Differential expression of Fos protein in the rat brain induced by performance of avoidance or escape in the elevated T-maze

Analysis of Fos protein expression was used to map brain areas activated by exposure of male Wistar rats to the elevated T-maze, an animal model of an xiety where tasks of inhibitory avoidance or one-way escape can be separate ly performed. The apparatus consists of three elevated arms - one enclosed and two open. In the inhibitory avoidance task - considered to represent le arned fear - the time taken by rats to leave from the enclosed arm in three consecutive trials is measured. One-way escape task is measured by recordi ng the time taken by animals to withdraw from the open arm and is thought t o reflect innate fear. Control animals were placed three times at the end o f the transversal arm of a T-maze composed of three enclosed arms and withd rawal latencies from this arm was similarly measured. Performance of avoida nce task increased Fos-like immunoreactivity in the medial amygdaloid nucle us, in the anterior hypothalamic nucleus and in the median raphe nucleus. I n contrast, performance of escape task enhanced Fos-like immunoreactivity i n the basolateral amygdaloid nucleus and in the dorsal periaqueductal gray matter of the mesencephalon. Both behavioural tasks promoted an increase in Fos-like immunoreactivity in the paraventricular nucleus of the thalamus a nd in the dorsomedial hypothalamic nucleus. Therefore, the obtained results indicate that different sets of brain structures were, respectively, activ ated by inhibitory avoidance and one-way escape. This evidence supports the original hypothesis that two types of fear/anxiety are generated in the el evated T-maze. (C) 2001 Published by Elsevier Science B.V.