The basolateral amygdala (BLA) is important for assigning emotional weight to environmental stimuli to guide learning, discrimination, and adaptive vigilance. The contribution of neuromodulator inputs such as dopamine to this process is unclear. Here, we recorded in vivo BLA dopamine signals across emotional learning paradigms. We show that BLA dopamine scales with a stimulus's emotional intensity, but not value or associative strength, and reward-predictive cues evoke BLA dopamine signals that diminish, rather than grow, with training. In a complex learning context, where rats discriminated between multiple valenced associations, the magnitude of cue-evoked BLA dopamine re-scaled to report the level of relative emotional saliency. Threat and safety cues prompted larger, sustained dopamine signals compared to reward and neutral cues. Together, our data reveal a pattern of dopamine encoding with a unique contribution to learning, for dynamic disambiguation of affective states.

INTRODUCTION:Despite the widespread impact of opioid use disorder, pharmacological options for treatment remain limited. Recent studies find that cocaine exposure decreases the expression of the glutamate transporter GLT-1 in the nucleus accumbens (NAc) and that treatment with the beta-lactam antibiotic ceftriaxone rescues this loss of expression and reduces cue-induced reinstatement to cocaine self-administration. The novel beta-lactam derivative MC-100093 (093) lacks antimicrobial properties but crosses the blood-brain barrier more rapidly and retains the beneficial effects of ceftriaxone following cocaine. However, 093 effects following oxycodone exposure have not been examined. METHODS:We used intravenous self-administration (IVSA) of oxycodone in rats to test if 093 can attenuate oxycodone seeking. Membrane expression of GLT-1 in the NAc was investigated using western blots. Conditioned place preference (CPP) was used to test the effect of oxycodone and cocaine alone on GLT-1 expression. RESULTS:We find that 093 injections following IVSA of oxycodone in rats did not reduce cue-induced reinstatement. Interestingly, western blot analysis revealed that 093 failed to upregulate the expression of GLT-1 in the NAc of oxycodone-exposed animals. Follow-up CPP experiments suggest that oxycodone exposure alone does not decrease GLT-1 expression as cocaine does. CONCLUSIONS:Our results indicate that drug-specific reductions in NAc GLT-1 expression may be necessary for 093's efficacy. Further investigation into 093 and other opioids is needed to fully understand their relationship with GLT-1 expression and beta-lactams.

Cocaine-induced changes in nucleus accumbens shell (NAcSh) medium spiny neurons (MSNs) differ based on dopamine receptor subtype expression, the sex of the animal, and for females, phase of the estrous cycle. These findings highlight the need to account for both sex and estrous cycle when studying drug-mediated alterations in neurophysiology. Whether MSNs of the nucleus accumbens core (NAcC), which serve different aspects of reward function, will exhibit similar sex and estrous cycle effects with cocaine administration was investigated. Mice underwent a 5-day locomotor sensitization paradigm via daily cocaine administration (15 mg/kg, s.c.) followed by a 1- to 4-day drug-free abstinence period. We examined NAcC MSN excitability by obtaining ex vivo whole-cell recordings from differentially labeled dopamine D1-receptor expressing MSNs (D1R-MSNs) and dopamine D2-receptor expressing MSNs (D2R-MSNs) obtained from male mice or female mice that were either in estrus or diestrus. In this mouse strain, male and female mice sensitized to cocaine to a similar degree. In males, there were no cocaine-induced changes in NAcC D1R-MSN or D2R-MSN excitability. When comparing MSN subtypes, D2R-MSNs exhibited greater excitability. In saline-treated females, D1R-MSN excitability fluctuated across the estrous cycle with increased excitability during estrus. Following cocaine, estrous cycle-dependent D1R-MSN excitability was arrested, fixed at an intermediate value between estrus and diestrus when compared to saline controls. D2R-MSNs did not change across the estrous cycle or following cocaine. When comparing MSN subtypes, in diestrus, D2R-MSNs were more excitable under saline conditions, but indistinguishable from D1R-MSNs following cocaine. In contrast, during estrus, D1R- was indistinguishable from D2R-MSN excitability in saline treated animals, but with cocaine, D2R-MSNs displayed heightened excitability. There are fundamental sex differences in cocaine-induced changes to the excitability of D1R-MSNs in the NAcC. After cocaine exposure, female mice in diestrus saw a significant main effect change in MSN excitability, an inversion of what had previously been demonstrated in the NAcSh. These data suggest that there are fundamental sex differences in the neuropharmacological effect of cocaine in males versus females that are shell- and core-specific. There are sex- and estrous-cycle dependent changes to D1R-MSNs in the NAcC that are sensitive to cocaine exposure. In males, cocaine has no effect on altering D1R- or D2R- MSNs excitability. During the estrous cycle, D1R-MSNs exhibit increased excitability during estrus. This fluctuation is halted by cocaine, such that D1R-MSNs recorded in diestrus show increased excitability following cocaine exposure whereas female D1R-MSNs recorded in estrus have decreased excitability. The nucleus accumbens core (NAcC) is a brain region associated with regulating motivated behavior. The primary neuronal populations of the NAcC are dopamine D1 receptor expressing medium spiny neurons (D1R-MSNs) and dopamine D2 receptor expressing medium spiny neurons (D2R-MSNs). No studies exist which examine sex differences and estrous cycle effects in the NAcC following cocaine administration. Using ex vivo electrophysiology, we found inherent sex- and estrous-cycle differences in cocaine-induced MSN neuroplasticity. Following cocaine exposure, D1R-MSN excitability was unaffected in males, increased in females recorded during the diestrus phase, and decreased in females recorded during estrus. This ran counter to estrous cycle effects under drug-naive conditions where D1R-MSN excitability was higher in estrus versus diestrus. The estrous cycle effects on D1R-MSNs were eliminated following cocaine administration. For both sexes, D2R-MSN excitability was not impacted following cocaine. These results highlight fundamental sex differences in neurophysiology that might underpin differences in addiction.

Adaptive decision making relies on proper discrimination and prediction of positive and negative events. The basolateral amygdala (BLA) is central to this valence encoding, assigning emotional value to stimuli to drive appropriate behavioral responses. The ventral tegmental area (VTA), which is classically known to regulate associative learning and incentive motivation via dopamine projections to the striatum, also contains strong dopamine projections to the BLA, but this system has received much less attention. Here, we investigated how in vivo BLA dopamine signaling is engaged durning learning. We show that reward cues evoke BLA dopamine signals that diminish, rather than grow, with training. As the complexity of the learning context was increased, where rats actively differentiated between various cue types signaling threat, reward, safety, and neutral associations, the magnitude of cue-evoked BLA dopamine responses was largest early in training and reported the level of perceived emotional saliency. Fear and safety cues prompted larger, sustained dopamine signals compared to reward and neutral cues, an effect that was more apparent in female rats, compared to males. Together, our findings broaden the theoretical landscape of dopamine heterogeneity, showing that BLA dopamine supports dynamic disambiguation of relative stimulus importance by non-associatively encoding sensory state transitions, independent of value. These signals reflect a scalar readout of emotional salience to prime, rather than track, learning.

Biological sex as a defining variable in drug sensitivity remains poorly understood. Here, we combine behavioral and electrophysiological analyses to examine the influence of sex and gonadal hormones on cocaine-induced psychomotor sensitization and nucleus accumbens shell (NAcSh) plasticity in the prominent C57BL/6J mouse strain. Males exhibited greater cocaine-evoked locomotor activity than females; castration attenuated responses, whereas ovariectomy enhanced them. This behavioral phenotype is opposite to what occurs in rats. A 10-14 day abstinence period abolished the sex difference in intact animals, and gonadectomy reduced cocaine-induced behavioral plasticity. Recordings from 309 medium spiny neurons revealed sex-dependent NAcSh plasticity. In males, cocaine decreased neuronal excitability, while in females it induced estrous cycle-dependent plasticity characterized by reduced excitability during diestrus relative to estrus. These effects were driven by cocaine-induced modulation of voltage-gated sodium channels. Cocaine potentiated glutamatergic strength in males but elicited estrous cycle-dependent depotentiation in females. These adaptations in excitability and glutamatergic strength were abolished by gonadectomy, and paralleled diminished behavioral plasticity during abstinence. These data illustrate that biological sex and hormonal milieu critically shape cocaine-induced plasticity, offering a more nuanced framework than the traditional notion of heightened female sensitivity to drugs of abuse.

Recent studies have implicated the ethanol metabolite, acetic acid, as neuroactive, perhaps even more so than ethanol itself. In this study, we investigated sex-specific metabolism of ethanol (1, 2, and 4 g/kg) to acetic acid in vivo to guide electrophysiology experiments in the accumbens shell (NAcSh), a key node in the mammalian reward circuit. There was a sex-dependent difference in serum acetate production, quantified via ion chromatography only at the lowest dose of ethanol (males > females). Ex vivo electrophysiology recordings of NAcSh medium spiny neurons (MSN) in brain slices demonstrated that physiological concentrations of acetic acid (2 mM and 4 mM) increased NAcSh MSN excitability in both sexes. N -methyl- D -aspartate receptor (NMDAR) antagonists, AP5 and memantine, robustly attenuated the acetic acid-induced increase in excitability. Acetic acid-induced NMDAR-dependent inward currents were greater in females compared to males and were not estrous cycle dependent. These findings suggest a novel NMDAR-dependent mechanism by which the ethanol metabolite, acetic acid, may influence neurophysiological effects in a key reward circuit in the brain from ethanol consumption. Furthermore, these findings also highlight a specific sex-dependent sensitivity in females to acetic acid-NMDAR interactions. This may underlie their more rapid advancement to alcohol use disorder and increased risk of alcohol related neurodegeneration compared to males.

ABSTRACT Cocaine-induced plasticity in the nucleus accumbens shell of males occurs primarily in D1 dopamine receptor expressing neurons (D1-MSNs), with little if any impact on D2 dopamine receptor neurons (D2-MSNs). Using ex vivo whole cell recordings in male and female mice, we observe alterations in D1-MSN excitability across the estrous cycle similar in magnitude to the actions of cocaine in males. Furthermore, cocaine shifts estrous cycle-dependent plasticity from intrinsic excitability changes in D1-MSNs to D2-MSNs. Overall, while there are similar cocaine-induced disparities regarding the relative excitability of D1-MSN versus D2-MSN between the sexes, in males this is mediated through reduced D1-MSN excitability, whereas in females it is due to heightened D2-MSN excitability.

Background The nucleus accumbens (NAc) is an important region in motivation and reward. Glutamatergic inputs from the infralimbic cortex (ILC) to the shell region of the NAc (NAcSh) have been implicated in driving the motivation to seek reward through repeated action-based behavior. While this has primarily been studied in males, observed sex differences in motivational circuitry and behavior suggest that females may be more sensitive to rewarding stimuli. These differences have been implicated for the observed vulnerability in women to substance use disorders. Methods We used an optogenetic self-stimulation task in addition to ex vivo electrophysiological recordings of NAcSh neurons in mouse brain slices to investigate potential sex differences in ILC-NAcSh circuitry in reward-seeking behavior. Glutamatergic neurons in the ILC were infected with an AAV delivering DNA encoding for channelrhodopsin. Entering the designated active corner of an open field arena resulted in photostimulation of the ILC terminals in the NAcSh. Self-stimulation occurred during two consecutive days of testing over three consecutive weeks: first for 10 Hz, then 20 Hz, then 30 Hz. Whole-cell recordings of medium spiny neurons in the NAcSh assessed both optogenetically evoked local field potentials and intrinsic excitability. Results Although both sexes learned to seek the active zone, within the first day, females entered the zone more than males, resulting in a greater amount of photostimulation. Increasing the frequency of optogenetic stimulation amplified female reward-seeking behavior. Males were less sensitive to ILC stimulation, with higher frequencies and repeated days required to increase male reward-seeking behavior. Unexpectedly, ex vivo optogenetic local field potentials in the NAcSh were greater in slices from male animals. In contrast, female medium-spiny neurons (MSNs) displayed significantly greater intrinsic neuronal excitability. Conclusions Taken together, these data indicate that there are sex differences in the motivated behavior driven by glutamate within the ILC-NAcSh circuit. Though glutamatergic signaling was greater in males, heightened intrinsic excitability in females appears to drive this sex difference.

The nucleus accumbens shell (NAcSh) is critically important for reward valuations, yet it remains unclear how valuation information is integrated in this region to drive behaviour during reinforcement learning. Using an optogenetic spatial self-stimulation task in mice, here we show that contingent activation of different excitatory inputs to the NAcSh change expression of different reward-related behaviours. Our data indicate that medial prefrontal inputs support place preference via repeated actions, ventral hippocampal inputs consistently promote place preferences, basolateral amygdala inputs produce modest place preferences but as a byproduct of increased sensitivity to time investments, and paraventricular inputs reduce place preferences yet do not produce full avoidance behaviour. These findings suggest that each excitatory input provides distinct information to the NAcSh, and we propose that this reflects the reinforcement of different credit assignment functions. Our finding of a quadruple dissociation of NAcSh input-specific behaviours provides insights into how types of information carried by distinct inputs to the NAcSh could be integrated to help drive reinforcement learning and situationally appropriate behavioural responses.

OBJECTIVE:Although previous studies have discussed the promise of deep brain stimulation (DBS) as a possible treatment for substance use disorders (SUDs) and collected researcher perspectives on possible ethical issues surrounding it, none have consulted people with SUDs themselves. We addressed this gap by interviewing people with SUDs.METHODS:Participants viewed a short video introducing DBS, followed by a 1.5-hour semistructured interview on their experiences with SUDs and their perspective on DBS as a possible treatment option. Interviews were analyzed by multiple coders who iteratively identified salient themes.RESULTS:We interviewed 20 people in 12-step-based, inpatient treatment programs (10 [50%] White/Caucasian, 7 Black/African American [35%], 2 Asian [10%], 1 Hispanic/Latino [5%], and 1 [5%] Alaska Native/American Indian; 9 women [45%], 11 men [55%]). Interviewees described a variety of barriers they currently faced through the course of their disease that mirrored barriers often associated with DBS (stigma, invasiveness, maintenance burdens, privacy risks) and thus made them more open to the possibility of DBS as a future treatment option.CONCLUSIONS:Individuals with SUDs gave relatively less weight to surgical risks and clinical burdens associated with DBS than previous surveys of provider attitudes anticipated. These differences derived largely from their experiences living with an often-fatal disease and encountering limitations of current treatment options. These findings support the study of DBS as a treatment option for SUDs, with extensive input from people with SUDs and advocates.

Introduction: Preclinical literature, frequently utilizing rats, suggests females display a more rapid advancement of substance abuse and a greater risk of relapse following drug abstinence. In clinical populations, it is less clear as to what extent biological sex is a defining variable in the acquisition and maintenance of substance use. Even without considering environmental experiences, genetic factors are presumed to critically influence the vulnerability to addiction. Genetically diverse mouse models provide a robust tool to examine the interactions between genetic background and sex differences in substance abuse. Methods: We explored mouse strain variability in male versus female behavioral sensitization to cocaine. Locomotor sensitization was observed following 5 consecutive days of subcutaneous cocaine across three genetically different mice strains: C57BL/6J, B6129SF2/J, and Diversity Outbred (DO/J). Results: Sex differences in cocaine locomotor sensitization were dependent on mouse strain. Specifically, we observed opposing sex differences in locomotor sensitization, with male C57BL/6J and female B6129SF2/J mice displaying heightened activity compared to their opposite sex counterparts. Conversely, no sex differences were observed in the DO/J mice. Acute cocaine administration resulted in locomotor differences across strains in male, but not female, mice. The magnitude of sensitization (or lack thereof) also varied by genetic background. Conclusions: While sex differences in drug addiction may be observed, these effects can be mitigated, or even reversed, depending on genetic background. The clinical implications are that in the absence of understanding the genetic variables underlying vulnerability to addiction, sex provides little information regarding the predisposition of an individual to drug abuse.

Background and Aims: Deep brain stimulation (DBS) has shown promise as a treatment option for substance use disorders (SUDs), but may have unique ethical risks due to stigma and other factors. Previous studies have elicited researcher and clinician opinions on those risks, but none have studied perspectives of people living with SUDs. Methods: Participants were recruited through a national inpatient treatment network employing purposive sampling for representation of minoritized groups and diversity of substances. Participants viewed a short video introducing DBS, followed by a 1.5 hour semi-structured interview on their experiences with SUDs and their perspectives on DBS as a future treatment option. Interviews were analyzed by multiple coders who iteratively identified salient themes. Results: We interviewed 20 people in 12-step based, inpatient treatment programs (10 [50%] white/Caucasian, 7 Black/African American [35%], 2 Asian [10%], 1 Hispanic/Latino [5%], and 1 [5%] Alaska Native/American Indian; 11 [45%] women). Interviewees described a variety of barriers they currently faced through the course of their disease that mirrored barriers often associated with DBS (stigma, invasiveness, maintenance burdens, privacy risks). The majority of respondents expressed interest in DBS as a future treatment option, emphasizing the importance of exploring novel treatment options and keeping individual treatment goals as key guiding considerations. Conclusions: The perspectives of people with lived experience of SUDs contrasted with previous surveys of provider attitudes on DBS for SUDs. Individuals with SUDs gave relatively less weight to surgical risks and clinical burdens associated with DBS. These differences derived largely from their experiences living with an often-fatal disease, encountering limitations of current treatment options, and their familiarity with 12-step treatment paradigms that prioritize having multiple therapeutic tools. These findings support the study of DBS as a treatment option for SUDs, with extensive input from people with SUDs and advocates.

Sunk cost sensitivity describes escalating decision commitment with increased spent resources. On neuroeconomic foraging tasks, mice, rats, and humans show similar escalations from sunk costs while quitting an ongoing countdown to reward. In a new analysis taken across computationally parallel foraging tasks across species and laboratories, we find that these behaviors primarily occur on choices that are economically inconsistent with the subject's other choices, and that they reflect not only the time spent, but also the time remaining, suggesting that these are change-of-mind re-evaluation processes. Using a recently proposed change-of-mind drift-diffusion model, we find that the sunk cost sensitivity in this model arises from decision-processes that directly take into account the time spent (costs sunk). Applying these new insights to experimental data, we find that sensitivity to sunk costs during re-evaluation decisions depends on the information provided to the subject about the time spent and the time remaining.

Although ethanol consumption leads to an array of neurophysiological alterations involving the neural circuits for reward, the underlying mechanisms remain unclear. Acetic acid is a major metabolite of ethanol with high bioactivity and potentially significant pharmacological importance in regulating brain function. Yet, the impact of acetic acid on reward circuit function has not been well explored. Given the rewarding properties associated with ethanol consumption, we investigated the acute effects of ethanol and/or acetic acid on the neurophysiological function of medium spiny neurons of the nucleus accumbens shell, a key node in the mammalian reward circuit. We find that acetic acid, but not ethanol, provided a rapid and robust boost in neuronal excitability at physiologically relevant concentrations, whereas both compounds enhanced glutamatergic synaptic activity. These effects were consistent across both sexes in C57BL/6J mice. Overall, our data suggest acetic acid is a promising candidate mediator for ethanol effects on mood and motivation that deserves further investigation.NEW & NOTEWORTHY Ethanol consumption disrupts many neurophysiological processes leading to alterations in behavior and physiological function. The possible involvement of acetic acid, produced via ethanol metabolism, has been insufficiently explored. Here, we demonstrate that acetic acid contributes to rapid neurophysiological alterations in the accumbens shell. These findings raise the interesting possibility that ethanol may serve as a prodrug-generating acetic acid as a metabolite-that may influence ethanol consumption-associated behaviors and physiological responses by altering neurophysiological function.

A central question in aging and Alzheimer’s disease (AD) is when and how neural substrates underlying decision-making are altered. Here we show that while APP mice, a commonly used mouse model of AD, were able to learn Restaurant Row, a complex neuroeconomic decision-making task, they were significantly impaired in procedural, habit-forming, aspects of cognition and relied heavily on deliberation when making decisions. Surprisingly, these behavioral changes are associated with amyloid-beta (Aβ) pathology and network remodeling in the striatum, a key brain region involved in procedural cognition. Furthermore, APP mice and control mice relied on distinct sex-specific strategies in this neuroeconomic task. These findings provide foundational pillars to examine how aging and age-related neurodegenerative diseases impact decision-making across sexes. They also highlight the need for complex behavioral tasks that allow for the dissociation of competing neurally-distinct decision-making circuits to get an accurate picture of changes in neurodegenerative models of human disease.

In a recent bioRxiv preprint, Ott et al. argue that sensitivities to sunk costs that have been reported in two serial foraging tasks (the Restaurant Row task in mice and rats, and the Web-Surf task in humans) may be due to simple consequences of the way that subjects perform these tasks and not due to an actual sensitivity to sunk costs. However, several variants of these tasks have been studied, in which the sensitivity to sunk costs changes. In order to test the Ott et al. model against these experimental observations, we simulated the model under these additional experimental conditions. We find that it is incompatible with the actual data. While we applaud the simplicity of the Ott et al. model, we must reject it as an explanation for the observed sensitivity to sunk costs seen in these tasks. We thus conclude that the alternative explanation - that mice, rats, and humans are sensitive to actual sunk costs in these tasks - is a better explanation for the data.

OBJECTIVES/GOALS: Decision-making impairments in addiction can arise from dysfunction in distinct neural circuits. Such processes can be dissociated by measuring complex, computationally distinct behaviors within an economic framework. We aim to characterize computational changes conserved across models of addiction. METHODS/STUDY POPULATION: We used neuroeconomic tasks capable of dissociating neurally separable decision processes using behavioral analyses equally applicable to humans and rodents. We tested 12 human cocaine-users and 9 healthy controls on the Web-Surf task designed to match the rodent Restaurant Row task on which 27 mice were trained and then exposed to saline (n = 10), cocaine (n = 7), or morphine (n = 10). All subjects foraged for rewards (humans: entertaining videos; mice: food) of varying costs (1-30s delays) and subjective value (humans: genres; mice: flavors) by making serial accept or reject decisions while on a limited time budget, balancing the utility of wanting desirable rewards despite conflicting costs. RESULTS/ANTICIPATED RESULTS: When encountering unique offers for rewards with a delay above one’s willingness to wait, cocaine-treated mice like cocaine-exposed humans were less likely to appropriately reject economically disadvantageous offers. Furthermore, these mice and humans did so despite spending more time deliberating between future options. In contrast, morphine-treated mice displayed distinct impairments when given the opportunity to correct past mistakes, a process we previously demonstrated was uniquely sensitive to alterations in strength of synaptic connectivity of the infralimbic-accumbens shell circuit in mice. We anticipate human opioid-users will mirror these latter, computationally distinct findings. DISCUSSION/SIGNIFICANCE OF IMPACT: These data elucidate facets of addiction shared across species yet fundamentally distinct between disease subtypes. Our translational approach can help shed light on conserved pathophysiological mechanisms in order to identify novel diagnostic parameters and computational targets for intervention.