Effects of age on thermoregulatory responses during cold exposure in a nonhuman primate, Microcebus murinus

1 Mécanismes Adaptatifs et Évolution, UMR Centre National de la Recherche Scientifique/Museum National d'Histoire Naturelle 7179, Brunoy, France; and 2 Neurobiologie de la Croissance et de la Sénescence, UMR 549 Institut National de la Santé et de la Recherche Médicale, Paris, France Submitted 31 August 2007 ; accepted in final form 3 June 2008 Cold resistance appears altered with aging. Among existing hypotheses, the impaired capacity in response to cold could be related to an altered regulation of plasma IGF-1 concentration. The combined effects of age and cold exposure were studied in a short-living primate, the gray mouse lemur ( Microcebus murinus ), which adjusts its energy balance using a daily torpor phase, to avoid high energy cost of normothermia maintenance. Changes in body mass, core temperature, locomotor activity, and caloric intake were monitored under 9-day exposures to 25°C and 12°C in captive animals in winter conditions. Short-term (after 2 days) and long-term (after 9 days) cold-induced changes in IGF-1 levels were also evaluated. In thermoneutral conditions (25°C), general characteristics of the daily rhythm of core temperature were preserved with age. At 12°C, age-related changes were mainly characterized by a deeper hypothermia and an increased frequency of torpor phases, associated with a loss of body mass. A short-term cold-induced decrease in plasma IGF-1 levels was observed. IGF-1 levels returned to basal values after 9 days of cold exposure. No significant effect of age could be evidenced on IGF-1 response. However, IGF-1 levels of cold-exposed aged animals were negatively correlated with the frequency of daily torpor. Responses exhibited by aged mouse lemurs exposed to cold revealed difficulties in the maintenance of normothermia and energy balance and might involve modulations of IGF-1 levels. autonomic thermoregulation; cold exposure; insulin-like growth factor; aging; Microcebus murinus Address for reprint requests and other correspondence: J. Terrien, Mécanismes Adaptatifs et Évolution, UMR CNRS/MNHN 7179, 1 Ave. du Petit Château, 91800 Brunoy, France (e-mail: terrien{at}mnhn.fr )