Effects of motor activity on the elicitation and modification of the startle reflex in rats

Abstract

In order to examine the effects of efferent processes on the elicitation and modification of startle behavior, we administered startle-eliciting stimuli to rats while they were engaged in spontaneous motor activity. When tone bursts (Experiment 1) or electric shocks (Experiment 2) were used to elicit the reflex, its amplitude was substantially less when the rats were active than when they were quiet. Grooming, face washing, and consuming were associated with the greatest reduction. The ability of a 50-dB auditory prepulse to inhibit a subsequent auditory startle was also reduced during activity (Experiment 3). The amount of inhibition produced by a prepulse was decreased even when the baseline startle responses were equated in quiet and activity by varying the intensity of the eliciting stimulus, indicating that the reduction was not due to an artificial "floor effect" (Experiment 4). The study demonstrated that both sensory and motor events affect reflexive responses in the rat, as is known for the human.Variation in the strength of an elicited reflex can be attributed in large part to the different properties of the eliciting stimulus and the conditions under which it is presented. The amplitude of the acoustic startle reflex in the rat (Fleshler, 1965) and in the human (Berg, 1974) is related to the tonal frequency of the eliciting stimulus (Foss, 1985), its intensity (Hoffman & Searle, 1968), duration (Marsh, Hoffman, & Stitt, 1973), rise time (Ison, 1978), and repetition rate (Davis, 1970). In addition, lawful modification of the startle reflex results from varying the intensity and lead time of sensory stimuli presented prior to or accompanying the eliciting stimulus (Hoffman & Searle, 1968; Ison & Hammond, 1971;Krauter, Leonard, & Ison, 1973). Thus, elicitation and modification of the startle reflex are inherently dependent on the characteristics of external sensory inputs which temporally surround the response.In addition to these external sensory events, variation in reflex strength appears to depend on internal efferent processes as well. In laboratory animals, stimuli paired with noxious events facilitate the startle reaction, an effect hypothesized to result from their conditioned elicitation of emotional reactions (Brown, Kalish, & Farber, 1951;Davis & Astrachan, 1978). In the human, Jendrassik (1883) demonstrated that when patients pulled oneThis work was supported in part by a research grant from the United States Environmental Protection Agency, R-8068201, and a NSF predoctoral fellowship award to John R. Wecker. Although this research was supported by the U.S. Environmental Protection Agency, it has not been subjected to the agency's peer and policy review. Therefore, it does not reflect the view of the agency and no official endorsement should be inferred.Portions of this paper were presented at the annual meeting of the Eastern Psychological Association, April 1981, New York. The authors wish to thank K. Sheldon and S. Rumsey for technical assistance, and A. Eastwood for editorial review. Send...

Endogenous neurotensin is involved in estrous cycle related alterations in prepulse inhibition of the acoustic startle reflex in female rats

“…Despite the prediction of circadian regulation of PPI in male rats based on the activity dependent reduction in the ability of a prepulse to inhibit a subsequent startle response as reported by Wecker and Ison (1986), circadian regulation of PPI in male rats was not found when PPI was measured in a 4 hour time frame between 2-6 hours after lights on or off (Weiss et al, 1999). In accordance with these results, we report no significant overall effect of light status (i.e.…”

Hyperactivity, decreased startle reactivity, and disrupted prepulse inhibition following disinhibition of the rat ventral hippocampus by the GABAA receptor antagonist picrotoxin

“…Previous work has indicated that motor activity may decrease startle reactivity and also PPI (Wecker and Ison 1986;Plappert et al 1993). Whereas in particular grooming had a strong effect, gross postural changes, such as turning, did not affect startle and PPI (Wecker and Ison 1986).…”

“…Whereas in particular grooming had a strong effect, gross postural changes, such as turning, did not affect startle and PPI (Wecker and Ison 1986). Picrotoxin infusion into the ventral hippocampus induced increased locomotor activity, which results from gross postural changes, while there was no evidence of increased grooming.…”

Activation of Amygdala CholecystokininBReceptors Potentiates the Acoustic Startle Response in the Rat

“…(100 nM in 5 l; Frankland et al, 1996). Because decreases in motor activity are associated with increases in startle amplitudes (Wecker and Ison, 1986;Plappert et al, 1993), it is necessary to test whether drug infusions have nonspecific effects on locomotor activity in experiments such as these. However, we found that similar doses of pentagastrin had no effect on locomotor activity over a similar time course.…”

“…To control for the possibility that increases in startle amplitudes result from decreases in motor activity (Wecker and Ison, 1986;Plappert et al, 1993), in Experiment 2 we tested whether similar intra-amygdala infusions of pentagastrin affect locomotor activity. A randomly selected subset (n ϭ 24) of rats tested for startle in Experiment 1 was used in this experiment.…”