Effects of Housing Condition and Acute Nicotine on Impulsive Choice in Lewis and Fischer 344 Rats

Impulsive choice is defined as choice for a smaller, more immediate reinforcer relative to a larger, delayed reinforcer, and is commonly studied using delay-discounting procedures. There are many variables that contribute to impulsive choice, including biological and environmental determinants. The present study examined both of these variables by evaluating effects of housing condition (single versus paired) on impulsive choice in Lewis (LEW) and Fischer 344 (F344) rats, at baseline and following acute nicotine administration. A within-session procedure was used in which choice was between one food pellet delivered immediately and three food pellets delivered after a delay. The delay to three food pellets was increased systematically across blocks within a session and indifference points were calculated. Paired housing significantly reduced impulsive choice for both rat strains relative to single housing (archival data). In addition, when singly housed, choice was more impulsive for LEW rats relative to F344 rats at baseline. When pair housed, this strain difference was attenuated. Following acute nicotine administration, impulsive choice was significantly reduced at 0.3 mg/kg for singly housed LEW rats and 1.0 mg/kg for singly housed F344 rats. However, when pair housed, 0.3 and 1.0 mg/kg both reduced impulsive choice regardless of rat strain. Thus, previously reported effects of environmental enrichment (i.e., reduced impulsive choice) seem to be, as least in part, due to social housing. It also appears as though effects of nicotine on impulsive choice are baseline-dependent and paired housing may make impulsive choice in F344 rats more sensitive to effects of nicotine