Limbic control of endocrine glands in aged rats

Two weeks after bilateral lesions in the dorsal and ventral hippocampus, septum, and basolateral amygdala, plasma concentrations of ACTH, TSH, corticosterone, aldosterone, and thyroxine were determined in 5-6 month-old (adult) and 24-26-month-old (aged) male Wistar rats. The results indicate that with age, limbic system control over the hypothalamic-pituitary- adrenal/thyroid axes changes, although these changes are not uniform. Thus, the inhibitory influences of the dorsal/ventral hippocampus and septum on ACTH release tend to diminish as age increases. However, the inhibitory influence of the amygdala on ACTH appears to become enhanced during the aging process. The data also support an enhanced sensitivity of the adrenal cortex to ACTH during aging. In adult animals, lesions of the dorsal/ventral hippocampus and amygdala result in significantly decreased plasma concentrations of TSH consistent with a stimulatory influence of these regions on TSH release. Lesions in the septum, however, lead to significantly increased TSH secretion in these animals. To these finding, lesions of the dorsal/ventral hippocampus and amygdala in aged animals resulted in significantly increased TSH secretion, while results of septal lesions were not significant.