Phenotypic and genetic relations between initial response to electric shock and rate of avoidance learning in mice

Abstract

The first experiment was designed to determine what proportion of the betweenstrain variation in rate of avoidance learning could be attributed to strain differences in sensitivity and response topography to electric shock. Measures of jumping at six shock intensities for four inbred strains were collected in a pretest of shock sensitivity. They were then used to derive a shock intensity for each strain which yielded the same amount of jumping for all strains. Avoidance training was administered to other mice of the same age and strains using the same apparatus and shock source as in the pretest. When training was given with a 180 μa shock, significant strain differences were observed in latency of the first escape and total errors to a learning criterion during both jump-out and one-way avoidance training. A large strain by training procedure interaction was found, as well. When training was administered with shock levels which yielded equal jumping in the pretest, strain differences in latency of the first escape were totally eliminated. However, the magnitude of strain differences in the rate of avoidance learning was not changed substantially. A second experiment examined two F₁ hybrid strains and a four-way cross of the inbred strains tested in the first experiment. Results indicated that initial response to shock is characterized by intermediate inheritance, while rate of avoidance learning exhibits significant dominant inheritance. Although significant genetic differences in both initial response to shock and rate of avoidance learning were detected in the present experiments, it is concluded that the former cannot account for the latter.