Long-term sensitization of Fos-responsivity in the rat central nervous system after a single stressful experience

There is considerable evidence for a role of stressful experiences in psych osomatic disorders in humans, but the mechanisms leading to altered respons ivity and the relative contributions of central and peripheral neuronal cha nges, however, are still under debate. To investigate the contribution of s pecific brain areas to sensitized responsivity, rats were exposed to a sing le brief session of inescapable footshocks (preshocked) or no shocks (contr ol) in a,gridcage. Two weeks later, an electrified prod was inserted in the home cage for 15 min and the behaviour recorded. One hour later rats were perfused and brain sections were stained for Fos protein immunoreactivity. The number of Fos positive neurons was quantified in 27 brain areas. No sig nificant difference in behaviour was found between the groups during the sh ock prod challenge. A significantly higher number of Fos positive neurons w as found in preshocked rats compared to controls in the following brain are as: agranular insular cortex, frontal cortex, nucleus accumbens, bed nucleu s of the stria terminalis, basolateral amygdala, CA1 area of the hippocampu s, paraventricular hypothalamic nucleus, dorsolateral central grey, locus c oeruleus, nucleus of the solitary tract and lateral paragigantotellular nuc leus. We conclude that altered reactivity to stressful challenges in brain areas involved in neuroendocrine and autonomic control may play a role in l ong-term sensitization of neuroendocrine and autonomic responses in preshoc ked rats under conditions where behavioural sensitization is not expressed. (C) 1999 Elsevier Science B.V. Ail rights reserved.