Performance of α7 nicotinic receptor null mutants is impaired in appetitive learning measured in a signaled nose poke task

Wild-type and mutant mice lacking expression of alpha 5, alpha 7, beta 2, beta 3, or beta 4 neuronal nicotinic cholinergic receptors (nAChRs) were compared on a signaled nose poke task, a multi-phased task used to measure appetitive learning and impulsivity. In the early phases of training, mutants of all nicotinic lines did not differ compared to wild types in the days to reach criterion when mice were required to nose poke for a sucrose reward on FR1 or FR3 schedules, or in their ability to respond to an auditory clicker to receive a sucrose reward. However, mutants lacking alpha 7 nAChRs, but not lines lacking other nAChRs, showed impairments when task difficulty was increased such that an auditory stimulus was presented on a variable schedule and mice were required to withhold their responses until the presentation of the auditory cue to obtain a reward. alpha 7 mutants were impaired compared to wild types in appetitive learning as measured by the percentage of conditioned responses but overcame their deficits with extensive training for 10 days. However, when efficiency ratios were used to measure impulsivity, alpha 7 mutants exhibited lower efficiency ratios even after 10 days of training. These results support a role of the 0 nicotinic receptor in mediating appetitive learning and suggest a potential role for the alpha 7 nAChRs in the regulation of behavioral disinhibition. (C) 2005 Elsevier B.V. All rights reserved.