Adverse Childhood Experiences and alcohol use among U.S.-born and immigrant Latinx youth: the roles of social support and stress hormones

The biobehavioral correlates of Adverse Childhood Experiences (ACEs) among Latinx youth have been strikingly understudied. The purpose of this study was to 1) examine the effects of T-ACEs (e.g., maltreatment, family dysfunction) and E-ACEs (e.g., family deportation, community violence) in alcohol use, 2) test whether social support moderated these associations and 3) explore whether ACEs and alcohol use were related via adrenocortical hormones (i.e., cortisol, dehydroepiandrosterone [DHEA]). A total of 100 Latinx youth, between the ages of 13 and 19, participated in this study (53% female). Community samples of United States (U.S.)-born (N = 54) and immigrant Latinx (N = 46) youth provided morning saliva samples and completed self-report questionnaires. Results highlighted that for immigrant youth, social support buffered the effects of E-ACEs on alcohol use, F(9,89)= 3.34, p = .01, R2 = .25. Although our mediation hypothesis was not supported, the direct effects of T-ACEs (β = .25, t (94) = 2.21, p = .03) and E-ACES (β = -.24, t (94) = -2.23, p = .03) on DHEA were significant for the entire sample. Preventing maltreatment and reducing community-level adversities seem critical for optimal child development, as exposure to these may increase alcohol use risk and affect HPA Axis functioning. Increasing extrafamilial support may be particularly salient for immigrant Latinx youth, as many experience extended immigration-related periods of separation from family members.

Novel molecular mechanisms in Alzheimer’s disease: The potential role of DEK in disease pathogenesis

Alzheimer’s disease and age-related dementias (AD/ADRD) are debilitating diseases that exact a significant physical, emotional, cognitive, and financial toll on the individual and their social network. While genetic risk factors for early-onset AD have been identified, the molecular and genetic drivers of late-onset AD, the most common subtype, remain a mystery. Current treatment options are limited for the 35 million people in the United States with AD/ADRD. Thus, it is critically important to identify novel molecular mechanisms of dementia-related pathology that may be targets for the development of new interventions. Here, we summarize the overarching concepts regarding AD/ADRD pathogenesis. Then, we highlight one potential molecular driver of AD/ADRD, the chromatin remodeling protein DEK. We discuss in vitro, in vivo, and ex vivo findings, from our group and others, that link DEK loss with the cellular, molecular, and behavioral signatures of AD/ADRD. These include associations between DEK loss and cellular and molecular hallmarks of AD/ADRD, including apoptosis, Tau expression, and Tau hyperphosphorylation. We also briefly discuss work that suggests sex-specific differences in the role of DEK in AD/ADRD pathogenesis. Finally, we discuss future directions for exploiting the DEK protein as a novel player and potential therapeutic target for the treatment of AD/ADRD.

In silico gene expression and pathway analysis of DEK in the human brain across the lifespan

DEK, a chromatin-remodelling phosphoprotein, is associated with various functions and biological pathways in the periphery, including inflammation, oncogenesis, DNA repair, and transcriptional regulation. We recently identified an association between DEK loss and central nervous system diseases, such as Alzheimer's. To understand DEK's potential role in disease, it is critical to characterize DEK in healthy human brain to distinguish between neural DEK expression and function in healthy versus diseased states like dementia. We utilized two public databases, BrainCloud and Human Brain Transcriptome, and analysed DEK mRNA expression across the lifespan in learning and memory relevant brain regions. Since DEK loss induces phenotypes associated with brain ageing (e.g., DNA damage and apoptosis), we hypothesized that neural DEK expression may be highest during foetal development and lower in elderly individuals. In agreement with this hypothesis, DEK was most prominently expressed during foetal development in all queried forebrain areas, relative to other ages. Consistent with its roles in the periphery, pathways related to DEK in the brain were associated with cellular proliferation, DNA replication and repair, apoptosis, and inflammation. We also found novel neural development-relevant pathways (e.g., synaptic transmission, neurite outgrowth, and myelination) to be enriched from genes correlated with DEK expression. These findings suggest that DEK is important for human brain development. Overall, we highlight age-related changes in neural DEK expression across the human lifespan and illuminate novel biological pathways associated with DEK that are distinct from normal brain ageing. These findings may further our understanding of how DEK impacts brain function and disease susceptibility.

Loss of DEK Expression Induces Alzheimer's Disease Phenotypes in Differentiated SH-SY5Y Cells

Alzheimer’s disease (AD) is the most common cause of dementia and is characterized by the buildup of β-amyloid plaques and neurofibrillary Tau tangles. This leads to decreased synaptic efficacy, cell death, and, consequently, brain atrophy in patients. Behaviorally, this manifests as memory loss and confusion. Using a gene ontology analysis, we recently identified AD and other age-related dementias as candidate diseases associated with the loss of DEK expression. DEK is a nuclear phosphoprotein with roles in DNA repair, cellular proliferation, and inhibiting apoptosis. Work from our laboratory determined that DEK is highly expressed in the brain, particularly in regions relevant to learning and memory, including the hippocampus. Moreover, we have also determined that DEK is highly expressed in neurons. Consistent with our gene ontology analysis, we recently reported that cortical DEK protein levels are inversely proportional to dementia severity scores in elderly female patients. However, the functional role of DEK in neurons is unknown. Thus, we knocked down DEK in an in vitro neuronal model, differentiated SH-SY5Y cells, hypothesizing that DEK loss would result in cellular and molecular phenotypes consistent with AD. We found that DEK loss resulted in increased neuronal death by apoptosis (i.e., cleaved caspases 3 and 8), decreased β-catenin levels, disrupted neurite development, higher levels of total and phosphorylated Tau at Ser262, and protein aggregates. We have demonstrated that DEK loss in vitro recapitulates cellular and molecular phenotypes of AD pathology.

Endocrine stress responsivity and social memory in 3xTg-AD female and male mice: A tale of two experiments

Stress confers risk for the development and progression of Alzheimer's disease (AD). Relative to men, women are disproportionately more likely to be diagnosed with this neurodegenerative disease. We hypothesized that sex differences in endocrine stress responsiveness may be a factor in this statistic. To test this hypothesis, we assessed basal and stress-induced corticosterone, social recognition, and coat state deterioration (surrogate for depression-like behavior) in male and female 3xTg-AD mice. Prior to reported amyloid plaque deposition, 3xTg females (4 months), but not 3xTg males, had heightened corticosterone responses to restraint exposure. Subsequently, only 3xTg females (6 months) displayed deficits in social memory concomitant with prominent β-amyloid (Aβ) immunostaining. These data suggest that elevated corticosterone stress responses may precede cognitive impairments in genetically vulnerable females. 3xTg mice of both sexes exhibited coat state deterioration relative to same-sex controls. Corticolimbic glucocorticoid receptor (GR) dysfunction is associated with glucocorticoid hypersecretion and cognitive impairment. Our findings indicate sex- and brain-region specific effects of genotype on hippocampal and amygdala GR protein expression. Because olfactory deficits may impede social recognition, in Experiment 2, we assessed olfaction and found no differences between genotypes. Notably, in this cohort, heightened corticosterone stress responses in 3xTg females was not accompanied by social memory deficits or coat state deterioration. However, coat state deterioration was consistent in 3xTg males. We report consistent heightened stress-induced corticosterone levels and Aβ pathology in female 3xTg-AD mice. However, the behavioral findings illuminate unknown inconsistencies in certain phenotypes in this AD mouse model.

Glucocorticoids regulate adipose tissue protein concentration in a depot- and sex-specific manner

Preclinical and clinical findings indicate that glucocorticoids (GC) induce lipid accumulation in visceral depots, while inhibiting lipid stores from subcutaneous depots. Whereas some suggest that this is due to adipose depot specific concentration of glucocorticoid receptors (GR) or 11beta-hydroxysteroid dehydrogenase 1 (11β-HSD1), others demonstrate these events emerge from increases in interleukin-1 beta (IL-1β) from macrophages within distinct depots. Regardless of the mechanisms, most of these studies occur in males and thus lack evaluation of sex differences. Here, we examined the impact of 2-week corticosterone (CORT) (3 mg/kg/day) or saline treatment on GR, 11β-HSD1 and IL-1β protein concentration in intra-abdominal (epididymal/parametrial, and visceral) and subcutaneous (inguinal) depots in male and female Sprague Dawley rats. The objective was to examine if factors that regulate GC-induced adipose depot metabolism and distribution, differ between males and females. CORT inhibited, but did not decrease, body weight gain in both sexes. 11β-HSD1 was similar between the sexes in all adipose depots. CORT increased IL-1β in both sexes only in gonadal adipose tissue. Overall, males had greater GR protein concentration in all adipose depots, whereas females had more IL-1β in intra-abdominal adipose depots. Given the male-biased increase in intra-abdominal GR protein concentration, the data suggest that males may be more prone to CORT-induced increases in visceral obesity, which may have implications for increased risk for metabolic diseases. Overall, the data suggest that the effects of GC signaling in adipose tissue are multifaceted, dependent on sex, and the inherent adipocyte characteristics.Lay summaryResearch supports that glucocorticoids (GC) induce visceral adipose tissue accumulation, however few studies have examined if these GC-mediated outcomes are similar between males and females. This study investigates if female rats differentially respond to corticosterone treatment. Results indicate that male rats may have an increased susceptibility to CORT-induced accumulation of visceral adipose tissue compared with females, which may have implication for sex-specific risk for metabolic diseases.

Palatable food reduces anxiety-like behaviors and HPA axis responses to stress in female rats in an estrous-cycle specific manner

Eating tasty foods dampens responses to stress - an idea reflected in the colloquial term 'comfort foods'. To study the neurobiological mechanisms by which palatable foods provide stress relief, we previously characterized a limited sucrose intake (LSI) paradigm in which male rats are given twice-daily access to 4 ml of 30% sucrose solution (vs. water as a control), and subsequently have reduced hypothalamic-pituitary-adrenocortical (HPA) axis responsivity and anxiety-related behaviors. Notably, women may be more prone to 'comfort feeding' than men, and this may vary across the menstrual cycle, suggesting the potential for important sex and estrous cycle differences. In support of this idea, LSI reduces HPA axis responses in female rats during the proestrus/estrus (P/E), as opposed to the diestrus 1/diestrus 2 (D1/D2) estrous cycle stage. However, the effect of LSI on anxiety-related behaviors in females remains unknown. Here we show that LSI reduced stress-related behaviors in female rats in the elevated plus-maze and restraint tests, but not in the open field test, though only during P/E. LSI also decreased the HPA axis stress response primarily during P/E, consistent with prior findings. Finally, cFos immunolabeling (a marker of neuronal activation) revealed that LSI increased post-restraint cFos in the central amygdala medial subdivision (CeM) and the bed nucleus of the stria terminalis posterior subnuclei (BSTp) exclusively during P/E. These results suggest that in female rats, palatable food reduces both behavioral and neuroendocrine stress responses in an estrous cycle-dependent manner, and the CeM and BSTp are implicated as potential mediators of these effects.

Effects of combined glucocorticoid/mineralocorticoid receptor modulation (CORT118335) on energy balance, adiposity, and lipid metabolism in male rats

Psychological stress and excess glucocorticoids are associated with metabolic and cardiovascular diseases. Glucocorticoids act primarily through mineralocorticoid (MR) and glucocorticoid receptors (GR), and compounds modulating these receptors show promise in mitigating metabolic and cardiovascular-related phenotypes. CORT118335 (GR/MR modulator) prevents high-fat diet-induced weight gain and adiposity in mice, but the ability of this compound to reverse obesity-related symptoms is unknown. Adult male rats were subcutaneously administered CORT118335 (3, 10, or 30 mg/kg) or vehicle once daily. A 5-day treatment with CORT118335 at 30 mg/kg induced weight loss in rats fed a chow diet by decreasing food intake. However, lower doses of the compound attenuated body weight gain primarily because of decreased calorific efficiency, as there were no significant differences in food intake compared with vehicle. Notably, the body weight effects of CORT118335 persisted during a 2-wk treatment hiatus, suggesting prolonged effects of the compound. To our knowledge, we are the first to demonstrate a sustained effect of combined GR/MR modulation on body weight gain. These findings suggest that CORT118335 may have long-lasting effects, likely due to GR/MR-induced transcriptional changes. Prolonged (18 days) treatment of CORT118335 (10 mg/kg) reversed body weight gain and adiposity in animals fed a high-fat diet for 13 wk. Surprisingly, this occurred despite a worsening of the lipid profile and glucose homeostasis as well as a disrupted diurnal corticosterone rhythm, suggesting GR agonistic effects in the periphery. We conclude that species and tissue-specific targeting may result in promising leads for exploiting the metabolically beneficial aspects of GR/MR modulation.

Sex differences in DEK expression in the anterior cingulate cortex and its association with dementia severity in schizophrenia

DEK is a chromatin-remodeling phosphoprotein found in most human tissues, but its expression and function in the human brain is largely unknown. DEK depletion in vitro induces cellular and molecular anomalies associated with cognitive impairment, including down-regulation of the canonical Wnt/β-catenin signaling pathway. ToppGene analyses link DEK loss to genes associated with various dementias and age-related cognitive decline. To examine the role of DEK in cognitive impairment in severe mental illness, DEK protein expression was assayed by immunoblot in the anterior cingulate cortex (ACC) of subjects with schizophrenia. Cognitive impairment is a core feature of schizophrenia and cognitive function in subjects was assessed antemortem using the clinical dementia rating (CDR) scale. DEK protein expression was not significantly altered in schizophrenia (n = 20) compared to control subjects (n = 20). Further analysis revealed significant reduction in DEK protein expression in women with schizophrenia, and a significant increase in expression in men with schizophrenia, relative to their same-sex controls. DEK protein expression levels were inversely correlated with dementia severity in women. Conversely, in men, DEK protein expression and dementia severity were positively correlated. Notably, there was no sex difference in DEK protein expression in the control group, suggesting that this sex difference is specific to schizophrenia and not due to inherent differences in DEK expression between males and females. These results suggest a novel, sex-specific role for DEK in cognitive performance and highlight a putative sex-specific link between central nervous system DEK protein expression and a neuropsychiatric disease that is commonly associated with cognitive impairment.

Adolescent environmental enrichment prevents behavioral and physiological sequelae of adolescent chronic stress in female (but not male) rats

The late adolescent period is characterized by marked neurodevelopmental and endocrine fluctuations in the transition to early adulthood. Adolescents are highly responsive to the external environment, which enhances their ability to adapt and recover from challenges when given nurturing influences, but also makes them vulnerable to aberrant development when exposed to prolonged adverse situations. Female rats are particularly sensitive to the effects of chronic stress in adolescence, which manifests as passive coping strategies and blunted hypothalamo-pituitary adrenocortical (HPA) stress responses in adulthood. We sought to intervene by exposing adolescent rats to environmental enrichment (EE) immediately prior to and during chronic stress, hypothesizing that EE would minimize or prevent the long-term effects of stress that emerge in adult females. To test this, we exposed male and female rats to EE on postnatal days (PND) 33-60 and implemented chronic variable stress (CVS) on PND 40-60. CVS consisted of twice-daily unpredictable stressors. Experimental groups included: CVS/unenriched, unstressed/EE, CVS/EE and unstressed/unenriched (n = 10 of each sex/group). In adulthood, we measured behavior in the open field test and forced swim test (FST) and collected blood samples following the FST. We found that environmental enrichment given during the adolescent period prevented the chronic stress-induced transition to passive coping in the FST and reversed decreases in peak adrenocortical responsiveness observed in adult females. Adolescent enrichment had little to no effect on males or unstressed females tested in adulthood, indicating that beneficial effects are specific to females that were exposed to chronic stress.

Palatable Food Affects HPA Axis Responsivity and Forebrain Neurocircuitry in an Estrous Cycle-specific Manner in Female Rats

Eating palatable foods can provide stress relief, but the mechanisms by which this occurs are unclear. We previously characterized a limited sucrose intake (LSI) paradigm in which twice-daily access to a small amount of 30% sucrose (vs. water as a control) reduces hypothalamic-pituitary-adrenocortical (HPA) axis responses to stress and alters neuronal activation in stress-regulatory brain regions in male rats. However, women may be more prone to 'comfort feeding' behaviors than men, and stress-related eating may vary across the menstrual cycle. This suggests that LSI effects may be sex- and estrous cycle-dependent. The present study therefore investigated the effects of LSI on HPA axis stress responsivity, as well as markers of neuronal activation/plasticity in stress- and reward-related neurocircuitry in female rats across the estrous cycle. We found that LSI reduced post-restraint stress plasma ACTH in female rats specifically during proestrus/estrus (P/E). LSI also increased basal (non-stress) FosB/deltaFosB- and pCREB-immunolabeling in the basolateral amygdala (BLA) and central amygdala specifically during P/E. Finally, Bayesian network modeling of the FosB/deltaFosB and pCREB expression data identified a neurocircuit that includes the BLA, nucleus accumbens, prefrontal cortex, and bed nucleus of the stria terminalis as likely being modified by LSI during P/E. When considered in the context of our prior results, the present findings suggest that palatable food reduces stress responses in female rats similar to males, but in an estrous cycle-dependent manner. Further, the BLA may contribute to the LSI effects in both sexes, whereas the involvement of other brain regions appears to be sex-dependent.

Estrogen signaling in the medial amygdala decreases emotional stress responses and obesity in ovariectomized rats

Declining estradiol (E2), as occurs during menopause, increases risk for obesity and psychopathology (i.e., depression, anxiety). E2 modulates mood and energy homeostasis via binding to estrogen receptors (ER) in the brain. The often comorbid and bidirectional relationship between mood and metabolic disorders suggests shared hormonal and/or brain networks. The medial amygdala (MeA) is abundant in ERs and regulates mood, endocrine, and metabolic stress responses; therefore we tested the hypothesis that E2 in the MeA mitigates emotional and metabolic dysfunction in a rodent model of surgical menopause. Adult female rats were ovariectomized (OVX) and received bilateral implants of E2 or cholesterol micropellets aimed at the MeA. E2-MeA decreased anxiety-like (center entries, center time) and depression-like (immobility) behaviors in the open field and forced swim tests (FST), respectively in ovariectomized rats. E2-MeA also prevented hyperphagia, body weight gain, increased visceral adiposity, and glucose intolerance in ovariectomized rats. E2-MeA decreased caloric efficiency, suggestive of increased energy expenditure. E2-MeA also modulated c-Fos neural activity in amygdalar (central and medial) and hypothalamic (paraventricular and arcuate) brain regions that regulate mood and energy homeostasis in response to the FST, a physically demanding task. Given the shared neural circuitry between mood and body weight regulation, c-Fos expression in discrete brain regions in response to the FST may be due to the psychologically stressful and/or metabolic demands of the task. Together, these findings suggest that the MeA is a critical node for mediating estrogenic effects on mood and energy homeostasis.

Evaluating social defeat as a model for psychopathology in adult female rodents

Social conflict is a predominant stressor in humans and is associated with increased risk for developing psychological illnesses including depression and anxiety. Overwhelmingly, more women suffer from these disorders, which may be due to increased stress sensitivity. Like humans, rodents experience a myriad of physiological and behavioral sequelae due to prolonged stress exposure. Although the motivation for social conflict may differ between humans and rodents, female rodents may provide an opportunity to explore the underlying mechanisms by which stress confers risk for psychopathology in women. Because most female rodents do not express spontaneous aggression, the majority of basic research examines the physiological and behavioral outcomes of social conflict in male rodents. However, there are instances where female rodents exhibit territorial (California mice and Syrian hamsters) and maternal aggression (rats, mice, and hamsters) creating a venue to examine sex differences in physiology and behavior in response to stress. While many studies rely upon nonsocial behavioral assays (e.g., elevated plus maze, forced swim test) to assess the impact of stress on emotionality, here we primarily focus on behavioral outcomes in social-based assays in rodents. This is critically important given that disruptions in social relationships can be a cause and consequence of neuropsychiatric diseases. Next, we briefly discuss how sex differences in the recruitment of neural circuitry and/or neurochemistry in response to stress may underlie sex differences in neuroendocrine and behavioral stress responses. Finally, the translational value of females in rodent stress models and considerations regarding behavioral interpretations of these models are discussed. © 2016 Wiley Periodicals, Inc.

Vesicular Glutamate Transporter 1 Knockdown in Infralimbic Prefrontal Cortex Augments Neuroendocrine Responses to Chronic Stress in Male Rats

Chronic stress-associated pathologies frequently associate with alterations in the structure and activity of the medial prefrontal cortex (mPFC). However, the influence of infralimbic cortex (IL) projection neurons on hypothalamic-pituitary-adrenal (HPA) axis activity is unknown, as is the involvement of these cells in chronic stress-induced endocrine alterations. In the current study, a lentiviral-packaged vector coding for a small interfering RNA (siRNA) targeting vesicular glutamate transporter (vGluT) 1 messenger RNA (mRNA) was microinjected into the IL of male rats. vGluT1 is responsible for presynaptic vesicular glutamate packaging in cortical neurons, and knockdown reduces the amount of glutamate available for synaptic release. After injection, rats were either exposed to chronic variable stress (CVS) or remained in the home cage as unstressed controls. Fifteen days after the initiation of CVS, all animals were exposed to a novel acute stressor (30-minute restraint) with blood collection for the analysis of adrenocorticotropic hormone (ACTH) and corticosterone. Additionally, brains were collected for in situ hybridization of corticotrophin-releasing hormone mRNA. In previously unstressed rats, vGluT1 siRNA significantly enhanced ACTH and corticosterone secretion. Compared with CVS animals receiving the green fluorescent protein control vector, the vGluT1 siRNA further increased basal and stress-induced corticosterone release. Further analysis revealed enhanced adrenal responsiveness in CVS rats treated with vGluT1 siRNA. Collectively, our results suggest that IL glutamate output inhibits HPA responses to acute stress and restrains corticosterone secretion during chronic stress, possibly at the level of the adrenal. Together, these findings pinpoint a neurochemical mechanism linking mPFC dysfunction with aberrant neuroendocrine responses to chronic stress.

A mixed glucocorticoid/mineralocorticoid receptor modulator dampens endocrine and hippocampal stress responsivity in male rats

Aberrant glucocorticoid secretion is implicated in the pathophysiology of stress-related disorders (i.e., depression, anxiety). Glucocorticoids exert biological effects via mineralocorticoid (MR) and glucocorticoid (GR) receptors. Previous data from our laboratory indicate that GR antagonism/modulation (i.e., mifepristone, CORT 108297) regulate endocrine, behavioral, and central stress responses. Because of the dynamic interplay between MR and GR on HPA axis regulation and emotionality, compounds targeting both receptors are of interest for stress-related pathology. We investigated the effects of CORT 118335 (a dual selective GR modulator/MR antagonist) on endocrine, behavioral, and central (c-Fos) stress responses in male rats. Rats were treated for five days with CORT 118335, imipramine (positive control), or vehicle and exposed to restraint or forced swim stress (FST). CORT 118335 dampened corticosterone responses to both stressors, without a concomitant antidepressant-like effect in the FST. Imipramine decreased corticosterone responses to restraint stress; however, the antidepressant-like effect of imipramine in the FST was independent of circulating glucocorticoids. These findings indicate dissociation between endocrine and behavioral stress responses in the FST. CORT 118335 decreased c-Fos expression only in the CA1 division of the hippocampus. Imipramine decreased c-Fos expression in the basolateral amygdala and CA1 and CA3 divisions of the hippocampus. Overall, the data indicate differential effects of CORT 118335 and imipramine on stress-induced neuronal activity in various brain regions. The data also highlight a complex relationship between neuronal activation in stress and mood regulatory brain regions and the ensuing impact on endocrine and behavioral stress responses.

Behavioral and physiological consequences of enrichment loss in rats

Significant loss produces the highest degree of stress and compromised well-being in humans. Current rodent models of stress involve the application of physically or psychologically aversive stimuli, but do not address the concept of loss. We developed a rodent model for significant loss, involving removal of long-term access to a rewarding enriched environment. Our results indicate that removal from environmental enrichment produces a profound behavioral and physiological phenotype with depression-like qualities, including helplessness behavior, hypothalamo-pituitary-adrenocortical axis dysregulation and overeating. Importantly, this enrichment removal phenotype was prevented by antidepressant treatment. Furthermore, the effects of enrichment removal do not occur following relief from chronic stress and are not duplicated by loss of exercise or social contact.

Hypothalamic-pituitary-adrenocortical axis dysfunction in epilepsy

Epilepsy is a common neurological disease, affecting 2.4million people in the US. Among the many different forms of the disease, temporal lobe epilepsy (TLE) is one of the most frequent in adults. Recent studies indicate the presence of a hyperactive hypothalamopituitary- adrenocortical (HPA) axis and elevated levels of glucocorticoids in TLE patients. Moreover, in these patients, stress is a commonly reported trigger of seizures, and stress-related psychopathologies, including depression and anxiety, are highly prevalent. Elevated glucocorticoids have been implicated in the development of stress-related psychopathologies. Similarly, excess glucocorticoids have been found to increase neuronal excitability, epileptiform activity and seizure susceptibility. Thus, patients with TLE may generate abnormal stress responses that both facilitate ictal discharges and increase vulnerability for the development of comorbid psychopathologies. Here, we will examine the evidence that the HPA axis is disrupted in TLE, consider potential mechanisms by which this might occur, and discuss the implications of HPA dysfunction for seizuretriggering and psychiatric comorbidities.

GABAergic Signaling within a Limbic-Hypothalamic Circuit Integrates Social and Anxiety-Like Behavior with Stress Reactivity

The posterior hypothalamic nucleus (PH) stimulates autonomic stress responses. However, the role of the PH in behavioral correlates of psychiatric illness, such as social and anxiety-like behavior, is largely unexplored, as is the neurochemistry of PH connectivity with limbic and neuroendocrine systems. Thus, the current study tested the hypothesis that GABAergic signaling within the PH is a critical link between forebrain behavior-regulatory nuclei and the neuroendocrine hypothalamus, integrating social and anxiety-related behaviors with physiological stress reactivity. To address this hypothesis, GABAA receptor pharmacology was used to locally inhibit or disinhibit the PH immediately before behavioral measures of social and anxiety-like behavior in rats. Limbic connectivity of the PH was then established by simultaneous co-injection of anterograde and retrograde tracers. Further, the role of PH GABAergic signaling in neuroendocrine stress responses was tested via inhibition/disinhibition of the PH. These studies determined a prominent role for the PH in the expression of anxiety-related behaviors and social withdrawal. Histological analyses revealed divergent stress-activated limbic input to the PH, emanating predominantly from the prefrontal cortex, lateral septum, and amygdala. PH projections also targeted both parvicellular and magnocellular peptidergic neurons in the paraventricular and supraoptic hypothalamus. Further, GABAA receptor pharmacology determined an excitatory effect of the PH on neuroendocrine responses to stress. These data indicate that the PH represents an important stress-integrative center, regulating behavioral processes and connecting the limbic forebrain with neuroendocrine systems. Moreover, the PH appears to be uniquely situated to have a role in stress-related pathologies associated with limbic-hypothalamic dysfunction.

Immediate post-defeat infusions of the noradrenergic receptor antagonist propranolol impair the consolidation of conditioned defeat in male Syrian hamsters

Social defeat occurs when an animal is attacked and subjugated by an aggressive conspecific. Following social defeat, male Syrian hamsters fail to display species-typical territorial aggression and instead exhibit submissive or defensive behaviors even when in the presence of a non-aggressive intruder. We have termed this phenomenon conditioned defeat (CD). The mechanisms underlying CD are not fully understood, but data from our lab suggest that at least some of the mechanisms are similar to those that mediate classical fear conditioning. The goal of the present experiment was to test the hypothesis that noradrenergic signaling promotes the consolidation of CD, as in classical fear conditioning, by determining whether CD is disrupted by post-training blockade of noradrenergic activity. In Experiment 1, we determined whether systemic infusions of the noradrenergic receptor antagonist propranolol (0, 1.0, 10, or 20mg/kg) given immediately after a 15 min defeat by a resident aggressor would impair CD tested 48 h later. Hamsters that were given immediate post-training infusions of propranolol (1.0, but not 10 or 20mg/kg) showed significantly less submissive behavior than did those given vehicle infusions supporting the hypothesis that there is noradrenergic modulation of the consolidation of a social defeat experience. In Experiment 2, we demonstrated that propranolol (1.0mg/kg) given immediately, but not 4 or 24h, after defeat impaired CD tested 48 h after defeat indicating that the window within which the memory for social defeat is susceptible to beta-adrenergic modulation is temporary. In Experiment 3, we examined whether central blockade of noradrenergic receptors could recapitulate the effect of systemic injections by giving an intracerebroventricular infusion of propranolol immediately after defeat and examining the effect on CD 24h later. Centrally administered propranolol (20 μg/3 μl but not 2 μg/3 μl) was also effective in dose-dependently reducing consolidation of CD. Collectively, the present results indicate that noradrenergic activity promotes the consolidation of CD and suggest that CD is a valuable model to study the processes by which emotion and stress modulate memory in an ethologically relevant context. These data also suggest that the popular conception in the clinical literature that the anxiolytic effect of propranolol is primarily due to the drug's peripheral effects may need to be reconsidered.

Neuroendocrine Function After Hypothalamic Depletion of Glucocorticoid Receptors in Male and Female Mice

Glucocorticoids act rapidly at the paraventricular nucleus (PVN) to inhibit stress-excitatory neurons and limit excessive glucocorticoid secretion. The signaling mechanism underlying rapid feedback inhibition remains to be determined. The present study was designed to test the hypothesis that the canonical glucocorticoid receptors (GRs) is required for appropriate hypothalamic-pituitary-adrenal (HPA) axis regulation. Local PVN GR knockdown (KD) was achieved by breeding homozygous floxed GR mice with Sim1-cre recombinase transgenic mice. This genetic approach created mice with a KD of GR primarily confined to hypothalamic cell groups, including the PVN, sparing GR expression in other HPA axis limbic regulatory regions, and the pituitary. There were no differences in circadian nadir and peak corticosterone concentrations between male PVN GR KD mice and male littermate controls. However, reduction of PVN GR increased ACTH and corticosterone responses to acute, but not chronic stress, indicating that PVN GR is critical for limiting neuroendocrine responses to acute stress in males. Loss of PVN GR induced an opposite neuroendocrine phenotype in females, characterized by increased circadian nadir corticosterone levels and suppressed ACTH responses to acute restraint stress, without a concomitant change in corticosterone responses under acute or chronic stress conditions. PVN GR deletion had no effect on depression-like behavior in either sex in the forced swim test. Overall, these findings reveal pronounced sex differences in the PVN GR dependence of acute stress feedback regulation of HPA axis function. In addition, these data further indicate that glucocorticoid control of HPA axis responses after chronic stress operates via a PVN-independent mechanism.

Adipocyte glucocorticoid receptors mediate fat-to-brain signaling

Stress-related (e.g., depression) and metabolic pathologies (e.g., obesity) are important and often co-morbid public health concerns. Here we identify a connection between peripheral glucocorticoid receptor (GR) signaling originating in fat with the brain control of both stress and metabolism. Mice with reduced adipocyte GR hypersecrete glucocorticoids following acute psychogenic stress and are resistant to diet-induced obesity. This hypersecretion gives rise to deficits in responsiveness to exogenous glucocorticoids, consistent with reduced negative feedback via adipocytes. Increased stress reactivity occurs in the context of elevated hypothalamic expression of hypothalamic-pituitary-adrenal (HPA) axis-excitatory neuropeptides and in the absence of altered adrenal sensitivity, consistent with a central cite of action. Our results identify a novel mechanism whereby activation of the adipocyte GR promotes peripheral energy storage while inhibiting the HPA axis, and provide functional evidence for a fat-to-brain regulatory feedback network that serves to regulate not just homeostatic energy balance but also responses to psychogenic stimuli.

Role of paraventricular nucleus-projecting norepinephrine/epinephrine neurons in acute and chronic stress

Chronic variable stress (CVS) exposure modifies the paraventricular nucleus of the hypothalamus (PVN) in a manner consistent with enhanced central drive of the hypothalamo-pituitary-adrenocortical (HPA) axis. As previous reports suggest that post-stress enhancement of norepinephrine (NE) action contributes to chronic stress regulation at the level of the PVN, we hypothesised that PVN-projecting NE neurons were necessary for the stress facilitatory effects of CVS. Following intra-PVN injection of saporin toxin conjugated to a dopamine beta-hydroxylase (DBH) antibody (DSAP), in rats PVN DBH immunoreactivity was almost completely eliminated, but immunoreactive afferents to other key regions involved in stress integration were spared (e.g. DBH fiber densities were unaffected in the central nucleus of the amygdala). Reductions in DBH-positive fiber density were associated with reduced numbers of DBH-immunoreactive neurons in the nucleus of the solitary tract and locus coeruleus. Following 2 weeks of CVS, DSAP injection did not alter stress-induced adrenal hypertrophy or attenuation of body weight gain, indicating that PVN-projecting NE [and epinephrine (E)] neurons are not essential for these physiological effects of chronic stress. In response to acute restraint stress, PVN-targeted DSAP injection attenuated peak adrenocorticotrophic hormone (ACTH) and corticosterone in controls, but only attenuated peak ACTH in CVS animals, suggesting that enhanced adrenal sensitivity compensated for reduced excitatory drive of the PVN. Our data suggest that PVN-projecting NE/E neurons contribute to the generation of acute stress responses, and are required for HPA axis drive (ACTH release) during chronic stress. However, loss of NE/E drive at the PVN appears to be buffered by compensation at the level of the adrenal.

The selective glucocorticoid receptor antagonist CORT 108297 decreases neuroendocrine stress responses and immobility in the forced swim test

Pre-clinical and clinical studies have employed treatment with glucocorticoid receptor (GR) antagonists in an attempt to limit the deleterious behavioral and physiological effects of excess glucocorticoids. Here, we examined the effects of GR antagonists on neuroendocrine and behavioral stress responses, using two compounds: mifepristone, a GR antagonist that is also a progesterone receptor antagonist, and CORT 108297, a specific GR antagonist lacking anti-progestin activity. Given its well-documented impact on neuroendocrine and behavioral stress responses, imipramine (tricyclic antidepressant) served as a positive control. Male rats were treated for five days with mifepristone (10mg/kg), CORT 108297 (30mg/kg and 60mg/kg), imipramine (10mg/kg) or vehicle and exposed to forced swim test (FST) or restraint stress. Relative to vehicle, imipramine potently suppressed adrenocorticotropin hormone (ACTH) responses to FST and restraint exposure. Imipramine also decreased immobility in the FST, consistent with antidepressant actions. Both doses of CORT 108297 potently suppressed peak corticosterone responses to FST and restraint stress. However, only the higher dose of CORT 108297 (60mg/kg) significantly decreased immobility in the FST. In contrast, mifepristone induced protracted secretion of corticosterone in response to both stressors, and modestly decreased immobility in the FST. Taken together, the data indicate distinct effects of each compound on neuroendocrine stress responses and also highlight dissociation between corticosterone responses and immobility in the FST. Within the context of the present study, our data suggest that CORT 108297 may be an attractive alternative for mitigating neuroendocrine and behavioral states associated with excess glucocorticoid secretion.

Role of prefrontal cortex glucocorticoid receptors in stress and emotion

BACKGROUND

Stress-related disorders (e.g., depression) are associated with hypothalamic-pituitary-adrenocortical axis dysregulation and prefrontal cortex (PFC) dysfunction, suggesting a functional link between aberrant prefrontal corticosteroid signaling and mood regulation.

METHODS

We used a virally mediated knockdown strategy (short hairpin RNA targeting the glucocorticoid receptor [GR]) to attenuate PFC GR signaling in the rat PFC. Adult male rats received bilateral microinjections of vector control or short hairpin RNA targeting the GR into the prelimbic (n = 44) or infralimbic (n = 52) cortices. Half of the animals from each injection group underwent chronic variable stress, and all were subjected to novel restraint. The first 2 days of chronic variable stress were used to assess depression- and anxiety-like behavior in the forced swim test and open field.

RESULTS

The GR knockdown confined to the infralimbic PFC caused acute stress hyper-responsiveness, sensitization of stress responses after chronic variable stress, and induced depression-like behavior (increased immobility in the forced swim test). Knockdown of GR in the neighboring prelimbic PFC increased hypothalamic-pituitary-adrenocortical axis responses to acute stress and caused hyperlocomotion in the open field, but did not affect stress sensitization or helplessness behavior.

CONCLUSIONS

The data indicate a marked functional heterogeneity of glucocorticoid action in the PFC and highlight a prominent role for the infralimbic GR in appropriate stress adaptation, emotional control, and mood regulation.

Identification of chronic stress-activated regions reveals a potential recruited circuit in rat brain

Chronic stress induces presynaptic and postsynaptic modifications in the paraventricular nucleus of the hypothalamus that are consistent with enhanced excitatory hypothalamo-pituitary-adrenocortical (HPA) axis drive. The brain regions mediating these molecular modifications are not known. We hypothesized that chronic variable stress (CVS) tonically activates stress-excitatory regions that interact with the paraventricular nucleus of the hypothalamus, culminating in stress facilitation. In order to identify chronically activated brain regions, ΔFosB, a documented marker of tonic neuronal activation, was assessed in known stress regulatory limbic and brainstem sites. Four experimental groups were included: CVS, repeated restraint (RR) (control for HPA habituation), animals weight-matched (WM) to CVS animals (control for changes in circulating metabolic factors due to reduced weight gain), and non-handled controls. CVS, (but not RR or WM) induced adrenal hypertrophy, indicating that sustained HPA axis drive only occurred in the CVS group. CVS (but not RR or WM) selectively increased the number of FosB/ΔFosB nuclei in the nucleus of the solitary tract, posterior hypothalamic nucleus, and both the infralimbic and prelimbic divisions of the medial prefrontal cortex, indicating an involvement of these regions in chronic drive of the HPA axis. Increases in FosB/ΔFosB-immunoreactive cells were observed following both RR and CVS in the other regions (e.g. the dorsomedial hypothalamus), suggesting activation by both habituating and non-habituating stress conditions. The data suggest that unpredictable stress uniquely activates interconnected cortical, hypothalamic, and brainstem nuclei, potentially revealing the existence of a recruited circuitry mediating chronic drive of brain stress effector systems.

Neural regulation of the stress response: glucocorticoid feedback mechanisms

The mammalian stress response is an integrated physiological and psychological reaction to real or perceived adversity. Glucocorticoids are an important component of this response, acting to redistribute energy resources to both optimize survival in the face of challenge and to restore homeostasis after the immediate challenge has subsided. Release of glucocorticoids is mediated by the hypothalamo-pituitary-adrenal (HPA) axis, driven by a neural signal originating in the paraventricular nucleus (PVN). Stress levels of glucocorticoids bind to glucocorticoid receptors in multiple body compartments, including the brain, and consequently have wide-reaching actions. For this reason, glucocorticoids serve a vital function in negative feedback inhibition of their own secretion. Negative feedback inhibition is mediated by a diverse collection of mechanisms, including fast, non-genomic feedback at the level of the PVN, stress-shut-off at the level of the limbic system, and attenuation of ascending excitatory input through destabilization of mRNAs encoding neuropeptide drivers of the HPA axis. In addition, there is evidence that glucocorticoids participate in stress activation via feed-forward mechanisms at the level of the amygdala. Feedback deficits are associated with numerous disease states, underscoring the necessity for adequate control of glucocorticoid homeostasis. Thus, rather than having a single, defined feedback ‘switch’, control of the stress response requires a wide-reaching feedback ‘network’ that coordinates HPA activity to suit the overall needs of multiple body systems.

Deletion of forebrain glucocorticoid receptors impairs neuroendocrine stress responses and induces depression-like behavior in males but not females

Dysfunction in central glucocorticoid signaling is implicated in hypothalamic-pituitary-adrenocortical (HPA) axis dysregulation and major depression. In comparison with men, women are twice as likely to suffer from depression and have heightened HPA axis responses to stress. We hypothesized that this striking increase in stress vulnerability in females may be because of sex differences in central glucocorticoid signaling. The current study tests the role of the forebrain type II glucocorticoid receptor (GR) on HPA axis function in female mice and depression-like behavior in both female and male mice. This was accomplished by using mice with selective deletion of GR in forebrain cortico-limbic sites including the prefrontal cortex, hippocampus, and basolateral amygdala (forebrain glucocorticoid receptor knockout mouse (FBGRKO)). In order to examine HPA axis function in female FBGRKO, we measured nadir, peak circadian and restraint-induced corticosterone concentrations in female FBGRKO. The data indicate that unlike male FBGRKO, basal and stress-induced corticosterone concentrations are not increased in female FBGRKO. Given the pronounced effect of central glucocorticoid signaling on mood, we also examined the necessity of corticolimbic GR on depression-like behavior with the sucrose preference and forced swim tests (FST) in male and female FBGRKO mice. Consistent with previous studies, male FBGRKO displayed increased depression-like behavior as indicated by greater immobility in the FST and decreased sucrose preference compared with littermate controls, effects that were not observed in females. Overall the findings indicate a marked sex difference in the function of forebrain GR on HPA axis regulation and depression-like behaviors, and may have implications for therapeutic approaches using GR-modulating drugs.

Differential effects of glucocorticoids on energy homeostasis in Syrian hamsters

Syrian hamsters, like many humans, increase food intake and body adiposity in response to stress. We hypothesized that glucocorticoids (cortisol and corticosterone) mediate these stress-induced effects on energy homeostasis. Because Syrian hamsters are dual secretors of cortisol and corticosterone, differential effects of each glucocorticoid on energy homeostasis were investigated. First, adrenal intact hamsters were injected with varying physiological concentrations of cortisol, corticosterone, or vehicle to emulate our previously published defeat regimens (i.e., 1 injection/day for 5 days). Neither food intake nor body weight was altered following glucocorticoid injections. Therefore, we investigated the effect of sustained glucocorticoid exposure on energy homeostasis. This was accomplished by implanting hamsters with supraphysiological steady-state pellets of cortisol, corticosterone, or cholesterol as a control. Cortisol, but not corticosterone, significantly decreased food intake, body mass, and lean and fat tissue compared with controls. Despite decreases in body mass and adiposity, cortisol significantly increased circulating free fatty acids, triglyceride, cholesterol, and hepatic triglyceride concentrations. Although corticosterone did not induce alterations in any of the aforementioned metabolic end points, Syrian hamsters were responsive to the effects of corticosterone since glucocorticoids both induced thymic involution and decreased adrenal mass. These findings indicate that cortisol is the more potent glucocorticoid in energy homeostasis in Syrian hamsters. However, the data suggest that cortisol alone does not mediate stress-induced increases in food intake or body mass in this species.

Chronic stress, energy balance and adiposity in female rats

Stress preferentially increases the consumption of high fat foods in women, suggesting the interaction of these two factors may disproportionately predispose women toward excess weight gain. In the present study, female rats were exposed to a chronic high fat or chow diet and were exposed to 4weeks of chronic variable stress (CVS) or served as home cage controls. Control females exposed to a high fat diet displayed many symptoms of the metabolic syndrome including increased body weight gain, total and visceral adiposity and insulin and leptin concentrations relative to all groups. However, CVS-high fat, CVS chow and control chow groups had similar body weight gain and caloric efficiency. This finding suggests that CVS increases energy expenditure much more in females exposed to a high fat diet relative to those fed a standard chow diet. The CVS-high fat group had increased adiposity and increased circulating leptin and insulin concentrations, despite the fact that their body weight did not differ from the controls. These results underscore the importance of assessing the degree of adiposity, rather than body weight alone, as an index of overall metabolic health. Overall, the data indicate that in female rats, chronic stress prevents high fat diet related increases in body weight, but does not prevent high fat diet induced increases in adiposity when compared to chow-fed females.

Decreased glucose tolerance and plasma adiponectin:resistin ratio in a mouse model of post-traumatic stress disorder

AIMS/HYPOTHESIS

Obesity and type 2 diabetes are among the most serious health pathologies worldwide. Stress has been proposed as a factor contributing to the development of these health risk factors; however, the underlying mechanisms that link stress to obesity and diabetes need to be further clarified. Here, we study in mice how chronic stress affects dietary consumption and how that relationship contributes to obesity and diabetes.

METHODS

C57BL/6J mice were subjected to chronic variable stress (CVS) for 15 days and subsequently fed with a standard chow or high-fat diet. Food intake, body weight, respiratory quotient, energy expenditure and spontaneous physical activity were measured with a customised calorimetric system and body composition was measured with nuclear magnetic resonance. A glucose tolerance test was also applied and blood glucose levels were measured with a glucometer. Plasma levels of adiponectin and resistin were measured using Lincoplex kits.

RESULTS

Mice under CVS and fed with a high-fat diet showed impaired glucose tolerance associated with low plasma adiponectin:resistin ratios.

CONCLUSIONS/INTERPRETATION

This study demonstrates, in a novel mouse model, how post-traumatic stress disorder enhances vulnerability for impaired glucose metabolism in an energy-rich environment and proposes a potential adipokine-based mechanism.

Opposing effects of chronic stress and weight restriction on cardiovascular, neuroendocrine and metabolic function

Chronic stress is associated with dysregulation of energy homeostasis, but the link between the two is largely unknown. For most rodents, periods of chronic stress reduce weight gain. We hypothesized that these reductions in weight are an additional homeostatic challenge, contributing to the chronic stress syndrome. Experiment #1 examined cardiovascular responsivity following exposure to prolonged intermittent stress. We used radio-telemetry to monitor mean arterial pressure and heart rate in freely moving, conscious rats. Three groups of animals were tested: chronic variable stress (CVS), weight-matched (WM), and controls. Using this design, we can distinguish between effects due to stress and effects due to the changing body weight. WM, but not CVS, markedly reduced basal heart rate. Although an acute stress challenge elicited similar peak heart rate, WM expedited the recovery to baseline heart rate. The data suggest that CVS prevents the weight-induced attenuation of cardiovascular stress reactivity. Experiment #2 investigated hypothalamic-pituitary-adrenal axis and metabolic hormone reactivity to novel psychogenic stress. WM increased corticosterone area under the curve. CVS blunted plasma glucose, leptin, and insulin levels in response to restraint. Experiment #3 tested the effects of WM and CVS on PVN oxytocin and corticotrophin-releasing hormone mRNA expression. CVS increased, while WM reduced PVN CRH mRNA expression, whereas both CVS and WM reduced dorsal parvocellular PVN oxytocin mRNA. Overall, the data suggest that weight loss is unlikely to account for the deleterious effects of chronic stress on the organism, but in fact produces beneficial effects that are effectively absent or indeed, reversed in the face of chronic stress exposure.

Stress vulnerability during adolescent development in rats

Adolescent development is proposed to represent a time of increased susceptibility to stress. During adolescence, the brain demonstrates a high level of plasticity and can be positively or negatively affected by the environment. This study tests the hypothesis that adolescent development is a stage of enhanced vulnerability to chronic stress. Male Sprague-Dawley rats were exposed to our 14-d chronic variable stress (CVS) paradigm at three developmental stages: 1) early adolescence (35 d; age at initiation of CVS); 2) late adolescence (50 d); or 3) adulthood (80 d). We examined the effects of CVS on the following: 1) depression-like behavior; 2) somatic indices; 3) hypothalamic-pituitary-adrenal (HPA) axis activity; and 4) neuropeptide expression in the hypothalamus. Results show, regardless of age, CVS exposure: 1) decreased body weight; 2) increased adrenal size; 3) decreased fat weight; and 4) increased HPA response to stress. The somatic effects of CVS were exaggerated in late adolescent animals, and late adolescent animals were the only group where CVS decreased oxytocin expression and increased basal corticosterone. In response to CVS, adult animals increased immobility during the forced-swim test while early and late adolescent animals were resistant to the effects of chronic stress on depression-like behavior. Results show that adolescent animals were protected from the effect of chronic stress on depression-like behavior while late adolescent animals were more susceptible to the somatic, HPA axis, and neuropeptide effects of chronic stress. Thus, adolescent development is a unique window of vulnerabilities and protections to the effects of chronic stress.

Mifepristone decreases depression-like behavior and modulates neuroendocrine and central hypothalamic-pituitary-adrenocortical axis responsiveness to stress

Glucocorticoid dyshomeostasis is observed in a proportion of depressed individuals. As a result, glucocorticoid receptor (GR) antagonists are currently being tested as potential anti-depressants. The current study was designed to test the efficacy of mifepristone, a GR antagonist, in mitigating behavioral, neuroendocrine and central nervous system (CNS) responses to an acute stressor. Adult male rats were treated for 5 days with mifepristone (10 mg/kg) and then exposed to the forced swim test (FST). Treatment with mifepristone decreased immobility and increased swimming (but not climbing) behavior in the FST, consistent with anti-depressant action. In addition, mifepristone dampened the ACTH response to FST exposure. In the CNS, mifepristone increased c-Fos expression in all subdivisions of the medial prefrontal cortex (mPFC) and decreased neuronal activity in some subdivisions of the hippocampus including the CA2, CA3, and hilus region of the dentate gyrus in animals exposed to FST. In contrast, mifepristone increased neuronal activity in the ventral subiculum (output region of the hippocampus) and decreased c-Fos expression in the central amygdala (CeA) in animals exposed to FST. These data suggest that anti-depressant efficacy and perhaps HPA dampening properties of RU486 are related to alterations in key limbic circuits mediating CNS stress responses, resulting in enhanced stress inhibition (via the mPFC and ventral subiculum) as well as decreased stress excitation (central amygdala). Overall the data suggest that drugs targeting the glucocorticoid receptor may ameliorate stress dysfunction associated with depressive illness.

Stress activation of IL-6 neurons in the hypothalamus

An emerging literature attests to the ability of psychological stress to alter the inflammatory cytokine environment of the body. While the ability of stress to cause cytokine release is well established, the neural pathways involved in this control have yet to be identified. This study tests the hypothesis that IL-6 neurons of the hypothalamo-neurohypophyseal system (HNS), a neural pathway proposed to secrete IL-6 into the circulation, are activated in response to psychological stress. Colocalization studies confirm robust expression of IL-6 in cell bodies and fibers of vasopressin (but not oxytocin) neurons of the paraventricular (PVN) and supraoptic nucleus (SON) of the rat hypothalamus. In response to restraint, there was a greater increase in c-Fos expression in SON IL-6-positive (IL-6+) neurons. In addition, both psychogenic (restraint) or systemic stress (hypoxia) lead to phosphorylated ERK induction only in IL-6+ magnocellular neurons, indicating selective activation of the MAPK signaling pathway in the IL-6 subset of magnocellular neurons. Finally, restraint upregulated IL-6 mRNA expression in both the PVN and SON, which was accompanied by a four-fold increase in circulating IL-6. The data indicate that noninflammatory stressors selectively activate IL-6 magnocellular neurons, upregulate IL-6 gene expression in the PVN and SON, and increase plasma IL-6. In summary, results show that IL-6 neurons of the HNS are a recruited component of the response to psychological stress.

The medial amygdala modulates body weight but not neuroendocrine responses to chronic stress

Stress pathologies such as depression and eating disorders (i.e. anorexia nervosa) are associated with amygdalar dysfunction, which are linked with hypothalamic-pituitary-adrenal axis (HPA) axis hyperactivity. The medial amygdaloid nucleus (MeA), a key output nucleus of the amygdaloid complex, promotes HPA axis activation to acute psychogenic stress and is in a prime position to mediate the deleterious effects of chronic stress on physiology and behaviour. The present study tests the hypothesis that the MeA is necessary for the development of maladaptive physiological changes caused by prolonged stress exposure. Male rats received bilateral ibotenate or sham lesions targeting the MeA and one half underwent 2 weeks of chronic variable stress (CVS) or served as home cage controls. Sixteen hours post CVS, all animals were exposed to an acute restraint challenge. CVS induced thymic involution, adrenal hypertrophy, and attenuated body weight gain and up-regulation of hypothalamic corticotrophin-releasing hormone mRNA expression. Consistent with previous literature, lesions of the MeA dampened stress-induced increases in corticosterone after 30 min of exposure to acute restraint stress. However, this effect was independent of CVS exposure, suggesting that the MeA may not be critical for modulating neuroendocrine responses after chronic HPA axis drive. Interestingly, lesion of the MeA modestly exaggerated the stress-induced attenuation of weight gain. Overall, the data obtained suggest that the MeA modulates the neuroendocrine responses to acute but not chronic stress. In addition, the data suggest that the MeA may be an important neural component for the control of body weight in the face of chronic stress.

Gonadal hormones modulate the display of conditioned defeat in male Syrian hamsters

It has been widely reported that gonadal hormones influence the display of aggression in Syrian hamsters; conversely, much less is known about whether gonadal hormones modulate submissive/defensive behaviors in these animals. Following social defeat, male hamsters no longer display normal territorial aggression but instead display submissive/defensive behavior in the presence of a smaller opponent, a phenomenon we have termed conditioned defeat (CD). The purpose of the present study was to examine the effect of gonadal hormones on the display of CD in male hamsters. In Experiment 1, males were castrated or sham-operated. The castrated males were significantly more submissive following social defeat relative to their intact counterparts. The increased submissive behavior in the castrated males during CD testing was particularly surprising, given the fact that they were attacked significantly less during CD training. In Experiment 2a, males were castrated and given hormone replacement. Castrated males treated with testosterone or dihydrotestosterone displayed significantly less submissive behavior following social defeat than did those treated with cholesterol or estradiol. Finally, in Experiment 2b, there was no effect of hormone replacement on aggressive behavior in non-defeated hamsters suggesting that the decrease in submissive behavior in males treated with dihydrotestosterone or testosterone is specific to being previously defeated. Taken together the data indicate that the presence of androgens reduces the display of submission in defeated male hamsters. More importantly, these findings suggest that androgens may have a protective effect against the development of depression-like or anxiety-like behaviors following exposure to an ethologically relevant stressor.

Sex differences in psychopathology: of gonads, adrenals and mental illness

Stress-related disorders such as anxiety and depression are disproportionately prevalent in women. Women are more likely to experience depression and anxiety disorders during periods of marked hormonal fluctuations, suggesting that gonadal hormones are involved in stress pathology. Depression and anxiety are both associated with aberrant secretion of glucocorticoids, which also show marked fluctuations across the reproductive cycle and in response to gonadal steroids. Thus, interactions between gonadal and stress hormones may play a major role in predisposing females to stress-related disease. The purpose of this brief review is to highlight preclinical data regarding the role of estrogens in depression and anxiety-like behaviors. While it is evident the exogenous estrogens modulate affective behavior in rodents, there is some disagreement in the literature, perhaps related to experimental designs that vary with respect to administration parameters and stress. Beneficial effects of estrogens on mood are most likely due to estrogen receptor (ER)beta signaling. The antidepressant and anxiolytic effects of ERbeta are consistent with its role in attenuating glucocorticoid responses to stress, suggesting that estrogens, acting at ERbeta, may improve mood by suppressing glucocorticoid hyperactivity. However, additional studies demonstrate that ERbeta signaling in the hippocampus is sufficient to induce antidepressant and anxiolytic behaviors. Thus, ERbeta may improve mood via primary actions on hypothalamic (i.e., paraventricular nucleus) and/or extra-hypothalamic sites. Overall, the preclinical research suggests that selective ER modulators targeting ERbeta may be an attractive alternative or adjunct treatment to currently prescribed antidepressants or anxiolytics.

Influence of ruminal and postruminal carbohydrate infusion on visceral organ mass and adipose tissue accretion in growing beef steers1

Forty crossbred beef steers (243 +/- 2 kg of BW) with ruminal and abomasal infusion catheters were used to test 2 hypotheses: 1) visceral mass is responsive to energy input and site of carbohydrate (CHO) infusion and 2) rate and site of adipose accretion are dependent on site of CHO infusion and complexity. Treatments included a pelleted, forage-based, basal diet fed at 161 (LI) or 214 (HI) kcal of ME/(kg of BW(0.75) x d), LI plus ruminal (R-SH) or abomasal (A-SH) infusion of a partial starch hydrolysate (SH), and LI plus abomasal infusion of glucose (A-G). The basal diet was fed in 12 equal portions daily at 2-h intervals, with starch and glucose infused over a 22-h period at rates of 12.6 and 14.4 g/(kg of BW(0.75) x d). After 35 d of infusion, steers were slaughtered; and visceral organ and adipose mass, subcutaneous adipose thickness over the 5th and 12th rib, and LM intramuscular fat concentration were determined. Total intake energy (IE) increased (P = 0.0001) with ME intake. Dietary IE was similar between LI and CHO treatments, but total IE increased (P < 0.001) with CHO infusion. Greater dietary ME intake and CHO infusion increased or tended (P < or = 0.09) to increase final BW and HCW. As a percentage of empty BW, total stomach complex, rumen, omasum, liver, pancreas, and kidney weights were greater (P < or = 0.05) for HI vs. LI. Stomach complex, rumen, pancreas, and kidney weights as a percentage of empty BW were greater (P < or = 0.05) for R-SH vs. A-SH. Compared with ASH, A-G increased (P < or = 0.02) total and mucosal weights from the 10-cm sections of the ileum. Increases in rumen mass were associated with no change or an increase in rumen total and mucosal DNA concentrations. Greater dietary ME tended (P = 0.06) to increase subcutaneous fat thickness at the 5th rib but did not affect alimentary adipose accretion on an empty BW basis. Omental and total alimentary adipose weights were increased (P < or = 0.04) by A-G compared with A-SH. Although SH infusion did not alter adiposity, there was a consistent numerical pattern in total alimentary and subcutaneous fat depots with CHO infusion (A-G > ASH > R-SH). Our findings demonstrate that increasing ruminal CHO supply results in a disproportionate increase in rumen mass, whereas increasing small intestinal CHO supply does not alter gastrointestinal organ mass. Small intestinal energy in the form of glucose resulted in greater adipose accretion, particularly the omental depot.

Sex and estrous cycle differences in the display of conditioned defeat in Syrian hamsters

We have reported that there is a sex difference in the behavioral response to social defeat in hamsters. While previously defeated male hamsters fail to display normal territorial aggression and instead produce submissive/defensive behavior, a phenomenon that we have termed conditioned defeat (CD), only a small portion of previously defeated females exhibit CD. In Experiment 1, we tested the hypothesis that CD varies over the estrous cycle and found that previously defeated female hamsters tested on diestrus 2 and proestrus were more likely to exhibit CD than were females tested on diestrus 1 and estrus. In Experiment 2, we found that regardless of hormonal status, non-defeated females displayed normal territorial aggression, indicating that the behavioral changes observed in Experiment 1 were not due to a cyclic variation in submissive behavior independent of a previous defeat encounter. In Experiment 3, we found that females tested 4 days after defeat responded similarly to those tested 1 day after defeat suggesting that the hormonal status of females on the day of testing is a more important determinant of the behavioral response to defeat than is the hormonal status on the day of defeat training. Finally, in Experiment 4, we monitored anxiety-like behaviors in diestrous 1 and proestrous females in an open field arena and found that there was no effect of cycle on any of the observed behavioral measures, suggesting that the observed differences in CD are not the result of differences in generalized anxiety-like behaviors across the estrous cycle.

Social defeat and footshock increase body mass and adiposity in male Syrian hamsters

Obesity is a world-wide epidemic, and many factors, including stress, have been linked to this growing trend. After social stress (i.e., defeat), subordinate laboratory rats and most laboratory mice become hypophagic and, subsequently, lose body mass; the opposite is true of subordinate Syrian hamsters. After social defeat, Syrian hamsters become hyperphagic and gain body mass compared with nonstressed controls. It is unknown whether this increase in body mass and food intake is limited to subordinate hamsters. In experiment 1, we asked, do dominant hamsters increase food intake, body mass, and adiposity after an agonistic encounter? Subordinate hamsters increased food intake and body mass compared with nonstressed controls. Although there was no difference in food intake or absolute body mass between dominant and nonstressed control animals, cumulative body mass gain was significantly higher in dominant than in nonstressed control animals. Total carcass lipid and white adipose tissue (WAT) (i.e., retroperitoneal and epididymal WAT) masses were significantly increased in subordinate, but not dominant, hamsters compared with nonstressed controls. In experiment 2, we asked, does footshock stress increase food intake, body mass, and adiposity. Hamsters exposed to defeat, but not footshock stress, increased food intake relative to nonstressed controls. In animals exposed to defeat or footshock stress, body mass, as well as mesenteric WAT mass, increased compared with nonstressed controls. Collectively, these data demonstrate that social and nonsocial stressors increase body and lipid mass in male hamsters, suggesting that this species may prove useful for studying the physiology of stress-induced obesity in some humans.

Social defeat increases food intake, body mass, and adiposity in Syrian hamsters

Overeating and increases in body and fat mass are the most common responses to day-to-day stress in humans, whereas stressed laboratory rats and mice respond oppositely. Group housing of Syrian hamsters increases body mass, adiposity, and food intake, perhaps due to social confrontation-induced stress. In experiment 1 we asked, Does repeated social defeat increase food intake, body mass, and white adipose tissue (WAT) mass in Syrian hamsters? Male hamsters subjected to the resident-intruder social interaction model and defeated intermittently 15 times over 34 days for 7-min sessions significantly increased their food intake, body mass, and most WAT masses compared with nondefeated controls. Defeat significantly increased terminal adrenal norepinephrine, but not epinephrine, content. In experiment 2 we asked, Are 15 intermittent resident-intruder interactions necessary to increase body mass and food intake? Body mass and food intake of subordinate hamsters defeated only once were similar to those of nondefeated controls, but four or eight defeats similarly and significantly increased these responses. In experiment 3 we asked, Do intermittent defeats increase adiposity and food intake more than consecutive defeats? Four intermittent or consecutive defeats similarly and significantly increased food intake and body mass compared with nondefeated controls, but only intermittent defeats significantly increased all WAT masses. Consecutive defeats significantly increased mesenteric and inguinal WAT masses. Plasma leptin, but not insulin, concentrations were similarly and significantly increased compared with nondefeated controls. Collectively, social defeat, a natural stressor, significantly increased food intake, body mass, and adiposity in Syrian hamsters and may prove useful in determining mechanisms underlying human stress-induced obesity.

Rapid detection of Salmonella from hydrodynamic pressure-treated poultry using molecular beacon real-time PCR

A real-time polymerase chain reaction (PCR) assay was evaluated to detect Salmonella in hydrodynamic pressure (HDP)-treated chicken using molecular beacon probes available as a commercial kit (iQ-Check, Bio-Rad Laboratories). The sensitivity and accuracy of the assay were compared with the conventional USDA microbiological procedure using artificially contaminated minced chicken. Chicken fillets were irradiated at 10 kGy to completely destroy any naturally occurring Salmonella. These fillets were minced and inoculated with as low as 2+/-1 cfu of S. typhimurium per 25 g chicken. The minced chicken samples were vacuum packed in multi-layer barrier bags, heat shrunk, and treated with HDP. Results showed that all inoculated samples (n=36) were detected by the PCR assay and conventional USDA procedure. Similarly, all uninoculated controls (n=11) were negative by both PCR assay and USDA procedure. As few as 2+/-1 cfu could be detected from 25 g HDP-treated chicken following 16-18 h enrichment in buffered peptone water. Real-time PCR proved to be an effective method for Salmonella detection in HDP-treated chicken with high sensitivity and more importantly, a rapid and high-throughput detection in 18 h, compared to 3-8 days for the conventional microbiological methods. HDP treatment, which has been reported to reduce spoilage bacteria in various meats, was unable to kill pathogenic Salmonella in minced chicken.

Gonadal hormones modulate the display of submissive behavior in socially defeated female Syrian hamsters

There are striking differences in the behavioral response to social defeat between male and female Syrian hamsters. Whereas males exhibit a prolonged behavioral response to defeat (i.e., conditioned defeat), many females remain aggressive or show only a transient submissive response following defeat. The current study tested the hypothesis that sex steroids underlie this differential behavioral responsivity to social defeat. Female hamsters were ovariectomized and implanted with Silastic capsules containing estradiol (E(2)), testosterone (T), progesterone (P), dihydrotestosterone (DHT), or a blank capsule (no hormone replacement). After a 3-week recovery period, each subject was placed inside the home cage of a larger, more aggressive female for four 5-min defeat trials. The following day, each animal was tested for conditioned defeat by testing it in its own home cage in the presence of a smaller, non-aggressive intruder. Submissive, aggressive, social, and nonsocial behaviors were subsequently scored. Hamsters receiving E(2) or T displayed significantly lower levels of submissive behavior than did animals receiving P, DHT, or no hormone replacement. There were no significant differences in aggressive behavior among groups. These data suggest that gonadal hormones can influence submissive behavior in female hamsters. Collectively, these results suggest that the sex differences observed in conditioned defeat may, in part, be explained by sex differences in circulating gonadal hormones.

Conditioned defeat in male and female Syrian hamsters

A brief exposure to social defeat in male Syrian hamsters (Mesocricetus auratus) leads to profound changes in the subsequent agonistic behavior exhibited by the defeated animals. Following defeat in the home cage of an aggressive conspecific, male hamsters will subsequently fail to defend their home territory even if the intruder is a smaller, nonaggressive male. This phenomenon has been called conditioned defeat. In Experiment 1, we examined the duration of conditioned defeat by repeatedly testing (every 3-5 days) defeated hamsters with a nonaggressive intruder. We found that conditioned defeat occurs in all defeated male hamsters and persists for a prolonged period of time (at least 33 days) in the majority of male hamsters tested despite the fact that these animals are never attacked by the nonaggressive intruders. In Experiment 2, we examined whether conditioned defeat could be induced in female Syrian hamsters. While conditioned defeat occurred in some females, they displayed only low levels of submissive/defensive behavior and, in contrast to males, the conditioned defeat response did not persist beyond the first test. These results suggest that in male hamsters conditioned defeat is a profound, persistent behavioral change characterized by a total absence of territorial aggression and by the frequent display of submissive and defensive behaviors. Conversely, social defeat in female hamsters does not appear to induce long-term behavioral changes. Finally, in Experiment 3, we determined that plasma adrenocorticotropin-like immunoreactivity increases in females following social defeat in a manner similar to that seen in males, suggesting that the disparate behavioral reactions of males and females are not due to sex differences in the release of, or response to, plasma adrenocorticotropin.

Expression of myostatin pro domain results in muscular transgenic mice

Myostatin, a member of the TGF-beta family, negatively regulates skeletal muscle development. Depression of myostatin activity leads to increased muscle growth and carcass lean yield. In an attempt to down-regulate myostatin, transgenic mice were produced with a ribozyme-based construct or a myostatin pro domain construct. Though the expression of the ribozyme was detected, muscle development was not altered by the ribozyme transgene. However, a dramatic muscling phenotype was observed in transgenic mice carrying the myostatin pro domain gene. Expression of the pro domain transgene at 5% of beta-actin mRNA levels resulted in a 17-30% increase in body weight (P < 0.001). The carcass weight of the transgenic mice showed a 22-44% increase compared with nontransgenic littermates at 9 weeks of age (16.05 +/- 0.67 vs. 11.16 +/- 0.28 g in males; 9.99 +/- 0.38 vs. 8.19 +/- 0.19 g in females, P < 0.001). Extreme muscling was present throughout the whole carcass of transgenic mice as hind and fore limbs and trunk weights, all increased significantly (P < 0.001). Epididymal fat pad weight, an indicator of body fat, was significantly decreased in pro domain transgenic mice (P < 0.001). Analysis of muscle morphology indicated that cross-sectional areas of fast-glycolytic fibers (gastrocnemius) and fast-oxidative glycolytic fibers (tibialis) were larger in pro domain transgenic mice than in their controls (P < 0.01), whereas fiber number (gastrocnemius) was not different (P > 0.05). Thus, the muscular phenotype is attributable to myofiber hypertrophy rather than hyperplasia. The results of this study suggest that the over-expression of myostatin pro domain may provide an alternative to myostatin knockouts as a means of increasing muscle mass in other mammals.

Recombinant bovine somatotropin (rbST) increases size and proportion of fast-glycolytic muscle fibers in semitendinosus muscle of creep-fed steers

The objective of this study was to determine the effect of recombinant bovine somatotropin (rbST) on muscle fiber histology and histochemistry in creep-fed beef steers. Crossbred steer calves were assigned to one of two treatment groups: control (sham-injected; n = 12) or rbST-injected (0.09 mg x kg(-1) x d(-1); n = 12). Calves were injected every 14 d starting at d 28 of age until weaning at 205 d of age. Biopsies of the semitendinosus muscle were performed on d 100, and slaughter samples of semitendinosus muscle were collected for muscle fiber analyses on d 206. The rbST-treated calves had larger (P = 0.045) fast-twitch-glycolytic (FG) fibers [2,564 +/- 10 vs 2,351 +/- 11 microm2 cross-sectional area, respectively] than controls. No differences (P = 0.36) between rbST-treated and control steers in cross-sectional area were detected for slow-twitch-oxidative (SO) [1,192 +/- 20 vs 1,148 +/- 22 microm2, respectively] or fast-twitch-oxidative-glycolytic (FOG) fibers [1,484 +/- 35 vs 1,403 +/- 38 microm2, respectively]. The percentage distribution for FOG fibers was greater for control calves than for the rbST-treated calves (38.4 vs 34.9 +/- 0.1%, respectively; P = 0.014), whereas the percentage distribution for FG fibers was greater in the rbST-treated calves than for control calves (53.5 vs 48.4 +/- 0.2%, respectively; P = 0.03). The percentage distribution for SO fibers tended to be greater for the control calves than for the rbST-treated calves (13.1 vs 11.7 +/- 0.1%, respectively; P = 0.07). The percentage of FG fibers increased with age (45.4 vs 56.6 +/- 0.8%, respectively; P = 0.001), whereas the percentage distribution of SO (14.3 vs 10.5 +/- 0.5%, respectively) and FOG fibers (40.3 vs 32.9 +/- 0.7%, respectively) decreased (P = 0.001) from d 100 to d 206. The increased longissimus muscle area and dissectable lean tissue in rbST-treated calves are associated with a greater percentage of FG fibers, which possess larger cross-sectional areas than the other fibers.

Growth performance and adipose tissue deposition in barrows fed n-methyl-D,L-aspartate

We previously reported that broilers fed n-methyl-D,L-aspartate (NMA) exhibited enhanced feed conversion efficiency and decreased percentage of fat in carcasses. In this experiment, growth performance and backfat thickness were evaluated in barrows fed NMA. Poland China x Yorkshire barrows weighing 68.8 +/- 1.7 kg (mean +/- SE) were allowed ad libitum access to feed containing NMA at levels of either 0 (n = 7), 100 (n = 6), 200 (n = 8), or 300 (n = 8) mg/kg for 36 d. Barrows were slaughtered at 99.5 +/- 2.3 kg BW. There was no effect (P > 0.1) of NMA on ADG or feed consumption. Gain:feed ratio decreased (P < 0.03) in a linear fashion with increasing level of NMA. There was a cubic effect (P < 0.05) of NMA treatment on first-rib backfat thickness. In response to graded levels of NMA, backfat thickness at the 10th rib (P < 0.08) and last rib (P < 0.03) increased in a linear fashion. The NMA had no effect (P > 0.1) on backfat thickness measured at the lumbar vertebra or longissimus muscle area measured at the 10th rib interface. The percentage of lean in the carcass decreased in a linear fashion (P < 0.05) in response to increasing levels of NMA in the diet. In summary, NMA had an overall negative effect on growth performance and carcass yield characteristics in barrows. The dichotomous effects of NMA on feed efficiency and body composition in poultry and swine warrants further scrutiny.

Quality and sensory characteristics of selected post-rigor, early deboned broiler breast meat tenderized using hydrodynamic shock waves

Our first objective was to determine the effects of explosive amount and distance of the explosive to the meat surface in the Hydrodyne process on broiler breast tenderness. Early deboned (EB) breasts were removed immediately after initial chill (45 min postmortem), stored for 24 h (4 C), and subjected to one of four Hydrodyne treatments (200 g at 20 cm, 350 g at 23 cm, 275 g at 20 cm, or 350 g at 20 cm). Breasts were water-cooked (78 C internal). Hydrodyne treatment (HYD) of 350 g at 20 cm produced the greatest reduction (28.3%) in Warner-Bratzler shear (WBS, 1.9-cm wide strips). This combination was the only treatment to improve tenderness (peak force 4.3 kg) to a level equivalent (P > 0.05) to aged controls (CA; peak force 3.1 kg). The second objective was to determine the quality and sensory characteristics of Hydrodyne-treated (350 g explosive at 20 cm) broiler breasts as compared with CA and EB. The WBS values (1.0-cm wide and thick strips) for CA (1.56 kg) were different from both HYD (3.7 kg) and EB breasts (4.7 kg). The CA resulted in more tender, flavorful, and juicer breasts than EB and HYD. The EB was higher in initial moisture release than HYD. The EB breasts with tenderness problems can be tenderized by the Hydrodyne process based on WBS results. However, higher levels of explosive may be required to optimize the tenderness improvement of EB breasts that vary significantly in initial tenderness.

Correlation between histochemically assessed fiber type distribution and isomyosin and myosin heavy chain content in porcine skeletal muscles

Highly sensitive enzyme assays developed to differentiate skeletal muscle fibers allow the recognition of three main fiber types: slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), and fast-twitch glycolytic (FG). Myosin, the predominant contractile protein in mammalian skeletal muscle, can be separated based on the electrophoretic mobility under nondissociating conditions into SM2, SM1, IM, FM3, and FM2 isoforms, or under dissociating conditions into myosin heavy chain (MHC) I, IIb, IIx/d, and IIa. The purpose of the present study was to determine whether the histochemical method of differentiation of fiber types is consistent with the electrophoretically identified isomyosin and MHC isoforms. These comparisons were made using serratus ventralis (SV), gluteus medius (GM), and longissimus muscles (LM) from 13 pigs. Two calculation methods for the histochemical assessed fiber type distribution were adopted. The first method incorporated the number of fibers counted for each fiber type and calculated a percentage of the total fiber number (fiber number percentage: FNP). The second method expressed the cross-sectional area of each fiber type as a percentage of the total fiber area measured per muscle (fiber area percentage: FAP). Independent of the calculation methods, correlation analyses revealed in all muscles a strong relation between SO fibers, the slow isomyosin (SM1 and SM2), and MHCI, as well as between the FG fibers, the fast isomyosin (FM3 and FM2), and MHCIIx/b content (P<.05). There were no correlations between FOG fiber population assessed by histochemical analysis and intermediate isoform (IM) or MHCIIa content. The present results did not provide conclusive evidence as to which of the calculation methods (FNP or FAP) was more closely related to myosin composition of skeletal muscles. Despite some incompatibility between the methods, the present study shows that histochemical as well as electrophoretic analyses yielded important information about the composition of porcine skeletal muscle. The combination of the two methods may be essential to accurately characterize porcine skeletal muscles.