Aging-induced changes in sex-steroidogenic enzymes and sex-steroid receptors in the cortex, hypothalamus and cerebellum

Estrogen and testosterone secretion from the mouse brain

Estrogen and testosterone are typically thought of as gonadal or adrenal derived steroids that cross the blood brain barrier to signal via both rapid nongenomic and slower genomic signalling pathways. Estrogen and testosterone signalling has been shown to drive interlinked behaviours such as social behaviours and cognition by binding to their cognate receptors in hypothalamic and forebrain nuclei. So far, acute brain slices have been used to study short-term actions of 17β-estradiol, typically using electrophysiological measures. For example, these techniques have been used to investigate, nongenomic signalling by estrogen such as the estrogen modulation of long-term potentiation (LTP) in the hippocampus. Using a modified method that preserves the slice architecture, we show, for the first time, that acute coronal slices from the prefrontal cortex and from the hypothalamus maintained in aCSF over longer periods i.e. 24 h can be steroidogenic, increasing their secretion of testosterone and estrogen. We also show that the hypothalamic nuclei produce more estrogen and testosterone than the prefrontal cortex. Therefore, this extended acute slice system can be used to study the regulation of steroid production and secretion by discrete nuclei in the brain.

Brain-derived estrogen: a critical player in maintaining cognitive health of aged female rats, possibly involving GPR30

Brain-derived estrogen is an endogenous neuroprotective agent, whether and how might this protective function with aging, especially postmenopausal drops in circulating estrogen, remain unclear. We herein subjected 6, 14, and 18 Mon female rats to mimic natural aging, and found that estrogen synthesis is more active in the healthy aged brain, as evidenced by the highest levels of mRNA and protein expression of aromatase, the key enzyme of E2 biosynthesis, among the three groups. Aromatase knockout in forebrain neurons (FBN-Aro-/-) impaired hippocampal and cortical neurons, and cognitive function in 18 Mon rats, compared to wild-type controls. Furthermore, estrogen nuclear receptors (ERα/β) displayed opposite changes, with a significant ERα decrease and ERβ increase, while membrane receptor GPR30 expressed stably in hippocampus during aging. Intriguingly, GPR30, but not ERα and ERβ, was decreased by FBN-Aro-/-. The results indicate that GPR30 is more sensitive to brain local E2 synthesis. Our findings provide evidence of a critical role for brain-derived estrogen in maintaining healthy brain function in older individuals, possibly involving GPR30.

Aging Is Associated With Lower Neuroactive Steroids and Worsened Outcomes Following Cerebral Ischemia in Male Mice

Ischemic stroke is a leading cause of disability and death, and aging is the main nonmodifiable risk factor. Following ischemia, neuroactive steroids have been shown to play a key role in cerebroprotection. Thus, brain steroid concentrations at the time of injury as well as their regulation after stroke are key factors to consider. Here, we investigated the effects of age and cerebral ischemia on steroid levels, behavioral outcomes, and neuronal degeneration in 3- and 18-month-old C57BL/6JRj male mice. Ischemia was induced by middle cerebral artery occlusion for 1 hour followed by reperfusion (MCAO/R) and analyses were performed at 6 hours after MCAO. Extended steroid profiles established by gas chromatography coupled with tandem mass spectrometry revealed that (1) brain and plasma concentrations of the main 5α-reduced metabolites of progesterone, 11-deoxycorticosterone, and corticosterone were lower in old than in young mice; (2) after MCAO/R, brain concentrations of progesterone, 5α-dihydroprogesterone, and corticosterone increased in young mice; and (3) after MCAO/R, brain concentrations of 5α-reduced metabolites of progesterone, 3α5α-tetrahydrodeoxycorticosterone, and 3β5α-tetrahydrodeoxycorticosterone were lower in old than in young mice. After ischemia, old mice showed increased sensori-motor deficits and more degenerating neurons in the striatum than young mice. Altogether, these findings strongly suggest that the decreased capacity of old mice to metabolize steroids toward the 5α-reduction pathway comparatively to young mice may contribute to the worsening of their stroke outcomes.

Brain-derived estrogen and neural function

Although classically known as an endocrine signal produced by the ovary, 17β-estradiol (E₂) is also a neurosteroid produced in neurons and astrocytes in the brain of many different species. In this review, we provide a comprehensive overview of the localization, regulation, sex differences, and physiological/pathological roles of brain-derived E₂ (BDE₂). Much of what we know regarding the functional roles of BDE₂ has come from studies using specific inhibitors of the E₂ synthesis enzyme, aromatase, as well as the recent development of conditional forebrain neuron-specific and astrocyte-specific aromatase knockout mouse models. The evidence from these studies support a critical role for neuron-derived E₂ (NDE₂) in the regulation of synaptic plasticity, memory, socio-sexual behavior, sexual differentiation, reproduction, injury-induced reactive gliosis, and neuroprotection. Furthermore, we review evidence that astrocyte-derived E₂ (ADE₂) is induced following brain injury/ischemia, and plays a key role in reactive gliosis, neuroprotection, and cognitive preservation. Finally, we conclude by discussing the key controversies and challenges in this area, as well as potential future directions for the field.

De Novo Synthesized Estradiol: A Role in Modulating the Cerebellar Function

The estrogen estradiol is a potent neuroactive steroid that may regulate brain structure and function. Although the effects of estradiol have been historically associated with gonadal secretion, the discovery that this steroid may be synthesized within the brain has expanded this traditional concept. Indeed, it is accepted that de novo synthesized estradiol in the nervous system (nE2) may modulate several aspects of neuronal physiology, including synaptic transmission and plasticity, thereby influencing a variety of behaviors. These modulations may be on a time scale of minutes via non-classical and often membrane-initiated mechanisms or hours and days by classical actions on gene transcription. Besides the high level, recent investigations in the cerebellum indicate that even a low aromatase expression can be related to the fast nE2 effect on brain functioning. These pieces of evidence point to the importance of an on-demand and localized nE2 synthesis to rapidly contribute to regulating the synaptic transmission. This review is geared at exploring a new scenario for the impact of estradiol on brain processes as it emerges from the nE2 action on cerebellar neurotransmission and cerebellum-dependent learning.

Effects of aging on testosterone and androgen receptors in the mesocorticolimbic system of male rats

As males age, systemic testosterone (T) levels decline. T regulates executive function, a collection of cognitive processes that are mediated by the mesocorticolimbic system. Here, we examined young adult (5 months) and aged (22 months) male Fischer 344 × Brown Norway rats, and measured systemic T levels in serum and local T levels in microdissected nodes of the mesocorticolimbic system (ventral tegmental area (VTA), nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC)). We also measured androgen receptor (AR) immunoreactivity (-ir) in the mesocorticolimbic system. As expected, systemic T levels decreased with age. Local T levels in mesocorticolimbic regions - except the VTA - also decreased with age. Mesocorticolimbic T levels were higher than serum T levels at both ages. AR-ir was present in the VTA, NAc, mPFC, and OFC and decreased with age in the mPFC. Taken together with previous results, the data suggest that changes in androgen signaling may contribute to changes in executive function during aging.

Sex differences in the brain expression of steroidogenic molecules under basal conditions and after gonadectomy

The brain is a steroidogenic tissue. It expresses key molecules involved in the synthesis and metabolism of neuroactive steroids, such as steroidogenic acute regulatory protein (StAR), translocator protein 18 kDa (TSPO), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenases (3β-HSD), 5α-reductases (5α-R) and 3α-hydroxysteroid oxidoreductases (3α-HSOR). Previous studies have shown that the levels of brain steroids are different in male and female rats under basal conditions and after gonadectomy. In the present study, we assessed gene expression of key neurosteroidogenic molecules in the cerebral cortex and cerebellum of gonadally intact and gonadectomised adult male and female rats. In the cerebellum, the basal mRNA levels of StAR and 3α-HSOR were significantly higher in females than in males. By contrast, the mRNA levels of TSPO and 5α-R were significantly higher in males. In the cerebral cortex, all neurosteroidogenic molecules analysed showed similar mRNA levels in males and females. Gonadectomy increased the expression of 5α-R in the brain of both sexes, although it affected the brain expression of StAR, TSPO, P450scc and 3α-HSOR in females only and with regional differences. Although protein levels were not investigated in the present study, our findings indicate that mRNA expression of steroidogenic molecules in the adult rat brain is sexually dimorphic and presents regional specificity, both under basal conditions and after gonadectomy. Thus, local steroidogenesis may contribute to the reported sex and regional differences in the levels of brain neuroactive steroids and may be involved in the generation of sex differences in the adult brain function.

Central intracrine DHEA synthesis in ageing-related neuroinflammation and neurodegeneration: therapeutic potential?

It is a well-known fact that DHEA declines on ageing and that it is linked to ageing-related neurodegeneration, which is characterised by gradual cognitive decline. Although DHEA is also associated with inflammation in the periphery, the link between DHEA and neuroinflammation in this context is less clear. This review drew from different bodies of literature to provide a more comprehensive picture of peripheral vs central endocrine shifts with advanced age—specifically in terms of DHEA. From this, we have formulated the hypothesis that DHEA decline is also linked to neuroinflammation and that increased localised availability of DHEA may have both therapeutic and preventative benefit to limit neurodegeneration. We provide a comprehensive discussion of literature on the potential for extragonadal DHEA synthesis by neuroglial cells and reflect on the feasibility of therapeutic manipulation of localised, central DHEA synthesis.

17 beta-estradiol synthesis modulates cerebellar dependent motor memory formation in adult male rats

Neurosteroid 17 beta-estradiol (E2) is a steroid synthesized de novo in the nervous system that might influence neuronal activity and behavior. Nevertheless, the impact of E2 on the functioning of those neural systems in which it is slightly synthesized is less questioned. The vestibulo-ocular reflex (VOR) adaptation, may provide an ideal arena for investigating this issue. Indeed, E2 modulates cerebellar parallel fiber-Purkinje cell synaptic plasticity that underlies encoding of VOR adaptation. Moreover, aromatase expression in the cerebellum of adult rodents is maintained at very low levels and localized to Purkinje cells. The significance of age-related maintenance of low levels of aromatase expression in the cerebellum on behavior, however, has yet to be explored. Our aim in this study was to determine whether E2 synthesis exerts an effective and persistent modulation of VOR adaptation in adult male rats. To answer this question, we investigated the acute effect of blocking E2 synthesis on gain increases and decreases in VOR adaptation using an oral dose (2.5 mg/kg) of the aromatase inhibitor Letrozole in peri-pubertal and post-pubertal male rats. We found that Letrozole acutely impaired gain increases and decreases in VOR adaptation without altering basal ocular-motor performance and that these effects were similar in peri-pubertal and post-pubertal rats. Thus, in adult male rats neurosteroid E2 effectively modulates VOR adaptation in both of the periods studied. These findings imply that the adult cerebellum uses E2 synthesis for modulating motor memory formation and suggest that low and extremely localized E2 production may play a role in adaptive phenomena.

The 5α-Reductase Inhibitor Finasteride Exerts Neuroprotection Against Ischemic Brain Injury in Aged Male Rats

Progesterone (P4) exerts potent neuroprotection both in young and aged animal models of stroke. The neuroprotection is likely to be mediated by allopregnanolone (ALLO) metabolized from P4 by 5α-reductase, since the neuroprotection is attenuated by the 5α-reductase inhibitor finasteride, which was done only with young animals though. Thus, we do not know the contribution of ALLO to the P4-induced neuroprotection in aged animals. We examined effects of finasteride on the P4-induced neuroprotection in aged (16-18-month-old) male rats subjected to transient focal cerebral ischemia. Transient focal cerebral ischemia was induced by left middle cerebral artery occlusion (MCAO) and occlusion of the bilateral common carotid arteries. MCAO rats were given an 8 mg/kg P4 6 h after MCAO followed by the same treatment once a day for successive 3 days. Finasteride, a 5α-reductase inhibitor, at 20 mg/kg was intraperitoneally injected 30 min prior to the P4-injections. P4 markedly reduced neuronal damage 72 h after MCAO, and the P4-induced neuroprotection was apparently suppressed by finasteride in the aged animals. However, post-ischemic administration of finasteride alone (20 mg/kg) significantly prevented neuronal damage and the impairment of Rotarod performance after MCAO in aged male rats, but not in young ones. The androgen receptor antagonist flutamide markedly suppressed the neuroprotection of finasteride in the cerebral cortex, but not in the striatum, suggesting the androgen receptor-dependent mechanism of the finasteride-induced neuroprotection in the cerebral cortex. Our findings suggested, for the first time, the potential of finasteride as a therapeutic agent in post-ischemic treatment of strokes in aged population.

Testosterone and Corticosterone in the Mesocorticolimbic System of Male Rats: Effects of Gonadectomy and Caloric Restriction

Steroid hormones can modulate motivated behaviors through the mesocorticolimbic system. Gonadectomy (GDX) is a common method to determine how steroids influence the mesocorticolimbic system, and caloric restriction (CR) is often used to invigorate motivated behaviors. A common assumption is that the effects of these manipulations on brain steroid levels reflects circulating steroid levels. We now know that the brain regulates local steroid levels in a region-specific manner; however, previous studies have low spatial resolution. Using ultrasensitive liquid chromatography tandem mass spectrometry, we examined steroids in microdissected regions of the mesocorticolimbic system (ventral tegmental area, nucleus accumbens, medial prefrontal cortex). We examined whether GDX or CR influences systemic and local steroids, particularly testosterone (T) and steroidogenic enzyme transcripts. Adult male rats underwent a GDX surgery and/or CR for either 2 or 6 weeks. Levels of T, the primary steroid of interest, were higher in all brain regions than in the blood, whereas corticosterone (CORT) was lower in the brain than in the blood. Importantly, GDX completely eliminated T in the blood and lowered T in the brain. Yet, T remained present in the brain, even 6 weeks after GDX. CR decreased both T and CORT in the blood and brain. Steroidogenic enzyme (Cyp17a1, 3β-hydroxysteroid dehydrogenase, aromatase) transcripts and androgen receptor transcripts were expressed in the mesocorticolimbic system and differentially affected by GDX and CR. Together, these results suggest that T is synthesized within the mesocorticolimbic system. These results provide a foundation for future studies examining how neurosteroids influence behaviors mediated by the mesocorticolimbic system.

Androgen Regulation of the Mesocorticolimbic System and Executive Function

Multiple lines of evidence indicate that androgens, such as testosterone, modulate the mesocorticolimbic system and executive function. This review integrates neuroanatomical, molecular biological, neurochemical, and behavioral studies to highlight how endogenous and exogenous androgens alter behaviors, such as behavioral flexibility, decision making, and risk taking. First, we briefly review the neuroanatomy of the mesocorticolimbic system, which mediates executive function, with a focus on the ventral tegmental area (VTA), nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and orbitofrontal cortex (OFC). Second, we present evidence that androgen receptors (AR) and other steroid receptors are expressed in the mesocorticolimbic system. Using sensitive immunohistochemistry and quantitative polymerase chain reaction (qPCR) techniques, ARs are detected in the VTA, NAc, mPFC, and OFC. Third, we describe recent evidence for local androgens ("neuroandrogens") in the mesocorticolimbic system. Steroidogenic enzymes are expressed in mesocorticolimbic regions. Furthermore, following long-term gonadectomy, testosterone is nondetectable in the blood but detectable in the mesocorticolimbic system, using liquid chromatography tandem mass spectrometry. However, the physiological relevance of neuroandrogens remains unknown. Fourth, we review how anabolic-androgenic steroids (AAS) influence the mesocorticolimbic system. Fifth, we describe how androgens modulate the neurochemistry and structure of the mesocorticolimbic system, particularly with regard to dopaminergic signaling. Finally, we discuss evidence that androgens influence executive functions, including the effects of androgen deprivation therapy and AAS. Taken together, the evidence indicates that androgens are critical modulators of executive function. Similar to dopamine signaling, there might be optimal levels of androgen signaling within the mesocorticolimbic system for executive functioning. Future studies should examine the regulation and functions of neurosteroids in the mesocorticolimbic system, as well as the potential deleterious and enduring effects of AAS use.

Role of Sex Hormones on Brain Mitochondrial Function, with Special Reference to Aging and Neurodegenerative Diseases

The mitochondria have a fundamental role in both cellular energy supply and oxidative stress regulation and are target of the effects of sex steroids, particularly the neuroprotective ones. Aging is associated with a decline in the levels of different steroid hormones, and this decrease may underline some neural dysfunctions. Besides, modifications in mitochondrial functions associated with aging processes are also well documented. In this review, we will discuss studies that describe the modifications of brain mitochondrial function and of steroid levels associated with physiological aging and with neurodegenerative diseases. A special emphasis will be placed on describing and discussing our recent findings concerning the concomitant study of mitochondrial function (oxidative phosphorylation, oxidative stress) and brain steroid levels in both young (3-month-old) and aged (20-month-old) male and female mice.

No effect of testosterone on behavior in aged Wistar rats

In men, aging is accompanied by a gradual decline in androgen secretion. Studies suggest beneficial effects of endogenous and exogenous testosterone on affective behavior and cognitive functions. The aim of this study was to describe behavioral and cognitive sex differences and to analyze the effects of long-term androgen deficiency in aged male rats. Thirty-months old rats divided into three groups (males, females and males gonadectomized as young adults) underwent a battery of behavioral tests assessing locomotor activity, anxiety, memory, anhedonia, sociability and depression-like behavior. No major effect of gonadectomy was found in any of the analyzed behavioral measures in male rats. The only consistent sex difference was confirmed in depression-like behavior with longer immobility time observed in males. In an interventional experiment, a single dose of testosterone had no effect on gonadectomized male and female rats in the forced swim test. In contrast to previous studies this comprehensive behavioral phenotyping of aged rats revealed no major role of endogenous testosterone. Based on our results long-term hypogonadism does not alter the behavior of aged male rats, neither does acute testosterone treatment. Whether these findings have any consequences on androgen replacement therapy in aged men remains to be elucidated.

Sex and the development of Alzheimer's disease

Men and women exhibit differences in the development and progression of Alzheimer's disease (AD). The factors underlying the sex differences in AD are not well understood. This Review emphasizes the contributions of sex steroid hormones to the relationship between sex and AD. In women, events that decrease lifetime exposure to estrogens are generally associated with increased AD risk, whereas estrogen-based hormone therapy administered near the time of menopause may reduce AD risk. In men, estrogens do not exhibit age-related reduction and are not significantly associated with AD risk. Rather, normal age-related depletions of testosterone in plasma and brain predict enhanced vulnerability to AD. Both estrogens and androgens exert numerous protective actions in the adult brain that increase neural functioning and resilience as well as specifically attenuating multiple aspects of AD-related neuropathology. Aging diminishes the activational effects of sex hormones in sex-specific manners, which is hypothesized to contribute to the relationship between aging and AD. Sex steroid hormones may also drive sex differences in AD through their organizational effects during developmental sexual differentiation of the brain. Specifically, sex hormone actions during early development may confer inherent vulnerability of the female brain to development of AD in advanced age. The combined effects of organizational and activational effects of sex steroids yield distinct sex differences in AD pathogenesis, a significant variable that must be more rigorously considered in future research. © 2016 Wiley Periodicals, Inc.

HPA Axis Genes, and Their Interaction with Childhood Maltreatment, are Related to Cortisol Levels and Stress-Related Phenotypes

Stress responses are controlled by the hypothalamus pituitary adrenal (HPA)-axis and maladaptive stress responses are associated with the onset and maintenance of stress-related disorders such as major depressive disorder (MDD). Genes that play a role in the HPA-axis regulation may likely contribute to the relation between relevant neurobiological substrates and stress-related disorders. Therefore, we performed gene-wide analyses for 30 a priori literature-based genes involved in HPA-axis regulation in 2014 subjects (34% male; mean age: 42.5) to study the relations with lifetime MDD diagnosis, cortisol awakening response, and dexamethasone suppression test (DST) levels (subsample N=1472) and hippocampal and amygdala volume (3T MR images; subsample N=225). Additionally, gene by childhood maltreatment (CM) interactions were investigated. Gene-wide significant results were found for dexamethasone suppression (CYP11A1, CYP17A1, POU1F1, AKR1D1), hippocampal volume (CYP17A1, CYP11A1, HSD3B2, PROP1, AVPRA1, SRD5A1), amygdala volume (POMC, CRH, HSD3B2), and lifetime MDD diagnosis (FKBP5 and CRH), all permutation p-values<0.05. Interactions with CM were found for several genes; the strongest interactions were found for NR3C2, where the minor allele of SNP rs17581262 was related to smaller hippocampal volume, smaller amygdala volume, higher DST levels, and higher odds of MDD diagnosis only in participants with CM. As hypothesized, several HPA-axis genes are associated with stress-related endophenotypes including cortisol response and reduced brain volumes. Furthermore, we found a pleiotropic interaction between CM and the mineralocorticoid receptor gene, suggesting that this gene plays an important moderating role in stress and stress-related disorders.

Cafeteria diet differentially alters the expression of feeding-related genes through DNA methylation mechanisms in individual hypothalamic nuclei

We evaluated the effect of cafeteria diet (CAF) on the mRNA levels and DNA methylation state of feeding-related neuropeptides, and neurosteroidogenic enzymes in discrete hypothalamic nuclei. Besides, the expression of steroid hormone receptors was analyzed. Female rats fed with CAF from weaning increased their energy intake, body weight, and fat depots, but did not develop metabolic syndrome. The increase in energy intake was related to an orexigenic signal of paraventricular (PVN) and ventromedial (VMN) nuclei, given principally by upregulation of AgRP and NPY. This was mildly counteracted by the arcuate nucleus, with decreased AgRP expression and increased POMC and kisspeptin expression. CAF altered the transcription of neurosteroidogenic enzymes in PVN and VMN, and epigenetic mechanisms associated with differential promoter methylation were involved. The changes observed in the hypothalamic nuclei studied could add information about their differential role in food intake control and how their action is disrupted in obesity.

Tyramide Signal Amplification Permits Immunohistochemical Analyses of Androgen Receptors in the Rat Prefrontal Cortex

Research on neural androgen receptors (ARs) has traditionally focused on brain regions that regulate reproductive and aggressive behaviors, such as the hypothalamus and amygdala. Although many cells in the prefrontal cortex (PFC) also express ARs, the number of ARs per cell appears to be much lower, and thus, AR immunostaining is often hard to detect and quantify in the PFC. Here, we demonstrate that biotin tyramide signal amplification (TSA) dramatically increases AR immunoreactivity in the rat brain, including critical regions of the PFC such as the medial PFC (mPFC) and orbitofrontal cortex (OFC). We show that TSA is useful for AR detection with both chromogenic and immunofluorescent immunohistochemistry. Double-labeling studies reveal that AR+ cells in the PFC and hippocampus are NeuN+ but not GFAP+ and thus primarily neuronal. Finally, in gonadally intact rats, more AR+ cells are present in the mPFC and OFC of males than of females. Future studies can use TSA to further examine AR immunoreactivity across ages, sexes, strains, and different procedures (e.g., fixation methods). In light of emerging evidence for the androgen regulation of executive function and working memory, these results may help understand the distribution and roles of ARs in the PFC.

Prostate Cancer: Is It a Battle Lost to Age?

Age is often considered an important non-modifiable risk factor for a number of diseases, including prostate cancer. Some prominent risk factors of prostate cancer include familial history, ethnicity and age. In this review, various genetic and physiological characteristics affected due to advancing age will be analysed and correlated with their direct effect on prostate cancer.

The suprachiasmatic nucleus: age-related decline in biological rhythms

Aging is associated with changes in sleep duration and quality, as well as increased rates of pathologic/disordered sleep. While several factors contribute to these changes, emerging research suggests that age-related changes in the mammalian central circadian clock within the suprachiasmatic nucleus (SCN) may be a key factor. Prior work from our group suggests that circadian output from the SCN declines because of aging. Furthermore, we have previously observed age-related infertility in female mice, caused by a mismatch between environmental light-dark cycles and the intrinsic, internal biological clocks. In this review, we address regulatory mechanisms underlying circadian rhythms in mammals and summarize recent literature describing the effects of aging on the circadian system.

Molecular cloning, characterization, tissue distribution and mRNA expression changes during the hibernation and reproductive periods of estrogen receptor alpha (ESR1) in Chinese alligator, Alligator sinensis

Chinese alligator, Alligator sinensis, is a critically endangered reptile species unique to China. Little is known about the mechanism of growth- and reproduction-related hormones gene expression in Chinese alligator. Estrogens play important roles in regulating multiple reproduction- and non-reproduction-related functions by binding to their corresponding receptors. Here, the full-length cDNA of estrogen receptor alpha (ERα/ESR1) was cloned and sequenced from Chinese alligator for the first time, which comprises 1764bp nucleotides and encodes a predicted protein of 587 amino acids. Phylogenetic analysis of ESR1 showed that crocodilians and turtles were the sister-group of birds. The results of real-time quantitative PCR indicated that the ESR1 mRNA was widely expressed in the brain and peripheral tissues. In the brain and pituitary gland, ESR1 was most highly transcribed in the cerebellum. But in other peripheral tissues, ESR1 mRNA expression level was the highest in the ovary. Compared with hibernation period, ESR1 mRNA expression levels were increased significantly in the reproductive period (P<0.05) in cerebellum, pituitary gland, liver, spleen, lung, kidney and ovary, while no significant change in other examined tissues (P>0.05). The ESR1 mRNA expression levels changes during the two periods of different tissues suggested that ESR1 might play an important role in mediation of estrogenic multiple reproductive effects in Chinese alligator. Furthermore, it was the first time to quantify ESR1 mRNA level in the brain of crocodilians, and the distribution and expression of ESR1 mRNA in the midbrain, cerebellum and medulla oblongata was also reported for the first time in reptiles.

Effects of Subchronic Finasteride Treatment and Withdrawal on Neuroactive Steroid Levels and Their Receptors in the Male Rat Brain

The enzymatic conversion of progesterone and testosterone by the enzyme 5alpha-reductase exerts a crucial role in the control of nervous function. The effects of finasteride in the brain, an inhibitor of this enzyme used for the treatment of human benign prostatic hyperplasia and androgenic alopecia, have been poorly explored. Therefore, the effects of a subchronic treatment with finasteride at low doses (3 mg/kg/day) and the consequences of its withdrawal on neuroactive steroid levels in plasma, cerebrospinal fluid and some brain regions as well as on the expression of classical and non-classical steroid receptors have been evaluated in male rats. After subchronic treatment (i.e., for 20 days) the following effects were detected: (i) depending on the compartment considered, alteration in the levels of neuroactive steroids, not only in 5alpha-reduced metabolites but also in its precursors and in neuroactive steroids from other steroidogenic pathways and (ii) an upregulation of the androgen receptor in the cerebral cortex and beta3 subunit of the GABA-A receptor in the cerebellum. One month after the last treatment (i.e., withdrawal period), some of these effects persisted (i.e., the upregulation of the androgen receptor in the cerebral cortex, an increase of dihydroprogesterone in the cerebellum, a decrease of dihydrotestosterone in plasma). Moreover, other changes in neuroactive steroid levels, steroid receptors (i.e., an upregulation of the estrogen receptor alpha and a downregulation of the estrogen receptor beta in the cerebral cortex) and GABA-A receptor subunits (i.e., a decrease of alpha 4 and beta 3 mRNA levels in the cerebral cortex) were detected. These findings suggest that finasteride treatment may have broad consequences for brain function.

Puerperal and parental experiences alter rat preferences for pup odors via changes in the oxytocin system

In the rat, induction of maternal behavior depends on the parity of the female. For example, nulliparous (NP) females need longer exposure to pups than multiparous (MP) or lactating (L) females to exhibit similar maternal behavior. In this study, we investigated the role of brain oxytocin in the approaching behavior of these female rats. Olfactory preferences for pup odors were examined for 8 consecutive days. Each preference test was followed by direct overnight exposure to pups. On the 8th day, MP and L, but not NP females showed robust pup-odor preferences. After the behavioral test, half of the females were exposed to pups for 2 h, whereas the other half were not. The females were then sacrificed to analyze brain oxytocin (OXT) and vasopressin (AVP) activities by cFos immunohistochemistry and to quantify their receptor mRNA expression using real-time PCR. In the paraventricular nucleus (PVN), the percentage of cFos-positive OXT neurons was significantly larger in MP and L females than in NP females after pup exposure. No significant differences were found in cFos expression in OXT neurons of the supraoptic nucleus (SON) or in AVP neurons of either the PVN or SON. Expression of OXT receptor mRNA in the medial preoptic area and amygdala of the control groups was also higher in MP females than in NP females. Finally, we demonstrated that infusion of OXT into the lateral ventricle of NP females promoted preferences for pup odors. These results indicate that puerperal and parental experiences enhance the responsiveness of OXT neurons in the PVN to pup stimuli and establish olfactory preferences for these odors in a parity-dependent manner.