Stress-induced changes in c-Fos and corticotropin releasing hormone immunoreactivity in the amygdala of the spontaneously hypertensive rat.

The present study was undertaken to test the hypothesis that dysregulation of the amygdala contributes to the exaggerated autonomic response to stress in an animal model of essential hypertension. Spontaneously hypertensive (SHR) and normotensive Wistar male rats were chronically instrumented and exposed to 20 min of either air jet stress (AJS) or air noise alone (CON). AJS induced a significant increase in both heart rate and arterial pressure that was greater in the SHR. AJS induced a significant increase in c-Fos-like immunoreactivity (FLI) throughout the caudal-rostral extent of the basolateral, medial, and central (CEA) subnuclei of the amygdala. Differences in FLI between strains were localized to the rostral CEA and the SHR expressed significantly less FLI. AJS also induced a significant increase in the number of corticotrophin releasing hormone (CRH) positive neurons in the CEA. Differences between strains were localized to the caudal CEA and the number of CRH-positive cells was significantly greater in the SHR. The stress-induced increase in CRH labeling in caudal CEA of the SHR was coupled to a greater increase in FLI in the rostral locus coeruleus (LC) of the SHR versus the Wistar. AJS also induced significant increases in FLI in several hypothalamus subnuclei, but no strain-related differences were identified. These results suggest for the first time that dysregulation of CRH-positive cells in the caudal CEA and reduced excitation and/or exaggerated inhibition of rostral CEA neurons may contribute to the exaggerated cardiovascular response to stress in the SHR, possibly through descending modulation of the rostral LC.