Identification of spinal neurons involved in the urethrogenital reflex in the female rat

Abstract

The urethrogenital (UG) reflex is a spinal sexual reflex that consists of autonomic and somatic nerve activity and vaginal, uterine, and anal sphincter contractions. The UG reflex is under tonic descending inhibition by neurons in the region of the nucleus paragigantocellularis (nPGi). The location of spinal neurons activated by the UG reflex was examined in the female rat using the immediate early gene, c-fos. In addition, the descending inputs from the nPGi onto fos-activated neurons was examined using the anterograde tracer biotin dextran amine injected into the nPGi. The UG reflex resulted in a significant increase in fos-positive nuclei in segments T12-S1, compared with experimental controls in which the UG reflex was not activated. Spinal circuits involved in the UG reflex include neurons relaying afferent information from the pudendal sensory nerve, in the dorsal horn and medial cord of L5-S1. Efferent output includes preganglionic neurons located in the lateral gray of L5-S1 and lateral and medial gray of T13-L2. Spinal interneurons involved in the UG reflex were found close to the preganglionic neurons and in the dorsal horn and intermediate and medial gray of T12-S1. NPGi inputs were found primarily on the autonomic efferents and interneurons in the medial and intermediate gray. These studies demonstrate multisegmental spinal circuits activated with the UG reflex and demonstrate that the descending inhibition from the nPGi is by means of preganglionic and somatic efferents and spinal interneurons closely associated with the efferent output.

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

“…Stimulation of the pelvic and pudendal nerves in the anesthetized cat resulted in an increase of fos-I nuclei in the superficial dorsal horn and medial gray of S1-S3 [29]. Other studies in females, have reported similar but relatively larger activation patterns of fos-immunoreactivity after vaginocervical stimulation, stimulation of the urethrogenital reflex and noxious stimulation of the bladder [5,6,13,15,26,35,41,58].…”

“…Neuroanatomical studies mapping spinal interneurons involved in pelvic organ function confirm that the DGC and lamina X contain neurons that transverse multiple spinal segments and project to the brain [26,35,36,[39][40][41]. Stimulation of the pudendal nerve and pelvic viscera increases electrophysiological activity of DGC neurons and their dendritic fields [25,30].…”

“…The spinal cord was delineated into five regions; dorsal horn (laminae I-III); intermediate gray (laminae IV, V, VI, VII); lateral gray (IML, lateral spinal nucleus and lateral gray of laminae IV, V, VI and VII); medial gray (lamina X, intermediomedial nucleus and laminae IV and V); and ventral horn (laminae VII, VIII, IX) ( figure 1E and F) [41]. The number and location of fos-I nuclei in each region (dorsal horn, lateral gray, intermediate gray and ventral horn) were counted from T11-S2 for each animal (~every 170 μm, this strategy gave around 6-10 sections per segment).…”

Novel spinal pathways identified by neuronal c-Fos expression after urethrogenital reflex activation in female guinea pigs

“…However, spinal circuitry is well conserved across mammalian species, so that pathways identified in laboratory mammals are highly likely to have close homologues in humans. A spinal reflex response to mechanical stimulation of the urethrogenital region, known as urethrogenital reflex (UGR), has been reported in both male and female rats (McKenna et al, 1991;Vathy and Marson, 1998;Marson et al, 2003;Marson and Gravitt, 2004). The responses to the UGR activation in female animals resemble those seen during sexual activity, including significant increases in pelvic blood flow and rhythmic contractions of the vagina and uterus (Bohlen et al, 1982a(Bohlen et al, , 1982bSipski, 2001).…”

“…Expression levels of an immediate-early proto-oncogene protein, c-Fos, in spinal cord neurons are increased by activation of nociceptive sensory neurons, providing a valuable tool to identify neurons within spinal nociceptive pathways (Morgan et al, 1987;Marson et al, 2003;Marson and Gravitt, 2004;Coggeshall, 2005;Wiedey et al, 2008;Gao and Ji, 2009;Wang et al, 2010). Indeed, immunohistochemical mapping of c-Fos expression has allowed the identification of several populations of spinal neurons activated by stimulation of pelvic and pudendal nerves as well as the UGR (Marson et al, 2003).…”