Lesions of the anteroventral third ventricle region exaggerate neuroendocrine and thermogenic but not behavioral responses to a novel environment

Abstract

of the anteroventral third ventricle region exaggerate neuroendocrine and thermogenic but not behavioral responses to a novel environment. Am J Physiol Regul Integr Comp Physiol 292: R137-R142, 2007. First published August 10, 2006; doi:10.1152/ajpregu.00465.2006.-Mild psychological stressors provoke an acute rise in core temperature (T C), stimulate the hypothalmo-pituitary-adrenocortical (HPA) axis, and induce various stress-related behaviors. In the present study, we examined the effect of ablation of the anteroventral third ventricle region (AV3V) on both physiological and behavioral responses to a novel environment. T C was monitored in male Sprague-Dawley rats, with either sham or AV3V lesions, during a 5-h exposure to a novel environment. Trunk blood was collected, in a second group of rats, for the assessment of plasma levels of ACTH and corticosterone. Novelty-induced grooming and rearing behaviors were assessed in a third group of animals. T C was elevated in all animals after 30 min in the novel environment, but the rise was exaggerated in rats with AV3V lesions (ϳ0.5°C). AV3V-lesion rats maintained a higher core temperature for 2 h before it returned to the same level as the control group. Plasma levels of ACTH and corticosterone were also exaggerated in the AV3V lesion group after 30 min in a novel environment. In contrast to the physiological responses, the behavioral measures of grooming and rearing revealed no differences between the groups. The results from the current study suggest that neurons within the AV3V region exert an inhibitory influence on the HPA axis and fever developed in response to stressful psychological stimuli. They also confirm that the physiological and hormonal components of the stress response are independent of certain behavioral measures of stress.Sprague-Dawley rats; grooming; adrenocorticotropic hormone; corticosterone; temperature; psychological stress FEVER CAN BE ELICITED BY EITHER physical or psychological stressors. While both febrile responses are mediated by PGE 2 (15, 21), there is a growing consensus that physical and psychological stressors utilize different prostaglandin E 2 receptor subtypes (EP 1 -EP 4 ) (25, 33) and separate neural circuits (6, 9, 28) to generate the elevation in core temperature (T C ). For example, physical stressors (e.g., infection, hemorrhage) are relayed directly with effector neurons in the hypothalamus, whereas psychological stressors (e.g., novelty, conditioned fear, restraint), which require comparison with previous experience to obtain biological significance, are first routed through limbic structures.The anteroventral third ventricular (AV3V) region, an anatomic area that encompasses the organum vasculosum of the lamina terminalis, the ventral portion of the median preoptic nucleus (MnPO), the anteroventral periventricular nucleus, and the periventricular hypothalamic nucleus (4), is thought to play a pivotal role in the modulation of LPS-induced fever. Fos-like immunoreactivity is elevated in the AV3V region after intravenou...

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