Developmental sex differences in glutamic acid decarboxylase (GAD(65)) and the housekeeping gene, GAPDH

Sexually differentiated microglia and CA1 hippocampal synaptic connectivity

Microglia have been shown to sculpt postnatal circuitry from birth up to adulthood due to their role in both synapse formation, synaptic pruning, and the elimination of weak, redundant synapses. Microglia are differentiated in a sex-dependent manner. In this study, we tested whether sexual differentiation of microglia results in sex-dependent postnatal reorganization of CA1 synaptic connectivity in the hippocampus. The stereological counting of synapses in mice using electron microscopy showed a continuous rise in synapse density until the fourth week, followed by a plateau phase and loss of synapses from the eighth week onwards, with no difference between sexes. This course of alteration in synapse numbers did not differ between sexes. However, selectively, on postnatal day (P) 14 the density of synapses was significantly higher in the female than in the male hippocampus. Higher synapse density in females was paralleled by higher activity of microglia, as indicated by morphological changes, CD68 expression, and proximity of microglia to synaptic sites. In Thy1-GFP mice, consistent with increased synapse numbers, bouton density was also clearly increased in females at P14. At this time point, CD47 expression, the "don't eat me" signal of neurons, was similar in males and females. The decrease in bouton density thereafter in conjunction with increased synapse numbers argues for a role of microglia in the formation of multispine boutons (MSB). Our data in females at P14 support the regulatory role of microglia in synapse density. Sexual differentiation of microglia, however, does not substantially affect long-term synaptic reorganization in the hippocampus.

Establishment and evaluation of a novel mouse model of peri/postmenopausal depression

Women are believed to be more vulnerable to develop depressive symptoms during the perimenopause compared to postmenopause. The traditional bilateral ovariectomy and chronic mild stress (CMS) stimulation animal model produces a postmenopausal depressive-like state but the transition from perimenopausal period to postmenopausal period was ignored. Thus we establish a novel animal model in which the mice were stimulated by CMS for three months and removed the ovaries by two-step operation, and then evaluate whether this novel model could be much better for preclinical study used as a peri/postmenopause depressive model. The present study systemically evaluated the changes induced by two-step ovariectomy plus CMS in the mice. The depression-like behaviors, the levels of corticosterone, estrogen, pro-inflammatory factors, neurotransmitters, as well as brain-derived neurotrophic factor were determined; the changes of estrogen receptors, serotonin receptors, uterine weight and bone microarchitecture were also observed. The results show that the behaviors and biochemical indexes of mice changed gradually over time. Our study suggests that this two-step ovariectomy operation plus CMS successfully establishes a more reasonable peri/postmenopausal depression animal model which effectively simulates the clinical symptoms of peri/postmenopausal depressive women.

Selection and evaluation of reference genes for analysis of mouse (Mus musculus) sex-dimorphic brain development

The development of the brain is sex-dimorphic, and as a result so are many neurological disorders. One approach for studying sex-dimorphic brain development is to measure gene expression in biological samples using RT-qPCR. However, the accuracy and consistency of this technique relies on the reference gene(s) selected. We analyzed the expression of ten reference genes in male and female samples over three stages of brain development, using popular algorithms NormFinder, GeNorm and Bestkeeper. The top ranked reference genes at each time point were further used to quantify gene expression of three sex-dimorphic genes (Wnt10b, Xist and CYP7B1). When comparing gene expression between the sexes expression at specific time points the best reference gene combinations are: Sdha/Pgk1 at E11.5, RpL38/Sdha E12.5, and Actb/RpL37 at E15.5. When studying expression across time, the ideal reference gene(s) differs with sex. For XY samples a combination of Actb/Sdha. In contrast, when studying gene expression across developmental stage with XX samples, Sdha/Gapdh were the top reference genes. Our results identify the best combination of two reference genes when studying male and female brain development, and emphasize the importance of selecting the correct reference genes for comparisons between developmental stages.

Hypothalamic vasopressin systems are more sensitive to the long term effects of social defeat in males versus females

Vasopressin signaling has important effects on the regulation of social behaviors and stress responses, and is considered a promising pathway to target for new therapeutics of stress-induced psychiatric disorders. Although there is evidence for sex differences in the behavioral effects of arginine vasopressin (AVP), few data have directly compared the effects of stress on endogenous AVP signaling in males and females. We used California mice (Peromyscus californicus) to study the short and long term effects of social defeat stress on AVP immunoreactive cells in the paraventricular nucleus (PVN) and the posteromedial bed nucleus of the stria terminalis (BNSTmp). Acute exposure to defeat increased AVP/c-fos cells in the PVN and SON of both males and females. In contrast, there were sex differences in the long term effects of defeat. Males but not females exposed to defeat had less avp mRNA in the PVN, and in two experiments defeat reduced the number of AVP positive cells in the caudal PVN of males but not females. Interestingly, during relatively benign social encounters with a target mouse, there was a rapid decrease in AVP percent staining (including cell bodies and fibers) in the PVN of males but not females. Defeat reduced AVP percent staining in males, but did not block the socially induced decrease in percent staining. When mice were tested in resident-intruder tests, males exposed to defeat were no less aggressive than control males whereas aggression was abolished in females. However, bouts of aggression were positively correlated with the number of AVP neurons in the BNSTmp of control males but not stressed males, suggesting that different mechanisms mediate aggression in control and stressed males. These data show that while acute AVP responses to defeat are similar in males and females, the long term effects of defeat on AVP are stronger in males.

Need for gender-specific pre-analytical testing: the dark side of the moon in laboratory testing

Many international organisations encourage studies in a sex-gender perspective. However, research with a gender perspective presents a high degree of complexity, and the inclusion of sex-gender variable in experiments presents many methodological questions, the majority of which are still neglected. Overcoming these issues is fundamental to avoid erroneous results. Here, pre-analytical aspects of the research, such as study design, choice of utilised specimens, sample collection and processing, animal models of diseases, and the observer's role, are discussed. Artefacts in this stage of research could affect the predictive value of all analyses. Furthermore, the standardisation of research subjects according to their lifestyles and, if female, to their life phase and menses or oestrous cycle, is urgent to harmonise research worldwide. A sex-gender-specific attention to pre-analytical aspects could produce a decrease in the time for translation from the bench to bedside. Furthermore, sex-gender-specific pre-clinical pharmacological testing will enable adequate assessment of pharmacokinetic and pharmacodynamic actions of drugs and will enable, where appropriate, an adequate gender-specific clinical development plan. Therefore, sex-gender-specific pre-clinical research will increase the gender equity of care and will produce more evidence-based medicine.

Sex- and age-specific differences in relaxin family peptide receptor expression within the hippocampus and amygdala in rats

Relaxin is an essential pregnancy-related hormone with broad peripheral effects mediated by activation of relaxin-like family peptide 1 receptors (RXFP1). More recent studies suggest an additional role for relaxin as a neuropeptide, with RXFP1 receptors expressed in numerous brain regions. Neurons in an area of the brainstem known as the nucleus incertus (NI) produce relaxin 3 (RLN3), the most recently identified neuropeptide in the relaxin family. RLN3 has been shown to activate both RXFP1 and relaxin-like family peptide receptor 3 (RXFP3) receptor subtypes. Studies suggest wide-ranging neuromodulatory effects of both RXFP1 and RXFP3 activation, although to date the majority of studies have been conducted in young males. In the current study, we examined potential sex- and age-related changes in RLN3 gene expression in the NI as well as RXFP1 and RXFP3 gene expression in the dorsal hippocampus (HI), ventral hippocampus (vHI) and amygdala (AMYG) using young adult (9-12weeks) and middle-aged (9-12months) male and female rats. In addition, regional changes in RXFP1 and RXFP3 protein expression were examined in the CA1, CA2/CA3 and dentate gyrus (DG) as well as within basolateral (BLA), central (CeA), and medial (MeA) amygdaloid nuclei. In the NI, RLN3 showed an age-related decrease in males. In the HI, only the RXFP3 receptor showed an age-related change in gene expression, however, both receptor subtypes showed age-related changes in protein expression that were region specific. Additionally, while gene and protein expression of both receptors increased with age in AMYG, these effects were both region- and sex-specific. Finally, overall males displayed a greater number of cells that express the RXFP3 protein in all of the amygdaloid nuclei examined. Cognitive and emotional processes regulated by activity within the HI and AMYG are modulated by both sex and age. The vast majority of studies exploring the influence of sex on age-related changes in the HI and AMYG have focused on sex hormones, with few studies examining the role of neuropeptides. The current findings suggest that changes in relaxin family peptides may contribute to the significant sex differences observed in these brain regions as a function of aging.

Valid application of western blotting

Western blotting is a powerful and commonly used tool to identify and quantify a specific protein in a complex mixture. However, the systematic errors in the application of western blotting analysis are frequently to be found, which may compromise the interpretation of results. To make a valid application of western blotting, it is essential to begin with three independent biological replicates. Subsequently, a more reliable normalization method is in urgent need for western blotting analysis and using reference proteins is the currently preferred method of normalization. Additionally, identification of valid reference proteins is crucial for western blotting analysis and it should be examined carefully in relation to the cell or tissue types when using housekeeping proteins as internal standards.

MeCP2 regulates GFAP expression within the developing brain

Mutations in MECP2 cause Rett syndrome (RTT), an X-linked neurodevelopmental disorder that primarily affects females. Individuals with RTT have increased glial fibrillary acidic protein (GFAP) expression in the brain. GFAP is an intermediate filament protein that is expressed predominately within astrocytes in the CNS. MeCP2 binds to methylated regions of the GFAP promoter region and suppresses GFAP expression in vitro. Therefore, we wanted to determine if transiently reducing MeCP2 expression would increase GFAP expression in the developing rat brain. Male and female rats received infusions of either MeCP2 or control siRNA targeting the amygdala during the first 3 days of postnatal life. Brains were collected after 6h or 2 weeks following the last infusion. MeCP2 siRNA increased GFAP mRNA and protein within the female, but not the male, amygdala on postnatal day (PN) 2. Two weeks following the infusion, levels returned to normal. MeCP2 siRNA targeting the hypothalamus also increases GFAP mRNA within the female hypothalamus on PN2, suggesting that the regulation is not brain region-specific. It appears that MeCP2 does not regulate all astrocyte markers in the developing female brain, but specifically regulates GFAP expression, as levels of S100β and vimentin were not altered in the female amygdala at either time point. These data contribute to the idea that the role of MeCP2 differs in the developing male versus female brain. Further elucidating the regulation and function of GFAP can contribute to our understanding of MeCP2 function and perhaps RTT etiology.

Prenatal ethanol exposure has sex-specific effects on hippocampal long-term potentiation

Alcohol consumption during pregnancy is deleterious to the developing brain of the fetus and leads to persistent deficits in adulthood. Long-term potentiation (LTP) is a biological model for learning and memory processes and previous evidence has shown that prenatal ethanol exposure (PNEE) affects LTP in a sex specific manner during adolescence. The objective of this study was to determine if there are sex specific differences in adult animals and to elucidate the underlying molecular mechanisms that contribute to these differences. Pregnant Sprague-Dawley dams were assigned to either; liquid ethanol, pair-fed or standard chow diet. In vivo electrophysiology was performed in the hippocampal dentate gyrus (DG) of adult offspring. LTP was induced by administering 400 Hz stimuli. Western blot analysis for glutamine synthetase (GS) and glutamate decarboxylase from tissue of the DG indicated that GS expression was increased following PNEE. Surprisingly, adult females did not show any deficit in N-methyl-D-aspartate (NMDA)-dependent LTP after PNEE. In contrast, males showed a 40% reduction in LTP. It was indicated that glutamine synthetase expression was increased in PNEE females, suggesting that altered excitatory neurotransmitter replenishment may serve as a compensatory mechanism. Ovariectomizing females did not influence LTP in control or PNEE animals, suggesting that circulating estradiol levels do not play a major role in maintaining LTP levels in PNEE females. These results demonstrate the sexually dimorphic effects of PNEE on the ability for the adult brain to elicit LTP in the DG. The mechanisms for these effects are not fully understood, but an increase in glutamine synthetase in females may underlie this phenomenon.

Protein oxidation seems to be linked to constitutive autophagy: a sex study

AIM

Although constitutive autophagy is linked to redox state and participates in cell homeostasis, it is scarcely known if redox state, autophagy, and lysosomal function depend on sex, a factor that largely influences health and diseases. Therefore, we evaluated the existence of sex differences in redox state and constitutive autophagy in rat tissues.

MAIN METHODS

7week old Sprague-Dawley rats were used to obtain organs. Malondialdehyde (MDA), and carbonylated proteins were measured by spectrophotometric methods for redox state assessment. The autophagy biomarkers Beclin-1, and microtubule-associated protein 1 light chain 3 (LC3), the mammalian target of rapamycin (mTOR; checkpoint in autophagic process), and the lysosomal associated membrane protein (LAMP-1; biomarker of lysosomes) were evaluated by Western blotting. Immunofluorescence analysis was also performed for LC3 and LAMP-1 colocalization.

KEY FINDINGS

In the heart, Beclin-1, and LC3-II/LC3-I were higher in males than in females suggesting that the male heart has a major constitutive autophagy and this was linked with higher levels of carbonyl groups, indicating that protein oxidation could play a role. In the liver, it was found that LAMP-1 was higher in males and greatly colocalized with LC3 indicating a larger number of autophagolysosomes. None of the above parameters was significantly different in the kidneys of both sexes with the exception of MDA, which was significantly higher in females.

SIGNIFICANCE

The above results suggest that sex differences exist in redox state and autophagy and they occur in an organ-specific way. Importantly, it seems that the protein oxidation is more linked with constitutive autophagy, at least in cardiac ventricles, in comparison with lipid peroxidation.

Prostaglandin E₂ regulates AMPA receptor phosphorylation and promotes membrane insertion in preoptic area neurons and glia during sexual differentiation

Sexual differentiation of the rodent brain is dependent upon the organizing actions of the steroid hormone, estradiol. In the preoptic area, a brain region critical for the expression of adult reproductive behavior, there are twice as many dendritic spine synapses per unit length on newborn male neurons compared to female neurons and this sex difference correlates with the expression of adult male copulatory behavior. The sex difference in the POA is achieved via estradiol's upregulation of the membrane-derived lipid signaling molecule prostaglandin E₂ (PGE₂); PGE₂ is necessary and sufficient to masculinize both dendritic spine density and adult sexual behavior in rats. We have previously shown that PGE₂ activates EP₂ and EP₄ receptors which increases protein kinase A (PKA) activity and that masculinized dendritic spine density and sex behavior are both dependent upon PKA as well as activation of AMPA type glutamate receptors. In the current experiments, we build upon this signaling cascade by determining that PGE₂ induces phosphorylation of the AMPA receptor subunit, GluR1, which leads to increased AMPA receptor insertion at the membrane. Treating female pups on the day of birth with PGE₂ induced the phosphorylation of GluR1 at the PKA-sensitive site within 2 hours of treatment, an effect that was blocked by co-administration of the PKA/AKAP inhibitor, HT31 with PGE₂. Brief treatment of mixed neuronal/glial POA cultures with PGE₂ or the cAMP/PKA stimulator, forskolin, increased membrane associated GluR1 in both neurons and glia. We speculate that PGE₂ induced increases in AMPA receptor associated with the membrane underlies our previously observed increase in dendritic spine density and is a critical component in the masculinization of rodent sex behavior.

Glyceraldehyde-3-phosphate dehydrogenase is a reliable internal control in Western blot analysis of leukocyte subpopulations from children

To study differences in the development of immunity, leukocytes from cord blood are often compared with those from adult peripheral blood. Western blot analysis is a common method for detecting proteins. In this study, we investigated the reliability of using different housekeeping proteins (β-actin, β-tubulin, and glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) as internal controls for different leukocyte subpopulations from infants, children, and adults. Our results showed that the expression levels of β-actin and β-tubulin were much lower in cord blood leukocytes than in adult leukocytes, and this expression pattern persisted in children up to 3 years old. Further study revealed that the β-actin expression level in newborns was especially lower in CD14-positive monocytes. However, cord blood and adult peripheral blood monocytes had similar expression levels of β-actin messenger RNA (mRNA). Further experiments showed that posttranslational regulation was responsible for the low β-actin expression level in neonatal monocytes. Thus, researchers should carefully assess the appropriate use of housekeeping gene-encoded proteins as internal standards to normalize samples for comparisons of different leukocyte populations from subjects of different ages. In this study, we determined that GAPDH was a more reliable internal control than others in Western blot analysis for comparing the development of immunity among infants, children, and adults.

Sex differences in epigenetic regulation of the estrogen receptor-alpha promoter within the developing preoptic area

Sex differences in the brain are largely organized by a testicular hormone surge that occurs in males shortly after birth. Although this hormone surge is transient, sex differences in brain and behavior are lasting. Here we describe a sex difference in DNA methylation of the estrogen receptor-alpha (ERalpha) promoter region within the developing rat preoptic area, with males exhibiting more DNA methylation within the ERalpha promoter than females. More importantly, we report that simulating maternal grooming, a form of maternal interaction that is sexually dimorphic with males experiencing more than females during the neonatal period, effectively masculinizes female ERalpha promoter methylation and gene expression. This suggests natural variations in maternal care that are directed differentially at males vs. females can influence sex differences in the brain by creating sexually dimorphic DNA methylation patterns. We also find that the early estradiol exposure may contribute to sex differences in DNA methylation patterns. This suggests that early social interaction and estradiol exposure may converge at the genome to organize lasting sex differences in the brain via epigenetic differentiation.

Expression of four housekeeping proteins in elderly patients with schizophrenia

We compared protein expression by Western blot analysis in four areas of postmortem brain from patients with schizophrenia and control subjects for several proteins that are often used as controls for Western blot studies: beta-tubulin, actin, glyceraldehyde-3-phosphate dehydrogenase, and valosin-containing protein. We did not detect any differences in expression between subjects with schizophrenia and a comparison group. These results suggest that all four proteins are suitable loading controls for postmortem studies of schizophrenia.

Mecp2 organizes juvenile social behavior in a sex-specific manner

Methyl-CpG-binding protein 2 (MeCP2) binds methylated DNA and recruits corepressor proteins to modify chromatin and alter gene transcription. Mutations of the MECP2 gene can cause Rett syndrome, whereas subtle reductions of MeCP2 expression may be associated with male-dominated social and neurodevelopmental disorders. We report that transiently decreased amygdala Mecp2 expression during a sensitive period of brain sexual differentiation disrupts the organization of sex differences in juvenile social play behavior. Interestingly, neonatal treatment with Mecp2 small interfering RNA within the developing amygdala reduced juvenile social play behavior in males but not females. Reduced Mecp2 expression did not change juvenile sociability or anxiety-like behavior, suggesting that this disruption is associated with subtle behavioral modification. This suggests that Mecp2 may have an overlooked role in the organization of sexually dimorphic behaviors and that male juvenile behavior is particularly sensitive to Mecp2 disruption during this period of development.

Selection of reference genes for quantitative real-time RT-PCR studies in mouse brain

Since a growing number of studies based on the real-time reverse transcriptase polymerase chain reaction (RT-PCR) continue to be published in order to highlight genes specifically involved in brain development, maturation, and function, the identification of reference genes suitable for this kind of experiments is now an urgent need in the neuroscience field. The aim of this work was to verify the suitability of some very common housekeeping genes (such as Gapdh, 18s, and B2m) and of some relatively new control genes (such as Pgk1, Tfrc, and Gusb) during mouse brain maturation. We tested the candidate reference genes in mouse whole brain, cerebellum, brain stem, hippocampus, medial septum, frontal neocortex, and olfactory bulb. Moreover, we reported the first complete study of Pgk1 expression throughout the development and the aging of mouse brain. Although no tested gene showed to be the optimal reference for all mouse brain regions, in general, the new housekeeping genes were highly stable in most of the analyzed regions. Above all, with few exceptions, Pgk1 showed to be a reliable control for the analyzed mouse brain regions during development, maturation, and aging.

Regulation of complexin 1 and complexin 2 in the developing human prefrontal cortex

Complexin 1 (CX1) and complexin 2 (CX2) are presynaptic proteins that modulate neurotransmitter release and are used as markers of inhibitory and excitatory synapses, respectively. The aim of this study was to gain insight into the development of inhibitory and excitatory synapses in human prefrontal cortex (PFC) by examining the expression of CX1 and CX2 in postmortem tissues. Relative complexin protein levels were measured by Western blotting in postmortem dorsolateral prefrontal cortex (DLPFC) of 42 subjects without neurological or psychiatric disease ranging in age from 18 gestational weeks to 25 years. Samples were batched a priori into fetal, 0-12 month, 1-5 years, 6-10 years, 11-15 years, 16-20 years, and 21-25 years age groups. CX1 and CX2 expression and CX2/CX1 demonstrated a significant effect of age group by ANOVA. Group CX1 level increased progressively across development and was lowest in the fetal group and highest in the young adult group, whereas group CX2 level increased between the fetal and the 6-10 years groups and then plateaued. Consistent with these divergent patterns, there was a significant effect of age group on CX2/CX1, which was higher in fetal and infant groups than in the young adult group. Furthermore, regression analysis demonstrated linear relationships of CX1 and CX2/CX1 with age, whereas CX2 was better described as having a curvilinear relationship with age. These data indicate that complexin expression increases during synaptic maturation in human DLPFC and that an increase in the influence of inhibitory synapses relative to that of excitatory synapses occurs during development in this cortical region.

Periadolescent stress exposure exerts long-term effects on adult stress responding and expression of prefrontal dopamine receptors in male and female rats

Recent research has demonstrated that experiential/environmental factors in early life can program the adult stress response in rats, and this is manifest as altered hypothalamic-pituitary-adrenocortical activity and behavior in response to a stressor. Very little work has been devoted to investigating whether the environment during adolescence plays a similar role in modulating ongoing developmental processes and how this might affect adult stress responding. Periadolescent predator odor (PPO) exposure was used here as a naturalistic model of repeated psychological stress. Behavioral and endocrine responses to PPO changed across the exposure period, and behavioral alterations persisted into adulthood. While adolescent rats showed pronounced avoidance responses upon initial PPO exposure, hyperactivity increased across the exposure period, especially in females. Corticosterone (cort) responses to stressor exposure also changed in females, with higher physiological baseline levels observed at the end of the exposure period. In adulthood, relative to rats who had received a control manipulation during adolescence, PPO-exposed rats were more fearful in a novel open field and displayed altered responses to a predator odor stress test in adulthood. Moreover, lower levels of the D2 dopamine (DA) receptor were measured in prefrontal (infralimbic and dorsopeduncular) cortices of PPO-exposed rats. These findings suggest that the adolescent period may represent a sensitive period during which developmental programming of the stress response occurs.

Dendritic pruning of the medial amygdala during pubertal development of the male Syrian hamster

The medial amygdala (Me), a brain region essential for mating behavior, changes in size during puberty. In pre-, mid-, and late pubertal (21, 35, and 49 days of age) male Syrian hamsters, we examined neuronal structure in Me and protein levels of spinophilin and synaptophysin in the amygdaloid complex for evidence of synaptic plasticity coincident with behavioral and physiological development. Body weight, testes weight, and testosterone levels increased during puberty. Mounting behavior, including ectopic, nonintromittive, and intromittive mounts, also increased. Neuronal structure in the posterodorsal medial amygdala (MePD) was assessed in Golgi-impregnated neurons. Pruning occurred during puberty in the number of dendrites emanating from the cell body and in terminal dendritic spine densities. Approximately half of all MePD neurons analyzed had an axon emanating from a dendrite rather than the cell body. However, prepubertal males were more likely to have the axon emanating from a higher order dendritic segment (secondary or tertiary) than were mid- and late pubertal males. Finally, protein levels in the amygdaloid complex varied with pubertal age. Spinophilin decreased, while synaptophysin and GAPDH protein levels increased. These results suggest that puberty is a period of dramatic synaptic plasticity in Me. Specifically, pruning of dendrites and spines, in combination with axonal changes, is likely to modify the afferent influences and electrophysiological properties of Me neurons. Because the Me is an integral component of a social behavior neural network, these changes may be related not only to sexual behavior, but also to other behaviors that mature during puberty, including aggressive, risk-taking, fear-related, and parental behaviors.

Focal adhesion kinase and paxillin: novel regulators of brain sexual differentiation?

Steroid-mediated sexual differentiation of the brain is a developmental process that permanently organizes the brain into a male or female phenotype. Previous studies in the rodent have examined the steroid-mediated mechanisms of male brain development. In an effort to identify molecules involved in female brain development, a high-throughput proteomics approach called PowerBlot was used to identify signaling proteins differentially regulated in the neonatal male and female rat hypothalamus during the critical period for brain sexual differentiation. Focal adhesion kinase (FAK) and paxillin, both members of the focal adhesion complex family of proteins, were significantly elevated in the newborn female compared with the male hypothalamus. Sex differences in these proteins were not detected in brain regions that are not subject to substantial organizational effects of steroids. Estrogens, the aromatized products of testosterone in the male, can both masculinize and defeminize the male brain. Daily estradiol administration to neonatal females significantly reduced FAK and paxillin in the hypothalamus, and aromatase inhibition increased paxillin in males to levels comparable with females. Androgens also appear to modulate paxillin levels in combination with estrogen action. Across development, hypothalamic levels of FAK were significantly elevated in females compared with males on postnatal d 6. Synaptic circuits in the hypothalamus develop sex differences perinatally. Estradiol treatment of cultured hypothalamic neurons significantly enhanced axon branching (P<0.01), consistent with the phenotype of FAK-deficient neurons. Together, these data implicate FAK and paxillin as regulators of sex differences in neuronal morphology.

Sex differences in the chloride cotransporters, NKCC1 and KCC2, in the developing hypothalamus

In immature neurones, high basal [Cl(-)](i) results in membrane depolarisation following GABA(A) receptor activation, which is critical for various developmental processes including steroid-mediated sexual differentiation of the hypothalamus. Previously, we demonstrated that oestradiol enhances GABA-mediated Ca(2+) influx in neonate hypothalamus and that Ca(2+) induced activation of the transcription factor, cyclicAMP response element binding protein (CREB), was higher in male (high oestradiol) relative to female neonate hypothalamus. Based on these results, we hypothesised that expression of developmentally regulated chloride cotransporters may be sexually dimorphic. Here, we investigate the expression of the chloride cotransporters, NKCC1 (Na-K-2Cl(-)) and KCC2 (K-Cl(-)) in neonate mediobasal hypothalamus of male and female rats. The NKCC1 transporter moves Cl(-) into cells and helps maintain depolarising GABA action while the KCC2 transporter has the opposite effect by moving Cl(-) out of cells. NKCC1 mRNA levels were higher in males than females on the day of birth (postnatal day 0; PND 0) and total NKCC1 protein levels were significantly higher in males than females on embryonic day (ED) 20 and PND0. Levels of activated phosphorylated NKCC1 (pNKCC1) were not sexually dimorphic. Females were treated with a masculinising dose of oestradiol benzoate (EB; 100 microg; EB-females) on PND0. Total NKCC1 protein levels in tissue processed on PND1 and PND2 were similar in EB-females and oil-treated PND0 males and females. However, pNKCC1 protein levels measured on PND2 (but not PND1) were significantly higher in EB-treated females relative to oil-treated males and females. By contrast, KCC2 mRNA levels were significantly lower in males relative to females on PND0. KCC2 protein was not detectable on ED20 or PND0 but was significantly lower in males relative to females on PND5. These results suggest a complex relationship between KCC2 and NKCC1 mRNA and protein in developing brain that is not easily linked to regulation by oestradiol.

Sex differences in oestrogen-induced p44/42 MAPK phosphorylation in the mouse brain in vivo

In addition to the classical direct genomic mechanisms of action, oestrogen also exerts poorly understood, nonclassical effects on the signalling system in neurones. In the present study, we investigated whether sex differences exist in gonadectomy- and oestrogen-induced effects on p44/42 mitogen-activated protein kinase (MAPK) phosphorylation in specific brain regions of mice. We demonstrate that MAPK immunoreactivity was not altered by gonadectomy or oestrogen treatment in either sex. However, we show that the level of phosphorylated MAPK (pMAPK) within the anteroventral periventricular nucleus (AVPV) was consistently higher in males than females irrespective of gonadal steroid hormone status. In addition, gonadectomy was found to decrease pMAPK immunoreactivity within the piriform cortex of males. Oestrogen increased pMAPK immunoreactivity in the medial preoptic area and AVPV of females, but failed to have the same effect in male mice. Overall, these results demonstrate a marked sex difference in oestrogen-induced alteration of MAPK phosphorylation in the brain in vivo.

Microglial expression of chemokine receptor CCR5 during rat forebrain development and after perinatal hypoxia–ischemia

The chemokine macrophage inflammatory protein 1alpha (CCL3) is expressed by immune cells in the normal and injured perinatal brain. To determine whether the chemokine receptor CCR5 is a relevant target for CCL3 in the brain, we used RT-PCR and immunocytochemistry to assess changes in CCR5 expression and localization in developing normal and injured rat forebrain. CCR5 protein was expressed predominately by resting and activated microglia until 2 weeks of age. Neonatal hypoxia-ischemia increased CCR5 mRNA expression while causing CCR5 internalization, indicating receptor activation. These data implicate CCR5 in microglial recruitment and activation during brain development and after neonatal brain injury.

Gene array profiling of large hypothalamic CNS regions in lactating and randomly cycling virgin mice

A dramatic example of neuronal and physiological plasticity in adult mammals occurs during the transition from a non-maternal to a maternal, lactating state. In this study, we compared gene expression within a large continuous region of the CNS involved in maternal behaviors (hypothalamus, preoptic regions, and nucleus accumbens) between lactating (L) (postpartum Day 7) and randomly cycling virgin (V) outbred mice. Using high-density oligonucleotide arrays representing 11,904 genes, two statistical algorithms were used to identify significant differences in gene expression: robust multiarray (P < 0.001) (n = 92 genes) and significance analysis of microarrays using a 10% false discover rate (n = 114 genes). 27 common genes were identified as significant using both techniques. A subset of genes (n = 5) were selected and examined by real-time PCR. Our findings were consistent with previous published work. For example, neuropeptide Y (NPY) and proenkephalin were elevated in L mice, whereas POMC was decreased. Increased levels of NPY Y2 receptor and polo-like kinase and decreased levels of endothelin receptor type b in L mice are examples of novel gene expression changes not previously identified. Expression differences occurred in broad classes. Together, our findings provide possible new material on gene expression changes that may support maternal behaviors. The advantages and drawbacks of sampling large CNS regions using arrays are discussed.

Microarray profiling of gene expression patterns in adult male rat brain following acute progesterone treatment

Progesterone can influence various behaviors in adult male rats, however, little is known about which particular genes are regulated by progesterone in the male rat brain. Using focused microarray technology, we where able to define a subset of genes that are responsive to progesterone. Nylon membrane-based cDNA microarrays were used to profile gene expression patterns in the preoptic area/mediobasal hypothalamus (POA/MBH) of male rat brain 7 h following a single injection of progesterone. RNA was isolated from the brains of 6 male rats injected with progesterone and 6 male rats injected with sesame oil. Next, we hybridized the RNA from each animal to individual cDNA microarrays that contained more than 100 target genes, all of which are involved in cAMP and or calcium signaling pathways. Direct side-by-side comparison of all 12 arrays revealed differences in the expression patterns of 12 different genes. We confirmed the data gathered from the arrays on 4 different genes using Real-Time PCR. These data begin to outline the important role played by progesterone in mediating changes in gene expression within the male brain.

Sex differences in Fos protein expression in the neonatal rat brain

Sex differences in the brain and behaviour are mostly a result of transient increases in testosterone during the perinatal period. Testosterone influences brain development primarily through aromatization to oestradiol and subsequent binding to oestrogen receptors. Although some studies report that steroid hormones regulate the expression of the inducible transcription factor, Fos, in developing brain, it is not known if there is a sex difference in Fos expression. Changes in Fos protein can be used as an indicator of neuronal/genomic activity. Thus, it provides a useful tool to identify brain regions responding directly or indirectly to steroid hormones. In a first experiment, we examined Fos protein expression in the developing male and female rat brain using western immunoblotting. Dissections were taken from male and female rat pups on the day of birth (postnatal day 0; PN 0), PN1, PN5, PN11 or PN20. Although there was no difference on PN 0, males expressed significantly greater levels of Fos protein on PN1, PN5 and PN20. In a second experiment, we localized the sex difference in Fos protein expression using immunocytochemistry. We found that males expressed significantly higher levels of Fos within a variety of brain regions. These data indicate a sex difference in Fos protein expression during brain development, suggesting a potential role for Fos in differentiating male from female rat brain.

Housekeeping proteins: A preliminary study illustrating some limitations as useful references in protein expression studies

A primary objective of many protein expression studies is to define expression patterns that can distinguish between normal and diseased states, enabling a better understanding of molecular events associated with disease development and progression and ultimately potentially finding novel markers or therapeutic targets. Exploration and confirmation of many proteins is often done using Western blotting with normalization against "housekeeping proteins", such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), beta-actin, or beta-tubulin, to correct for protein loading and factors, such as transfer efficiency. Increasingly, in studies examining gene transcript levels, it has been shown that some of the commonly used housekeeping genes may be unsuitable due to the influence of various physiological and pathological factors on their expression. This has not been examined to any great extent for proteins, however. This study examines the degree of variability of three commonly used "housekeeping" proteins (GAPDH, beta-actin, and beta-tubulin) together with class I beta-tubulin, with comparisons being made between a number of different established renal cancer cell lines, matched pairs of renal tumor and normal kidney lysates as well as nine different human tissues and highlights some of the problems encountered.

Effect of androgens on sexual differentiation of pituitary gamma-aminobutyric acid receptor subunit GABA(B) expression

Previous work demonstrated a sexually dimorphic ontogenic expression of gamma-aminobutyric acid receptors (GABA(B)R) in rat pituitary. As sex steroids determine sex-specific expression patterns, we now studied the effect of sex hormones on pituitary GABA(B)R expression. GABA(B)R subunits, measured by Western blot and by semi-quantitative RT-PCR and luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone measured by RIA were determined in two experimental designs: First experimental design: 8- and 15-day-old females (8F, 15F); 8F and 15F treated with 100 mug testosterone propionate (TP) on day 1 of life (8F100TP, 15F100TP), 8- and 15-day-old males (8M, 15M) and 8M and 15M castrated on day 1 (8MC, 15MC). Second experimental design: 8-day-old female and male animals: 8F, 8F100TP, 8F treated with 1 mug/day TP on days 1-4 (8F1TP), 8F treated with the androgen antagonist Flutamide (Flut: 2.5 mg/100 g BW of pregnant mother on days E17-E23) (8F-Flut), 8M, 8MC, 8M treated with Flut as above (8M-Flut) and 8MC-Flut. In these animals, in addition, GABA, glutamate, aspartate and taurine were measured by HPLC in hypothalami and cortex. In the first set of experiments, GABA(B1)R mRNA/protein expression was higher in 8F than in 15F, 8M or 15M. In 8F100TP, GABA(B1)R mRNA/protein decreased to male levels. TP treatment did not alter GABA(B1)R expression in 15F. There was no difference in GABA(B1)R expression between 8M and 15M and neonatal castration did not modify its expression. In the second set of experiments, TP (1 mug) or Flut did not modify GABA(B1)R in 8F, while 100 microg TP continued to decrease GABA(B1)R expression. In 8M, Flut, alone or with castration, increased GABA(B1)R mRNA/protein expression to 8F. Hypothalamic GABA content followed the same pattern as pituitary GABA(B)R expression in 8-day-old animals, suggesting a cross-regulation. With regard to hormonal levels, 100 microg, but not 1 microg TP altered gonadotropins at 8 days, although both treatments effectively androgenized females as evidenced by lack of cycling. We conclude that androgens, acting pre- and postnatally, decrease pituitary GABA(B)R subunit expression.

Microdissected region-specific gene expression analysis with methacarn-fixed, paraffin-embedded tissues by real-time RT-PCR

We have previously shown methacarn to be a versatile fixative for analysis of proteins, DNA, and RNA in paraffin-embedded tissues (PETs). In this study we analyzed its suitability for quantitative mRNA expression analysis of microdissected PET specimens using a real-time RT-PCR technique. Fidelity of expression in the methacarn-fixed PET sections, with reference to dose-dependent induction of cytochrome P450 2B1 in the phenobarbital-treated rat liver, was high in comparison with the unfixed frozen tissue case, even after hematoxylin staining. RNA yield from methacarn-fixed PET sections was equivalent to that in unfixed cryosections and was also not significantly affected by hematoxylin staining. Correlations between the expression levels of target genes and input amounts of extracted RNA in the range of 1-1000 pg were very high (correlation coefficients >0.98), the regression curves being similar to those with unfixed cryosections. Although cell numbers should be optimized for each target gene/tissue, >/=200 cells were necessary for accurate measurement in 10-microm-thick rat liver sections judging from the variation of measured value in small microdissected areas. These results indicate high performance with methacarn, close to that of unfixed tissues, regarding quantitative expression analysis of mRNAs in microdissected PET-specimens.

Distribution of glutamic acid decarboxylase, neurotensin, enkephalin, neuropeptide Y, and cholecystokinin neurons in the septo-preoptic region of male rats

Neurons in the lateral septum (LS) and preoptic area (POA) are known to play an inhibitory role in feminine sexual behavior regulation in male rats. In this study, the distribution of neurons containing glutamic acid decarboxylase (GAD) and of the peptidergic neurotransmitters neurotensin (NT), enkephalin (ENK), neuropeptide Y (NPY), and cholecystokinin (CCK), was examined immunohistochemically in the LS and POA of castrated male rats subcutaneously implanted with estrogen-containing Silastic tubes. Colchicine was injected into the lateral ventricle of the animals. The forebrain sections were immunostained for each substance. A large number of GAD-immunoreactive (ir) cells were found in the LS. Many NT-ir cells were seen in the intermediate and ventral parts of the LS at the rostral and middle levels. A considerable number of ENK-ir cells were scattered over the LS at the rostral and middle levels and were observed in the ventral part of the caudal LS. There were only a few NPY-ir cells in the LS. No CCK-ir cells were observed in the LS. In the POA, GAD-ir cells were observed in abundance. Many NT-ir cells were seen, especially in the medial preoptic nucleus. Some ENK-ir cells and a few NPY-ir cells were found in the medial POA. CCK-ir cells of the POA were restricted to the periventricular and paraventricular hypothalamic nuclei.

Steroid hormone modulation of olfactory processing in the context of socio-sexual behaviors in rodents and humans

Primer pheromones and other chemosensory cues are important factors governing social interactions and reproductive physiology in many species of mammals. Responses to these chemosignals can vary substantially within and between individuals. This variability can stem, at least in part, from the modulating effects steroid and non-steroid hormones exert on olfactory processing. Such modulation frequently augments or facilitates the effects that prevailing social and environmental conditions have on the reproductive axis. The mechanisms underlying the hormonal regulation of responses to chemosensory cues are diverse. They are in part behavioral, achieved through the modulation of chemoinvestigative behaviors, and in part a product of the modulation of the intrinsic responsiveness of the main and accessory olfactory systems to conspecific, as well as other classes, of chemosignals. The behavioral and non-behavioral effects complement one another to ensure that mating and other reproductive processes are confined to reproductively favorable conditions.

Glutamic acid decarboxylase (GAD65) immunoreactivity in brains of aggressive, adolescent anabolic steroid-treated hamsters

Chronic anabolic-androgenic steroid (AAS) treatment during adolescence facilitates offensive aggression in male Syrian hamsters (Mesocricetus auratus). The current study assessed whether adolescent AAS exposure influenced the immunohistochemical localization of glutamic acid decarboxylase (GAD65), the rate-limiting enzyme in the synthesis of gamma-aminobutyric acid (GABA), in areas of hamster brain implicated in aggressive behavior. Hamsters were administered high dose AAS throughout adolescence, scored for offensive aggression, and then examined for differences in GAD65 puncta to regions of the hamster brain important for aggression. When compared with control animals, aggressive AAS-treated hamsters showed significant increases in the area covered by GAD65 immunoreactive puncta in several of these aggression regions, including the anterior hypothalamus, ventrolateral hypothalamus, and medial amygdala. Conversely, aggressive AAS-treated hamsters showed a significant decrease in GAD65-ir puncta in the lateral septum when compared with oil-treated controls. However, no differences in GAD65 puncta were found in other aggression areas, such as the bed nucleus of the stria terminalis and central amygdala. Together, these results support a role for altered GAD65 synthesis and function in adolescent AAS-facilitated offensive aggression.

Age-related irreversible progressive nigrostriatal dopaminergic neurotoxicity in the paraquat and maneb model of the Parkinson's disease phenotype

While advancing age is the only unequivocally accepted risk factor for idiopathic Parkinson's disease, it has been postulated that exposure to environmental neurotoxicants combined with ageing could increase the risk for developing Parkinson's disease. The current study tested this hypothesis by exposing C57BL/6 mice that were 6 weeks, 5 months or 18 months old to the herbicide paraquat, the fungicide maneb or paraquat + maneb, a combination that produces a Parkinson's disease phenotype in young adult mice. Paraquat + maneb-induced reductions in locomotor activity and motor coordination were age dependent, with 18-month-old mice most affected and exhibiting failure to recover 24 h post-treatment. Three months post-treatment, reductions in locomotor activity and deficits in motor coordination were sustained in 5-month-old and further reduced in 18-month-old paraquat + maneb groups. Progressive reductions in dopamine metabolites and dopamine turnover were greatest in 18-month-old paraquat + maneb and paraquat groups 3 months post-treatment. Increased tyrosine hydroxylase enzyme activity compensated for striatal tyrosine hydroxylase protein and/or dopamine loss following treatment in 6-week-old and 5-month-old, but not 18-month-old paraquat and paraquat + maneb mice. Numbers of nigrostriatal dopaminergic neurons were reduced in all age groups following paraquat alone and paraquat + maneb exposure, but these losses, along with decreases in striatal tyrosine hydroxylase protein levels, were progressive in 18-month-old paraquat and paraquat + maneb groups between 2 weeks and 3 months post-exposure. Collectively, these data demonstrate enhanced sensitivity of the ageing nigrostriatal dopamine pathway to these pesticides, particularly paraquat + maneb, resulting in irreversible and progressive neurotoxicity.