Studying stress and homeostasis in tuco-tucos: unusual physiological traits revealed when laboratory and field studies work together

VERA F.; ZENUTO R.R.; ANTENUCCI C.D.

Mendoza, Argentina

Simposio; X international mammalogical congress; 2009

The talk will describe our recent findings about the physiology of the stress axis and regulation of blood glucose in Ctenomys talarum (tuco-tucos). The species exhibits various peculiarities with plasma levels of glucocorticoids (GCs, cortisol and corticosterone) that fall at the lower extreme of the mammalian range and contrast with extremely-high testosterone concentrations. Noteworthy, cortisol and corticosterone were found in similar amounts in the field, which contrasts with previous studies in other rodents showing marked differences in the concentrations of both GCs. Furthermore, cortisol and corticosterone showed different patterns of variation in free-living animals throughout the breeding cycle and were differently affected by captivity. Also, experiments in the field and laboratory revealed that only cortisol is responsive to acute stress in the species. All these evidence suggest differentiated physiological roles for cortisol and corticosterone in tuco-tucos. When we were evaluating the possibility of using blood glucose as a stress indicator in the species, we registered a decreased capacity of regulating glycemia in glucose tolerance tests (GTT) in comparison to mammalian standards. Though hystricomorph rodents are known to have an insulin molecule with a decreased biological activity, only one species –the naked mole rat- has previously shown  an impaired response in a GTT. All other species of caviomorphs rodents (South American hystricomorphs) assayed to date were able to regulate blood glucose in GTTs like non-hystricomorph mammals suggesting the existence of compensatory physiological traits. Importantly, blood glucose levels in field tuco-tucos were within the normal mammalian range which demonstrates that a larger capacity of regulating blood glucose is not actually required to achieve optimal concentrations. Our results indicate that species within the genus Ctenomys are very interesting models to explore the ecophysiology of the stress axis and blood glucose homeostasis in mammals.