The expression of GABA(A) receptor alpha2 subunit is upregulated by testosterone in rat cerebral cortex

Fibromyalgia pathogenesis explained by a neuroendocrine multistable model

Fibromyalgia (FM) is a central disorder characterized by chronic pain, fatigue, insomnia, depression, and other minor symptoms. Knowledge about pathogenesis is lacking, diagnosis difficult, clinical approach puzzling, and patient management disappointing. We conducted a theoretical study based on literature data and computational analysis, aimed at developing a comprehensive model of FM pathogenesis and addressing suitable therapeutic targets. We started from the evidence that FM must involve a dysregulation of central pain processing, is female prevalent, suggesting a role for the hypothalamus-pituitary-gonadal (HPG) axis, and is stress-related, suggesting a role for the HP-adrenocortical (HPA) axis. Central pathogenesis was supposed to involve a pain processing loop system including the thalamic ventroposterolateral nucleus (VPL), the primary somatosensory cortex (SSC), and the thalamic reticular nucleus (TRN). For decreasing GABAergic and/or increasing glutamatergic transmission, the loop system crosses a bifurcation point, switching from monostable to bistable, and converging on a high-firing-rate steady state supposed to be the pathogenic condition. Thereafter, we showed that GABAergic transmission is positively correlated with gonadal-hormone-derived neurosteroids, notably allopregnanolone, whereas glutamatergic transmission is positively correlated with stress-induced glucocorticoids, notably cortisol. Finally, we built a dynamic model describing a multistable, double-inhibitory loop between HPG and HPA axes. This system has a high-HPA/low-HPG steady state, allegedly reached in females under combined premenstrual/postpartum brain allopregnanolone withdrawal and stress condition, driving the thalamocortical loop to the high-firing-rate steady state, and explaining the connection between endocrine and neural mechanisms in FM pathogenesis. Our model accounts for FM female prevalence and stress correlation, suggesting the use of neurosteroid drugs as a possible solution to currently unsolved problems in the clinical treatment of the disease.

Hormonal coordination of motor output and internal prediction of sensory consequences in an electric fish

Steroid hormones remodel neural networks to induce seasonal or developmental changes in behavior. Hormonal changes in behavior likely require coordinated changes in sensorimotor integration. Here, we investigate hormonal effects on a predictive motor signal, termed corollary discharge, that modulates sensory processing in weakly electric mormyrid fish. In the electrosensory pathway mediating communication behavior, inhibition activated by a corollary discharge blocks sensory responses to self-generated electric pulses, allowing the downstream circuit to selectively analyze communication signals from nearby fish. These pulses are elongated by increasing testosterone levels in males during the breeding season. We induced electric-pulse elongation using testosterone treatment and found that the timing of electroreceptor responses to self-generated pulses was delayed as electric-pulse duration increased. Simultaneous recordings from an electrosensory nucleus and electromotor neurons revealed that the timing of corollary discharge inhibition was delayed and elongated by testosterone. Furthermore, this shift in the timing of corollary discharge inhibition was precisely matched to the shift in timing of receptor responses to self-generated pulses. We then asked whether the shift in inhibition timing was caused by direct action of testosterone on the corollary discharge circuit or by plasticity acting on the circuit in response to altered sensory feedback. We surgically silenced the electric organ of fish and found similar hormonal modulation of corollary discharge timing between intact and silent fish, suggesting that sensory feedback was not required for this shift. Our findings demonstrate that testosterone directly regulates motor output and internal prediction of the resulting sensory consequences in a coordinated manner.

The development of sensorimotor cortical oscillations is mediated by pubertal testosterone

Puberty is a period of substantial hormonal fluctuations, and pubertal hormones can modulate structural and functional changes in the developing brain. Many previous studies have characterized the neural oscillatory responses serving movement, which include a beta event-related desynchronization (ERD) preceding movement onset, gamma and theta responses coinciding with movement execution, and a post-movement beta-rebound (PMBR) response following movement offset. While a few studies have investigated the developmental trajectories of these neural oscillations serving motor control, the impact of pubertal hormone levels on the maturation of these dynamics has not yet been examined. Since the timing and tempo of puberty varies greatly between individuals, pubertal hormones may uniquely impact the maturation of motor cortical oscillations distinct from other developmental metrics, such as age. In the current study we quantified these oscillations using magnetoencephalography (MEG) and utilized chronological age and measures of endogenous testosterone as indices of development during the transition from childhood to adolescence in 69 youths. Mediation analyses revealed complex maturation patterns for the beta ERD, in which testosterone predicted both spontaneous baseline and ERD power through direct and indirect effects. Age, but not pubertal hormones, predicted motor-related theta, and no relationships between oscillatory responses and developmental metrics were found for gamma or PMBR responses. These findings provide novel insight into how pubertal hormones affect motor-related oscillations, and highlight the continued development of motor cortical dynamics throughout the pubertal period.

Towards screening the neurotoxicity of chemicals through feces after exposure to methylmercury or inorganic mercury in rats: A combined study using gut microbiome, metabolomics and metallomics

Mercury (Hg) is one of the chemicals that bring serious adverse effects to the environment and human beings. Methylmercury (MeHg) is a neurotoxin while inorganic Hg (IHg) is not. Early screening of the neurotoxicity of chemicals may help reduce the occurrence of neurological disorders by minimizing chemical exposure. This work proposed the combined application of gut microbiome, metabolomics and metallomics to differentiate the neurotoxicity between MeHg and IHg in rats. It was found that MeHg caused down-regulated Bacteroides, Firmicutes and Proteobacteria, and up-regulated Actinobacteria and Verrucomicrobia at phylum level, while MeHg caused up-regulated Verrucomicrobiaceae, Desulfovibrionaceae, Helicobacteraceae, Lachnospiraceae and down-regulated Rikenellaceae, Erysipelotrichaceae, Sutterellaceae, Anaeroplasmataceae and Coriobacteriaceae in feces than IHg did at family level; Besides, MeHg brought metabolites change in activation of gut-brain axis pathway than IHg did, such as Glutamate, γ-aminobutyric acid (GABA), Dopamine (DA) and Tryptophan. These differences between MeHg and IHg were further confirmed by the distribution of Hg in the intestine, as well as the level of brain-derived neurotrophic factor (BDNF) in the intestine, brain and serum. Therefore, the difference of toxicity between MeHg and IHg can be well distinguished through feces after exposure for only 24 h, which may be used for the screening of neurotoxicity of other chemicals.

Pubertal Testosterone Tracks the Developmental Trajectory of Neural Oscillatory Activity Serving Visuospatial Processing

Puberty is a period of substantial hormonal fluctuations that induce dramatic physical, neurological, and behavioral changes. Previous research has demonstrated that pubertal hormones modulate cortical development, as well as sex- and age-specific patterns of cognitive development during childhood and adolescence. However, the influence of pubertal hormones on the brain's functional development, specifically neural oscillatory dynamics, has yet to be fully examined. Thus, in the current study, we used magnetoencephalography to investigate the oscillatory dynamics serving visuospatial perception and attention, and testosterone levels and chronological age as measures of development. Within a sample of typically developing youth, age was associated with changes in alpha, theta, and gamma oscillatory activity. Novel testosterone-by-sex interactions in the gamma range were identified in critical areas of the visual and attention networks. Females had increased gamma activity with increasing testosterone in the right temporal-parietal junction and occipital cortices, while males showed increased gamma activity in the right insula with increasing testosterone. These findings reveal robust developmental alterations in the oscillatory dynamics serving visuospatial processing during childhood and adolescence and provide novel insight into the hormonal basis of sexually dimorphic patterns of functional brain development during the pubertal transition that is at least partially mediated by endogenous testosterone.

Sensory perception in autism

Autism is a complex neurodevelopmental condition, and little is known about its neurobiology. Much of autism research has focused on the social, communication and cognitive difficulties associated with the condition. However, the recent revision of the diagnostic criteria for autism has brought another key domain of autistic experience into focus: sensory processing. Here, we review the properties of sensory processing in autism and discuss recent computational and neurobiological insights arising from attention to these behaviours. We argue that sensory traits have important implications for the development of animal and computational models of the condition. Finally, we consider how difficulties in sensory processing may relate to the other domains of behaviour that characterize autism.

Exogenous Testosterone, Aging, and Changes in Behavioral Response of Gonadally Intact Male Mice

This study tested the hypothesis that aging significantly affects the influence of exogenous testosterone on neurobehavior in gonadally intact male mice. Groups of prepubertal and aged male mice received daily vehicle or testosterone propionate (TP; 2.5 or 5.0 mg/kg intraperitoneal [i.p.]) for 21 days. Behaviors were assessed on days 1 and 21. Weight gain was significant in prepubertal mice. Locomotion and rearing increased in prepubertal mice after first dose and decreased after last dose of TP. Rearing was suppressed in aged mice throughout. Suppression of grooming occurred in both age groups at day 21. Significant increase in working memory in both age groups was seen in the radial-arm maze (at specific doses) and in prepubertal mice in the Y-maze. Elevated plus maze test showed mixed anxiolytic/anxiogenic effects. Aged mice had higher serum testosterone. In conclusion, age is an important determinant for the influence of exogenous testosterone on behavior in gonadally intact male mice.

The impact of nandrolone decanoate on the central nervous system

Nandrolone is included in the class II of anabolic androgenic steroids (AAS) which is composed of 19-nor-testosterone-derivates. In general, AAS is a broad and rapidly increasing group of synthetic androgens used both clinically and illicitly. AAS in general and nandrolone decanoate (ND) in particular have been associated with several behavioral disorders. The purpose of this review is to summarize the literature concerning studies dealing with ND exposure on animal models, mostly rats that mimic human abuse systems (i.e. supraphysiological doses). We have focused in particular on researches that have investigated how ND alters the function and expression of neuronal signaling molecules that underlie behavior, anxiety, aggression, learning and memory, reproductive behaviors, locomotion and reward.

Development of the GABAergic system from birth to adolescence

The neurotransmitter GABA (γ-aminobutyric acid), acting via inotropic GABA(A) and metabotropic GABA(B) receptors, plays an essential role in a variety of distinct neuronal processes, including regulation of neuronal excitability, determination of temporal aspects of spike trains, control of the size and propagation of neuronal assemblies, generation of oscillatory activity, and neuronal plasticity. Although the developmental switch between excitatory and inhibitory GABA(A) receptor-mediated responses is widely appreciated, the fact that the postnatal maturation of the GABAergic system lasts until late adolescence is not so persuasively promoted. This review summarizes recent knowledge of the maturation of various aspects of the GABAergic systems, like functional expression of GABA synthesizing/degrading enzymes and transporters, density of GABAergic synapses, GABAergic projection patterns, GABA receptor subunit composition, and properties of GABAergic interneurons, with an emphasis on the late developmental alterations. In addition, some aspects of the development of mental capabilities during adolescence and their relation the delayed maturation of the GABAergic system are presented.

Testosterone reduces cumulative burying in female Wistar rats with minimal participation of estradiol

Testosterone exerts anxiolytic effects, but the participation of its aromatase metabolic product estradiol is controversial. Therefore, we used the defensive burying paradigm in female Wistar rats to explore testosterone's (1.0 mg/rat, s.c.) interactions with picrotoxin (a noncompetitive gamma-aminobutyric acid-A receptor [GABA(A)] antagonist; 1.0 mg/kg, i.p.), formestane (an aromatase inhibitor; 3.0 mg/rat, s.c.), and tamoxifen (an estrogen receptor-beta antagonist; 1.0 mg/kg, s.c.). Serum levels of testosterone, estradiol, and progesterone were determined in the same rats. Burying latency and locomotion did not significantly change. Systemic testosterone administration enhanced serum testosterone and estradiol levels and reduced defensive burying. This reduction in total burying was blocked by pretreatment with picrotoxin and tamoxifen, but not formestane. We conclude that testosterone produced anxiolytic-like effects in female rats that were mediated by actions at the GABA(A) receptor, with participation of the estradiol receptor-beta, rather than estradiol aromatization.

Progestin receptor is transiently expressed perinatally in neurons of the rat isocortex

Steroid hormones influence the development of numerous brain regions, including some that are not classically considered steroid-sensitive. For example, nuclear receptors for both androgen and estrogen have been detected in neonatal cortical cells. High levels of progestin binding and progestin receptor (PR) mRNA have also been reported in early perinatal isocortex. PR expression coincides with high levels of de novo progesterone produced within the cortex, suggesting that PR and its ligand influence the important developmental cortical processes occurring shortly after birth. In order to better understand the role PR plays in cortical development, we used the cellular-level resolution of immunohistochemistry and in situ hybridization (ISH) to characterize changes in perinatal PR expression within specific cortical lamina. PR immunoreactivity (PR-ir) was examined at embryonic days (E) 18, 20, 21, 22, and postnatal days (P) 1, 3, 6, 9, 13, and 27. We find that PR-ir is transiently expressed in specific lamina of frontal, parietal, temporal, and occipital cortex. PR-ir was observed in subplate cells on E18, in increasingly superficial lamina (primarily lamina V, then II/III) during early postnatal development, and was absent by P27. Double-labeling immunohistochemistry indicated that PR-ir colocalizes with the neuronal marker, microtubule associated protein-2, but not with the glial marker, nestin, nor with gamma-aminobutyric acid. These results suggest that specific subpopulations of cortical neurons may be transiently sensitive to progesterone, and that progesterone and its receptor may play a critical role in the fundamental mechanisms underlying normal cortical development.

Maternal effects and the evolution of brain size in birds: overlooked developmental constraints

A central dogma for the evolution of brain size posits that the maintenance of large brains incurs developmental costs, because they need prolonged periods to grow during the early ontogeny. Such constraints are supported by the interspecific relationship between ontological differences and relative brain size in birds and mammals. Given that mothers can strongly influence the development of the offspring via maternal effects that potentially involve substances essential for growing brains, we argue that such effects may represent an important but overlooked component of developmental constraints on brain size. To demonstrate the importance of maternal effect on the evolution of brains, we investigated the interspecific relationship between relative brain size and maternal effects, as reflected by yolk testosterone, carotenoids, and vitamins A and E in a phylogenetic study of birds. Females of species with relatively large brains invested more in eggs in terms of testosterone and vitamin E than females of species with small brains. The effects of carotenoid and vitamin A levels on the evolution of relative brain size were weaker and non-significant. The association between relative brain size and yolk testosterone was curvilinear, suggesting that very high testosterone levels can be suppressive. However, at least in moderate physiological ranges, the positive relationship between components of maternal effects and relative brain size may imply one aspect of developmental costs of large brains. The relationship between vitamin E and relative brain size was weakened when we controlled for developmental mode, and thus the effect of this antioxidant may be indirect. Testosterone-enhanced neurogenesis and vitamin E-mediated defence against oxidative stress may have key functions when the brain of the embryo develops, with evolutionary consequences for relative brain size.

Behavioral and physiological responses to anabolic-androgenic steroids

Anabolic-androgenic steroids (AAS) are synthetic derivatives of testosterone originally designed for therapeutic uses to provide enhanced anabolic potency with negligible androgenic effects. Although AAS continue to be used clinically today, the medical benefits of low therapeutic doses of AAS stand in sharp contrast to the potential health risks associated with the excessive doses self-administered not only by elite athletes and body builders, but by a growing number of recreational users, including adolescent boys and girls. The deleterious effects of AAS on peripheral organs and the incidence of altered behaviors in AAS abusers have been well documented in a number of excellent current reviews for clinical populations. However, a comparable synthesis of nonclinical studies has not been made. Our purpose in this review is to summarize the literature for animal models of the effects of supraphysiological doses of AAS (e.g. those that mimic human abuse regimes) on behaviors and on the neural circuitry for these behaviors. In particular, we have focused on studies in rodents that have examined how AAS alter aggression, sexual behaviors, anxiety, reward, learning, and locomotion and how AAS alter the expression and function of neurotransmitter systems and other signaling molecules that underlie these behaviors.

The effects of sex steroids on the formation of gap junctions between folliculo-stellate cells; a study in castrated male rats and ovariectomized female rats

We investigated the relationship between gap junction formation and the sex steroids testosterone, progesterone and 17beta-estradiol in the anterior pituitary glands of castrated male rats and ovariectomized female rats. Male and female 30-day-old Wistar-Imamichi strain rats were castrated or ovariectomized, and 30 days later they were subcutaneously injected with the above sex steroids. They were divided into six groups according to the injected materials: sesame oil (control), testosterone, progesterone, 17beta-estradiol, testosterone with 17beta-estradiol, and progesterone with 17beta-estradiol. Five rats from each group were sacrificed 1, 2, 3, 4 and 5 days after the injections, and the anterior pituitary glands were prepared for observation by transmission electron microscopy. We quantified the number of follicles and gap junctions and calculated the rate of occurrence of gap junctions as the ratio of the number of gap junctions existing between folliculo-stellate cells per intersected follicle profile in electron photomicrographs. The administration of testosterone to castrated male rats increased the rate of gap junctions between folliculo-stellate cells; however, progesterone and 17beta-estradiol did not affect the formation of gap junctions. The administration of progesterone to ovariectomized female rats increased the rate of gap junctions between folliculo-stellate cells; this progesterone effect was prevented by the simultaneous administration of 17beta-estradiol, which by itself did not affect the rate of gap junctions between folliculo-stellate cells. These observations indicate that the formation of gap junctions within the anterior pituitary gland is regulated differently by sex steroids in castrated male and ovariectomized female rats.

Anabolic androgenic steroids induce age-, sex-, and dose-dependent changes in GABA(A) receptor subunit mRNAs in the mouse forebrain

Chronic exposure to anabolic androgenic steroids (AAS) has deleterious effects on reproductive health in both human and animal subjects. Neurotransmission mediated by the gamma-aminobutyric acid type A (GABA(A)) receptor in the medial amygdala (MeA), the medial preoptic area (mPOA), and the ventromedial nucleus (VMN) of the hypothalamus plays a critical role in mediating sexual behaviors. Here we used semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) to examine levels of alpha(1), alpha(2), alpha(5), gamma(1), gamma(2), and epsilon subunit mRNAs in these three regions of the brain. Our results demonstrate that chronic exposure to either a high or a moderate dose of the AAS, 17alpha-methyltestosterone (17alpha-MeT), significantly decreased the levels of specific alpha and gamma subunit mRNAs in a manner that depended on the dose of AAS and age and sex of the animals. Specifically, the moderate dose of AAS elicited significant changes only in pubertal females and the majority of changes observed in pubertal animals with the high dose also occurred in females. In contrast, the moderate dose of AAS induced no significant changes in adult mice of either sex, while the high dose had effects in both males and females. In addition to determining the effects of chronic AAS treatment, a developmental analysis of drug-naïve animals demonstrated that GABA(A) receptor subunit mRNA levels in these regions of the forebrain undergo significant changes as animals proceed through puberty. These data demonstrate that the effects of AAS exposure on GABA(A) receptor expression are superimposed upon dynamic developmental changes that accompany the transition from puberty to adulthood.

GABA(A)-receptor expression in glioma cells is triggered by contact with neuronal cells

The expression of functional GABA(A)-receptors in glioma cells correlates with low malignancy of tumours and cell lines from glioma lack these receptors. Here we show that contact with neurons induces the expression of functional GABA(A)-receptors. C6 and F98 glioma cell lines were labelled by recombinant expression of enhanced green fluorescent protein injected into rat brain and studied in acute slices after two to three weeks of tumour growth. The cells responded to GABA or the specific agonist, muscimol with a current typical for GABA(A)-receptors, as studied with the patch-clamp technique. To get insight into the mechanism of GABA(A) receptor induction, the C6 or F98 cells were co-cultured with neurons, astrocytes, oligodendrocytes and microglia. Glioma cells expressed functional GABA(A) receptors within 24 h only in cultures where physical contact to neurons occurred. Activation of GABA(A)-receptors in the co-cultures attenuated glioma cell metabolism while blockade of the receptors increased metabolism. We conclude that with this form of interaction, neurons can influence tumour behaviour in the brain.

Transplanted neuroblasts differentiate appropriately into projection neurons with correct neurotransmitter and receptor phenotype in neocortex undergoing targeted projection neuron degeneration

Reconstruction of complex neocortical and other CNS circuitry may be possible via transplantation of appropriate neural precursors, guided by cellular and molecular controls. Although cellular repopulation and complex circuitry repair may make possible new avenues of treatment for degenerative, developmental, or acquired CNS diseases, functional integration may depend critically on specificity of neuronal synaptic integration and appropriate neurotransmitter/receptor phenotype. The current study investigated neurotransmitter and receptor phenotypes of newly incorporated neurons after transplantation in regions of targeted neuronal degeneration of cortical callosal projection neurons (CPNs). Donor neuroblasts were compared to the population of normal endogenous CPNs in their expression of appropriate neurotransmitters (glutamate, aspartate, and GABA) and receptors (kainate-R, AMPA-R, NMDA-R. and GABA-R), and the time course over which this phenotype developed after transplantation. Transplanted immature neuroblasts from embryonic day 17 (E17) primary somatosensory (S1) cortex migrated to cortical layers undergoing degeneration, differentiated to a mature CPN phenotype, and received synaptic input from other neurons. In addition, 23.1 +/- 13.6% of the donor-derived neurons extended appropriate long-distance callosal projections to the contralateral S1 cortex. The percentage of donor-derived neurons expressing appropriate neurotransmitters and receptors showed a steady increase with time, reaching numbers equivalent to adult endogenous CPNs by 4-16 weeks after transplantation. These results suggest that previously demonstrated changes in gene expression induced by synchronous apoptotic degeneration of adult CPNs create a cellular and molecular environment that is both permissive and instructive for the specific and appropriate maturation of transplanted neuroblasts. These experiments demonstrate, for the first time, that newly repopulating neurons can undergo directed differentiation with high fidelity of their neurotransmitter and receptor phenotype, toward reconstruction of complex CNS circuitry.