Mouse strains differ under a simple schedule of operant learning

Recent advances in understanding the composition of the human and mouse genomes have paved the way to a more detailed understanding of the influence of genes on behavior, particularly learning and memory. One problem with many learning paradigms is the great length of training time required to generate a stable baseline. Our goal for the current studies was to develop a method of rapidly assessing learning and to use it to compare various strains of mice. The acquisition of a simple nose-poke was determined in operant chambers with two nose-poke holes illuminated: a single nose poke in one hole resulted in the presentation of 0.01 ml evaporated milk; responses in the other hole did not result in dipper presentation. All mice of the B6JxImJ F1, C57BL/6J, 129X1/SvJ and C3H/HeJ mice emitted 50 or more correct operant responses, whereas fewer than 50% of 129X1/SvJ and 75-90% of mice of Balb/cByJ, DBA/2J and the outbred CD-1 mice emitted 50 or more correct operant responses. On average, C57BL/6J emitted 50 operative responses in less than 30 min, whereas DBA/2J mice required nearly 1 h to complete 50 operative responses. Other strains performed at intermediate levels. There was no apparent relationship between operant activity and locomotor activity that may have influenced response acquisition. These findings are consistent with those reported using other learning paradigms and provide a rapid method of learning assessment.