GABA receptors as broadcasters of sexually differentiating signals in the brain

Mechanisms of infantile epileptic spasms syndrome: What have we learned from animal models?

The devastating developmental and epileptic encephalopathy of infantile epileptic spasms syndrome (IESS) has numerous causes, including, but not limited to, brain injury, metabolic, and genetic conditions. Given the stereotyped electrophysiologic, age-dependent, and clinical findings, there likely exists one or more final common pathways in the development of IESS. The identity of this final common pathway is unknown, but it may represent a novel therapeutic target for infantile spasms. Previous research on IESS has focused largely on identifying the neuroanatomic substrate using specialized neuroimaging techniques and cerebrospinal fluid analysis in human patients. Over the past three decades, several animal models of IESS were created with an aim to interrogate the underlying pathogenesis of IESS, to identify novel therapeutic targets, and to test various treatments. Each of these models have been successful at recapitulating multiple aspects of the human IESS condition. These animal models have implicated several different molecular pathways in the development of infantile spasms. In this review we outline the progress that has been made thus far using these animal models and discuss future directions to help researchers identify novel treatments for drug-resistant IESS.

Hippocampal Metabolite Profiles in Two Rat Models of Autism: NMR-Based Metabolomics Studies

Autism spectrum disorders (ASDs) are increasingly being diagnosed. Hypotheses link ASD to genetic, epigenetic, or environmental factors. The role of oxidative stress and the imbalance between excitatory and inhibitory neurotransmission in the pathogenesis of ASD has been suggested. Rats in which ASD symptoms are induced by valproate (VPA) or thalidomide (THAL) application in utero are useful models in ASD studies. Our study investigated whether rats in ASD models show changes in metabolite levels in the brain consistent with the hypothetical pathomechanisms of ASD. Female rats were fed one dose of 800 mg/kg VPA or 500 mg/kg THAL orally on the 11th day of gestation, and 1-month offspring were used for the experiments. Metabolic profiles from proton nuclear magnetic resonance spectroscopy of hydrophilic and hydrophobic extracts of rat hippocampi were subjected to OPLS-DA statistical analysis. Large differences between both models in the content of several metabolites in the rat hippocampus were noticed. The following metabolic pathways were identified as being disturbed in both ASD models: steroid hormone biosynthesis; fatty acid biosynthesis; the synthesis and degradation of ketone bodies; glycerophospholipid metabolism; cholesterol metabolism; purine metabolism; arginine and proline metabolism; valine, leucine, and isoleucine biosynthesis and degradation. These results indicate disorders of energy metabolism, altered structure of cell membranes, changes in neurotransmission, and the induction of oxidative stress in the hippocampus. Our data, consistent with hypotheses of ASD pathomechanisms, may be useful in future ASD studies, especially for the interpretation of the results of metabolomics analysis of body fluids in rat ASD models.

Sex differences in pediatric traumatic brain injury

The response of the developing brain to traumatic injury is different from the response of the mature, adult brain. There are critical developmental trajectories in the young brain, whereby injury can lead to long term functional abnormalities. Emerging preclinical and clinical literature supports the presence of significant sex differences in both the response to and the recovery from pediatric traumatic brain injury (TBI). These sex differences are seen at all pediatric ages, including neonates/infants, pre-pubertal children, and adolescents. As importantly, the response to neuroprotective therapies or treatments can differ between male and females subjects. These sex differences can result from several biologic origins, and may manifest differently during the various phases of brain and body development. Recognizing and understanding these potential sex differences is crucial, and should be considered in both preclinical and clinical studies of pediatric TBI.

Sex differences of brain and their implications for personalized therapy

Nowadays, it is known that the sex differences regard many organs, e.g., liver, vessels, pancreas, lungs, bronchi and also the brain. Sex differences are not just a matter of ethical and moral principles, as they are central to explain many still unknown diseases and their understanding is a prerequisite to develop an effective therapy for each individual. This review reports on those sex differences that are not only macroscopic and morphological, but also involve molecular and functional dimorphism in the brain. It will recapitulate the main structural differences between male and female brain including the neurotransmission systems; in particular, the main objective is to identify a correlation, already known or to be investigated in the future, between the differences that characterize male and female brains from a morphological and biochemical point of view and neurological syndromes. This correlation could provide a starting point for future scientific research aimed to investigate and define a personalized therapy.

Sexual differentiation of microglia

Sex plays a role in the incidence and outcome of neurological illnesses, also influencing the response to treatments. Despite sexual differentiation of the brain has been extensively investigated, the study of sex differences in microglia, the brain's resident immune cells, has been largely neglected until recently. To fulfill this gap, our laboratory developed several tools, including cellular and animal models, which bolstered in-depth studies on sexual differentiation of microglia and its impact on brain physiology, as well as on the onset and progression of neurological disorders. Here, we summarize the current status of knowledge on the sex-dependent function of microglia, and report recent evidence linking these cells to the sexual bias in the susceptibility to neurological brain diseases.

A Calcium-Dependent Chloride Current Increases Repetitive Firing in Mouse Sympathetic Neurons

Ca2+-activated ion channels shape membrane excitability in response to elevations in intracellular Ca2+. The most extensively studied Ca2+-sensitive ion channels are Ca2+-activated K+ channels, whereas the physiological importance of Ca2+-activated Cl- channels has been poorly studied. Here we show that a Ca2+-activated Cl- currents (CaCCs) modulate repetitive firing in mouse sympathetic ganglion cells. Electrophysiological recording of mouse sympathetic neurons in an in vitro preparation of the superior cervical ganglion (SCG) identifies neurons with two different firing patterns in response to long depolarizing current pulses (1 s). Neurons classified as phasic (Ph) made up 67% of the cell population whilst the remainders were tonic (T). When a high frequency train of spikes was induced by intracellular current injection, SCG sympathetic neurons reached an afterpotential mainly dependent on the ratio of activation of two Ca2+-dependent currents: the K+ [IK(Ca)] and CaCC. When the IK(Ca) was larger, an afterhyperpolarization was the predominant afterpotential but when the CaCC was larger, an afterdepolarization (ADP) was predominant. These afterpotentials can be observed after a single action potential (AP). Ph and T neurons had similar ADPs and hence, the CaCC does not seem to determine the firing pattern (Ph or T) of these neurons. However, inhibition of Ca2+-activated Cl- channels with anthracene-9'-carboxylic acid (9AC) selectively inhibits the ADP, reducing the firing frequency and the instantaneous frequency without affecting the characteristics of single- or first-spike firing of both Ph and T neurons. Furthermore, we found that the CaCC underlying the ADP was significantly larger in SCG neurons from males than from females. Furthermore, the CaCC ANO1/TMEM16A was more strongly expressed in male than in female SCGs. Blocking ADPs with 9AC did not modify synaptic transmission in either Ph or T neurons. We conclude that the CaCC responsible for ADPs increases repetitive firing in both Ph and T neurons, and it is more relevant in male mouse sympathetic ganglion neurons.

Induced adverse effects of prenatal exposure to silver nanoparticles on neurobehavioral development of offspring of mice

Steadily increased use of silver nanoparticles (Ag-NPs), has increased the amount of its exposure to humans and animals. Current scarce knowledge about the influences of prenatal exposure to Ag-NPs on postnatal outcomes, motivated us to investigate whether being exposed to it during pregnancy has any effects on neurobehavioral development of the adult offspring. Thirty virgin female NMRI mice were mated and treated subcutaneously once every three days from gestation day 3 until delivery, by 0, 0.2 and 2 mg/kg of bodyweight (BW) of Ag-NPs. Behavioral functions of adult offspring including spatial memory, passive avoidance learning, stress, anxiety-like behaviors and locomotor activities were assessed by commonly used neurobehavioral paradigms and the results were compared according to treatment and sex. Prenatal exposure to Ag-NPs significantly impaired their cognitive behavior in the Morris water maze. Although no evidence was observed indicating more anxiety-like behaviors in the treated offspring in the elevated plus maze, the number of defecations and leanings in the open field assay and number of passages in the light-dark box were greater in groups prenatally treated by Ag-NPs. Most of the impairments were more apparent in the offspring which had been prenatally exposed to high doses of Ag-NPs, particularly female ones. The present study indicated that the exposure of pregnant animals to Ag-NPs may lead to various neurobehavioral disorders in their offspring. Thus, more attention should be paid to avoid exposure to Ag-NPs, especially from pregnant females.

The influence of sex-linked genetic mechanisms on attention and impulsivity

It is now generally agreed that there are inherent sex differences in healthy individuals across a number of neurobiological domains (including brain structure, neurochemistry, and cognition). Moreover, there is a burgeoning body of evidence highlighting sex differences within neuropsychiatric populations (in terms of the rates of incidence, clinical features/progression, neurobiology and pathology). Here, we consider the extent to which attention and impulsivity are sexually dimorphic in healthy populations and the extent to which sex might modulate the expression of disorders characterised by abnormalities in attention and/or impulsivity such as attention deficit hyperactivity disorder (ADHD), autism and addiction. We then discuss general genetic mechanisms that might underlie sex differences in attention and impulsivity before focussing on specific positional and functional candidate sex-linked genes that are likely to influence these cognitive processes. Identifying novel sex-modulated molecular targets should ultimately enable us to develop more effective therapies in disorders associated with attentional/impulsive dysfunction.

Annual Research Review: Development of the cerebral cortex: implications for neurodevelopmental disorders

The cerebral cortex has a central role in cognitive and emotional processing. As such, understanding the mechanisms that govern its development and function will be central to understanding the bases of severe neuropsychiatric disorders, particularly those that first appear in childhood. In this review, I highlight recent progress in elucidating genetic, molecular and cellular mechanisms that control cortical development. I discuss basic aspects of cortical developmental anatomy, and mechanisms that regulate cortical size and area formation, with an emphasis on the roles of fibroblast growth factor (Fgf) signaling and specific transcription factors. I then examine how specific types of cortical excitatory projection neurons are generated, and how their axons grow along stereotyped pathways to their targets. Next, I address how cortical inhibitory (GABAergic) neurons are generated, and point out the role of these cells in controlling cortical plasticity and critical periods. The paper concludes with an examination of four possible developmental mechanisms that could contribute to some forms of neurodevelopmental disorders, such as autism.

The neurochemical basis for the treatment of autism spectrum disorders and Fragile X Syndrome

Autism spectrum disorders (ASD) and Fragile X Syndrome (FXS) are neurodevelopmental disorders that share overlapping behavioral characteristics. While FXS is known to result from a specific genetic mutation, the causes of the majority of cases of ASD are unknown. Animal models of FXS have revealed new insight into the cellular and biochemical changes that occur in the central nervous system in this disorder, while human genetic studies on individuals with autism have identified sets of genes that may increase susceptibility to the disorder. Together these discoveries suggest overlapping biochemical characteristics and reveal new directions for the potential development of pharmacological therapies that might prove useful in the treatment of both FXS and ASD. In particular, delayed synaptic maturation, abnormal synaptic structure and/or function and alterations in intracellular signaling pathways have been linked to the pathogenesis of FXS and ASD. Aberrations in GABA(A) receptor ion channels and the G-protein coupled metabotropic glutamate and GABA(B) transmitter systems are also linked to both disorders and these receptors are currently at the forefront of preclinical and clinical research into treatments for both autism and Fragile X Syndrome.

When it comes to GABAergic responses and neonatal seizures--sex matters!

Dissociated Gender-Specific Effects of Recurrent Seizures on GABA Signaling in CA1 Pyramidal Neurons: Role of GABAA Receptors. Galanopoulou AS. J Neurosci 2008;28(7):1557–1567. Early in development, the depolarizing GABAAergic signaling is needed for normal neuronal differentiation. It is shown here that hyperpolarizing reversal potentials of GABAAergic post-synaptic currents ( EGABA) appear earlier in female than in male rat CA1 pyramidal neurons because of increased potassium chloride cotransporter 2 (KCC2) expression and decreased bumetanide-sensitive chloride transport in females. Three episodes of neonatal kainic acid-induced status epilepticus (3KA-SE), each elicited at postnatal days 4 (P4)–P6, reverse the direction of GABAAergic responses in both sexes. In males, 3KA-SE trigger a premature appearance of hyperpolarizing GABAAergic signaling at P9, instead of P14. This is driven by an increase in KCC2 expression and decrease in bumetanide-sensitive chloride cotransport. In 3KA-SE females, EGABA transiently becomes depolarizing at P8–P13 because of increase in the activity of a bumetanide-sensitive NKCC1 (sodium potassium chloride cotransporter 1)-like chloride cotransporter. However, females regain their hyperpolarizing GABAAergic signaling at P14 and do not manifest spontaneous seizures in adulthood. In maternally separated stressed controls, a hyperpolarizing shift in EGABA was observed in both sexes, associated with decreased bumetanide-sensitive chloride cotransport, whereas KCC2 immunoreactivity was increased in males only. GABAA receptor blockade at the time of 3KA-SE or maternal separation reversed their effects on EGABA. These data suggest that the direction of GABAA-receptor signaling may be a determining factor for the age- and sex-specific effects of prolonged seizures in the hippocampus, because they relate to normal brain development and possibly epileptogenesis. These effects differ from the consequences of severe stress.

Three hypotheses for developmental defects that may underlie some forms of autism spectrum disorder

PURPOSE OF REVIEW

Molecular and genetic insights into the etiology of autism spectrum disorders are now available. The field now needs to understand how these perturbations affect development and function of the brain.

RECENT FINDINGS

Herein I review the genetic mechanisms known to predispose to autism spectrum disorders, and attempt to consolidate many of these within cellular/molecular pathways that regulate development of neural systems that underlie cognition and social behaviors. In addition to the clear relationship of many susceptibility genes to activity-dependent neural responses, I propose the existence of three additional mechanisms that may contribute to autism spectrum disorders: evolutionary-driven expansion of cerebrum and cerebellar size; imbalance in the excitatory/inhibitory ratio in local and extended circuits; the hormonal effects of the male genotype.

SUMMARY

Understanding these mechanisms opens the possibility to therapeutic interventions.

Age-related changes in short-latency motor cortex inhibition

This study examined whether short-latency intracortical inhibition (SICI) and/or facilitation (ICF) changes with ageing, and if this can be attributed to age-related changes in the inhibition and/or corticospinal stimulus-response curves. SICI/ICF was studied in 17 "old" (63.1 +/- 4.2 years) and 13 "young" males (20.0 +/- 2.0 years) in both hemispheres using a paired-pulse transcranial magnetic stimulation paradigm at four interstimulus intervals (1, 3, 10 and 12 ms). Motor-evoked potentials were recorded from the first dorsal interosseous muscle at rest, with a conditioning intensity set at 5% stimulator output below the active threshold (aMT). Regardless of age, SICI was greater in the left compared with the right hemisphere. SICI was increased in old men at 3 ms in the left hemisphere and at 1 ms in the in both hemispheres, but ICF was not altered. However, aMT, and hence the conditioning stimulus intensity, was higher in old men. Comparisons of pairs of young and old men with the same aMT, and of SICI curves constructed relative to aMT, failed to show any age-related increase in SICI, although age-related changes in aMT accounted for less than 20% of the variability. Corticospinal stimulus-response characteristics did not influence SICI/ICF and appear not to be altered by ageing in men. When measured in resting muscles, SICI/ICF appears unaltered by age. But it remains unknown if, when assessed during movement preparation or movement, there are changes in SICI related to functional motor changes commonly associated with ageing, such as slowing of movement.

Müllerian inhibiting substance contributes to sex-linked biases in the brain and behavior

Many behavioral traits and most brain disorders are common to males and females but are more evident in one sex than the other. The control of these subtle sex-linked biases is largely unstudied and has been presumed to mirror that of the highly dimorphic reproductive nuclei. Sexual dimorphism in the reproductive tract is a product of Müllerian inhibiting substance (MIS), as well as the sex steroids. Males with a genetic deficiency in MIS signaling are sexually males, leading to the presumption that MIS is not a neural regulator. We challenge this presumption by reporting that most immature neurons in mice express the MIS-specific receptor (MISRII) and that male Mis(-/-) and Misrii(-/-) mice exhibit subtle feminization of their spinal motor neurons and of their exploratory behavior. Consequently, MIS may be a broad regulator of the subtle sex-linked biases in the nervous system.

Commentary: hormones, diet, and botanicals

In contrast to the high technology-driven interventions discussed in the previous presentations, hormonal therapy, diet, and botanicals are natural interventions that make use of homeostatic or traditional approaches. Clear advantages of these largely adjunctive therapies are discussed, as well as unique obstacles to bringing these alternative interventions into the mainstream.

Sexually dimorphic expression of KCC2 and GABA function

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate depolarizing effects, which result in activation of calcium-sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors acquire their classical hyperpolarizing signaling. The switch from depolarizing to hyperpolarizing GABA(A)-ergic signaling is triggered through the developmental shift in the balance of chloride cotransporters that either increase (i.e. NKCC1) or decrease (i.e. KCC2) intracellular chloride. The maturation of GABA(A) signaling follows sex-specific patterns, which correlate with the developmental expression profiles of chloride cotransporters. This has first been demonstrated in the substantia nigra, where the switch occurs earlier in females than in males. As a result, there are sensitive periods during development when drugs or conditions that activate GABA(A) receptors mediate different transcriptional effects in males and females. Furthermore, neurons with depolarizing or hyperpolarizing GABA(A)-ergic signaling respond differently to neurotrophic factors like estrogens. Consequently, during sensitive developmental periods, GABA(A) receptors may act as broadcasters of sexually differentiating signals, promoting gender-appropriate brain development. This has particular implications in epilepsy, where both the pathophysiology and treatment of epileptic seizures involve GABA(A) receptor activation. It is important therefore to study separately the effects of these factors not only on the course of epilepsy but also design new treatments that may not necessarily disturb the gender-appropriate brain development.

GABA(A) receptors in normal development and seizures: friends or foes?

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate excitatory effects resulting in activation of calcium sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors transmit inhibitory signals. The maturation of GABA(A) signaling follows sex-specific patterns, which appear to also be important for the sexual differentiation of the brain. The inhibitory effects of GABA(A) receptor activation have been widely exploited in the treatment of conditions where neuronal silencing is necessary. For instance, drugs that target GABA(A) receptors are the mainstay of treatment of seizures. Recent evidence suggests however that the physiology and function of GABA(A) receptors changes in the brain of a subject that has epilepsy or status epilepticus.This review will summarize the physiology of and the developmental factors regulating the signaling and function of GABA(A) receptors; how these may change in the brain that has experienced prior seizures; what are the implications for the age and sex specific treatment of seizures and status epilepticus. Finally, the implications of these changes for the treatment of certain forms of medically refractory epilepsies and status epilepticus will be discussed.

Estradiol and the developing brain

Estradiol is the most potent and ubiquitous member of a class of steroid hormones called estrogens. Fetuses and newborns are exposed to estradiol derived from their mother, their own gonads, and synthesized locally in their brains. Receptors for estradiol are nuclear transcription factors that regulate gene expression but also have actions at the membrane, including activation of signal transduction pathways. The developing brain expresses high levels of receptors for estradiol. The actions of estradiol on developing brain are generally permanent and range from establishment of sex differences to pervasive trophic and neuroprotective effects. Cellular end points mediated by estradiol include the following: 1) apoptosis, with estradiol preventing it in some regions but promoting it in others; 2) synaptogenesis, again estradiol promotes in some regions and inhibits in others; and 3) morphometry of neurons and astrocytes. Estradiol also impacts cellular physiology by modulating calcium handling, immediate-early-gene expression, and kinase activity. The specific mechanisms of estradiol action permanently impacting the brain are regionally specific and often involve neuronal/glial cross-talk. The introduction of endocrine disrupting compounds into the environment that mimic or alter the actions of estradiol has generated considerable concern, and the developing brain is a particularly sensitive target. Prostaglandins, glutamate, GABA, granulin, and focal adhesion kinase are among the signaling molecules co-opted by estradiol to differentiate male from female brains, but much remains to be learned. Only by understanding completely the mechanisms and impact of estradiol action on the developing brain can we also understand when these processes go awry.

Dissociated gender-specific effects of recurrent seizures on GABA signaling in CA1 pyramidal neurons: role of GABA(A) receptors

Early in development, the depolarizing GABA(A)ergic signaling is needed for normal neuronal differentiation. It is shown here that hyperpolarizing reversal potentials of GABA(A)ergic postsynaptic currents (E(GABA)) appear earlier in female than in male rat CA1 pyramidal neurons because of increased potassium chloride cotransporter 2 (KCC2) expression and decreased bumetanide-sensitive chloride transport in females. Three episodes of neonatal kainic acid-induced status epilepticus (3KA-SE), each elicited at postnatal days 4 (P4)-P6, reverse the direction of GABA(A)ergic responses in both sexes. In males, 3KA-SE trigger a premature appearance of hyperpolarizing GABA(A)ergic signaling at P9, instead of P14. This is driven by an increase in KCC2 expression and decrease in bumetanide-sensitive chloride cotransport. In 3KA-SE females, E(GABA) transiently becomes depolarizing at P8-P13 because of increase in the activity of a bumetanide-sensitive NKCC1 (sodium potassium chloride cotransporter 1)-like chloride cotransporter. However, females regain their hyperpolarizing GABA(A)ergic signaling at P14 and do not manifest spontaneous seizures in adulthood. In maternally separated stressed controls, a hyperpolarizing shift in E(GABA) was observed in both sexes, associated with decreased bumetanide-sensitive chloride cotransport, whereas KCC2 immunoreactivity was increased in males only. GABA(A) receptor blockade at the time of 3KA-SE or maternal separation reversed their effects on E(GABA). These data suggest that the direction of GABA(A)-receptor signaling may be a determining factor for the age and sex-specific effects of prolonged seizures in the hippocampus, because they relate to normal brain development and possibly epileptogenesis. These effects differ from the consequences of severe stress.

Timing of the developmental switch in GABA(A) mediated signaling from excitation to inhibition in CA3 rat hippocampus using gramicidin perforated patch and extracellular recordings

The timing of the developmental switch in the GABA(A) mediated responses from excitatory to inhibitory was studied in Wistar rat CA3 hippocampal pyramidal cells using gramicidin perforated patch-clamp and extracellular recordings. Gramicidin perforated patch recordings revealed a gradual developmental shift in the reversal potential of synaptic and isoguvacine-induced GABA(A) mediated responses from -55 +/- 4 mV at postnatal days P0-2 to -74 +/- 3 mV at P13-15 with a midpoint of disappearance of the excitatory effects of GABA at around P8. Extracellular recordings in CA3 pyramidal cell layer revealed that the effect of isoguvacine on multiple unit activity (MUA) switched from an increase to a decrease at around P10. The effect of synaptic GABA(A) mediated responses on MUA switched from an increase to a decrease at around P8. It is concluded that the developmental switch in the action of GABA via GABA(A) receptors from excitatory to inhibitory occurs in Wistar rat CA3 pyramidal cells at around P8-10, an age that coincides with the transition from immature to mature hippocampal rhythms. We propose that excitatory GABA contributes to enhanced excitability and ictogenesis in the neonatal rat hippocampus.

Sodium valproate stimulates potassium and chloride urinary excretion in rats: gender differences

BACKGROUND

The diuretic effect of valproates and its relation to urinary potassium (K+) and chloride (Cl-) excretion have not yet been investigated, so the aim of this study was to evaluate the influence of a single dose of sodium valproate (NaVPA) on 24-h urinary K+ and Cl- excretion in young adult Wistar rats of both genders. For measurement of K+ in urine, the same animals and samples as in our earlier publication were used (Pharmacology 2005 Nov, 75:111-115). The authors propose a new approach to the pathophysiological mechanisms of NaVPA effect on K+ and Cl- metabolism. Twenty six Wistar rats were examined after a single intragastric administration of 300 mg/kg NaVPA (13 NaVPA-male and 13 NaVPA-female), 28 control intact Wistar rats (14 males and 14 females) were studied as a control group. The 24-h urinary K+, Cl-, creatinine and pH levels were measured.

RESULTS

Total 24-h diuresis and 24-h diuresis per 100 g of body weight were found to be significantly higher in NaVPA-rats of both genders than in rats of the control group (p < 0.05). The data showed NaVPA to enhance 24-h K+ excretion in NaVPA-males and NaVPA-females with significant gender-related differences: 24-h K+ excretion in NaVPA-male rats was significantly higher than in control males (p = 0.003) and NaVPA-female rats (p < 0.001). Regarding the 24-h K+ excretion, NaVPA-female rats did not show a statistically significant difference versus females of the control group (p > 0.05). 24-h urinary K+ excretion per 100 g of body weight in NaVPA-male rats was significantly higher than in control males (p = 0.025). NaVPA enhanced Cl- urinary excretion: 24-h Cl- urinary excretion, 24-h urinary Cl- excretion per 100 g of body weight and the Cl-/creatinine ratio were significantly higher in NaVPA-male and NaVPA-female rats than in gender-matched controls (p < 0.05). 24-h chloriduretic response to NaVPA in male rats was significantly higher than in female rats (p < 0.05).

CONCLUSION

NaVPA causes kaliuretic and chloriduretic effects with gender-related differences in rats. Further investigations are necessary to elucidate the mechanism of such pharmacological effects of NaVPA.

Sex differences in the control of neuronal nitric oxide synthase by GABA-A receptors in the developing rat diencephalon

The nitric oxide free radical (NO(*)), which is synthesized by neuronal nitric oxide synthase (nNOS), is known to play an important morphogenetic role in the developing rat brain. In the cortex, the levels of nNOS are regulated by phosphorylated cAMP response element binding protein (pCREB) downstream of GABA-A receptor activation. During early stages of neonatal development, binding of GABA to its type A receptors leads to depolarization of the neuronal membrane. One of the developmental processes mediated through GABA-A receptors is the sexual differentiation of the brain. In the present work, we investigated the effect of GABA-A receptor activation on nNOS and pCREB immunoreactivity in the developing diencephalon of 5-day-old male and female rats. Our results showed that in the bed nucleus of the stria terminalis activation of GABA-A receptors leads to increased numbers of nNOS, and pCREB as well as nNOS-pCREB doubly immunopositive cells only in the males while in the posterior hypothalamus this effect is observed in both sexes. The GABA-A receptor-mediated increase in nNOS and pCREB is abolished when L-type voltage-gated Ca(2+) channels are blocked. These results indicate that the following mechanism could be operating in a gonadal hormone-dependent and brain area-specific manner during neonatal rat brain development: Depolarization following GABA-A receptor activation leads to opening of L-type voltage-gated calcium channels, resulting in an increased Ca(2+) influx, which in turn leads to phosphorylation, and thus activation of the transcription factor CREB; the phosphorylated CREB can then induce nNOS.

Developmental patterns in the regulation of chloride homeostasis and GABA(A) receptor signaling by seizures

GABA(A) receptors have dual functions during development. They depolarize immature neurons but hyperpolarize more mature neurons. This functional switch has been attributed to age-related differences in the relative abundance of cation chloride cotransporters, such as KCC2 and NKCC1, which regulate chloride homeostasis. Certain insults, such as trauma, ischemia, and seizures, if they occur when GABA(A)ergic signaling is hyperpolarizing, such as in the adult brain, can lead to reappearance of the immature, depolarizing synaptic responses to GABA(A) receptor activation. In certain cases, this has been associated with either reduced expression of KCC2 or increase in NKCC1. In epilepsy, the depolarizing effects of GABA(A) receptors have been proposed to be important for the acquisition and/or maintenance of the epileptic state. Using the kainic acid model of status epilepticus, we have studied the effects of repetitive neonatal episodes of status epilepticus on the expression of cation chloride cotransporter KCC2 in the neonatal hippocampus. In contrast to adults, seizures increased KCC2 mRNA expression in the CA3 region of the neonatal hippocampus. The contrasting patterns of regulation of KCC2 by seizures in mature and immature neurons may be one of the age-related factors that protect the neonatal brain against the development of epilepsy.

The cellular, molecular and ionic basis of GABA(A) receptor signalling

GABA(A) receptors mediate fast synaptic inhibition in the CNS. Whilst this is undoubtedly true, it is a gross oversimplification of their actions. The receptors themselves are diverse, being formed from a variety of subunits, each with a different temporal and spatial pattern of expression. This diversity is reflected in differences in subcellular targetting and in the subtleties of their response to GABA. While activation of the receptors leads to an inevitable increase in membrane conductance, the voltage response is dictated by the distribution of the permeant Cl(-) and HCO(3)(-) ions, which is established by anion transporters. Similar to GABA(A) receptors, the expression of these transporters is not only developmentally regulated but shows cell-specific and subcellular variation. Untangling all these complexities allows us to appreciate the variety of GABA-mediated signalling, a diverse set of phenomena encompassing both synaptic and non-synaptic functions that can be overtly excitatory as well as inhibitory.

Why sex matters for neuroscience

A rapidly burgeoning literature documents copious sex influences on brain anatomy, chemistry and function. This article highlights some of the more intriguing recent discoveries and their implications. Consideration of the effects of sex can help to explain seemingly contradictory findings. Research into sex influences is mandatory to fully understand a host of brain disorders with sex differences in their incidence and/or nature. The striking quantity and diversity of sex-related influences on brain function indicate that the still widespread assumption that sex influences are negligible cannot be justified, and probably retards progress in our field.

Sex- and cell-type-specific patterns of GABAAreceptor and estradiol-mediated signaling in the immature rat substantia nigra

The substantia nigra pars reticulata (SNR) is involved in movement and seizure control. In male but not female postnatal day 15 (PN15) rats, GABAA receptor agonists depolarize the SNR neurons and increase the expression of the calcium-regulated gene KCC2 (potassium/chloride cotransporter). Moreover, in PN15 rat SNR, 7beta-estradiol down-regulates KCC2 expression only in the presence of depolarizing GABAA receptor responses. The hypothesis tested here was that GABAA receptors and estradiol also regulate the expression of the phosphorylated form of the transcription factor cAMP responsive element binding protein (phosphoCREB), in PN15 rat SNR and substantia nigra pars compacta (SNC). Rats were injected with muscimol or 17beta-estradiol or their vehicles, and killed 1 h later. Sections were stained with an antibody specific for phosphoCREB alone or counterstained with either tyrosine hydroxylase (TH)- or parvalbumin (PRV)-specific antibodies. Muscimol increased phosphoCREB-ir in male but not in female SN neurons. Using gramicidin perforated patch clamp of PN14-15 SNC neuron, it was shown that muscimol bath application depolarized male SNC neurons but did not significantly alter membrane potential in females. In males, 17beta-estradiol decreased phosphoCREB expression in all studied cell types. In females, 17beta-estradiol did not influence phosphoCREB expression in PRV-ir SNR cells, but increased it in the dopaminergic SN neurons. These data suggest that GABAA receptor activation and estradiol promote the sexual differentiation of the SN in a cell-type-specific manner, by influencing calcium-regulated gene transcription, and therefore promoting the acquisition of sex-specific roles of the SN in movement and seizure control.

Sex-dependent maturation of GABAA receptor-mediated synaptic events in rat substantia nigra reticulata

The substantia nigra pars reticulata (SNR) plays important roles in movement and, in an age- and sex-dependent manner, in seizure control. GABAergic synaptic transmission is critical in both normal development and seizures. In many neuronal types it is excitatory early in development and later switches to the mature hyperpolarizing type. We assessed the time course of the switch of GABAA receptor-mediated postsynaptic currents (PSCs) in anterior SNR neurons of male and female developing rats using the gramicidin perforated patch clamp technique. The switch occurred in males around postnatal day (PN) 17 and in females around PN10. This sex dimorphism may play a role in several other recognized sex differences in the development of SNR and in its regulatory role in seizures.