Acoustically elicited behaviours in Lister hooded and Wistar rats

It has been reported previously that experimenter-presented 20-kHz tones at low intensities produce bursts of locomotor running in Lister hooded rats, but reduced locomotion (freezing) in Wistar rats. Because rats emit 20-kHz tones when stressed, it was proposed that this ultrasound-elicited running and freezing behaviour in Lister hooded and Wistar rats, respectively, rep resents a model for qualitative strain differences in fear behaviour. The p resent studies examined the acoustic specificity of acoustically elicited l ocomotor behaviours in Lister hooded and Wistar rats. In Experiment 1, it w as found that brief exposure (i.e., 15 s) of Lister hooded rats to tones at frequencies of 7, 12, or 20 kHz and intensities of 85-95 dB SPL, elicited running behaviour characterised by brief bursts of locomotion followed by p eriods of quiescence. Somewhat surprisingly, the 7- and 12 -kHz tones elici ted running behaviour at lower intensities than did the 20-kHz tones. In Ex periment 2, it was found that exposure of Lister hooded rats to the 20-kHz acoustic stimulus (91-101 dB, SPL) for a much longer duration, up to 9 min, resulted in episodic bursts of locomotion and convulsions in a significant proportion of subjects. Both the maximal velocity of locomotion and the li kelihood of occurrence of convulsions was related to the intensity of the a coustic stimulus. Exposure of Lister hooded rats to white noise for up to 9 min also elicited episodic bursts of locomotion and convulsions in an inte nsity-dependent manner. The white noise stimulus was found to be a more eff ective stimulus than the 20-kHz stimulus in this regard. In Experiment 3, i t was found that Lister hooded rats exhibited reduced locomotion when they were exposed to a low-intensity 20-kHz acoustic stimulus (e.g., 81 dB, SPL) . In Experiment 4, it was found that Wistar rats did not exhibit locomotor bursts or convulsions when presented with 20-kHz tones using stimulus param eters equal to and even greater than those that had been shown to be effect ive in producing locomotor bursts in Lister hooded rats. Rather, Wistar rat s exhibited only reduced locomotion. The present data indicate that (1) run ning behaviour in Lister hooded rats is not specific for the 20-kHz stimulu s. Moreover, (2) when compared to Lister hooded rats, Wistar rats are relat ively insensitive to the running and convulsions elicited by acoustic stimu li. Finally, (3) both Lister hooded and Wistar rats exhibited reduced locom otion when presented with the 20-kHz tones, although the range of stimulus intensities that produces freezing behaviour is much more limited in Lister hooded rats because of their propensity to exhibit locomotor bursting and convulsions. Thus, it appears that the difference between the two strains w ith respect to their unconditioned locomotor responses to novel acoustic st imuli relates to the fact that Lister hooded rats are uniquely susceptible to acoustically elicited locomotor bursts and/or convulsions. (C) 2000 Else vier Science Inc. All rights reserved.