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The purpose of this study was to examine the contribution of the central nucleus of the amygdala to the expression of stress-induced increase in corticosterone and renin secretion. Neurons in the central amygdaloid nucleus of male rats were destroyed by bilateral injections of ibotenic acid, a neurotoxin that destroys cells but leaves fibers of passage intact. Two weeks later, the rats were subjected to immobilization for 20 min or to a conditioned stress (conditioned emotional response) procedure. Central amygdala lesions inhibited the increases in plasma corticosterone after exposure to both conditioned stress and immobilization. Lesions in the lateral amygdala had no effect on the corticosterone response to either stressor. Lesions in the central amygdala attenuated the renin response to conditioned stress but not to immobilization. In contrast, lateral amygdala lesions potentiated the renin response to immobilization but did not affect the renin response to conditioned stress. The results confirm previous studies that demonstrate the importance of the central amygdaloid nucleus in the expression of corticosterone to immobilization stress. In addition, the results show that neurons within the central amygdaloid nucleus are necessary for the full expression of conditioned stress-induced increase in corticosterone and renin secretion. The results are discussed with respect to the potential pathways that mediate stress-induced increases in corticosterone and renin secretion.

The contribution of the bed nucleus of the stria terminalis (BST) to the expression of stress-induced increases in ACTH/corticosterone, prolactin and renin secretion was assessed. Neurons in the lateral part of the BST were destroyed with bilateral injections of the cell-selective neurotoxin ibotenic acid (1.5 µg in 0.1 µl of solution per side). Two weeks later, the rats were stressed using an immobilization or conditioned stress paradigm. Rats with lesions in the lateral part of the BST showed attenuated ACTH and corticosterone responses to conditioned stress. Bilateral ablation of lateral BST significantly reduced the prolactin secretory response to conditioned stress. The same lesions had no effect upon plasma increases in renin that occur in response to conditioned stress. Also, destruction of neurons in the BST did not affect immobilization-induced increases in ACTH, corticosterone, prolactin or renin. Previous studies have demonstrated that ibotenic acid lesions in the central amygdala reduce corticosterone and renin response to conditioned stress. Thus, both the BST and central amygdala are important for the adrenocortical response to conditioned stress. Neurons in the central nucleus of the amygdala are part of the circuitry that mediates renin responses to conditioned stress. Neurons in the BST are important for the full expression of prolactin responses to conditioned stress. The neuronal circuitry and stressor specificity in the mediation of prolactin, renin and ACTH/corticosterone responses are discussed.

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