Male and female rats exhibit comparable gaping behavior but activate brain regions differently during expression of conditioned nausea.

Twenty-five to fifty percent of patients undergoing chemotherapy will develop anticipatory nausea and vomiting (ANV), in which symptoms occur in anticipation of treatment. ANV is triggered by environmental cues and shows little response to traditional antiemetic therapy, suggesting that unique neural pathways mediate this response. Understanding the underlying neural mechanisms of this disorder is critical to the development of novel therapeutic interventions. The purpose of the present study was to identify brain areas activated during ANV and characterize sex differences in both the behavior and the brain areas activated during ANV. We used a rat model of ANV by pairing a novel context with the emetic drug lithium chloride (LiCl) to produce conditioned nausea behaviors in the LiCl-paired environment. We quantitated gaping, an analog of human vomiting, after acute or repeated LiCl in a unique environment. To identify brain regions associated with gaping, we measured c-fos activation by immunochemical staining after these same treatments. We found that acute LiCl activated multiple brain regions including the supraoptic nucleus of the hypothalamus, central nucleus of the amygdala, nucleus of the solitary tract and area postrema, none of which were activated during ANV. ANV activated c-fos expression in the frontal cortex, insula and paraventricular nucleus of the hypothalamus of males but not females. These data suggest that therapies such as ondansetron which target the area postrema are not effective in ANV because it is not activated during the ANV response. Further studies aimed at characterizing the neural circuits and cell types that are activated in the conditioned nausea response will help identify novel therapeutic targets for the treatment of this condition, improving both quality of life and outcomes for patients undergoing chemotherapy.

Sex and race differences of cerebrospinal fluid metabolites in healthy individuals.

INTRODUCTION: Analyses of cerebrospinal fluid (CSF) metabolites in large, healthy samples have been limited and potential demographic moderators of brain metabolism are largely unknown. OBJECTIVE: Our objective in this study was to examine sex and race differences in 33 CSF metabolites within a sample of 129 healthy individuals (37 African American women, 29 white women, 38 African American men, and 25 white men). METHODS: CSF metabolites were measured with a targeted electrochemistry-based metabolomics platform. Sex and race differences were quantified with both univariate and multivariate analyses. Type I error was controlled for by using a Bonferroni adjustment (0.05/33 = .0015). RESULTS: Multivariate Canonical Variate Analysis (CVA) of the 33 metabolites showed correct classification of sex at an average rate of 80.6% and correct classification of race at an average rate of 88.4%. Univariate analyses revealed that men had significantly higher concentrations of cysteine (p < 0.0001), uric acid (p < 0.0001), and N-acetylserotonin (p = 0.049), while women had significantly higher concentrations of 5-hydroxyindoleacetic acid (5-HIAA) (p = 0.001). African American participants had significantly higher concentrations of 3-hydroxykynurenine (p = 0.018), while white participants had significantly higher concentrations of kynurenine (p < 0.0001), indoleacetic acid (p < 0.0001), xanthine (p = 0.001), alpha-tocopherol (p = 0.007), cysteine (p = 0.029), melatonin (p = 0.036), and 7-methylxanthine (p = 0.037). After the Bonferroni adjustment, the effects for cysteine, uric acid, and 5-HIAA were still significant from the analysis of sex differences and kynurenine and indoleacetic acid were still significant from the analysis of race differences. CONCLUSION: Several of the metabolites assayed in this study have been associated with mental health disorders and neurological diseases. Our data provide some novel information regarding normal variations by sex and race in CSF metabolite levels within the tryptophan, tyrosine and purine pathways, which may help to enhance our understanding of mechanisms underlying sex and race differences and potentially prove useful in the future treatment of disease.

The Effects of Tryptophan Enhancement and Depletion on Plasma Catecholamine Levels in Healthy Individuals.

OBJECTIVE: Central nervous system (CNS) serotonin (5-HT) exerts both excitatory and inhibitory effects on the sympathetic nervous system (SNS) in animals. In this study, we examine the effects of tryptophan enhancement and depletion on plasma catecholamine levels in humans. METHODS: The total sample consisted of 164 healthy men and women who were tested for 2 days. Seventy-nine participants were randomized to a tryptophan enhancement condition and 85 to a tryptophan depletion condition. Both protocols consisted of a "sham day," followed by an "active day." Blood samples for assessment of plasma norepinephrine and epinephrine levels were collected before and after tryptophan enhancement/depletion. Data were analyzed using general linear models. Separate analyses were conducted for each study arm and for each measure. RESULTS: In the depletion condition, both epinephrine (F(5,330) = 2.69, p = .021) and norepinephrine (F(5,335) = 2.79, p = .018) showed small increases on active versus "sham" depletion days. There were also significant day by time interactions for epinephrine (F(3,171) = 39.32, p < .0001) and norepinephrine (F(3,195) = 31.09, p < .0001) levels in the enhancement arm. Tryptophan infusion resulted in a marked increase in epinephrine (Premean = 23.92 (12.23) versus Postmean = 81.57 (62.36)) and decrease in norepinephrine (Premean = 257.2 (106.11) versus Postmean = 177.04 (87.15)), whereas levels of both catecholamines were stable on the "sham day." CONCLUSIONS: CNS 5-HT exerts both inhibitory and excitatory effects on SNS activity in humans, potentially due to stimulation of CNS 5-HT receptors that have shown to have inhibitory (5-HT1A) and excitatory (5-HT1A and/or 5-HT2) SNS effects in animal models.

Withdrawal from Brief Repeated Alcohol Treatment in Adolescent and Adult Male and Female Rats.

BACKGROUND: Early initiation of alcohol drinking has been associated with increased risk of alcohol dependence in adulthood. Although negative affect mediated in part by corticotropin-releasing factor (CRF) is a strong motivator for alcohol consumption in adults, comparisons of alcohol withdrawal in adolescents and adults generally have not included CRF-related measures such as anxiety. The purpose of the present study was to compare withdrawal signs including anxiety-like behavior after a brief multiday alcohol treatment in adolescent and adult male and female rats. METHODS: Animals were treated with a 5-day regimen of alcohol injections (3 daily intraperitoneal injections of 1.5 g/kg at 3-hour intervals, total of 15) starting on postnatal day (PN) 28 or PN 70. Spontaneous withdrawal signs and anxiety-like behavior (light/dark box) were assessed 18 hours after the last injection as described. One cohort of rats was treated with alcohol, killed 18 hours after the last injection, and blood was collected to assess corticosterone. Another cohort of rats was treated with alcohol or vehicle, given 1, 2, or 3 alcohol injections (1.5 g/kg), and killed 1 hour after final injection to determine blood alcohol concentration (BAC). Finally, adult and adolescent males and females received 5 days of alcohol or vehicle treatment followed by a final challenge with alcohol (3 g/kg), and blood was collected for corticosterone. RESULTS: BAC was comparable in adolescents and adults. Spontaneous withdrawal signs were comparable in adolescents and adults, and no sex differences were observed. Anxiety-like behaviors (time and distance in light, latency to emerge, and light entries) differed in alcohol- and vehicle-treated adults but not adolescents. Corticosterone was not elevated at withdrawal. Alcohol increased corticosterone significantly in vehicle-treated animals, but both adolescents and adults were tolerant to alcohol-induced elevation of corticosterone after 5 days of alcohol treatment. CONCLUSIONS: These findings suggest that adolescents experience milder negative affect during withdrawal from brief alcohol exposures relative to adults but comparable suppression of hypothalamic-pituitary-adrenal axis function.

Platelet aggregation and mental stress induced myocardial ischemia: Results from the Responses of Myocardial Ischemia to Escitalopram Treatment (REMIT) study.

BACKGROUND: Mental stress-induced myocardial ischemia (MSIMI) is common in patients with ischemic heart disease (IHD) and associated with a poorer cardiovascular prognosis. Platelet hyperactivity is an important factor in acute coronary syndrome. This study examined associations between MSIMI and resting and mental stress-induced platelet activity. METHODS: Eligible patients with clinically stable IHD underwent a battery of 3 mental stress tests during the recruitment phase of REMIT study. MSIMI was assessed by echocardiography and electrocardiography. Ex vivo platelet aggregation in response to ADP, epinephrine, collagen, serotonin, and combinations of serotonin plus ADP, epinephrine, and collagen were evaluated as was platelet serotonin transporter expression. RESULTS: Of the 270 participants who completed mental stress testing, and had both resting and post-stress platelet aggregation evaluation , 43.33% (n=117) met criteria for MSIMI and 18.15% (n=49) had normal left ventricular response to stress (NLVR). The MSIMI group, relative to the NLVR groups, demonstrated heightened mental stress-induced aggregation responses, as measured by area under the curve, to collagen 10µM (6.95[5.54] vs. -14.23[8.75].; P=0.045), epinephrine 10µM (12.84[4.84] vs. -6.40[7.61].; P=0.037) and to serotonin 10 µM plus ADP 1 µM (6.64[5.29] vs. -27.34[8.34]; P<.001). The resting platelet aggregation and serotonin transporter expression, however, were not different between the two groups. CONCLUSIONS: These findings suggest that the dynamic change of platelet aggregation caused by mental stress may underlie MSIMI. While the importance of these findings requires additional investigation, they raise concern given the recognized relationship between mental stress-induced platelet hyperactivity and cardiovascular events in patients with IHD.

Association of depressive and anxiety symptoms with 24-hour urinary catecholamines in individuals with untreated high blood pressure.

OBJECTIVE: Depression and anxiety are considered risk factors for cardiovascular disease (CVD). The explanatory mechanisms, however, are still to be characterized. One proposed pathophysiological pathway is dysregulation of the autonomic nervous system, including heightened sympathetic nervous system activity. This study examined the relationship between symptoms of depression, anxiety, and sympathetic nervous system activity in individuals with untreated high blood pressure. METHODS: A total of 140 participants with untreated high blood pressure (55% white, 38.5% female, mean [standard deviation] age = 45.5 [8.55] years) collected urine over a 24-hour period on 3 separate occasions. Urine samples were assayed for mean 24-hour epinephrine (EPI24) and norepinephrine excretion. Depressive symptoms were assessed using the Beck Depression Inventory, with anxiety symptoms assessed using the Spielberger State-Trait Anxiety Inventory. RESULTS: Depression and anxiety scores were intercorrelated (r = 0.76, p < .001). EPI24 was positively correlated with anxiety (r = 0.20, p = .02) but not depression (r = 0.02, p = .77), whereas 24-hour urinary norepinephrine excretion was not correlated with anxiety (r = 0.10, p = .21) or with depression (r = 0.07, p = .39). Regression models, accounting for sex, age, body mass index, race, mean systolic ambulatory blood pressure, tobacco use, alcohol use, physical activity, and sleep efficiency confirmed that anxiety was associated with EPI24 excretion (p = .023) and that depressive symptoms were not (p = .54). CONCLUSIONS: Anxiety was associated with heightened sympathoadrenal activity, suggesting a biological pathway through which anxiety could increase CVD risk. Anxiety and depression may confer increased CVD risk via different mechanisms.

Associations between central nervous system serotonin, fasting glucose, and hostility in African American females.

BACKGROUND: Previous research has shown an association between hostility and fasting glucose in African American women. Central nervous system serotonin activity is implicated both in metabolic processes and in hostility related traits. PURPOSE: The purpose of this study is to determine whether central nervous system serotonin influences the association between hostility and fasting glucose in African American women. METHODS: The study consisted of 119 healthy volunteers (36 African American women, 27 White women, 21 White males, and 35 African American males, mean age 34 ± 8.5 years). Serotonin related compounds were measured in cerebrospinal fluid. Hostility was measured by the Cook-Medley Hostility Scale. RESULTS: Hostility was associated with fasting glucose and central nervous system serotonin related compounds in African American women only. Controlling for the serotonin related compounds significantly reduced the association of hostility to glucose. CONCLUSIONS: The positive correlation between hostility and fasting glucose in African American women can partly be explained by central nervous system serotonin function.

Dietary manipulation of serotonergic and dopaminergic function in C57BL/6J mice with amino acid depletion mixtures.

Amino acid (AA) depletion techniques have been used to decrease serotonin (5-HT) and/or dopamine (DA) synthesis after administration of a tryptophan (acute tryptophan depletion, ATD) or phenylalanine/tyrosine-free (phenylalanine-tyrosine depletion, PTD) AA formula and are useful as neurochemical challenge procedures to study the impact of DA and 5-HT in patients with neuropsychiatric disorders. We recently demonstrated that the refined Moja-De ATD paradigm decreases brain 5-HT synthesis in humans and mice and lowers brain 5-HT turnover. In the present study we validated the neurochemical effects of three developed AA formulas on brain 5-HT and DA function in mice. To distinguish the direct and indirect effects of such mixtures on 5-HT and DA and to determine whether additive depletion of both could be obtained simultaneously, we compared the effects of ATD for 5-HT, PTD for DA, and a combined monoamine depletion mixture (CMD) compared to a control condition consisting of a balanced amino acid mixture. Food-deprived male C57BL/6J mice were gavaged with AA mixtures. Serum and brain samples were collected and analyzed for determination of tryptophan (Trp), tyrosine (Tyr), 5-HT, 5-HIAA, DA, DOPAC and HVA levels. ATD was the most effective at decreasing Trp, 5-HT and 5-HIAA. In contrast, PTD reduced Tyr globally but HVA only in certain brain regions. Although CMD affected both 5-HT and DA synthesis, it was less effective when compared with ATD or PTD alone. The present results demonstrate that two newly developed PTD and CMD formulas differentially impact brain 5-HT and DA synthesis relative to 5-HT-specific ATD Moja-De. Different effects on 5-HT and DA function by these mixtures suggest that the exact composition may be a critical determinant for effectiveness with respect to the administered challenge procedure.

Applying the Research Domain Criteria to Rodent Studies of Sex Differences in Chronic Stress Susceptibility.

Women have a 2-fold increased rate of stress-associated psychiatric disorders such as depression and anxiety, but the mechanisms that underlie this increased susceptibility remain incompletely understood. Historically, female subjects were excluded from preclinical studies and clinical trials. Additionally, chronic stress paradigms used to study psychiatric pathology in animal models were developed for use in males. However, recent changes in National Institutes of Health policy encourage inclusion of female subjects, and considerable work has been performed in recent years to understand biological sex differences that may underlie differences in susceptibility to chronic stress-associated psychiatric conditions. Here, we review the utility as well as current challenges of using the framework of the National Institute of Mental Health's Research Domain Criteria as a transdiagnostic approach to study sex differences in rodent models of chronic stress including recent progress in the study of sex differences in the neurobehavioral domains of negative valence, positive valence, cognition, social processes, and arousal.

Depressive symptoms and mental stress-induced myocardial ischemia in patients with coronary heart disease.

OBJECTIVES: The aim of this study was to examine the associations between depressive symptoms and mental stress-induced myocardial ischemia (MSIMI) in patients with coronary heart disease (CHD). METHODS: Adult patients with documented CHD were recruited for baseline mental stress and exercise stress screening testing as a part of the enrollment process of the Responses of Myocardial Ischemia to Escitalopram Treatment trial. Patients were administered the Beck Depression Inventory II and the Center for Epidemiologic Studies Depression Scale. After a 24-48-hour ß-blocker withdrawal, participants completed three mental stress tests followed by a treadmill exercise test. Ischemia was defined as a) any development or worsening of any wall motion abnormality and b) reduction of left ventricular ejection fraction at least 8% by transthoracic echocardiography and/or ischemic ST-segment change by electrocardiography during stress testing. MSIMI was considered present when ischemia occurred in at least one mental test. Data were analyzed using logistic regression adjusting for age, sex, and resting left ventricular ejection fraction. RESULTS: One hundred twenty-five (44.2%) of 283 patients were found to have MSIMI, and 93 (32.9%) had ESIMI. Unadjusted analysis showed that Beck Depression Inventory II scores were positively associated with the probability of MSIMI (odds ratio = 0.1.30: 95% confidence interval = 1.06-1.60, p = .013) and number of MSIMI-positive tasks (all p < .005). These associations were still significant after adjustment for covariates (p values <.05). CONCLUSIONS: In patients with CHD, depressive symptoms were associated with a higher probability of MSIMI. These observations may enhance our understanding of the mechanisms contributing to the association of depressive symptoms to future cardiovascular events. Trial Registration Clinicaltrials.gov identifier: NCT00574847.

Effect of escitalopram on mental stress-induced myocardial ischemia: results of the REMIT trial.

IMPORTANCE: Mental stress can induce myocardial ischemia and also has been implicated in triggering cardiac events. However, pharmacological interventions aimed at reducing mental stress-induced myocardial ischemia (MSIMI) have not been well studied. OBJECTIVE: To examine the effects of 6 weeks of escitalopram treatment vs placebo on MSIMI and other psychological stress-related biophysiological and emotional parameters. DESIGN, SETTING, AND PARTICIPANTS: The REMIT (Responses of Mental Stress Induced Myocardial Ischemia to Escitalopram Treatment) study, a randomized, double-blind, placebo-controlled trial of patients with clinically stable coronary heart disease and laboratory-diagnosed MSIMI. Enrollment occurred from July 24, 2007, through August 24, 2011, at a tertiary medical center. INTERVENTIONS: Eligible participants were randomized 1:1 to receive escitalopram (dose began at 5 mg/d, with titration to 20 mg/d in 3 weeks) or placebo over 6 weeks. MAIN OUTCOMES AND MEASURES: Occurrence of MSIMI, defined as development or worsening of regional wall motion abnormality; left ventricular ejection fraction reduction of 8% or more; and/or horizontal or down-sloping ST-segment depression of 1 mm or more in 2 or more leads, lasting for 3 or more consecutive beats, during 1 or more of 3 mental stressor tasks. RESULTS: Of 127 participants randomized to receive escitalopram (n = 64) or placebo (n = 63), 112 (88.2%) completed end point assessments (n = 56 in each group). At the end of 6 weeks, more patients taking escitalopram (34.2% [95% CI, 25.4%-43.0%]) had absence of MSIMI during the 3 mental stressor tasks compared with patients taking placebo (17.5% [95% CI, 10.4%-24.5%]), based on the unadjusted multiple imputation model for intention-to-treat analysis. A significant difference favoring escitalopram was observed (odds ratio, 2.62 [95% CI, 1.06-6.44]). Rates of exercise-induced ischemia were slightly lower at 6 weeks in the escitalopram group (45.8% [95% CI, 36.6%-55.0%]) than in patients receiving placebo (52.5% [95% CI, 43.3%-61.8%]), but this difference was not statistically significant (adjusted odds ratio; 1.24 [95% CI, 0.60-2.58]; P = .56). CONCLUSIONS AND RELEVANCE: Among patients with stable coronary heart disease and baseline MSIMI, 6 weeks of escitalopram, compared with placebo, resulted in a lower rate of MSIMI. There was no statistically significant difference in exercise-induced ischemia. Replication of these results in multicenter settings and investigations of other medications for reducing MSIMI are needed. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00574847.

Responses of mental stress-induced myocardial ischemia to escitalopram treatment: background, design, and method for the Responses of Mental Stress Induced Myocardial Ischemia to Escitalopram Treatment trial.

BACKGROUND: Mental stress-induced myocardial ischemia (MSIMI) is common in patients with clinically stable coronary heart disease (CHD) and is associated with poor outcomes. Depression is a risk factor of MSIMI. The REMIT trial investigates whether selective serotonin reuptake inhibitor (SSRI) treatment can improve MSIMI. The rationale and outline of the study are described. METHOD: In this single-center randomized clinical trial, adult patients with clinically stable CHD are recruited for baseline mental and exercise stress testing assessed by echocardiography. In addition, psychometric questionnaires are administered, and blood samples are collected for platelet activity analysis. Patients who demonstrate MSIMI, defined by new abnormal wall motion, ejection fraction reduction ≥8%, and/or development of ischemic ST change in electrocardiogram during mental stress testing, are randomized at a 1:1 ratio to escitalopram or placebo for 6 weeks. Approximately 120 patients with MSIMI are enrolled in the trial. The stress testing, platelet activity assessment, and psychometric questionnaires are repeated at the end of the 6-week intervention. The hypothesis of the study is that SSRI treatment improves MSIMI via mood regulation and modification of platelet activity. CONCLUSION: The REMIT study examines the effect of SSRI on MSIMI in vulnerable patients with CHD and probes some potential underlying mechanisms.

Rapastinel accelerates loss of withdrawal signs after repeated morphine and blunts relapse to conditioned place preference.

The purpose of the present study was to evaluate the efficacy of rapastinel, an allosteric modulator of NMDA receptor function, to accelerate the loss of opioid withdrawal symptoms and blunt or prevent relapse to morphine conditioned place preference (CPP) in rats. Two studies were conducted. In study 1, adult and adolescent male and female rats were treated with increasing doses of morphine (5 mg/kg, bid to 25 mg/kg bid) for 5 days. On day 6 animals were treated with naloxone (1 mg/kg) and withdrawal was assessed. They were then treated with saline or rapastinel (5 mg/kg) on days 6 and 8, and withdrawal was assessed on day 9. Rapastinel treated animals exhibited significantly lower levels of withdrawal signs on day 9. No sex or age differences were observed. In Study 2, CPP for morphine was established in adult rats (males and females) by 4 daily pairings with saline and morphine (am/pm alternation). They were tested for CPP on day 5, and then treated with rapastinel (5 mg/kg) or saline daily on days 6-10 of extinction. On day 11 they received a final dose of rapastinel or saline followed by extinction trial. On day 12, animals received 1 mg/kg of morphine and were tested for relapse. Rapastinel did not affect extinction of CPP, but rapastinel-treated animals spent significantly less time in the previously morphine-paired side than saline-treated animals during the relapse trial. These findings of accelerated loss of withdrawal signs and blunted relapse to CPP suggest that rapastinel could provide an adjunctive therapy for opioid dependence during initiation of pharmacotherapy for opioid dependence.

Maternal diet disrupts the placenta-brain axis in a sex-specific manner.

High maternal weight is associated with detrimental outcomes in offspring, including increased susceptibility to neurological disorders such as anxiety, depression and communicative disorders. Despite widespread acknowledgement of sex biases in the development of these disorders, few studies have investigated potential sex-biased mechanisms underlying disorder susceptibility. Here, we show that a maternal high-fat diet causes endotoxin accumulation in fetal tissue, and subsequent perinatal inflammation contributes to sex-specific behavioural outcomes in offspring. In male offspring exposed to a maternal high-fat diet, increased macrophage Toll-like receptor 4 signalling results in excess microglial phagocytosis of serotonin (5-HT) neurons in the developing dorsal raphe nucleus, decreasing 5-HT bioavailability in the fetal and adult brains. Bulk sequencing from a large cohort of matched first-trimester human samples reveals sex-specific transcriptome-wide changes in placental and brain tissue in response to maternal triglyceride accumulation (a proxy for dietary fat content). Further, fetal brain 5-HT levels decrease as placental triglycerides increase in male mice and male human samples. These findings uncover a microglia-dependent mechanism through which maternal diet can impact offspring susceptibility for neuropsychiatric disorder development in a sex-specific manner.

Low- and high-testosterone individuals exhibit decreased aversion to economic risk.

Testosterone is positively associated with risk-taking behavior in social domains (e.g., crime, physical aggression). However, the scant research linking testosterone to economic risk preferences presents inconsistent findings. We examined the relationship between endogenous testosterone and individuals' economic preferences (i.e., risk preference, ambiguity preference, and loss aversion) in a large sample (N = 298) of men and women. We found that endogenous testosterone levels have a significant U-shaped association with individuals' risk and ambiguity preferences, but not loss aversion. Specifically, individuals with low or high levels of testosterone (more than 1.5 SD from the mean for their gender) were risk and ambiguity neutral, whereas individuals with intermediate levels of testosterone were risk and ambiguity averse. This relationship was highly similar in men and women. In contrast to received wisdom regarding testosterone and risk, the present data provide the first robust evidence for a nonlinear association between economic preferences and levels of endogenous testosterone.

The effects of peri-adolescent alcohol use on the developing hippocampus.

Adolescence is a period of continued brain development. Regions of the brain, such as the hippocampus, continue to undergo refinement and maturation throughout adolescence and into early adulthood. Adolescence is also a time of heightened sensitivity to novelty and reward, which contribute to an increase in risk-taking behaviors including the use of drugs and alcohol. Importantly, binge drinking is highly prevalent among adolescents and emerging adults. The hippocampus which is important for the integration of emotion, reward, homeostasis, and memory is particularly vulnerable to the neurotoxic effects of alcohol. In this chapter, we cover the fundamentals of hippocampal neuroanatomy and the current state of knowledge of the acute and chronic effects of ethanol in adolescent humans and adolescent rodent models. We focus on the hippocampal-dependent behavioral, structural, and neurochemical changes and identify knowledge gaps in our understanding of age-dependent neurobiological effects of alcohol use.

Behavior and Fos activation reveal that male and female rats differentially assess affective valence during CTA learning and expression.

Females are more affected by psychiatric illnesses including eating disorders, depression, and post-traumatic stress disorder than males. However, the neural mechanisms mediating these sex differences are poorly understood. Animal models can be useful in exploring such neural mechanisms. Conditioned taste aversion (CTA) is a behavioral task that assesses how animals process the competition between associated reinforcing and aversive stimuli in subsequent task performance, a process critical to healthy behavior in many domains. The purpose of the present study was to identify sex differences in this behavior and associated neural responses. We hypothesized that females would value the rewarding stimulus (Boost®) relative to the aversive stimulus (LiCl) more than males in performing CTA. We evaluated behavior (Boost® intake, LiCl-induced behaviors, ultrasonic vocalizations (USVs), CTA performance) and Fos activation in relevant brain regions after the acute stimuli [acute Boost® (AB), acute LiCl (AL)] and the context-only task control (COT), Boost® only task (BOT) and Boost®-LiCl task (BLT). Acutely, females drank more Boost® than males but showed similar aversive behaviors after LiCl. Females and males performed CTA similarly. Both sexes produced 55 kHz USVs anticipating BOT and inhibited these calls in the BLT. However, more females emitted both 22 kHz and 55 kHz USVs in the BLT than males: the latter correlated with less CTA. Estrous cycle stage also influenced 55 kHz USVs. Fos responses were similar in males and females after AB or AL. Females engaged the gustatory cortex and ventral tegmental area (VTA) more than males during the BOT and males engaged the amygdala more than females in both the BOT and BLT. Network analysis of correlated Fos responses across brain regions identified two unique networks characterizing the BOT and BLT, in both of which the VTA played a central role. In situ hybridization with RNAscope identified a population of D1-receptor expressing cells in the CeA that responded to Boost® and D2 receptor-expressing cells that responded to LiCl. The present study suggests that males and females differentially process the affective valence of a stimulus to produce the same goal-directed behavior.