Androgen receptors in Purkinje neurons are modulated by systemic testosterone and sexual training in a region-specific manner in the male rat

Androgen receptors and sociosexual behaviors in mammals: The limits of generalization

Circulating testosterone is easily aromatized to estradiol and reduced to dihydrotestosterone in target tissues and elsewhere in the body. Thus, the actions of testosterone can be mediated either by the estrogen receptors, the androgen receptor or by simultaneous action at both receptors. To determine the role of androgens acting at the androgen receptor, we need to eliminate actions at the estrogen receptors. Alternatively, actions at the androgen receptor itself can be eliminated. In the present review, I will analyze the specific role of androgen receptors in male and female sexual behavior as well as in aggression. Some comments about androgen receptors and social recognition are also made. It will be shown that there are important differences between species, even between strains within a species, concerning the actions of the androgen receptor on the behaviors mentioned. This fact makes generalizations from one species to another or from one strain to another very risky. The existence of important species differences is often ignored, leading to many misunderstandings and much confusion.

The integrated brain network that controls respiration

Respiration is a brain function on which our lives essentially depend. Control of respiration ensures that the frequency and depth of breathing adapt continuously to metabolic needs. In addition, the respiratory control network of the brain has to organize muscular synergies that integrate ventilation with posture and body movement. Finally, respiration is coupled to cardiovascular function and emotion. Here, we argue that the brain can handle this all by integrating a brainstem central pattern generator circuit in a larger network that also comprises the cerebellum. Although currently not generally recognized as a respiratory control center, the cerebellum is well known for its coordinating and modulating role in motor behavior, as well as for its role in the autonomic nervous system. In this review, we discuss the role of brain regions involved in the control of respiration, and their anatomical and functional interactions. We discuss how sensory feedback can result in adaptation of respiration, and how these mechanisms can be compromised by various neurological and psychological disorders. Finally, we demonstrate how the respiratory pattern generators are part of a larger and integrated network of respiratory brain regions.

On the role of sex steroids in biological functions by classical and non-classical pathways. An update

The sex steroid hormones (SSHs) play several roles in regulation of various processes in the cardiovascular, immune, muscular and neural systems. SSHs affect prenatal and postnatal development of various brain structures, including regions associated with important physiological, behavioral, cognitive, and emotional functions. This action can be mediated by either intracellular or transmembrane receptors. While the classical mechanisms of SSHs action are relatively well examined, the physiological importance of non-classical mechanism of SSHs action through membrane-associated and transmembrane receptors in the brain remains unclear. The most recent summary describing the role of SSHs in different body systems is lacking. Therefore, the aim of this review is to discuss classical and non-classical signaling pathways of testosterone and estradiol action via their receptors at functional, cellular, tissue level and to describe the effects on various body systems and behavior. Particular emphasis will be on brain regions including the hippocampus, hypothalamus, frontal cortex and cerebellum.

Changes in Hippocampal Androgen Receptor Density and Behavior in Sprague-Dawley Male Rats Exposed to a Low-Pressure Blast Wave

Objective

The purpose of this study was to examine the effect of exposure of a low-intensity blast wave on androgen receptor (AR) density in the hippocampus and the potential influence on behavioral and cognitive responses.

Methods

Sprague-Dawley rats were randomly assigned to either a blast exposed group (n = 27) or an unexposed (control) group (n = 10). Animals were treated identically, except that rats within the control group were not exposed to any of the characteristics of the blast wave. Behavior measures were conducted on day seven post-exposure. The rats were initially assessed in the elevated plus maze followed by the acoustic startle response paradigm. Spatial memory performance using the Morris water-maze test was assessed at 8-days post-exposure, for seven consecutive days. Following all behavioral tests AR immunofluorescence staining was performed in different hippocampal subregions.

Results

A significant elevation in anxiety index (p < 0.001) and impaired learning (p < 0.015) and spatial memory (p < 0.0015) were noted in exposed rats. In addition, a significant attenuation of the AR was noted in the CA1 (p = 0.006) and dentate gyrus (p = 0.031) subregions of the hippocampus in blast exposed animals. Correlational analyses revealed significant associations between AR and both anxiety index (r = -.36, p = 0.031) and memory (r = -0.38, p = 0.019).

Conclusions

The results of this study demonstrate that exposure to a low-pressure blast wave resulted in a decrease in AR density, which was associated with significant behavioral and cognitive changes.

Deciphering the Biological Mechanisms Underlying the Genome-Wide Associations between Computerized Device Use and Psychiatric Disorders

Computerized device use (CDU) is societally ubiquitous but its effects on mental health are unknown. We performed genetic correlation, Mendelian randomization, and latent causal variable analyses to identify shared genetic mechanisms between psychiatric disorders (Psychiatric Genomics Consortium; 14,477 < N < 150,064) and CDU (UK Biobank; N = 361,194 individuals). Using linkage disequilibrium score regression, we detected strong genetic correlations between "weekly usage of mobile phone in last 3 months" (PhoneUse) vs. attention deficit hyperactivity disorder (ADHD; rg = 0.425, p = 4.59 × 10-29) and "plays computer games" (CompGaming) vs. schizophrenia (SCZ; rg = -0.271, p = 7.16 × 10-26). Focusing on these correlations, we used two sample MRs to detect the causal relationships between trait pairs by treating single nucleotide polymorphisms as non-modifiable risk factors underlying both phenotypes. Significant bidirectional associations were detected (PhoneUse→ADHD β = 0.132, p = 1.89 × 10-4 and ADHD→PhoneUse β = 0.084, p = 2.86 × 10-10; CompGaming→SCZ β = -0.02, p = 6.46 × 10-25 and CompGaming→SCZ β = -0.194, p = 0.005) and the latent causal variable analyses did not support a causal relationship independent of the genetic correlations between these traits. This suggests that molecular pathways contribute to the genetic overlap between these traits. Dopamine transport enrichment (Gene Ontology:0015872, pSCZvsCompGaming = 2.74 × 10-10) and DRD2 association (pSCZ = 7.94 × 10-8; pCompGaming = 3.98 × 10-25) were detected in SCZ and CompGaming and support their negative correlative relationship. FOXP2 was significantly associated with ADHD (p = 9.32 × 10-7) and PhoneUse (p = 9.00 × 10-11) with effect directions concordant with their positive genetic correlation. Our study demonstrates that epidemiological associations between psychiatric disorders and CDUs are due, in part, to the molecular mechanisms shared between them rather than a causal relationship. Our findings imply that biological mechanisms underlying CDU contribute to the psychiatric phenotype manifestation.

Sexual Behavior and Synaptic Plasticity

Although sex drive is present in many animal species, sexual behavior is not static and, like many other behaviors, can be modified by experience. This modification relies on synaptic plasticity, a sophisticated mechanism through which neurons change how they process a given stimulus, and the neurophysiological basis of learning. This review addresses the main plastic effects of steroid sex hormones in the central nervous system (CNS) and the effects of sexual experience on the CNS, including effects on neurogenesis, intracellular signaling, gene expression, and changes in dendritic spines, as well as behavioral changes.

Changes in multiunit activity pattern in cerebellar cortex associated to olfactory cues during sexual learning in male rats

The cerebellum is a structure of the central nervous system which has been previously studied with different techniques and animal models and even humans, so it is associated with multiple functions such as cognition, memory, emotional processing, balance, control of movement, among others. Its relationship with sensory systems has already been explored, however, the role it plays in olfactory processing in the cerebellum is unclear. Several hypotheses have been proposed from work done in humans and animal models with neuroimaging and immunohistochemical techniques. Everything seems to indicate that the cerebellar function is of vital importance for the olfactory perception, being able to be controlling not only the olfactory aspect, but also the olfactory processing. In this study we analyzed the multiunit activity in the granular layer of the cerebellar vermis during olfactory stimulation: a session being sexually naive and during four sessions of sexual behavior learning. The amplitude was compared between male naive and sexual experts, as well as between olfactory stimuli. The amplitude of the sexually experienced rats showed the highest values compared to naive ones. Odor of receptive female causes the greatest amplitudes, however, in the control group the amplitude increased when they were sexually experts. The motor, sensory and associative learning generated by the acquisition of sexual experience modifies the activation pattern in the cerebellum by presenting neutral odors or associated with a reward.

Prenatal Exposure to DEHP Induces Neuronal Degeneration and Neurobehavioral Abnormalities in Adult Male Mice

Phthalates are a family of synthetic chemicals that are used in producing a variety of consumer products. Di-(2-ethylhexyl) phthalate (DEHP) is an widely used phthalate and poses a public health concern. Prenatal exposure to DEHP has been shown to induce premature reproductive senescence in animal studies. In this study, we tested the hypothesis that prenatal exposure to DEHP impairs neurobehavior and recognition memory in her male offspring and we investigated one possible mechanism-oxidative damage in the hippocampus. Pregnant CD-1 female mice were orally administered 200 μg, 500 mg, or 750 mg/kg/day DEHP or vehicle from gestational day 11 until birth. The neurobehavioral impact of the prenatal DEHP exposure was assessed at the ages of 16-22 months. Elevated plus maze and open field tests were used to measure anxiety levels. Y-maze and novel object recognition tests were employed to measure memory function. The oxidative damage in the hippocampus was measured by the levels of oxidative DNA damage and by Spatial light interference microscopic counting of hippocampal neurons. Adult male mice that were prenatally exposed to DEHP exhibited anxious behaviors and impaired spatial and short-term recognition memory. The number of hippocampal pyramidal neurons was significantly decreased in the DEHP mice. Furthermore, DEHP mice expressed remarkably high levels of cyclooxygenase-2, 8-hydroxyguanine, and thymidine glycol in their hippocampal neurons. DEHP mice also had lower circulating testosterone concentrations and displayed a weaker immunoreactivity than the control mice to androgen receptor expression in the brain. This study found that prenatal exposure to DEHP caused elevated anxiety behavior and impaired recognition memory. These behavioral changes may originate from neurodegeneration caused by oxidative damage and inflammation in the hippocampus. Decreased circulating testosterone concentrations and decreased expression of androgen receptor in the brain also may be factors contributing to the impaired neurobehavior in the DEHP mice.

Unraveling age, puberty and testosterone effects on subcortical brain development across adolescence

The onset of adolescence in humans is marked by hormonal changes that give rise to secondary sexual characteristics, noted as puberty. It has, however, proven challenging to unravel to what extent pubertal changes may have organizing effects on the brain beyond chronological age, as reported in animal studies. The present longitudinal study aimed to characterize the unique effects of age and puberty on subcortical brain volumes and included three waves of data collection at two-year intervals and 680 T1-weighted MRI scans of 271 participants (54% females) aged between 8 and 29 years old. Generalized additive mixed model procedures were used to assess the effects of age, self-report pubertal status and testosterone level on basal ganglia, thalamus, hippocampus, amygdala and cerebellum gray matter volumes. We observed age-related increases in putamen and pallidum volumes, and decreases in accumbens and thalamus volumes, all show larger volumes in boys than girls. Only the cerebellum showed an interaction effect of age by sex, such that males showed prolonged increases in cerebellar volume than females. Next, we showed that changes in self-report puberty status better described developmental change than chronological age for most structures in males, and for caudate, pallidum and hippocampal volumes in females. Furthermore, changes in testosterone level were related to development of pallidum, accumbens, hippocampus and amygdala volumes in males and caudate and hippocampal volumes in females. The modeling approach of the present study allowed us to characterize the complex interactions between chronological age and pubertal maturational changes, and the findings indicate puberty unique changes in brain structure that are sex specific.

Role of the androgen receptor in the central nervous system

The involvement of gonadal androgens in functions of the central nervous system was suggested for the first time about half a century ago. Since then, the number of functions attributed to androgens has steadily increased, ranging from regulation of the hypothalamic-pituitary-gonadal axis and reproductive behaviors to modulation of cognition, anxiety and other non-reproductive functions. This review focuses on the implication of the neural androgen receptor in these androgen-sensitive functions and behaviors.

Exploring the role of testosterone in the cerebellum link to neuroticism: From adolescence to early adulthood

Previous research has found an association between a smaller cerebellar volume and higher levels of neuroticism. The steroid hormone testosterone reduces stress responses and the susceptibility to negative mood. Together with in vitro studies showing a positive effect of testosterone on cerebellar gray matter volumes, we set out to explore the role of testosterone in the relation between cerebellar gray matter and neuroticism. Structural magnetic resonance imaging scans were acquired, and indices of neurotic personality traits were assessed by administering the depression and anxiety scale of the revised NEO personality inventory and Gray's behavioural avoidance in one hundred and forty-nine healthy volunteers between 12 and 27 years of age. Results demonstrated an inverse relation between total brain corrected cerebellar volumes and neurotic personality traits in adolescents and young adults. In males, higher endogenous testosterone levels were associated with lower scores on neurotic personality traits and larger cerebellar gray matter volumes. No such relations were observed in the female participants. Analyses showed that testosterone significantly mediated the relation between male cerebellar gray matter and measures of neuroticism. Our findings on the interrelations between endogenous testosterone, neuroticism and cerebellar morphology provide a cerebellum-oriented framework for the susceptibility to experience negative emotions and mood in adolescence and early adulthood.

Androgen Receptor Involvement in Rat Amelogenesis: An Additional Way for Endocrine-Disrupting Chemicals to Affect Enamel Synthesis

Endocrine-disrupting chemicals (EDCs) that interfere with the steroid axis can affect amelogenesis, leading to enamel hypomineralization similar to that of molar incisor hypomineralization, a recently described enamel disease. We investigated the sex steroid receptors that may mediate the effects of EDCs during rat amelogenesis. The expression of androgen receptor (AR), estrogen receptor (ER)-α, and progesterone receptor was dependent on the stage of ameloblast differentiation, whereas ERβ remained undetectable. AR was the only receptor selectively expressed in ameloblasts involved in final enamel mineralization. AR nuclear translocation and induction of androgen-responsive element-containing promoter activity upon T treatment, demonstrated ameloblast responsiveness to androgens. T regulated the expression of genes involved in enamel mineralization such as KLK4, amelotin, SLC26A4, and SLC5A8 but not the expression of genes encoding matrix proteins, which determine enamel thickness. Vinclozolin and to a lesser extent bisphenol A, two antiandrogenic EDCs that cause enamel defects, counteracted the actions of T. In conclusion, we show, for the first time, the following: 1) ameloblasts express AR; 2) the androgen signaling pathway is involved in the enamel mineralization process; and 3) EDCs with antiandrogenic effects inhibit AR activity and preferentially affect amelogenesis in male rats. Their action, through the AR pathway, may specifically and irreversibly affect enamel, potentially leading to the use of dental defects as a biomarker of exposure to environmental pollutants. These results are consistent with the steroid hormones affecting ameloblasts, raising the issue of the hormonal influence on amelogenesis and possible sexual dimorphism in enamel quality.

Time course of the effect of status epilepticus induced in the developing rat on γ-amino butyric acid and glutamate cerebellar concentration

INTRODUCTION

Status epilepticus (SE) is an epileptic condition that can cause cerebellar atrophy and loss of Purkinje cells in both humans and research animals. Cerebellum is a region rich in γ-aminobutyric acid (GABA) and glutamate, and some studies have shown that their concentrations may be altered after convulsions. However, there are no studies showing the effect of seizures on different cerebellar regions in developing rats. Time course of the effect of status epilepticus induced in the developing rat on γ-amino butyric acid and glutamate cerebellar concentration.

METHODS

SE was induced using the lithium-pilocarpine model; control rats were injected with saline solution. At 6h, 24h, and 1 month after SE o saline injection, rats were anaesthetised with pentobarbital and decapitated, and cerebella were extracted. The vermis and hemispheres were dissected and homogenised in 0.1M perchloric acid containing 4mM sodium bisulfite. Homogenates were centrifuged and supernatant was used to quantify GABA, and glutamate tissue concentrations by HPLC coupled with fluorometric detection.

RESULTS

SE did not alter GABA and glutamate tissue concentration in the cerebellar vermis and hemispheres.

CONCLUSION

The developing rat cerebellum is resistant to both short- and long-term neurochemical changes induced by SE.

Prenatal exposure to sodium valproate alters androgen receptor expression in the developing cerebellum in a region and age specific manner in male and female rats

Valproic acid (VPA) is an anti-epileptic drug with teratogenicity activity that has been related to autism. In rodents, exposure to VPA in utero leads to brain abnormalities similar than those reported in the autistic brain. Particularly, VPA reduces the number of Purkinje neurons in the rat cerebellum parallel to cerebellar abnormalities found in autism. Thus, we injected pregnant females on embryonic day 12 either with VPA (600mg/kg, i.p.) or 0.9% saline solution and obtained the cerebellum from their offspring at different postnatal time points. Testosterone has been linked to autism and plays an important role during brain development. Therefore, we identified and analyzed the androgen receptor (AR) by immunohistochemistry and densitometry, respectively. We found VPA decreases AR density in the superficial Purkinje layer only in cerebellar lobule 8 at PN7, but increased it at PN14 compared to control in males. In females, VPA decreased AR density in the superficial Purkinje layer in cerebellar lobule 6 at PN14, but increased it in lobule 9 at the same time point. No differences were found in the deep Purkinje layer of any cerebellar lobule in terms of AR density neither in males nor females. We additionally found a particular AR density decreasing in both superficial and deep regions across development in the majority of cerebellar lobules in males, but in all cerebellar lobules in females. Thus, our results indicate that VPA disrupts the AR ontogeny in the developing cerebellum in an age and region specific manner in male and female rats. Future epigenetic studies including the evaluation of histone deacetylases (HDAC's) might shed light these results as HDAC's are expressed by Purkinje neurons, interact with the AR and are VPA targets. This work contributes to the understanding of the cerebellar development and it might help to understand the role of the cerebellum in neurodevelopmental disorders such as autism.