Identification of CNS Neurons Innervating the Levator Ani and Ventral Bulbospongiosus Muscles in Male Rats

Abstract

Introduction The pelvic striated muscles play an important role in mediating erections and ejaculation, and together these muscles compose a tightly coordinated neuromuscular system that is androgen sensitive and sexually dimorphic. Aim To identify spinal and brains neurons involved in the control of the levator ani (LA) and bulbospongiosus (BS) in the male adult and preadolescent rat. Methods Rats were anesthetized, and the transsynaptic retrograde tracer pseudorabies virus (PRV) was injected into the LA muscle of adults or the ventral BS muscle in 30-day-old rats. After 3–5 days rats were sacrificed, and PRV-labeled neurons in the spinal cords and brains were identified using immunohistochemistry. The presence of gastrin-releasing peptide (GRP) in the lumbar spinal neurons was examined. Main Outcomes Measures The location and number of PRV-labeled neurons in the spinal cord and brain and GRP colocalization in the lumbar spinal cord. Results PRV-labeled spinal interneurons were found distributed throughout T11-S1 of the spinal cord, subsequent to dorsal medial motoneuron infection. The majority of spinal interneurons were found in the lumbosacral spinal cord in the region of the dorsal gray commissure and parasympathetic preganglionic neurons. Preadolescent rats had more PRV-labeled spinal interneurons at L5-S1 where the motoneurons were located but relatively less spread rostrally in the spinal cord compared with adults. Lumbar spinothalmic neurons in medial gray of L3-L4 co-localized PRV and GRP. In the brain consistent labeling was seen in areas known to be involved in male sexual behavior including the ventrolateral medulla, hypothalamic paraventricular nucleus, and medial preoptic area. Conclusion Common spinal and brain pathways project to the LA and BS muscles in the rat suggesting that these muscles act together to coordinate male sexual reflexes. Differences may exist in the amount of synaptic connections/neuronal pathways in adolescents compared with adults.

Megaloneurite, a giant neurite of vasoactive intestinal peptide and nitric oxide synthase in the aged dog and identification by human sacral spinal cord

“…Interestingly, different pelvic organs may be innervated by a convergent pathways [85]. Coordinate sexual reflexes may also need integrated central regulation pathways in spinal cord and brain [86]. VIP may be relevant to the neural control of micturition [87,88], constipation [89], erectile function [23,79,90].…”

Sexually dimorphic nuclei in the spinal cord control male sexual functions

“…Using HVEM, we further demonstrated that the terminals of GRP neurons may form 3-D multiple synapses with the dendrites of SPN neurons revealed by a double immunohistochemical study (Oti et al, 2012). Using a viral trans-synaptic retrograde tracing technique, Dobberfuhl et al (2014) recently reported that after the pseudorabies virus (PRV) injection into the levator ani muscle, about a half of PRV-positive neurons in the medial gray at the upper lumbar spinal cord level expressed GRP. Interestingly, very few PRV-labeled spinal interneurons were found in the medial region of the upper lumbar spinal cord in preadolescent pups.…”

A sexually dimorphic peptidergic system in the lower spinal cord controlling penile function in non-human primates

“…10,11,13,18 The SAN provides autonomic preganglionic fibers to the genitalia. 21,22 Spinal GRP-positive axons have also been shown to make direct synaptic contacts with somatic motor neurons of the spinal nucleus of bulbocavernosus (SNB) located in the sacral spinal cord in male rats, 33,34 and GRP-sensitive receptors are expressed by rat SNB motor neurons. 10,25 The SNB in rats, which innervates the striated perineal muscles attached to the base of the penis, 9,35-37 is homologous with the human Onuf's nucleus, a sexually dimorphic nucleus located in the motor neuron pools of the sacral spinal cord that has an important role in the micturition and defecatory as well as in rhythmic contractions of perineal muscles during orgasm.…”