Climbing task in rats: Females were more intrinsically motivated than males

Abstract

Paradigms of motivation often examine the performance of subjects in tasks associated with rewards. In this study, the aim was to develop a new behavioural test associating a natural reward (familiar food) to an effort task in rats (climbing a ladder). Wistar rats (both sexes, 90–120 days) were familiarised with food (chow, chocolate, corn flakes, fruit loops) in their home cage for four days before being tested for food preference. Food preference varied from rat to rat. Afterwards, rats were randomly allocated into the two groups, spontaneous (females, n = 10; males, n = 11) or reinforced (females, n = 9; males, n = 10) right before the training in the ladder. The climbing-task test consisted of one session of fifteen minutes (pre-trial) followed by two training sessions and a test trial of five minutes each, at 1, 7 and 14 days after pre-trial, respectively. In the pre-trial, more females climbed spontaneously the ladder than males (females: 11 out of 19, males: 3 out of 21). Food or training were minor reinforcements to climbing the ladder for male rats. In contrast, training decreased latency to climbing in females of both experimental groups and increased climbing frequency of reinforced females in the test trial. Summarising, female rats were more intrinsically motivated to climb the ladder than males. In contrast with males, incentives increased motivation in female rats to perform the effort task. Hence, at the current moment, climbing-task test seems more promising to estimate motivation in female rats.