The air-puff startle is an example of a simple behavior in mammals. Following the startle reaction, rats assume a defensive-like, immobile posture (DIP) of approximately 2-5 s in length. The aim of the present study was to examine the effect of bilateral lesions of the nucleus locus coeruleus/subcoeruleus (LC/SC) on the DIP. Using male Sprague-Dawley rats, the DIP period in the air-puff startle was measured with a digital stop watch. The DIP period was defined as the time between the application of the air-puff stimuli and the first motion after the startle reaction. For air-puff stimulation (14.4 psi in strength, 0.1 s in duration), compressed house air was presented as a transient through a vinyl tube suspended 2.5 cm above the rat's head. Two weeks before the experiment, the rats received bilateral injections of 6 microg of the neurotoxin 6-hydroxydopamine to specifically lesion noradrenaline-containing neurons of the LC/SC. In the sham-lesioned rats (n=8), the DIP period did not significantly alter compared with that before operation. In contrast, in the LC/SC-lesioned rats (n=9), the DIP period significantly reduced to 78% of the values before lesions. The results suggest that the LC/SC is involved in the development of the DIP. We speculate that the DIP period is an attentional state and vigilance condition because LC/SC neurons have been implicated in the regulation of the attentional state and vigilance.
2010 IBRO. Published by Elsevier Ltd. All rights reserved.