AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 2 219-R227, Copyright © 1985 by American Physiological Society
Diurnal changes in thermoregulatory behavior in rats with medial preoptic lesions
R. Szymusiak, A. DeMory, E. M. Kittrell and E. Satinoff
Rats with medial preoptic area (MPOA) damage lack adequate autonomic
thermoregulatory reflexes but can behaviorally regulate their body
temperatures (Tb) in the cold and heat. We examined the performance of such
rats on 90-min behavioral thermoregulatory tests. Tests were conducted
during the day and night to determine the preferred Tb at different phases
of the circadian Tb rhythm. The amplitude of this rhythm was exaggerated
after electrolytic MPOA lesions; differences of 3-4 degrees C between daily
peaks and troughs were seen (from 37 degrees C during day to 40-41 degrees
C at night) compared with control variations of only 1.5-2.0 degrees C
(from 36.0-36.5 degrees C during day to 38 degrees C at night). When
escaping cold during the day or night or when escaping heat at night, both
MPOA-damaged and control rats maintained Tb within +/- 0.5 degrees C of
initial values. When escaping heat during the day, control and MPOA-damaged
rats allowed their TbS at the end of the 90-min behavioral tests to rise to
normal night levels (38 degrees C for controls and 40-41 degrees C for MPOA
rats). These results demonstrate that rats with MPOA damage behaviorally
defend the different phases of their exaggerated Tb rhythm in a manner
similar to that of controls. Therefore the exaggerated swings in Tb seen in
these preparations have an active regulated component and are not simply
passive results of an excessive rhythm in heat production or heat
conservation.
