The influence of stimulus pairing and of the shuttle-shock contingency in the performance of shuttle responses to a buzzer by weanling rats

Abstract

Weanling (20-day old) and adult Wistar rats were submitted to four different training procedures in a shuttle-box. Each of the training procedures involved 50 5-sec buzzers and a variable number of 1.5 mA footshocks. Performances of shuttle responses to the buzzer was similar in both age groups both in a “no pairing-no contingency” situation (shocks at random intervals from buzzers irrespective of the performance of shuttle responses or not), and in a classical conditioning situation (shocks paired to buzzers on every trial, also irrespective of whether or not there was shuttling to the buzzer). However, the incidence of shuttle responses to the buzzer was much lower in the weanling group in two other tests in which there was a contingency of shocks upon shuttle responses: one in which the buzzer-shock interval was randomly variable (i.e., no “pairing”), and another one in which the two stimuli were paired (a typical two-way avoidance paradigm). It is concluded that 20-day old rats are unable to cope with a shuttle-shock instrumental contingency, while being as able as adult rats to develop shuttle responses through a drive process or through a “pairing” (classical) process.