Thermoregulatory effects of central injection of noradrenaline in the Richardson's ground squirrel ( Spermophilus richardsonii)

Abstract

1. The simultaneous changes of heat production (HP), heat loss (HL) and rectal temperature (Tb) in the Richardson's ground squirrel ( Spermophilus richardsonii) to intracerebroventricular injections of noradrenaline (NA) (5.0–12.5 μg) were studied during different phases of the annual hibernation cycle, and at warm (23°C) and cold (5°C) ambient temperatures. 2. All injections resulted in activation of HP and hyperthermia, except at the lowest dose (5.0 μg) in the cold. 3. There was little difference in NA-induced increases of HP, HL or Tb between warm and cold ambient temperatures in ground squirrels in their hibernating phase. 4. During the hibernating phase, the highest dose of NA (12.5 μg) elicited greater increases of HP and Tb than during the nonhibernating phase. 5. These results indicate that modifications in central noradrenergic pathways controlling HP vary with annual cycles of hibernation.