Descending spinal projections from the rostral gigantocellular reticular nuclei complex

Abstract

Electrophysiological and physiological studies have suggested that the ventral medullary gigantocellular reticular nuclei (composed of the gigantocellular ventralis and pars alpha nuclei as well as the adjacent lateral paragigantocellular nucleus; abbreviated Gi-LPGi complex) provide descending control of pelvic floor organs (Mackel [1979] J. Physiol. (Lond.) 294:105-122; Hubscher and Johnson [1996] J. Neurophysiol. 76:2474-2482; Hubscher and Johnson [1999] J. Neurophysiol. 82:1381-1389; Johnson and Hubscher [1998] Neuroreport 9:341-345). Specifically, this complex of paramedian reticular nuclei has been implicated in the inhibition of sexual reflexes. In the present study, an anterograde fluorescent tracer was used to investigate direct descending projections from the Gi-LPGi complex to retrogradely labeled pudendal motoneurons (MN) in the male rat. Our results demonstrated that, although a high density of arborizations from Gi-LPGi fibers appears to be in close apposition to pudendal MNs, this relationship also applies to other MNs throughout the entire spinal cord. The Gi-LPGi also projects to spinal autonomic regions, i.e., both the intermediolateral cell column and the sacral parasympathetic nucleus, as well as to regions of the intermediate gray, which contain interneurons involved in the organization of pelvic floor reflexes. Lastly, throughout the length of the spinal cord, numerous neurons located primarily in laminae VII-X, were retrogradely labeled with Fluoro-Ruby after injections into the Gi-LPGi. The diffuse descending projections and arborizations of this pathway throughout the spinal cord suggest that this brainstem area is involved in the direct, descending control of a variety of spinal activities. These results are in contrast with our observations of the discrete projections of the caudal nucleus raphe obscurus, which target the autonomic and somatic MNs involved specifically in sexual and eliminative functions (Hermann et al. [1998] J. Comp. Neurol. 397:458-474).

Activation and inhibition of the micturition reflex by penile afferents in the cat

“…Penile afferents project to the paragigantocellularis region of the medial reticular formation (20), and afferents activated by DNP stimulation, urethral infusion, and bladder distension converge on neurons in the medullary reticular formation (26). The ventral medullary gigantocellular reticular nuclei (which consists partially of the lateral paragigantocellular nucleus) projects to the intermediate gray and sacral parasympathetic nucleus of the sacral spinal cord (23). The convergence of penile somatic and bladder parasympathetic pathways is not surprising considering that DNP afferents and parasympathetic efferents are involved in erectile function (43).…”

Nucleus paragigantocellularis afferents in male and female rats: Organization, gonadal steroid receptor expression, and activation during sexual behavior

“…Descending projections from the nPGi to spinal cell groups outside of those devoted to the somatic component of genital reflexes have been noted, including the intermediolateral cell column and the sacral parasympathetic nucleus (Holstege et al, 1979;Hermann et al, 2003). In addition, the nPGi projects to the LC in rats (Aston-Jones et al, 1986;Luppi et al, 1995), and this nPGi-LC pathway has been implicated in a number of arousal-dependent functions (Chen and Engberg, 1989;Clark and Proudfit, 1991;Clayton and Williams, 2000).…”

“…Projections from the nPGi terminate onto the spinal motor neurons that innervate the bulbospongiosus and ischiocavernosus muscles (Tang et al, 1999;Murphy and Marson, 2000;Hermann et al, 2003); these muscles are critical to the control of erection and ejaculation (McKenna and Nadelhaft, 1986;Holmes et al, 1991). Bilateral lesions of the nPGi in male rats decrease mount and intromission frequency, as well as ejaculation latency, and increase the number of ejaculations to satiety (Yells et al, 1992(Yells et al, , 1994.…”

Psychopharmacology of male rat sexual behavior: modeling human sexual dysfunctions?

“…Moreover, these findings fit with the idea that spinal genitourinary circuits are under inhibitory control of supraspinal brainstem structures presumably mediated by 5-HT. [24][25][26] Effects of SSRIs on ejaculation in humans The frequently reported sexual side effects of SSRIs in men suggest an important role of 5-HT in human ejaculatory behavior. 27 As described previously, in several human studies, we and others have demonstrated that various SSRIs such as paroxetine, sertraline and fluoxetine are able to delay ejaculation in men with premature ejaculation.…”