Reward-enhancing effects of d-amphetamine and its interactions with nicotine were greater in female rats and persisted across schedules of reinforcement

Repeated exposure to physiologically effective doses of contraceptive hormones ethinyl estradiol or levonorgestrel do not alter the reinforcing effects of a brief visual stimulus in ovary-intact rats

Estradiol and progesterone potentiate and attenuate reward processes, respectively. Despite these well-characterized effects, there is minimal research on the effects of synthetic estrogens (e.g., ethinyl estradiol, or EE) and progestins (e.g., levonorgestrel, or LEVO) contained in clinically-utilized hormonal contraceptives. The present study characterized the separate effects of repeated exposure to EE or LEVO on responding maintained by a reinforcing visual stimulus. Forty ovary-intact female Sprague-Dawley rats received either sesame oil vehicle (n = 16), 0.18 μg/day EE (n = 16), or 0.6 μg/day LEVO (n = 8) subcutaneous injections 30-min before daily one-hour sessions. Rats' responding was maintained by a 30-sec visual stimulus on a Variable Ratio-3 schedule of reinforcement. The day after rats' last session, we determined rats estrous cycle phase via vaginal cytology before sacrifice and subsequently weighing each rat's uterus to further verify the contraceptive hormone manipulation. The visual stimulus functioned as a reinforcer, but neither EE nor LEVO enhanced visual stimulus maintained responding. Estrous cytology was consistent with normal cycling in vehicle rats and halting of normal cycling in EE and LEVO rats. EE increased uterine weights consistent with typical uterotrophic effects observed with estrogens, further confirming the physiological impacts of our EE and LEVO doses. In conclusion, a physiologically effective dose of neither EE nor LEVO did not alter the reinforcing efficacy of a visual stimulus reinforcer. Future research should characterize the effects of hormonal contraceptives on responding maintained by other reinforcer types to determine the generality of the present findings.

Varenicline but not cotinine increased the value of a visual stimulus reinforcer in rats: No evidence for synergy of the two compounds

Smoking is the leading cause of preventable death worldwide, with <7 % of smoking cessation attempts being met with success. Nicotine, the main addictive agent in cigarettes, enhances the reinforcing value of other environmental rewards. Under some circumstances, this reward enhancement maintains nicotine consumption. Varenicline (i.e., cessation aid Chantix™) also has reward-enhancement effects via nicotinic acetylcholine receptor agonism (nAChRs) - albeit less robust than nicotine. Cotinine is the major metabolite of nicotine. Recent studies suggest that cotinine is a positive allosteric modulator (PAM) and/or a weak agonist at nAChRs. Thus, cotinine may enhance the behavioral effects of nAChR compounds such as varenicline and/or exert some behavioral effects alone. We used 20 (10M, 10F) Sprague-Dawley rats to assess reward-enhancement within-subjects by examining responding maintained by a reinforcing visual stimulus on a Variable Ratio 2 schedule of reinforcement. To assess the reward-enhancing effects of cotinine, rats received one injection of cotinine (saline, 0.1, 0.3, 1.0, 3.0, 6.0 mg/kg) before each 1 h session. To assess cotinine and varenicline interactions, rats received an injection of cotinine (saline, 0.1, 1.0, or 6.0 mg/kg) and of varenicline (saline, 0.1, 0.3, 1.0, or 3.0 mg/kg) before the session. While we replicated prior work identifying reward-enhancement by 0.1, 0.3, and 1.0 mg/kg varenicline, cotinine alone did not produce reward-enhancement nor augment the reward-enhancing effects of varenicline. Future studies may consider examining the reward-enhancing effects of cotinine with other reinforcers or co-administered with other smoking cessation aids such as bupropion.

The co-use of nicotine and prescription psychostimulants: A review of their behavioral and neuropharmacological interactions

BACKGROUND

Nicotine is commonly co-used with other psychostimulants. These high co-use rates have prompted much research on interactions between nicotine and psychostimulant drugs. These studies range from examination of illicitly used psychostimulants such as cocaine and methamphetamine to prescription psychostimulants used to treat attention deficit hyperactivity disorder (ADHD) such as methylphenidate (Ritalin™) and d-amphetamine (active ingredient of Adderall™). However, previous reviews largely focus on nicotine interactions with illicitly used psychostimulants with sparse mention of prescription psychostimulants. The currently available epidemiological and laboratory research, however, suggests high co-use between nicotine and prescription psychostimulants, and that these drugs interact to modulate use liability of either drug. The present review synthesizes epidemiological and experimental human and pre-clinical research assessing the behavioral and neuropharmacological interactions between nicotine and prescription psychostimulants that may contribute to high nicotine-prescription psychostimulant co-use.

METHODS

We searched databases for literature investigating acute and chronic nicotine and prescription psychostimulant interactions. Inclusion criteria were that participants/subjects had to experience nicotine and a prescription psychostimulant compound at least once in the study, in addition to assessment of their interaction.

RESULTS AND CONCLUSIONS

Nicotine clearly interacts with d-amphetamine and methylphenidate in a variety of behavioral tasks and neurochemical assays assessing co-use liability across preclinical, clinical, and epidemiological research. The currently available research suggests research gaps examining these interactions in women/female rodents, in consideration of ADHD symptoms, and how prescription psychostimulant exposure influences later nicotine-related outcomes. Nicotine has been less widely studied with alternative ADHD pharmacotherapy bupropion, but we also discuss this research.

The incentive amplifying effects of nicotine: Roles in alcohol seeking and consumption

Nicotine has a unique profile among drugs of abuse. To the noninitiated user, nicotine has powerful aversive effects and its relatively weak euphorigenic effects undergo rapid tolerance. Despite this, nicotine is commonly abused despite negative heath consequences, and nicotine users have enormous difficulty quitting. Further, nicotine is one of the most commonly co-abused substances, in that it is often taken in combination with other drugs. One explanation of this polydrug use is that nicotine has multiple appetitive and consummatory conditioning effects. For example, nicotine is a reinforcement enhancer in that it can potently increase the incentive value of other stimuli, including those surrounding drugs of abuse such as alcohol. In addition, nicotine also has a unique profile of neurobiological effects that alter regulation of alcohol intake and interoception. This review discusses the psychological and biological mechanisms surrounding nicotine's appetitive conditioning and consummatory effects, particularly its interactions with alcohol.

Investigating sex differences and the effect of drug exposure order in the sensory reward-enhancing effects of nicotine and d-amphetamine alone and in combination

Nicotine enhances the rewarding effects of other environmental stimuli; this reward-enhancement encourages and maintains nicotine consumption. Nicotine use precedes other psychostimulant use, but receiving a stimulant prescription also predicts future smoking. Previously, no study has investigated effects of drug exposure order in reward-enhancement, nor with nicotine and d-amphetamine. Thus, we aimed to investigate how drug exposure order impacted the reward-enhancing effects of nicotine and d-amphetamine, alone and in combination. We used 20 male and 20 female Sprague-Dawley rats. Enhancement was investigated within-subjects by examining responding maintained by a visual stimulus reinforcer following a pre-session injection of either d-amphetamine (Sal, 0.1, 0.3, or 0.6 mg/kg) or nicotine (Sal, 0.03, 0.06, 0.1, 0.3 mg/kg). Twenty rats (10 M, 10 F) completed enhancement testing with nicotine before d-amphetamine. The other 20 rats (10 M, 10 F) completed testing with d-amphetamine before nicotine. Following these phases, rats were then given two pre-session injections: one of d-amphetamine (Sal, 0.1, 0.3, or 0.6 mg/kg) and another of nicotine (Sal, 0.03, 0.06, 0.1, or 0.3 mg/kg). Experiencing amphetamine before nicotine increased reward-enhancing effects of nicotine. Females exhibited greater effects of d-amphetamine on reward-enhancement, with no effect of exposure order. During the interaction phase, receiving nicotine before amphetamine enhanced the interaction between nicotine and d-amphetamine for females whereas amphetamine before nicotine heightened this interaction for males. From this, prior and current amphetamine use, in addition to sex, should be considered when treating nicotine dependency and when examining factors driving poly-substance use involving nicotine and d-amphetamine. Keywords: Adderall, ADHD, Dexedrine, operant, smoking, polysubstance use.