Behavioral Neuroscience

The midsession reversal (MSR) task is frequently used to study behavioral flexibility and decision strategies in animals. In a typical version of the task, subjects complete 80 trials in which they choose between two simultaneously presented stimuli, S1 and S2. During the first 40 trials, responses to S1 are reinforced, whereas responses to S2 are not. The contingencies then reverse without warning: From trial 41 to 80, only responses to S2 are reinforced. In birds, performance in this task is often characterized by anticipatory and perseverative errors around the reversal point, suggesting a reliance on elapsed time since the session began. In contrast, rats tested in operant conditioning chambers typically show near-optimal performance with few errors, a pattern often interpreted as evidence that rats rely primarily on local reinforcement cues rather than temporal information. The present study investigated whether rats exclusively rely on local cues in the MSR task or whether temporal information also contributes to the decision process. Two groups of rats were trained with different intertrial intervals (ITIs; 5 s or 10 s) while the reversal point remained fixed at Trial 41. During acquisition, both groups diplayed similar learning rates and near-optimal steady-state performance with minimal anticipatory or perseverative errors. However, when the ITI was manipulated in probe sessions, systematic shifts in switching behavior emerged. Rats adjusted their choices according to the temporal midpoint experienced during training rather than the nominal trial number of the reversal. These results suggest that rats rely on a mixed strategy that integrates local reinforcement cues with global timing information. Temporal control may therefore be present even when it is not expressed during standard training conditions.

Endocannabinoid (eCB) signaling is a key regulator of reward-related dopaminergic signaling, particularly in response to drugs of abuse, such as cocaine. To date, our understanding of this mechanism has primarily been limited to male subjects. Prior work establishes that female cocaine users have more adverse outcomes, and female rats show greater sensitivity to cannabinoid type 1 receptor (CB1R) regulation of cocaine self-administration. Therefore, we hypothesize that female rats exhibit enhanced eCB regulation of cocaine-evoked dopamine (DA). We used in vivo fiber photometry recording of the dopamine biosensor, dLight 1.3b, in the nucleus accumbens medial shell (NAcms) in response to cocaine in male and female rats. Rats were pretreated with cannabinoid-targeting drugs to investigate the effects of CB1R inactivation or augmentation of the eCB 2-AG on cocaine-evoked DA. Our results revealed that CB1R inactivation attenuates cocaine-evoked DA in male and female rats, but females showed enhanced sensitivity for CB1R regulation of cocaine-evoked DA. Cocaine-evoked DA was enhanced by augmenting 2-AG levels, and females again showed increased sensitivity to this manipulation. Finally, females show greater cocaine-evoked DA when in a non-estrous cycle compared to estrous, reinforcing that estrous cycle is a determinant of cocaine-evoked DA. These data indicate that females show enhanced eCB regulation of cocaine-evoked DA signaling, underscoring the importance of sex as a biological variable in our understanding of endocannabinoid regulation of drug reward. HighlightsO_LICB1R inactivation attenuates cocaine-evoked DA in NAcms, preferentially in females C_LIO_LI2-AG augmentation via MAGL inhibition enhances cocaine-evoked DA, with female bias C_LIO_LIEstrous phase modulates the dopamine response to a high dose of cocaine in females C_LIO_LIMale and female rats show similar baseline DA and locomotor responses to cocaine C_LI

Physical activity offers myriad benefits to health and well-being, in humans and other animals as well. In rodents, voluntary wheel running can attenuate the effects of both physical and social stressors on rodent social behavior. Whether wheel running affects rodent social behaviors per se remains less well understood. We conducted the current study to test whether home cage access to running wheels impacts the social behaviors of adult, group-housed C57BL/6J female mice during same-sex interactions with novel females. Group-housed females were either given continuous home cage running wheel access or a standard paper hut starting at weaning, and as adults, social behaviors were measured during interactions with novel females. In two cohorts, we found that 5 weeks of running wheel access during adolescence reduced the time that subject females spent investigating a novel female and also tended to reduce total ultrasonic vocalizations produced during interactions. These effects were not reversed by a 2-week period of running wheel removal but were recapitulated in a different cohort by 2 weeks of running wheel access in adulthood. Unexpectedly, we found that these effects on female social behavior were not due to wheel running per se, because females raised from weaning with immobile running wheels also showed low rates of social behaviors during same-sex interactions in adulthood. Overall, we find that the presence of a running wheel in the home cage has an enduring inhibitory influence on female social behavior during same-sex interactions, a finding that has implications for the design of studies that include same-sex interactions between female mice.

In rats, cue-induced opioid craving intensifies (incubates) during abstinence from opioid self-administration and then remains high for a prolonged period. The prolonged plateau models persistent vulnerability to cue-induced craving and relapse in humans recovering from opioid use disorder. However, a very significant contributor to relapse vulnerability in these individuals is the presence of negative affective states that can persist for months to years, far beyond physical dependence. The goal of this study was to determine if the incubation of craving model recapitulates this aspect of relapse vulnerability. We began by comparing rats trained to self-administer oxycodone using a regimen leading to persistent elevation of cue-induced craving (6 h/d x 10 d) and rats trained to self-administer saline. We assessed somatic withdrawal signs in early abstinence and conducted behavioral tests modeling negative affect (open field, social preference, sucrose preference, and elevated plus maze) in late abstinence. Some somatic withdrawal signs were greater in oxycodone rats on abstinence day (AD)1, but cumulative scores did not differ between groups on AD1-3. On AD41-46, no group differences were found in behavioral tests modeling negative affect. To compare early and late abstinenceperiods, a second cohort of rats self-administered saline and oxycodoneand then received two cue-induced seeking tests (AD1 and AD40; oxycodone rats exhibited incubation of craving) and two series of negative affect tests (AD2-7 and AD41-48). While some time-dependent changes in affect were observed within each group, they were suggestive of reduced anxiety-like behavior in oxycodone rats. Finally, because rats are single-housed during our incubation studies, we compared drug-naive rats after 8-9 weeks of single vs pair housing and found no difference in behavioral tests modeling negative affect. We conclude that the persistence of elevated cue-induced craving observed after a standard opioid incubation regimen is not accompanied by negative affective states, probably due to lower drug intake during the intravenous regimen compared to non-contingent escalating dose regimens typically used to study withdrawal signs. This does not negate the utility of the incubation model for studying cue-induced opioid craving and its neurobiological basis.

Animals exposed to pairings of a neutral stimulus with reward acquire a conditioned response to the neutral stimulus. A prominent hypothesis, formalized in the Temporal Difference (TD) learning algorithm, is that animals learn to predict the future reward associated with the neutral stimulus ("value"). Though the TD algorithm does not explicitly specify what drives conditioned responding, a typical assumption is that it reflects the animals estimate of value. In TD learning, value estimates are updated using reward prediction error (RPE, the discrepancy between observed and predicted reward), and are thought to be signaled by the phasic activity of midbrain dopamine neurons. This hypothesis posits that dopamines effects on conditioned responding are mediated entirely by its effects on learning. However, recent experimental and theoretical evidence suggests that dopamine may play a more direct role in modulating conditioned responding. We use a combination of data analysis and computational modeling to probe the relationship between dopamine and conditioned responding. Our results suggest that dopamine directly modulates conditioned responding, in addition to its role in learning. These findings can be captured by a model in which dopamine RPE acts both indirectly (via learning) and directly on conditioned responding.

The nucleus accumbens (NAc) and its excitatory input from the medial prefrontal cortex (mPFC) form a critical circuit underlying drug-induced plasticity associated with addiction-related behaviors. However, baseline differences in excitatory signaling across NAc subcircuits and sex-specific neuroadaptations following opioid self-administration remain poorly understood. Here, we examined synaptic signaling in mPFC-NAc pathways in drug-naive mice and after abstinence from remifentanil self-administration. Under drug-naive conditions, AMPA receptor- mediated glutamatergic signaling was generally elevated in D2 medium spiny neurons (MSNs) of both the NAc core and shell across sexes, while females exhibited greater excitatory signaling in D1 MSNs of the NAc core compared with males. Pathway-specific analyses revealed that prelimbic cortex (PL) inputs to NAc core D2 MSNs displayed enhanced calcium-permeable AMPA receptor (CP-AMPAR) signaling and increased presynaptic release relative to D1 MSNs. Following abstinence from remifentanil self-administration, miniature excitatory postsynaptic current analyses showed increased excitatory drive at D1 MSNs and decreased drive at D2 MSNs, largely restricted to the NAc core. At PL-Core D1 MSN synapses, remifentanil reduced AMPA/NMDA ratios, consistent with increased CP-AMPAR incorporation in males and females, while increasing presynaptic signaling exclusively in males. In contrast, PL-Core D2 MSN synapses showed a reduction in presynaptic signaling across sex, while ostensibly weakening postsynaptic signaling selectively in males through reductions in CP-AMPAR signaling. At infralimbic cortex (IL)-shell inputs, a reduction in AMPAR rectification indices at D1 MSN synapses was produced by remifentanil, while release probability was decreased at D2 MSN synapses in males only. Together, these findings reveal sex- and pathway-specific synaptic adaptations within mPFC-NAc circuits that may be obscured by global measures of excitatory transmission and identify baseline circuit differences that may shape opioid-induced plasticity.

Nearly one third of women of reproductive age in the United States are prescribed opioids annually; 14% of women fill an opioid prescription during pregnancy, and one in five report misuse. Opioid use during pregnancy has given rise to an increasing population of infants born with gestational opioid exposure. Although substantial clinical work has focused on treating these infants as they experience opioid withdrawal symptoms at the time of birth, notably few studies have examined the effects of gestational opioid exposure on brain development and long-term cognitive function. During typical brain development, endogenous opioids and their receptors are highly expressed by neural progenitor cells, neurons, and glia where they modulate cell proliferation, differentiation, and maturation. Thus, any disruption to the endogenous opioid system during the critical period of brain development may have lasting consequences on brain cell populations and the behaviors they influence. Indeed, opioid-exposed infants have smaller brains than age-matched peers and show significant neurodevelopmental impairment; they also have higher rates of learning disability at school age. To investigate how exposure to exogenous opioids during brain development affects neural maturation in the hippocampus, a brain region critical for learning and memory, our lab has developed a clinically relevant perigestational morphine exposure rat model. The current study reports that perigestational exposure to morphine delays postnatal hippocampal neuronal maturation, alters astrocyte and oligodendrocyte proliferation, and alters expression of brain-derived neurotrophic factor (BDNF), a protein crucial for healthy brain growth. Furthermore, we show that environmental enrichment rescues BDNF deficits, offering evidence for the effectiveness of non-invasive, non-pharmacological intervention for developmental consequences of perigestational opioid exposure.

Male odor induces various behavioral and physiological responses across the reproductive cycle in female mice. Although male odor preference in females is reduced during pregnancy, how it changes across later stages of the reproductive cycle, including nursing and weaning, remains unclear. Here, we found that male odor preference is lost during pregnancy and nursing. To identify the olfactory systems involved in these changes, we examined neural activity using c-Fos immunohistochemistry. Male odor exposure during nursing increased neural activity in the accessory olfactory bulb and the posteroventral medial amygdala (MeApv), a key node of the accessory olfactory system, as well as in subdivisions of the central amygdala, but not in the ventromedial hypothalamus or the bed nucleus of the stria terminalis. Finally, lesions of the MeApv prevented the loss of male preference during nursing, indicating that the MeApv is required for suppression of male preference during this stage.

Only a subset of heroin users develop addiction, characterized by binge-like heroin use and preference for heroin over other rewards, including social rewards. We recently established a rat model of these features. We trained rats to lever-press for social interaction and heroin (or saline, control) infusions and then tested heroin- and social-seeking and heroin-vs.-social choice. During 3-5 abstinence weeks, we used 2-deoxy-2-[{superscript 1}F]fluoro-D-glucose (FDG) PET imaging to assess regional brain metabolic activity at rest (homecage) and during heroin and social seeking. We assessed regional differences in FDG uptake using unbiased voxel-wise analysis and statistical parametric mapping, and correlated FDG uptake with principle-component-analysis-derived addiction severity score incorporating heroin intake, binge-like episodes, and heroin preference. Compared with saline-trained rats, heroin-trained rats showed overall higher FDG uptake across multiple brain regions at rest and during both reward-seeking tests. Comparison of heroin-vs.-social-seeking in heroin-trained rats showed higher uptake in claustrum/lateral striatum and auditory cortex during social seeking. Analysis of individual differences showed that addiction severity was primarily associated with metabolic alterations under resting conditions rather than during heroin- or social-seeking. At rest, higher addiction severity was associated with lower uptake in piriform cortex and higher uptake in ventral hippocampus, whereas during heroin-seeking, addiction severity was associated with lower uptake in post-subiculum and cerebellum. Addiction severity was not associated with differences in social seeking or FDG uptake during social seeking. These findings identify neurometabolic features of social and heroin seeking and heroin addiction vulnerability that can potentially serve as brain biomarkers and targets for neuromodulation. Significance StatementHeroin addiction develops in only a subset of users, yet the determinants of vulnerability versus resilience to addiction remain largely unknown. We combined a rat model capturing key features of heroin addiction, including binge-like heroin intake and preference for heroin over social interaction, with behavioral heroin- and social-seeking assays and longitudinal whole-brain metabolic imaging using FDG-PET. We identified distinct patterns of neurometabolic alterations associated with heroin self-administration and addiction severity at rest and in the context of heroin seeking. In contrast, heroin self-administration and addiction severity were not significantly associated with neurometabolic alterations during social seeking. These findings highlight brain-wide neurometabolic features of vulnerability to heroin addiction that can serve as brain biomarkers and targets for neuromodulation.

Perceptual learning is a temporally dynamic process involving the acquisition and integration of sensory information necessary for adaptive decision making. Resolving the neural basis of perceptual learning could uncover new therapeutic targets for schizophrenia and other neurodevelopmental disorders that implicate impaired perceptual acuity. In the present study, we developed a novel touchscreen task which utilizes orientation discrimination to assess visual perceptual learning (VPL) in male and female rats. Based on previous evidence we hypothesised that VPL would depend on inhibitory neurotransmission mediated by {gamma}-amino butyric acid (GABA). Segregating subjects based on poor learning (lower tertile) and good learning (upper tertile) revealed dose-dependent improvements in VPL in poor learners following the administration of a GABA-B agonist (R-baclofen) and an 5 subunit specific GABA-A (GABRA5) positive allosteric modulator (alogabat) administered early in learning. Poor VPL performance was associated with a significant reduction in GABRA5 expression in dorsal regions of the prefrontal cortex (PFC), most notably the prelimbic cortex. Reduced GABRA5 expression in this region was co-localized to somatostatin- and parvalbumin-expressing interneurons. These findings indicate that inter-individual variation in the expression of GABRA5 in selective PFC populations of inhibitory interneurons may determine the speed and acuity of VPL. Based on these findings, interventions that restore GABRA5 signalling in the PFC may hold therapeutic relevance for neuropsychiatric disorders involving deficits in perceptual learning.

BackgroundLoss of control over drinking is a hallmark feature of alcohol use disorder (AUD) that is modeled preclinically through escalation of ethanol consumption and aversion-resistant drinking. Prior work with other reinforcers suggests that within-session unpredictable, intermittent access (uIntA) promotes loss of control over intake. However, the effect of uIntA on voluntary ethanol consumption is unknown. MethodsMale and female Long-Evans rats (n=9-10/group) underwent seven weeks of daily voluntary ethanol (20% v/v) drinking sessions under either a continuous access (ContA) or uIntA schedule. Following four weeks of baseline, rats were rendered dependent using a two-week chronic intermittent ethanol vapor exposure procedure. Daily testing was maintained through one week into withdrawal from vapor exposure. On the final day of testing, ethanol was adulterated with quinine (30 mg/L) to assess aversion-resistant drinking. ResultsRats drinking under ContA and uIntA exhibited similar levels of average daily ethanol consumption at baseline. However, uIntA elicited a more robust dependence-induced escalation of ethanol consumption compared to ContA, with uIntA sustaining escalation through early protracted withdrawal. Additionally, while rats with ContA to ethanol remained sensitive to quinine even after chronic ethanol vapor exposure, uIntA promoted aversion-resistant drinking in ethanol dependent rats. ConclusionsThese results demonstrate that, compared to ContA, uIntA maintains ethanol drinking and exacerbates AUD-related symptomatology while also providing researchers with the ability to capture additional measures of motivation and drinking patterns without increasing experimental burden. This work positions uIntA as a powerful tool to assess psychological and neurobiological factors underlying loss of control over drinking.

The advent and widespread uptake of combination antiretroviral therapy dramatically changed the epidemiological features of human immunodeficiency virus type 1 (HIV-1), whereby older individuals (>50 years of age) account for approximately 50% of HIV-1 seropositive individuals in the United States. Nevertheless, to date, there is no extant in vivo biological system to model the unique age-related neurocognitive impairments observed in HIV-1 seropositive individuals. Herein, the utility of the HIV-1 transgenic (Tg) rat as a biological system to model age-related neurocognitive impairments and neuroanatomical alterations was evaluated. Older adult HIV-1 Tg rodents (i.e., >12 months of age upon testing initiation), relative to their control counterparts, exhibited profound neurocognitive alterations characterized by impairments in stimulus-reinforcement learning, sustained attention, and selective attention; neurocognitive deficits which support a fundamental distortion of temporal processing. Neuronal dysfunction in older adult HIV-1 Tg animals was characterized by structural alterations in pyramidal neurons, and their associated dendritic spines, in the medial prefrontal cortex and abnormal accumulation of amyloid beta (A{beta}). Interestingly, the abnormal accumulation of A{beta} mechanistically underlies, at least in part, the profound dendritic spine dysmorphology in male, but not female, HIV-1 Tg rats. More critically, however, neuronal dysfunction mechanistically underlies neurocognitive impairments in both male and female HIV-1 Tg rodents, whereby neuronal dysfunction accounts for 65.4% and 60.8% of the variance in neurocognitive function, respectively. Establishing the utility of the HIV-1 Tg rat for age-related neurocognitive impairments is fundamental to disentangling the role of HIV-1 viral proteins and comorbidities in neurocognitive function.

Dopamine (DA) neurons of the midbrain project throughout the striatum, including the nucleus accumbens core (NAc) and are thought to co-release ATP with DA from vesicles. The mechanisms of evoked NAc ATP release and clearance and their relationship to exocytotic DA transmission are largely unexplored and the focus of the present work. Using fast scan cyclic voltammetry (FSCV), we measured simultaneous ATP and DA transmission in response to pharmacological manipulations of release and reuptake cellular machinery. ATP transmission is tightly coupled to that of DA, though ATP release concentrations are typically smaller. Manipulations that increase DA transmission (increased release via 4-aminopyridine Kv channel blockade or decreased uptake via cocaine) also increase ATP transmission, though to a smaller extent. Blocking DA vesicular packaging (reserpine) or action potentials (lidocaine), results in attenuated DA and ATP release. Interestingly, reserpine or lidocaine can result in completely abolished DA release, but not a complete prevention in ATP release, suggesting a secondary source for ATP transmission thats not dependent on DA terminals. Both transmitters were reduced to a similar extent following nAChR blockade, demonstrating that nAChR activation regulates ATP in addition to DA. Surprisingly, cocaine inhibition of DATs reduced clearance for both ATP and DA, which correlated with one another when cocaine concentration was highest. There was also a strong relationship between the effect of cocaine on release of ATP and DA. As the first FSCV study to examine evoked NAc ATP release, this paper bridges prior work to confirm the strong association between ATP and DA in the mesolimbic circuit and identifies unexpected overlap in mechanisms regulating their transmission. Our results contribute novel evidence of both vesicular and non-vesicular ATP release in the NAc and demonstrate that extracellular ATP is a modulator of DA terminal function.

Background and aimsPerseverative behaviours are commonly assessed using operant paradigms in which rodents work for drugs or food under physiological deprivation, limiting translational relevance to some behavioural addictions. Here we validated an operant paradigm in which the acquired behaviour is driven neither by physiological needs nor hedonic responses. MethodsMice were trained to lever-press for green light. Exp.1 used a within-subjects design to examine lever discrimination and whether responding could be "satiated" by light preexposure. Exp.2 examined instrumental contingency using a between-subjects design, with light delivery equated between contingent and non-contingent groups. Exp.3 replaced green light with dim red light producing less retinal photoreceptor excitation but comparable heat to assess non-photic cues. Exp.4 examined whether green light could affect food seeking different motivational states. ResultsIn Exp.1, green light supported lever discrimination. Among high responders, the satiation effect was modest (<15% reduction) and did not deter lever pressing. In Exp.2, instrumental contingency promoted response acquisition whereas random light delivery did not. In Exp.3, dim red light failed to sustain behaviour, producing [~]50% response decrement. In Exp.4, light potentiated food seeking under ad libitum feeding. Discussion and conclusionsResponse-contingent light serves as a reward to establish operant responding, which cannot be explained by alerting effects or thermal cues. Our study bridges the gap between animal models and findings from humans that coloured light may exacerbate smartphone use and that light therapy may reshape reward circuits in individuals with Internet gaming disorder symptoms [Li et al. (2026) Advanced Science 13:e14044].

Relapse to opioid use during abstinence is often triggered by drug-associated cues but the persistence of this effect across the lifespan is unknown. Using a rat model, we found that relapse provoked by heroin-predictive discriminative stimuli persisted for over one year of abstinence, suggesting enduring, potentially lifelong opioid relapse vulnerability.

Humans order numbers in space from left to right, with smaller quantities represented preferentially in the left hemispace and larger ones in the right hemispace. The direction of this mental number line (MNL), or more generally of number-space associations (NSA), is influenced by cultural habits such as reading and writing direction. However, a growing body of evidence from pre-verbal infants and non-human animals suggests that number-space mappings may also have biological foundations. In non-human primates, evidence for a directional MNL remains mixed, partly due to small sample sizes and methodological heterogeneity. Here, we tested samples of rhesus (Macaca mulatta) and crab-eating macaques (Macaca fascicularis) across two experiments using spontaneous food-related tasks. In Experiment 1, monkeys chose between identical food quantities (1x1 to 24x24) presented on the left and right. No systematic spatial choice bias emerged as a function of numerical magnitude, and hand use did not differ across exact numerical pairs, although exploratory analyses revealed magnitude-related modulations of manual responses. In Experiment 2, monkeys were habituated to small (4x4) or large (16x16) quantities and subsequently tested with the alternative quantity. Result showed significantly more leftward choices following numerical decreases (16[-&gt;]4) and more rightward choices following numerical increases (4[-&gt;]16), indicating that relative numerical context, rather than absolute magnitude, elicited directional spatial biases. These findings suggest that in macaques, number-space associations emerge most robustly in comparative contexts involving expectancy violations of magnitude.

An increasing number of epidemiological and experimental studies have demonstrated a bidirectional relationship between mood disorders and the circadian system, with disrupted circadian rhythms contributing to depressive states, and their restoration playing a key role in antidepressants effects. In this context, we sought to examine whether key molecular targets of antidepressants exhibit diurnal regulatory patterns. Naive adult male and female C57BL/6 mice were euthanized at 3-hour intervals beginning at Zeitgeber Time 0 (ZT0), and hippocampal (HC) and medial prefrontal cortex (mPFC) tissues were collected for RT-qPCR and western blot analyses. We observed statistically significant diurnal rhythmicity in all analyzed transcripts (cFos, Arc, Nr4a1, Dusp1, Dusp5, and Dusp6) in both HC and mPFC samples, with peak expression occurring during the dark (active) phase (ZT15-18). Phosphorylation levels of TrkBY816 (tropomyosin-related kinase) and GSK3{beta}S9 (glycogen synthase kinase 3{beta}) also showed periodic rhythmicity, peaking during the light (inactive) phase. Levels of p-ERK2T185/Y187 (extracellular-signal regulated kinase) did not display rhythmicity, but peaked during the light phase in the HC, especially in males. Collectively, these findings demonstrate that antidepressant targets are subject to diurnal regulation, highlighting the importance of integrating circadian biology and time-of-day as relevant variables in the development of translationally relevant antidepressant research. HighlightsO_LIKey molecular targets of antidepressants exhibit diurnal regulation in adult mice C_LIO_LIDiurnal patterns were conserved across targets, sexes, and brain regions (HC&PFC) C_LIO_LIcFos, Arc, Nr4a1, Dusp1,5,6 mRNAs display peak expression during the dark phase C_LIO_LITrkBY816 and GSK3{beta}S9 phosphorylation peak during the light (inactive) phase C_LIO_LIAntidepressant mechanisms may be linked with circadian and sleep-wake dynamics C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=102 SRC="FIGDIR/small/716906v1_ufig1.gif" ALT="Figure 1"> View larger version (25K): org.highwire.dtl.DTLVardef@1e65e60org.highwire.dtl.DTLVardef@13e302corg.highwire.dtl.DTLVardef@1ccc25forg.highwire.dtl.DTLVardef@1ed10d3_HPS_FORMAT_FIGEXP M_FIG C_FIG

The Reln gene encodes the extracellular glycoprotein Reelin that regulates synaptic plasticity and activity-dependent gene expression with implications in several neuropsychiatric disorders, including substance use disorder. While reduced Reln expression alters responses to psychostimulants and cannabinoid, its role in opioid-related behaviors remains unknown. Here, we examined whether Reln haploinsufficiency modifies behavioral and molecular responses to the synthetic opioid fentanyl. Heterozygous Reeler (Reln+/-) mice and wild-type littermates were assessed using using complementary contingent and non-contingent models of fentanyl exposure, including multi-phase fentanyl intravenous self-administration paradigm, conditioned place preference paradigm, locomotor assay, and dorsal striatal immediate early gene expression. Reln haploinsufficiency did not alter acquisition, extinction, or cue-induced reinstatement during self-administration, indicating stable opioid reinforcement and relapse-like behavior. Progressive ratio testing revealed a sex-dependent effect in which male Reln+/- mice showed reduced motivation for fentanyl compared to male wild-type mice. In contrast, following passive fentanyl exposure, Reln+/- mice exhibited enhanced fentanyl-induced locomotion and increased Fos immunoreactivity in the dorsal striatum, while CPP remained unchanged. Together, these findings demonstrate that Reln haploinsufficiency does not substantially modify opioid reinforcement or cue-driven drug seeking but enhances acute pharmacological sensitivity to fentanyl. These results identify Reln as a modulatory factor in opioid-responsive neural circuits that preferentially influences acute drug-evoked neuronal activation rather than the associative learning processes underlying opioid reinforcement.

Cognitive flexibility, switching behaviour responses to changing task demands, is classically attributed to the prefrontal cortex. Yet thalamocortical circuits involving the mediodorsal thalamus (MD) and thalamic nucleus reuniens (Re) are dysfunctional across a range of neurological conditions with cognitive flexibility deficits. Interventions involving thalamocortical interactions may offer therapeutic benefits. Here we examined the effects of MD or Re bilateral glutamatergic neurotoxic damage in rats on cognitive flexibility using the attentional set-shifting task. Rats must attend to a sensory dimension that reliably predicts reward (intradimensional shift, ID) followed by a shift in attention to a previously irrelevant sensory dimension when contingencies change (extradimensional shift, ED). We found MD rats required more trials to criterion in the ED, while Re rats showed significant impairments on the first of three ID subtasks (ID1) only. Both MD and Re rats required more trials to criterion to complete each subtask than Sham controls. Intraperitoneal noradrenaline (atipamezole 1mg/kg), given 30 minutes prior to the task reduced trials to criterion across all rats, improving cognitive flexibility even after thalamic damage. These findings demonstrate the influence MD and Re contribute to cognitive flexibility and support noradrenergic regulation of thalamocortical circuits as potential therapeutic targets for cognitive flexibility dysfunction.

Dietary choice plays a critical role in metabolic and neurological health, yet the biological factors that shape macronutrient preference remain poorly understood. Evidence from both humans and rodents suggests potential sex differences in the attractiveness of specific nutrients, though findings have been inconsistent and often rely on self-report or diets with mixed macronutrient composition. The present study examined sex differences in macronutrient preference and food-directed behavior in mice using a controlled three-food choice paradigm. Adult male (n = 12) and female (n = 11) C57BL/6J mice were given simultaneous access to foods consisting of fat, sucrose, or a fat-carbohydrate combination across 14 days. Intake, latency to approach, and time spent near each food source were quantified, and estrous cycle stage was monitored in females. Female mice consumed significantly more food than males overall, driven by a selective increase in fat intake. Behavioral measures paralleled these results, with females spending more time in proximity to fat-associated food zones. In contrast, males preferentially consumed the fat-carbohydrate combination and showed weaker nutrient-specific engagement. Estrous cycle stage modestly influenced feeding behavior, with estrus associated with increased overall intake and greater consumption of combination diets, reflecting elevated carbohydrate intake. These findings demonstrate robust sex differences in macronutrient preference and suggest that hormonal state may selectively modulate nutrient-specific feeding behavior.