Projections of the paraventricular nucleus of the hypothalamus to the sexually dimorphic lumbosacral region of the spinal cord

Lumbar regions L₅-L₆ of the spinal cord of the male rat contain the sexually dimorphic motor nuclei, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN), which innervate perineal muscles, the bulbocavernosus and the ischiocavernosus, respectively. This neuromuscular system controls penile reflexes which are essential to male reproductive success. Oxytocin has been shown to induce penile reflexes and the site of action for these effects is the PVN. Since PVN is known to project to cervical and thoracic levels of spinal cord, the present study examined projections of the PVN to the L₅-L₆ region of the spinal cord. WGA-HRP was injected into the region of L₅-L₆, aimed at the SNB and DLN and their dendritic extents, in intact male, castrated male and female rats. WGA-HRP-labelled cell bodies were found in the parvocellular subnuclei of PVN, as well as regions of the lateral hypothalamus and the dorsal area of the hypothalamus. These results demonstrate that the PVN projects to lumbar levels of the spinal cord that are sexually dimorphic and androgen-dependent. This suggests that PVN may modulate the activity of these motoneurons.