Metabolism and binding of androgens in the spinal cord of the rat

Effect of Chronic Tibolone Administration on Memory and Choline Acetyltransferase and Tryptophan Hydroxylase Content in Aging Mice

Gonadal steroids exert different effects on the central nervous system (CNS), such as preserving neuronal function and promoting neuronal survival. Estradiol, progesterone, and testosterone reduce neuronal loss in the CNS in animal models of neurodegeneration. However, hormone replacement therapy has been associated with higher rates of endometrial, prostate, and breast cancer. Tibolone (TIB), the metabolites of which show estrogenic and progestogenic effects, is an alternative to reduce this risk. However, the impact of TIB on memory and learning, as well as on choline acetyltransferase (ChAT) and tryptophan hydroxylase (TPH) levels in the hippocampus of aging males, is unknown. We administered TIB to aged C57BL/6J male mice at different doses (0.01 or 1.0 mg/kg per day for 12 weeks) and evaluated its effects on memory and learning and the content of ChAT and TPH. We assessed memory and learning with object recognition and elevated T-maze tasks. Additionally, we determined ChAT and TPH protein levels in the hippocampus by Western blotting. TIB administration increased the percentage of time spent on the novel object in the object recognition task. In addition, the latency of leaving the enclosed arm increased in both TIB groups, suggesting an improvement in fear-based learning. We also observed decreased ChAT content in the group treated with the 0.01 mg/kg TIB dose. In the case of TPH, no changes were observed with either TIB dose. These results show that long-term TIB administration improves memory without affecting locomotor activity and modulates cholinergic but not serotonergic systems in the hippocampus of aged male mice.

The role of orphan G protein-coupled receptors in the modulation of pain: A review

G protein-coupled receptors (GPCRs) comprise a large number of receptors. Orphan GPCRs are divided into six families. These groups contain orphan receptors for which the endogenous ligands are unclear. They have various physiological effects in the body and have the potential to be used in the treatment of different diseases. Considering their important role in the central and peripheral nervous system, their role in the treatment of pain has been the subject of some recent studies. At present, there are effective therapeutics for the treatment of pain including opioid medications and non-steroidal anti-inflammatory drugs. However, the side effects of these drugs and the risks of tolerance and dependence remain a major problem. In addition, neuropathic pain is a condition that does not respond to currently available analgesic medications well. In the present review article, we aimed to review the most recent findings regarding the role of orphan GPCRs in the treatment of pain. Accordingly, based on the preclinical findings, the role of GPR3, GPR7, GPR8, GPR18, GPR30, GPR35, GPR40, GPR55, GPR74, and GPR147 in the treatment of pain was discussed. The present study highlights the role of orphan GPCRs in the modulation of pain and implies that these receptors are potential new targets for finding better and more efficient therapeutics for the management of pain particularly neuropathic pain.

Activity-Based Physical Rehabilitation with Adjuvant Testosterone to Promote Neuromuscular Recovery after Spinal Cord Injury

Neuromuscular impairment and reduced musculoskeletal integrity are hallmarks of spinal cord injury (SCI) that hinder locomotor recovery. These impairments are precipitated by the neurological insult and resulting disuse, which has stimulated interest in activity-based physical rehabilitation therapies (ABTs) that promote neuromuscular plasticity after SCI. However, ABT efficacy declines as SCI severity increases. Additionally, many men with SCI exhibit low testosterone, which may exacerbate neuromusculoskeletal impairment. Incorporating testosterone adjuvant to ABTs may improve musculoskeletal recovery and neuroplasticity because androgens attenuate muscle loss and the slow-to-fast muscle fiber-type transition after SCI, in a manner independent from mechanical strain, and promote motoneuron survival. These neuromusculoskeletal benefits are promising, although testosterone alone produces only limited functional improvement in rodent SCI models. In this review, we discuss the (1) molecular deficits underlying muscle loss after SCI; (2) independent influences of testosterone and locomotor training on neuromuscular function and musculoskeletal integrity post-SCI; (3) hormonal and molecular mechanisms underlying the therapeutic efficacy of these strategies; and (4) evidence supporting a multimodal strategy involving ABT with adjuvant testosterone, as a potential means to promote more comprehensive neuromusculoskeletal recovery than either strategy alone.

The relationship of bone-tumor-induced spinal cord astrocyte activation and aromatase expression to mechanical hyperalgesia and cold hypersensitivity in intact female and ovariectomized mice

Recently, our group established a relationship between tumor-induced spinal cord astrocyte activation and aromatase expression and the development of bone tumor nociception in male mice. As an extension of this work, we now report on the association of tumor-induced mechanical hyperalgesia and cold hypersensitivity to changes in spinal cord dorsal horn GFAP and aromatase expression in intact (INT) female mice and the effect of ovariectomy on these parameters. Implantation of fibrosarcoma cells produced robust mechanical hyperalgesia in INT animals, while ovariectomized (OVX) females had significantly less mechanical hyperalgesia. Cold hypersensitivity was apparent by post-implantation day 7 in INT and OVX females compared to their saline-injected controls and increased throughout the experiment. The decrease in mechanical hyperalgesia in OVX females was mirrored by significant decreases in spinal astrocyte activity in laminae I-II, III-IV, V-VI and X and aromatase expression in laminae V-VI and X in the dorsal horn of tumor-bearing animals. Administration of the aromatase inhibitor letrozole reduced tumor-induced hyperalgesia in INT females only suggesting that the tumor-induced increase in aromatase expression and its associated increase in spinal estrogen play a role in the development of bone tumor-induced hyperalgesia. Finally, intrathecal (i.t.) administration of 17β-estradiol caused a significant increase in tumor-induced hyperalgesia in INT tumor-bearing females. Since i.t. 17β-estradiol increases tumor pain and ovariectomy significantly decreases tumor pain, as well as spinal aromatase, estrogen may play a critical role in the spinal cord response to the changing tumor environment and the development of tumor-induced nociception.

Colocalization of aromatase in spinal cord astrocytes: differences in expression and relationship to mechanical and thermal hyperalgesia in murine models of a painful and a non-painful bone tumor

While spinal cord astrocytes play a key role in the generation of cancer pain, there have been no studies that have examined the relationship of tumor-induced astrocyte activation and aromatase expression during the development of cancer pain. Here, we examined tumor-induced mechanical hyperalgesia and cold allodynia, and changes in Glial fibrillary acid protein (GFAP) and aromatase expression in murine models of painful and non-painful bone cancer. We demonstrate that implantation of fibrosarcoma cells, but not melanoma cells, produces robust mechanical hyperalgesia and cold allodynia in tumor-bearing mice compared to saline-injected controls. Secondly, this increase in mechanical hyperalgesia and cold allodynia is mirrored by significant increases in both spinal astrocyte activity and aromatase expression in the dorsal horn of fibrosarcoma-bearing mice. Importantly, we show that aromatase is only found within a subset of astrocytes and not in neurons in the lumbar spinal cord. Finally, administration of an aromatase inhibitor reduced tumor-induced hyperalgesia in fibrosarcoma-bearing animals. We conclude that a painful fibrosarcoma tumor induces a significant increase in spinal astrocyte activation and aromatase expression and that the up-regulation of aromatase plays a role in the development of bone tumor-induced hyperalgesia. Since spinal aromatase is also upregulated, but to a lesser extent, in non-painful melanoma bone tumors, it may also be neuroprotective and responsive to the changing tumor environment.

The effects of testosterone and insulin-like growth factor 1 on motor system form and function

In this perspective article, we review the effects of selected anabolic hormones on the motoric system and speculate on the role these hormones may have on influencing muscle and physical function via their impact on the nervous system. Both muscle strength and anabolic hormone levels decline around middle age into old age over a similar time period, and several animal and human studies indicate that exogenously increasing anabolic hormones (e.g., testosterone and insulin-like growth factor-1 (IGF-1)) in aged subjects is positively associated with improved muscle strength. While most studies in humans have focused on the effects of anabolic hormones on muscle growth, few have considered the impact these hormones have on the motoric system. However, data from animals demonstrate that administering either testosterone or IGF-1 to cells of the central and peripheral motor system can increase cell excitability, attenuate atrophic changes, and improve regenerative capacity of motor neurons. While these studies do not directly indicate that changes in anabolic hormones contribute to reduced human performance in the elderly (e.g., muscle weakness and physical limitations), they do suggest that additional research is warranted along these lines.

Distribution of androgen and oestrogen receptors-α in the seminal vesicle-related spinal neurones in male rats

The seminal vesicles are male accessory sex glands that contribute much of the seminal fluid volume. Previous studies have suggested that the majority of autonomic innervations to the rat seminal vesicles originate from the bilateral major pelvic ganglia. Many preganglionic autonomic neurones innervating the pelvic ganglion were expressed androgen receptors (AR) or oestrogen receptor (ER)-α immunoreactivity. However, direct neuroanatomic data regarding the distribution of AR and ER-α in seminal vesicle related-spinal neurones are lacking. In the present study, a nonvirulent pseudorabies virus (PRV-152 strain) was used in a retrograde tracing experiment. Four days after PRV injection into the seminal vesicles of male rats, spinal cord sections were prepared. Double- and triple-fluorescence techniques using AR and ER-α with choline acetyltransferase (ChAT) and PRV were used to investigate the AR and ER-α distribution in the seminal vesicles related spinal neurones in male rats. In lamina X, 14% of the PRV-labelled neurones in the L1-L4 segments and 43% in the L5-S1 segments were double-labelled with AR. In the L1-L4 segments, 6% of PRV-labelled neurones and 26% in the L5-S1 segments were double-labelled with ER-α. In the intermedial cell column area, 10% of PRV-labelled neurones in the L1-L4 segments and 47% of PRV-labelled neurones in the L5-S1 segments were double-labelled with AR. Up to 16% of PRV-labelled neurones in the L5-S1 segments were double-labelled with ER-α. No PRV-labelled neurones in the L1-L4 segments were double-labelled with ER-α. However, for the AR and ER-α/PRV/ChAT triple-fluorescence experiments, very few seminal vesicle preganglionic neurones expressed AR or ER-α. Our data suggests that many spinal interneurones but not preganglionic neurones involved in the seminal vesicle control in male rats were double-labelled with AR or ER-α, and they were mainly located at the parasympathetic level in the spinal cord.

Dissociating behavioral, autonomic, and neuroendocrine effects of androgen steroids in animal models

Developments in behavioral assessment, autonomic and/or baseline reactivity, psychopharmacology, and genetics, have contributed significantly to the assessment of performance-enhancing drugs in animal models. Particular classes of steroid hormones: androgenic steroids are of interest. Anecdotally, the performance enhancing effects of androgens are attributed to anabolic events. However, there is a discrepancy between anecdotal evidence and investigative data. While some androgen steroids may promote muscle growth (myogenesis), effects of androgens on performance enhancement are not always seen. Indeed, some effects of androgens on performance may be attributable to their psychological and cardiovascular effects. As such, we consider androgen effects in terms of their behavioral, autonomic, and neuroendocrine components. Techniques are discussed in this chapter, some of which are well established, while others have been more recently developed to study androgen action. Androgens may be considered for their positive impact, negative consequence, or psychotropic properties. Thus, this review aims to elucidate some of the effects and/or mechanisms of androgens on behavioral, autonomic, and/or neuroendocrine assessment that may underlie their controversial performance enhancing effects.

5α-Reduced glucocorticoids: a story of natural selection

5α-Reduced glucocorticoids (GCs) are formed when one of the two isozymes of 5α-reductase reduces the Δ(4-5) double bond in the A-ring of GCs. These steroids are largely viewed inert, despite the acceptance that other 5α-dihydro steroids, e.g. 5α-dihydrotestosterone, retain or have increased activity at their cognate receptors. However, recent findings suggest that 5α-reduced metabolites of corticosterone have dissociated actions on GC receptors (GRs) in vivo and in vitro and are thus potential candidates for safer anti-inflammatory steroids. 5α-Dihydro- and 5α-tetrahydro-corticosterone can bind with GRs, but interest in these compounds had been limited, since they only weakly activated metabolic gene transcription. However, a greater understanding of the signalling mechanisms has revealed that transactivation represents only one mode of signalling via the GR and recently the abilities of 5α-reduced GCs to suppress inflammation have been demonstrated in vitro and in vivo. Thus, the balance of parent GC and its 5α-reduced metabolite may critically affect the profile of GR signalling. 5α-Reduction of GCs is up-regulated in liver in metabolic disease and may represent a pathway that protects from both GC-induced fuel dyshomeostasis and concomitant inflammatory insult. Therefore, 5α-reduced steroids provide hope for drug development, but may also act as biomarkers of the inflammatory status of the liver in metabolic disease. With these proposals in mind, careful attention must be paid to the possible adverse metabolic effects of 5α-reductase inhibitors, drugs that are commonly administered long term for the treatment of benign prostatic hyperplasia.

Estrogen synthesis in the spinal dorsal horn: a new central mechanism for the hormonal regulation of pain

The data summarized here suggest the existence of a new central pathway for the hormonal regulation of pain. These data mainly collected in quail, a useful model in neuroendocrinology, demonstrate that numerous neurons in the superficial laminae of the spinal cord express aromatase (estrogen-synthase). Chronic and systemic blockade of this enzyme in quail alters nociception within days, indicating that the slow genomic effects of sex steroids on nociception classically observed in mammals also occur in birds and require aromatization of androgens into estrogens. However, by contrast with these slow effects, acute intrathecal inhibition of aromatase in restricted spinal cord segments reveals that estrogens can also control nociception much faster, within 1 min, presumably through the activation of a nongenomic pathway and in a manner that depends on an immediate response to fast activation/deactivation of local aromatase activity. This emergent central and rapid paracrine mechanism might permit instantaneous and segment-specific changes in pain sensitivity; it draws new interesting perspectives for the study of the estrogenic control of pain, thus far limited to the classical view of slow genomic changes in pain, depending on peripheral estrogens. The expression of aromatase in the spinal cord in other species and in other central nociception-related areas is also briefly discussed.

In vivo evidence for an increase in 5alpha-reductase activity in the rat central nervous system following morphine exposure

In the present study, the effects of acute and chronic morphine exposure on testosterone concentrations in the central nervous system (CNS) and serum were investigated in rats. Acute morphine administration (5 mg/kg, s.c.) reduced significantly testosterone levels in serum and spinal cord but not in the brain. Following chronic morphine administration (orally for 21 days), the brain testosterone was also significantly reduced as well as serum and spinal cord. Since, the decrease in testosterone levels following morphine exposure was more obvious in the CNS than serum, we suggested that it cannot be caused by only a direct decline in testosterone levels in periphery, and an increased local metabolism of testosterone in the CNS might be attributed in these effects. This hypothesis was supported with the findings that pretreatment with finasteride, a 5alpha-reductase inhibitor (5 mg/kg, s.c.) blocked testosterone elimination from the CNS following morphine exposure. Moreover, the serum concentration of 5alpha-reduced metabolites of testosterone, dihydrotestosterone and 3alpha-diol glucuronide was increased significantly following chronic morphine exposure, but not after co-treatment with finasteride. These results suggest that morphine exposure increase the CNS activity of 5alpha-reductase, which is an important metabolizing enzyme for testosterone.

Influence of the paraventricular nucleus and oxytocin on the retrograde stain of pubococcygeus muscle motoneurons in male rats

Lumbosacral cord motoneurons innervating the pubococcygeus muscle (Pcm) at the pelvic floor of male rats were analyzed. We showed previously that these motoneurons participate in sexual functions and are sensitive to fluctuations of systemic androgen and estrogen. Though estrogen receptors have not been identified in Lamina IX at these spinal areas, the release of oxytocin from the paraventricular nucleus of the hypothalamus (PvN) has been found to control pelvic sexual physiology. We therefore worked on the hypothesis that steroid hormones in the PvN induce the release of oxytocin at the lumbosacral level to modulate the function of Pcm motoneurons. Four experiments were developed, and results were observed with the retrograde staining of motoneurons with horseradish peroxidase. Data indicated that morphometric parameters of Pcm motoneurons were significantly reduced after castration or blocking of the steroids at the PvN site, or following complete transection of the spinal cord at the T8 level. In each case, the reduction of the stain was recovered after intrathecal treatment with oxytocin. Thus, present results show that Pcm motoneurons respond to spinal oxytocin. The conclusive model that we propose is that steroids stimulate the PvN, causing the nucleus to release oxytocin at the level of the lumbosacral spinal cord, and the release of the peptide regulates the spread of the stain of Pcm motoneurons. This work also shows that motoneurons distal to a transected area in the spinal cord could respond to exogenous oxytocin, an important finding for the research of spinal cord lesioned subjects.

Receptors to steroid hormones and aromatase are expressed by cultured motoneurons but not by glial cells derived from rat embryo spinal cord

The aim of this study was to examine the expression of aromatase and receptors to steroid hormones in cultured motoneurons (MNs). We first developed an original method for obtaining rat MN cultures. Dissociated E15 rat spinal cords were purified using metrizamide and bovine serum albumin density gradients, and cells were then seeded on the culture substratum. We optimized the culture parameters and found that simple addition of rat muscle extract (ME) and conditioned culture medium (CM) from glial cell lines (GCL) derived from spinal cord were sufficient to obtain almost pure MN cultures. MNs were characterized by the presence of specific MN markers and electrophysiology. MNs could be kept alive for 2 weeks. We demonstrate that ME and CM are essential for MN development and survival respectively. Immunocytochemistry and aromatase activity assay indicated the presence of androgen and estrogen receptors as well as aromatase in MNs but not in GCL. This is the first report demonstrating the presence of both female and male sex hormone receptors and a key enzyme in steroid hormone metabolism in MNs and its absence in GCL, at least in our culture conditions. This in vitro model appears to be valuable for elucidating the impact of the sex hormone circuit in neuronal maturation. The relevance of this model for the comprehension of neurodegenerative diseases is discussed.

Increase in testosterone metabolism in the rat central nervous system by formalin-induced tonic pain

The effects of formalin-induced tonic pain (FITP) on testosterone (T) concentrations in the central nervous system (CNS) and serum were investigated in rats. T was nearly eliminated from the brain and spinal cord 1.5 and 24 h after a single subcutaneous injection (100 microl/rat, sc) of 5% formalin and its levels were similar to that seen following castration. In serum, T concentrations were decreased significantly 1.5 h following formalin injection, but after 24 h, the serum level of T was within normal range. T concentrations in the brain, spinal cord, and serum were not modified 20 min after formalin injection. Pretreatment of rats with finasteride, a 5alpha-reductase (5alpha-R) inhibitor (5 mg/kg, sc) blocked T elimination from the brain and spinal cord by FITP, but it failed to prevent decrease in serum T. However, 3 h after administration of exogenous T (5 mg/kg, sc), FITP did not cause a significant decrease in T levels in the CNS and serum. These results suggest that FITP eliminates endogenous T in the brain and spinal cord by increasing 5alpha-R activity in the CNS.

Localization of oestrogen receptors in the sensory and motor areas of the spinal cord in Japanese quail (Coturnix japonica)

In Japanese quail, the presence of aromatase (oestrogen synthase) in the dorsal horn of the spinal cord suggests that spinal sensory processes might be controlled by local actions of oestrogens. This is supported by the presence of oestrogen receptors and aromatase in the dorsal horn of the spinal cord in rats, and by the alteration of sensitivity by oestrogens in various mammalian species and also in canaries. We investigated whether oestrogens that are locally produced in the quail spinal cord can bind to specific receptors in the vicinity of their site of synthesis. We demonstrate the presence of numerous oestrogen receptor alpha-immunoreactive (ERalpha-ir) cell nuclei, predominantly in laminae II and, to a lesser extent, I and III of the dorsal horn of the spinal cord (i.e. in the area where aromatase was previously identified). ERalpha-ir cells were also seen in various parts of the intermediate zone (laminae V-VII). This presence of ERalpha-ir cells in the dorsal horn and intermediate zone fits in well with the distribution of ERalpha-ir cells in homologous areas in mammals, including rats. Only a few labelled cells were found in the ventral horn in the cervical, brachial, thoracic and first lumbar segments, but a conspicuous dense group of large ERalpha-ir cells was identified in lamina IX of the ventral horn in synsacral segments 8-10, which contain the motoneurones innervating the muscles of the cloacal gland. The presence of ERalpha-ir cells in lamina IX of these synsacral segments in quail contrasts with the finding that motoneurones innervating penile muscles in rats contain androgen, but not oestrogen receptors, and are influenced by androgens rather than by oestrogens. Together, these data suggest that spinal actions of oestrogens may modulate the sensory and motor systems that participate in reproduction, as well as other nonreproductive functions in quail.

Sexual dimorphism in the spontaneous recovery from spinal cord injury: a gender gap in beneficial autoimmunity?

Immune cells have been shown to contribute to spontaneous recovery from central nervous system (CNS) injury. Here we show that adult female rats and mice recover significantly better than their male littermates from incomplete spinal cord injury (ISCI). This sexual dimorphism is wiped out and recovery is worse in adult mice deprived of mature T cells. After spinal cord contusion in adult rats, functional recovery (measured by locomotor scores in an open field) was significantly worse in females treated with dihydrotestosterone prior to the injury than in placebo-treated controls, and significantly better in castrated males than in their noncastrated male littermates. Post-traumatic administration of the testosterone receptor antagonist flutamide promoted the functional recovery in adult male rats. These results, in line with the known inhibitory effect of testosterone on cell-mediated immunity, suggest that androgen-mediated immunosuppression plays a role in ISCI-related immune dysfunction and can therefore partly explain the worse outcome of ISCI in males than in female. We suggest that females, which are more prone to develop autoimmune response than males, benefit from this response in cases of CNS insults.

Brain androgen and progesterone metabolizing enzymes: biosynthesis, distribution and function

This review summarizes the biosynthesis, cell type-distribution and function of brain aromatase cytochrome P450 (P450aro) and 5alpha-reductase enzymes. This overview covers the impact of the steroid products of the P450aro and 5alpha-reductase enzymes in establishing sexually dimorphic brain structures, specifically the sexually dimorphic nucleus of the preoptic area (SDN) and the anteroventral periventricular nucleus (AVPV). Additionally, since metabolites of the P450aro and 5alpha-reductase enzymes are known to regulate the calcium-binding protein, calbindin (CALB), CALB is reviewed in relationship to its potential role in determining sexually dimorphic brain structures. Finally, recent reports indicate that phytoestrogens inhibit P450aro and 5alpha-reductase activities in peripheral tissue sites, therefore, the effects of phytoestrogens on brain P450aro and 5alpha-reductase are briefly considered and the impact of consuming a high vs. a low phytoestrogen diet on visual spatial memory in male and female rats is presented.

Ovariectomy attenuates dendritic growth in hormone-sensitive spinal motoneurons

The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). Dendritic development of SNB motoneurons in male rats is biphasic, initially showing exuberant growth through 4 weeks of age followed by a retraction to mature lengths by 7 weeks of age. The initial growth is steroid dependent, attenuated by castration or aromatase inhibition, and supported by hormone replacement. Dendritic retraction is also steroid sensitive and can be prevented by testosterone treatment, but is unaffected by aromatase inhibition. Together, these results suggest a role for estrogens during the initial growth phase of SNB development. In this study, we tested whether ovarian hormones could support SNB somal and dendritic development. Motoneuron morphology was assessed in normal males and in females perinatally masculinized with dihydrotestosterone and then either ovariectomized or left intact. SNB motoneurons were retrogradely labeled with cholera toxin-HRP at 4 or 7 weeks of age and reconstructed in three dimensions. Initial growth of SNB dendrites was reduced after ovariectomy in masculinized females. However, no differences in dendritic length were seen at 7 weeks of age between intact and ovariectomized masculinized females, and lengths in both groups were significantly lower than those of normal males. Together with previous findings, these results suggest that estrogens are involved in the early growth of SNB dendrites, but not in their subsequent retraction.

Localization and controls of aromatase in the quail spinal cord

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are located mostly in laminae I-III, with additional sparse cells being present in the medial part of lamina V and, at the cervical level exclusively, in lamina X around the central canal. Radioenzyme assays based on the measurement of tritiated water release confirmed the presence of substantial levels of aromatase activity throughout the rostrocaudal extent of the spinal cord. Contrary to what is observed in the brain, this enzyme activity and the number of aromatase-immunoreactive cells in five representative segments of the spinal cord are not different in sexually mature males or females and are not influenced in males by castration with or without testosterone treatment. The aromatase activity and the numbers of aromatase-immunoreactive cells per section are higher at the brachial and thoracic levels than in the cervical and lumbar segments. These experiments demonstrate for the first time the presence of local estrogen production in the spinal cord of a higher vertebrate. This production was localized in the sensory fields of the dorsal horn, where estrogen receptors have been identified previously in several avian and mammalian species, suggesting an implication of aromatase in the modulation of sensory (particularly nociceptive) processes.

Androgen-sensitive preganglionic neurons innervate the male rat pelvic ganglion

In adult male rats many pelvic autonomic ganglion cells change in structure and function after androgen deprivation. In this study we have investigated whether preganglionic neurons in the lumbar and sacral spinal cord that innervate these ganglion cells are also androgen-sensitive. Numerous spinal neurons retrogradely labelled from the pelvic ganglion possessed androgen receptor immunoreactivity and this was diminished by castration or enhanced by additional testosterone exposure. These comprised 27-77% of all preganglionic neurons innervating the pelvic ganglion, depending on the spinal level and whether animals were administered testosterone prior to sacrifice or not. When adult animals were castrated, no change occurred in the soma size or number of primary dendrites in these lumbar or sacral preganglionic neurons. Mean dendrite length was also determined in lumbar preganglionic neurons supplying the pelvic ganglion, but was not affected by castration. However, the total volume of lumbar preganglionic terminal varicosities supplying each noradrenergic pelvic ganglion cell decreased in parallel with the volume of the target neuron. These studies show that many preganglionic autonomic neurons involved in pelvic reflexes are androgen-sensitive, but that androgens selectively influence particular neuronal compartments. The prevalence of androgen receptors in these neurons suggests that testosterone may directly influence gene expression of preganglionic neurons. Together these studies suggest that testosterone (or a metabolite) has widespread actions on pelvic reflex circuits during adulthood and that under conditions of diminished circulating androgens a variety of reflex activities may not function optimally.

5 alpha-reductase isozymes in the central nervous system

The enzyme 5 alpha-reductase (5 alpha-R) activates several delta 4-3keto steroids to more potent derivatives which may also acquire new biological actions. Testosterone gives rise to the most potent natural androgen dihydrotestosterone (DHT), and progesterone to dihydroprogesterone (DHP), a precursor of the endogenous anxiolytic/anesthetic steroid tetrahydroprogesterone (THP). Two isoforms of 5 alpha-R, with a limited degree of homology, different biochemical properties and distinct tissue distribution have been cloned: 5 alpha-R type 1 and type 2. In androgen-dependent structures DHT is almost exclusively formed by 5 alpha-R type 2; 5 alpha-R type 1 is widely distributed in the body, with the highest levels in the liver, and may be involved in steroid catabolism. In the brain, the roles of the two isozymes are still largely unknown. This brief review will summarize recent experimental data from our laboratory which try to assign possible functional roles to the process of 5 alpha-reduction, and to the two 5 alpha-R isoforms in the CNS.

Fos induced by mating or noncontact sociosexual interaction is colocalized with androgen receptors in neurons within the forebrain, midbrain, and lumbosacral spinal cord of male rats

This study was designed to determine the extent to which Fos immunoreactivity (induced either by mating or noncontact sociosexual interaction) and androgen receptor (AR) immunoreactivity are colocalized in brain and spinal cord of male rats. Some males (Mated) were allowed to mate to ejaculation; others (Social Controls) were placed with females but physical contact was prevented by a wire mesh screen; remaining males (Isolated) were placed alone in the test jar for the duration of the test period. After testing, brains and spinal cords were examined for AR and Fos immunoreactivity (ir). PG21 anti-AR and anti-c-fos primary antibodies were visualized by fluorescence microscopy using cyanine-conjugated and fluorescein-conjugated secondary antibodies. In both brain and spinal cord, the number of Fos-ir neurons varied according to group: Mated males > Social Controls > Isolated males. Fos was highly localized in subsets of AR-ir neurons within the medial preoptic nucleus, bed nucleus of the stria terminalis, dorsomedial nucleus of the amygdala, and central tegmental field. Fos was also localized in subsets of AR-ir neurons within the L5, L6, and S1 segments of the spinal cord. Spinal cord concentrations of AR-ir and Fos-ir neurons were greatest in Lamina X, and the vast majority of Fos-ir neurons in the dorsal part of Lamina X were also AR-ir. Thus, in both brain and spinal cord, androgen-sensitive neurons are active during mating, and transmission of sexually relevant information from cord to brain is probably accomplished via hormone-sensitive spinal neurons.

The 5alpha-reductase in the central nervous system: expression and modes of control

The present paper will summarize two important aspects of the interactions between steroids and the brain, which have recently been studied in the authors' laboratory. In particular the paper will consider data on: (1) the significance of the two isoforms of the 5alpha-R during brain ontogenesis and development, and (2) the cross-talk between glial and neuronal elements, particularly in relation to the metabolism of sex hormones. (1) The data obtained have shown that the 5alpha-R type 1 enzyme is constitutively expressed in the rat CNS at all stages of brain development. Moreover, the expression of the 5alpha-R type 1 is similar in males and in females, and does not appear to be controlled by androgens. The gene expression of the 5alpha-R type 2 is totally different. This isoform appears to be expressed in the rat brain almost exclusively in the late fetal/early post-natal life and is controlled by testosterone. (2) The present data show that two cell lines derived respectively from a rat glioma (C6 cell line) and from a human astrocytoma (1321N1 cell line) are able to convert testosterone and progesterone into their corresponding 5alpha-reduced metabolites dihydrotestosterone and dihydroprogesterone. The possibility that secretory products of normal and tumoral brain cells might be able to influence steroid metabolism occurring in the two glial cell lines previously mentioned has been considered.

Steroid metabolism in the mammalian brain: 5alpha-reduction and aromatization

Several steroid molecules, including androgens, estrogens, progestagens, and corticostereroids, are able to modulate the brain development and functions. These compounds are not always active in their own natural molecular configuration but they often need to be transformed at the level of their target cells into 'active metabolites'. The two major metabolic pathways that transform steroids in the brain are: the 5alpha-reductase-3alpha-hydroxy-steroid dehydrogenase and the aromatase pathways. Both are present in the brain and probably exert specific roles in the mechanism of action of hormonal steroids. In this article we briefly review some important findings achieved in our own and in other laboratories concerning the cellular and subcellular brain distribution, development, regulation, cloning, and molecular characterization of the involved enzymes. In particular, the recent identification of two isoforms of the 5alpha-reductase, the type 1 and type 2, possessing different structural, biochemical, and distribution characteristics has attracted a considerable attention. The few data available on their brain distribution have been carefully considered. Finally, we have tried to focus on the role of the steroid metabolites in the brain, both when they interact with genomic and with membrane receptors. In particular, some unpublished observations on the effects of two 5alpha-reductase inhibitors on progesterone-induced anesthesia, a phenomenon mediated through the GABA(A) receptor, are presented.

Timing and duration of dihydrotestosterone treatment affect the development of motoneuron number and morphology in a sexually dimorphic rat spinal nucleus

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males, but reduced or absent in adult females. This dimorphism is due to the presence of androgens during development. Perinatal treatment of females with testosterone (T), or a combination of dihydrotestosterone (DHT) and estrogen (E+D females) from embryonic (E) day 16 through postnatal (P) day 5, results in a masculine number of SNB motoneurons and the retention of the target muscles. Perinatal treatment with estrogen alone does not masculinize the SNB; prenatal treatment with DHT alone from E17-E22 results in a feminine number of SNB motoneurons and a significantly altered motoneuron morphology and connectivity. To determine if masculinization of the SNB involves the interaction of estrogen and DHT or results from a longer exposure to DHT alone, the number, morphology, and connectivity of SNB motoneurons in females treated with DHT both pre- and post-natally (from E16-P5) were examined. At E22, DHTP (E16-P5) females have SNB motoneuron numbers identical to E+D and normal females, but far fewer than normal males, thus indicating that T is essential for prenatal masculinization. After E22, SNB motoneuron number declines precipitously in normal females but remains stable in DHTP (E16-P5) females and E+D females, which do not differ from normal males at P10. These results demonstrate that DHT can completely masculinize SNB motoneuron number without any synergistic actions with estrogen, and suggest that the development of SNB motoneuron number is strictly an androgen-mediated event. In adulthood, horseradish peroxidase histochemistry reveals that the connectivity, dendritic length, and soma size of SNB motoneurons in DHTP (E16-P5) females are identical to those of normal males but differ significantly from those of DHTP (E17-E22) females. These data suggest that the altered connectivity in DHTP (E17-E22) females is not simply a hormone-specific effect, but the result of a truncated hormone exposure. Thus, DHT can fully masculinize SNB morphology and connectivity if given during the appropriate period of development. It is suggested that while T may be required to masculinize the SNB prenatally, DHT may be involved in masculinizing postnatal aspects of SNB development.

Prenatal flutamide alters sexually dimorphic nuclei in the spinal cord of male rats

The effects of prenatal exposure to the antiandrogen flutamide on two sexually dimorphic nuclei of the lumbar spinal cord, the dorsolateral nucleus (DLN) and the spinal nucleus of the bulbocavernosus (SNB), were investigated. Rat dams were given daily injections of 5 mg flutamide or vehicle alone from day 11 through 21 of pregnancy. The spinal cords and perineal morphology of their male and female offspring were examined in adulthood. Flutamide reduced the number of SNB and DLN neurons, reduced the somal and nuclear area of SNB neurons, and reduced the weight of the perineal muscles in males. Flutamide produced no effect in females. No sexual dimorphism was found in the mean somal area of DLN neurons, but a sexual dimorphism was found in the distribution of somal areas in our samples; females had proportionately more large neurons than males. Flutamide-treated males also had proportionately more large neurons than control males but fewer than females. A sexual dimorphism was found in the nuclear areas of DLN neurons but flutamide did not influence this trait.

Androgen metabolism in the brain

The paper summarizes the most recent views on androgen metabolism in the brain. In particular it will be shown that: (1) the enzyme 5 alpha-reductase is particularly concentrated in the white matter; (2) 5 alpha-reductase is also present in the myelin; 5 alpha-reductase is present in higher concentrations in neurons (isolated or cultured) that in glial cells (astrocytes and oligodendrocytes); (4) only neurons possess the capability of aromatizing androgens to estrogens; and (5) a possible role of steroid metabolism in the control of the process of myelinogenesis is suggested.

Androgen binding in peripheral tissues of fetal rhesus macaques: effects of androgen metabolism in liver

In rhesus monkeys sexual differentiation of the brain and reproductive tract (RT) is androgen-dependent. Presumably these effects are mediated through the androgen receptor (AR). The AR has not been characterized in fetal tissues such as liver, kidney, heart, spinal cord and RT in this species. We characterized AR binding using [3H]R1881 as the ligand in cytosols from tissues obtained on days 100-138 of gestation. Scatchard analyses revealed a single, saturable, high affinity AR in liver, kidney, heart, spinal cord and RT. The apparent dissociation constant (Kd) ranged from 0.52 to 0.85 nM with no significant tissue differences. The number of AR (Bmax; fmol/mg protein) differed significantly (P less than 0.01) between tissues (liver greater than RT much greater than kidney greater than or equal to heart greater than or equal to spinal cord). Radioinert testosterone (T) and 5 alpha-dihydrotestosterone (DHT) but not androstenedione, progesterone, estradiol-17 beta, estrone or cortisol in a 50-fold molar excess inhibited [3H]R1881 binding to the AR in spinal cord, heart, kidney and RT. However, in liver only DHT competed significantly (P less than 0.01) for binding. This difference in binding of DHT vs T in the liver was further investigated by incubating liver and kidney cytosols with [3H]DHT and [3H]T at 4 degrees C. We identified the metabolic products by mobility on Sephadex LH-20 columns and reverse isotope dilution. Liver cytosols metabolized [3H]DHT to 5 alpha-androstane- 3 alpha,17 beta-diol (5 alpha-diol) and [3H]T to 5 beta-androstane-3 alpha, 17 beta-diol (5 beta-diol) at 4 degrees C. In contrast, kidney cytosols metabolized [3H]DHT while [3H]T remained unchanged. Further studies indicated that a 50-fold molar excess of 5 alpha-diol inhibited the binding of [3H]R1881 in liver cytosols by about 50% whereas the same molar concentration of 5 beta-diol had no effect. These data demonstrate the presence of AR in peripheral tissues of fetal rhesus monkeys and suggest that androgens through their receptors may affect development of these tissues. Liver cytosols are capable of metabolizing T and DHT at 4 degrees C at conditions similar to those used for measuring cytosolic AR. However, T and DHT are metabolized differently, generating different isomers which have different affinities for hepatic AR.

Evidence for androgen receptors in sexually dimorphic perineal muscles of neonatal male rats. Absence of androgen accumulation by the perineal motoneurons

During development, survival of the sexually dimorphic spinal nucleus of the bulbocavernosus (SNB) and its target perineal muscles, the bulbocavernosus (BC) and the levator ani (LA) is androgen-dependent. To define androgen's site of action in masculinizing SNB system structures, we examined whether or not androgen receptors are present in SNB motoneurons and/or BC/LA muscles of neonatal male rats. Using a receptor binding assay, we have identified androgen-binding factors in the neonatal BC/LA (Bmax = 13.5 fmol/mg protein; Kd = 4.69 nM) for the first time. In contrast, androgen autoradiography provided no evidence that neonatal spinal motoneurons accumulate androgens. These results support the hypothesis that BC/LA muscles are a primary site of androgen action for masculinizing SNB system structures, and that androgen need not interact with SNB motoneurons directly to sexually differentiate them.

Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: IV. Masculinization of the spinal nucleus of the bulbocavernosus with testosterone metabolites

The spinal nucleus of the bulbocavernosus (SNB) is a sexually dimorphic motor nucleus in the rat lumbar spinal cord. SNB motoneurons and their perineal target muscles are present in adult males but reduced or absent in females. This sexual dimorphism is due to the presence of androgen during development; females treated with testosterone (T) perinatally have a masculine SNB system. To assess whether masculinization of the SNB could involve the conversion of testosterone into its active metabolites, dihydrotestosterone (DHT) and estrogen, we examined the development of the SNB in females treated perinatally with estrogen alone or in combination with dihydrotestosterone. Counts of motoneurons in the developing SNB in all groups showed the typical prenatal increase followed by a differential postnatal decline; the incidence of degenerating cells reflected this decline. Motoneuron numbers and the frequency of degenerating cells in females treated with estrogen (E) alone did not differ from those of normal females, with both groups losing large numbers of motoneurons and having a high incidence of degenerating cells. In contrast, females treated with both estrogen and dihydrotestosterone did not show the female-typical decline in motoneuron number and had a low, masculine incidence of degenerating cells. By postnatal day 10, females treated with estrogen and dihydrotestosterone had a fully masculine SNB motoneuron number, suggesting that dihydrotestosterone alone or in conjunction with estrogen may be involved in the development of the sexually dimorphic SNB system.

Adrenocorticoid action in the spinal cord: some unique molecular properties of glucocorticoid receptors

1. Glucocorticoid hormones affect several functions of the spinal cord, such as synaptic transmission, biogenic amine content, lipid metabolism, and the activity of some enzymes (ornithine decarboxylase, glycerolphosphate dehydrogenase), indicating that this tissue is a target of adrenal hormones. 2. Corticosterone, the main glucocorticoid of the rat, is detected at all regional levels of the spinal cord, and cold stress increases this steroid, predominantly in the cervical regions. 3. Intracellular glucocorticoid receptors have been found in the spinal cord, with higher concentrations in the cervical and lumbar enlargements. Prima facie, these receptors presented biochemical, stereospecifical, and physicochemical properties similar to those of receptors found in other regions of the nervous system. The prevalent form in the spinal cord is the type II receptor, although type I is also present in small amounts. 4. The type II glucocorticoid receptor of the spinal cord shows an affinity lower (Kd 3.5 nM) than that of the hippocampal type II site (Kd 0.7 nM) when incubated with [3H]dexamethasone. This condition may impair the nuclear translocation of the spinal cord receptor. 5. Another peculiar property of spinal cord type II site is a greater affinity for DNA-cellulose binding than the hippocampal receptor during heat-induced transformation. Also, the spinal cord receptor shows resistance to the action of RNAse A, an enzyme which increases DNA-cellulose binding of the hippocampal receptor, indicating that both receptors may be structurally different. 6. Therefore, it is possible that a different subclass of type II, or "classical glucocorticoid receptor," is present in the spinal cord. This possibility makes the cord a useful system for studying diversity of glucocorticoid receptors of the nervous system, especially the relationship between receptor structure and function.

Androgen increases the number of cells in fetal mouse spinal cord cultures: implications for motoneuron survival

Androgen effects were studied in organotypic cultures of the E12 fetal mouse lumbosacral spinal cord labeled in utero with [3H]thymidine on E10. Following continuous exposure to androgens for one month in vitro, the number of labeled cells was significantly increased in whole explants, and in hemisected segments in the presence or absence of co-cultured fetal thigh muscle. Because lumbosacral motoneurons undergo their final mitosis predominantly on E10 and thus remain permanently labeled, the results suggest that androgens increase neuronal numbers by directly modulating motoneuron survival rather than stimulating mitosis. These findings demonstrate for the first time that in addition to the well documented role of the muscle target in motoneuron survival, the direct neuronotrophic effects of androgen at the level of the spinal cord must also be considered.

In vitro steroid metabolism by rat retina

We have previously detected progesterone, dehydroepiandrosterone, androstenedione, testosterone and estrone in rat retina. The present experiments show that the presence of these steroids in the retina may not be due to local biosynthesis. On the other hand, they demonstrate considerable 5 alpha-reductase and 3 beta-hydroxysteroid dehydrogenase activities in the rat retina. The significance of these activities in the retina is discussed.