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Drug use is highly concordant among members of adolescent and young adult peer groups. One potential explanation for this observation is that drugs may increase the reinforcing effects of social contact, leading to greater motivation to establish and maintain contact with other members of the peer group. Several classes of drugs, particularly drugs that increase synaptic dopamine, increase the reinforcing effects of contextual stimuli, but the extent to which these drugs enhance the reinforcing effects of social contact is not known. The purpose of this study was to determine the extent to which drugs that increase synaptic dopamine, norepinephrine, and serotonin enhance the positive reinforcing effects of social contact. To this end, male and female Long-Evans rats were pretreated with acute doses of the selective dopamine reuptake inhibitor, WIN-35,428, the selective norepinephrine reuptake inhibitor, atomoxetine, the selective serotonin reuptake inhibitor, fluoxetine, the nonselective monoamine reuptake inhibitor, cocaine, and the nonselective monoamine releasers d-amphetamine and (±)-MDMA. Ten minutes later, the positive reinforcing effects of 30-s access to a same-sex social partner was examined on a progressive ratio schedule of reinforcement. To determine whether the reinforcement-altering effects of these drugs were specific to the social stimulus, the reinforcing effects of a nonsocial stimulus (30-s access to an athletic sock of similar size and coloring as another rat) was determined in control subjects. WIN-35,428, d-amphetamine, and cocaine, but not atomoxetine, fluoxetine, or MDMA, dose-dependently increased breakpoints maintained by a social partner under conditions in which responding maintained by a nonsocial stimulus was not affected. These data indicate that increases in extracellular dopamine, but not extracellular norepinephrine or serotonin, increases the positive reinforcing effects of social contact in both male and female rats. These data also provide support for the hypothesis that some drugs with high abuse liability increase the motivation to establish and maintain contact with social peers.

Boredom coping strategies were incorporated with control-value theory variables of control, value, boredom and academic performance to test an integrated model of the antecedents and effects of boredom experienced while studying among university students. A diverse sample of 177 Australian university students with a mean age of 29.64 years (SD = 10.03 years) completed an online survey for the study. Independently, students’ lower appraisals of value and control for their course of study were associated with higher experiences of boredom. Additionally, a conditional process analysis revealed dually moderated mediation where the interaction of control and value appraisals negatively predicted experience of boredom while studying, and the combination of higher boredom and a high tendency for behavioural avoidance coping was subsequently linked to lower academic performance. Practical implications for students and universities are discussed, as well as suggestions about future research to further extend our understanding in these important areas of research.

Drug-using peers are recognized as a leading factor influencing drug use among adolescents and young adults. One mechanism by which peers influence drug use is by providing social reinforcement for using drugs. Social reinforcement may be provided in multiple ways, including by making social contact contingent on drug use (i.e., an individual must use drugs to gain/maintain access to a peer). The purpose of this study was to develop a preclinical model in which intravenous cocaine self-administration was positively reinforced by access to a social partner. Young adult male rats were trained to self-administer cocaine in operant conditioning chambers with a guillotine door that could be opened to an adjacent compartment housing either a social partner or a non-social stimulus. Once cocaine self-administration was established, the guillotine door was activated, and cocaine intake was reinforced by brief access to either a social (age- and sex-matched peer) or non-social (black-and-white athletic sock) stimulus. Contingent access to a social partner rapidly increased cocaine self-administration. Total cocaine intake was 2- to 3-fold greater in rats assigned to the social versus non-social condition across a 100-fold dose range. Cocaine intake rapidly increased when rats in the original non-social group were later provided with social partners, whereas cocaine intake resisted change and remained elevated when rats in the original social group had their partners removed. These data indicate that contingent access to a social partner increases drug intake and suggest that social reinforcement may represent a vulnerability factor that is particularly resistant to psychosocial interventions.

RationalePrevious studies have shown that gonadal hormones influence opioid self-administration in female rodents, but very few studies have examined these effects in male rodents. ObjectivesThe purpose of this study was to examine the effects of chronic hormone treatment on intravenous heroin self-administration in gonadectomized male rats using both physiological and supraphysiological doses of testosterone, estradiol, or progesterone.MethodsGonadectomized male rats were surgically implanted with intravenous catheters and trained to self-administer heroin on a fixed ratio (FR1) schedule of reinforcement. Using a between-subjects design, rats were treated daily with testosterone (0.175 or 1.75 mg, sc), estradiol (0.0005 or 0.005 mg, sc), progesterone, (0.0125 or 0.125 mg, sc), or their vehicles. After 14 days of chronic treatment, a dose–effect curve was determined for heroin (0.0003—0.03 mg/kg/infusion) over the course of one week. ResultsNeither testosterone nor estradiol altered responding maintained by heroin. In contrast, the high dose of progesterone (0.125 mg) reduced responding maintained by all doses of heroin to saline-control levels. This dose of progesterone did not reduce responding maintained by food on a progressive ratio schedule in either food-restricted or food-sated rats.ConclusionsThese data indicate that exogenous progesterone or a pharmacologically active metabolite selectively decreases heroin intake in male rodents, which may have therapeutic implications for men with opioid use disorder.

RationaleHeroin intake decreases during the proestrus phase of the estrous cycle in female rats. Circulating concentrations of both estradiol and progesterone peak during proestrus, and it is not known which of these hormones, or their combination, are responsible for these effects.ObjectivesThe purpose of this study was to determine the effects of estradiol, progesterone, and their combination on heroin self-administration in female rats.MethodsIn Experiment 1, the estrous cycle of intact female rats was tracked daily. If a rat was in proestrus, either the estrogen receptor antagonist, raloxifene, the progesterone receptor antagonist, mifepristone, or their combination was administered 30 min prior to a heroin self-administration session. In Experiment 2, separate groups of ovariectomized female rats were treated chronically with exogenous estradiol, progesterone, estradiol + progesterone, or vehicle, and heroin intake was examined over a 100-fold dose range.ResultsIn Experiment 1, raloxifene, but not mifepristone, significantly blocked proestrus-associated decreases in heroin intake. In Experiment 2, estrogentreated rats self-administered less heroin than any other group and significantly less heroin than rats treated with progesterone.ConclusionsThese data suggest that (1) estradiol but not progesterone is responsible for proestrus-associated decreases in heroin intake and (2) estradiol decreases heroin intake relative to progesterone. These data differ from those reported previously with stimulants and suggest that estrogen-based pharmacotherapies may be of value to women with opioid use disorder.

Current research in serial pattern learning suggests parallel processing in acquisition and retention of structured serial patterns but the effects of interference and spaced practice had not yet been assessed. Interference impairs acquisition and retention of serial pattern elements, while spacing practice improves acquisition. Previous work has demonstrated that structured elements and elements that violate structure are learned concurrently through different mechanisms. While data suggest that the presence of a violation element does not interfere with acquisition of structured elements, little work has been done to evaluate how a violation element affects retention of structured elements. In order to assess the effects of interference on retention, rats were trained to criterion on one of two serial patterns: a pattern that contained two types of structured elements (chunk-boundary and within-chunk elements) or a pattern that contained structured elements with an added violation element. Rats were then tested for retention of both structured elements at 24-hour, 2-, 4-week retention intervals. The presence of the violation element impaired retention of chunk-boundary elements without affecting retention of within-chunk elements. A third experiment assessed how spacing practice over longer periods of time affected acquisition of the violation element in male and female rats. Spaced practice improved acquisition of the violation element relative to massed practice in only female rats. These studies demonstrated that acquisition, while resistant to interference, is improved by spaced training. Additionally, Experiments 1 and 2 found that retention for different types of elements are differentially susceptible to interference. The present studies provide further support for parallel processing in serial pattern learning and that separate processes are differentially impacted by interference and spaced practice.

Abstract Heroin intake decreases during the proestrus phase of the estrous cycle in female, Long-Evans rats. The purpose of this study was to (1) determine if proestrus-induced decreases in heroin intake extend across rat strains and (2) determine if proestrus-induced decreases in responding extend to a nondrug reinforcer. Female rats were implanted with intravenous catheters and trained to self-administer heroin. Estrous cycle was tracked daily for the duration of the study. During testing, Lewis, Sprague-Dawley, and Long Evans rats self-administered low (0.0025 mg/kg) and high (0.0075 mg /kg) doses of heroin (Experiment 1) and then self-administered sucrose (Experiment 2) on fixed ratio (FR1) schedules of reinforcement. Heroin intake decreased significantly during proestrus in all three rat strains under at least one dose condition; however, sucrose intake did not decrease during proestrus in any strain. These data indicate that responding maintained by heroin, but not a nondrug reinforcer, significantly decreases during proestrus in female rats and that these effects are consistent across rat strain. Competing Interest Statement The authors have declared no competing interest.

Ambient mass spectrometry is an analytical approach that enables ionization of molecules under open-air conditions with no sample preparation and very fast sampling times. Rapid evaporative ionization mass spectrometry (REIMS) is a relatively new type of ambient mass spectrometry that has demonstrated applications in both human health and food science. Here, we present an evaluation of REIMS as a tool to generate molecular scale information as an objective measure for the assessment of beef quality attributes. Eight different machine learning algorithms were compared to generate predictive models using REIMS data to classify beef quality attributes based on the United States Department of Agriculture (USDA) quality grade, production background, breed type and muscle tenderness. The results revealed that the optimal machine learning algorithm, as assessed by predictive accuracy, was different depending on the classification problem, suggesting that a “one size fits all” approach to developing predictive models from REIMS data is not appropriate. The highest performing models for each classification achieved prediction accuracies between 81.5–99%, indicating the potential of the approach to complement current methods for classifying quality attributes in beef.

The magnitude and pace of global change demand rapid assessment of nature and its contributions to people. We present a fine-scale global modeling of current status and future scenarios for several contributions: water quality regulation, coastal risk reduction, and crop pollination. We find that where people’s needs for nature are now greatest, nature’s ability to meet those needs is declining. Up to 5 billion people face higher water pollution and insufficient pollination for nutrition under future scenarios of land use and climate change, particularly in Africa and South Asia. Hundreds of millions of people face heightened coastal risk across Africa, Eurasia, and the Americas. Continued loss of nature poses severe threats, yet these can be reduced 3- to 10-fold under a sustainable development scenario.