Male rats choose higher doses of nicotine in anticipation of a future non-drug period

Abstract

Humans and animals use information about future access to rewards to influence their behaviour in the present, however the evidence for this is largely anecdotal. Here we use the nicotine intravenous self-administration paradigm to ask whether rats can use an auditory stimulus signalling a long (450 s) signalled time-out on the next trial to influence their nicotine intake in the present. Rats were trained to choose between low (15 µg/kg/infusion), medium (30 µg/kg/infusion) or high (60 µg/kg/infusion) doses of nicotine on any given trial. Trials either had a ‘light’ trial with no tone and a standard 20 s post-infusion time-out, a ‘short-tone’ trial where a tone was presented but the time-out remained at 20 s, or a ‘long-tone’ trial where a second tone played and was accompanied by a long 450 s time-out period. During training rats clearly showed that dose selection was based on both the dose on the previous trial and the latency between infusions. When tones were presented, rats shifted their preference from the low dose to the high dose when the long-delay tone was presented, and this choice was particularly pronounced when the rat had previously selected a low dose. Together these findings are the first evidence that rats can regulate their nicotine intake in the present in anticipation of a future non-drug period. This result is discussed with respect to theories of negative reinforcement.