Behavioural Brain Research

Post-Traumatic Stress Disorder (PTSD) commonly occurs alongside Traumatic Brain Injury (TBI), yet the chronic behavioral consequences of combined neurotrauma (i.e., PTSD and TBI) across the sexes remain unclear. Using a mouse model combining Single Prolonged Stress (SPS) as a model for PTSD and Controlled Cortical Impact (CCI) as a model for TBI, we assessed gait, anxiety-like behavior, and contextual fear learning and extinction at 2, 4, and 12-weeks post-injury. Combined neurotrauma produced early and persistent gait impairments in both sexes, delayed changes to anxiety-like behavior characterized by reduced avoidance of an anxiogenic environment, and long-lasting contextual fear recall deficits. Impaired learning was observed in males, where they demonstrated reduced fear acquisition and diminished extinction rates at later time points while females showed no deficits. Across testing and sex, peak deficits emerged at 4 weeks post-neurotrauma. Together, these findings define a sex- and time-dependent behavioral phenotype following combined neurotrauma and underscore the importance of modeling comorbidity to capture the temporal and neurobehavioral consequences of trauma exposure that more closely reflect clinical populations.

Cognitive deficits are a major contributor to disability in numerous neuropsychiatric and neurodegenerative disorders, yet effective pharmacological treatments remain limited. Ferulic acid eicosyl ester (FAE-20), a natural constituent of the plant Rhodiola rosea, has previously been identified as an enhancer of simple forms of Pavlovian conditioning in flies, bees, and mice. Here, we investigated whether FAE-20 has further potential to enhance cognitive flexibility, working memory, or spatial learning in mice, and explored potential neurobiological mechanisms underlying such enhancement. Cognitive flexibility was assessed using the attentional set-shifting task (ASST). Subchronic FAE-20 treatment significantly improved ASST performance in both male and female young adult mice, indicating enhanced cognitive flexibility. In contrast, no effects were observed on spatial working memory, assessed by spontaneous alternations in the Y-maze, or on spatial learning in the Barnes maze in either young or aged mice. Notably, FAE-20 enabled spatial learning in the Barnes maze in a subgroup of aged mice that failed to learn the task under vehicle treatment. Histological analyses using c-Fos immunohistochemistry as a marker of neural activity and doublecortin expression and spine density as markers of hippocampal plasticity revealed sex-specific effects on components of the ascending arousal system. FAE-20 increased the activation of orexinergic neurons in the lateral hypothalamus of male mice, whereas it reduced the activity of cholinergic neurons in the laterodorsal tegmental nucleus of females. No effects were detected on hippocampal neurogenesis or dendritic spine density. These findings suggest that the cognitive effects of FAE-20 are selective, depending on the cognitive demands of the task and the baseline cognitive abilities of the animals, and may be mediated, at least in part, by modulation of arousal-related neural circuits. HighlightsO_LIFAE-20 enhanced cognitive flexibility in young adult mice C_LIO_LIEffects of FAE-20 were strongest in demanding cognitive tasks C_LIO_LIAged poor learners benefited from FAE-20 treatment C_LIO_LIFAE-20 activated hypothalamic orexin neurons in male mice C_LIO_LIFAE-20 modulated ascending arousal systems in a sex-specific manner C_LI

Intergroup conflict is one of the most significant issues in human society. In the 1950s, Sherif et al. reported that intergroup conflict could be artificially induced in boys through intergroup competition with tug-of-war and ball games. Since this iconic study, researchers have developed various experimental methods to replicate intergroup competition and/or conflicts. However, although intergroup conflicts in wild animals are often reported, it has been difficult to establish a situation of intergroup conflict in laboratory rodents that is discriminable from aggressive behavior individually. In this study, we established a novel experimental paradigm for intergroup competition in mice in which the members of each group shared objectives and tasks. Adult male ICR/Jcl mice were housed in groups of six, divided into two teams of three and repeatedly performed a competitive Tsunahiki task (tsunahiki means tug-of-war in Japanese). The competitive Tsunahiki task was conducted in an open field divided into two experimental fields, with three ropes stuck to a wall separating the fields. The mice were required to pull two ropes out faster than their opponent team to win, and only the winners could proceed to the reward area separated by a guillotine door. We demonstrated that the experience of the competitive Tsunahiki task induced attack bites selectively toward members of the other team (out-group members). Our findings suggest that intergroup competition induces intergroup conflict in mice, providing a technical breakthrough in elucidating the detailed neuroscientific mechanisms underlying intergroup conflict.

Opioid Use Disorder (OUD) remains a prominent threat to global health. Genetic background influences the susceptibility of developing OUD, although specific genetic factors remain elusive. Rodent models that differ in susceptibility to escalation and dysregulation of opioid use are valuable tools to facilitate discovery of genetic pathways. Phenotypes associated with the development of OUD were compared in seven classic inbred rat strains (M520/N, WKY/NCrl, F344/NCrl, F344/Stm, LEW/Crl, LEW/SSNHsd, LE/Stm) from the Hybrid Rat Diversity Panel (HRDP). A two-phase self-administration paradigm was utilized to assess characteristics of the acquisition of oxycodone self-administration during daily 2-h sessions, and the escalation of oxycodone use during daily 12-h sessions. Genetic background influenced the acquisition of oxycodone self-administration as indicated by differences in the initiation of responding for oxycodone during each session and different amounts of oxycodone intake. We observed that escalation of oxycodone intake between-sessions was strain dependent, and the within-session distribution of oxycodone intake was strongly influenced by strain. The M520/N strain engaged in a unique pattern of intake, characterized by rapid initiation of oxycodone responding during the acquisition phase and a significant burst-like responding during escalation. Strain-dependent sex differences were also observed in several acquisition and escalation metrics. Of interest, burst responding was more prevalent in females of the M520/N strain compared to males. Together, these data indicate that genetic background influences not only overall oxycodone intake, but specific within- and between-session metrics that capture patterns of consumption across the substance use trajectory.

Working memory has been considered a delay-dependent retention system, but variability in delay duration across species and tasks suggests that task-intrinsic factors may also contribute. Here, we investigated the effects of delay duration (75 s vs. 150 s) and task distance (0 m vs. 2 m) on working memory using a T-maze delayed alternation task with a movable home-cage apparatus in rats. At the 150-s delay, accuracy was 9% lower at 0 m than at 2 m (75% vs. 84%), with a similar numerical tendency observed at the 75-s delay (4% lower). A two-way repeated measures ANOVA revealed significant main effects of both task distance and delay duration, with no significant interaction (p = 0.217). Post hoc pairwise comparisons indicated that accuracy in the 0-m condition was significantly lower at 150 s than at 75 s (adjusted p = 0.038). At the 150-s delay, accuracy was also significantly lower in the 0-m condition than in the 2-m condition (adjusted p = 0.019). These results suggest that working memory retention is influenced not only by temporal constraints but also by task-intrinsic factors such as task distance, with the observed effects appearing independent and consistent with a two-factor framework.

RationalePsychedelic compounds such as psilocybin have attracted growing interest for their potential therapeutic effects in psychiatric disorders, with improvements in cognitive flexibility proposed as a possible mechanism of action. However, the effects of psychedelics on cognitive flexibility remain poorly understood. ObjectiveThis study aimed to examine the acute and post-acute effects of psilocybin (0.1, 0.3, 1 mg/kg) and lysergic acid diethylamide (LSD, (0.02, 0.04, 0.08 mg/kg) on cognitive flexibility in male rats. MethodsThis was tested using two variants of the probabilistic reversal learning task (PRLT): a touchscreen-based operant task and a more ethological foraging-based task. ResultsIn the touchscreen PRLT, acute psilocybin disrupted task engagement, with animals completing fewer trials and showing increased trial initiation latency, although psilocybin also showed a trend toward faster initial rule acquisition. However, psilocybin did not significantly alter the number of rule changes achieved, a canonical measure of cognitive flexibility, or feedback sensitivity. LSD similarly produced limited acute effects, although the highest dose reduced lose-shift probability, suggesting decreased sensitivity to negative feedback under some conditions. Post-acute effects of psilocybin were minimal in both PRLT variants and, where LSD effects were observed these occurred across different doses and timepoints without a consistent pattern. ConclusionsOverall, these findings suggest that serotonergic psychedelics do not robustly enhance reversal learning in these paradigms and that apparent learning effects may reflect transient disruptions in task engagement rather than improvements in cognitive flexibility. These results also highlight potential limitations of these PRLT paradigms for detecting psychedelic-induced changes in cognitive flexibility in rodents.

Fear conditioning studies have historically relied on freezing as the primary measure of conditioned fear despite evidence that defensive responding is behaviorally diverse and sexually dimorphic. The endogenous opioid system, particularly mu-opioid receptor (MOR) signaling, is known to regulate fear learning and conditioned analgesia, yet its role in alternative fear-related behaviors and sex differences remains unclear. Here, we investigated the effects of systemic naloxone administration prior to auditory fear conditioning on freezing, darting, shock responsivity, and ultrasonic vocalizations (USVs) in male and female rats. Adult Sprague Dawley rats received naloxone (5 mg/kg, i.p.) or saline prior to conditioning and underwent fear recall testing 24 hours later. Naloxone produced sex- and behavior-specific effects across conditioning and recall. During conditioning, naloxone increased freezing in males during baseline and early tone presentations, while females exhibited reduced shock-response velocity and increased post-shock freezing. Naloxone did not significantly alter darting or USV production during conditioning. During recall, freezing behavior did not differ across groups. Naloxone-treated females, however, exhibited a distinct alarm-calling pattern, with fewer callers overall but increased call output among those that vocalized. These findings suggest that MOR antagonism differentially alters distinct components of fear expression in a sex-dependent manner and support the idea that freezing and alarm calling may reflect separable aspects of fear processing.

Early life adversity can produce persistent changes during development that increase vulnerability to neuropsychiatric disorders. Although disruptions in reward processing are widely recognized as a hallmark of these disorders, reward is not a single construct. Distinct forms of reward including social interaction and primary rewards such as food rely on overlapping but dissociable neural circuitry and may be differentially affected by adverse experiences. Here, we used a rodent model of neonatal predator odor exposure (POE) to determine how early life threat influences motivation for social and sucrose reward in adulthood using operant procedures. Neonatal POE reduced adult motivation for a social reinforcer during an operant social self-administration task, whereas motivation for a sucrose reinforcer was unchanged. However, we did find a significant difference in sucrose self-administration with POE females pressing more for sucrose than control females. These findings demonstrate that neonatal threat does not produce a generalized deficit in motivation but rather selectively alters motivation across distinct reward domains. Together, this work identifies social reward as a particularly vulnerable behavioral domain following early life threat and provides new insight into how adverse developmental experiences shape adult reward-related behavior.

Planaria exhibit remarkable regenerative ability, including the capacity to regrow complete heads and brains after decapitation. Here, we re-investigated whether regenerated planaria can preserve learned avoidance behavior, a phenomenon that has been reported previously but has been difficult to study due to unreliable experimental protocols. Using a light-to-food associative conditioning paradigm, planaria were trained to override their normal photophobic preference and then decapitated. Following a two-week regeneration period, behavioral responses to the conditioned stimulus were re-evaluated. Results indicated that the majority of regenerated planaria retained the learned response, supporting a model in which behavioral patterns can regenerate as well as anatomical patterns. By establishing a consistent, low-cost, and effective protocol for studying memory persistence through regeneration, such work may help inform future research on memory loss, resilience, and recovery in neurodegenerative diseases.

Older adults are among the fastest growing groups of traumatic brain injury (TBI) patients and sustain disproportionately poor chronic outcomes. Despite this, the preclinical aging-TBI literature is limited. Beyond the limited presence of aging TBI studies, most studies published in this domain use moderate-to-severe, open head models of TBI, rather than closed head models of mild TBI (mTBI) and repetitive mTBI (rmTBI), the most clinically prevalent presentation. Whether age modulates the chronic behavioral consequences of rmTBI is unknown. In the current study, young (3-4 months) and aged (18-19 months) male C57BL/6 mice received either five mTBIs on alternating days to model rmTBI or sham procedures and underwent behavioral testing in the chronic phase for spatial memory and anxiety-related behavior. Because cross-age behavioral comparisons are confounded by age-related declines in activity and by large sample sizes necessary to detection interaction effects, we applied a three-tier analytical framework combining within-age comparisons, sham-normalized inter-age comparisons, and factorial two-way ANOVA. Contrary to our hypothesis that aging would worsen rmTBI behavioral deficits, age produced domain-divergent effects. Spatial memory deficits were directionally consistent in both young and aged mice but was attenuated in the aged group. Conversely, anxiety-related behavior emerged selectively in the aged mice showing increased thigmotaxis. Locomotion was driven by age alone, with no injury effect, confirming that the aged anxiety signal was not a locomotor artifact. A post-hoc sensitivity analysis indicated that resolving the Age x Injury interaction effect would require at least 44 animals per group. These findings show that age shapes the affective, but not the cognitive, consequences of chronic rmTBI, and underscoring that statistical strategy is inseparable from design in factorial injury studies.

Tau protein has been implicated as an important mediator of traumatic brain injury (TBI). Adult human brain expresses 6 tau isoforms expressing 3 (3R) or 4 (4R) microtubule binding sites; adult mouse brain expresses only 4R tau. A role for tau isoform expression on TBI disease course is tested using wild-type C57/BL6 mice (WT) and C57/BL6 with a knocked-in human tau coding region (MAPTKI). Uninjured WT and MAPTKI mice have similar brain histology and behavior as they age. At subacute times (14 days post-injury (DPI)), injured MAPTKI mice have less white matter damage with similar neuronal loss as WT. At chronic times (90DPI), MAPTKI mice demyelinate while WT mice remyelinate. At 14DPI, tau phosphorylation differs between WT and MAPTKI mice. At 90DPI, thioflavin-S+ protein aggregates in MAPTKI corpus callosum are higher than WT. At 14 or 90DPI, WT and MAPTKI mice acquire Barnes maze, WT retention is impaired at 14DPI and MAPTKI retention impaired at 90DPI. At 14DPI, only MAPTKI mice acquire and retain active place avoidance; at 90DPI, only WT mice acquire active place avoidance. At 14DPI, only injured MAPTKI mice acquire alternating T-maze. These data suggest that WT and MAPTKI differ in both subacute and chronic disease course. At 14DPI, WT mice have greater white matter damage and behavioral impairments than MAPTKI mice. At 90DPI, impairments in WT mice partially recover, yet worsen in MAPTKI mice. This data suggests that 3R tau isoform expression alters the disease course of head injury. HighlightsPost-injury disease course of MAPTKI mice expressing 3R and 4R tau differs from wild-type mice expressing only 4R tau. At subacute times post-injury, MAPTKI mice have less white matter, yet similar gray matter, injury than wild-type mice. At chronic times post-injury, white matter damage in MAPTKI worsens. At subacute times post-injury, MAPTKI mice have fewer behavioral deficits than wild type mice. At chronic times post-injury, MAPTKI mice develop behavioral deficits not present at subacute times.

Human interlocutors have strong expectations that guide when, how, and what is communicated, but the evolutionary origins of such normative expectations remain poorly understood. Vocal accommodation in marmosets, where individuals modify their calls to match partners, offers a potential model. Within an interactive closed-loop playback paradigm, marmosets experienced partner calls that either converged toward or diverged away from their own call structure. Marmosets responded affiliatively to convergence, whereas diverging calls elicited protest vocalizations. Importantly, the protests stopped when the calls converged again. Effects were partner-specific, indicating that marmosets expect bond partners, but not strangers, to converge during a conversation. Furthermore, individuals modified their calls to restore similarity to dissimilar partner playbacks. These findings identify marmoset vocal accommodation as a socially regulated behavior with normative properties.

Optimising the currently heterogenous efficacy of transcranial direct current stimulation (tDCS) interventions for motor learning requires identifying stimulation parameters facilitating performance while accounting for age-related differences in baseline performance and mechanisms underlying neuroplasticity. We systematically explored anodal tDCS intensity effects on implicit motor sequence learning (IMSL) in young and older adults. The study utilised a randomised, double-blind, counterbalanced crossover design. Ninety-six healthy participants (48 young adults, 48 older adults) completed a serial reaction time task (SRTT) with online sham or anodal tDCS over M1 at intensities of 1, 2, and 3 mA. The next day, memory consolidation was assessed in a recall test. Both age groups demonstrated IMSL and consolidation across conditions. While 1 mA tDCS improved IMSL in young adults by reducing reaction times, higher intensities had no significant benefit compared to sham. In older adults, anodal tDCS did not affect general task performance compared to sham, but 1mA tDCS acutely impaired selective sequence learning. The results demonstrate age-dependent and non-linear dose-dependent effects of anodal tDCS on IMSL. This underscores the necessity for age-adapted protocols for experimental and clinical tDCS applications. Future research should explore neurophysiological reasons for reduced tDCS efficacy in older adults found in the present study.

Motivational deficit is a prevalent symptom across a wide range of neurodegenerative and neuropsychiatric disorders. Despite its clinical importance, first-line treatments for these disorders fail to effectively treat this symptom domain. In animal models, motivation is typically assessed in the context of extrinsic reward, where reward is delivered for completing an effortful action. However, many motivated behaviours occur in the absence of a tangible reward and are instead driven by intrinsic motivation. Previous work has shown that an extrinsic motivation task (effort for reward (EfR)) and an intrinsic motivation task (effort based forage (EBF) task) show opposing responses to a range of pharmacological manipulations. However, it is not clear whether intrinsic and extrinsic motivation dissociate in the context of endogenous behavioural variation. We therefore investigated whether these tasks were sensitive to behavioural variation across three different strains of mice (C57Bl/6JJRi, 129S2/SvPasOrlRj and BALB/cJRi) and whether strain profiles diverged across tasks. Here, we found that BALB/c mice showed the lowest levels of foraging in the EBF task, indicative of a low intrinsic motivational state but showed the highest levels of high effort responding in the EfR task, indicative of a high extrinsic motivational state. These differences were not driven by an anxiety-related phenotype and were therefore indicative of a motivation phenotype divergence across tasks. This work highlights the importance of moving away from considering motivation on a single axis, as findings can diverge depending on the nature of the motivational process. This has important implications for both phenotypic interpretation and the development of treatments targeting motivational dysfunction.

Huntingtons disease (HD) is a progressive neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin (HTT) gene. The disease is characterized by movement disorders, and it also presents with personality changes, including apathy and aggression, along with cognitive decline. While most animal models for HD have been validated for motor deficits, less is known about alterations in other behavioral functions. Here, we performed a longitudinal study to analyze the behavior of a knock-in mouse model of HD with a chimeric mouse/human exon 1 containing 140 CAG repeats inserted in the murine huntingtin gene. We specifically inquired about the onset of cognitive impairments in knock-in mice and whether changes in various behavioral functions such as locomotion, anxiety, and cognition correlate at the individual level. Our data indicate that female and male knock-in mice exhibit reductions in body weight, novelty-induced locomotion, and remote spatial memory retrieval. However, social behavior, working, and short-term memory remain unaffected. Within knock-in mice, lower open-field activity correlated with poorer remote memory performance. Moreover, CAG repeat length negatively correlated with locomotor activity and spatial memory, indicating that greater repeat expansion predicts more severe behavioral impairment. These findings identify early affective changes, followed by selective long-term memory and locomotor deficits, in knock-in mice, supporting this model as a useful platform for studying prodromal HD and repeat-length-dependent disease variability. HighlightsO_LICAG140 knock-in mice show early anxiety, later reduced locomotion and memory deficits C_LIO_LILong-term and remote memory are impaired while short-term and working memory are spared C_LIO_LILower locomotion at the age of 8 months correlates with poorer memory at 14 months of age in individual CAG140 knock-in mice C_LIO_LIGreater CAG repeat length predicts worse locomotion and memory C_LI

Abstract Objectives To evaluate and compare the neuro-behavioural safety profiles of piroxicam and nitroglycerine by investigating their differential effects on cognitive function, spatial and recognition memory, and hippocampal neurochemistry in a di-oestrous female Wistar rat model. Methods Female Wistar rats at di-oestrous were randomly assigned to receive distilled water, piroxicam, or nitroglycerine orally for four consecutive days. Following treatment, spatial and recognition memory were evaluated using standard behavioural paradigms. Hippocampal tissues were analysed for acetylcholinesterase and glutamate activity, oxidative stress markers, and neuroinflammatory indices. Results Piroxicam improved recognition memory and was associated with increased glutamatergic activity and a compensatory rise in superoxide dismutase. However, it also elicited elevated nitric oxide signaling, lipid peroxidation, and localized neuroinflammatory markers in the hippocampus. In contrast, nitroglycerine impaired non-spatial memory during di-oestrous. Although both treatments preserved working memory, they produced distinct effects on object recognition, memory discrimination, oxidative stress parameters, and neuroinflammatory mediators. Conclusions Piroxicam and nitroglycerine exert differential effects on cognition and hippocampal neurochemistry during di-oestrous. Piroxicam improved recognition memory and produced distinct hippocampal neurochemical alterations, whereas nitroglycerine impaired recognition memory. These findings highlight the influence of menstrual pain therapeutics on cognitive function and hippocampal physiology under hormonally sensitive conditions. Keywords: cognitive function; cognitive impairment; cyclooxygenase inhibitors; neuroinflammation; neurochemistry

Theft, including shoplifting, extorts a pervasive societal and economic burden. However, the neurobehavioral mechanisms underlying recurrent theft remain sparsely understood. In this study, we investigated social cognition deficits in theft recidivists with kleptomania (TR+K) and instrumental theft recidivists without kleptomania (TR-K) compared to control subjects without criminal records (CT), for which the Social Norms Questionnaire (SNQ-22) to assess explicit moral knowledge, alongside the Dictator Game (DG) and Hawk-Dove Game (HDG) to evaluate discretionary and competitive resource allocation with others, respectively, were administered. Bayesian statistical analyses revealed that all groups demonstrated comparable social norm recognition in SNQ-22 and prosociality in the DG. However, distinct behavioral profiles emerged in specific contexts, such that TR+K exhibited more unfairness than CT and TR-K at discretionary resource allocations in the DG, whereas in the HDG, TR-K demonstrated more aggressive, resource-monopolizing responses, particularly when against an aggressive opponent, than CT and TR+K. These results suggest that theft recidivism may stem from contextual failures rather than general deficits in moral knowledge, which are distinct between TR+K rooted in the internal factor, such as heightened loss aversion, and TR-K characterized by impulsivity over the external factor, such as social conflicts with others.

Despite the well-established health benefits of exercise, adherence to physical activity remains low, highlighting the need to identify biological factors that regulate the initiation and persistence of exercise behavior. Here, we tested whether ovarian hormone state at the onset of voluntary wheel running (VWR) influences both immediate and long-term exercise behavior in female rats. Females that initiated VWR during proestrus (Pro) ran farther, spent more time running, and ran at higher speeds on the first day of wheel access than females initiating VWR outside of Pro. Remarkably, initiating VWR during Pro also produced persistent increases in running distance, duration, speed, and escalation across subsequent weeks, despite normal cycling through other estrous phases. In contrast, exogenous estradiol (E2) administered at VWR initiation did not alter day-1 behavior, but increased running distance and duration across subsequent weeks without affecting running speed or escalation. To determine whether dorsal striatal dopamine contributes to these effects, we inhibited the substantia nigra (SN) to dorsolateral striatum (DLS) pathway on the first day of VWR. This manipulation reduced the immediate and long-term effects of initiating VWR during Pro on running duration and distance but not speed or escalation. These findings identify behavioral initiation as a critical window during which hormones and nigrostriatal signaling influence future engagement in physical activity. Furthermore, analysis of individual components of VWR architecture reveals that distinct features of VWR behavior can be dissociated mechanistically and thus could be used to investigate separate motivational processes underlying physical activity.

RationaleAppetitive Pavlovian cues can drive maladaptive reward seeking via stimulus-reward memories. Disrupting memory reconsolidation offers a potential strategy to reduce their influence, but evidence for {beta}-adrenergic blockade with propranolol is inconsistent across behavioural paradigms, particularly relative to NMDA receptor antagonism. ObjectivesWe tested whether propranolol disrupts reconsolidation of appetitive sucrose memories in a discriminative goal-tracking paradigm, and compared its effects with those of the most commonly used NMDA receptor antagonist, MK-801. MethodsAdult Lister hooded rats underwent discriminative Pavlovian conditioning. Thirty minutes before a brief memory reminder (non-reinforced or reinforced), rats received systemic drug treatment or saline control. In study 1, MK-801 (0.1 mg/kg) was administered to male rats. In study 2, propranolol (10 mg/kg) was administered to equal numbers of male and female rats. Goal-tracking was tested drug-free at 1 and 8 days. ResultsIn study 1, MK-801 impaired subsequent discriminated responding at test. These effects were observed not only when reminder was non-reinforced as in previous successful demonstrations, but also with reinforced reminder. In study 2, Propranolol also impaired subsequent goal-tracking, regardless of reminder type, and the effects were consistent across sexes. ConclusionsPropranolol can disrupt reconsolidation of appetitive goal-tracking memories to a similar extent as MK-801 under conditions that promote memory destabilisation. These findings demonstrate that {beta}-adrenergic blockade can impair appetitive memory reconsolidation in a goal-tracking paradigm, challenging prior null findings and revitalising the potential for propranolol-based interventions in maladaptive reward-seeking behaviours.

Chlorpyrifos is a widely used organophosphate pesticide that exerts its primary toxic effect through inhibition of acetylcholinesterase (AChE). Although the acute neurotoxicity of chlorpyrifos is well characterized, the lasting biochemical, behavioral, and epigenetic consequences of sub-chronic exposure remain poorly understood, particularly when considering sex-specific differences. Therefore, we exposed male and female C57BL/6J mice to either peanut oil (n=19), low chlorpyrifos exposure (1 mg/kg/day; n=19), or high chlorpyrifos exposure (10 mg/kg/day n=10) repeatedly for 21 days via subcutaneous injection. Blood AChE activity, behavior, and hippocampal DNA methylation were measured across groups. During exposure, AChE activity decreased in both males and females but only returned to baseline after behavioral testing in females exposed to low chlorpyrifos levels. Behavioral tests also revealed a sex-specific phenotype, with females in the low exposure group exhibiting reduced forced swim test immobility and a significant time by exposure interaction in open field habituation. No significant behavioral effects were observed in males. Significant DNA methylation changes were observed at 3,538 CpG sites in male and female mice after high exposure. Sex-specific analyses revealed two female-specific differentially methylated CpGs after high exposure. Pathways enriched for differentially methylated genes included several related to synaptic remodeling, cholinergic synapse, and various endocrine systems. These findings demonstrate that repeated high chlorpyrifos exposure leads to persistent cholinergic disruption and DNA methylation changes. However, the female-specific behavioral changes seen are independent of AChE activity and widespread DNA methylation changes, suggesting additional mechanisms, present only in females, may underlie behavioral sensitivity to chlorpyrifos. New and NoteworthySub-chronic chlorpyrifos exposure in adult mice produced dose-dependent blood AChE suppression and widespread hippocampal DNA methylation changes in both sexes, with pathway enrichment including cholinergic synapse and endocrine systems. Behavioral effects were subtle, with females in the low exposure group showing reduced forced swim immobility and altered locomotor habituation. Notably, the female-specific behavioral changes seen are independent of AChE activity and DNA methylation changes, suggesting novel mechanisms may underlie female behavioral sensitivity to chlorpyrifos.