Estradiol derived from testosterone in prenatal life affects the development of catecholamine systems in the frontal cortex in the male rat

Sex-specific Effects of Endocrine-disrupting Chemicals on Brain Monoamines and Cognitive Behavior

The period of brain sexual differentiation is characterized by the development of hormone-sensitive neural circuits that govern the subsequent presentation of sexually dimorphic behavior in adulthood. Perturbations of hormones by endocrine-disrupting chemicals (EDCs) during this developmental period interfere with an organism's endocrine function and can disrupt the normative organization of male- or female-typical neural circuitry. This is well characterized for reproductive and social behaviors and their underlying circuitry in the hypothalamus and other limbic regions of the brain; however, cognitive behaviors are also sexually dimorphic, with their underlying neural circuitry potentially vulnerable to EDC exposure during critical periods of brain development. This review provides recent evidence for sex-specific changes to the brain's monoaminergic systems (dopamine, serotonin, norepinephrine) after developmental EDC exposure and relates these outcomes to sex differences in cognition such as affective, attentional, and learning/memory behaviors.

The effects of early life stress on motivated behaviors: A role for gonadal hormones

Motivated behaviors are controlled by the mesocorticolimbic dopamine (DA) system, consisting of projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and prefrontal cortex (PFC), with input from structures including the medial preoptic area (mPOA). Sex differences are present in this circuit, and gonadal hormones (e.g., estradiol and testosterone) are important for regulating DA transmission. Early life stress (ELS) also regulates the mesocorticolimbic DA system. ELS modifies motivated behaviors and the underlying DA circuitry, increasing risk for disorders such as substance use disorder, major depression, and schizophrenia. ELS has been shown to change gonadal hormone signaling in both sexes. Thus, one way that ELS could impact mesocorticolimbic DA is by altering the efficacy of gonadal hormones. This review provides evidence for this idea by integrating the gonadal hormone, motivation, and ELS literature to argue that ELS alters gonadal hormone signaling to impact motivated behavior. We also discuss the importance of these effects in the context of understanding risk and treatments for psychiatric disorders in men and women.

Sex differences in fear extinction

Despite the exponential increase in fear research during the last years, few studies have included female subjects in their design. The need to include females arises from the knowledge gap of mechanistic processes underlying the behavioral and neural differences observed in fear extinction. Moreover, the exact contribution of sex and hormones in relation to learning and behavior is still largely unknown. Insights from this field could be beneficial as fear-related disorders are twice as prevalent in women compared to men. Here, we review an up-to-date summary of animal and human studies in adulthood that report sex differences in fear extinction from a structural and functional approach. Furthermore, we describe how these factors could contribute to the observed sex differences in fear extinction during normal and pathological conditions.

The PPARα agonist fenofibrate attenuates disruption of dopamine function in a maternal immune activation rat model of schizophrenia

Aims

Prenatal maternal immune activation (MIA) is associated with a risk to develop schizophrenia and affects dopamine systems in the ventral tegmental area (VTA), key region in the neurobiology of psychoses. Considering the well‐described sex differences in schizophrenia, we investigated whether sex affects MIA impact on dopamine system and on schizophrenia‐related behavioral phenotype. Furthermore, considering peroxisome proliferator‐activated receptor‐α (PPARα) expression in the CNS as well as its anti‐inflammatory and neuroprotective properties, we tested if PPARα activation by prenatal treatment with a clinically available fibrate (fenofibrate) may mitigate MIA‐related effects.

Methods

We induced MIA in rat dams with polyriboinosinic‐polyribocytidylic acid (Poly I:C) and assessed prepulse inhibition and dopamine neuron activity in the VTA by means of electrophysiological recordings in male and female preweaned and adult offspring.

Results

Poly I:C‐treated males displayed prepulse inhibition deficits, reduced number and firing rate of VTA dopamine neurons, and paired‐pulse facilitation of inhibitory and excitatory synapses. Prenatal fenofibrate administration attenuated detrimental effects induced by MIA on both the schizophrenia‐like behavioral phenotype and dopamine transmission in male offspring.

Conclusion

Our study confirms previous evidence that females are less susceptible to MIA and highlights PPARα as a potential target for treatments in schizophrenia.

Ethanol actions on the ventral tegmental area: novel potential targets on reward pathway neurons

The ventral tegmental area (VTA) evaluates salience of environmental stimuli and provides dopaminergic innervation to many brain areas affected by acute and chronic ethanol exposure. While primarily associated with rewarding and reinforcing stimuli, recent evidence indicates a role for the VTA in aversion as well. Ethanol actions in the VTA may trigger neuroadaptation resulting in reduction of the aversive responses to alcohol and a relative increase in the rewarding responses. In searching for effective pharmacotherapies for the treatment of alcohol abuse and alcoholism, recognition of this imbalance may reveal novel strategies. In addition to conventional receptor/ion channel pharmacotherapies, epigenetic factors that control neuroadaptation to chronic ethanol treatment can be targeted as an avenue for development of therapeutic approaches to restore the balance. Furthermore, when exploring therapies to address reward/aversion imbalance in the action of alcohol in the VTA, sex differences have to be taken into account to ensure effective treatment for both men and women. These principles apply to a VTA-centric approach to therapies, but should hold true when thinking about the overall approach in the development of neuroactive drugs to treat alcohol use disorders. Although the functions of the VTA itself are complex, it is a useful model system to evaluate the reward/aversion imbalance that occurs with ethanol exposure and could be used to provide new leads in the efforts to develop novel drugs to treat alcoholism.

Strategy set-shifting and response inhibition in adult rats exposed to an environmental polychlorinated biphenyl mixture during adolescence

Converging evidence from studies with animal models and humans suggests that early developmental exposure to polychlorinated biphenyls (PCBs) leads to deficits in cognitive flexibility and inhibitory control. These processes are mediated to a large extent by the prefrontal cortex, thus we examined the effects of PCB exposure during adolescence-a period of robust prefrontal cortical development-on both processes. Specifically, we used operant set-shifting and differential reinforcement of low rates of responding (DRL) tasks to assess cognitive flexibility and response inhibition, respectively. One male and one female pup from each of 14 litters were assigned to each of three treatment groups: 0, 3 or 6mgPCB/kg/day. Rats were dosed orally from postnatal day (PND) 27-50 to capture the whole period of adolescence in rats. At approximately PND 90, they began testing in the set-shifting task which included an initial visual cue discrimination, an extra-dimensional shift to a position discrimination and a reversal of the position discrimination. There were no statistically significant group differences in errors to criterion on visual cue discrimination or on the shift from visual to position discrimination in either males or females. During the position reversal, the 6mg/kg PCB males made significantly fewer errors to reach criterion than control males. The 3mg/kg PCB males showed a trend in the same direction, but this did not reach statistical significance. Interestingly, error analysis revealed that PCB-exposed males made significantly fewer perseverative errors than controls in this phase. No group differences were observed in females. These results suggest a male-specific effect of adolescent PCB-exposure on the reversal phase of the set-shifting task. Following set-shifting, rats progressed to the DRL task in which they were required to withhold responding for a specified period of time (15s) in order to receive a reinforcer. There were no exposure-related group differences in total presses or efficiency ratio in males or in females. In summary, there were subtle sex-specific effects of adolescent PCB exposure on the reversal phase of a set-shifting task, but no effects of exposure on performance on a DRL15 task, suggesting an effect on cognitive flexibility but not response inhibition.

Cocaine self-administration in male and female rats perinatally exposed to PCBs: Evaluating drug use in an animal model of environmental contaminant exposure

Polychlorinated biphenyls (PCBs) are ubiquitous environmental toxicants known to adversely impact human health. Ortho-substituted PCBs affect the nervous system, including the brain dopaminergic system. The reinforcing effects of psychostimulants are typically modulated via the dopaminergic system, so this study used a preclinical (i.e., rodent) model to evaluate whether developmental contaminant exposure altered intravenous self-administration (IV SA) for the psychostimulant cocaine. Long-Evans rats were perinatally exposed to 6 or 3 mg/kg/day of PCBs throughout gestation and lactation and compared with nonexposed controls. Rats were trained to lever press for a food reinforcer in an operant chamber under a fixed-ratio 5 (FR5) schedule and later underwent jugular catheterization. Food reinforcers were switched for infusions of 250 μg of cocaine, but the response requirement to earn the reinforcer remained. Active lever presses and infusions were higher in males during response acquisition and maintenance. The same sex effect was observed during later sessions which evaluated responding for cocaine doses ranging from 31.25-500 μg. PCB-exposed males (not females) exhibited an increase in cocaine infusions (with a similar trend in active lever presses) during acquisition, but no PCB-related differences were observed during maintenance, examination of the cocaine dose-response relationship, or progressive ratio (PR) sessions. Overall, these results indicated perinatal PCB exposure enhanced early cocaine drug-seeking in this preclinical model of developmental contaminant exposure (particularly the males), but no differences were seen during later cocaine SA sessions. As such, additional questions regarding substance abuse proclivity may be warranted in epidemiological studies evaluating environmental contaminant exposures. (PsycINFO Database Record

From molecules to behavior: An integrative theory of autism spectrum disorder

Autism spectrum disorder (ASD) comprises a group of neurodevelopmental disorders for which various theories have been proposed. Each theory brings valuable insights and has experimental evidence backing it, yet none provides an overarching explanation for each of the pathological aspects involved in ASD. Here we present an integrative theory of ASD, centered on a sequence of events spanning from the molecular to the behavioral level. We propose that an abnormality in the interplay between retinoic acid and sex hormones predisposes an individual to specific molecular malfunctions. In turn, this molecular syndrome generates an altered brain connectivity between the cerebellum, the midbrain dopaminergic areas, and the prefrontal cortex. Lastly, this disconnection would generate specific behavioral traits traditionally involved in ASD. Therefore, this paper represents a step forward in unifying different levels of pathological features into novel integrated testable hypotheses.

Emergence of sex differences in the development of substance use and abuse during adolescence

Substance use and abuse begin during adolescence. Male and female adolescent humans initiate use at comparable rates, but males increase use faster. In adulthood, more men than women use and abuse addictive drugs. However, some women progress more rapidly from initiation of use to entry into treatment. In animal models, adolescent males and females consume addictive drugs similarly. However, reproductively mature females acquire self-administration faster, and in some models, escalate use more. Sex/gender differences exist in neurobiologic factors mediating both reinforcement (dopamine, opioids) and aversiveness (CRF, dynorphin), as well as intrinsic factors (personality, psychiatric co-morbidities) and extrinsic factors (history of abuse, environment especially peers and family) which influence the progression from initial use to abuse. Many of these important differences emerge during adolescence, and are moderated by sexual differentiation of the brain. Estradiol effects which enhance both dopaminergic and CRF-mediated processes contribute to the female vulnerability to substance use and abuse. Testosterone enhances impulsivity and sensation seeking in both males and females. Several protective factors in females also influence initiation and progression of substance use including hormonal changes of pregnancy as well as greater capacity for self-regulation and lower peak levels of impulsivity/sensation seeking. Same sex peers represent a risk factor more for males than females during adolescence, while romantic partners increase risk for women during this developmental epoch. In summary, biologic factors, psychiatric co-morbidities as well as personality and environment present sex/gender-specific risks as adolescents begin to initiate substance use.

Sex-dependent diversity in ventral tegmental dopaminergic neurons and developmental programing: A molecular, cellular and behavioral analysis

The knowledge that diverse populations of dopaminergic neurons within the ventral tegmental area (VTA) can be distinguished in terms of their molecular, electrophysiological and functional properties, as well as their differential projections to cortical and subcortical regions has significance for key brain functions, such as the regulation of motivation, working memory and sensorimotor control. Almost without exception, this understanding has evolved from landmark studies performed in the male sex. However, converging evidence from both clinical and pre-clinical studies illustrates that the structure and functioning of the VTA dopaminergic systems are intrinsically different in males and females. This may be driven by sex differences in the hormonal environment during adulthood ('activational' effects) and development (perinatal and/or pubertal 'organizational' effects), as well as genetic factors, especially the SRY gene on the Y chromosome in males, which is expressed in a sub-population of adult midbrain dopaminergic neurons. Stress and stress hormones, especially glucocorticoids, are important factors which interact with the VTA dopaminergic systems in order to achieve behavioral adaptation and enable the individual to cope with environmental change. Here, also, there is male/female diversity not only during adulthood, but also in early life when neurobiological programing by stress or glucocorticoid exposure differentially impacts dopaminergic developmental trajectories in male and female brains. This may have enduring consequences for individual resilience or susceptibility to pathophysiological change induced by stressors in later life, with potential translational significance for sex bias commonly found in disorders involving dysfunction of the mesocorticolimbic dopaminergic systems. These findings highlight the urgent need for a better understanding of the sexual dimorphism in the VTA if we are to improve strategies for the prevention and treatment of debilitating conditions which differentially affect men and women in their prevalence and nature, including schizophrenia, attention/deficit hyperactivity disorder, autism spectrum disorders, anxiety, depression and addiction.

Prenatal Stress Produces Persistence of Remote Memory and Disrupts Functional Connectivity in the Hippocampal-Prefrontal Cortex Axis

Prenatal stress is a risk factor for the development of neuropsychiatric disorders, many of which are commonly characterized by an increased persistence of aversive remote memory. Here, we addressed the effect of prenatal stress on both memory consolidation and functional connectivity in the hippocampal-prefrontal cortex axis, a dynamical interplay that is critical for mnemonic processing. Pregnant mice of the C57BL6 strain were subjected to restraint stressed during the last week of pregnancy, and male offspring were behaviorally tested at adulthood for recent and remote spatial memory performance in the Barnes Maze test under an aversive context. Prenatal stress did not affect the acquisition or recall of recent memory. In contrast, it produced the persistence of remote spatial memory. Memory persistence was not associated with alterations in major network rhythms, such as hippocampal sharp-wave ripples (SWRs) or neocortical spindles. Instead, it was associated with a large decrease in the basal discharge activity of identified principal neurons in the medial prefrontal cortex (mPFC) as measured in urethane anesthetized mice. Furthermore, functional connectivity was disrupted, as the temporal coupling between neuronal discharge in the mPFC and hippocampal SWRs was decreased by prenatal stress. These results could be relevant to understand the biological basis of the persistence of aversive remote memories in stress-related disorders.

Prenatal exposure to psychostimulants increases impulsivity, compulsivity, and motivation for rewards in adult mice

Given the widespread use and misuse of methamphetamine (METH) and methylphenidate (MPD), especially in relation to women of childbearing age, it is important to consider the long-lasting effects of these drugs on the brain of the developing fetus. Male and female C57Bl/6J mice were prenatally exposed to METH (5mg/kg), MPD (10mg/kg), or saline. Following a 3-month washout, behavioral analysis using the 5-Choice Serial Reaction Time Task (5CSRTT) was performed on adult mice. After reaching training criteria, performance on a pseudo-random intertrial interval test session revealed decrements in 5CSRTT behavior. Prenatally-treated METH and MPD mice demonstrated significant increases in impulsivity, compulsivity, and motivation for reward compared to their saline controls. There were sex by drug interactions indicating a possible sexually dimorphic response to these prenatal drug exposures. Of particular clinical interest, we find that mice prenatally exposed to METH or MPD express characteristics of both inhibitory control decrements and heightened motivation for rewards, which represent core symptoms of addiction and other impulse control disorders.

Developmental exposure to polychlorinated biphenyls reduces amphetamine behavioral sensitization in Long-Evans rats

PCBs have long been known to affect dopamine (DA) function in the brain. The current study used an amphetamine behavioral sensitization paradigm in rats developmentally exposed to PCBs. Long-Evans rats were given perinatal exposure to 0, 3, or 6mg/kg/day PCBs and behavioral sensitization to d-amphetamine (AMPH) was assessed in one adult male and female/litter. Non-exposed (control) males showed increasing locomotor activity to repeated injections of 0.5mg/kg AMPH, typical of behavioral sensitization. PCB-exposed males showed greater activation to the initial acute AMPH injection, but sensitization occurred later and was blunted relative to controls. Sensitization in control females took longer to develop than in the males, but no exposure-related differences were observed. Analysis of whole brain and serum AMPH content following a final IP injection of 0.5mg/kg revealed no differences among the exposure groups. Overall, these results indicated developmental PCB exposure can alter the motor-stimulating effects of repeated AMPH injections. Males developmentally exposed to PCBs appeared to be pre-sensitized to AMPH, but quickly showed behavioral tolerance to the same drug dose. Results also revealed the behavioral effect was not due to exposure-induced alterations in AMPH metabolism following PCB exposure.

Sex matters during adolescence: testosterone-related cortical thickness maturation differs between boys and girls

Age-related changes in cortical thickness have been observed during adolescence, including thinning in frontal and parietal cortices, and thickening in the lateral temporal lobes. Studies have shown sex differences in hormone-related brain maturation when boys and girls are age-matched, however, because girls mature 1–2 years earlier than boys, these sex differences could be confounded by pubertal maturation. To address puberty effects directly, this study assessed sex differences in testosterone-related cortical maturation by studying 85 boys and girls in a narrow age range and matched on sexual maturity. We expected that testosterone-by-sex interactions on cortical thickness would be observed in brain regions known from the animal literature to be high in androgen receptors. We found sex differences in associations between circulating testosterone and thickness in left inferior parietal lobule, middle temporal gyrus, calcarine sulcus, and right lingual gyrus, all regions known to be high in androgen receptors. Visual areas increased with testosterone in boys, but decreased in girls. All other regions were more impacted by testosterone levels in girls than boys. The regional pattern of sex-by-testosterone interactions may have implications for understanding sex differences in behavior and adolescent-onset neuropsychiatric disorders.

Sexual differentiation of the brain and ADHD: what is a sex difference in prevalence telling us?

Sexual differentiation of the brain is a function of various processes that prepare the organism for successful reproduction in adulthood. Release of gonadal steroids during both the perinatal and the pubertal stages of development organizes many sex differences, producing changes in brain excitability and morphology that endure across the lifespan. To achieve these sexual dimorphisms, gonadal steroids capitalize on a number of distinct mechanisms across brain regions. Comparison of the developing male and female brain provides insight into the mechanisms through which synaptic connections are made, and circuits are organized that mediate sexually dimorphic behaviors. The prevalence of most psychiatric and neurological disorders differ in males versus females, including disorders of attention, activity and impulse control. While there is a strong male bias in incidence of attention deficit and hyperactivity disorders, the source of that bias remains controversial. By elucidating the biological underpinnings of male versus female brain development, we gain a greater understanding of how hormones and genes do and do not contribute to the differential vulnerability in one sex versus the other.

Effects of prenatal and postnatal exposure to amitraz on norepinephrine, serotonin and dopamine levels in brain regions of male and female rats

The effects of maternal exposure to amitraz on brain region monoamine levels of male and female offspring rats at 60 days of age were observed. Maternal and offspring body weight, physical and general activity development were unaffected by the exposure of dams to amitraz (20mg/kgbw, orally on days 6-21 of pregnancy and 1-10 of lactation). Male and female offspring were sacrificed at 60 days of age and possible alterations in the content and metabolism of NE, DA and 5-HT were determined in brain regions by HPLC. The results showed that all these neurotransmitter systems were altered in a brain regional-related manner. In male and female offspring, amitraz induced a significant decrease in the prefrontal cortex 5-HT and its metabolite 5-HIAA and DA and its metabolites DOPAC and HVA levels with interaction of sex. Nevertheless, we verified that striatum DA and 5-HT and corresponding metabolite contents decreased in male and female offspring without statistical distinction of sex. In contrast, amitraz did not modify 5-HT content, but caused an increase in 5-HIAA content in the medulla oblongata and hippocampus in male and female offspring. Alterations in the hippocampus DA, DOPAC and HVA levels after amitraz exposure were also observed displaying a sex interaction. NE levels also showed a decrease after amitraz treatment in the prefrontal cortex and striatum without statistical sex interaction, but MHPG levels decreased in both regions with a sex interaction. Amitraz evoked increases in 5-HT turnover in the prefrontal cortex as well as in DA turnover in the striatum and hippocampus but decreases in NE turnover in the hypothalamus, prefrontal cortex and striatum. The present findings indicated that maternal exposure to amitraz altered noradrenergic, serotonergic and dopaminergic neurochemistry in their offspring in the prefrontal cortex, striatum and hippocampus, and those variations could be related to several alterations in the functions in which these brain regions are involved.

Gonadectomy and hormone replacement affects in vivo basal extracellular dopamine levels in the prefrontal cortex but not motor cortex of adult male rats

Gonadectomy in adult male rats is known to impair performance on dopamine (DA)-dependent prefrontal cortical tasks and selectively dysregulate end points in the mesoprefrontal DA system including axon density. In this study, in vivo microdialysis and high-pressure liquid chromatography were used to determine whether short (4 day)- and/or long-term (28 day) gonadectomy and hormone replacement might also influence the more functionally relevant metric of basal extracellular DA level/tone. Assessments in medial prefrontal cortex revealed that DA levels were significantly lower than control in 4-day gonadectomized rats and similar to control in 4-day gonadectomized animals supplemented with both testosterone and estradiol. Among the long-term treatment groups, DA levels were significantly higher than control in gonadectomized rats and gonadectomized rats given estradiol but were similar to control in rats given testosterone. In contrast, extracellular DA levels measured in motor cortex were unaffected by long- or short-term gonadectomy. The effects of gonadectomy and hormone replacement on prefrontal cortical DA levels observed here parallel previously identified effects on prefrontal DA axon density and could represent hormone actions relevant to the modulation of DA-dependent prefrontal cortical function and perhaps its dysfunction in disorders such as schizophrenia, attention deficit hyperactivity disorder, and autism where males are disproportionately affected relative to females.

Sex differences in the adolescent brain

Adolescence is a time of increased divergence between males and females in physical characteristics, behavior, and risk for psychopathology. Here we will review data regarding sex differences in brain structure and function during this period of the lifespan. The most consistent sex difference in brain morphometry is the 9-12% larger brain size that has been reported in males. Individual brain regions that have most consistently been reported as different in males and females include the basal ganglia, hippocampus, and amygdala. Diffusion tensor imaging and magnetization transfer imaging studies have also shown sex differences in white matter development during adolescence. Functional imaging studies have shown different patterns of activation without differences in performance, suggesting male and female brains may use slightly different strategies for achieving similar cognitive abilities. Longitudinal studies have shown sex differences in the trajectory of brain development, with females reaching peak values of brain volumes earlier than males. Although compelling, these sex differences are present as group averages and should not be taken as indicative of relative capacities of males or females.

Sex differences in stress response circuitry activation dependent on female hormonal cycle

Understanding sex differences in stress regulation has important implications for understanding basic physiological differences in the male and female brain and their impact on vulnerability to sex differences in chronic medical disorders associated with stress response circuitry. In this functional magnetic resonance imaging study, we demonstrated that significant sex differences in brain activity in stress response circuitry were dependent on women's menstrual cycle phase. Twelve healthy Caucasian premenopausal women were compared to a group of healthy men from the same population, based on age, ethnicity, education, and right handedness. Subjects were scanned using negative valence/high arousal versus neutral visual stimuli that we demonstrated activated stress response circuitry [amygdala, hypothalamus, hippocampus, brainstem, orbitofrontal cortex (OFC), medial prefrontal cortex (mPFC), and anterior cingulate gyrus (ACG)]. Women were scanned twice based on normal variation in menstrual cycle hormones [i.e., early follicular (EF) compared with late follicular-midcycle (LF/MC) menstrual phases]. Using SPM8b, there were few significant differences in blood oxygenation level-dependent (BOLD) signal changes in men compared to EF women, except ventromedial nucleus (VMN), lateral hypothalamic area (LHA), left amygdala, and ACG. In contrast, men exhibited significantly greater BOLD signal changes compared to LF/MC women on bilateral ACG and OFC, mPFC, LHA, VMN, hippocampus, and periaqueductal gray, with largest effect sizes in mPFC and OFC. Findings suggest that sex differences in stress response circuitry are hormonally regulated via the impact of subcortical brain activity on the cortical control of arousal, and demonstrate that females have been endowed with a natural hormonal capacity to regulate the stress response that differs from males.

Developmental exposure to PCBs and/or MeHg: effects on a differential reinforcement of low rates (DRL) operant task before and after amphetamine drug challenge

The current study assessed the effects of developmental PCB and/or MeHg exposure on an operant task of timing and inhibitory control and determined if amphetamine (AMPH) drug challenges differentially affected performance. Long-Evans rats were exposed to corn oil (control), PCBs alone (1 or 3 mg/kg), MeHg alone (1.5 or 4.5 ppm), the low combination (1 mg/kg PCBs+1.5 ppm MeHg), or the high combination (3 mg/kg PCBs+4.5 ppm MeHg) throughout gestation and lactation. An environmentally relevant, formulated PCB mixture was used. Male and female offspring were trained to asymptotic performance on a differential reinforcement of low rates (DRL) operant task as adults. PCB-exposed groups had a lower ratio of reinforced to non-reinforced responses than controls. Groups exposed to MeHg alone were not impaired and the deficits observed in PCB-exposed groups were not seen when PCBs were co-administered with MeHg. AMPH was less disruptive to responding in males receiving PCBs alone, MeHg alone, and 1.0 mg/kg PCB+1.5 ppm MeHg. Paradoxically, the disruption in responding by AMPH in males given 3.0 mg/kg PCB+4.5 ppm MeHg did not differ from controls. Exposed females from all treatment groups did not differ from controls in their AMPH response. Overall, the findings suggest that developmental exposure to PCBs can decrease DRL performance. Co-exposure to MeHg seemed to mitigate the detrimental effects of PCBs on performance. The finding that the disruptive effects of AMPH on DRL performance were lessened in some groups of exposed males suggests that alterations in dopaminergic functioning may have a role in behavioral changes seen after perinatal PCB and MeHg exposure.

Region and sex differences in constituent dopamine neurons and immunoreactivity for intracellular estrogen and androgen receptors in mesocortical projections in rats

Many cortical and prefrontal functions show sex differences in their development, adult capacity, and dysfunction in disorders like schizophrenia. Correlations between circulating gonadal hormones and certain prefrontal functions have also been identified in humans and experimental animal models. Although multiple mechanisms may be involved, such hormone sensitivities/sex differences could be related to gonadal steroid actions on another regulator of cortical/prefrontal cortical function, the mesocortical dopamine system. Thus, although it is well known that perturbations in prefrontal dopamine signaling induce behavioral deficits, it is also known that several endpoints of these afferents are sensitive to gonadal steroids and/or are sexually dimorphic. This study explored possible substrates for this in two ways: by comparing the distributions of immunoreactivity for intracellular estrogen (alpha and beta) and androgen receptors among retrogradely labeled dopaminergic and nondopaminergic mesocortical neurons projecting to prefrontal, premotor, and primary motor cortices, areas in which male rat dopamine axons are differentially hormone-sensitive; and by comparing anatomical data in males and females. These analyses revealed region-, cell-, and sex-specific specializations in receptor localization that paralleled established patterns of mesocortical hormone sensitivity, including the androgen sensitivity of dopamine axons and dopamine-dependent functions in prefrontal cortex. It was also found that the proportions of dopamine neurons making up mesocortical projections were approximately 30% in males, whereas in females, significantly more constituent cells were dopaminergic. Together, these features may be part of the neurobiology giving mesocortical afferents their hormone sensitivities and/or sex differences in physiology, function, and dysfunction in disease.

Hypothalamic abnormalities in schizophrenia: sex effects and genetic vulnerability

BACKGROUND

This is a unique hypothalamic magnetic resonance imaging (MRI) study in schizophrenia, an important region in the limbic system. We hypothesized abnormal volumetric increases, with greater severity in multiplex families (more than one ill member) compared with simplex families (one ill). We tested the hypothesis that normal hypothalamic sexual dimorphism is disrupted in schizophrenia.

METHODS

Eighty-eight DSM-III-R schizophrenia cases (40 simplex and 48 multiplex), 43 first-degree nonpsychotic relatives, and 48 normal comparisons systematically were compared. A 1.5-Tesla General Electric scanner was used to acquire structural MRI scans, and contiguous 3.1-mm slices were used to segment anterior and posterior hypothalamus. General linear model for correlated data and generalized estimating equations were used to compare cases, relatives, and controls on right and left hypothalamus, controlled for age, sex, and total cerebral volume. Spearman's correlations of hypothalamic volumes with anxiety were calculated to begin to examine arousal correlates with structural abnormalities.

RESULTS

Findings demonstrated significantly increased hypothalamic volume in cases and nonpsychotic relatives, particularly in regions of paraventricular and mammillary body nuclei, respectively. This increase was linear from simplex to multiplex cases, was positively correlated with anxiety, and had a greater propensity in women.

CONCLUSIONS

Findings suggest important implications for understanding genetic vulnerability of schizophrenia and the high rate of endocrine abnormalities.

Sex, hormones and affective arousal circuitry dysfunction in schizophrenia

Women with schizophrenia express affective disturbances disproportionately more than men. Brain regions implicated in the affective arousal circuitry also regulate the hypothalamic-pituitary-adrenal and -gonadal systems, which are dysfunctional in schizophrenia. This review will argue that understanding the etiology of affective arousal deficits in schizophrenia is intimately connected with characterizing the role of neuroendocrine dysfunction and sex effects in schizophrenia. Further, the etiology of these neuroendocrine deficits begins during fetal development, during a period of time that coincides with the sexual differentiation of the brain and the vulnerability for schizophrenia. Studying the links between deficits in neuroendocrine systems and the affective arousal system in schizophrenia will provide clues to understanding the development of sex differences in schizophrenia and thereby its etiology.

Morphometric and statistical analysis of macro- and microscopic characteristics of the brain and their relationships with adrenocortical histophysiology in newborn rats

A direct relationship between the weights of the brain and hemisphere and parameters characterizing the development of the cortex and its neurons in intact newborn rats was revealed. Parameters of brain development in newborn rats correlate with 3beta-hydroxysteroid dehydrogenase activity in the adrenal zona glomerulosa.

Prenatal exposure to bisphenol A impairs sexual differentiation of exploratory behavior and increases depression-like behavior in rats

Perinatal exposure to bisphenol A (BPA, 0.1 and 1 ppm in drinking water applied to mother rats for 6 weeks) has been shown to impair the sexual differentiation in exploratory behavior, but the exact critical period of this disrupting effect is still unknown. In this study, we examined the effects of prenatal exposure to BPA (0.1 ppm in drinking water applied to dams during the final week of pregnant) on emotional and learning behaviors in addition to exploratory behavior. Estimated daily intake was 15 microg/kg/day, below the reference dose (RfD) in the United States and the daily tolerable intake (TDI) in Japan (50 microg/kg/day). The rats were successively tested in open-field test, elevated plus maze test, passive avoidance test and forced swimming test during development from 6 to 9 weeks of juvenile period. Prenatal exposure to BPA mainly affected male rats and abolished sex differences in rearing behavior in the open-field test and struggling behavior in the forced swimming test. BPA increased the immobility of male rats in the forced swimming test. The avoidance learning and behaviors in the elevated plus maze were not affected. The present study demonstrates that male rats at the final week of prenatal period are sensitive to BPA, which impairs sexual differentiation in rearing and struggling behavior and facilitate depression-like behavior.

Hormonal cycle modulates arousal circuitry in women using functional magnetic resonance imaging

Sex-specific behaviors are in part based on hormonal regulation of brain physiology. This functional magnetic resonance imaging (fMRI) study demonstrated significant differences in activation of hypothalamic-pituitary-adrenal (HPA) circuitry in adult women with attenuation during ovulation and increased activation during early follicular phase. Twelve normal premenopausal women were scanned twice during the early follicular menstrual cycle phase compared with late follicular/midcycle, using negative valence/high arousal versus neutral visual stimuli, validated by concomitant electrodermal activity (EDA). Significantly greater magnitude of blood oxygenation level-dependent signal changes were found during early follicular compared with midcycle timing in central amygdala, paraventricular and ventromedial hypothalamic nuclei, hippocampus, orbitofrontal cortex (OFC), anterior cingulate gyrus (aCING), and peripeduncular nucleus of the brainstem, a network of regions implicated in the stress response. Arousal (EDA) correlated positively with brain activity in amygdala, OFC, and aCING during midcycle but not in early follicular, suggesting less cortical control of amygdala during early follicular, when arousal was increased. This is the first evidence suggesting that estrogen may likely attenuate arousal in women via cortical-subcortical control within HPA circuitry. Findings have important implications for normal sex-specific physiological functioning and may contribute to understanding higher rates of mood and anxiety disorders in women and differential sensitivity to trauma than men.

Regional, Laminar and Cellular Distribution of Immunoreactivity for ERβ in the Cerebral Cortex of Hormonally Intact, Postnatally Developing Male and Female Rats

Estrogen influences cerebral cortical development. Among the receptors involved are classical (ERalpha) and beta (ERbeta) intracellular estrogen receptors. In the first 2 weeks of postnatal life, cortical ERalpha is transiently expressed at much higher levels than in adulthood. In this study, development of ERbeta was examined by mapping ERbeta immunoreactivity in relation to major cortical regions, layers and cell types in postnatal male and female rats that were 1-28 postnatal days (PND) old. These studies revealed that ERbeta-immunoreactive nuclei were present in the allocortices on PND 1 but were not detected in isocortex until PND 7. Allocortical labeling was also higher on PND 1 than at all later ages, while in isocortical areas low numbers of ERbeta nuclei were seen on PND 7 that rose to higher, near adult densities by PND 21. Finally, double labeling showed that ERalpha was expressed mainly in neurons immunopositive for calretinin, while ERbeta was localized predominantly in parvalbumin-immunoreactive cells. Thus, the postnatal cortical developments of ERbeta and ERalpha occur according to different timetables, different patterns and in association with different cortical cells. It thus seems it likely that the two also make distinct contributions to postnatal cortical development and/or sexual differentiation.

Administration of 17alpha-ethinylestradiol during pregnancy elicits modifications of maternal behavior and emotional alteration of the offspring in the rat

Intraperitoneal administration of 17alpha-ethinylestradiol (15 microg.kg(-1)) in pregnant rats, every day from day 9 to day 14 of pregnancy, elicited a high percentage of abortions. Quantification of maternal behavior showed that treated dams took better care of their pups than control dams, injected with the vehicle only, did. Postnatal reflexes, which reflect maturational rate, were established more promptly in the offspring of treated dams than in the offspring of control dams. However, when adult, the rats born from treated dams developed anxiety- and depressive-like behaviors. All these results are explained by the effects of the exogenous estrogen on the developing brain of the fetuses.

Dopamine and serotonin: influences on male sexual behavior

Steroid hormones regulate sexual behavior primarily by slow, genomically mediated effects. These effects are realized, in part, by enhancing the processing of relevant sensory stimuli, altering the synthesis, release, and/or receptors for neurotransmitters in integrative areas, and increasing the responsiveness of appropriate motor outputs. Dopamine has facilitative effects on sexual motivation, copulatory proficiency, and genital reflexes. Dopamine in the nigrostriatal tract influences motor activity; in the mesolimbic tract it activates numerous motivated behaviors, including copulation; in the medial preoptic area (MPOA) it controls genital reflexes, copulatory patterns, and specifically sexual motivation. Testosterone increases nitric oxide synthase in the MPOA; nitric oxide increases basal and female-stimulated dopamine release, which in turn facilitates copulation and genital reflexes. Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT(2C) receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT(1A) receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins. One means for this inhibition is a decrease in dopamine release in the mesolimbic tract.

Prenatal exposure of Long-Evans rats to 17alpha-ethinylestradiol modifies neither latent inhibition nor prepulse inhibition of the startle reflex but elicits minor deficits in exploratory behavior

Prenatal administration of synthetic estrogens in humans as well as lower mammals was reported to alter behavior in adulthood. The alterations remain to be characterized according to specific pathophysiological hypotheses. In this study, three common behavioral models of schizophrenia were tested, i.e., latent inhibition (LI), prepulse inhibition of the startle response (PPI) and hyperlocomotion under amphetamine. Female Long-Evans rats were injected i.p. with a solution of 17alpha-ethinylestradiol (15 microg kg(-1)) everyday from day 9 to 14 of pregnancy, and behavioral characteristics of their offspring, raised by Wistar foster mothers, were compared to those of rats born from dams injected with the vehicle only, over the same gestation period. LI was tested in a conditioned taste aversion and a conditioned passive avoidance paradigm followed by a parametric study of PPI and an evaluation of locomotion in an open field under saline or amphetamine (1.5 mg kg(-1)). Histological brain measurements were also carried out in a subset of the same rats. Neither LI nor PPI was altered using methods that had proven sensitive in previous pharmacological studies. Treated rats' locomotion was impaired, but amphetamine did not elicit a differential enhancement. A thinner Amon's horn layer was observed in their hippocampus. This indicates that standard models of schizophrenia did not fit to the behavioral abnormalities found by others and confirmed in this study. They were not due to the abnormal maternal care to pups elicited by the treatment.

Sexually dimorphic effects of prenatal stress on cognition, hormonal responses, and central neurotransmitters

Exposure to stress during gestation results in physiological and behavioral alterations that persist into adulthood. This study examined the effects of prenatal stress on the postnatal expression of sexually differentiated cognitive, hormonal, and neurochemical profiles in male and female rats. Pregnant dams were subjected to restraint stress three times daily for 45 min during d 14-21 of pregnancy. The offspring of control and prenatally stressed dams were tested for anxiety-related and cognitive behaviors, stress and gonadal steroid hormone levels, as well as monoamines and metabolite levels in selected brain regions. Postnatal testosterone levels (measured at 1 and 5 d) did not differ between controls and prenatally stressed animals. In adulthood, the serum corticosterone response to stress was attenuated in prenatally stressed females, eliminating the sex difference normally observed in this parameter. Prenatally stressed females exhibited higher anxiety levels, evidenced by longer open field entry latencies. Prenatal stress had no effect on object recognition memory, but eliminated the advantage normally seen in the male performance of a spatial memory task. Neurochemical profiles of prenatally stressed females were altered toward the masculine phenotype in the prefrontal cortex, amygdala, and hippocampus. Thus, prenatal stress altered subsequent cognitive, endocrine, and neurochemical responses in a sex-specific manner. These data reinforce the view that prenatal stress affects multiple aspects of brain development, interfering with the expression of normal behavioral, neuroendocrine, and neurochemical sex differences. These data have implications for the effects of prenatal stress on the development of sexually dimorphic endocrine and neurological disorders.

Sex-specific development of cortical monoamine levels in mouse

Several mental health disorders exhibit sex differences in monoamine levels associated with dimorphic cortical ontogeny. Studies in rodents support the notion that monoamines can profoundly modulate morphogenesis. Here, we show significant sex and hemisphere differences in BALB/cByJ mice on postnatal day 3 for dopamine (DA) and serotonin (5-TH), supporting the notion that sex differences in early monoaminergic ontogeny may result in dimorphic cortical development. Such sex differences may also influence differential behavioral and/or clinical outcomes.

Androgen receptor expression in the developing male and female rat visual and prefrontal cortex

Gonadal steroid hormones are known to influence the development of the cerebral cortex of mammals. Steroid hormone action involves hormone binding to cytoplasmic or nuclear receptors, followed by DNA binding and gene transcription. The goals of the present study were twofold: to determine whether androgen receptors are present during development in two known androgen sensitive regions of the rat cerebral cortex, the primary visual cortex (Oc1) and the anterior cingulate/frontal cortex (Cg1/Fr2); and to determine whether androgen receptor (AR) expression in these regions differs between developing males and females. We used immunocytochemistry to detect AR protein on postnatal days 0, 4, and 10, and in situ hybridization to detect AR mRNA on postnatal day 10 in male and female rats. The level of AR expression was specific to the cortical region, with higher AR immunoreactive cell density and more AR mRNA in Oc1 than in Cg1/Fr2. AR immunoreactive cell density increased with age in both regions. Finally, on postnatal day 10, males had a higher AR immunoreactive cell density and more AR mRNA in Oc1 than did females. Thus, the presence of ARs may allow androgens to directly influence the development the cerebral cortex.

Effects of dopamine and estrogen upon cortical neurons that express parvalbumin in vitro

The purpose of these experiments was to study the effects of dopamine (DA) and 17 beta-estradiol (EST) upon parvalbumin expression in rodent frontal cortex during development. Organotypic slice cultures of the frontal cortex were prepared from neonatal rats (postnatal day 2/3) and maintained for 14 days in vitro in serum-enriched medium and medium treated with either DA, EST or DA+EST. Cultured slices were then fixed and immunostained for parvalbumin immunoreactivity. Under control conditions, parvalbumin immunoreactive somata and fibers were primarily found in the deep laminae. In comparison, slices in all treatment groups exhibited a pattern of parvalbumin expression that was significantly different than controls. Specifically, DA treatment increased the percentage of parvalbumin immunoreactive somata, dendritic length and density in the deep cortical layers, but not in the superficial cortical layers. Both EST and DA+EST treatments induced similar changes in both the deep and the superficial cortical layers. These treatment induced changes represent more mature patterns of parvalbumin expression when compared to controls, indicating that both DA and EST enhance cortical expression of the protein.

Aging and sex influence the anatomy of the rat anterior cingulate cortex

Cognitive processes supported by the prefrontal cortex undergo an age-related decline. Until very recently, nonhuman animal models of aging have relied on the exclusive use of male subjects. This study was designed to investigate the influence of age, sex, and ovarian hormonal state on anatomy of the rat medial prefrontal cortex (anterior cingulate cortex). Dendritic tree extent and spine density were examined in young adult (3-5 mos.) and aged (20-24 mos.) male and female rats. Young adult females were examined either at proestrus or estrus, and aged females were examined in one of two reproductively senescent (estropausal) phases, persistent estrus or persistent diestrus. Neither the estrous cycle nor state of estropause influenced spine density or dendritic tree extent. However, the anatomy of the anterior cingulate cortex of young adult rats was sexually dimorphic, with males having greater dendritic spine density as well as arborization. While there was a reduction in density and tree extent with age for both sexes, this reduction was more pronounced for males, resulting in a disappearance of most sex differences with age. Thus the results of this study suggest that aging of the rodent cerebral cortex may follow a sexually dimorphic pattern.

Regional, laminar, and cellular distribution of immunoreactivity for ER alpha and ER beta in the cerebral cortex of hormonally intact, adult male and female rats

Behavioral, biochemical and anatomical studies suggest that estrogen stimulates structure and/or function in the adult cerebral cortex. The studies presented here used immunocytochemistry to map the alpha and beta isoforms of intracellular estrogen receptors (ER alpha, ER beta) in major subdivisions of adult rat cortex to identify potential sites for relevant receptor-mediated hormone actions. These studies revealed that immunoreactivity for ER alpha (ER alpha-IR) and ER beta (ER beta-IR) was present in most cortical areas, was associated exclusively with neurons, and was similar in males and females. Each receptor isoform also had its own unique distribution with respect to cortical regions, layers, and cells. In sensorimotor areas, for example, ER beta-IR was more prominent than ER alpha-IR, and was concentrated in layer V neurons that were immunoreactive for parvalbumin. In contrast, ER alpha-IR was scattered among parvalbumin-immunonegative cells in layers II/III and V/VI. Likewise, in entorhinal cortex, ER beta-IR was present in calbindin-containing cells in layers III-VI, while ER alpha-IR was restricted to small numbers of calbindin-negative neurons in infragranular layers. In sum, ER beta-IR and ER alpha-IR were differentially distributed both with respect to cortical compartments and with respect to each other. Accordingly, estrogen activation at these two sites may be anticipated to impact disparate sets of cortical circuits, cells, and functions.

Effects of maternal exposure to a reconstituted mixture of polychlorinated biphenyls on sex-dependent behaviors and steroid hormone concentrations in rats: dose-response relationship

In a previous experiment, maternal exposure to a polychlorinated biphenyl (PCB) mixture reconstituted according to the congener pattern found in human breast milk resulted in decreased aromatase activity in the brain of newborn male rats, together with feminization of sweet preference behavior in adult male littermates. Both mixtures led to similar reductions of serum testosterone and testes weights. The purpose of the present study was (1) to examine the dose-response relationship for the reconstituted mixture and (2) to study if the rewarding properties of testosterone are affected at levels sufficient to alter sweet preference behavior. Female rats were fed diets with 0, 5, 20, or 40 mg PCBs/kg diet, resulting in an average daily intake of 0, 0.5, 2, or 4 mg/kg body wt. Exposure started 50 days prior to mating and was continued until birth of the offspring. A dose-dependent elevation of sweet preference was found in adult male offspring, indicating feminization of this sexually dimorphic behavior. Examination of conditioned place preference revealed a preference for the testosterone-paired side at the highest exposure condition. In weanling female offspring, dose-dependent reductions of serum testosterone and estradiol concentrations were detected. In addition, testosterone concentrations were reduced in a dose-dependent manner in adult male littermates long after termination of exposure. PCB concentrations in adipose tissue from offspring of the low dose group (0.5 mg/kg body wt) were approximately 10 times higher than values at the upper margin of current human exposure. Taken together, results indicate long-lasting and dose-dependent changes in sex-dependent behaviors and levels of sex steroid hormones in rats following developmental exposure to a PCB mixture that resembles the breast milk pattern.

Prenatal exposure to ethinylestradiol elicits behavioral abnormalities in the rat

Pregnant rats were i.p. injected with a solution of 17alpha-ethinylestradiol (15 microg kg(-1)) every day between day 9 and day 14 of pregnancy and the behavior of the offspring was compared to that of rats born from dams injected with the vehicle only during the same gestational period. The percentage of neonatal death was dramatically high in the prenatally treated group. Growth of the surviving animals was even better than that of controls, but when adult, they exhibited a number of behavioral abnormalities: increased spontaneous motor activity, decreased exploratory behavior, impaired cognitive processing, qualitatively different exploratory drive, and/or persevering behavior, increased anxiety-like behavior and social neophobia. These behavioral alterations, which resemble a number of psychiatric syndromes, suggest that ethinylestradiol altered the ontogenesis of different parts of the central nervous system involved in cognitive and emotional processes. However, it cannot be excluded that the changes in behavior of ethinylestradiol exposed offspring were due to the abnormal maternal behavior of the estradiol treated dams.

Early androgen treatment decreases cognitive function and catecholamine innervation in an animal model of ADHD

The spontaneously hypertensive rat (SHR) has been used as an animal model of attention deficit hyperactivity disorder (ADHD). The present study was designed to determine whether exposure to elevated androgen levels early in development demonstrated impairments in cognitive functioning, neuroendocrine control, and brain development parallel to those seen in ADHD children. The animals (SHR and Wistar (WKY) controls) were implanted with testosterone on postnatal day 10 and tested for behavior in a spatial cognition paradigm on postnatal day 45. Plasma samples were collected for determination of adrenocorticotrophin hormone (ACTH) and corticosterone levels as indicators of the basal tone of the pituitary-adrenal neuroendocrine axis. In addition, the density of tyrosine hydroxylase-immunoreactive fibers (an indicator of catecholamine innervation) in the frontal cortex was compared between animals. The current data show that early testosterone treatment in SHR animals resulted in additional deficits in spatial memory in the water maze, but was ineffective in altering the response of WKY animals. Furthermore, SHR rats had high basal ACTH and low corticosterone levels that may indicate a dysfunctional stress axis similar to other reports in humans with persistent ADHD. Finally, there was a further suppression of tyrosine hydroxylase-immunoreactivity in the frontal cortex of androgen-treated SHR rats. These results support the hypothesis that early androgen treatment may support the neurobiology of animals with genetic predisposition to hyperactivity, impulsivity and inattention in a manner consistent with the enhanced expression of ADHD-like behaviors.

Developmental exposure of rats to a reconstituted PCB mixture or aroclor 1254: effects on organ weights, aromatase activity, sex hormone levels, and sweet preference behavior

Polychlorinated biphenyls (PCBs) are lipophilic industrial chemicals which are regularly detected in human breast milk, serum, and tissues. They possess hormone-modulating properties, and, when transferred transplacentally to the developing fetus, PCBs have been shown to induce persistent sex-specific neurobehavioral deficits. Interactions of PCBs with sex steroid-modulated neural differentiation could in part account for such effects. To test this hypothesis, female Long-Evans rats were exposed via food containing 40 mg/kg of either a reconstituted PCB mixture (RM), composed according to the congener-pattern in human breast milk, or the technical PCB mixture Aroclor 1254 (A1254). The exposure period started 50 days prior to mating and was terminated at birth (postnatal day 0: PND 0). Aromatase (CYP 19) activity was determined in hypothalamus/preoptic area (HPOA) brain-sections from newborn male pups. This enzyme converts testosterone (T) to 17beta-estradiol (E(2)) and plays a key role in sexual brain differentiation. Moreover, serum concentrations of T and E(2), physical development, organ weights, exposure levels, and sex-specific behavior were evaluated at different life stages. On PND 0, a reduced aromatase activity was detected in the HPOA of male RM-pups compared to controls. Female RM-weanlings exhibited significantly elevated uterine wet weights on PND 21, which is a marker for estrogenic activity. In the adult stage (PND 170), male offspring with maternal exposure to either PCB mixture showed markedly reduced testes weights and serum testosterone levels, thus demonstrating persistent antiandrogenic effects. On PND 180, male RM-rats exhibited a behavioral feminization in a sweet preference test, suggesting long-lasting changes in neuronal brain organization caused by the perinatally suppressed aromatase activity. The results suggest that maternal exposure to the RM, the pattern of which is similar to the PCB spectrum in human milk, results in more distinct effects on sex steroid-dependent processes and behavior than the technical PCB mixture A1254. PCB levels in brain and adipose tissue of the exposed offspring lay within 1-2 orders of magnitude above background concentrations in humans.

Targeted ablation of gonadotrophs in transgenic mice affects embryonic development of lactotrophs

Ablation of pituitary gonadotrophs was obtained in transgenic mice expressing diphtheria toxin A (DTA) under control of the -313/+48 bovine glycoprotein hormone alpha-subunit (alphaSU) promoter, previously shown to be active in mouse gonadotrophs but not in thyrotrophs. Development of hormone-producing cell types was assessed on the day of birth by computer-assisted image analysis on paraffin-embedded, immunostained pituitary sections. Six out of 50 transgenic F0 ('founder') mice (3 males and 3 females) showed a nearly complete disappearance of gonadotrophs but not of thyrotrophs. The number of lactotrophs and the relative area occupied by PRL-immunoreactivity were significantly reduced in the gonadotroph-depleted mice. The size of lactotroph clusters was smaller in the absence of gonadotrophs. The number and immunoreactive area of corticotrophs and somatotrophs, on the other hand, were not significantly affected by gonadotroph ablation. Based on the reported evidence that fetal ovaries do not produce steroid hormones as a result of lack of expression of at least three of the steroidogenic enzymes, P450scc, P450c17, and P450arom, the present observations can hardly be explained by a decline in estrogen levels due to gonadotroph ablation. Rather, the present data indicate that gonadotrophs directly stimulate the development of lactotrophs during fetal and early postnatal life, consistent with previous in vitro observations, and/or that gonadotrophs may share a cell-lineage relationship with a subpopulation of lactotrophs.

Gonadectomy in adult life increases tyrosine hydroxylase immunoreactivity in the prefrontal cortex and decreases open field activity in male rats

The prefrontal cortices in rats participate in a range of cognitive, emotional, and locomotor functions that are dependent on its rich catecholamine innervation. Sex differences identified in many of these functions suggest that the prefrontal cortex is also influenced by gonadal hormones. Previous studies have shown that prefrontal catecholamines can be modified by changes in the hormone environment in developing animals. The present analyses, carried out in male rats gonadectomized as adults, with and without supplementation with testosterone proprionate, and examined at intervals from two days to 10 weeks after surgery, revealed that both the anatomical organization of prefrontal catecholamine afferents, and a behavioral measure sensitive to their selective lesioning remain highly responsive to changes in testicular hormones in adulthood. Thus, gonadectomy in adult male rats rapidly led to a large but transient decrease in the density of tyrosine hydroxylase immunoreactivity in all layers of the dorsal anterior cingulate cortex. This was followed by a sustained period in which immunoreactivity in the supragranular layers returned to levels that were just below normal (between 72 and 79% of normal), and labeling in deep laminae stabilized at considerably elevated innervation densities (approximately 150% of normal). Neither the acute decrease nor the chronic over-innervation characteristic of gonadectomized animals was observed in rats that were gonadectomized and supplemented with testosterone proprionate. Open field activity assessed along a corresponding 10 week timeline showed that gonadectomized animals were significantly less active than hormonally intact controls, a behavioral pattern opposite to the hyperactivity which persists following prefrontal dopamine lesions. Gonadectomized animals supplemented with testosterone proprionate, on the other hand, had open field scores that were not significantly different from controls. Taken together, these findings indicate that the adult hormone environment provides a significant, and seemingly functionally significant influence over the catecholamine innervation of the rat prefrontal cortex. Such lifelong responsiveness of the prefrontal cortical catecholamines to circulating hormones suggests that gonadal steroids are an active component of the biology of normal adult cognition, and may also have relevance for cortical dysfunction in disorders such as schizophrenia which are not only strongly tied to the catecholamines, but exhibit considerable biases among men and women as well.

Perinatal gonadectomy exerts regionally selective, lateralized effects on the density of axons immunoreactive for tyrosine hydroxylase in the cerebral cortex of adult male rats

The catecholamine innervation of the cerebral cortex is essential for its normal operations and is implicated in cortical dysfunction in mental illness. Previous studies in rats have shown that the maturational tempo of these afferents is highly responsive to changes in gonadal hormones. The present findings show that perinatal hormone manipulation also has striking, region- and hemisphere-specific consequences for cortical catecholamines in adulthood. The effect of perinatal gonadectomy on catecholamines was examined in representative sensory, motor, and association cortices of adult male rats by combining hormone manipulation with immunocytochemistry for tyrosine hydroxylase, a rate-limiting enzyme in catecholamine biosynthesis. Qualitative and quantitative comparison of immunoreactivity in rats perinatally gonadectomized or sham-operated revealed complex changes in gonadectomized subjects; in cingulate cortex, TH immunoreactivity was strongly and bilaterally diminished, in sensory and motor cortices, axon density was decreased in left hemispheres, but was minimally affected on the right, and in a premotor cortex, gonadectomy was without significant effect in either hemisphere. Corresponding analyses in gonadectomized rats supplemented with testosterone revealed a protective influence, albeit one in which TH immunoreactivity so showed regional and hemispheric variability in responsiveness to hormone replacement. These complex patterns of TH sensitivity suggest highly asymmetric hormone stimulation of cortical catecholamines. Such discriminative action may contribute to sex differences in the functional maturation and lateralization of the cortex and may also have bearing on disorders such as dyslexia, which show sexual dimorphisms, and in which functional laterality of the cortex may be particularly at issue.