Endurance treadmill training in rats alters CRH activity in the hypothalamic paraventricular nucleus at rest and during acute running according to its period

Running training on the treadmill increases the resting hypothalamic corticotropin-releasing hormone (CRH) content in rats, though is still unknown whether and how it occurs in the parvocellular region of the hypothalamic paraventricular nucleus (PVN) where is a predominant region of pituitary-adrenal activity and where CRH and arginine vasopressin (AVP) are colocalized. We thus aimed at examining whether treadmill training would alter the CRH and AVP mRNA levels in the PVN at rest and during acute running with different lengths of a training regime. Male Wistar rats were subjected to treadmill running (approximately 25 m/min, 60 minutes/day, 5 times/week) for training regimes of 0, 1, 2 or 4 weeks. All training regimes induced an adrenal hypertrophy. Plasma corticosterone levels before acute running increased with lengthening the training period. Four weeks of training produced a significant increase in the resting CRH, but not AVP, mRNA levels in the PVN though relatively shorter training regimes did not. Acute responses of lactate and ACTH release were reduced after 2 and 4 weeks of training, respectively. The responsive PVN CRH mRNA level to acute running decreased with 4 weeks of training but increased with relatively shorter training regimes. These results indicate that running training changes the PVN CRH biosynthetic activity with the regime lasting for 4 weeks, which follows adaptive changes in adrenal functions. Thus, running training-induced changes in hypothalamic CRH activity would originate from the PVN and be induced according to the training period.