SEXUALLY DIMORPHIC NEURON NUMBER IN LUMBOSACRAL DORSAL-ROOT GANGLIA OF THE RAT - DEVELOPMENT AND STEROID REGULATION

Rats possess a sexually dimorphic neuromuscular system that controls p enile reflexes critical for copulation. This system includes two motor nuclei in the lumbar cord and their target musculature in the perineu m. The spinal nucleus of the bulbocavernosus (SNB) and the dorsolatera l nucleus (DLN) motoneuron populations and their target perineal muscl es are much larger in males than in females. The sex difference in mot oneuron number develops via androgen-regulated differential cell death during the perinatal period; androgen also regulates retention of the target muscles. The developmental pattern and steroid sensitivity of peripheral afferents to the SNB/DLN motor nuclei were previously unkno wn. In order to characterize the peripheral sensory component of the d imorphic SNB/DLN system, the neurons of the relevant dorsal root gangl ia (DRGs) were quantified in terms of number, size, and androgen sensi tivity at various perinatal ages. DRG neuron number is greatest prenat ally, then decreases in both sexes after birth; the timing and pattern of neuron number development are similar to those seen in the SNB and DLN. Postnatally, males have more DRG neurons than females, as a resu lt of greater neuron death in the DRGs of females. Females treated wit h testosterone propionate during the perinatal period exhibit masculin e development of DRG neuron number. Thus, the normal development of DR G neuron number parallels that of the SNB/DLN motor nuclei and target muscles in pattern and timing, is sexually dimorphic, and is regulated by androgen. (C) 1993 John Wiley & Sons, Inc.