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Background: Rats reared in social isolation exhibit various cognitive and behavioural abnormalities in adulthood. However, impulsivity following this treatment still remains unclear, especially in response to medications used in attention deficit hyperactivity disorder, such as amphetamine. Methods: Using an isolation-rearing (IR) manipulation, the present study examined the effects of IR on impulsive action and impulsive choice when also treated with doses of d-amphetamine, by employing the five-choice serial reaction time task (5-CSRTT) and a temporal discounting of reward task (TDRT), respectively. Results: IR rats showed similar acquisition of the 5-CSRTT. Amphetamine increased premature responding in both groups; however, IR rats showed less responding overall. For the TDRT, IR rats revealed a greater preference for the large but delayed reward during task acquisition (i.e. were less impulsive) with a higher rate of nose poking during the delay, and exhibited a compressed dose-response function (i.e. reduced dose sensitivity) for amphetamine. Discussion: Impulsive action and impulsive choice were reduced in IR rats under certain conditions, and a blunted response to d-amphetamine was found on these measures. These reductions in impulsivity contrast with locomotor hyperactivity normally shown in IR rats and the findings have implications for the utility of IR as a model of psychopathology. [ABSTRACT FROM AUTHOR]

Rationale: Heavy smokers exhibit greater levels of impulsive choice and behavioural disinhibition than non-smokers. To date, however, the relationship between nicotine use and differing dimensions of impulsivity has not been systematically assessed. Objectives: A series of studies was designed to assess the acute dose-response effects of nicotine and the nicotinic receptor antagonist mecamylamine alone, and in combination with nicotine, on impulsive choice and behavioural disinhibition in rats. Methods: Separate groups of rats were trained on a symmetrically reinforced go/no-go task to measure levels of disinhibition and a systematic delayed reward task to measure levels of impulsive choice. Once trained, all animals in each task were treated acutely with nicotine (0.125, 0.25, 0.5 and 1.0 mg/kg), mecamylamine (0.1, 0.3 and 1.0 mg/kg) and varying doses of mecamylamine (0.1, 0.3 and 1.0 mg/kg) prior to nicotine (0.5 mg/kg). An additional experiment assessed the effects of alterations in primary motivation (presatiation and fasting) on performance in both tasks. Results: Acute nicotine increased both impulsive choice and behavioural disinhibition, effects that were blocked by pre-treatment with mecamylamine. Mecamylamine when administered alone did not alter impulsive behaviour. The lack of effect of presatiation on performance measures suggests that the observed nicotine-induced impulsivity cannot be attributed to the anorectic activity of the compound. Conclusions: Present findings support the hypothesis that heightened impulsivity in smokers may in part be a consequence of the direct acute effects of nicotine. As such, drug-induced changes in impulsivity may play a critical role in the transition to and maintenance of nicotine dependence. [ABSTRACT FROM AUTHOR]

Impulsivity is a key feature of many psychopathologies such as mania, personality disorders or attention deficit–hyperactivity disorder (ADHD). Most experimental paradigms assessing impulsive behaviour also require non-specific capacities such as time estimation. This may interact with the measures and mask the beneficial effects of psychostimulants—the most commonly used treatment for ADHD—on impulsivity, given that these drugs speed up the internal clock. The present experiment investigated the effects of suppressing behaviours non-specific to impulsivity in a fixed consecutive number (FCN) schedule and examined whether amphetamine, previously shown to increase impulsive responses in this task, could have beneficial effects when impulsive responses are promoted. Food-deprived rats were trained to press one lever of a two-lever operant chamber eight times before pressing the other lever to obtain food. Premature ending of responses resulted in absence of food delivery and reset the counter. A cue light indicating the required number of presses was present (FCN8cue) and removed after training (FCN8). Rats were then trained under an FCN16cue schedule to be challenged with d-amphetamine (0.125, 0.25 and 0.5 mg/kg). The cue improved performances, and similar scores were obtained under FCN16cue compared to FCN8. Premature responses under these two conditions were unrelated. Amphetamine reduced impulsive responses in FCN16cue at the lower dose. Suppression of capacities non-specific to impulsivity in the FCN schedule, associated with conditions that permit the expression of inhibitory deficits, allows the beneficial effects of psychostimulants observed clinically to be evidenced experimentally. [ABSTRACT FROM AUTHOR]