Delineation of responsive AVP-containing neurons to running stress in the hypothalamus

Abstract

Running becomes a stress, termed running stress, if it persists above the lactate threshold (LT) and results in enhanced plasma ACTH level in humans. Although the exact underlying regulation mechanism is still uncertain, hypothalamic AVP has been shown to play a dominant role in running-induced ACTH release. It is still not known, however, whether running stress activates the hypothalamic AVP-containing neurons that are involved in the activation of the ACTH response. For this reason, we applied our rat running stress model, in which both plasma ACTH and osmolality levels increase just above LT running (supra-LT running), to delineate which hypothalamic AVP neurons were responsive to running stress. Rats were previously habituated to running and then subjected to a 30-min run either just below or above the LT. Plasma samples were collected from these animals to determine ACTH and osmolality levels. Brains were prepared for immunocytochemistry for both AVP/Fos in the hypothalamus and enzyme immunoassay for the stalk median eminence (SME) AVP content. Only supra-LT running resulted in an increase in the number of Fos/AVP-immunoreactive neurons in both the parvocellular paraventricular nucleus (pPVN) and the magnocellular supraoptic nucleus (SON) accompanied by increased ACTH and plasma osmolality levels. Similarly, running reduced the SME content of the AVP. We thus found that AVP-containing neurons located in both the pPVN and SON are responsive to running stress just above the LT.

Possible inhibitory role of prolactin-releasing peptide for ACTH release associated with running stress

“…The reason for this discrepancy is unclear at present; however, it is possible that the role of brain PrRP in ACTH release depends upon the type of stress stimuli used. We previously reported that running stress activates AVP neurons in the pPVN and the SON (32). Other previous studies have also shown that AVP, rather than CRH, might play a major role in the facilitation of ACTH release during running (1,38), suggesting that the running stress may differ from other types of stress in which ACTH secretion is mainly regulated by CRH.…”

“…We previously showed that supra-LT running increased ACTH and blood lactate concentrations, which have been used as indexes of running stress (32,39). The running paradigm was composed of both below-and supra-LT, which are typical exercise intensities that induce different hormonal and metabolic responses to running (44,45), as shown in Fig.…”

“…We had previously shown that supra-LT running induces both ACTH release and elevation of blood lactate accumulation (32,39). These two parameters had been established as indexes of running stress.…”

“…To examine the regulating mechanism underlying running stress, we established the rat treadmill running model and used it to identify anatomic activation of the parvocellular part of the hypothalamic paraventricular nucleus (pPVN) and the supraoptic nucleus (SON) during running stress (32,39). The next step in our studies will be to identify the nuclei or neuropeptides that regulate ACTH release during running stress via pPVN and SON activation.…”

Inhibition of Stress-Induced Adrenocorticotropin and Prolactin Secretion Mediating Hypophysiotropic Factors by Antagonist of AMPA Type Glutamate Receptor

“…Some evidence has been reported showing that glutamate affected CRH or AVP at the levels of the ME. Saito et al [32] recently reported that running stress decreased the ME content of AVP and increased in the plasma concentrations of ACTH in male rats, and they suggested that the reduction of the AVP content in the ME might be the result of an increase of AVP release into the portal blood. In the present study, NBQX-induced suppression of ACTH secretion may have been mediated by the inhibition of CRH and AVP release into the portal vein.…”