Widespread exposure to per- and polyfluoroalkyl substances (PFAS) poses substantial health risks to humans and animals. PFAS have the propensity to bioaccumulate in organs such as the testes, wherein they have been implicated in adverse effects on sperm production and quality. Here, we sought to understand the multigenerational implications of such effects by chronically subjecting three generations of mice to an environmentally relevant PFAS cocktail and subsequently investigating impacts on reproduction, behavior and offspring development. This strategy confirmed that testicular accumulation of PFAS is correlated with compromised rates of sperm production and alterations to the sperm epigenome but did not compromise the overall fertility or behavioral outcomes explored in PFAS-exposed males. Notably, the negative effects were more pronounced in F1 offspring compared with subsequent F2 and F3 generations. These data support mounting evidence of adverse associations between PFAS exposure and reproductive capacity, but suggest the risk posed by PFAS is not amplified across three generations.

Rates of binge drinking have converged significantly between the sexes over recent decades, driven by increased rates of alcohol misuse in women. However, understanding of the fundamental circuitry and neurobiology driving alcohol use in females, or how this may differ from male subjects remains underexplored. Here, we quantified c-Fos expression across 40 brain regions in alcohol naïve, alcohol anticipating and binge-like drinking male and female mice. The basolateral amygdala (BLA) was of particular interest given the robust sex differences in c-Fos expression, with female mice showing greater alcohol-associated expression. This was confirmed with in vivo calcium imaging revealing greater and more prolonged BLA responsivity at the onset of alcohol intake in female mice. To functionally test this, we used chemogenetic inhibition, however non-specific inhibition of the BLA broadly reduced alcohol and other reward intake in both sexes. Given the diversity of BLA efferent projections we assessed sex differences in c-Fos expression in BLA efferent projections following alcohol consumption drinking, identifying preferential activation of the BLA to nucleus accumbens core (AcbC) projection in female mice. Precision chemogenetic inhibition of the BLA→AcbC pathway reduced binge-like alcohol intake sex-specifically in females. Together, this study uncovers sex differences in the neural circuits engaged in binge-like drinking, highlighting the BLA→AcbC projection may in part underpin sex differences in alcohol misuse. This provides further evidence of distinct neurobiological drivers of alcohol-related behaviors between the sexes.

Comorbidity between post-traumatic stress disorder (PTSD) and alcohol use is common and mutually-reinforcing, yet there are no pharmacological strategies that specifically target trauma-linked escalation of alcohol intake. We evaluated whether 3,4-methylenedioxymethamphetamine (MDMA), given in a therapy-adjunctive fashion (30 min before fear extinction), could facilitate extinction of conditioned fear and reduce alcohol consumption in a rat model that combines fear conditioning, binge-like alcohol access, abstinence, and re-exposure. Inbred alcohol-preferring (iP) and outbred Wistar rats of both sexes underwent auditory fear conditioning, voluntary ethanol drinking, and subsequently fear extinction after MDMA or vehicle administration, with drug-free extinction recall and alcohol consumption assessed thereafter. Fear conditioning increased voluntary alcohol intake only in iP rats, suggesting a genotype-related fear-alcohol contingency. MDMA acutely reduced freezing during extinction, but ultimately reshaped across-session freezing patterns in a strain- and sex-dependent manner. There were no lasting MDMA treatment effects on next-day drug-free recall. MDMA also altered on-drug fear-expression during extinction without affecting later recall in an iP rat cohort without prior alcohol exposure, indicating the effect is not secondary to drinking history. Critically, MDMA prevented the shock-related increase in alcohol consumption but only in iP rats. These data suggest MDMA's most reliable action in this model is to disrupt trauma-linked escalation of alcohol intake in genetically- and experientially- vulnerable rats, rather than to globally enhance fear extinction.

Alcohol misuse remains a leading cause of preventable death worldwide, prompting research into novel pharmacotherapies for alcohol use disorder (AUD). This study investigated the therapeutic potential of full agonism or positive allosteric modulation of the serotonin 2C receptor (5-HT2CR) in addressing alcohol binge drinking and seeking behaviours in mice. Using a drinking-in-the-dark paradigm and a context-induced reinstatement model following punishment-imposed abstinence, we assessed the acute effects of 5-HT2CR ligands lorcaserin, CYD-1-79, VA012 and CTW0415 on alcohol intake and seeking behaviours in mice. Results showed that while lorcaserin effectively reduced both alcohol consumption and seeking behaviours, the 5-HT2CR positive allosteric modulators (PAMs) did not significantly alter these behaviours over the range of doses examined. These findings suggest that 5-HT2CR PAMs, at the tested doses, may lack intrinsic efficacy in modulating alcohol use. However, our lorcaserin data demonstrate that targeting 5-HT2CR remains a valid approach to reduce behaviours associated with AUD.

As technology rapidly advances, the evidence for the efficacy of brain-based therapeutics, such as repetitive transcranial magnetic stimulation (rTMS), for the treatment of numerous neurological and neuropsychiatric conditions continues to grow. Indeed, promising therapeutic results to date have led to several international regulatory bodies approving the use of rTMS for the treatment of depression, tobacco smoking cessation, migraines and obsessive-compulsive disorder. This is encouraging, as the use of rTMS could be successfully expanded to treat other indications such as alcohol use disorder. This review outlines the current clinical literature on the use of rTMS to treat alcohol use disorder with a focus on rTMS parameters. We aim to understand if stimulation parameter flexibility may open the door to tailored treatment for alcohol use disorder. We emphasize that whilst rTMS presents as a promising new therapeutic option for alcohol use disorder, the current evidence for its efficacy and our understanding of optimal treatment parameters are limited. Finally, we highlight the gaps that need to be filled when considering the use of rTMS to treat alcohol use disorder.

BACKGROUND:A defining feature of alcohol use disorder that has captured the attention of fundamental researchers is "persistent use despite negative consequences." The last two decades have seen the preclinical field adopt the use of punishment to model the adverse consequences associated with alcohol use. However, existing research has focused on rats as the model of choice and alcohol consumption as the prevailing outcome measure. Additionally, the predictive validity of these models, that is, testing currently approved FDA treatments, is yet to be realized. METHODS:Here, we examined punishment-imposed abstinence in mice using foot shock and measured reinstatement of alcohol-seeking following exposure to alcohol-associated cues and environmental contexts. RESULTS:We showed that mice voluntarily abstain from alcohol use when it is paired with a foot shock. Alcohol-associated cues and environmental contexts produced reinstatement of alcohol-seeking behavior. Finally, the predictive validity of our model was tested using naltrexone and varenicline, two medications to treat alcohol use disorder. Both naltrexone and varenicline reduced reinstatement of alcohol-seeking in male and female mice. CONCLUSIONS:Together, these data suggest that mice can display reinstatement of alcohol-seeking behavior following voluntary abstinence, and this model could be used to identify new medications for relapse prevention induced by environmental cues and contexts.

Maintaining abstinence and preventing relapse are key to the successful recovery from alcohol use disorder. There are two main ways individuals with alcohol use disorder abstain from alcohol use: forced (e.g., incarceration) and voluntary. Voluntary abstinence is often evoked due to the negative consequences associated with excessive alcohol consumption. This study investigated relapse-like behavior to alcohol seeking following acute, forced, and voluntary abstinence. Male rats had increased operant self-administration responding throughout training compared to females; however, females consumed greater amounts of alcohol in g/kg. Both male and female rats achieved voluntary abstinence, which was induced using an electric barrier on the operant chamber floor with alcohol readily available during this period. Interestingly, male rats that underwent voluntary abstinence displayed reduced alcohol seeking compared to males in the acute and forced abstinence groups. This difference in alcohol seeking behavior across abstinence groups was not observed in female rats. Quantification of neuronal activation (Fos protein) revealed numerous brain regions (e.g., ventral subiculum and lateral habenula) to be associated with the reduced reinstatement propensity seen in male rats that underwent voluntary abstinence. Additionally, hierarchical clustering found enhanced functional connectivity and coordination in the male voluntary abstinence group compared to the male forced abstinence group. Collectively, these data implicate a sexual dimorphism in the effect that voluntary abstinence, at least in the model employed here, has on relapse-like behavior. This maybe driven by reduced neuronal activation at a network level and enhanced functional connectivity and integration. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Reward-seeking involves the engagement and computation of multiple physiological and motivational parameters. The lateral hypothalamus (LH) is a necessary node in the circuits that control food-seeking and motivation. One group of cells that plays an important yet incompletely understood role in these processes are the orexin/hypocretin (OX/HT) neurons. OX/HT cells are located exclusively within the LH and are implicated in feeding, arousal, and reward-seeking behavior. Importantly, the role of OX/HT neurons in consummatory versus reward-seeking actions is not fully defined, nor are the circuits that control the activity of these neurons under different behavioral states. Here we show that OX/HT neurons respond in real time to food presentation and that this response is modulated by differences in metabolic state. We observed increased OX/HT neuron activity on approach to food, but this activity trended towards pre-approach levels by the start of the consummatory phase. Next, we studied ventrostriatopallidal (VSP) inputs to the OX/HT neurons. Using optogenetics and cell type-specific electrophysiology, we found that ventral pallidum inputs onto OX/HT neurons exert strong inhibitory (and weak excitatory) effects whereas the lateral nucleus accumbens shell provides weaker direct inhibitory connections with OX/HT neurons. These findings reveal that the activity of OX/HT neurons is strongly modulated by metabolic and hedonic state. Further, OX/HT neurons is primarily associated with food approach and that the effect of VSP-terminal output is to suppress OX/HT activity.

The insular cortex is a multifunctional and richly connected region of the cerebral cortex, critical in the neural integration of external stimuli and internal signals. Well-served for this role by a large network of afferent and efferent connections, the mouse insula can be simplified into an anterior, medial and posterior portion. Here we focus on the medial subregion, a once over-looked area that has gained recent attention for its involvement in an array of behaviours. Although the connections of medial insular cortex neurons have been previously identified, their precise glutamatergic phenotype remains undefined (typically defined by the presence of the subtype of vesicular glutamate transporters). Hence, we combined Cre knock-in mouse lines and adeno-associated viral tracing to distinguish between the expression of the two major vesicular glutamate transporters, type 1 (vGlut1) and 2 (vGlut2), in the subregion’s neuronal inputs and outputs. Our results determined that the medial insula has extensive glutamatergic efferents expressing both vGlut1 and vGlut2 throughout the neuraxis. In contrast, a more conservative number of glutamatergic inputs were observed, with exclusively vGlut2+ projections received from hypothalamic and thalamic regions. Taken together, we demonstrate that vGlut1- and vGlut2-expressing networks of this insular subdivision have distinct connectivity patterns, including a greater abundance of vGlut1+ fibres innervating hypothalamic regions and the extended amygdala. These findings provide insight into the distinct chemo-architecture of this region, which may facilitate further investigation into the role of the medial insula in complex behaviour.

Impaired motivational drive is a key feature of depression. Chronic stress is a known antecedent to the development of depression in humans and depressive-like states in animals. Whilst there is a clear relationship between stress and motivational drive, the mechanisms underpinning this association remain unclear. One hypothesis is that the endocrine system, via corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN; PVNCRH), initiates a hormonal cascade resulting in glucocorticoid release, and that excessive glucocorticoids change brain circuit function to produce depression-related symptoms. Another mostly unexplored hypothesis is that the direct activity of PVNCRH neurons and their input to other stress- and reward-related brain regions drives these behaviors. To further understand the direct involvement of PVNCRH neurons in motivation, we used optogenetic stimulation to activate these neurons 1 h/day for 5 consecutive days and showed increased acute stress-related behaviors and long-lasting deficits in the motivational drive for sucrose. This was associated with increased Fos-protein expression in the lateral hypothalamus (LH). Direct stimulation of the PVNCRH inputs in the LH produced a similar pattern of effects on sucrose motivation. Together, these data suggest that PVNCRH neuronal activity may be directly responsible for changes in motivational drive and that these behavioral changes may, in part, be driven by PVNCRH synaptic projections to the LH.

Persistent substance use despite negative consequences is a key facet of substance use disorder. The last decade has seen the preclinical field adopt the use of punishment to model adverse consequences associated with substance use. This has largely involved the pairing of drug use with either electric foot shock or quinine, a bitter tastant. Whilst at face value, these punishers may model aspects of the physical and psychological consequences of substance use, such models are yet to assist the development of approved medications for treatment. This review discusses progress made with animal models of punishment to understand the behavioral consequences of persistent substance use despite negative consequences. We highlight the importance of examining sex differences, especially when the behavioral response to punishment changes following drug exposure. Finally, we critique the translational value these models provide for the substance use disorder field.

Key Clinical MessageThis case suggests using dual orexin receptor antagonists to treat alcohol use disorder and comorbid sleep disorders may be effective, commencing treatment in withdrawal and continuing it to prevent relapse.AbstractEffective medications for the treatment of alcohol use disorder are limited. This is partially due to the heterogenous nature of the symptomatology associated with alcohol use disorder and the abundance of presenting comorbidities. One common, and often overlooked, symptom that occurs during withdrawal of alcohol use is sleep disruption. Here, we report a case study of a participant with comorbid alcohol use disorder and insomnia. This participant was treated with a dual orexin receptor antagonist, suvorexant (Belsomra®), currently approved to treat insomnia. We demonstrate improvements in alcohol cravings, physical and psychological health, and sleep outcomes with treatment. These data support abundant preclinical and emerging clinical data in this space. The findings from this case report highlight the potential for suvorexant to treat comorbid alcohol use disorder and insomnia with fully powered, randomized controlled trials moving forward.

The nucleus accumbens shell is a critical node in reward circuitry, encoding environments associated with reward. Long-range inputs from the ventral hippocampus (ventral subiculum) to the nucleus accumbens shell have been identified, yet their precise molecular phenotype remains to be determined. Here we used retrograde tracing to identify the ventral subiculum as the brain region with the densest glutamatergic (VGluT1–Slc17a7) input to the shell. We then used circuit-directed translating ribosome affinity purification to examine the molecular characteristics of distinct glutamatergic (VGluT1, VGluT2–Slc17a6) ventral subiculum to nucleus accumbens shell projections. We immunoprecipitated translating ribosomes from this population of projection neurons and analysed molecular connectomic information using RNA sequencing. We found differential gene enrichment across both glutamatergic projection neuron subtypes. In VGluT1 projections, we found enrichment of Pfkl, a gene involved in glucose metabolism. In VGluT2 projections, we found a depletion of Sparcl1 and Dlg1, genes known to play a role in depression- and addiction-related behaviours. These findings highlight potential glutamatergic neuronal-projection-specific differences in ventral subiculum to nucleus accumbens shell projections. Together these data advance our understanding of the phenotype of a defined brain circuit.

It is well-established that stress and negative affect trigger eating disorder symptoms and that the brains of men and women respond to stress in different ways. Indeed, women suffer disproportionately from emotional or stress-related eating, as well as associated eating disorders such as binge eating disorder. Nevertheless, our understanding of the precise neural circuits driving this maladaptive eating behavior, particularly in women, remains limited. We recently established a clinically relevant model of 'emotional' stress-induced binge eating whereby only female mice display binge eating in response to an acute "emotional" stressor. Here, we combined neuroanatomic, transgenic, immunohistochemical and pathway-specific chemogenetic approaches to investigate whole brain functional architecture associated with stress-induced binge eating in females, focusing on the role of Vglut2 projections from the paraventricular thalamus (PVTVglut2+) to the medial insular cortex in this behavior. Whole brain activation mapping and hierarchical clustering of Euclidean distances revealed distinct patterns of coactivation unique to stress-induced binge eating. At a pathway-specific level, PVTVglut2+ cells projecting to the medial insular cortex were specifically activated in response to stress-induced binge eating. Subsequent chemogenetic inhibition of this pathway suppressed stress-induced binge eating. We have identified a distinct PVTVglut2+ to insular cortex projection as a key driver of "emotional" stress-induced binge eating in female mice, highlighting a novel circuit underpinning this sex-specific behavior.

Projections to the striatum are well-identified. For example, in the ventral striatum, two major inputs to the medial nucleus accumbens shell include the ventral subiculum and basolateral amygdala. However, the chemical phenotype(s) of these projection neurons remain unclear. In this study, we examined amygdalostriatal and corticostriatal connectivity in rats using injections of the retrograde tracer cholera toxin b into the nucleus accumbens shell. To determine the neurotransmitter identity of projection neurons, we combined retrograde tracing with RNAscope in-situ hybridization, using mRNA probes against vesicular transporters associated with glutamatergic (VGluT1 - Slc17a7, VGluT2 - Slc17a6) or GABAergic (VGaT - Slc32a1) neurotransmission. Confocal imaging was used to examine vesicular transporter mRNA expression in the ventral subiculum and basolateral amygdala inputs to the nucleus accumbens shell. Both projections contained mostly VGluT1-expressing neurons. Interestingly, almost a quarter of ventral subiculum to nucleus accumbens shell projections co-expressed VGluT1 and VGluT2 compared to a relatively small number (similar to 3%) that were co-expressed in basolateral amygdala to nucleus accumbens shell afferents. However, almost a quarter of basolateral amygdala to nucleus accumbens shell projections were VGaT-positive. These findings highlight the diverse proportions of glutamatergic and GABAergic afferents in two major projections to the nucleus accumbens shell and raise important questions for functional studies.

Abstract Muscarinic acetylcholine receptors (mAChRs) have been shown to mediate alcohol consumption and seeking. Both M4 and M5 mAChRs have been highlighted as potential novel treatment targets for alcohol use disorders (AUD). Similarly, M1 mAChRs are expressed throughout reward circuitry, and their signaling has been implicated in cocaine consumption. However, whether the same effects are seen for alcohol consumption, or whether natural reward intake is inadvertently impacted is still unknown. To determine the role of M1 mAChRs in alcohol consumption, we tested operant self‐administration of alcohol under both fixed ratio (FR3) and progressive ratio (PR3‐4) schedules. Enhancing M1 mAChR signaling (via the M1 PAM‐Agonist PF‐06767832, 1 mg/kg, i.p.) reduced operant alcohol consumption on a fixed schedule but had no effect on motivation to acquire alcohol. To determine whether these actions were specific to alcohol, we examined the effects of M1 enhancement on natural reward (sucrose) self‐administration. Systemic administration of PF‐06767832 (1 mg/kg, i.p.) also reduced operant sucrose self‐administration, suggesting the actions of the M1 receptor may be non‐selective across drug and natural rewards. Finally, to understand whether this reduction extended to natural consummatory behaviors, we assessed home cage standard chow and water consumption. M1 enhancement via systemic PF‐06767832 administration reduced food and water consumption. Together our results suggest the M1 PAM‐agonist, PF‐06767832, non‐specifically reduces consummatory behaviors that are not associated with motivational strength for the reward. These data highlight the need to further characterize M1 agonists, PAMs, and PAM‐agonists, which may have varying degrees of utility in the treatment of neuropsychiatric disorders including AUD.

Compulsive overeating of palatable food is thought to underlie some forms of obesity. Similarities are often observed in the behavioural symptomology and the neuropathophysiology underlying substance use disorder and compulsive overeating. As such, preclinical animal models which assess addiction-like behaviour towards food may assist the understanding of the neurobiology underlying overeating behaviour. Further, the relation-ship between these behaviours and the propensity for diet-induced obesity warrants examination. In this study we investigated the relationship between the propensity for diet-induced obesity (DIO) and addiction-like behaviour towards highly palatable food in C57BL/6 J mice as measured by a 3-criteria model. We also examined the extent to which performance on this 3-criteria model predicted two key hallmark features of addiction - resistance to extinction and relapse propensity (as measured by reinstatement of lever pressing). C57BL/6 J mice were allowed free access to a palatable diet for 8 weeks then separated by weight gain into DIO-prone and DIO-resistant subgroups. Access to palatable food was then restricted to daily operant self -administration sessions whereby addiction-like behaviour towards a high-fat high-sugar food reward was assessed using a 3-criteria model similar to that used to assess addiction-like behaviour towards drugs of abuse. In contrast to findings in rats, no difference in addiction-like behaviour towards food was observed between obesity prone (OP) and obesity resistant (OR) mice. Similarly, principal components analysis found no distinct patterns in the relationship between addiction-like behaviours across treatment groups. This suggests that the strain and species of rodent may be critical for studying the mechanisms underlying pathological over-consumption. Further analysis revealed that the extent of performance on the 3-criteria model correlated with the propensity for C57BL/6 J mice to both extinguish food seeking behaviour and "relapse" after a period of withdrawal. This finding was evident across all groups, regardless of DIO. Collectively, these data validate the 3 -criteria model as a robust model to comprehensively assess food addiction-like behaviour in mice, regardless of prior food intake history.