PS-04-009 The lumbar spinal cord neurons putatively involved in ejaculation are sexually dimorphic already in pre-pubertal mice

Abstract

The expression of ejaculation is thought to require a well-defined population of lumbar spino-thalamic (LSt) neurons which co-express several neuropeptides, including galanin. In adult rats and humans LSt neurons are significantly more numerous in males than in females. Here we investigated whether this sexual dimorphism is established already before puberty. A transgenic mouse line expressing green fluorescent protein driven by the galanin promoter, was used to directly visualize galaninergic neurons and fibers in the postnatal spinal cord (P4). Transverse sections of the cord were made to map the segmental distribution of galanin expression. Wholemount spinal cords were fixed with paraformaldehyde and cleared with a fructose-based protocol to view and count entire neuron pools, comparing male vs. female siblings from the same litter. Image stacks were acquired with a brightfield fluorescence microscope, deconvolved and analyzed in ImageJ software. Fluorescent reporter expression in the early postnatal mouse largely matched what previously described for galanin using immunohistochemistry in adult tissue. A notable exception was evidence for galanin expression in motoneurons, a phenomenon known to occur transiently during ontogenesis in rat and human. Crucially, brightly fluorescent neurons were present in the expected location of the LSt population (the lumbar enlargement, dorsolaterally of the ependymal canal) in both males and females. Moreover, in each pair of siblings (n=6) they were more numerous in the male than in the female (by 22±4% mean±sd; p=0.03 Wilcoxon paired test; median=1029 in males, 855 in females).