Substance use disorder is a chronic, relapsing condition characterized by preoccupation with acquiring or taking a drug, to the detriment of other healthy behaviors. Even after long periods of abstinence from the drug, there is a high chance of relapse in the presence of stress or cues of drug availability, rendering short-term treatment strategies inadequate. A major barrier to the success of treatments for substance use disorder is that drug users tend to be more impulsive than the general population: they are less able to appropriately inhibit reward-seeking behaviors, and tend to overvalue short-term reward acquisition over long-term benefits. This impulsivity can predispose certain individuals toward developing substance use disorder, but there is also compelling evidence that a history exposure to drugs of abuse can induce impulsivity in animals with no preexisting differences in behavior. While this is well established in tasks of risky decision making and intertemporal choice, it has not been investigated in tests of effort allocation. Evidence is presented herein that rats assessed in protracted withdrawal from methamphetamine (mAMPH) show a unique behavioral pattern when given the opportunity to work for rewards: effort expenditure is enhanced when animals are given a choice between rewarded action and unrewarded inaction, and reward value is steeply discounted by increasing effort demands when in the presence of an acceptable alternative reward source.

The neural mechanisms underlying impulsive choice in mAMPH withdrawal are unclear. It has been hypothesized that mAMPH disrupts top-down executive control over reward seeking by interfering with neurotransmission in the frontal cortex. It has also been proposed that drug-induced neural changes in the basal ganglia, especially reduction in expression of the dopamine D2 receptor, may underlie impulsive behavior. The present work expands on these hypotheses by showing that mAMPH withdrawal, but not mAMPH exposure, is related to decreased striatal D2 expression. Additionally, steep effortful discounting in mAMPH withdrawal was mimicked by pharmacologic activation of D2-expressing medium spiny neurons in the striatum.

Finally, the above findings are considered in the framework of evolutionary theory to answer the question of why natural selection has favored traits which left the body vulnerable to this kind of manipulation. It is proposed that natural selection on foraging behavior favored the development of decision rules which adapt reward seeking behavior to suit the relative reward density and distribution in the environment. Exposure to and withdrawal from mAMPH provides misleading information to this system, leading to impulsive behavior which persists long after the cessation of drug use. Implications of this hypothesis for treatment of substance use disorders are discussed.

Molluscum contagiosum is a self-limited disease that presents as small papules with central umbilication. Similar to herpes simplex virus type 1 (HSV-1) and tinea corporis, participation in wrestling is a risk factor for molluscum infection in children and adults. Referred to as herpes gladiatorum, HSV-1 causes cutaneous or ocular infections in wrestlers. We propose that molluscum contagiosum be referred to as “molluscum gladiatorum” when infection occurs in the context of wrestling. We report a case of a high school wrestler who presented with molluscum lesions on his neck.

Although it is well established that Marine Protected Areas (MPAs) are effective tools for augmenting the abundance of fished species, effects on biodiversity and community assembly are less clear. Many rockfish species were overfished in the California Current Ecosystem at the turn of the 21st century, and establishment of two large MPAs in the Southern California Bight, the Cowcod Conservation Areas (CCAs), alongside favorable environmental conditions helped rebuild overfished rockfish stock by 2020. Here, we evaluate the impacts of the CCAs and environment on rockfish diversity and assemblage structure using a 16-year time series (1998-2013) of genetically-identified rockfish larvae. We demonstrate that while rockfish richness generically increased across the time series, the greatest increases occurred inside CCAs when temperature was low and dissolved oxygen high. Using multivariate methods (ordination and generalized linear latent variable models), we also find a clear species assemblage shift after the 2001 CCA implementations, driven largely by increased presence/abundance of rockfishes targeted by fisheries. Our results suggest that the large and sustained MPAs along the southern California coast have induced increases in the diversity of rockfish reproductive output, driven largely by the direct effects of fishing cessation on targeted species.