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.

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.

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.

Effect of sex on ethanol consumption and conditioned taste aversion in adolescent and adult rats.

RATIONALE: Vulnerability to alcoholism is determined by many factors, including the balance of pleasurable vs. aversive alcohol-induced sensations: pleasurable sensations increase intake, while aversive sensations decrease it. Female sex and adolescent age are associated with lower sensitivity to intake-reducing effects and more rapid development of alcohol abuse. OBJECTIVES: This study assessed voluntary drinking and the aversive effects of alcohol to determine whether these measures are inversely related across the sexes and development. METHODS: Voluntary drinking of 20 % ethanol in an every-other-day (EOD) availability pattern and the dose-response relationship of ethanol conditioned taste aversion (CTA) were assessed in male and female adolescent and adult rats. RESULTS: CTA was sex specific in adult but not adolescent rats, with adult females exhibiting less aversion. Voluntary ethanol consumption varied according to age and individual differences but was not sex specific. Adolescents initially drank more than adults, exhibited greater day-to-day variation in consumption, were more susceptible to the alcohol deprivation effect, and took longer to establish individual differences in consumption patterns. CONCLUSIONS: These results show that the emergence of intake patterns differs between adolescents and adults. Adolescents as a group initiate drinking at high levels but decrease intake as they mature. A subset of adolescents maintained high drinking levels into adulthood. In contrast, most adults consumed at steady, low levels, but a small subset quickly established and maintained high-consumption patterns. Adolescents also showed marked deprivation-induced increases. Sex differences were not observed in EOD drinking during either adolescence or adulthood.

Sex differences in the neurochemical and functional effects of MDMA in Sprague-Dawley rats.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA; "Ecstasy") use has been associated with acute toxicities and persistent depletion of the neurotransmitter serotonin (5-HT). OBJECTIVES: This study investigates whether sex differences in the acute and long-term effects of MDMA exist. METHODS: Male and female rats received saline or 15 mg/kg MDMA, ip, bid for 4 days. Temperature was monitored on days 1 and 4. Locomotor activity was measured in a second cohort of animals on days 1 and 4 and after recovery on day 14. The effects of MDMA on performance in a plus maze task and brain levels of serotonin (5-HT) and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in a third cohort of animals 2 weeks after the last MDMA treatment. RESULTS: Locomotor activity and temperature increased after MDMA administration on day 1. The drug-induced increases in temperature but not locomotion attenuated with repeated MDMA administration. Male and female MDMA-treated rats spent less time in the open arms of the elevated plus maze and had less 5-HT and 5-HIAA in all brain regions 2 weeks after the end of treatment. Temperature effects of MDMA and persistent effects on plus maze and brain serotonin content were similar in males and females. In contrast, females exhibited markedly greater locomotor stimulation after acute MDMA and also showed sensitization to an acute challenge 2 weeks later. CONCLUSIONS: MDMA elicits substantially greater locomotor activation in female rats than in males, but persistent effects on anxiety and serotonin content were similar in males and females.