Utilization of long-acting injectable monthly depot buprenorphine for opioid use disorder (OUD) in Kentucky, before and after COVID-19 related buprenorphine access policy changes.

INTRODUCTION: Long-acting injectable buprenorphine (LAI-bup) formulations have advantages over transmucosal buprenorphine (TM-bup), but barriers may limit their utilization. Several policies shifted during the COVID-19 pandemic to promote buprenorphine access. The federal government expanded telemedicine treatment for opioid use disorder and Kentucky (KY) Medicaid lifted prior authorization requirements (PAs) for LAI-bup (i.e., Sublocade®). This retrospective cohort study evaluated changes in LAI-bup access, utilization, and retention before and after these policy changes in KY. METHODS: Individual-level TM-bup and LAI-bup dispensing record data from KY's prescription drug monitoring program examined LAI-bup utilization and retention, without a >30-day gap in coverage, for patients starting a new episode of LAI-bup treatment. Two key time periods were examined: pre-policy changes (Apr 1, 2019 - Dec 31, 2019) and post-policy changes (Apr 1, 2020 - Dec 31, 2020). Data on PA requests among Medicaid managed care organizations and availability of LAI-bup Risk Evaluation and Mitigation Strategy (REMS)-certified pharmacies were also obtained. A multivariable Cox proportional hazard regression model analysis compared pre- versus post-policy period treatment discontinuation. RESULTS: The number of patients initiating LAI-bup increased from 211 to 481 over the two periods. By the end of the post-policy period, 24.3 % of eligible patients were retained on LAI-bup, versus 12.5 % in the pre-policy change period. The adjusted hazard ratio, comparing discontinuation during the post- versus pre-policy change periods, was 0.70 (95 % confidence interval: 0.55-0.89). There were also more REMS-certified pharmacies and providers in the post-policy change period. CONCLUSIONS: LAI-bup access, utilization, and retention increased after several policy changes.

Telemedicine Buprenorphine Initiation and Retention in Opioid Use Disorder Treatment for Medicaid Enrollees.

Importance: Early COVID-19 mitigation strategies placed an additional burden on individuals seeking care for opioid use disorder (OUD). Telemedicine provided a way to initiate and maintain transmucosal buprenorphine treatment of OUD. Objective: To examine associations between transmucosal buprenorphine OUD treatment modality (telemedicine vs traditional) during the COVID-19 public health emergency and the health outcomes of treatment retention and opioid-related nonfatal overdose. Design, Setting, and Participants: This retrospective cohort study was conducted using Medicaid claims and enrollment data from November 1, 2019, to December 31, 2020, for individuals aged 18 to 64 years from Kentucky and Ohio. Data were collected and analyzed in June 2022, with data updated during revision in August 2023. Exposures: The primary exposure of interest was the modality of the transmucosal buprenorphine OUD treatment initiation. Relevant patient demographic and comorbidity characteristics were included in regression models. Main Outcomes and Measures: There were 2 main outcomes of interest: retention in treatment after initiation and opioid-related nonfatal overdose after initiation. For outcomes measured after initiation, a 90-day follow-up period was used. The main analysis used a new-user study design; transmucosal buprenorphine OUD treatment initiation was defined as initiation after more than a 60-day gap in buprenorphine treatment. In addition, uptake of telemedicine for buprenorphine was examined, overall and within patients initiating treatment, across quarters in 2020. Results: This study included 41 266 individuals in Kentucky (21 269 women [51.5%]; mean [SD] age, 37.9 [9.0] years) and 50 648 individuals in Ohio (26 425 women [52.2%]; mean [SD] age, 37.1 [9.3] years) who received buprenorphine in 2020, with 18 250 and 24 741 people initiating buprenorphine in Kentucky and Ohio, respectively. Telemedicine buprenorphine initiations increased sharply at the beginning of 2020. Compared with nontelemedicine initiation, telemedicine initiation was associated with better odds of 90-day retention with buprenorphine in both states (Kentucky: adjusted odds ratio, 1.13 [95% CI, 1.01-1.27]; Ohio: adjusted odds ratio, 1.19 [95% CI, 1.06-1.32]) in a regression analysis adjusting for patient demographic and comorbidity characteristics. Telemedicine initiation was not associated with opioid-related nonfatal overdose (Kentucky: adjusted odds ratio, 0.89 [95% CI, 0.56-1.40]; Ohio: adjusted odds ratio, 1.08 [95% CI, 0.83-1.41]). Conclusions and Relevance: In this cohort study of Medicaid enrollees receiving buprenorphine for OUD, telemedicine buprenorphine initiation was associated with retention in treatment early during the COVID-19 pandemic. These findings add to the literature demonstrating positive outcomes associated with the use of telemedicine for treatment of OUD.

Contributions of a central registry to monitor methadone -treatment through the HEALing Communities Study.

OBJECTIVE: To describe the process of establishing a Methadone Central Registry (MCR) as part of the HEALing (Helping to End Addiction Long-termSM) Communities Study (HCS) and to support recommendations with evidence of its functionality relative to Medicaid claims data for monitoring utilization of methadone, an evidence-based treatment for opioid use disorder. DESIGN AND PARTICIPANTS: The manuscript authors were active participants in establishing the MCR and include representation from state government, Opioid Treatment Programs (OTPs), and HCS university partners. Secondary data were obtained from Kentucky's (KY's) MCR and Medicaid claims from July 2020 through June 2021. The functionality of data obtained from the MCR, as measured by data completeness and timeliness, is compared with Medicaid claims, the current standard. MAIN OUTCOMES: Central registry and Medicaid data were each aggregated statewide and at the HCS-KY county level. Dual levels of analysis were selected to inform stakeholders at the study and state levels. Descriptive statistics were calculated for the number of patients in methadone treatment. RESULTS: Statewide, the MCR provided a daily record of all individuals receiving methadone through an OTP within 72 hours. In contrast, Medicaid claims processing lagged 9 months and captured 57-62 percent of patients in the MCR. CONCLUSIONS: Replacing a fax-based system, an MCR meets the converging need of providers, regulatory authorities, and researchers to monitor utilization, patient dual enrollment, and treatment outcomes. Implementation strategies included key stakeholder engagement, state partner leadership, training, and federal funding. Adoption of an MCR is recommended.

Trends in Use of Medication to Treat Opioid Use Disorder During the COVID-19 Pandemic in 10 State Medicaid Programs.

Importance: Federal and state agencies granted temporary regulatory waivers to prevent disruptions in access to medication for opioid use disorder (MOUD) during the COVID-19 pandemic, including expanding access to telehealth for MOUD. Little is known about changes in MOUD receipt and initiation among Medicaid enrollees during the pandemic. Objectives: To examine changes in receipt of any MOUD, initiation of MOUD (in-person vs telehealth), and the proportion of days covered (PDC) with MOUD after initiation from before to after declaration of the COVID-19 public health emergency (PHE). Design, Setting, and Participants: This serial cross-sectional study included Medicaid enrollees aged 18 to 64 years in 10 states from May 2019 through December 2020. Analyses were conducted from January through March 2022. Exposures: Ten months before the COVID-19 PHE (May 2019 through February 2020) vs 10 months after the PHE was declared (March through December 2020). Main Outcomes and Measures: Primary outcomes included receipt of any MOUD and outpatient initiation of MOUD via prescriptions and office- or facility-based administrations. Secondary outcomes included in-person vs telehealth MOUD initiation and PDC with MOUD after initiation. Results: Among a total of 8 167 497 Medicaid enrollees before the PHE and 8 181 144 after the PHE, 58.6% were female in both periods and most enrollees were aged 21 to 34 years (40.1% before the PHE; 40.7% after the PHE). Monthly rates of MOUD initiation, representing 7% to 10% of all MOUD receipt, decreased immediately after the PHE primarily due to reductions in in-person initiations (from 231.3 per 100 000 enrollees in March 2020 to 171.8 per 100 000 enrollees in April 2020) that were partially offset by increases in telehealth initiations (from 5.6 per 100 000 enrollees in March 2020 to 21.1 per 100 000 enrollees in April 2020). Mean monthly PDC with MOUD in the 90 days after initiation decreased after the PHE (from 64.5% in March 2020 to 59.5% in September 2020). In adjusted analyses, there was no immediate change (odds ratio [OR], 1.01; 95% CI, 1.00-1.01) or change in the trend (OR, 1.00; 95% CI, 1.00-1.01) in the likelihood of receipt of any MOUD after the PHE compared with before the PHE. There was an immediate decrease in the likelihood of outpatient MOUD initiation (OR, 0.90; 95% CI, 0.85-0.96) and no change in the trend in the likelihood of outpatient MOUD initiation (OR, 0.99; 95% CI, 0.98-1.00) after the PHE compared with before the PHE. Conclusions and Relevance: In this cross-sectional study of Medicaid enrollees, the likelihood of receipt of any MOUD was stable from May 2019 through December 2020 despite concerns about potential COVID-19 pandemic-related disruptions in care. However, immediately after the PHE was declared, there was a reduction in overall MOUD initiations, including a reduction in in-person MOUD initiations that was only partially offset by increased use of telehealth.

Prenatal syphilis screening among pregnant Medicaid enrollees by sexually transmitted infection history as well as race and ethnicity.

BACKGROUND: Congenital syphilis can cause severe morbidity, including miscarriage and stillbirth, and rates are increasing rapidly within the United States. However, congenital syphilis can be prevented with early detection and treatment of syphilis during pregnancy. Current screening recommendations propose that all women should be screened early in pregnancy, whereas women with elevated risks for congenital syphilis should be screened again later in pregnancy. The rapid increase in congenital syphilis rates suggests that there are still gaps in prenatal syphilis screening. OBJECTIVE: This study aimed to examine associations between the odds of prenatal syphilis screening and sexually transmitted infection history or other patient characteristics across 3 states with elevated rates of congenital syphilis. STUDY DESIGN: We used the Medicaid claims data from Kentucky, Louisiana, and South Carolina for women with deliveries between 2017 and 2021. Within each state, we examined the log-odds of prenatal syphilis screening as a function of the mother's health history, demographic factors, and Medicaid enrollment history. Patient history was established using a 4-year lookback period of the Medicaid claims data; in state A, sexually transmitted infection surveillance data were used to improve the sexually transmitted infection history. RESULTS: The prenatal syphilis screening rates varied by state, ranging from 62.8% to 85.1% of deliveries to women without a recent history of sexually transmitted infections and from 78.1% to 91.1% of deliveries to women with a previous sexually transmitted infection. For the main outcome of syphilis screening at any time during pregnancy, deliveries associated with previous sexually transmitted infections had 1.09 to 1.37 times higher adjusted odds ratios of undergoing screening. Deliveries to women with continuous Medicaid coverage throughout the first trimester also had higher odds of syphilis screening at any time (adjusted odds ratio, 2.45-3.15). Among deliveries to women with a previous sexually transmitted infection, only 53.6% to 63.6% underwent first-trimester screening and this rate was still just 55.0% to 69.5% when considering only deliveries to women with a previous sexually transmitted infection and full first-trimester Medicaid coverage. Fewer delivering women underwent third-trimester screening (20.3%-55.8% of women with previous sexually transmitted infection). Compared with deliveries to White women, deliveries to Black women had lower odds of first-trimester screening (adjusted odds ratio, 0.85 in all states) but higher odds of third-trimester screening (adjusted odds ratio, 1.23-2.03), potentially impacting maternal and birth outcomes. For state A, linkage to surveillance data doubled the rate of detection of a previous sexually transmitted infection because 53.0% of deliveries by women with a previous sexually transmitted infection would not have had sexually transmitted infection history detected using Medicaid claims alone. CONCLUSION: A previous sexually transmitted infection and continuous preconception Medicaid enrollment were associated with higher rates of syphilis screening, but Medicaid claims alone do not fully capture the sexually transmitted infection history of patients. The overall screening rates were lower than would be expected given that all women should undergo prenatal screening, but the rates in the third trimester were particularly low. Of note, there are gaps in early screening for non-Hispanic Black women who had lower odds of first-trimester screening when compared with non-Hispanic White women despite being at elevated risk for syphilis.

Peer-induced cocaine seeking in rats: Comparison to nonsocial stimuli and role of paraventricular hypothalamic oxytocin neurons.

The purpose of this study was to determine if social vs nonsocial cues (peer vs light/tone) can serve as discriminative stimuli to reinstate cocaine seeking. In addition, to assess a potential mechanism, an oxytocin (OT) promoter-linked hM3Dq DREADD was infused into the paraventricular nucleus of the hypothalamus to determine whether peer-induced cocaine seeking is decreased by activation of OT neurons. Male rats underwent twice-daily self-administration sessions, once with cocaine in the presence of one peer (S+) and once with saline in the presence of a different peer (S-). Another experiment used similar procedures, except the discriminative stimuli were nonsocial (constant vs flashing light/tone), with one stimulus paired with cocaine (S+) and the other paired with saline (S-). A third experiment injected male and female rats with OTp-hM3Dq DREADD or control virus into PVN and tested them for peer-induced reinstatement of cocaine seeking following clozapine (0.1 mg/kg). Although acquisition of cocaine self-administration was similar in rats trained with either peer or light/tone discriminative stimuli, the latency to first response was reduced by the peer S+, but not by the light/tone S+. In addition, the effect of the conditioned stimulus was overshadowed by the peer S+ but not by the light/tone S+. Clozapine blocked the effect of the peer S+ in rats receiving the OTp-hM3Dq DREADD virus, but not in rats receiving the control virus. These results demonstrate that a social peer can serve as potent trigger for drug seeking and that OT in PVN modulates peer-induced reinstatement of cocaine seeking.

Effects of the glucocorticoid receptor antagonist PT150 on stress-induced fentanyl seeking in male and female rats.

RATIONALE: Opioid use disorder (OUD) is highly comorbid with stress-related disorders, and stress can serve as a trigger for reinstatement of drug seeking. Glucocorticoid receptor (GR) antagonists such as mifepristone (RU-486) may be effective against stress-induced drug seeking. In the current study, PT150 (formerly ORG-34517), a more selective GR antagonist, was tested using two models of stress-induced drug seeking, namely footshock and yohimbine. METHODS: Adult male and female Sprague-Dawley rats were trained to self-administer fentanyl (2.5 µg/kg/infusion, i.v.) in a model of escalation. Rats then received 7 days of abstinence, followed by extinction; PT150 (0, 50 or 100 mg/kg in Nutella®; p.o.) treatment started on the first day of extinction training and continued daily until the end of the study. Following 14 days of extinction, rats were tested for reinstatement following footshock and yohimbine (0, 1, or 2 mg/kg; i.p.), tested in counterbalanced order; PT150 or placebo treatment occurred prior to each extinction and reinstatement session. RESULTS: Prior to initiation of PT150 treatment, females self-administered greater levels of fentanyl during 1-h sessions compared to males; however, when switched to 6-h sessions, males and females self-administered similar levels of fentanyl and showed a similar escalation of intake over time. PT150 had no effect on extinction of self-administration. While both footshock and yohimbine reinstated fentanyl seeking, only footshock-induced reinstatement was decreased by PT150 (50 and 100 mg/kg). The effect of PT150 on footshock-induced reinstatement was driven primarily by males. CONCLUSION: The glucocorticoid antagonist PT150 reduces shock-induced fentanyl seeking, suggesting it may be effective against stress-induced relapse, although the sex difference in response may need further exploration.

Escalation and reinstatement of fentanyl self-administration in male and female rats.

RATIONALE: Escalation of drug intake and craving are two DSM-5 hallmark symptoms of opioid use disorder (OUD). OBJECTIVES: This study determined if escalation of intake as modeled by long access (LgA) self-administration (SA) and craving measured by reinstatement are related. METHODS: Adult male and female Sprague-Dawley rats were trained to self-administer fentanyl across 7 daily 1-h short access (ShA) sessions, followed by 21 SA sessions of either 1- or 6-h duration (ShA or LgA). Following 14 1-h extinction sessions, Experiment 1 assessed reinstatement induced by either fentanyl (10 or 30 µg/kg) or yohimbine (1 or 2 mg/kg), and Experiment 2 assessed reinstatement induced by a drug-associated cue light. RESULTS: Females acquired fentanyl SA faster than males. When shifted to LgA sessions, LgA rats escalated fentanyl intake, but ShA rats did not; no reliable sex difference in the rate of escalation was observed. In extinction, compared to ShA rats, LgA rats initially responded less and showed less decay of responding across sessions. A priming injection of fentanyl induced reinstatement, with LgA rats reinstating more than ShA rats at the 30 µg/kg dose. Yohimbine (1 mg/kg) also induced reinstatement, but there was no effect of access group or sex. With cue-induced reinstatement, LgA females reinstated less than LgA males and ShA females. CONCLUSION: Among the different reinstatement tests assessed, escalation of fentanyl SA increased only drug-primed reinstatement, suggesting a limited relationship between escalation of drug intake and craving (reinstatement) for OUD.

Effect of early life social adversity on drug abuse vulnerability: Focus on corticotropin-releasing factor and oxytocin.

Early life adversity can set the trajectory for later psychiatric disorders, including substance use disorders. There are a host of neurobiological factors that may play a role in the negative trajectory. The current review examines preclinical evidence suggesting that early life adversity specifically involving social factors (maternal separation, adolescent social isolation and adolescent social defeat) may influence drug abuse vulnerability by strengthening corticotropin-releasing factor (CRF) systems and weakening oxytocin (OT) systems. In adulthood, pharmacological and genetic evidence indicates that both CRF and OT systems are directly involved in drug reward processes. With early life adversity, numerous studies show an increase in drug abuse vulnerability measured in adulthood, along a concomitant strengthening of CRF systems and a weakening of OT systems. Mechanistic studies, while relatively few in number, are generally consistent with the theme that strengthened CRF systems and weakened OT systems mediate, at least in part, the link between early life adversity and drug abuse vulnerability. Establishing a direct role of CRF and OT in mediating the relation between early life social stressors and drug abuse vulnerability will inform clinical researchers and practitioners toward the development of intervention strategies to reduce risk among those suffering from early life adversities. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Effect of a social peer on risky decision making in male Sprague Dawley rats.

Adolescence is a period associated with increased risk taking and peer relations. Research has shown that age is correlated with vulnerability to peer pressure, with youth being more influenced by peers compared with adults, leading to exacerbated risk taking, including risk for drug abuse. Preclinical research suggests that these findings may also be applicable to rodents, as younger rats find social interaction rewarding and are prone to risky behavior. However, there is little research on the effect of social interaction on rodent models of risky decision making. This study examined risky decision making utilizing a dual-compartment apparatus that consisted of two adjacent operant conditioning chambers separated by a wire mesh screen partition that allowed for limited social interaction. Male rats performed a risky decision making task in which they had a choice between a small reinforcer and larger reinforcer that was associated with a mild footshock, which increased in probability across the session. Rats were initially trained during adolescence and performance on the task was assessed in the presence or absence of a peer in the adjacent chamber during young adulthood. Results revealed that there was less risk discounting, leading to greater preference for the larger, risky reinforcer, in rats that had daily exposure to a social peer during training. These results provide evidence that social influence on risk taking can be modeled in rats, perhaps having implications for drug abuse risk. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Changes in fentanyl demand following naltrexone, morphine, and buprenorphine in male rats.

BACKGROUND: Individuals with opioid use disorder (OUD) exhibit high levels of economic demand for opioids, with high levels of consumption and relative insensitivity to changes in price. Because the medications used to treat OUD in medication-assisted therapy (MAT) act as antagonists or agonists at µ opioid receptors, they may alter the relationship between price and opioid intake. METHODS: This study examined demand for a commonly abused synthetic prescription opioid, fentanyl, in male rats following s.c. pre-treatment with naltrexone (0.1-1.0 mg/kg), morphine (0.3-3.0 mg/kg) or buprenorphine (0.3-3.0 mg/kg). We normalized demand curves to intake at the lowest price and estimated effects on elasticity (sensitivity to changes in price). Rats were first trained to earn fentanyl (5 µg/kg/infusion) on a fixed ratio schedule, then they underwent daily training under a threshold procedure designed to produce within-session demand curve estimates. Rats received 14 threshold sessions before undergoing a series of tests encompassing each drug, at each dose. RESULTS: Elasticity was increased by pretreatment with naltrexone, morphine or buprenorphine. Morphine also decreased initial intake, when the price for fentanyl was lowest. In contrast, initial intake was increased by naltrexone (according to an inverted-U shaped curve). The effects of naltrexone did not persist after the test session, but morphine and buprenorphine continued affecting demand elasticity 24 h or 48 h after the test, respectively. CONCLUSIONS: These results indicate that fentanyl demand is sensitive to blockade or activation of opioid receptors by the drug classes used for MAT in humans.

Adolescent impulsivity as a sex-dependent and subtype-dependent predictor of impulsivity, alcohol drinking and dopamine D2 receptor expression in adult rats.

Impulsivity is a personality trait associated with a heightened risk for drug use and other psychiatric conditions. Because impulsivity-related disorders typically emerge during adolescence, there has been interest in exploring methods for identifying adolescents that will be at risk to develop substance use disorders in adulthood. Here, we used a rodent model to assess inhibitory control (impulsive action) and impulsive decision making (impulsive choice) during adolescence (43-50 days old) or adulthood (93-100 days old) and then examined the impact of development on these impulsivity traits by re-testing rats 50 days later. Impulsive action was not stable from adolescence to adulthood in male rats and was lowest in adult male rats, relative to adolescents and female rats. Impulsive choice was stable across development and unaffected by age or sex. Next, we examined the connection between our model of impulsivity and two measures relevant to substance abuse research: the initiation of voluntary alcohol drinking and dopamine D2 receptor (D2 R) expression in the prelimbic prefrontal cortex. Consumption of saccharin-sweetened ethanol during 30-minute sessions in adulthood was associated with adolescent, but not adult, impulsive action, particularly in male rats. Prelimbic D2 R expression was reduced in individuals with high levels of impulsive choice, and this relationship appeared to be strongest among female rats. The results of this study demonstrate that impulsive choice, along with its connection to D2 R expression, is relatively unchanged by the process of development. For impulsive action, however, individual levels of impulsivity during adolescence predict drinking in adulthood despite changes in the measure during development.

Social reinstatement: a rat model of peer-induced relapse.

BACKGROUND: An important factor that can lead to drug relapse is to re-associate with drug-using social peers, but there is little literature on the effect of social peers on relapse in animal models. METHODS: The current study used a dual-compartment operant conditioning apparatus that allowed adult male rats to respond for cocaine in the presence of a conspecific. In experiment 1, rats were trained to self-administer cocaine in the presence of a social peer that was separated by a wire screen partition and then that peer was used as a reinstatement cue following a period of extinction. In the next experiments, rats were trained on alternating sessions to self-administer cocaine in the presence of one peer and to self-administer saline in the presence of a different peer using either a single-active lever procedure (experiment 2) or a double-active lever procedure (experiment 3). Following extinction of responding in the absence of the peers, the effect of re-exposure to the cocaine- and saline-associated peers on reinstatement of drug seeking was determined. This was tested using both single- and double-active lever procedures. RESULTS: In experiment 1, a peer that was present throughout cocaine self-administration was able to reinstate cocaine seeking following a period of extinction. In experiments 2 and 3, drug seeking was reinstated by the cocaine-associated peer (S+), but not the saline-associated peer (S-). This discrimination occurred when using either the single-active lever procedure or double-active lever procedure. CONCLUSION: These results indicate that a social peer can be used as a discriminative stimulus to signal cocaine availability and that re-introduction of a peer previously paired with cocaine can reinstate cocaine seeking, confirming clinical reports that peer affiliation among abstinent cocaine users is an important determinant of relapse.

Effects of ß-hydroxy-ß-methyl butyrate on working memory and cognitive flexibility in an animal model of aging.

OBJECTIVES: Normal aging results in cognitive decline and nutritional interventions have been suggested as potential approaches for mitigating these deficits. Here, we used rats to investigate the effects of short- and long-term dietary supplementation with the leucine metabolite ß-hydroxy-ß-methyl butyrate (HMB) on working memory and cognitive flexibility. METHODS: Beginning ∼12 months of age, male and female Long-Evans rats were given twice daily access to sipper tubes containing calcium HMB (450 mg/kg) or vehicle (285 mg/kg calcium lactate) in a sucrose solution (20% w/v). Supplementation continued for 1 or 7 months (middle- and old-age (OA) groups, respectively) before testing began. Working memory was assessed by requiring rats to respond on a previously sampled lever following various delays. Cognitive flexibility was assessed by training rats to earn food according to a visual strategy and then, once acquired, shifting to an egocentric response strategy. RESULTS: Treatment with HMB improved working memory performance in middle-age (MA) males and OA rats of both sexes. In the cognitive flexibility task, there was a significant age-dependent deficit in acquisition of the visual strategy that was not apparent in OA males treated with HMB. Furthermore, HMB ameliorated an apparent deficit in visual strategy acquisition in MA females. DISCUSSION: Together, these findings suggest that daily nutritional supplementation with HMB facilitates learning and improves working memory performance. As such, HMB supplementation may mitigate age-related cognitive deficits and may therefore be an effective tool to combat this undesirable feature of the aging process.

Sex differences in behavior and neural development and their role in adolescent vulnerability to substance use.

Adolescents are especially prone to risky behavior and to the emergence of psychological disorders like substance abuse, anxiety and depression. However, there is a sex (or gender) difference in this vulnerability, with females being more prone to developing internalizing disorders and males being more likely to engage in risky behavior and drug use. While several researchers have proposed that there is a relationship between corticolimbic circuit development and adolescent vulnerability, the current proposed models do not take sex differences into account. In this review, we explore recent findings from both human and rodent studies of sex differences during adolescence. In particular, we consider epidemiological studies on the factors that contribute to the development of substance abuse and internalizing disorders, laboratory studies on reward-related and decision-making behavior, and neuroanatomical studies on the development of several structures in the corticolimbic circuit (i.e., prefrontal cortex [PFC], amygdala and striatum). We then integrate these recent findings into models of adolescent vulnerability to substance use that have previously not addressed sex differences. Lastly, we discuss methodological considerations for the interpretation and design of studies on sex (or gender) differences during adolescence while highlighting some opportunities for future investigations.

Effects of amphetamine exposure in adolescence or young adulthood on inhibitory control in adult male and female rats.

Heightened impulsivity is a feature of some psychiatric disorders, including addiction, that also have sex-specific patterns of expression. The relationship between addiction and impulsivity may be driven by drug-induced changes in behavior caused by long term adaptations in signaling within the medial prefrontal cortex (mPFC). Here, we used a response inhibition task that is sensitive to changes in mPFC function to examine the effects of sex and exposure to amphetamine (AMPH) on impulsive action and vigilance. We also examined drug-induced alterations in glutamatergic and dopaminergic signaling through challenge injections with the NMDA receptor antagonist MK-801 (dizocilpine) and AMPH. Male and female Sprague Dawley rats were injected (i.p.) with saline or 3 mg/kg AMPH every other day during adolescence (postnatal day (P) 27-45) or adulthood (P85-103). Starting on P125-135, rats were tested for their ability to lever press for a food reward during periods of signaled availability and withhold responding during a "premature response" phase. In experiment 1, rats received challenge injections (i.p.) of MK-801 and AMPH followed by tests of task performance and locomotor activity. In experiment 2, rats received intra-mPFC infusion of MK-801. We found that females had better inhibitory control and poorer vigilance than males and that AMPH exposure had both sex- and age-of-exposure dependent effects on impulsivity. Systemic drug challenges disrupted task performance, particularly in females, and increased impulsivity while intra-mPFC infusions had modest effects. AMPH exposure did not affect responses to drug challenges. Together, these results suggest that sex mediates both trait and drug-induced impulsivity.

Age and sex differences in reward behavior in adolescent and adult rats.

Compared to adults, adolescents are at heightened risk for drug abuse and dependence. One of the factors contributing to this vulnerability may be age-dependent differences in reward processing, with adolescents approaching reward through stimulus-directed, rather than goal-directed, processes. However, the empirical evidence for this in rodent models of adolescence, particularly those that investigate both sexes, is limited. To address this, male and female rats that were adolescents (P30) or adults (P98) at the start of the experiment were trained in a Pavlovian approach (PA) task and were subsequently tested for the effects of reward devaluation, extinction, and re-acquisition. We found significant interactions between age and sex: females had enhanced acquisition of PA and poorer extinction, relative to males, while adolescents and females were less sensitive to reward devaluation than male adults. These results suggest that females and adolescents exhibit reward behavior that is more stimulus-directed, rather than goal-directed.

Fos expression in response to dopamine D3-preferring phenylpiperazine drugs given with and without cocaine.

WC 44 and WC 10 are phenylpiperazines with low (23 fold) to moderate (42 fold) selectivity for dopamine D3 receptors (D3Rs) over D2Rs, respectively. WC 44 is a full D3R agonist in the forskolin-stimulated adenylyl cyclase (AC) assay, whereas WC 10 has little efficacy. In contrast to their opposite effects in the AC assay, these drugs often produce similar behavioral effects, suggesting that the AC assay does not predict the efficacy of these drugs in vivo. Here, we examined whether Fos protein expression induced by these drugs would be more consistent with their behavioral effects in vivo. Rats received either vehicle, WC 10 (5.6 mg/kg, i.p.), WC 44 (10.0 mg/kg, i.p), cocaine (10.0 mg/kg, i.p.), or cocaine with WC 10 (5.6 mg/kg, i.p.) or with WC 44 (10.0 mg/kg, i.p). Locomotion was monitored for 90 min and the brains were harvested for immunohistochemistry. Both WC 10 and WC 44 decreased spontaneous and cocaine-induced locomotion. Both compounds also increased Fos expression relative to saline in the dorsal striatum and nucleus accumbens core and shell, and relative to cocaine alone in the nucleus accumbens shell. The findings suggest that even though these compounds have different efficacy in the AC bioassy, they produce similar brain activation and attenuation of cocaine hyperlocomotion. Together with our previous research demonstrating that these compounds down-shift the cocaine self-administration dose-effect function, the findings support the idea that D3R-selective compounds may be useful for cocaine dependence medications development.