Colocalization of estrogen receptor alpha and NMDA-2D mRNAs in amygdaloid and hypothalamic nuclei of the mouse brain

Sexual differentiation of estrogen receptor alpha subpopulations in the ventromedial nucleus of the hypothalamus

Estrogen receptor (ER) α-expressing neurons in the ventrolateral area of the ventromedial hypothalamus (VMHvl) are implicated in the control of many behaviors and physiological processes, some of which are sex-specific. Recently, three sex-differentiated ERα subpopulations have been discovered in the VMHvl marked by co-expression with tachikinin1 (Tac1), reprimo (Rprm), or prodynorphin (Pdyn), that may subserve specific functions. These markers show sex differences in adulthood: females have many more Tac1/Esr1 and Rprm/Esr1 co-expressing cells, while males have more Pdyn/Esr1 cells. In this study, we sought to understand the development of these sex differences and pinpoint the sex-differentiating signal. We examined developmental changes in the number of Esr1 cells co-expressing Tac1, Rprm or Pdyn using single-molecule in situ hybridization. We found that both sexes have similarly high numbers of Tac1/Esr1 and Rprm/Esr1 cells at birth, but newborn males have many more Pdyn/Esr1 cells than females. However, the number of cells with Tac1/Esr1 and Rprm/Esr1 co-expression markedly decreases by weaning in males, but not females, leading to sex differences in neurochemical expression. Female mice administered testosterone at birth have expression patterns akin to male mice. Thus, a substantial neurochemical reorganization of the VMHvl occurs in males between birth and weaning that likely underlies the previously reported sex differences in behavioral and physiological responses to estrogens in adulthood.

Subregional Differences in Alcohol Modulation of Central Amygdala Neurocircuitry

Alcohol use disorder is a highly significant medical condition characterized by an impaired ability to stop or control alcohol use, compulsive alcohol seeking behavior, and withdrawal symptoms in the absence of alcohol. Understanding how alcohol modulates neurocircuitry critical for long term and binge-like alcohol use, such as the central amygdala (CeA), may lead to the development of novel therapeutic strategies to treat alcohol use disorder. In clinical studies, reduction in the volume of the amygdala has been linked with susceptibility to relapse to alcohol use. Preclinical studies have shown the involvement of the CeA in the effects of alcohol use, with lesions of the amygdala showing a reduction in alcohol drinking, and manipulations of cells in the CeA altering alcohol drinking. A great deal of work has shown that acute alcohol, as well as chronic alcohol exposure via intake or dependence models, alters glutamatergic and GABAergic transmission in the CeA. The CeA, however, contains heterogeneous cell populations and distinct subregional differences in neurocircuit architecture which may influence the mechanism by which alcohol modulates CeA function overall. The current review aimed to parse out the differences in alcohol effects on the medial and lateral subregions of the CeA, and what role neuroinflammatory cells and markers, the endocannabinoid system, and the most commonly studied neuropeptide systems play in mediating these effects. A better understanding of alcohol effects on CeA subregional cell type and neurocircuit function may lead to development of more selective pharmacological interventions for alcohol use disorder.

Targeted sequencing of the LRRTM gene family in suicide attempters with bipolar disorder

Glutamatergic signaling is the primary excitatory neurotransmission pathway in the brain, and its relationship to neuropsychiatric disorders is of considerable interest. Our previous attempted suicide genome-wide association study, and numerous studies investigating gene expression, genetic variation, and DNA methylation have implicated aberrant glutamatergic signaling in suicide risk. The glutamatergic pathway gene LRRTM4 was an associated gene identified in our attempted suicide genome-wide association study, with association support seen primarily in females. Recent evidence has also shown that glutamatergic signaling is partly regulated by sex-related hormones. The LRRTM gene family encodes neuronal leucine-rich transmembrane proteins that localize to and promote glutamatergic synapse development. In this study, we sequenced the coding and regulatory regions of all four LRRTM gene members plus a large intronic region of LRRTM4 in 476 bipolar disorder suicide attempters and 473 bipolar disorder nonattempters. We identified two male-specific variants, one female- and five male-specific haplotypes significantly associated with attempted suicide in LRRTM4. Furthermore, variants within significant haplotypes may be brain expression quantitative trait loci for LRRTM4 and some of these variants overlap with predicted hormone response elements. Overall, these results provide supporting evidence for a sex-specific association of genetic variation in LRRTM4 with attempted suicide.

CB1 and ethanol effects on glutamatergic transmission in the central amygdala of male and female msP and Wistar rats

The central amygdala (CeA) is involved in the processing of anxiety and stress and plays a role in ethanol consumption. Chronic ethanol recruits stress systems in the CeA, leading to aversive withdrawal symptoms. Although primarily GABAergic, CeA contains glutamatergic afferents, and we have reported inhibitory effects of ethanol on locally evoked glutamatergic responses in CeA of Wistar and Marchigian Sardinian alcohol-preferring (msP) rats. Notably, msP rats display enhanced anxiety, stress and alcohol drinking, simulating the alcohol-dependent phenotype. Endocannabinoids are also involved in regulation of stress, and we previously demonstrated that cannabinoid receptor type 1 (CB₁ ) activation decreases CeA GABAergic signaling and blocks ethanol enhancement of GABAergic signaling. Here, we sought to investigate the effects of CB₁ activation (WIN 55,212-2; Win) and antagonism (AM251) with and without acute ethanol on glutamatergic synapses in CeA of female and male Wistar and msP rats. Using intracellular sharp pipette electrophysiology, we examined the effects of CB₁ compounds on locally evoked excitatory postsynaptic potentials (EPSPs) in CeA and compared effects between strains, gender and estrous cycle. Acute ethanol decreased EPSP amplitudes in Wistars, and in male but not female msPs. Win decreased EPSP amplitudes in msPs, and in male but not female Wistars. Combined application of Win and ethanol resulted in strain-specific effects in female rats. We found no tonic CB₁ signaling at glutamatergic synapses in CeA of any groups, and no interaction with ethanol. Collectively, these observations demonstrate sex-strain-specific differences in ethanol and endocannabinoid effects on CeA glutamatergic signaling.

Central amygdalar nucleus treated with orexin neuropeptides evoke differing feeding and grooming responses in the hamster

Interaction of the orexinergic (ORXergic) neuronal system with the excitatory (glutamate, l-Glu) or the inhibitory (GABA) neurosignaling complexes evokes major homeostatic physiological events. In this study, effects of the two ORXergic neuropeptides (ORX-A/B) on their receptor (ORX-2R) expression changes were correlated to feeding and grooming actions of the hibernating hamster (Mesocricetus auratus). Infusion of the central amygdala nucleus (CeA) with ORX-A caused hamsters to consume notable quantities of food, while ORX-B accounted for a moderate increase. Interestingly the latter neuropeptide was responsible for greater frequencies of grooming with respect to both controls and the hamsters treated with ORX-A. These distinct behavioral changes turned out to be even greater in the presence of l-Glu agonist (NMDA) while the α1 GABAA receptor agonist (zolpidem, Zol) greatly reduced ORX-A-dependent feeding bouts. Moreover, ORX-A+NMDA mainly promoted greater ORX-2R expression levels with respect to ORX-A-treated hamsters while ORX-B+Zol was instead largely responsible for a down-regulatory trend. Overall, these features point to CeA ORX-2R sites as key sensory limbic elements capable of regulating eating and grooming responses, which may provide useful insights regarding the type of molecular mechanism(s) operating during feeding bouts.

Organization of Estrogen-Associated Circuits in the Mouse Primary Auditory Cortex

Sex steroid hormones influence the perceptual processing of sensory signals in vertebrates. In particular, decades of research have shown that circulating levels of estrogen correlate with hearing function. The mechanisms and sites of action supporting this sensory-neuroendocrine modulation, however, remain unknown. Here we combined a molecular cloning strategy, fluorescence in-situ hybridization and unbiased quantification methods to show that estrogen-producing and -sensitive neurons heavily populate the adult mouse primary auditory cortex (AI). We also show that auditory experience in freely-behaving animals engages estrogen-producing and -sensitive neurons in AI. These estrogen-associated networks are greatly stable, and do not quantitatively change as a result of acute episodes of sensory experience. We further demonstrate the neurochemical identity of estrogen-producing and estrogen-sensitive neurons in AI and show that these cell populations are phenotypically distinct. Our findings provide the first direct demonstration that estrogen-associated circuits are highly prevalent and engaged by sensory experience in the mouse auditory cortex, and suggest that previous correlations between estrogen levels and hearing function may be related to brain-generated hormone production. Finally, our findings suggest that estrogenic modulation may be a central component of the operational framework of central auditory networks.

The effects of glutamate receptor agonists and antagonists on mouse hypothalamic and hippocampal neuronal activity shown through manganese enhanced MRI

Manganese enhanced MRI (MEMRI) is an imaging paradigm that can be used to assess neuronal activity in vivo. Here we investigate, through the use of MEMRI, the influence of receptor dynamics on neuronal activity in the hypothalamus and hippocampus focusing on the glutamate receptor signalling system. We demonstrate that intraperitoneal (i.p.) administration of monosodium glutamate (MSG) and the ionotropic glutamate receptor (iGluR) agonists NMDA and AMPA resulted in significantly increased signal intensity (SI) in the arcuate nucleus (ARC), the suprachiasmatic nucleus (SCN) and the CA3 region of the hippocampus of mice consistent with increased neuronal activity. Administration of the NMDA receptor antagonist MK-801 resulted in significantly decreased SI in the paraventricular nucleus (PVN) consistent with decreased neuronal activity. Co-administration of MSG and the AMPA receptor antagonist NBQX attenuated the increase in SI observed in the ARC from MSG alone, suggesting MEMRI may be applicable to the study of receptor dynamics in vivo. We also observed that administration of the various iGluR agonists and antagonists modulated SI in the lateral ventricle and that high dose MSG (300 mg) caused a hitherto unseen enhancement in SI in the entire cortical/subarachnoid region. In conclusion, MEMRI reveals changes in neuronal activity in response to iGluR agonists and antagonists in the CNS in vivo as well as revealing multifaceted effects beyond those attributable to neuronal activity alone.

Distinct α subunit variations of the hypothalamic GABAA receptor triplets (αβγ) are linked to hibernating state in hamsters

Background

The structural arrangement of the γ-aminobutyric acid type A receptor (GABA_AR) is known to be crucial for the maintenance of cerebral-dependent homeostatic mechanisms during the promotion of highly adaptive neurophysiological events of the permissive hibernating rodent, i.e the Syrian golden hamster. In this study, in vitro quantitative autoradiography and in situ hybridization were assessed in major hypothalamic nuclei. Reverse Transcription Reaction-Polymerase chain reaction (RT-PCR) tests were performed for specific GABA_AR receptor subunit gene primers synthases of non-hibernating (NHIB) and hibernating (HIB) hamsters. Attempts were made to identify the type of αβγ subunit combinations operating during the switching ON/OFF of neuronal activities in some hypothalamic nuclei of hibernators.

Results

Both autoradiography and molecular analysis supplied distinct expression patterns of all α subunits considered as shown by a strong (p < 0.01) prevalence of α₁ ratio (over total α subunits considered in the present study) in the medial preoptic area (MPOA) and arcuate nucleus (Arc) of NHIBs with respect to HIBs. At the same time α₂ subunit levels proved to be typical of periventricular nucleus (Pe) and Arc of HIB, while strong α₄ expression levels were detected during awakening state in the key circadian hypothalamic station, i.e. the suprachiasmatic nucleus (Sch; 60%). Regarding the other two subunits (β and γ), elevated β₃ and γ₃ mRNAs levels mostly characterized MPOA of HIBs, while prevalently elevated expression concentrations of the same subunits were also typical of Sch, even though this time during the awakening state. In the case of Arc, notably elevated levels were obtained for β₃ and γ₂ during hibernating conditions.

Conclusion

We conclude that different αβγ subunits are operating as major elements either at the onset of torpor or during induction of the arousal state in the Syrian golden hamster. The identification of a brain regional distribution pattern of distinct GABA_AR subunit combinations may prove to be very useful for highlighting GABAergic mechanisms functioning at least during the different physiological states of hibernators and this may have interesting therapeutic bearings on neurological sleeping disorders.

An ex vivo multi-electrode approach to evaluate endogenous hormones and receptor subtype pharmacology on evoked and spontaneous neuronal activity within the ventromedial hypothalamus; translation from female receptivity

INTRODUCTION

The ventromedial hypothalamus (VMH) controls female rodent copulatory behavior, which can be modulated by injection of various compounds into the VMH. Aim. The aim was to determine whether evoked excitatory postsynaptic potentials (EPSPs) or single-unit activity within the VMH ex vivo is a better parameter to predict lordosis.

METHODS

VMH slices were placed onto a 64 microelectrode chip and spontaneous single-unit activity was recorded or slices stimulated to evoke EPSPs.

MAIN OUTCOME MEASURES

The sodium channel blocker, tetrodotoxin and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX) inhibited EPSPs, confirming EPSPs were glutamatergic in origin. The GABA(A) antagonist bicuculline potentiated EPSPs implying endogenous GABA tone. Single-unit activity was abolished by tetrodotoxin but unaffected by DNQX or bicuculline.

RESULTS

Glutamatergic neurotransmission was greatest during metestrous and following ovariectomization. The number of regions within the VMH eliciting single-unit activity was reduced following ovariectomy without changing spike frequency. Adrenergic agents increasing lordosis via the VMH in vivo, decreased glutamate neurotransmission but increased single-unit activity. Conversely, agents decreasing lordosis via the VMH increased glutamatergic neurotransmission and inhibited single-unit activity (8-OH-DPAT, [D-Ala(2), N-Me-Phe(4), Gly-ol(5)]-enkephalin, corticotropin releasing factor, bicuculline). Melanocortin and pituitary adenylate cyclase-activating polypeptide agonists had no effect.

CONCLUSIONS

Here we present a novel, robust VMH in vitro technique that (i) is consistent with the hypothesis that glutamate via non-NMDA receptors inhibits lordosis; (ii) glutamate is under the endogenous tone of GABA and steroid hormones; (iii) inhibition of lordosis during metestrous and following ovariectomy potentiates glutamatergic neurotransmission; (iv) activation of G(q)- and G(i)-coupled receptors decreases and increases glutamate neurotransmission, respectively, with an inverse correlation on single-unit activity; (v) activation of G(s)-coupled receptors has no direct effect on glutamate or single-unit activity; and (vi) potency, receptor subtypes and localization can be determined prior to in vivo studies.

Estrogen regulates the expression of N-methyl-D-aspartate (NMDA) receptor subunit epsilon 4 (Grin2d), that is essential for the normal sexual behavior in female mice

Estrogen plays important roles in the reproductive behavior of animals. In the present study, we found that the Grin2d gene of mouse possessed half-sites of the estrogen-responsive element (ERE) in the 3'-untranslated region (UTR). Quantitative PCR analysis showed that the reduced Grin2d mRNA expression in the hypothalamus of the ovariectomized mice was restored by estrogen administration. Downregulation of Grin2d mRNA expression was also detected in the hypothalamus of estrogen receptor alpha-knockout female mice. Moreover, estrogen-induced lordosis response was decreased in Grin2d-knockout mice. These results suggest that estrogen regulates lordosis behavior through the regulation of Grin2d expression in the hypothalamus of female mice.

Isoflurane anesthesia interferes with the expression of cocaine-induced sensitization in female rats

Repeated cocaine administration results in a progressive sensitization of behavior which typically occurs more readily in female rats than in males. Our recent studies of rats undergoing surgical procedures revealed that following anesthesia, females sensitized less than males receiving identical repeated cocaine injections. Since isoflurane acts primarily by increasing the effects of the inhibitory neurotransmitter gamma-amino butyric acid (GABA) and reducing the effects of the excitatory amino acid glutamate, these amino acids may play more prominent roles in sensitization to cocaine in females than previously understood. In order to examine the effects of isoflurane on cocaine-sensitization, we administered cocaine (15 mg/kg i.p) or saline to adult male and female Sprague-Dawley rats for 9 days; on day 10, half of the rats were subjected to isoflurane anesthesia and the other half did not receive anesthesia. On day 11, rats were given their last dose of either cocaine or saline. We recorded behaviors for 1h on days 1, 9 and 11. Locomotor activity and stereotyped behaviors were quantified using photo beam monitors and the scoring of video tapes, respectively. Results indicated that a single exposure to isoflurane significantly dampens the stereotypic behavior associated with repeated cocaine administration in females but not in males. They further suggest that either GABA or glutamate play more prominent roles in cocaine-sensitization behavior in females than in males.

Estradiol replacement enhances sleep deprivation-induced c-Fos immunoreactivity in forebrain arousal regions of ovariectomized rats

To understand how female sex hormones influence homeostatic mechanisms of sleep, we studied the effects of estradiol (E2) replacement on c-Fos immunoreactivity in sleep/wake-regulatory brain areas after sleep deprivation (SD) in ovariectomized rats. Adult rats were ovariectomized and implanted subcutaneously with capsules containing 17β-E2(10.5 μg; to mimic diestrous E2levels) or oil. After 2 wk, animals with E2capsules received a single subcutaneous injection of 17β-E2(10 μg/kg; to achieve proestrous E2levels) or oil; control animals with oil capsules received an oil injection. Twenty-four hours later, animals were either left undisturbed or sleep deprived by “gentle handling” for 6 h during the early light phase, and killed. E2treatment increased serum E2levels and uterus weights dose dependently, while attenuating body weight gain. Regardless of hormonal conditions, SD increased c-Fos immunoreactivity in all four arousal-promoting areas and four limbic and neuroendocrine nuclei studied, whereas it decreased c-Fos labeling in the sleep-promoting ventrolateral preoptic nucleus (VLPO). Low and high E2treatments enhanced the SD-induced c-Fos immunoreactivity in the laterodorsal subnucleus of the bed nucleus of stria terminalis and the tuberomammillary nucleus, and in orexin-containing hypothalamic neurons, with no effect on the basal forebrain and locus coeruleus. The high E2treatment decreased c-Fos labeling in the VLPO under nondeprived conditions. These results indicate that E2replacement modulates SD-induced or spontaneous c-Fos expression in sleep/wake-regulatory and limbic forebrain nuclei. These modulatory effects of E2replacement on neuronal activity may be, in part, responsible for E2's influence on sleep/wake behavior.

Oestradiol up-regulates glutamine synthetase mRNA and protein expression in the hypothalamus and hippocampus: implications for a role of hormonally responsive glia in amino acid neurotransmission

Rapidly emerging evidence suggests that glial cells in the central nervous system are sensitive to oestrogen actions. However, the functional consequences of the cellular mechanisms of these cells have proven difficult to study in vivo because of the intimate relationships between neurones and glia. Microarray technology offers the potential to uncover steroid hormone regulation of glial-specific genes that may play a role in hormone-dependent neuronal-glial interactions. Analysis of transcriptomes from the medial basal hypothalamus (MBH) of oestradiol and vehicle-treated adult ovariectomised mice revealed an up-regulation of several glial specific genes by oestradiol, including glutamine synthetase (GS), which facilitates the conversion of glutamate to glutamine and plays an integral role in amino acid neurotransmission. In situ hybridisation confirmed that oestradiol treatment resulted in an up-regulation of GS gene expression in the arcuate and ventromedial nuclei of the MBH, as well as the medial amygdala and hippocampus. Moreover, oestradiol increased protein expression of GS in both the MBH and hippocampus. Neurones are incapable of de novo net synthesis of glutamate from glucose and are dependent on glial-provided precursors such as glutamine to renew their amino acid transmitter pools. Thus, oestradiol induced expression of GS suggests a significant role for glial cells in hormonal modulation of glutamatergic neurotransmission important to female reproductive behaviours, neuroendocrine physiology and cognitive functions.

CNS arousal mechanisms bearing on sex and other biologically regulated behaviors

It now seems possible to move beyond analyzing only the mechanisms for specific sexual behaviors to the analysis of 'generalized arousal' that underlies all motivated behaviors. Our science has advanced sufficiently to attack mechanisms linking specific motivations to these general arousal mechanisms that intrinsically activate all biologically-regulated behaviors including ingestive behaviors. Learning from the well-developed reproductive behavior paradigm, we know that sex hormone effects on hypothalamic neurons have been studied to a point where receptor mechanisms are relatively well understood, a neural circuit for a sex steroid-dependent behavior has been worked out, and several functional genomic regulations have been discovered. Here we focus for the first time on three chemical systems that signal 'generalized arousal' and which impact hormone-dependent hypothalamic neurons of importance to sexual arousal: histamine, norepinephrine and enkephalin. Progress in linking generalized arousal to specific motivational mechanisms is reviewed.

Anxiolytic property of estrogen related to the changes of the monoamine levels in various brain regions of ovariectomized rats

Anxiety is a symptom reflecting the dysregulation of monoaminergic neurotransmitters which may be modulated by estrogen. In our current study, we investigated the effects of chronic estrogen administration (10 microg/kg, s.c. for 4 weeks) on anxiety-like behavior using the elevated plus-maze with the corresponding changes of monoamines in the brain regions contributing to anxiety. The behavioral test revealed that estrogen-treated rats (Ovx+E(2)) spent more time in the open arm of the maze as well as a higher time/entry ratio in open arms than ovariectomized (Ovx) rats, indicating an anxiolytic property of estrogen. The increase in open arm time corresponded to an increase in uterine weight, indicated a correlation between the function of estrogen and its anxiolytic effect. Measurements of brain monoamines following estrogen treatment revealed decreases in norepinephrine, dopamine and serotonin in all of the brain regions studied, which also lead to an increase in turnover rates. The concentrations of norepinephrine in caudate putamen, of dopamine in nucleus accumbens, of serotonin in frontal cortex, hippocampus, caudate putamen, nucleus accumbens, and substantia nigra and of the serotonin metabolite, the 5-hydroxyindolacetic acid in substantia nigra of Ovx+E(2) rats were significantly lower than those of Ovx rats. Interestingly, the uterine weight was negatively correlated with the changes of dopamine and serotonin (with the exception of the hippocampus), suggesting a regulatory role of estrogen on these systems. From these data, we concluded that, in fact, there is a relationship between estrogen and monoamines (i.e. serotonin, dopamine) in modulating the anxiety-like behaviors in female rats.

Functional genomics of sex hormone-dependent neuroendocrine systems: specific and generalized actions in the CNS

Sex hormone effects on hypothalamic neurons have been worked out to a point where receptor mechanisms are relatively well understood, a neural circuit for a sex steroid-dependent behavior has been determined, and several functional genomic regulations have been discovered and conceptualized. With that knowledge in hand, we approach deeper problems of explaining sexual arousal and generalized CNS arousal. After a brief summary of arousal mechanisms, we focus on three chemical systems which signal generalized arousal and impact hormone-dependent hypothalamic neurons of behavioral importance: histamine, norepinephrine and enkephalin.

Estradiol modulation of astrocytic form and function: implications for hormonal control of synaptic communication

There is a growing appreciation for the importance of glial cells to overall brain function. For decades, glial cells have been considered relatively passive supporters of nerve cell function, providing only structural and metabolic support to the communicating neurons. Now, rapidly emerging evidence demonstrates that glial cells are active participants in the processes of synaptic patterning and synaptic transmission. Like their neuronal neighbors residing in steroid sensitive brain regions, glial cells demonstrate a responsiveness to gonadal steroids that has been best characterized by physical changes in their morphology. However, because of their intimate relationship, the nature of neuronal-glial interactions has been challenging to study in vivo and until recently, the functional relevance of steroid-induced changes in glial morphology to neuroendocrine functions could only be implied from anatomical and in vitro studies. The advent of microarray technology offers the potential to uncover steroid regulation of glial-specific genes that may play a role in hormone-dependent neuronal-glial interactions. Our microarray analysis of the rodent hypothalamus has revealed that estradiol increases the expression of a number of glial-specific genes, including glutamine synthetase, an enzyme that inactivates glutamate through its conversion to glutamine. Given that glutamine is the predominant precursor for releasable pools of glutamate, our observation that estradiol increases glutamine synthetase gene and protein expression suggests that hormonal regulation of glutamate neurotransmission involves hormonally responsive glia. Thus, hormonally responsive glia may play a pivotal role in estradiol-mediated synaptic transmission underlying neuroendocrine function.

The endocrine disruptor atrazine accounts for a dimorphic somatostatinergic neuronal expression pattern in mice

It has now been established that a large number of man-made and natural chemicals are capable of interfering with the action of natural hormones. In this category "endocrine disruptors" such as the herbicide atrazine, when administered at ecological low doses (1 or 100 microg/kg per day) from gestational day 14 to postnatal day 21, provided a clear dimorphic neurodegenerative pattern in some brain areas of the domestic mouse (Mus musculus). Indeed, the high concentration (100 microg/kg per day) with respect to the low concentration (1 microg/kg per day) induced relevant neuronal damage in extrahypothalamic sites, such as the cortical and striatal areas in both sexes. Marked alterations in other areas, including the hippocampal and hypothalamic nuclei, were mostly typical of the female. At the neuronal level, the neuropeptide somatostatin, specific for the secretion of growth hormone, seemed to be a major target of atrazine effects, as demonstrated by evident subtype2,3,5 receptor mRNA differences of this neuropeptide, at least for the first two subtypes. In particular, a very strong (p < 0.001) upregulation of subtype2 expressing neurons was detected in female hypothalamic areas, specifically the suprachiasmatic nucleus, whereas a similar downregulatory trend was reported for some extrahypothalamic areas such as the striatum. Interestingly, very strong upregulatory and downregulatory actions were detected for neurons expressing subtype3 in male hypothalamic and amygdalar regions and in the cortical and hippocampal areas, respectively. Overall, it appears that these first neurotoxicological effects of atrazine are very likely linked to dimorphic expression patterns of specific somatostatin subtypes in discrete but key hypothalamic and extrahypothalamic areas of Mus musculus.

Glutamatergic stimulation of the medial amygdala induces steroid dependent c-fos expression within forebrain nuclei responsive to mating stimulation

Neurons within the posterodorsal medial amygdala of female rats are known to process vaginocervical stimulation received during mating through N-methyl-D-aspartate channel activation, conveying information to downstream hypothalamic cell groups that modulate neuroendocrine function. Stimulation of these neurons with an excitatory amino acid cocktail of glutamate, aspartate and glycine initiates 10-12 days of prolactin surge secretion that normally are observed only after the receipt of vaginocervical stimulation. Posterodorsal medial amygdala neurons responsive to vaginocervical stimulation also contain estrogen and progesterone receptors. The present experiment examined which downstream sites involved in prolactin secretion show c-fos expression following glutamate receptor activation within the posterodorsal medial amygdala and whether ovarian steroids influence cellular activation in these areas. Ovariectomized female rats implanted with unilateral cannulas directed at the posterodorsal medial amygdala received injections of estradiol benzoate and progesterone or oil before infusion treatment with either excitatory amino acid or control PBS. An additional group of estradiol benzoate+progesterone-treated females was infused with 1.0 microM glycine alone in PBS. Infusions were administered three times at 30 min intervals. FOS induction 90 min after infusion was determined immunohistochemically on the sides ipsilateral and contralateral to the infusion. Of the examined regions, excitatory amino acid treatment and hormone treatment induced three patterns of c-fos expression: 1) responses to both excitatory amino acid and hormone treatment [posterodorsal medial amygdala, medial preoptic area, ventrolateral ventromedial hypothalamic nucleus, bed nucleus of the stria terminalis]; 2) responses to estradiol benzoate+progesterone treatment only [anteroventral periventricular nucleus and dorsomedial nucleus]; and 3) responses to excitatory amino acid only [arcuate nucleus, suprachiasmatic nucleus, and paraventricular nucleus]. These data identify possible circuits by which vaginocervical stimulation, via activation of posterodorsal medial amygdala glutamate-type receptors, initiates and coordinates a series of events within a larger neuroendocrine circuit important for pregnancy.

The Histaminergic Signaling System Exerts a Neuroprotective Role against Neurodegenerative-Induced Processes in the Hamster

The neurotoxic 3-nitropropionic acid (3-NP), a freckled milk vetch-derived inhibitor of mitochondrial enzymatic processes that is capable of mimicking the typical pathological features of neurodegenerative disorders, behaved in a differentiated manner in a hibernating rodent (hamster) with respect to a nonhibernating rodent (rat). Treatment of the two rodents with both an acute and chronic 3-NP dose supplied deleterious neuronal effects due to distinct histamine receptor (H(n)R) transcriptional activities, especially in the case of the rat. In hamsters, these treatment modalities accounted for overall reduced global activity in a freely moving environment and overt motor symptoms such as hindlimb dystonia and clasping with respect to the greater abnormal motor behaviors in rats. This behavioral difference appeared to be strongly related to qualitative fewer neuronal alterations and, namely, lesser crenated cell membranes, swollen mitochondria, and darkened nuclei in hamster brain areas. Moreover, a mixed H(1,3)R mRNA expression pattern was reported for both rodents treated with a chronic 3-NP dose as demonstrated by predominantly low H1R mRNA levels (>50%) in rat striatum and cortex, whereas extremely high H3R levels (>80%) characterized the lateral and central amygdala nuclei plus the striatum of hamsters. Interestingly, the H3R antagonist (thioperamide) blocked 3-NP-dependent behaviors plus induced an up-regulation of H1R levels in mainly the above-reported hamster amygdalar nuclei. Overall, these results show, for the first time, that a major protective role against neurodegenerative events appears to be strongly related to the expression activity of H(1,3)R subtypes of amygdalar neurons in this hibernating model.

Estrogen neuroprotection against the neurotoxic effects of ethanol withdrawal: potential mechanisms

Ethanol withdrawal (EW) produces substantial neurotoxic effects, whereas estrogen is neuroprotective. Given observations that both human and nonhuman female subjects often show less impairment following EW, it is reasonable to hypothesize that estrogens may protect females from the neurotoxic effects of ethanol. This article is based on the assumption that the behavioral deficits seen following EW are produced in part by neuronal death triggered by oxidative insults produced by EW. The EW leads to activation of protein kinase C, especially PKCepsilon, which subsequently triggers apoptotic downstream events such as phosphorylation of nuclear factor-kappaB (NFkappaB) complex. On phosphorylation, active NFkappaB translocates to the nucleus, binds to DNA, and activates caspases, which trigger DNA fragmentation and apoptosis. In contrast, estrogens are antioxidant, inhibit overexpression of PKCepsilon, and suppress expression of NFkappaB and caspases. Estrogen treatment reduces the behavioral deficits seen during EW and attenuates molecular signals of apoptosis. The effects of ethanol and estrogen on each step in the signaling cascade from ethanol exposure to apoptosis are reviewed, and potential mechanisms by which estrogen could produce neuronal protection against the neurotoxicity produced by EW are identified. These studies serve as a guide for continuing research into the mechanisms of the neuroprotective effects of estrogen during EW and for the development of potential estrogen-based treatments for male and female alcoholics.

Hormonal symphony: steroid orchestration of gene modules for sociosexual behaviors

Genes induced by estrogens in the mammalian forebrain influence a variety of neural functions. Among them, reproductive behavior mechanisms are very well understood. Their functional genomics provide a theoretical paradigm for linking genes to neural circuits to behavior. We propose that estrogen-induced genes are organized in modules: Growth of hypothalamic neurons; Amplification of the estrogen effect by progesterone; Preparative behaviors; Permissive actions on sex behavior circuitry; and Synchronization of mating behavior with ovulation. These modules may represent mechanistic routes for CNS management of successful reproduction. Moreover, new microarray results add estrogen-dependent genes, including some expressed in glia, suggesting possible hormone-dependent neuronal/glial coordination.

Comparison of in vivo and in vitro subcellular localization of estrogen receptors alpha and beta in oligodendrocytes

The existence of estrogen receptors (ERs) in oligodendrocytes (OLGs) in vivo and in vitro is unresolved, as their presence has been reported in some studies and their absence in others. Using molecular and immunocytochemical techniques, we describe the subcellular localization of ERalpha and ERbeta in OLGs in vivo and in vitro. Both ERalpha and ERbeta are detected in an immortalized OLG cell line and in enriched OLG cultures by RT-PCR and western blot. Immunocytochemistry of OLGs from enriched cultures shows ERalpha receptors are nuclear, whereas ERbeta receptors are cytoplasmic. Confocal and deconvolution microscopy of enriched OLG cultures reveals ERbeta immunoreactivity is concentrated in perikarya and veins of OLG membrane sheets; lesser reactivity is present in their plasma membranes and nuclei. In vivo, we readily detect ERalpha in neurons but not in OLGs, even though we used different fixation procedures and different ERalpha antibodies. The presence of ERalpha in cultured OLGs may be due to culture media that contains factors stimulating ERalpha expression but are reduced in normal brain. In vivo, ERbeta immunoreactivity is readily detectable in OLG cytoplasm and in myelin sheaths. Incubation of glial cultures without or with increasing concentrations of 17beta-estradiol (E2) shows that E2 significantly accelerates OLG process formation.

Hormonal and genetic influences underlying arousal as it drives sex and aggression in animal and human brains

Estrogen treatment induces transcription and increases excitability and reproductive behavior. Estrogens provide the structural basis for increased synaptic activity and greater behavior-facilitating output. Administration of progesterone amplifies the effect of estrogens on mating behavior. The role of GnRH is to synchronize reproductive behavior with the ovulatory surge of LH. A causal connection can be charted from one individual gene to human social behavior, but only via six causal links. Glia, meninges and neurons may participate, under the influence of sex hormones, in the direction of sex behavior. Neural and genetic mechanisms for motivation may lead to biological understanding of functions that apply to the most primitive aspects of human mental functioning. With respect to aggression, besides testosterone and its metabolites, serotonergic projections to the forebrain play an important role.

Estrogen and thyroid hormone receptor interactions: physiological flexibility by molecular specificity

The influence of thyroid hormone on estrogen actions has been demonstrated both in vivo and in vitro. In transient transfection assays, the effects of liganded thyroid hormone receptors (TR) on transcriptional facilitation by estrogens bound to estrogen receptors (ER) display specificity according to the following: 1) ER isoform, 2) TR isoform, 3) the promoter through which transcriptional facilitation occurs, and 4) cell type. Some of these molecular phenomena may be related to thyroid hormone signaling of seasonal limitations upon reproduction. The various combinations of these molecular interactions provide multiple and flexible opportunities for relations between two major hormonal systems important for neuroendocrine feedbacks and reproductive behaviors.

Isoform specificity for oestrogen receptor and thyroid hormone receptor genes and their interactions on the NR2D gene promoter

Oestrogens are critical for the display of lordosis behaviour and, in recent years, have also been shown to be involved in synaptic plasticity. In the brain, the regulation of ionotropic glutamate receptors has consequences for excitatory neurotransmission. Oestrogen regulation of the N-methyl-d-aspartate receptor subunit 2D (NR2D) has generated considerable interest as a possible molecular mechanism by which synaptic plasticity can be modulated. Since more than one isoform of the oestrogen receptor (ER) exists in mammals, it is possible that oestrogen regulation via the ERalpha and ERbeta isoforms on the NR2D oestrogen response element (ERE) is not equivalent. In the kidney fibroblast (CV1) cell line, we show that in response to 17beta-oestradiol, only ERalpha, not ERbeta, could upregulate transcription from the ERE which is in the 3' untranslated region of the NR2D gene. When this ERE is in the 5' position, neither ERalpha nor ERbeta showed transactivation capacity. Thyroid hormone receptor (TR) modulation of ER mediated induction has been shown for other ER target genes, such as the preproenkephalin and oxytocin receptor genes. Since the various TR isoforms exhibit distinct roles, we hypothesized that TR modulation of ER induction may also be isoform specific. This is indeed the case. The TRalpha1 isoform stimulated ERalpha mediated induction from the 3'-ERE whereas the TRbeta1 isoform inhibited this induction. This study shows that isoforms of both the ER and TR have different transactivation properties. Such flexible regulation and crosstalk by nuclear receptor isoforms leads to different transcriptional outcomes and the combinatorial logic may aid neuroendocrine integration.