Dopamine neurons signal the salience of environmental stimuli, influencing learning and motivation. However, research has not yet identified whether dopamine neurons also modulate the salience of memory content. Dopamine neuron activity in the ventral tegmental area (VTA) increases in response to novel objects and diminishes as objects become familiar through repeated presentations. We proposed that the declined rate of dopamine neuron activity during familiarization affects the salience of a familiar object's memory. This, in turn, influences the degree to which an animal distinguishes between familiar and novel objects in a subsequent novel object recognition (NOR) test. As such, a single familiarization session may not sufficiently reduce dopamine activity, allowing the memory of a familiar object to maintain its salience and potentially attenuating NOR. In contrast, multiple familiarization sessions could lead to more pronounced dopamine activity suppression, strengthening NOR. Our data in mice reveals that, compared to a single session, multiple sessions result in decreased VTA dopamine neuron activation, as indicated by c-Fos measurements, and enhanced novelty discrimination. Critically, when VTA dopamine neurons are chemogenetically inhibited during a single familiarization session, NOR improves, mirroring the effects of multiple familiarization sessions. In summary, our findings highlight the pivotal function of dopamine neurons in familiarity and suggest a role in modulating the salience of memory content.

Background: Despite the existence of effective pharmacotherapies, rates of opioid use disorder and opioid overdose deaths have continued to increase. Emergency department (ED) visits provide an important opportunity to engage in treatment patients with untreated opioid use disorder (OUD). Case management implemented in other settings is effective in linking those with opioid and other drug use disorders to longer-term treatment, but research has not established its efficacy in the ED. Here we report the results of a trial of Strengths-Based Case Management (SBCM) for people with untreated OUD who are identified during ED visits, with the primary goal of linking them to pharmacologic treatment. Methods: The study identified patients with untreated OUD during a treatment episode at a large urban ED. The study randomly assigned three hundred participants in 1:1 ratio to receive SBCM or screening, assessment, and referral (SAR) to OUD treatment. Those assigned to SBCM received up to six sessions of SBCM with the primary goal of linkage to treatment. Primary outcomes were initiation of treatment and engagement in pharmacotherapy for OUD. The study defined a "successful outcome " for opioid use as a 3-month urine negative for illicit opioids and no more than 2 days of self-reported opioid misuse in the 4 weeks prior to the 3-month interview. Results: Rates of treatment initiation were not significantly different in the SBCM and SAR groups (57.4% vs. 49.7%, respectively, p > 0.05), nor did engagement in pharmacotherapy differ significantly between groups (p > 0.05). During the 90 days following the index ED visit, SBCM and SAR participants engaged in pharmacotherapy for a mean of 21.8% (SD = 35.1%) versus 17.7% (SD = 31.0%) of days, respectively. Likewise, no significant difference occurred between groups in rates of "successful opioid use outcome " as defined a priori (p > 0.05), although self-reported opioid use over the entire 6-month follow-up period was lower in the SBCM group (10.8 vs. 13.4 days/month, p = 0.042). Conclusions: SBCM-ED did not improve OUD treatment initiation and engagement in this ED study. Although these findings do not necessarily generalize to all EDs, other approaches, such as direct referral or initiation of treatment in the ED, have considerable empirical support, and should be implemented where they are feasible.

Background As the USA grapples with an opioid epidemic, medical emergency departments (EDs) have become a critical setting for intervening with opioid-dependent patients. Brief interventions designed to bridge the gap from acute ED care to longer-term treatment have shown limited efficacy for this population. Strength-based case management (SBCM) has shown strong effects on treatment linkage among patients with substance use disorders in other healthcare settings. This study aimed to investigate whether SBCM is an effective model for linking opioid-dependent ED patients with addiction treatment and pharmacotherapy. Here, we describe the implementation and challenges of adapting SBCM for the ED (SBCM-ED). Study rationale, design, and baseline characteristics are also described. Methods This study compared the effects of SBCM-ED to screening, assessment, and referral alone (SAR) on treatment linkage, substance use, and functioning. We recruited participants from a public hospital in NYC. Working alliance between case managers and participants and the feasibility of SBCM implementation were evaluated. Baseline data from the randomized sample were analyzed for group equivalency. Outcomes analyses are forthcoming. Results Three hundred adult participants meeting DSM-IV criteria for opioid dependence were randomly assigned to either SBCM, in which they received a maximum of six case management sessions within 90 days of enrollment, or SAR, in which they received a comprehensive referral list and pamphlet outlining drug use consequences. No significant differences were found between groups at baseline on demographic or substance use characteristics. All SAR participants and 92.6% of SBCM-ED participants initiated their assigned intervention. Over half of SBCM-ED first sessions occurred in the ED on the day of enrollment. Case managers developed a strong working alliance with SBCM-ED participants after just one session. Conclusion Interventions that exceed SBIRT were accepted by an opioid-dependent patient population seen in an urban medical ED. At the time of study funding, this trial was one of the first to focus specifically on this population in this challenging setting. The successful implementation of SBCM demonstrates its adaptability to the ED and may serve as a potential model for EDs seeking to adopt an intervention that overcomes the barrier between the ED encounter and more intensive treatment. Trial registration ClinicalTrials.gov NCT02586896 . Registered on 27 October 2015.

Chronic food restriction potentiates behavioral and cellular responses to drugs of abuse and D-1 dopamine receptor agonists administered systemically or locally in the nucleus accumbens (NAc). However, the alterations in NAc synaptic transmission underlying these effects are incompletely understood. AMPA receptor trafficking is a major mechanism for regulating synaptic strength, and previous studies have shown that both sucrose and d-amphetamine rapidly alter the abundance of AMPA receptor subunits in the NAc postsynaptic density (PSD) in a manner that differs between food-restricted and adlibitum fed rats. In this study we examined whether food restriction, in the absence of reward stimulus challenge, alters AMPAR subunit abundance in the NAc PSD. Food restriction was found to increase surface expression and, specifically, PSD abundance, of GluA1 but not GluA2, suggesting synaptic incorporation of GluA2-lacking Ca2+-permeable AMPARs (CP-AMPARs). Naspm, an antagonist of CP-AMPARs, decreased the amplitude of evoked EPSCs in NAc shell, and blocked the enhanced locomotor response to local microinjection of the D-1 receptor agonist, SKF-82958, in food-restricted, but not adlibitum fed, subjects. Although microinjection of the D-2 receptor agonist, quinpirole, also induced greater locomotor activation in food-restricted than adlibitum fed rats, this effect was not decreased by Naspm. Taken together, the present findings are consistent with the synaptic incorporation of CP-AMPARs in D-1 receptor-expressing medium spiny neurons in NAc as a mechanistic underpinning of the enhanced responsiveness of food-restricted rats to natural rewards and drugs of abuse.

With respect to feeding, insulin is typically thought of as a satiety hormone, acting in the hypothalamus to limit ingestive behavior. However, accumulating evidence suggests that insulin also has the ability to alter dopamine release in the striatum and influence food preferences. With increased access to high calorie foods, Western societies have a high prevalence of obesity, accompanied by insulin insensitivity. Little is known about how insulin is trafficked into the brain following food consumption and whether insulin insensitivity in the periphery is mirrored in the central nervous system. We investigated insulin receptor activation in the ventral striatum of rats receiving water or 16% glucose either orally or intragastrically. We also investigated whether glucose-induced insulin receptor activation was altered in food-restricted (FR) or diet-induced obesity (OB) rat models. Lastly, we examined whether insulin plays a significant role in flavor-nutrient preference learning. Glucose intake stimulated a rapid increase in insulin receptor activity in the ventral striatum of FR and ad libitum (AL) fed rats, but not OB rats. Similarly, both AL and FR, but not OB rats demonstrated significant flavor-nutrient preferences. However AL rats receiving brief inhibition of insulin activity during conditioning failed to acquire a significant flavor-nutrient preference. These findings suggest that impaired insulin receptor activation in the ventral striatum may result in inaccurate valuation of nutritive foods, which could lead to overconsumption of food or the selection of foods that don't accurately meet the body's current physiological needs.

Weight-loss dieting often leads to loss of control, rebound weight gain, and is a risk factor for binge pathology. Based on findings that food restriction (FR) upregulates sucrose-induced trafficking of glutamatergic AMPA receptors to the nucleus accumbens (NAc) postsynaptic density (PSD), this study was an initial test of the hypothesis that episodic "breakthrough" intake of forbidden food during dieting interacts with upregulated mechanisms of synaptic plasticity to increase reward-driven feeding. Ad libitum (AL) fed and FR subjects consumed a limited amount of 10% sucrose, or had access to water, every other day for 10 occasions. Beginning three weeks after return of FR rats to AL feeding, when 24-h chow intake and rate of body weight gain had normalized, subjects with a history of sucrose intake during FR consumed more sucrose during a four week intermittent access protocol than the two AL groups and the group that had access to water during FR. In an experiment that substituted noncontingent administration of d-amphetamine for sucrose, FR subjects displayed an enhanced locomotor response during active FR but a blunted response, relative to AL subjects, during recovery from FR. This result suggests that the enduring increase in sucrose consumption is unlikely to be explained by residual enhancing effects of FR on dopamine signaling. In a biochemical experiment which paralleled the sucrose behavioral experiment, rats with a history of sucrose intake during FR displayed increased abundance of pSer845-GluA1, GluA2, and GluA3 in the NAc PSD relative to rats with a history of FR without sucrose access and rats that had been AL throughout, whether they had a history of episodic sucrose intake or not. A history of FR, with or without a history of sucrose intake, was associated with increased abundance of GluA1. A terminal 15-min bout of sucrose intake produced a further increase in pSer845-GluA1 and GluA2 in subjects with a history of sucrose intake during FR. Generally, neither a history of sucrose intake nor a terminal bout of sucrose intake affected AMPA receptor abundance in the NAc PSD of AL subjects. Together, these results are consistent with the hypothesis, but the functional contribution of increased synaptic incorporation of AMPA receptors remains to be established.