Regulation of intravenously self-administered nicotine in rats

HIV Infection and Neurocognitive Disorders in the Context of Chronic Drug Abuse: Evidence for Divergent Findings Dependent upon Prior Drug History

The fronto-striatal circuitry, involving the nucleus accumbens, ventral tegmental area, and prefrontal cortex, mediates goal-directed behavior and is targeted by both drugs of abuse and HIV-1 infection. Acutely, both drugs and HIV-1 provoke increased dopamine activity within the circuit. However, chronic exposure to drugs or HIV-1 leads to dysregulation of the dopamine system as a result of fronto-striatal adaptations to oppose the effects of repeated instances of transiently increased dopamine. Specifically, chronic drug use leads to reduced dopaminergic tone, upregulation of dopamine transporters, and altered circuit connectivity, sending users into an allosteric state in which goal-directed behaviors are dysregulated (i.e., addiction). Similarly, chronic exposure to HIV-1, even with combination antiretroviral therapy (cART), dysregulates dopamine and dopamine transporter function and alters connectivity of the fronto-striatal circuit, contributing to apathy and clinical symptoms of HIV-1 associated neurocognitive disorders (HAND). Thus, in a drug user also exposed to HIV-1, dysregulation of the fronto-striatal dopamine circuit advances at an exacerbated rate and appears to be driven by mechanisms unique from those seen with chronic drug use or HIV-1 exposure alone. We posit that the effects of drug use and HIV-1 infection on microglia interact to drive the progression of motivational dysfunction at an accelerated rate. The current review will therefore explore how the fronto-striatal circuit adapts to drug use (using cocaine as an example), HIV-1 infection, and both together; emphasizing proper methods and providing future directions to develop treatments for pathologies disrupting goal-directed behaviors and improve clinical outcomes for affected patients. Graphical Abstract Drug use and HIV-1 in the fronto-striatal circuit. Drugs of abuse and HIV-1 infection both target the fronto-striatal circuit which mediates goal-directed behavior. Acutely, drugs and HIV-1 increase dopamine activity; in contrast chronic exposure produces circuit adaptions leading to dysregulation, addiction and/or apathy. Comorbid drug use and HIV-1 infection may interact with microglia to exacerbate motivational dysregulation.

Sex differences in attenuation of nicotine reinstatement after individual and combined treatments of progesterone and varenicline

Tobacco use is the largest cause of preventable mortality in the western world. Even after treatment, relapse rates for tobacco are high, and more effective pharmacological treatments are needed. Progesterone (PRO), a female hormone used in contraceptives, reduces stimulant use but its effects on tobacco addiction are unknown. Varenicline (VAR) is a commonly used medication that reduces tobacco use. The present study examined sex differences in the individual vs. combined effects of PRO and VAR on reinstatement of nicotine-seeking behavior in a rat model of relapse. Adult female and male Wistar rats self-administered nicotine (NIC, 0.03mg/kg/infusion) for 14days followed by 21days of extinction when no cues or drug were present. Rats were then divided into 4 treatment groups: control (VEH+SAL), PRO alone (PRO+SAL), VAR alone (VEH+VAR) and the combination (PRO+VAR). Reinstatement of nicotine-seeking behavior induced by priming injections of NIC or caffeine (CAF), presentation of cues (CUES), and the combination of drugs and cues (e.g. NIC+CUES, CAF+CUES) were tested after extinction. Male and female rats did not differ in self-administration of nicotine or extinction responding, and both showed elevated levels of responding to the CAF+CUES condition. However, males, but not females, reinstated active lever-pressing to the NIC+CUES condition, and that was attenuated by both VAR and VAR+PRO treatment. Thus, males were more sensitive to NIC+CUE-induced reinstatement than females, and VAR alone and VAR combined with PRO effectively reduced nicotine relapse.

Sex differences in reinstatement of cocaine-seeking with combination treatments of progesterone and atomoxetine

Two repurposed medications have been proposed to treat cocaine abuse. Progesterone, a gonadal hormone, and atomoxetine, a medication commonly used to treat attention deficit/hyperactivity disorder, have both been separately shown to reduce cocaine self-administration and reinstatement (i.e., relapse). The goal of the present study was to examine sex differences in the individual effects of PRO and ATO as well as the combination PRO+ATO treatment on cocaine (COC), caffeine (CAF), and/or cue-primed reinstatement of cocaine-seeking. Adult male and female Wistar rats lever-pressed under a FR 1 schedule for cocaine infusions (0.4mg/kg/inf). After 14 sessions of stable responding in daily 2-h sessions, rats underwent a 21-day extinction period when no drug or drug-related stimuli were present. Rats were then separated into four groups that received PRO (0.5mg/kg) alone (PRO+SAL), ATO (1.5mg/kg) alone (VEH+ATO), control (VEH+SAL) or combination (PRO+ATO) treatments prior to the reinstatement condition. Reinstatement of cocaine-seeking to cues and/or drug injections of cocaine or caffeine was tested after extinction. During maintenance, females self-administered more cocaine than males, but no sex differences were seen during extinction. Females showed greater cocaine-seeking than males after a CAF priming injection. Individual treatment with ATO did not decrease reinstatement under any priming condition; however, the combination treatment decreased cocaine-seeking under the COC+CUES priming condition in males, and both PRO alone and the combination treatment decreased cocaine-seeking in the CAF+CUES condition in females. Overall, PRO alone was only effective in reducing reinstatement in females, while the combination treatment was consistently effective in reducing reinstatement in both sexes.

A glimpse into the future - Personalized medicine for smoking cessation

The devastating consequences of tobacco smoking for individuals and societies motivate studies to identify and understand the biological pathways that drive smoking behaviors, so that more effective preventions and treatments can be developed. Cigarette smokers respond to nicotine in different ways, with a small number of smokers remaining lifelong low-level smokers who never exhibit any symptoms of dependence, and a larger group becoming nicotine dependent. Whether or not a smoker transitions to nicotine dependence has clear genetic contributions, and variants in the genes encoding the α5-α3-β4 nicotinic receptor subunits most strongly contribute to differences in the risk for developing nicotine dependence among smokers. More recent work reveals a differential response to pharmacologic treatment for smoking cessation based on these same genetic variants in the α5-α3-β4 nicotinic receptor gene cluster. We anticipate a continuing acceleration of the translation of genetic discoveries into more successful treatment for smoking cessation. Given that over 400,000 people in the United States and over 5 million people world-wide die each year from smoking related illnesses, an improved understanding of the mechanisms underlying smoking behavior and smoking cessation must be a high public health priority so we can best intervene at both the public health level and the individual level. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Temporal horizons of cigarette satiety: determining the window of time over which recent smoking influences motivation to smoke

One of the hallmarks of drug addiction is a limitation of the temporal horizon of events that affect the behavior of drug users. The purpose of this experiment was to examine the time period over which smoking was influenced by an earlier opportunity to smoke. Baseline sessions measured how much was smoked in a current opportunity when it was preceded by a 2-h wait time in which no smoking was allowed. After the baseline phase, we examined the effects of temporal distance when an earlier opportunity to smoke (upon completion of a fixed ratio 100) preceded current smoking (upon completion of a progressive ratio). Temporal distance between these two opportunities to smoke was varied from 0 to 120 min. We found that current smoking for the group was reduced from baseline levels when the temporal distance was 0 min. At temporal distances ranging from 30 to 90 min, the individual's smoking returned to levels that were similar to baseline. Breakpoints were also a function of earlier smoking, and latencies to first puff of the session followed a similar trend. These findings provide evidence of the limited temporal horizons related to smoking bouts of smokers and may provide a useful measure for metabolism differences across populations. In addition, we suggest that the quantitative description of satiety provided by our procedures may validate drug replacement therapies involved in cessation treatments.