femal e SNB motoneurons significantly increased from PND1 through PND25. The size of the motoneurons also significantly increased in both sexes, however, un til PND15 male gerbil SNB showed two significantly different sized populati ons of motoneurons. These data suggest the development of the SNB in the Mo ngolian gerbil is delayed, compared to the rat, and may continue well beyon d the perinatal time period. (C) 2001 Elsevier Science B.V. All rights: res erved.