Central c-fos expression following 20kHz/ultrasound induced defence behaviour in the rat.

Exposure of rats to aversive stimuli produces specific defence behaviour including the emission of 20-27kHz ultrasonic calls. Recent studies in this laboratory have shown that rats exposed to a 20kHz ultrasound tone display flight behaviour similar to that seen naturally, or following stimulation of brain regions associated with anxiety and defence. The present study examines the effect of ultrasound exposure on the central expression of the immediate early gene c-fos in the rat, in order to examine the brain structures activated by such behaviour. Ultrasound presentation produced rapid locomotor activity characteristic of defence behaviour, including brisk running and jumping behaviour. Animals showed dense c-fos like immunoreactivity in the dorsal periaqueductal grey matter, basolateral, medial, central amygdala, paraventricular thalamic nuclei and the dorsomedial nuclei of the hypothalamus, which was significantly greater than in either home-cage or arena control rats. These results suggest that exposure to artificially generated ultrasound can induce defence behaviour which is associated with activity in brain regions important in mediating aversion. This technique offers the potential of generating unconditioned aversive behaviour in rats in a non invasive way.