Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis.

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERß), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Brain Specific Estrogen Ameliorates Cognitive Effects of Surgical Menopause in Mice.

Menopause is a major endocrinological shift that leads to an increased vulnerability to the risk factors for cognitive impairment and dementia. This is thought to be due to the loss of circulating estrogens, which exert many potent neuroprotective effects in the brain. Systemic replacement of estrogen post-menopause has many limitations, including increased risk for estrogen-sensitive cancers. A more promising therapeutic approach therefore might be to deliver estrogen only to the brain thus limiting adverse peripheral side effects. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in post-menopausal mice. We modeled surgical menopause via bilateral ovariectomy (OVX). We treated mice with the pro-drug 10ß,17ß-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17ß-estradiol only in the brain. Young (2.5-month) and middle-aged (11-month-old) female C57BL/6J mice received ovariectomy and a subcutaneous implant containing vehicle (cholesterol) or DHED. At 3.5 months old (young group) and 14.5 months old (middle-aged group), mice underwent behavior testing to assess memory. DHED did not significantly alter metabolic status in middle-aged, post-menopausal mice. In both young and middle-aged mice, the brain-specific estrogen DHED improved spatial memory. Additional testing in middle-aged mice also showed that DHED improved working and recognition memory. These promising results lay the foundation for future studies aimed at determining if this intervention is as efficacious in models of dementia that have comorbid risk factors.

Postsynaptic density radiation signature following space irradiation.

Introduction: The response of the brain to space radiation is an important concern for astronauts during space missions. Therefore, we assessed the response of the brain to 28Si ion irradiation (600 MeV/n), a heavy ion present in the space environment, on cognitive performance and whether the response is associated with altered DNA methylation in the hippocampus, a brain area important for cognitive performance. Methods: We determined the effects of 28Si ion irradiation on object recognition, 6-month-old mice irradiated with 28Si ions (600 MeV/n, 0.3, 0.6, and 0.9 Gy) and cognitively tested two weeks later. In addition, we determined if those effects were associated with alterations in hippocampal networks and/or hippocampal DNA methylation. Results: At 0.3 Gy, but not at 0.6 Gy or 0.9 Gy, 28Si ion irradiation impaired cognition that correlated with altered gene expression and 5 hmC profiles that mapped to specific gene ontology pathways. Comparing hippocampal DNA hydroxymethylation following proton, 56Fe ion, and 28Si ion irradiation revealed a general space radiation synaptic signature with 45 genes that are associated with profound phenotypes. The most significant categories were glutamatergic synapse and postsynaptic density. Discussion: The brain's response to space irradiation involves novel excitatory synapse and postsynaptic remodeling.

Contributions of gonadal hormones in the sex-specific organization of context fear learning.

It is widely established that gonadal hormones are fundamental to modulating and organizing the sex-specific nature of reproductive behaviors. Recently we proposed that context fear conditioning (CFC) may emerge in a sex-specific manner organized prior to the pubertal surge of gonadal hormones. Here we sought to determine the necessity of male and female gonadal hormones secreted at critical periods of development upon context fear learning. We tested the organizational hypothesis that neonatal and pubertal gonadal hormones play a permanent role in organizing contextual fear learning. We demonstrate that the postnatal absence of gonadal hormones by neonatal orchiectomy (oRX) in males and ovariectomy (oVX) in females resulted in an attenuation of CFC in adult males and an enhancement of CFC in adult females. In females, the gradual introduction of estrogen before conditioning partially rescued this effect. However, the decrease of CFC in adult males was not rescued by introducing testosterone before conditioning. Next, at a further point in development, preventing the pubertal surge of gonadal hormones by prepubertal oRX in males resulted in a reduction in adult CFC. In contrast, in females, prepubertal oVX did not alter adult CFC. However, the adult introduction of estrogen in prepubertal oVX rats reduced adult CFC. Lastly, the adult-specific deletion of gonadal hormones by adult oRX or oVX alone or replacement of testosterone or estrogen did not alter CFC. Consistent with our hypothesis, we provide initial evidence that gonadal hormones at early periods of development exert a vital role in the organization and development of CFC in male and female rats.

Changes in Corticotropin-Releasing Factor Receptor Type 1, Co-Expression with Tyrosine Hydroxylase and Oxytocin Neurons, and Anxiety-Like Behaviors across the Postpartum Period in Mice.

INTRODUCTION: Corticotropin-releasing factor and its primary receptor (CRFR1) are critical regulators of behavioral and neuroendocrine stress responses. CRFR1 has also been associated with stress-related behavioral changes in postpartum mice. Our previous studies indicate dynamic changes in CRFR1 levels and coupling of CRFR1 with tyrosine hydroxylase (TH) and oxytocin (OT) neurons in postpartum mice. In this study, we aimed to determine the time course of these changes during the postpartum period. METHODS: Using a CRFR1-GFP reporter mouse line, we compared postpartum mice at five time points with nulliparous mice. We performed immunohistochemistry to assess changes in CRFR1 levels and changes in co-expression of TH/CRFR1-GFP and OT/CRFR1-GFP across the postpartum period. Mice were also assessed for behavioral stress responses in the open field test. RESULTS: Relative to nulliparous mice, CRFR1 levels were elevated in the anteroventral periventricular nucleus (AVPV/PeN) but were decreased in the medial preoptic area from postpartum day 1 (P1) through P28. In the paraventricular hypothalamus (PVN), there is a transient decline in CRFR1 mid-postpartum with a nadir at P7. Co-localization of CRFR1 with TH-expressing neurons was also altered with a transient decrease found in the AVPV/PeN at P7 and P14. Co-expression of CRFR1 and OT neurons of the PVN and supraoptic nucleus was dramatically altered with virtually no co-expression found in nulliparous mice, but levels increased shortly after parturition and peaked near P21. A transient decrease in open field center time was found at P7, indicating elevated anxiety-like behavior. CONCLUSION: This study revealed various changes in CRFR1 across the postpartum period, which may contribute to stress-related behavior changes in postpartum mice.

Sex differences in androgen receptor, estrogen receptor alpha, and c-Fos co-expression with corticotropin releasing factor expressing neurons in restrained adult mice.

Gonadal hormone actions through androgen receptor (AR) and estrogen receptor alpha (ERα) regulate sex differences in hypothalamic-pituitary-adrenal (HPA) axis responsivity and stress-related behaviors. Here we tested whether corticotropin releasing factor (CRF) expressing neurons, which are widely known to regulate neuroendocrine and behavioral stress responses, co-express AR and ERα as a potential mechanism for gonadal hormone regulation of these responses. Using Crh-IRES-Cre::Ai9 reporter mice we report high co-localization of AR in CRF neurons within the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), medial amygdala (MeA), and ventromedial hypothalamus (VMH), moderate levels within the central amygdala (CeA) and low levels in the paraventricular hypothalamus (PVN). Sex differences in CRF/AR co-expression were found in the principal nucleus of the BST (BSTmpl), CeA, MeA, and VMH (males>females). CRF co-localization with ERα was generally lower relative to AR co-localization. However, high co-expression was found within the MPOA, AVPV, and VMH, with moderate co-expression in the arcuate nucleus (ARC), BST, and MeA and low levels in the PVN and CeA. Sex differences in CRF/ERα co-localization were found in the BSTmpl and PVN (males>females). Finally, we assessed neural activation of CRF neurons in restraint-stressed mice and found greater CRF/c-Fos co-expression in females in the BSTmpl and periaqueductal gray, while co-expression was higher in males within the ARC and dorsal CA1. Given the known role of CRF in regulating behavioral stress responses and the HPA axis, AR/ERα co-expression and sex-specific activation of CRF cell groups indicate potential mechanisms for modulating sex differences in these functions.

Sociosexual behavior requires both activating and repressive roles of Tfap2e/AP-2ε in vomeronasal sensory neurons.

Neuronal identity dictates the position in an epithelium, and the ability to detect, process, and transmit specific signals to specified targets. Transcription factors (TFs) determine cellular identity via direct modulation of genetic transcription and recruiting chromatin modifiers. However, our understanding of the mechanisms that define neuronal identity and their magnitude remain a critical barrier to elucidate the etiology of congenital and neurodegenerative disorders. The rodent vomeronasal organ provides a unique system to examine in detail the molecular mechanisms underlying the differentiation and maturation of chemosensory neurons. Here, we demonstrated that the identity of postmitotic/maturing vomeronasal sensory neurons (VSNs), and vomeronasal-dependent behaviors can be reprogrammed through the rescue of Tfap2e/AP-2ε expression in the Tfap2eNull mice, and partially reprogrammed by inducing ectopic Tfap2e expression in mature apical VSNs. We suggest that the TF Tfap2e can reprogram VSNs bypassing cellular plasticity restrictions, and that it directly controls the expression of batteries of vomeronasal genes.

A subpopulation of oxytocin neurons initiate expression of CRF receptor 1 (CRFR1) in females post parturition.

Oxytocin (OT) is essential for successful reproduction, particularly during parturition and lactation. During the postpartum period, OT also influences maternal behavior to promote bonding between mothers and their newborns, and increases stress resilience. However, the mechanism by which stress influences OT neuron activity and OT release has remained unclear. Here, we provide evidence that a subpopulation of OT neurons initiate expression of the receptor for the stress neuropeptide Corticotropin Releasing Factor (CRF), CRFR1, in reproductive females. OT neuron expression of CRFR1 begins at the first parturition and increases during the postpartum period until weaning. The percentage of OT neurons that express CRFR1 increases with successive breeding cycles until it reaches a plateau of 20-25% of OT neurons. OT neuron expression of CRFR1 in reproductive females is maintained after they are no longer actively breeding. CRFR1 expression leads to activation of OT neurons when animals are stressed. We propose a model in which direct CRF signaling to OT neurons selectively in reproductive females potentiates OT release to promote stress resilience in mothers.

Androgen Regulation of Corticotropin Releasing Factor Receptor 1 in the Mouse Brain.

Stress-related mood disorders like anxiety and depression are more prevalent in women than men and are often associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation. Androgen actions through androgen receptors (ARs) decrease HPA axis responses and stress-associated behaviors. Corticotropin releasing factor (CRF) and its binding to CRF receptor 1 (CRFR1) is also critical for regulation of the HPA axis, anxiety, and depression. We first determined CRFR1/AR co-localization patterns in male and female CRFR1-GFP mice. High co-localization was found within the paraventricular nucleus (PVN), dorsolateral and anteroventral subdivisions of the bed nucleus of the stria terminalis (BSTdl and BSTav), medial preoptic area (MPOA), and posterodorsal medial amygdala (MePD). We next determined whether the non-aromatizable androgen dihydrotestosterone (DHT) regulates CRFR1 expression and stress-induced activation of CRFR1-expressing cells. In the PVN, CRFR1-GFP cell number decreased following gonadectomy (GDX), but DHT treatment reversed this effect. GDX-DHT treated mice also had a decreased CRFR1-GFP cell number within the BSTdl compared to gonad intact and GDX-untreated groups. Following restraint stress GDX-blank mice showed fewer c-Fos/CRFR1 co-localized neurons in the MePD compared to gonad intact and GDX-DHT groups indicating decreased stress-induced activation of CRFR1 neurons following GDX. Higher plasma corticosterone (CORT) was found in GDX males compared to GDX-DHT and sham males following restraint stress, with a negative correlation between PVN CRFR1+ neurons and corticosterone levels 30- and 90-min following restraint. Together these findings show androgens can directly alter CRFR1 levels in the brain which may have implications for sex differences in regulation of the HPA axis and stress-related behaviors.

Estimating the glutamate transporter surface density in distinct sub-cellular compartments of mouse hippocampal astrocytes.

Glutamate transporters preserve the spatial specificity of synaptic transmission by limiting glutamate diffusion away from the synaptic cleft, and prevent excitotoxicity by keeping the extracellular concentration of glutamate at low nanomolar levels. Glutamate transporters are abundantly expressed in astrocytes, and previous estimates have been obtained about their surface expression in astrocytes of the rat hippocampus and cerebellum. Analogous estimates for the mouse hippocampus are currently not available. In this work, we derive the surface density of astrocytic glutamate transporters in mice of different ages via quantitative dot blot. We find that the surface density of glial glutamate transporters is similar in 7-8 week old mice and rats. In mice, the levels of glutamate transporters increase until about 6 months of age and then begin to decline slowly. Our data, obtained from a combination of experimental and modeling approaches, point to the existence of stark differences in the density of expression of glutamate transporters across different sub-cellular compartments, indicating that the extent to which astrocytes limit extrasynaptic glutamate diffusion depends not only on their level of synaptic coverage, but also on the identity of the astrocyte compartment in contact with the synapse. Together, these findings provide information on how heterogeneity in the spatial distribution of glutamate transporters in the plasma membrane of hippocampal astrocytes my alter glutamate receptor activation out of the synaptic cleft.

Alterations in corticotropin-releasing factor receptor type 1 in the preoptic area and hypothalamus in mice during the postpartum period.

Corticotropin-releasing factor (CRF) signaling through CRF receptor 1 (CRFR1) regulates autonomic, endocrine, and behavioral responses to stress, as well as behavioral changes during the maternal period. Previous work in our lab reported higher levels of CRFR1 in female, compared to male, mice within the rostral anteroventral periventricular nucleus (AVPV/PeN), a brain region involved in maternal behaviors. In this study, we used CRFR1-GFP reporter mice to investigate whether the reproductive status (postpartum vs. nulliparous) of acutely stressed females affects levels of CRFR1 in the AVPV/PeN and other regions involved in maternal functions. Compared to nulliparous, postpartum day 14 females showed increased AVPV/PeN CRFR1-GFP immunoreactivity and an elevated number of restraint stress-activated AVPV/PeN CRFR1 cells as assessed by immunohistochemical co-localization of CRFR1-GFP and phosphorylated CREB (pCREB). The medial preoptic area (MPOA) and paraventricular hypothalamus (PVN) of postpartum mice showed modest decreases in CRFR1-GFP immunoreactivity, while increased CRFR1-GFP/pCREB co-expressing cells were found in the PVN following restraint stress relative to nulliparous mice. Tyrosine hydroxylase (TH) and CRFR1-GFP co-localization was also assessed in the AVPV/PeN and other regions and revealed a decrease in co-localized neurons in the AVPV/PeN and ventral tegmental area of postpartum mice. Corticosterone analysis of restrained mice revealed blunted peak, but elevated recovery, levels in postpartum compared to nulliparous mice. Finally, we investigated projection patterns of AVPV/PeN CRFR1 neurons using female CRFR1-Cre mice and revealed dense efferent projections to several preoptic, hypothalamic, and hindbrain regions known to control stress-associated and maternal functions. Together, these findings contribute to our understanding of the neurobiology that might underlie changes in stress-related functions during the postpartum period.

Circadian Modulation of Neurons and Astrocytes Controls Synaptic Plasticity in Hippocampal Area CA1.

Most animal species operate according to a 24-h period set by the suprachiasmatic nucleus (SCN) of the hypothalamus. The rhythmic activity of the SCN modulates hippocampal-dependent memory, but the molecular and cellular mechanisms that account for this effect remain largely unknown. Here, we identify cell-type-specific structural and functional changes that occur with circadian rhythmicity in neurons and astrocytes in hippocampal area CA1. Pyramidal neurons change the surface expression of NMDA receptors. Astrocytes change their proximity to synapses. Together, these phenomena alter glutamate clearance, receptor activation, and integration of temporally clustered excitatory synaptic inputs, ultimately shaping hippocampal-dependent learning in vivo. We identify corticosterone as a key contributor to changes in synaptic strength. These findings highlight important mechanisms through which neurons and astrocytes modify the molecular composition and structure of the synaptic environment, contribute to the local storage of information in the hippocampus, and alter the temporal dynamics of cognitive processing.

A CRH Receptor Type 1 Agonist Increases GABA Transmission to GnRH Neurons in a Circulating-Estradiol-Dependent Manner.

GnRH neurons are central regulators of reproduction and respond to factors affecting fertility, such as stress. Corticotropin-releasing hormone (CRH) is released during stress response. In brain slices from unstressed controls, CRH has opposite, estradiol-dependent effects on GnRH neuron firing depending on the CRH receptor activated; activating CRHR-1 stimulates whereas activating CRHR-2 suppresses activity. We investigated possible direct and indirect mechanisms. Mice were ovariectomized and either not treated further (OVX) or given a capsule producing high positive feedback (OVX + E) or low negative feedback (OVX + low E) physiologic circulating estradiol levels. We tested possible direct effects on GnRH neurons by altering voltage-gated potassium currents. Two types of voltage-gated potassium currents (transient IA and sustained IK) were measured; neither CRHR-1 nor CRHR-2 agonists altered potassium current density in GnRH neurons from OVX + E mice. Further, neither CRH nor receptor-specific agonists altered action potential generation in response to current injection in GnRH neurons from OVX + E mice. To test the possible indirect actions, GABAergic postsynaptic currents were monitored. A CRHR-1 agonist increased GABAergic transmission frequency to GnRH neurons from OVX + E, but not OVX, mice, whereas a CRHR-2 agonist had no effect. Finally, we tested if CRH alters the firing rate of arcuate kisspeptin neurons, which provide an important excitatory neuromodulatory input to GnRH neurons. CRH did not acutely alter firing activity of these neurons from OVX, OVX + E or OVX + low E mice. These results suggest CRH increases GnRH neuron activity in an estradiol-dependent manner in part by activating GABAergic afferents. Mechanisms underlying inhibitory effects of CRH remain unknown.

Roles for androgens in mediating the sex differences of neuroendocrine and behavioral stress responses.

Estradiol and testosterone are powerful steroid hormones that impact brain function in numerous ways. During development, these hormones can act to program the adult brain in a male or female direction. During adulthood, gonadal steroid hormones can activate or inhibit brain regions to modulate adult functions. Sex differences in behavioral and neuroendocrine (i.e., hypothalamic pituitary adrenal (HPA) axis) responses to stress arise as a result of these organizational and activational actions. The sex differences that are present in the HPA and behavioral responses to stress are particularly important considering their role in maintaining homeostasis. Furthermore, dysregulation of these systems can underlie the sex biases in risk for complex, stress-related diseases that are found in humans. Although many studies have explored the role of estrogen and estrogen receptors in mediating sex differences in stress-related behaviors and HPA function, much less consideration has been given to the role of androgens. While circulating androgens can act by binding and activating androgen receptors, they can also act by metabolism to estrogenic molecules to impact estrogen signaling in the brain and periphery. This review focuses on androgens as an important hormone for modulating the HPA axis and behaviors throughout life and for setting up sex differences in key stress regulatory systems that could impact risk for disease in adulthood. In particular, impacts of androgens on neuropeptide systems known to play key roles in HPA and behavioral responses to stress (corticotropin-releasing factor, vasopressin, and oxytocin) are discussed. A greater knowledge of androgen action in the brain is key to understanding the neurobiology of stress in both sexes.

Sex-dependent effects of chronic variable stress on discrete corticotropin-releasing factor receptor 1 cell populations.

Anxiety and depression are strikingly more prevalent in women compared with men. Dysregulation of corticotropin-releasing factor (CRF) binding to its cognate receptor (CRFR1) is thought to play a critical role in the etiology of these disorders. In the present study, we investigated whether there were sex differences in the effects of chronic variable stress (CVS) on CRFR1 cells using CRFR1-GFP reporter mice experiencing a 9-day CVS paradigm. Brains were collected from CVS and stress naïve female and male mice following exposure to the open field test. This CVS paradigm effectively increased anxiety-like behavior in female and male mice. In addition, we assessed changes in activation of CRFR1 cells (co-localization with c-Fos and phosphorylated CREB (pCREB)) in stress associated brain structures, including two sexually dimorphic CRFR1 cell groups in the anteroventral periventricular nucleus (AVPV/PeN; F>M) and paraventricular hypothalamus (PVN; M>F). CVS increased CRFR1-GFP cell number as well as the number of CRFR1/pCREB co-expressing cells in the female but not male AVPV/PeN. In the PVN, the number of CRFR1/pCREB co-expressing cells was overall greater in males regardless of treatment and CVS resulted in a male-specific reduction of CRFR1/c-Fos cells. In addition, CVS induced a female-specific reduction in CRFR1/c-Fos cells within the anteroventral bed nucleus of the stria terminalis and both sexes exhibited a reduction in CRFR1/c-Fos co-expressing cells following CVS within the ventral basolateral amygdala. Overall, these sex-specific effects of CVS on CRFR1 populations may have implications for sex differences in stress-induction of mood disorders.

A sexually dimorphic distribution of corticotropin-releasing factor receptor 1 in the paraventricular hypothalamus.

Sex differences in neural structures are generally believed to underlie sex differences reported in anxiety, depression, and the hypothalamic-pituitary-adrenal axis, although the specific circuitry involved is largely unclear. Using a corticotropin-releasing factor receptor 1 (CRFR1) reporter mouse line, we report a sexually dimorphic distribution of CRFR1 expressing cells within the paraventricular hypothalamus (PVN; males > females). Relative to adult levels, PVN CRFR1-expressing cells are sparse and not sexually dimorphic at postnatal days 0, 4, or 21. This suggests that PVN cells might recruit CRFR1 during puberty or early adulthood in a sex-specific manner. The adult sex difference in PVN CRFR1 persists in old mice (20-24 months). Adult gonadectomy (6 weeks) resulted in a significant decrease in CRFR1-immunoreactive cells in the male but not female PVN. CRFR1 cells show moderate co-expression with estrogen receptor alpha (ERα) and high co-expression with androgen receptor, indicating potential mechanisms through which circulating gonadal hormones might regulate CRFR1 expression and function. Finally, we demonstrate that a psychological stressor, restraint stress, induces a sexually dimorphic pattern of neural activation in PVN CRFR1 cells (males >females) as assessed by co-localization with the transcription/neural activation marker phosphorylated CREB. Given the known role of CRFR1 in regulating stress-associated behaviors and hormonal responses, this CRFR1 PVN sex difference might contribute to sex differences in these functions.

Stress-induced neural activation is altered during early withdrawal from chronic methamphetamine.

Chronic methamphetamine (MA) use can lead to increased symptoms of depression and anxiety during abstinence. Less is known about the specific brain regions that are altered following repeated MA that may be associated with these behavioral perturbations. Furthermore, MA has been reported to recruit and activate microglia in the brain, which may exacerbate stress-associated behavioral changes. In the present study, male and female mice were injected with MA (5 mg/kg) or saline once daily for 10 days, and during early withdrawal were assessed for alterations in immediate early gene (c-Fos) responses to a forced swim stressor. Chronic MA exposure increased floating and decreased swim time in the forced swim test in male and female mice tested 48 h after the final dose, indicating elevated depressive-like behavior. Furthermore, assessment of nest building, a measure of distress or despair-like behavior, revealed a sex-specific effect with only MA-treated females showing impairments. The c-Fos response to forced swim was attenuated by prior MA exposure in the central amygdala, CA3 hippocampal region, prefrontal cortex, and bed nucleus of the stria terminalis (BST). In the BST this attenuation occurred only in males. Neither the total number of microglia or activated microglia were altered by chronic MA exposure in regions examined. The primary findings indicate that chronic MA exposure attenuates activation of select stress-associated brain regions, a dysregulation that might contribute to alterations in mood-related behaviors.

Correction: ApoE2 Exaggerates PTSD-Related Behavioral, Cognitive, and Neuroendocrine Alterations.

Following the publication of this article the authors noted an error in figure 4. In sub-panels D-F, the y-axis should read "apoE (ng/mg protein)" as opposed to "apoE (ng/ml)". The authors apologize for any inconvenience caused.

Characterization and gonadal hormone regulation of a sexually dimorphic corticotropin-releasing factor receptor 1 cell group.

Corticotropin-releasing factor binds with high affinity to CRF receptor 1 (CRFR1) and is implicated in stress-related mood disorders such as anxiety and depression. Using a validated CRFR1-green fluorescent protein (GFP) reporter mouse, our laboratory recently discovered a nucleus of CRFR1 expressing cells that is prominent in the female rostral anteroventral periventricular nucleus (AVPV/PeN), but largely absent in males. This sex difference is present in the early postnatal period and remains dimorphic into adulthood. The present investigation sought to characterize the chemical composition and gonadal hormone regulation of these sexually dimorphic CRFR1 cells using immunohistochemical procedures. We report that CRFR1-GFP-ir cells within the female AVPV/PeN are largely distinct from other dimorphic cell populations (kisspeptin, tyrosine hydroxylase). However, CRFR1-GFP-ir cells within the AVPV/PeN highly co-express estrogen receptor alpha as well as glucocorticoid receptor. A single injection of testosterone propionate or estradiol benzoate on the day of birth completely eliminates the AVPV/PeN sex difference, whereas adult gonadectomy has no effect on CRFR1-GFP cell number. These results indicate that the AVPV/PeN CRFR1 is regulated by perinatal but not adult gonadal hormones. Finally, female AVPV/PeN CRFR1-GFP-ir cells are activated following an acute 30-min restraint stress, as assessed by co-localization of CRFR1-GFP cells with phosphorylated (p) CREB. CRFR1-GFP/pCREB cells were largely absent in the male AVPV/PeN. Together, these data indicate a stress and gonadal hormone responsive nucleus that is unique to females and may contribute to sex-specific stress responses.