Spinal Nucleus Of Bulbocavernosus Research Articles

Mapping Motor Neuron Vulnerability in the Neuraxis of Male SOD1G93A Mice Reveals Widespread Loss of Androgen Receptor Occurring Early in Spinal Motor Neurons.

Sex steroid hormones have been implicated as disease modifiers in the neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Androgens, signalling via the androgen receptor (AR), predominate in males, and have widespread actions in the periphery and the central nervous system (CNS). AR translocates to the cell nucleus when activated upon binding androgens, whereby it regulates transcription of target genes via the classical genomic signalling pathway. We previously reported that AR protein is decreased in the lumbar spinal cord tissue of symptomatic male SOD1G93A mice. Here, we further explored the changes in AR within motor neurons (MN) of the CNS, assessing their nuclear AR content and propensity to degenerate by endstage disease in male SOD1G93A mice. We observed that almost all motor neuron populations had undergone significant loss in nuclear AR in SOD1G93A mice. Interestingly, loss of nuclear AR was evident in lumbar spinal MNs as early as the pre-symptomatic age of 60 days. Several MN populations with high AR content were identified which did not degenerate in SOD1G93A mice. These included the brainstem ambiguus and vagus nuclei, and the sexually dimorphic spinal MNs: cremaster, dorsolateral nucleus (DLN) and spinal nucleus of bulbocavernosus (SNB). In conclusion, we demonstrate that AR loss directly associates with MN vulnerability and disease progression in the SOD1G93A mouse model of ALS.

High-Voltage Electron Microscopy Reveals Direct Synaptic Inputs from a Spinal Gastrin-Releasing Peptide System to Neurons of the Spinal Nucleus of Bulbocavernosus

The spinal nucleus of bulbocavernosus (SNB) is a sexually dimorphic motor nucleus located in the anterior horn of the fifth and sixth lumbar segments of the spinal cord that plays a significant role in male sexual function. We recently found that a sexually dimorphic expression of gastrin-releasing peptide (GRP) in the lumbar spinal cord regulates male copulatory reflexes. Although it is reported that these systems are both profoundly regulated by circulating androgen levels in male rats, no direct evidence has been reported regarding GRP synaptic inputs onto SNB motoneurons. The aim of the current study was to determine the axodendritic synaptic inputs of spinal GRP neurons to SNB motoneurons. Immunoelectron microscopy, combined with a retrograde tracing technique using high-voltage electron microscopy (HVEM), provided a three-dimensional visualization of synaptic contacts from the GRP system in the lumbar spinal cord onto SNB motoneurons. HVEM analysis clearly demonstrated that GRP-immunoreactive axon terminals directly contact dendrites that extend into the dorsal gray commissure from the SNB. These HVEM findings provide an ultrastructural basis for understanding how the spinal GRP system regulates male sexual behavior.

Testosterone modulates Ca v2.2 calcium channels’ functional expression at rat levator ani neuromuscular junction

Spinal nucleus of bulbocavernosus and its target musculature, the bulbocavernosus and levator ani muscles, are sexually dimorphic, and their sexual differentiation depends on plasmatic levels of testosterone. Electrophysiological and immunocytochemical studies have demonstrated that at mammalian adult neuromuscular junctions only P/Q-type Ca 2+ channels (Ca v2.1), mediate evoked transmitter release. Here we report that N-type Ca 2+ channel (Ca v2.2) blocker ω-Conotoxin GVIA, as well as Ca v2.1 blocker ω-Agatoxin IVA, significantly reduced quantal content of transmitter release by ∼ 80% and ∼70% respectively at levator ani muscle of the adult rats, indicating that neuromuscular transmission is jointly mediated by both types of channels. In these synapses, we also observed that castration and restitution of plasmatic testosterone in rats resulted in changes in the sensitivity to ω-Conotoxin GVIA. Castration induced, whereas testosterone treatment avoided, functional loss of Ca v2.2, as mediators of transmitter release in these synapses. Strikingly, the expression and localization of α 1B subunits, which form the pore of the Ca v2.2 channel, were similar at control, gonadectomized and gonadectomized testosterone-treated rats, suggesting that testosterone may regulate the coupling mechanisms between Ca v2.2 and transmitter release at the neuromuscular junctions of these sexually dimorphic motoneurons.

Succinate dehydrogenase activity of sexually dimorphic muscles of rats.

Muscles of the male rat perineum attaching to the penis are the ischiocavernosus, the medial bulbocavernosus (BC), and the dorsal BC, also known as the levator ani (LA). The BC and the LA muscles are innervated by a morphologically, neurochemically, and physiologically homogeneous pool of motoneurons, the spinal nucleus of BC (SNB). The purpose of the present study was to determine whether BC and LA muscle fibers constitute histochemically and biochemically homogeneous populations, reflecting the homogeneity of the innervating motoneuron pool. Histochemical fiber type was based on the pH lability of myofibrillar adenosinetriphosphatase. Activity of the mitochondrial enzyme succinate dehydrogenase (SDH) was determined by using a quantitative histochemical procedure. A nonsexually dimorphic, androgen-insensitive muscle, the medial gastrocnemius (MG), was used as control. The superficial regions of the MG, BC, and LA muscles were composed exclusively of type IIb muscle fibers, whereas the fiber type composition of the deep region of the MG was mixed: 28.3% type I, 20.6% type IIa, 40.1% type IIx, and 11.0% type IIb. The SDH activities of type IIb fibers in the deep region of the MG ranged from 1.20 to 9.00 (mean 3.72 +/- 0.40) mmol fumarate.liter tissue-1.min-1. Fiber SDH activities in the superficial region of the MG ranged from 0.04 to 2.70 (mean 1.20 +/- 0.21) mmol fumarate.liter tissue-1.min-1. In the BC muscle, the SDH activities of the type IIb fibers ranged from undetectable to 1.80 with a mean of 0.62 +/- 0.05 mmol fumarate.liter tissue-1.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens and indoleamines interact to control sexual dimorphisms in the rat spinal cord

Previous studies have shown that (i) androgen administration and (ii) depletion of serotonin can independently masculinise parts of the medial preoptic area and groups of motor neurons in the lumbosacral spinal cord when applied during the early postnatal period. We report here that these two control mechanisms interact in the neonatal female rat. Serotonin depletion by p-chlorophenyl alanine extends the ‘critical period’ during which androgens can act to stabilise neuron numbers within two sexually dimorphic motor neuron groups in segments L 5–S 1 (the spinal nucleus of bulbocavernosus and the dorsolateral nucleus), probably by slowing the rate of naturally occurring cell death. A non-dimorphic group of motor neurons (the ventromedial nucleus) was unaffected.

The effects of serotonin manipulation during the postnatal period on the development of sexually dimorphic and non-dimorphic lumbosacral motor neuron groups in the albino Swiss rat

Serotonin (5-HT) may act during development as a neurotrophic agent. Evidence suggests that sexually dimorphic regions of the mammalian nervous system (which often possess sexually dimorphic patterns of 5-HT innervation) could provide a model for this aspect of 5-HT action. Albino Swiss rat pups were treated with p-chlorophenyl alanine (pCPA, 200 mg/kg) or 5-hydroxytryptophan (5-HTP, 75 mg/kg) for 14 days after birth. As adults, the number of motor neurons in the sexually dimorphic spinal nucleus of bulbocavernosus (SNB) and dorsolateral nucleus (DLN), together with the non-dimorphic ventromedial nucleus (VM) were analysed. Postnatal treatment with 5-HTP had a general effect of increasing motor neuron numbers in all three groups. However, pCPA treatment had a marked and specific effect on SNB neuron numbers, increasing these in both sexes (+250% in females and +60% in males) compared with control animals. The results suggest that the postnatal innervation of ventral horn motor neurons by 5-HT-containing terminals may affect cell death at this time.

Maintenance of the spinal nucleus of bulbocavernosus and perineal muscles in female Albino Swiss rats treated with perinatal dihydrotestosterone

Female Albino Swiss rats were exposed to 5 alpha-dihydrotestosterone benzoate (DHTB) for the last 4 days of gestation, or for 4 days after birth, or both. Post-natal DHTB exposure (as well as pre-plus post-natal exposure) resulted in a 2-3-fold increase in the number of motor neurones forming the spinal nucleus of bulbocavernosus (SNB); numbers were intermediate between those found in normal females (approximately 40) and males (approximately 200). These DHTB-treated groups also possessed perineal muscles which were approximately 25% of the weight of those in normal males. Transverse sections of one of the muscles (levator ani) showed that it had approximately half the muscle fibres of normal males. Females exposed prenatally to DHTB showed a small (but significant) rise in SNB numbers, but had no recognizable perineal muscles.

Neonatal hormone manipulations and the maintenance of perineal muscles and their motor neurones in Albino Swiss rats

Newborn female Albino Swiss rats received testosterone propionate, dihydrotestosterone benzoate or oestradiol benzoate for 4 days after birth. The neonatal administration of all three hormones maintained neurones of the spinal nucleus of bulbocavernosus (SNB) complex in adulthood at levels intermediate between those found in normal females (approximately 40 neurones) and those found in normal males (approximately 220 neurones). Dihydrotestosterone benzoate was the most effective treatment. Oestradiol benzoate, while as potent as testosterone propionate in maintaining SNB neurone numbers, could not maintain the perineal muscles which are their normal target. Dihydrotestosterone benzoate and testosterone propionate maintained both neurones and muscles. Newborn male Albino Swiss rats received either the aromatase inhibitor 4-OH-androstenedione, or the 5 alpha-reductase inhibitor aza-steroid 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one(4-MA). Only neonatal treatment with 4-MA led to reduced SNB neurone numbers in adulthood, but the reduction was modest (-16%). The results of the two experiments suggest that several hormones can maintain SNB neurone numbers in Albino Swiss rats, but that 5 alpha-reduced metabolites of testosterone may be particularly effective.