Comparison of two sensitization paradigms of the acoustic startle response in Wistar and Sprague-Dawley rats

An increase in general responsiveness after aversive stimulation has provided a most widely accepted and well-understood sensitization paradigm. According to a second paradigm (based on the dual process theory of habituation and sensitization), not only additional aversive stimuli, but also the response-eliciting stimuli themselves, induce sensitization. To relate these two sensitization paradigms, we compared the course of startle response parameters during repetitive acoustic stimulation with the change in startle amplitude after electric footshocks in outbred Wistar and Sprague- Dawley rats. Compared to the Wistar rats used, the Sprague-Dawley rats showed a lower response decrement and a shortened latency during repetitive stimulation, both of which are indicators of increased sensitization by the startle-eliciting stimuli. In addition, the Sprague-Dawley rats also demonstrated a reduced increase in startle amplitude following footshock. This was postulated to be a consequence of the strong sensitization by startle-eliciting stimuli, which interferes with sensitization elicited by footshock. Because our Wistar and Sprague-Dawley rats did not differ in initial startle amplitude, but mainly in susceptibility to sensitization, further comparisons of these genetically different stocks of rats seem to be of potential value in studying differences in fear-motivated behavior.