Adolescent Female Rats Research Articles

Impact of pubertal onset on region-specific Esr2 expression.

In female rats, pubertal onset is associated with maturation of the medial prefrontal cortex (mPFC) and mPFC-mediated behaviours. These behavioural and anatomical changes are likely a result of the effects of oestrogens at the nuclear oestrogen receptor (ER)β, which is expressed at higher levels than the ERα isoform in the adult mPFC. Researchers have previously quantified ERβ protein and Esr2 RNA in rodents during early postnatal development and adulthood, although an adolescent-specific trajectory of this receptor in the mPFC has not been documented. Given that Esr2 expression can fluctuate in the presence or absence of oestrogens, puberty and the subsequent rise in gonadal hormones could influence levels of ERβ in the adolescent brain. To further explore this, we used RNAscope® technology to quantify the amount of Esr2 mRNA in pre-pubertal adolescent, recently post-pubertal adolescent and adult female rats. We show that Esr2 expression decreases significantly in the mPFC, striatum and motor cortex between pre-pubertal adolescence and adulthood. In the mPFC, this decrease occurs rapidly at pubertal onset, with no significant decrease in Esr2 levels between the recently post-pubertal and adult cohort. By contrast, the striatum and motor cortex had no significant differences in the amount of Esr2 mRNA between pre- and post-pubertal females. Insofar as the amount of Esr2 expression is proportional to functional ERβ, these results suggest ERβ decreases in a region-specific pattern in response to pubertal onset and highlight a role for this receptor in the maturational events that occur in the female rat mPFC at puberty.

Influence of Vitamin D on the Vasoactive Effect of Estradiol in a Rat Model of Polycystic Ovary Syndrome.

We examined the vasoactive effect of estradiol in a rat model of early PCOS and the influence of vitamin D deficiency (VDD). We created a model of chronic hyperandrogenism and VDD in adolescent female Wistar rats (N = 46) with four experimental groups: vitamin D supplemented (T-D+), VDD (T-D-), hyperandrogenic and vitamin D supplemented (T+D+), and hyperandrogenic and VDD (T+D-). T+ groups received an 8-week-long transdermal Androgel treatment, D-animals were on vitamin D-reduced diet and D+ rats were supplemented orally with vitamin D3. Estrogen-induced vasorelaxation of thoracic aorta segments were measured with a wire myograph system with or without the inhibition of endothelial nitric oxide synthase (eNOS) or cyclooxygenase-2 (COX-2). The distribution of estrogen receptor (ER), eNOS and COX-2 in the aortic wall was assessed by immunohistochemistry. VDD aortas showed significantly lower estradiol-induced relaxation independently of androgenic status that was further decreased by COX-2 inhibition. COX-2 inhibition failed to alter vessel function in D+ rats. Inhibition of eNOS abolished the estradiol-induced relaxation in all groups. Changes in vascular function in VDD were accompanied by significantly decreased ER and eNOS staining. Short-term chronic hyperandrogenism failed to, but VDD induced vascular dysfunction, compromised estrogen-dependent vasodilatation and changes in ER and eNOS immunostaining.

Adolescent female rats prone to the activity based anorexia (ABA) paradigm have altered hedonic responses and cortical astrocyte density compared to resistant animals

ObjectiveAnhedonia, which in part involves the lack of pleasure in consuming palatable food, is a long-lasting symptom observed in patients both when acutely ill and when long term recovered from Anorexia Nervosa. The neurocircuitry underlying this phenomenon is not well understood. Here we use the preclinical activity-based anorexia (ABA) model in adolescent female rats to assess the impact of excessive exercise, limited food intake and acute weight loss, on adolescent female rat orofacial responding to intraoral sucrose, as measured by the taste reactivity test (TRT). Animals were identified as either prone or resistant to this paradigm based on a weight loss criterion. Measures of food intake, running wheel activity, taste reactivity and medial prefrontal cortex astrocyte expression were compared across groups. MethodsAdolescent female rats implanted with an intraoral catheter were given a TRT using 1 M (M) sucrose at baseline, max weight loss (25% weight loss from start of ABA or 7 full days on the paradigm) or 10 days recovered from the ABA paradigm. Animals were sacrificed after the final TRT and astrocyte density was measured via immunohistochemistry. ResultsAnimals resistant to the ABA paradigm ran less than prone animals during the ABA period. Additionally, we found that resistant animals displayed more cumulative ‘liking’ responses to sucrose compared to prone animals at maximum weight loss. Finally, we found prone animals 10-days recovered from ABA had reduced medial prefrontal cortex astrocyte density compared to levels in resistant animals. DiscussionRats presented with the physiological challenge of the ABA paradigm either adapt their behavior to stabilize their body weight (i.e. resistant), or rapidly lose weight (i.e. prone). Furthermore, we found that prone animals have reduced orofacial responding to 1 M sucrose at maximum weight loss compared to responses in resistant animals, and this anhedonia-like behavior may be a result of reduced astrocyte density that affects cortical function.

Δ 9-Tetrahydrocannabinol During Adolescence Reprograms the Nucleus Accumbens Transcriptome, Affecting Reward Processing, Impulsivity, and Specific Aspects of Cocaine Addiction-Like Behavior in a Sex-Dependent Manner.

BackgroundCannabis exposure during adolescence is associated with emotional and motivational alterations that may entail an enhanced risk of developing psychiatric disorders. In rodent models, exposure to cannabinoids during adolescence leads to increased self-administration of opiates and cocaine, however, the psychological and neural mechanisms and the sex-specificity of this phenomenon are largely unknown.MethodsWe exposed male and female adolescent rats to Δ9-tetrahydrocannabinol (THC) and studied at adulthood the effects of such treatment on psychological processes related to reward, such as Pavlovian conditioned approach, Pavlovian to instrumental transfer, habit formation and waiting impulsivity. In the light of these data and given the involvement of the nucleus accumbens in the processes examined, we performed an RNASeq transcriptomic study and assessed cocaine addiction-like behavior.ResultsTHC exposure increased goal-tracking (in males and females) and enhanced Pavlovian to instrumental transfer (especially in males) but did not affect habit formation. THC-exposed rats exhibited subtle, state-dependent changes in premature responding in the 2-CSRTT task. RNASeq data showed gene expression alterations in a marked sex-specific manner. While no effects were found on the acquisition of cocaine self-administration or punished drug-seeking, rats exposed to THC self-administered more cocaine under a progressive ratio schedule (males), had a higher rebound upon returning to continuous access to the drug (females) and showed reduced drug-seeking after 30 days of withdrawal (females).ConclusionsAdolescent THC affects specific aspects of reward- (and cocaine-) guided behavior and the function of a key brain region mediating these effects, in a remarkable sex-specific manner.

Is the Activity-Based Anorexia Model a Reliable Method of Presenting Peripheral Clinical Features of Anorexia Nervosa?

Anorexia nervosa (AN) causes the highest number of deaths among all psychiatric disorders. Reduction in food intake and hyperactivity/increased anxiety observed in AN are also the core features of the activity-based anorexia animal model (ABA). Our aim was to assess how the acute ABA protocol mimics common AN complications, including gonadal and cardiovascular dysfunctions, depending on gender, age, and initial body weight, to form a comprehensive description of ABA as a reliable research tool. Wheel running, body weight, and food intake of adolescent female and male rats were monitored. Electrocardiography, heart rate variability, systolic blood pressure, and magnetic resonance imaging (MRI) measurements were performed. Immediately after euthanasia, tissue fragments and blood were collected for further analysis. Uterine weight was 2 times lower in ABA female rats, and ovarian tissue exhibited a reduced number of antral follicles and decreased expression of estrogen and progesterone receptors. Cardiovascular measurements revealed autonomic decompensation with prolongation of QRS complex and QT interval. The ABA model is a reliable research tool for presenting the breakdown of adaptation mechanisms observed in severe AN. Cardiac and hormonal features of ABA with underlying altered neuroendocrine pathways create a valid phenotype of a human disease.

Sex Differences in Neurophysiological Changes Following Voluntary Exercise in Adolescent Rats.

Background: Adolescence is a period of time characterized by the onset of puberty and is marked by cognitive and social developments and gross physical changes that can play a role in athletic performance. Sex differences are present with differences in body size, height, physiology and behavior which contribute to differences in athletic performance as well. Pre-clinical studies representing this active group are lacking.Methods: Acute and chronic effects of exercise were evaluated. Male and female adolescent rats were given voluntary access to a running wheel for 10 consecutive days. Running behavior (males and females) and estrous cycling (females only) were analyzed daily. A second group was given 10 days of voluntary access to a running wheel, then rested for 10 days to determine the long-term effects of exercise on the adolescent brain. Brain and muscle tissue were harvested at 10 and 20 day time points to understand exercise-dependent changes in mitochondrial activity and neuroplasticity. Animal cohorts were carried out at two different sites: University of California Los Angeles and Pepperdine University.Results: On average, running distance, intensity of run, and length of running bout increased for both male and female rats across the 10 days measured. Females ran significantly further and for longer intervals compared to males. Cortical and muscle expression of PGC1α showed similar levels at 10 days regardless of sex and exercise. There was a significant increase in expression at 20 days in all groups correlating with body size (p's < 0.05). Cortical and hippocampal levels of BDNF were similar across all groups, however, BDNF was significantly higher in exercised females at the acute compared to long-term time point.Discussion: Adolescent rats allowed 10 days of exercise show changes in physiologic function. There are sex differences in running behavior not impacted by sex hormones. These results are important to further our understanding of how exercise impacts the adolescent brain.

The Long-Term Effects of Neonatal Inflammatory Pain on Cognitive Function and Stress Hormones Depend on the Heterogeneity of the Adolescent Period of Development in Male and Female Rats.

Exposure to stress at an early age programs the HPA axis which can lead to cognitive deficits in adults. However, it is not known whether these deficits emerge in adulthood or are expressed earlier in life. The aims of the study were to investigate (1) the immediate effects of early injury-induced stress in one-day-old (P1) and repeated stress on at P1 and P2 rat pups on plasma corticosterone levels; and (2) examine the subsequent long-term effects of this early stress on spatial learning and memory, and stress reactivity in early P26-34 and late P45-53 adolescent male and female rats. Intra-plantar injection of formalin induced prolonged and elevated levels of corticosterone in pups and impaired spatial learning and short- and long-term memory in late adolescent males and long-term memory in early adolescent females. There were sex differences in late adolescence in both learning and short-term memory. Performance on the long-term memory task was better than that on the short-term memory task for all early adolescent male and female control and stressed animals. Short-term memory was better in the late age control rats of both sexes and for formalin treated females as compared with the early age rats. These results are consistent with an impaired function of structures involved in memory (the hippocampus, amygdala, prefrontal cortex) after newborn pain. However, activation of the HPA axis by neonatal pain did not directly correlate with spatial learning and memory outcomes and the consequences of neonatal pain remain are likely multi-determined.

N-Cadherin Regulates GluA1-Mediated Depressive-Like Behavior in Adolescent Female Rat Offspring following Prenatal Stress

Background: The incidence of depression is twice higher in women than in men, and gender differences in the prevalence rates first emerge around puberty. Prenatal stress (PS) induces gender-dependent depressive-like behavior in adolescent offspring, but the neuro-physiological mechanisms remain unclear. Our study aimed to investigate the possible neuro-physiological mechanisms of gender-dependent depressive-like behavior in PS adolescent offspring and further explored the possibility of treating depression in adolescent female rats. Methods: The pregnant rats were exposed to restraint stress in the third trimester for 7 days. The depressive-like behavior and the expression of N-cadherin and AMPARs in the hippocampus of adolescent offspring rats were assessed. 10 mg/kg AMPAR antagonist CNQX and 10 mg/kg N-cadherin antagonist ADH-1 were intraperitoneally injected into female adolescent offspring, respectively; 0.2 µg AMPAR agonist CX546 was administered to the dentate gyrus of male adolescent offspring to determine the role of N-cadherin-AMPARs in depressive-like behavior of the offspring following PS. Results: We found that PS increased N-cadherin expression, which upregulated GluA1 expression in the dentate gyrus, mediating depressive-like behavior in adolescent female rat offspring by reducing PSD-95. In addition, ADH-1 and CNQX improved depressive-like behavior in adolescent female offspring following PS. Furthermore, injection of the CX546 into the dentate gyrus induced depressive-like behavior in PS male offspring. Conclusion: The gender-dependent expression of N-cadherin-GluA1 pathway in adolescent offspring in the dentate gyrus was the key factor in gender differences of depressive-like behavior following PS.

Alcohol drinking during early adolescence activates microglial cells and increases frontolimbic Interleukin-1 beta and Toll-like receptor 4 gene expression, with heightened sensitivity in male rats compared to females

Adolescent drinking is risky because neural circuits in the frontal lobes are undergoing maturational processes important for cognitive function and behavioral control in adulthood. Previous studies have shown that myelinated axons in the medial prefrontal cortex (mPFC) are particularly sensitive to alcohol drinking, especially in males. Pro-inflammatory mediators like toll-like receptor 4 (TLR4) and interleukin-1 beta (IL1b) have been implicated in alcohol induced-inflammation and demyelination; thus, herein we test the hypothesis that voluntary alcohol drinking early in adolescence elicits a pro-inflammatory state that is more pronounced in the brain of males compared to females. Adolescent male and female Wistar rats self-administered sweetened alcohol or sweetened water from postnatal days 28–42 and separate sets of brains were processed for 1) immunolabeling for ionized calcium-binding adapter molecule 1 to analyze microglial cell morphology, or 2) qPCR analysis of gene expression of pro-inflammatory mediators. Binge drinking alcohol activated microglia in the mPFC and hippocampus of both males and females, suggesting that voluntary alcohol exposure initiates an inflammatory response. Il1b mRNA was upregulated in the mPFC of both sexes. Conversely, Tlr4 mRNA levels were elevated after drinking only in males, which could explain more robust effects of alcohol on myelin in this region in developing males compared to females. Il1b mRNA changes were not observed in the hippocampus, but alcohol elevated Tlr4 mRNA in both sexes, highlighting regional specificity in inflammatory responses to alcohol. Overall, these findings give insight into potential mechanisms by which low-to-moderate voluntary alcohol intake impacts the developing brain.This article is part of the special Issue on ‘Vulnerabilities to Substance Abuse’.

Adolescent nicotine treatment causes robust locomotor sensitization during adolescence but impedes the spontaneous acquisition of nicotine intake in adult female Wistar rats

Very few people are able to quit smoking, and therefore it is essential to know which factors contribute to the development of compulsive nicotine use. These studies aimed to investigate if early-adolescent nicotine exposure causes locomotor sensitization and affects anxiety-like behavior and the spontaneous acquisition of intravenous nicotine self-administration. Early-adolescent male and female rats were treated with nicotine from postnatal (P) days 24 to 42, and anxiety-like behavior and locomotor activity were investigated one day after the cessation of nicotine treatment and in adulthood (>P75). The spontaneous acquisition of nicotine self-administration was also investigated in adulthood. The rats self-administered 0.03 mg/kg/infusion of nicotine for six days under a fixed-ratio (FR) 1 schedule and four days under an FR2 schedule (3-h sessions). Repeated nicotine administration increased locomotor activity, rearing, and stereotypies in a small open field in adolescent male and female rats. One day after the last nicotine injection, the percentage of open arm entries in the elevated plus-maze test was decreased in the males and increased in the females. However, locomotor activity in the small open field was unaffected. Adolescent nicotine treatment did not affect anxiety-like behavior and locomotor activity in adulthood. During the 10-day nicotine self-administration period, the females had a higher level of nicotine intake than the males. Adolescent nicotine treatment decreased nicotine intake in the females. In conclusion, these findings indicate that repeated nicotine administration during adolescence causes robust behavioral sensitization and leads to lower nicotine intake in females throughout the acquisition period in adulthood in rats.

Age, Sex and Strain Respond Differently to Acute Ritalin (Methylphenidate) Exposure

The dose-dependent response to variable methylphenidate (MPD) doses on the behavior of male and female adolescent (post-natal day 39) and adult (post-natal day 60) rats of three different genetic strains was studied to examine whether there are sex, age and strain dependent differences in response to MPD. Twenty-four male and twenty-four female groups were used. The 48 groups each had an N=8. The results show that female adolescents and adult rats of Sprague-Dawley (SD) and Spontaneous Hyperactive Rat (SHR) strains were more sensitive to the acute exposure of MPD. Furthermore, female adult rats of the SD, SHR and Wistar-Kyoto (WKY) strains generally responded with greater increase in locomotor activity than the adolescent females of these strains. In the WKY strain, adolescent males tended to experience a greater increase in activity than adult males. Lastly, significant differences in response to MPD also were observed among the three genetic strains. These variable responses to the acute dose of MPD reinforce the need to study the effects of this psychostimulant across the various sexes, ages and strains.

The Long‐Term Effects of Repeated Heroin Vapor Inhalation During Adolescence in Adult Wistar Rats

Although inhalation is a common route for the administration of illicit opioid drugs, there are only a few animal studies on the effects of inhaled opioids. The present work aimed to assess the behavioral effects of repeated heroin vapor exposure during adolescence on measures of nociception, anxiety, and locomotor activity later in adulthood. To this end, adolescent female and male Wistar rats were exposed to heroin vapor for 30 minutes twice daily for 10 days starting on PND 36. Upon reaching adulthood, warm-water tail-withdrawal tests were performed to assess baseline thermal nociception, and anxiety-like behavior was measured in an elevated-plus maze. Next, locomotor activity was measured in an open field arena. The persistence of nociceptive effects was examined after a period of time, starting 29 weeks of age. This included assessments on baseline thermal nociception across a range of temperatures and warm-water tail-withdrawal tests following injected heroin. We report effects on baseline thermal nociception at 12 weeks of age and an increase in anxiety-like behavior in the elevated-plus maze. Additionally, locomotor behavior was affected by adolescent heroin vapor. When baseline nociception was once again measured at 29 weeks of age, the effects adolescent heroin vapor persisted and the anti-nociceptive effects of injected heroin were blunted in animals previously exposed to heroin vapor. The findings here recapitulate the nociceptive and anxiogenic effects of opioids reported in previous studies using parenteral injection as the route of administration and extend them to inhalation, a common yet understudied route of administering opioid drugs. Importantly, we report a persistence of effects of opioid exposure on nociception that is not well-described in the current literature.

Age-specific treatment effects of orexin/hypocretin-receptor antagonism on methamphetamine-seeking behavior

BackgroundWorldwide methamphetamine (METH) use has increased significantly over the last 10 years, and in the US, METH dependence has sky-rocketed among individuals with opioid use disorder. Of significant concern, METH use is gaining popularity among groups with susceptibility to developing severe substance use disorders, such as women and adolescents. Nevertheless, there is no established pharmacotherapy for METH addiction. Emerging evidence has identified the orexin/hypocretin system as an important modulator of reward-driven behavior and a potential target for the treatment of drug addiction and relapse. However, to date, there have been no investigations into the therapeutic efficacy of orexin/hypocretin receptor antagonists for METH-motivated behavior in adolescents or adults. In the present study, we examined the effects of selective antagonists of the orexin-1 (SB-334867, 20 mg/kg) and orexin-2 (TCS-OX2-29, 20 mg/kg) receptors on the reinstatement of METH seeking in both adolescent and adult male and female rats. MethodsRats were trained to self-administer METH (0.05 mg/kg/inf, iv) during two 2-h sessions/day for 5 days. Following 20 sessions of extinction over 10 days, a within-subjects design was used to test for METH seeking precipitated by METH (1 mg/kg, ip) or METH cues after systemic pretreatment with SB-334867 or TCS-OX2-29. ResultsSB-334867 reduced cue-induced reinstatement in males and females, regardless of age. Additionally, METH-induced METH seeking was attenuated by SB-334867 in adolescents and by TCS-OX2-29 in adults. ConclusionSelective orexin/hypocretin receptor antagonists have significant therapeutic potential for diminishing METH-seeking behavior, although their treatment efficacy may be influenced by age.

Tetrahydrocannabinol (THC) Exacerbates Inflammatory Bowel Disease in Adolescent and Adult Female Rats

Inflammatory Bowel Disease (IBD) is a life-long disorder that often begins between the ages of 15 and 30. Anecdotal reports suggest cannabinoids may be an effective treatment. This study sought to determine whether home cage wheel running is an effective method to assess IBD, and whether Tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis, can restore wheel running depressed by IBD. Adolescent and adult female Sprague-Dawley rats were individually housed in a cage with a running wheel. Rats were injected with trinitrobenzene sulphonic acid (TNBS) into the rectum to induce IBD-like symptoms. One day later, both vehicle and TNBS treated rats were injected with a low dose of THC (0.32 mg/kg, s.c.) or vehicle. Administration of TNBS depressed wheel running in adolescent and adult rats. No antinociceptive effect of THC was evident when administered 1 day after TNBS. In fact, administration of THC prolonged TNBS-induced depression of wheel running for over 5 days in adolescent and adult rats. These results show that home cage wheel running is depressed by TNBS-induced IBD, making it a useful tool to evaluate the behavioral consequences of IBD, and that administration of THC, instead of producing antinociception, exacerbates TNBS-induced IBD. PerspectiveThis article advances research on inflammatory bowel disease in two important ways: 1) Home cage wheel running is a new and sensitive tool to assess the behavioral consequences of IBD in adolescent and adult rats; and 2) Administration of the cannabinoid THC exacerbates the negative behavioral effects of IBD.

Abstract P799: Nicotine Along With Oral Contraceptive Exposure Alters Brain Lipid Metabolism and Exacerbates Ischemic Injury in Female Rats

Background: Smoking-derived nicotine (N) and oral contraceptives (OC) synergistically exacerbate both global and focal ischemic brain damage in females. While the underlying mechanisms remain elusive, our published study showed that OC exacerbate N toxicity via altered mitochondrial electron transport chain function. Because mitochondria play a central role in cellular metabolism, we examined the metabolic fingerprint of adolescent and adult female rat brains exposed to N +/- OC. Methods: Adolescent (6 weeks old) and adult (12 weeks old) Sprague-Dawley female rats were randomly (n = 8/group) exposed to either saline, N (4.5 mg/kg) +/- OC for 16-21 days. Following treatment, brain tissue was harvested for unbias metabolomic analysis (performed by Metabolon Inc.). The metabolomic profile was complemented with western blot analysis and enzyme activity measurements. Results: Pathway enrichment analysis showed significant alterations in lipid metabolism. Adolescent but not adult females treated with N, OC and N+OC compared to saline showed significant increases in carnitine conjugated fatty acid metabolites such as arachidonoylcarnitine (C20:4), docosahexaenoylcarnitine (C22:6) and stearoylcarnitine (C18). These changes in fatty acyl carnitines were accompanied by an increase in a subset of free fatty acids, suggesting elevated fatty acid β-oxidation in the mitochondria to meet energy demand. In support, 3-hydroxybutyrate (BHBA) was significantly lower in OC and N+OC treatment group in adolescent animals, implying a complete shunting of acetyl CoA for energy production via TCA cycle. BHBA is a ketone body that increases in concentration as lipid oxidation rates increase with acetyl CoA accumulation. Reduced BHBA levels may also suggest mitochondrial dysfunction in response to OC and N+OC treatment. Conclusion: The observed changes in the metabolic fingerprint and fatty acid metabolism reflect a general alteration in energy metabolism with nicotine treatment exclusively in young animals and these changes are enhanced by N+OC treatment. Discerning the exact effects of N +/- OC on overall brain metabolism and the molecular mechanisms affecting mitochondrial function at different ages will open a new window for future therapeutic intervention.

Pain in the Developing Brain: Early Life Factors Alter Nociception and Neurobiological Function in Adolescent Rats.

Although adverse early experiences prime individuals to be at increased risk for chronic pain, little research has examined the trauma–pain relationship in early life or the underlying mechanisms that drive pathology over time. Given that early experiences can potentiate the nociceptive response, this study aimed to examine the effects of a high-fat, high-sugar (HFHS) diet and early life stress (maternal separation [MS]) on pain outcomes in male and female adolescent rats. Half of the rats also underwent a plantar-incision surgery to investigate how the pain system responded to a mildly painful stimuli in adolescence. Compared with controls, animals that were on the HFHS diet, experienced MS, or had exposure to both, exhibited increased anxiety-like behavior and altered thermal and mechanical nociception at baseline and following the surgery. Advanced magnetic resonance imaging demonstrated that the HFHS diet and MS altered the maturation of the brain, leading to changes in brain volume and diffusivity within the anterior cingulate, amygdala, corpus callosum, nucleus accumbens, and thalamus, while also modifying the integrity of the corticospinal tracts. The effects of MS and HFHS diet were often cumulative, producing exacerbated pain sensitivity and increased neurobiological change. As early experiences are modifiable, understanding their role in pain may provide targets for early intervention/prevention.

Prefrontal NMDA-receptor antagonism disrupts encoding or consolidation but not retrieval of incidental context learning

The Context Preexposure Facilitation Effect (CPFE) is a variant of contextual fear conditioning in which learning about the context, acquiring a context-shock association, and retrieval of this association occur separately across three phases (context preexposure, immediate-shock training, and retention). We have shown that prefrontal inactivation or muscarinic-receptor antagonism prior to any phase disrupts retention test freezing during the CPFE in adolescent rats (Heroux et al., 2017; Robinson-Drummer et al., 2017). Furthermore, the medial prefrontal cortex (mPFC) is the only region in which robust learning-related expression of the immediate early genes c-Fos, Arc, Egr-1 and Npas4 is observed during immediate-shock training in the CPFE (Asok et al., 2013; Heroux et al., 2018; Schreiber et al., 2014). However, the role of prefrontal NMDA-receptor plasticity in supporting preexposure- and training-day processes of the CPFE is not known. Therefore, the current study examined the effects of intra-mPFC infusion of the NMDA-receptor antagonist MK-801 or saline vehicle prior to context preexposure (Experiment 1) or immediate-shock training (Experiment 2) in adolescent Long-Evans male and female rats. This infusion given prior to context preexposure but not training abolished retention test freezing, with no difference between MK-801-infused rats and non-associative controls preexposed to an alternative context (pooled across drug). These results demonstrate a role of prefrontal NMDA-receptor plasticity in the acquisition and/or consolidation of incidental context learning (i.e., encoded in the absence of reinforcement). In contrast, this plasticity is not required for context retrieval, or acquisition, expression, or consolidation of a context-shock association during immediate-shock training in the CPFE. These experiments add to a growing body of work implicating the mPFC in Pavlovian contextual fear conditioning processes in rodents.

Neuroendocrine and neuroimmune responses in male and female rats: evidence for functional immaturity of the neuroimmune system during early adolescence.

Adolescence is a developmental period characterized by rapid behavioral and physiological changes, including enhanced vulnerability to stress. Recent studies using rodent models of adolescence have demonstrated age differences in neuroendocrine responses and blunted neuroimmune responding to pharmacological challenges. The present study was designed to test whether this neuroimmune insensitivity would generalize to a non-pharmacological stress challenge. Male and female adolescent (P29-33) and adult (P70-80) Sprague Dawley rats were exposed to intermittent footshock for one-, two-, or two-hours+recovery. Plasma corticosterone and progesterone levels as well as gene expression of several cytokines and c-Fos gene expression in the paraventricular nucleus of the hypothalamus (PVN), the medial amygdala (MeA), and the ventral hippocampus (vHPC) were analyzed. The results of the present study demonstrated differences in response to footshock, with these differences dependent on age, sex, and brain region of interest. Adult males and females demonstrated time-dependent increases in IL-1β and IL-1R2 in the PVN, with these changes not evident in adolescent males and substantially blunted in adolescent females. TNFα expression was decreased in all regions of interest, with adults demonstrating more suppression relative to adolescents and age differences more apparent in males than in females. IL-6 expression was affected by footshock predominantly in the vHPC of adolescent and adult males and females, with females demonstrating prolonged elevation of IL-6 gene expression. In summary, central cytokine responses to acute stressor exposure are blunted in adolescent rats, with the most pronounced immaturity evident for the brain IL-1 signaling system.

Pre-reproductive stress in adolescent female rats alters oocyte microRNA expression and offspring phenotypes: pharmacological interventions and putative mechanisms

Pre-reproductive stress (PRS) to adolescent female rats alters anxiogenic behavior in first (F1)- and second-generation (F2) offspring and increases mRNA expression of corticotropin-releasing factor receptor type 1 (Crhr1) in oocytes and in neonate offspring brain. Here, we ask whether the expression of Crhr1 and Crhr1-targeting microRNA is altered in brain, blood, and oocytes of exposed females and in the brain of their neonate and adult F1 and F2 offspring. In addition, we inquire whether maternal post-stress drug treatment reverses PRS-induced abnormalities in offspring. We find that PRS induces a selective increase in Crhr1-targeting mir-34a and mir-34c in blood and oocytes, while non-Crhr1 microRNA molecules remain unaltered. PRS induces similar microRNA changes in prefrontal cortex of F1 and F2 neonates. In adult animals, cortical Crhr1, but not mir-34, expression is affected by both maternal and direct stress exposure. Post-PRS fluoxetine (FLX) treatment increases pup mortality, and both FLX and the Crhr1 antagonist NBI 27914 reverse some of the effects of PRS and also have independent effects on F1 behavior and gene expression. PRS also alters behavior as well as gene and miRNA expression patterns in paternally derived F2 offspring, producing effects that are different from those previously found in maternally derived F2 offspring. These findings extend current knowledge on inter- and trans-generational transfer of stress effects, point to microRNA changes in stress-exposed oocytes as a potential mechanism, and highlight the consequences of post-stress pharmacological interventions in adolescence.

Altered social recognition memory and hypothalamic neuropeptide expression in adolescent male and female rats following prenatal alcohol exposure and/or early-life adversity

Prenatal alcohol exposure (PAE) and early-life adversity (ELA) both negatively impact social neurobehavioral development, including social recognition memory. Importantly, while individuals with PAE are more likely to experience ELA, relatively few studies have assessed the interaction of these two early insults on adolescent social behavior development. Here, we combine animal models of PAE and ELA to investigate both their unique and interactive effects on social neurobehavioral function in early and late adolescent male and female rats. Behavioral testing was followed by assessment of hypothalamic expression of oxytocin (OT) and vasopressin (AVP), key neuropeptides in the regulation of social behavior. Our results indicate that PAE and ELA have unique sex- and age-specific effects on social recognition memory and OT/AVP expression, with more pronounced neurobehavioral changes observed in males than in females in both early and late adolescence. Specifically, ELA impaired social recognition in early adolescent females regardless of prenatal treatment, while males showed deficits in both early and late adolescence in response to unique and interactive effects of PAE and ELA. Neurobiological data suggest that these perinatal insults differentially impact the OT and AVP systems in a sexually dimorphic manner, such that the OT system appears to be particularly sensitive to PAE in males while the AVP system appears to be more vulnerable to ELA in females. Taken together, our data provide novel insight into how the early postnatal environment may mediate outcomes of PAE as well as the power of animal models to interrogate the relationship between these pre- and postnatal insults.