The role of target muscles in the expression of calcitonin gene-related peptide mRNA in the spinal nucleus of the bulbocavernosus

Turning sex inside-out: Peripheral contributions to sexual differentiation of the central nervous system

Sexual differentiation of the nervous system occurs via the interplay of genetics, endocrinology and social experience through development. Much of the research into mechanisms of sexual differentiation has been driven by an implicit theoretical framework in which these causal factors act primarily and directly on sexually dimorphic neural populations within the central nervous system. This review will examine an alternative explanation by describing what is known about the role of peripheral structures and mechanisms (both neural and non-neural) in producing sex differences in the central nervous system. The focus of the review will be on experimental evidence obtained from studies of androgenic masculinization of the spinal nucleus of the bulbocavernosus, but other systems will also be considered.

The role of RXFP2 in mediating androgen-induced inguinoscrotal testis descent in LH receptor knockout mice

LH receptor knockout (LhrKO) male mice exhibit a bilateral cryptorchidism resulting from a developmental defect in the gubernaculum during the inguinoscrotal phase of testis descent, which is corrected by testosterone replacement therapy (TRT). In vivo and in vitro experiments were conducted to investigate the roles of the androgen receptor (AR) and RXFP2 signals in regulation of gubernacular development in LhrKO animals. This study demonstrated that AR and RXFP2 proteins were expressed in the gubernaculum during the entire postnatal period. TRT normalized gubernacular RXFP2 protein levels inLhrKO mice. Organ and primary cell cultures of gubernacula showed that 5alpha-dihydrotestosterone (DHT) upregulated the expression of Rxfp2 which was abolished by the addition of an AR antagonist, flutamide. A single s.c. testosterone injection also led to a significant increase in Rxfp2 mRNA levels in a time-dependent fashion in LhrKO animals. DHT, natural and synthetic insulin-like peptide 3 (INSL3), or relaxin alone did not affect proliferation of gubernacular mesenchymal cells, while co-treatments of DHT with either INSL3 or relaxin resulted in an increase in cell proliferation, and they also enhanced the mesenchymal cell differentiation toward the myogenic pathway, which included a decrease in a mesenchymal cell marker, CD44 and the expression of troponin. These effects were attenuated by the addition of flutamide, siRNA-mediated Rxfp2 knockdown, or by an INSL3 antagonist. Co-administration of an INSL3 antagonist curtailed TRT-induced inguinoscrotal testis descent in LhrKO mice. Our findings indicate that the RXFP2 signaling pathway plays an important role in mediating androgen action to stimulate gubernaculum development during inguinoscrotal testis descent.

Site-specific estrogen and progestin regulation of orphanin FQ/nociceptin and nociceptin opioid receptor mRNA expression in the female rat limbic hypothalamic system

The distributions of orphanin FQ (OFQ/N; also known as nociceptin) and its cognate receptor, opioid receptor-like receptor-1 (NOP), overlap steroid-responsive regions throughout reproductive circuits of the limbic system and hypothalamus. For example, in the ventromedial nucleus of the hypothalamus (VMH), OFQ/N facilitates lordosis in female rats through estrogen and progesterone regulation of nociceptin activity. We studied estrogen and progesterone regulation of OFQ/N and NOP mRNA expression in limbic-hypothalamic reproductive circuits. Ovariectomized rats were treated with 17beta-estradiol-benzoate (2 microg) and 26 hours later with oil or progesterone (500 microg) and were killed 30 hours after initial treatment. Alternate brain sections were processed for OFQ/N or NOP mRNA in situ hybridization. High levels of hybridization for NOP and OFQ/N and overlapping distributions were observed throughout the limbic hypothalamic reproductive circuits; however, in VMH, only NOP expression was observed. Estrogen treatment increased NOP mRNA expression in anteroventral periventricular nucleus (AVPV), median preoptic nucleus, and VMH. Subsequent progesterone treatment did not alter estrogen-induced expression of NOP mRNA in VMH or median preoptic nucleus but reduced expression in the AVPV. OFQ/N mRNA levels were also regulated by steroids. In the caudal part of the posterodorsal medial amygdala, estrogen increased OFQ/N mRNA levels, and progesterone did not alter this increase, whereas, in the medial part of the medial preoptic nucleus, estrogen and progesterone were needed to increase OFQ/N mRNA levels. Steroid regulation of OFQ/N and NOP in the medial preoptic nucleus and VMH is consistent with emerging data indicating that this opioid system regulates female reproduction.

Morphological alteration in oro-facial CGRP containing motoneurons due to congenital thyroid hypofunction

Under congenital thyroid hypofunction, the oro-facial large and small calcitonin gene-related peptide (CGRP) immunoreactive motoneurons were classified into strong, moderate, weak and negative intensity in offspring weaned rats. While 50% of neurons in the trigeminal motor nucleus (Mo5) were of the large type, this value dropped to 30% in hypothyroid pups. Hypothyroid trigeminal accessory nucleus (Mo5-AC) contained 10% large motoneurons versus about 45% in normal pups. Normal facial nucleus (Mo7) had 20% large motoneurons in contrast with 10% in hypothyroid pups. These values are significant in comparison with the normal pattern of oro-facial CGRP positive immunoreactive motoneurons as well as those devoid of immunostaining.

Testosterone prevents synaptic loss in the perineal motoneuron pool in the spinal cord in male rats exposed to chronic stress

Chronic stress is known to induce disorders of reproductive neuroendocrine functions. Motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in male rats play an important role in copulatory behavior. In the present study, it was examined whether chronic stress would alter synaptic organization of the SNB motoneurons and whether androgen would modify the changes under chronic stress. Five male rats were under restraint stress for 5 days per week for 3 weeks, and five males implanted subcutaneously with Silastic capsules containing testosterone were also exposed to stress. Five males served as unstressed controls. After 3 weeks of restraint stress, cholera toxin-horseradish peroxidase (CT-HRP) was injected into the bulbocavernosus muscles and animals were killed 2 days later. The spinal cords containing the SNB were dissected, processed with a modified tetramethylbenzidine (TMB) method for visualization of retrogradely transported CT-HRP, and examined ultrastructurally. Neuronal structures apposing the membranes of 150 SNB motoneurons (total for three groups) were analyzed by measuring the percentage of somatic membranes covered by synaptic contacts. The mean percentage of somatic membranes covered by synapses in males exposed to chronic stress was significantly less than that in controls or stressed males treated with testosterone. Size and number of synaptic contacts per unit length of somatic membranes in males exposed to stress were also significantly less than those in controls or stressed males treated with testosterone. There was no significant difference in any of the parameters between controls and stressed males treated with testosterone. Changes in plasma levels of testosterone showed the same profile as changes in the synaptic contacts. These results suggest that the SNB motoneurons of male rats exposed to chronic stress retain a considerable synaptic plasticity in response to androgen, and that androgen treatment can rescue the SNB system in male rats when under chronic restraint stress.

Increase in motoneurons in the spinal nucleus of the bulbocavernosus of prepubertally castrated male Mongolian gerbils following delayed treatment with testosterone

Sexual dimorphism in the spinal nucleus of the bulbocavernosus (SNB) of the Mongolian gerbil is achieved by two periods of postnatal increase, one in the first month after birth and one at puberty. The pubertal increase in motoneuron number is of particular interest because it occurs in a nearly adult animal. The purpose of this research was threefold. The first was to determine the response of the SNB in prepubertally castrated male gerbils receiving delayed hormone replacement as adults. Testosterone propionate (TP) treatment resulted in numbers of SNB motoneurons comparable to those seen in intact males, whereas androgen metabolites were less effective. The second purpose was to determine the latency of motoneurons to appear in response to TP. New SNB motoneurons appeared within 2 days of delayed TP replacement in prepubertally castrated males, and 16 days of treatment did not further increase SNB motoneuron numbers. The response of the motoneurons to TP appeared more rapid than the response of the bulbocavernosus (BC) muscle, scent gland, and seminal vesicles. The third purpose was to determine whether the new cells were connected to a target muscle. After 16 days of TP treatment, more motoneurons were labeled in the SNB following injection of a retrograde tract tracer into the BC muscle compared with the number seen in control animals. Thus, new motoneurons appeared in the SNB of prepubertally castrated male Mongolian gerbils within 2 days of the start of delayed TP treatment and were connected to a target within 16 days of TP treatment.

Androgen stimulates neuronal plasticity in the perineal motoneurons of aged male rats

Ten aged male rats (24 months of age) were castrated and implanted subcutaneously with Silastic capsules containing testosterone (T)(5 males) or nothing (5 males). Five sham-castrated males (25 months of age) served as controls. Four weeks after castration, cholera toxin-horseradish peroxidase (CT-HRP) was injected into the bulbocavernosus muscles and animals were killed 2 days later. The spinal cords containing the spinal nucleus of the bulbocavernosus (SNB) were dissected, processed with a modified tetramethylbenzidine method for visualization of retrogradely transported CT-HRP, and examined ultrastructurally. Neuronal structures apposing the membranes of 150 CT-HRP-labeled SNB motoneurons were analyzed by measuring the percentage of somatic membranes covered by synaptic contacts, synaptoid contacts, and neuron-neuron contacts. Most of the neuronal structures in the control and experimental SNB motoneurons consisted of synaptic contacts. The mean percentage of somatic membranes covered by synapses in castrated, aged males treated with T was significantly greater than that in control or castrated animals. Size and number of synaptic contacts per unit length of somatic membranes in castrated, aged males treated with T were also significantly greater than those in control or castrated animals. Plasma levels of T in castrated, aged males treated with T were significantly greater than that in controls. These results suggest that the SNB motoneurons of aged male rats retain a considerable synaptic plasticity in response to androgen, and that androgen may be, at least in part, involved in the process of aging of the SNB system in male rats.

Downhill running preferentially increases CGRP in fast glycolytic muscle fibers

Calcitonin gene-related peptide (CGRP) is present in some spinal cord motoneurons and at neuromuscular junctions in skeletal muscle. We previously reported increased numbers of CGRP-positive (CGRP+) motoneurons supplying hindlimb extensors after downhill exercise (Homonko DA and Theriault E, Inter J Sport Med 18: 1-7, 1997). The present study identifies the responding population with respect to muscle and motoneuron pool and correlates changes in CGRP with muscle fiber type-identified end plates. Twenty seven rats were divided into the following groups: control and 72 h and 2 wk postexercise. FluoroGold was injected into the soleus, lateral gastrocnemius, and the proximal (mixed fiber type) or distal (fast-twitch glycolytic) regions of the medial gastrocnemius (MG). Untrained animals ran downhill on a treadmill for 30 min. The number of FluoroGold/CGRP+ motoneurons within proximal and distal MG increased by 72 h postexercise (P<0.05). No significant changes were observed in soleus or lateral gastrocnemius motoneurons postexercise. The number of alpha-bungarotoxin/CGRP+ motor end plates in the MG increased exclusively at fast-twitch glycolytic muscle fibers 72 h and 2 wk postexercise (P<0.05). One interpretation of these results is that unaccustomed exercise preferentially activates fast-twitch glycolytic muscle fibers in the MG.

Preproenkephalin mRNA levels are regulated by acute stress and estrogen stimulation

Enkephalins facilitate female reproductive behavior. Within the limbic system and hypothalamus, estrogen induced the expression of preproenkephalin (PPE) mRNA. Estrogen injection caused a biphasic increase in the PPE mRNA levels within the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The first peak of PPE mRNA levels occurred within an hour, and the second 24 to 48 h after subcutaneous injection of estrogen. The present studies indicated that the rapid first peak of PPE mRNA expression was stress induced, whereas the second peak was estrogen induced. In the posterodorsal medial amygdala but not in the ventromedial hypothalamic nucleus, the antiestrogen, tamoxifen, did not inhibit the first peak, but blocked the second peak of PPE mRNA expression. Subcutaneous oil injection induced a 1-h peak of PPE mRNA levels but not a 24-h peak. Peak levels of plasma corticosterone were coincident with peak PPE mRNA levels. Adrenalectomy plus a constant, low level of corticosterone eliminated the injection-induced increase of corticosterone levels and the subsequent increase in PPE mRNA expression in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. The present results indicate that both stress steroids and estrogen positively regulate PPE mRNA levels in the ventromedial hypothalamic nucleus and posterodorsal medial amygdala. These results are consistent with the hypothesis that acute, mild stress may contribute to the activation of circuits that facilitate reproductive behavior in the female.

Maldescendus testis

Maldescendus testis is a common congenital abnormality occurring in 2-5% of full-term boys at birth in the Western countries. By 3 months of age, the incidence rate spontaneously reduces to 1-2% in this group. The etiology of the disorder is not known, but normal hypothalamo-pituitary-gonadal axis is usually a prerequisite for normal descent of the testes. Abnormal sexual differentiation is associated with maldescent. However, the majority of boys with maldescended testes show no endocrine abnormalities after birth. Several defects in developmental genes, such as homeobox genes and Insl3, have been described to cause cryptorchidism in mice, and disturbances in the regulation of these genes or their mutations may explain etiology of a large part of human testicular maldescent in the future. Increased degeneration of germ cells can be observed in undescended testes after the first year, and therefore early treatment is recommended. Surgical treatment is the most effective and reliable method to bring testes into the scrotum, but hormone treatment with either hCG or GnRH analogues can be considered, particularly in cases where testes can be palpated in high scrotal position. The efficacy of hormone treatment is less than 20% and depends on the initial location of the testis. Nonpalpable testes rarely descend with hormone treatment. Both surgery and hormone treatment can have untoward effects. Treatment with hCG has been associated with an inflammation-like reaction in the testes and an increased rate of apoptosis of germ cells leading to a reduced adult size of the testes. Vascular complications can occur during surgery, particularly in staged orchidopexies. Men with a history of undescended testis have an increased risk of testicular cancer. Impaired fertility is another long-term risk associated to maldescended testes. Fertility potential may be improved by early treatment. Although our knowledge on cryptorchidism has increased considerably during the last decades, many questions remain to be answered: Is the incidence rate increasing? What is causing maldescent? Do hormones have any role in the treatment?

Lack of carbachol response indicates the absence of cholinergic receptors in sacs associated with undescended testis

BACKGROUND/PURPOSE

The mechanism of testicular descent remains controversial. The processus vaginalis (PV) contains smooth muscle and should have contractile activity that may contribute to descent. This study was designed to evaluate the smooth muscle of PVs associated with incomplete obliteration for spontaneous activities and responses to various stimuli, to determine if differences exist according to sex, diagnostic source, or location of the testis.

MATERIALS

Peritoneal samples (n = 4); sacs from girls (n = 8) and boys with inguinal hernia (n = 12); and sacs from boys with hydrocele (n = 3), hydrocele of the cord (n = 2), or undescended testis (n = 7) were used for the current study. Tissues were attached to the isometric force displacement transducer in an organ bath containing mammalian Ringer's solution at 37 degrees C. Spontaneous mechanical activity and contractile responses of tissues to the electrical field stimulation, phenylephrine, carbachol, and serotonin were recorded. The values obtained from boys and girls with inguinal hernia and from boys with either undescended or descended testis were compared through Fisher's Exact test.

RESULTS

There were no statistically significant differences in patient age between groups. Among the parameters studied, only the carbachol response of the sacs associated with undescended testis showed a significant difference compared with the others (P = .001). None of the sacs associated with undescended testis responded to carbachol, whereas all of the sacs from boys and girls with inguinal hernia responded to carbachol.

CONCLUSIONS

Lack of carbachol response suggests the absence of cholinergic receptors within the sacs associated with undescended testis. The lack of cholinergic receptors may play a role in the failure of the process of testicular descent by hindering either PV elongation into the scrotum or a possible propulsive activity of the PV on the testis.

Direct androgenic regulation of calcitonin gene-related peptide expression in motoneurons of rats with mosaic androgen insensitivity

The spinal nucleus of the bulbocavernosus (SNB) and its target muscles, bulbocavernosus and levator ani (BC/LA), form a sexually dimorphic neuromuscular circuit whose development and maintenance are androgen-dependent. The mechanisms whereby androgen regulates gene expression in the SNB of adult rats are largely unknown, although a retrograde influence from the BC/LA muscles has been suggested to underlie the suppression of calcitonin gene-related peptide (CGRP) expression observed in SNB motoneurons after systemic androgen treatment. A mosaic paradigm was used to determine the site of action of androgen in the regulation of CGRP expression in SNB motoneurons. As a consequence of random X chromosome inactivation, androgenized female rats heterozygous for the tfm androgen receptor (AR) mutation (XwtXtfm-mosaics) express a mosaic of androgen-sensitive and androgen-insensitive motoneurons in the SNB, whereas the BC/LA target musculature appears to be uniformly sensitive to androgens. In adult mosaics, testosterone administration resulted in a reduction in the proportion of androgen-sensitive cells expressing CGRP, whereas no such reduction was observed in the androgen-insensitive population, indicating that neuronal AR plays an essential role in the neuromuscular regulation of CGRP expression in these motoneurons. This provides the first in vivo demonstration of AR regulation of gene expression unambiguously localized to a neuronal population.

Increased activity in the form of endurance training increases calcitonin gene-related peptide content in lumbar motoneuron cell bodies and in sciatic nerve in the rat

The relative content of calcitonin gene-related peptide in lumbar motoneuron cell bodies (semiquantitative immunohistochemistry) and sciatic nerve was examined in rats who had previously undergone a 16-week period of endurance training on a motor-driven treadmill. Soleus motoneurons were identified in the spinal cord by their fluorescence following injection of FluoroGold into the muscle one week before killing. In sedentary rats, calcitonin gene-related peptide was detectable in 76-90% of motoneurons, with no difference in the proportions of negative cells, or in the mean staining intensity of positive cells, between soleus and neighbouring (presumptive fast hindlimb muscle) unlabelled moto-neurons. In endurance-trained rats, the estimated content of calcitonin gene-related peptide was significantly increased (90%) in cell bodies of soleus and neighbouring motoneurons, with no training-induced alterations in the proportions of calcitonin gene-related peptide-positive cells in either sample. The content of the neuropeptide was also significantly higher (37%) in sciatic nerve of endurance-trained rats. Relative accumulation of calcitonin gene-related peptide proximal to a sciatic nerve ligature applied 4 h before, however, was unchanged. The increases in calcitonin gene-related peptide in motoneuron cell bodies and sciatic nerve axons following endurance training may indicate an up-regulation of the synthesis, transport and terminal release of this neuropeptide, which could play a significant role in other morphological and functional adaptations which are known to occur at the neuromuscular junction following this chronic change in activity level.

Protracted elevation of neuronal nitric oxide synthase immunoreactivity in axotomised adult pudendal motor neurons

Neuronal nitric oxide synthase immunoreactivity (NOS1-ir) in sacral motor neurons of normal adult cats was compared with that in cats surviving 1-10 wk after unilateral transection and ligation of the pudendal nerve. Levels of immunostaining were measured by microdensitometry. In nonoperated cats 60% of motor neurons in the ventrolateral nucleus (VL) and Onuf's nucleus (ON) showed high levels of NOS1-ir with lower NOS1-ir in 40%. Following axotomy, motor neurons in ON on both sides of the cord showed an acute rise in mean level of NOS1-ir at 1 wk, with a further increase at 2 wk. Mean levels of NOS1-ir in the ipsilateral and contralateral ON remained elevated at 10 wk after axotomy. Elevation of NOS1-ir occurred in the VL with a similar time-course to that in ON, implying a wider response in motor nuclei synaptically coupled to ON. Measurements of neuronal size in ON and VL revealed an increase in neuronal size in ON but not VL, indicating increased NOSI-ir in ON was not an artifact of neuronal atrophy. The proportion of motor neurons in ON and VL possessing higher levels of NOS1-ir increased from 60% in controls to 100% at 2-3 wk postaxotomy. The proportion slightly declined by 8 wk due to re-emergence of motor neurons exhibiting low NOS1-ir, but remained greater than normal at 10 wk in both nuclei. Based on evidence from related analyses of synaptology, we argue that acute axotomy induced alterations in presynaptic complement which increased overall Ca2+ influx and thereby stimulated NOS1-ir.

Synaptic changes in the perineal motoneurons of aged male rats

Cholera toxin-horseradish peroxidase (CT-HRP) was injected into the bulbocavernosus muscles of young (2 months of age) and old (19-20 months of age) male rats, and animals were killed 2 days later. The spinal cords containing the spinal nucleus of the bulbocavernosus (SNB) were dissected, processed with a modified tetramethylbenzidine method for visualization of retrogradely transported CT-HRP, and examined ultrastructurally. Neuronal structures apposing the membranes of 120 CT-HRP-labeled SNB motoneurons were analyzed by measuring the percentage of somatic membranes covered by synaptic contacts, synaptoid contacts, and neuron-neuron contacts. Most of the neuronal structures in the young and old SNB motoneurons consisted of synaptic contacts. The mean percentage of somatic membranes covered by synapses in old rats was significantly smaller than that in young ones. Size and number of synaptic contacts per unit length of somatic membranes in old animals were also significantly reduced. Plasma levels of testosterone in old males were significantly smaller than those in young ones. These age-related changes in synaptic inputs to SNB motoneurons and plasma levels of androgen seem to correlate with aging of the SNB system.

Hormonally induced neuronal plasticity in the adult motoneurons

Sex steroids are known to play a crucial role in reproductive neuroendocrine functions in adulthood. A number of neurons in the neuroendocrine brain contain sex steroid receptors, and are thought to be a key element of functional neural circuits that are regulated by sex steroids. Motoneurons in the spinal nucleus of the bulbocavernosus in adult male rodents are one of the androgen-sensitive neural substrates. In the spinal nucleus of the bulbocavernosus, castration of adult male rats results in a significant decrease in the somatic size and dendritic length of the motoneurons, and in the number and size of chemical and electrical (gap junction) synapses onto these motoneurons. Androgen treatment of castrates reverses these changes. Furthermore, androgen has been reported to be involved in regulation of androgen receptor expression and gene expression of structural proteins such as beta-actin, beta-tubulin and gap junction channels in these motoneurons. The findings suggest that androgen induces morphological and molecular changes in the motoneurons that reflect their neural functions, and may provide evidence for the mechanisms of hormonally induced neuronal plasticity in the motoneurons in adulthood.

Androgen receptor (AR) immunoreactivity in rat pudendal motoneurons: implications for accessory proteins

Pudendal motoneurons in male rats are located in two sexually dimorphic motoneuronal pools: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). SNB motoneurons innervate sexually dimorphic muscles bulbocavernosus (BC) and levator ani (LA) and the sexually monomorphic external anal sphincter (EAS) muscle. DLN motoneurons innervate either the sexually dimorphic ischiocavernosus (IC) muscle or the sexually monomorphic external urethral sphincter (EUS) muscle. Previous observations indicate that the size of BC, LA, and IC motoneurons in males is sensitive to adult androgen manipulations, whereas the size of EAS and EUS motoneurons is not, raising the question of whether this difference in androgen sensitivity among pudendal motoneurons reflects a difference in androgen receptor (AR) expression. AR immunocytochemistry using the PG-21 antiserum was carried out on spinal cord tissue from normal adult male rats in which specific pudendal motoneuronal subpopulations were identified with retrograde markers. Over 90% of BC, LA, and IC motoneurons displayed AR immunoreactivity in their nuclei. Among motoneurons in the SNB, significantly fewer EAS motoneurons had AR-positive nuclei, which may contribute to the reported failure of EAS motoneurons to morphologically respond to changes in androgen levels. However, within the DLN, despite the fact that IC but not EUS motoneurons are reported to respond to androgen with an increase in soma size, IC and EUS motoneurons had the same proportion of AR-positive nuclei. These results indicate that androgen receptors, while necessary, are not sufficient to confer androgen sensitivity to cells.

Anabolic-androgenic steroid induced alterations in choline acetyltransferase messenger RNA levels of spinal cord motoneurons in the male rat

The effect of chronic supraphysiological doses of anabolic-androgenic steroids, such as those illegally used by recreational, amateur and professional athletes to increase muscle mass and strength, on motoneurons has not been established. The choline acetyltransferase activity levels of perineal muscles in the male rat are modulated by plasma testosterone levels. These muscles are innervated by the sexually dimorphic motoneurons of the spinal nucleus of the bulbocavernosus. Since the primary source of choline acetyltransferase in muscle is motoneuronal, testosterone may modulate perineal muscle choline acetyltransferase activity by regulating choline acetyltransferase messenger RNA levels in motoneurons. The purpose of this study was to determine if choline acetyltransferase messenger RNA levels in cervical and lumbar spinal motoneurons are affected by chronic (four weeks) changes of plasma testosterone levels in the adult male rat. Using in situ hybridization, choline acetyltransferase messenger RNA levels were analysed in four motor columns: the spinal nucleus of the bulbocavernosus, the retrodorsal lateral nucleus of the lumbar spinal cord, and the lateral motor columns of the cervical and lumbar spinal cords. Chronic exposure to supraphysiological levels of testosterone (five- to ten-times physiologic levels) significantly increased choline acetyltransferase messenger RNA in all four motor columns. Subsequent to castration, choline acetyltransferase messenger RNA levels decreased in motoneurons of the spinal nucleus of the bulbocavernosus and the retrodorsal lateral nucleus. This observation suggests that the decrease in choline acetyltransferase activity levels of muscles innervated by spinal nucleus of the bulbocavernosus motoneurons may be due to changes in choline acetyltransferase protein levels. Indeed, testosterone replacement therapy of castrated males prevented the decline of choline acetyltransferase messenger RNA levels in motoneurons. The results of this study demonstrate that anabolic-androgenic steroids can affect the levels of specific messenger RNAs in motoneuron populations throughout the spinal cord suggesting that motoneuronal characteristics are modulated by circulating anabolic-androgenic steroid levels regardless of the purported "androgen sensitivity" of the specific neuromuscular system.

Distribution of vasopressin and oxytocin receptors in the rat spinal cord: sex-related differences and effect of castration in pudendal motor nuclei

The distribution of vasopressin and oxytocin receptors was established by in vitro autoradiography in the spinal cord of adult rats of either sex, as well as in male castrates. In both males and females, high concentrations of vasopressin binding sites were found in a few groups of somatic motoneurons: the large lateral group at the cervicothoracic junction in segments C8 and Th1; the small medial group in segments L3-L5; and the pudendal and retrodorsolateral nuclei in segments L5-L6. The extension and intensity of labelling in pudendal nuclei were markedly lower in females than in males, in particular in the dorsomedial nucleus, where binding was either not or hardly detectable. Gonadectomy in males resulted in a significant reduction of binding in pudendal nuclei, but not in other labelled motor nuclei. Moderate amounts of vasopressin binding sites were also found evenly distributed throughout the central gray at all segmental levels. Oxytocin binding sites were detectable in all spinal segments, but in low amounts and restricted to the superficial layers of the dorsal horn. The abundance of vasopressin binding sites in the central gray suggests that vasopressin may be involved in most spinal functions. The permanent expression of vasopressin binding sites in pudendal motor nuclei of is particular interest with regard to the known plasticity of pudendal motoneurons.

alpha-CGRP mRNA levels in motoneurons innervating specific rat muscles

Along with acetylcholine, motoneurons express several neuromodulatory peptides. The most extensively studied of these peptides is calcitonin gene-related peptide (CGRP). CGRP modulates the biochemical, physiological and metabolic properties of skeletal muscle primarily through activation of membrane receptors. Virtually all motor pool contain motoneurons that are immunoreactive for CGRP. The purpose of this study was to determine the proportions of motoneurons that express alpha-CGRP in motor pools innervating muscles with different motor unit compositions. These include the soleus, extensor digitorum longus, tensor fascia latae and the diaphragm muscles as well as the spinal nucleus of the bulbocavernosus. The spinal nucleus of the bulbocavernosus provides innervation to the bulbocavernosus/levator ani muscle complex and the external anal sphincter muscle. The spinal nucleus of the bulbocavernosus contained the greatest proportion of alpha-CGRP mRNA-positive motoneurons, followed in descending rank order by the tensor fascia latae, the extensor digitorum longus, the soleus and the diaphragm motor pools. In addition, significant differences between motor pools were observed in the mean relative alpha-CGRP mRNA level among those motoneurons expressing alpha-CGRP. The highest mean relative alpha-CGRP mRNA level was observed in soleus and the extensor digitorum longus motor pools; followed in descending rank order by the tensor fascia latae, the diaphragm and the spinal nucleus of the bulbocavernosus. We have previously shown that muscle contractile inactivity increases the number of motoneurons that express alpha-CGRP and in the relative mRNA levels. The results of the present study suggest that the proportion of motoneurons within a motor pool that express alpha-CGRP may be closely related to the contractile activity (i.e. activation history) of the target muscle.

Selective localization and regulated release of calcitonin gene-related peptide from dense-core vesicles in engineered PC12 cells

Introduction of the gene for calcitonin into the neuroendocrine PC12 cell line resulted in the expression of the neuronal-specific splice product, calcitonin gene-related peptide (CGRP). Expression of this neuropeptide did not require treatment of the PC12 cells with NGF. By all available criteria, including biochemical, immunological, and morphological analysis, we have determined that the CGRP in stably transfected PC12 cells is sorted selectively into the large, dense-core catecholamine-containing secretory vesicles. Conversely, the CGRP is excluded from the small, synaptophysin-rich vesicles present in the same cells. Stimulation conditions that trigger the release of catecholamines cause a parallel burst in the release of CGRP. In all these respects, the engineered PC12 cells process the foreign CGRP in a manner similar to that seen in spinal motor neurons in vivo. These results indicate that this small (37 amino acids) peptide contains sorting information sufficient for targeting to large, dense-core vesicles in heterologous cells, placing very narrow constraints on the possible location of sorting signals. In addition, this CGRP-expressing cell line opens the possibility of studying the physiological role of CGRP in the establishment and maintenance of neuromuscular contacts.

Induction of CCK mRNA levels in the limbic-hypothalamic circuit: time course and site-specific effects of estrogen

Estrogenic regulation of cholecystokinin (CCK) and its receptors is correlated with the initiation and termination of lordosis behavior. To understand the effect of circulating estrogen concentration on the temporal aspects of CCK mRNA expression in the posterodorsal medial amygdaloid nucleus (MeApd) and the central part of the medial preoptic nucleus (MPNc) of the limbic-hypothalamic circuit, ovariectomized female rats were treated with a 10 mm Silastic capsule filled with estradiol, a bolus injection of 50 micrograms estradiol benzoate or 2 micrograms estradiol benzoate every 4 days for five "cycles." In situ hybridization was used to compare the relative changes of CCK mRNA levels at 0 h to levels measured at 6, 12, 24, 48, 72, or 96 h after estrogen administration. In the MPNc and the MeApd, the 10-mm capsule significantly increased and maintained CCK mRNA levels from 6 to 96 h. The range of the increase was 3.0-5.1-fold in the MPNc and 2.8-5.0 in the MeApd. The 50-micrograms injections significantly increased and maintained CCK mRNA levels in the MPNc from 12 to 96 h (range of the increase 2.4-4.1-fold) and in the MeApd from 24 to 96 h (range of the increase 2.2-2.8-fold). The repeated administration of 2 micrograms estrogen induced a significant increase of message levels in the MPNc at 12 and 24 h that were 4.2- and 4.7-fold, respectively. In the MeApd this estrogen treatment did not significantly increase CCK mRNA. These studies demonstrate that small doses (2 micrograms) of estrogen that mimic the pattern and circulating levels of estrogen dramatically stimulate CCK mRNA levels in the limbic-hypothalamic circuit. To further study this steroid stimulation, ovariectomized female rats were implanted with estradiol-filled cannulae into the bed nucleus of the stria terminalis or MeA. Estrogen elevated CCK mRNA levels locally in each nucleus. Implants in the bed nucleus also elevated CCK mRNA levels in the MeApd indicating that physiologic estrogen stimulation of CCK in the MeApd is the result of both local and distal transsynaptic elevation of CCK mRNA levels. The sitespecific induction of CCK mRNA levels within the limbic-hypothalamic nuclei provides another important facet of estrogenic modulation of CCK induction.

Expression of mRNA for the N-methyl-D-aspartate (NMDAR1) receptor and vasoactive intestinal polypeptide (VIP) co-exist in enteric neurons of the rat

Anatomical, physiological and pharmacological evidence suggests that vasoactive intestinal polypeptide neurons are important mediators of the descending inhibitory component of intestinal peristalsis. Pharmacological data also indicate that glutamate may modulate intestinal motility. Recently, we demonstrated that mRNA coding for the glutamate N-methyl-D-aspartate (NMDA) receptor is expressed by rat enteric neurons. In order to ascertain whether NMDA receptor message is expressed by vasoactive intestinal polypeptide (VIP) neurons, we employed a double in situ hybridization technique. We hybridized tissue sections from the stomach, ileum and descending colon of adult rats with an NMDAR1 oligoprobe and a VIP oligonucleotide. Enteric neurons expressing mRNA for both NMDA and VIP were found in the myenteric and submucosal ganglia at all of the sampling sites. These data suggest that the mechanism for glutamatergic excitation is present in VIP-containing enteric neurons.

Importance of target innervation in recovery from axotomy-induced loss of androgen receptor in rat perineal motoneurons

In adult male rats, axotomy of the spinal nucleus of the bulbocavernosus (SNB) motoneurons transiently down-regulates androgen receptor (AR) immunoreactivity. The present study investigates the importance of target reinnervation in the recovery of AR expression in axotomized SNB motoneurons after short (up to 5 days) and long (1 to 6 weeks) periods of recovery. In the long-term recovery experiment, animals were divided into two groups. In one, the two stumps of the cut pudendal nerve, which carries the axons of the SNB motoneurons, were sutured together immediately after axotomy. In the second group, the proximal stump was ligated immediately after axotomy to prevent target reinnervation. Axotomy of the SNB motoneurons caused a significant down-regulation in AR immunoreactivity within 3 days. At 6 weeks, AR immunoreactivity was still depressed in ligated animals but had recovered to control levels in resutured animals. The recovery in the resutured group was coincident with the first signs of reinnervation of the target perineal muscles, although reinnervation seemed to lag behind AR immunoreactivity. SNB soma size was significantly reduced 2 weeks after axotomy and returned to control levels after 6 weeks of recovery only in the resutured animals. These findings suggest that the target perineal muscles play a role in the regulation of AR expression and androgen sensitivity in the SNB motoneurons, perhaps mediated by muscle-derived trophic factors.

Axotomy transiently down-regulates androgen receptors in motoneurons of the spinal nucleus of the bulbocavernosus

Testosterone is an important trophic factor for motoneurons in the spinal nucleus of the bulbocavernosus (SNB), and SNB motoneurons are more responsive to testosterone than are other motoneurons. Axonal injury during early postnatal life prevents the normal development of steroid-sensitivity by adult SNB motoneurons. Axonal injury also causes changes in the expression by motoneurons of a wide range of proteins, including the up-regulation of trophic factor receptors. We have used a polyclonal antibody (PG-21; G.S. Prins) to study the expression of androgen receptors in SNB motoneurons after axonal injury. PG-21 labeled motoneuronal nuclei in the lower lumbar spinal cord of rats in a pattern that matched autoradiographic reports of androgen accumulation in this region of the nervous system. A population of numerous, small cells located dorsal to the central canal also showed evidence of androgen receptor expression. Cutting the axons of SNB motoneurons in adulthood or in development caused a decrease in androgen receptor immunoreactivity in SNB motoneurons. This is the first report that a trophic factor receptor in motoneurons is down-regulated after axonal injury, and is interesting in light of reports that testosterone treatment can facilitate motoneuronal regeneration after nerve cut. Androgen receptor levels subsequently returned to normal, regardless of the age at axotomy, providing no evidence for a lasting effect of developmental axotomy on androgen receptor levels in SNB motoneurons. Thus, axotomy-induced down-regulation of androgen receptors does not underlie the inability of SNB motoneurons to respond to androgen treatment several months after pudendal nerve cut in development.

Current concepts in the pathophysiology of testicular undescent

At present, we believe that descent of the testes within the human is a complex event mediated by both hormonal and mechanical factors. We hypothesize that descent of the testes occurs as a result of the secretion of an androgen-independent factor from a normal testis (descendin). This paracrine factor is responsible for the rapid proliferation (outgrowth) of the ipsilateral gubernaculum. The development of the gubernaculum results in creating a dilated inguinal canal, the width of which matches the testicular width. Descent of the testes through the inguinal canal is an interplay between abdominal pressure, a patent processus vaginalis, and androgen-induced gubernacular regression. We hypothesize that androgens (under control of an intact hypothalamic pituitary axis) alter the viscoelastic properties of the gubernaculum, reducing the turgidity of the gubernaculum and allowing intra-abdominal pressure to push the testis into the scrotum. Cryptorchidism can therefore result when any one or more of the involved factors malfunction.

Motoneurons dorsolateral to the central canal innervate perineal muscles in the Mongolian gerbil

The Mongolian gerbil provides a model in which sexually dimorphic areas in the hypothalamus are correlated with sociosexual behaviors such as scent marking and male copulatory behavior. To extend this model, investigations were conducted to determine whether sexually dimorphic areas existed in the spinal cord that could be relevant to male sexual behavior. The focus of these investigations was the perineal muscles associated with the penis. Therefore, this research identified the spinal motoneurons that innervate the bulbocavernosus, levator ani, anal sphincter, and ischiocavernosus muscles of Mongolian gerbils. The motoneuron pool that innervates the bulbocavernosus, levator ani, and anal sphincter was designated the spinal nucleus of the bulbocavernosus (SNB), as for other species of rodents. The motoneuron pool innervating the ischiocavernosus was identified as the dorsolateral nucleus, again, to be consistent with the designation for other rodents. The motoneurons of the gerbil SNB were distributed dorsolateral to the central canal in the lumbosacral transition zone of the spinal column. These motoneurons are located in the region classically defined as area X of the spinal cord. The number of SNB motoneurons was sexually dimorphic, with male gerbils having about five times as many SNB motoneurons as do female gerbils. The size of SNB motoneurons was also sexually dimorphic. The SNB motoneurons of males were 1.5 times larger than the SNB motoneurons of females. The effects of adult castration on the male SNB were also studied. After castration, the size, but not the number, of SNB motoneurons in males was significantly decreased. This decrease was prevented by testosterone treatment. The percentage of calcitonin gene-related peptide (CGRP)-immunoreactive SNB motoneurons was also affected by adult castration. The percentage of CGRP-immunoreactive motoneurons was significantly decreased after adult castration. Again, this decrease was reversed by testosterone treatment. These findings suggest that the SNB of gerbils is sexually dimorphic and is sensitive to circulating levels of gonadal steroids. The unique placement of the SNB motoneurons suggests that an alternative laminar organizational scheme may be necessary for Mongolian gerbil.

Androgenic, not estrogenic, steroids alter neuromuscular synapse elimination in the rat levator ani

Developmental synapse elimination in the rat levator ani (LA) muscle is sensitive to gonadal androgen. This process occurs faster in castrated male rats that lack gonadal testosterone and is largely prevented by testosterone treatment. Because testosterone can be irreversibly converted into either androgenic metabolites such as dihydrotestosterone or estrogenic metabolites such as estradiol, the present experiment sought to determine which of these metabolites account for testosterone's effect. Male rat pups at postnatal day 7 (P7) were castrated and given daily subcutaneous injections of one of 5 possible treatments for 3 weeks (P7-P28): (1) testosterone propionate (TP), (2) dihydrotestosterone propionate (DHTP), (3) estradiol benzoate (EB), (4) a combination of DHTP and EB or (5) sesame oil vehicle. At the end of treatment, the LA and extensor digitorum longus (EDL) muscles were dissected and their motor nerve terminals were stained with tetranitroblue tetrazolium. Hormone effects on synapse elimination were evaluated by counting the number of motor axons that contacted individual muscle fibers. The lumbosacral spinal cord was also dissected and processed histologically to examine the motoneurons in the spinal nucleus of the bulbocavernosus (SNB), which innervates the LA. Hormone effects on SNB motoneuron size were assessed by measuring the cross-sectional area of SNB motoneuronal somata and nuclei. We report that DHTP mimics the effects of TP on synapse elimination in the LA muscle, but that EB, acting either alone or together with DHTP, has little or no effect on this process. Synapse elimination in the EDL was unaffected by any hormone treatment. TP or DHTP, but not EB, increase the size of SNB motoneurons. We conclude that testosterone or its androgenic metabolites influence synapse elimination in the LA and probably exert these effects via androgen receptors.

Calcitonin gene-related peptide-like immunoreactivity, in botulinum toxin-paralysed rat muscles

Changes in calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) at the motor endplates of botulinum toxin-paralysed rat muscles were investigated using immunohistochemistry. One day following toxin injection, a dramatic increase in CGRP-LI was detected at the motor endplates and within preterminal axons of the soleus and gastrocnemius muscles. The upregulation of CGRP-LI persisted throughout the period during which muscle fibres were paralysed and new neuromuscular junctions were being formed by the growing sprouts. Decline of CGRP-LI at the motor endplates coincided with clinical recovery. Both up- and down-regulation of CGRP-LI took place earlier in the soleus than in the gastrocnemius muscle. Up-regulation of CGRP-LI was also detected in a subpopulation of motor axons in the sciatic nerves and in the spinal motor neurons innervating the paralysed muscles. These results indicate that levels of CGRP are regulated, at least partly, by changes in the target innervation. They also suggest an important role for CGRP in the regenerative processes following muscle paralysis.

Capsaicin increases the frequency of cryptorchidism in flutamide-treated rats

Capsaicin, a specific neurotoxin that irreversibly results in degeneration of sensory C fibers of the peripheral nerves, was investigated for its ability to affect testicular descent. In particular, we investigated the ability of prenatal flutamide, postnatal capsaicin or combined prenatal flutamide with postnatal capsaicin to induce undescended testes in rats. Within these treatment groups the frequency of maldescent was 42% in the animals treated prenatally with flutamide, 32% with postnatal capsaicin, and 100% with prenatal flutamide and postnatal capsaicin. Of interest, it was found that all animals that received capsaicin had maldevelopment of the scrotum. Our data suggest that capsaicin increased the frequency of cryptorchidism in rats prenatally treated with flutamide, perhaps by inhibition of scrotal development. These findings indicate that sensory nerves to the scrotum may affect scrotal development and testicular descent.

Calcitonin gene-related peptide receptors in the gubernaculum of normal rat and 2 models of cryptorchidism

We investigated calcitonin gene-related peptide binding in the gubernaculum from a normal rat, a TS rat (congenitally cryptorchid from unknown causes) and a flutamide rat (cryptorchid secondary to prenatal antiandrogen treatment). Gubernacular sections from 2-day-old male pups were incubated with 125iodine-calcitonin gene-related peptide with various concentrations of unlabeled calcitonin gene-related peptide. After exposure to x-ray film, developed film was quantified by computerized densitometry. The binding analysis showed that concentrations of calcitonin gene-related peptide receptors were 22.9 +/- 2.12, 13.5 +/- 1.70 and 30.3 +/- 2.63 (mean plus or minus standard error of mean, fmol./mg. polymer) for each rat, respectively, and there were significant differences between the normal and TS rats (p < 0.01), and the normal and flutamide rats (p < 0.05). However, there was no significant difference in the dissociation constant among the 3 models. This result shows that deficiency and excess of calcitonin gene-related peptide binding in the gubernaculum are associated with cryptorchidism. Calcitonin gene-related peptide released from the genitofemoral nerve may regulate its own receptor concentration to control gubernacular motility in vivo.

Calcitonin gene-related peptide-like immunoreactivity in spinal motoneurons of the male mouse is affected by castration and genotype

Calcitonin gene-related peptide (CGRP) is found in motoneurons of the mammalian spinal cord, including motoneurons of the androgen-dependent spinal nucleus of the bulbocavernosus (SNB) of the mouse. Motoneurons of the SNB innervate the bulbocavernosus (BC), a striated muscle involved in penile reflexes. CGRP is though to be a trophic factor produced by motoneurons to regulate the expression of the acetylcholine receptor at the neuromuscular junction. In rats, the number of SNB motoneurons containing CGRP is increased by gonadal steroids. This regulation appears to rely on an activity-dependent factor produced by the BC muscle. The purpose of the present study was to examine, using immunohistochemistry, the steroid dependence of CGRP in the SNB of male house mice. Genotypic differences in the steroid regulation of CGRP immunoreactivity were examined in three strains of mice that differ in their behavioral sensitivity to castration. The results demonstrate that castration reduces the number of CGRP-positive SNB motoneurons in mice. The magnitude of the change in CGRP in response to castration and the length of time required following castration to alter CGRP were dependent on genotype. Interestingly, the effect of castration in mice, to reduce the number of CGRP-immunoreactive SNB motoneurons, is opposite in direction from the increase in CGRP SNB motoneurons observed in rats observed following castration. These experiments suggest that androgens may alter neuromuscular junction function of mouse SNB by regulating the production of CGRP in a species-specific, genotypically dependent fashion.

Expression of mRNA for the N-methyl-D-aspartate (NMDAR1) receptor by the enteric neurons of the rat

In this study, in situ hybridization techniques were employed to map the distribution of enteric neurons which express mRNA for the glutamate N-methyl-D-aspartate receptor 1 (NMDAR1). We hybridized tissue sections from the stomach, duodenum, ileum and descending colon of adult rats with a 1.43-kB riboprobe cleaved from a clone of the NMDA receptor. Enteric neurons expressing the mRNA were found in both myenteric and submucosal ganglia at each of the sampling sites. Possible functions of NMDA receptors on enteric neurons are discussed.

Flutamide-induced testicular undescent in the rat is associated with alterations in genitofemoral nerve morphology

Androgen regulation of testicular descent is an established fact. However, the mechanisms by which androgens assert their influence is unknown. One of the leading hypotheses regarding androgenic control of testicular descent is based upon the assumption that testosterone regulates the development of the sexually dimorphic genitofemoral nucleus and nerve (GFN). To investigate whether or not alterations in the genitofemoral nerve are indeed androgen dependent and associated with testicular undescent, we administered flutamide in a time-specific manner to pregnant Sprague-Dawley rats. The GFN of ten animals with unilateral intra-abdominal testicular undescent was compared with the contralateral GFN associated with the descended testicle. Digital microscopic evaluations found that the GFN associated with testicular undescent did express altered morphologic abnormalities. Specifically, the GFN associated with the cryptorchid testicle had significant reductions in the neural diameter (.0169 +/- .0024 mm.2 versus .0275 +/- .0079 mm.2; p < .01), the number of large myelinated fibers per mm.2 (8.4 +/- 3.3 versus 18.8 +/- 5; p < .001) and the number of small myelinated nerve fibers per mm.2 (632 +/- 87.4 versus 1090.7 +/- 104.3; p < .001). These data suggest that testicular undescent in the rat is associated with morphologic alterations in the ipsilateral genitofemoral nerve. The exact mechanism of how these alterations are related to cryptorchidism remains to be elucidated.

Androgenic regulation of expression of beta-tubulin messenger ribonucleic acid in motoneurons of the spinal nucleus of the bulbocavernosus

Expression of beta-tubulin mRNA was examined in androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in adult male rats by in situ hybridization histochemistry using cDNA encoding mouse beta-tubulin. Hybridizable beta-tubulin mRNA was localized in the somata and proximal dendrites of SNB motoneurons. Removal of androgen by castration significantly reduced the expression level of beta-tubulin mRNA in the SNB motoneurons, whereas the change was prevented by testosterone treatment. On the contrary, castration or testosterone treatment did not induce any changes in the expression level of beta-tubulin mRNA in the androgen-insensitive motoneurons of the retrodorsolateral nucleus. These results suggest that androgen regulates the expression of beta-tubulin gene in the SNB motoneurons and may provide evidence for the molecular mechanisms of hormonally-induced neuronal plasticity in the SNB motoneurons.

Ontogeny of calcitonin gene-related peptide immunoreactivity in rat lumbar motoneurons: delayed appearance and sexual dimorphism in the spinal nucleus of the bulbocavernosus

Immunoreactivity for calcitonin gene-related peptide (CGRP) has been observed in both adult and embryonic rat motoneurons. However, the developmental pattern of CGRP expression in motoneurons has not been systematically examined and the role of CGRP in neuromuscular development is poorly understood. We have mapped the ontogeny of CGRP-like immunoreactivity in three motoneuron pools of the rat lumbar spinal cord from birth through adulthood. Immunoreactivity was uniformly high in lateral horn motoneurons (the retrodorsolateral nucleus) of males and females at all ages examined. The majority of motoneurons of the dorsolateral nucleus also were positive throughout postnatal development although the percentage of positive motoneurons was slightly higher in males than in females. In contrast, virtually no motoneurons of the spinal nucleus of the bulbocavernosus, located in the medial ventral horn, were positive for CGRP in neonatal rats. CGRP-like immunoreactivity was delayed in this nucleus until approximately postnatal day 6 in males and day 27 in females. Because these three motoneuronal nuclei are differentially sensitive to early androgen and differ with respect to the timing of several developmental milestones, these observations have implications for the regulation and possible roles of CGRP in developing motor systems.

Differential regulation of alpha-calcitonin gene-related peptide and preprocholecystokinin messenger RNA expression in alpha-motoneurons: effects of testosterone and inactivity induced factors

alpha-Calcitonin gene-related peptide expression in alpha-motoneurons is regulated by spinal cord transection, axotomy and testosterone, but to date there are no studies which examine the regulation of cholecystokinin expression in motoneurons. In the present study, we compared the regulation of preprocholecystokinin and alpha-calcitonin gene-related peptide messenger RNA levels in motoneurons of the spinal nucleus of the bulbocavernosus. Previously, we demonstrated that manipulations which decrease activity in target muscles of the spinal nucleus of the bulbocavernosus motoneurons increase alpha-calcitonin gene-related peptide message and peptide levels in spinal nucleus of the bulbocavernosus motoneurons. This muscle-nerve interaction is mediated by a soluble factor which is increased by castration. We now report that decreasing plasma testosterone levels decreased preprocholecystokinin messenger RNA levels. Testosterone replacement at the time of castration restored preprocholecystokinin messenger RNA levels to intact values. Injections of crude extracts prepared from denervated bulbocavernosus/levator ani into the homologous muscles of gonadally intact rats increased the levels of alpha-calcitonin gene-related peptide messenger RNA in spinal nucleus of the bulbocavernosus motoneurons. The levels of preprocholecystokinin messenger RNA did not differ in rats injected with denervated bulbocavernosus/levator ani extract or buffer, both of which were significantly higher than in intact, untreated rats. The results of the present experiments imply that levels of preprocholecystokinin and alpha-calcitonin gene-related peptide messenger ribonucleic acid are differentially regulated in spinal nucleus of the bulbocavernosus motoneurons.