Journal of Applied Physiology, Vol 49, Issue 6 942-945, Copyright © 1980 by American Physiological Society
Effects of repeated heat exposure on hypothalamic sensitivity to norepinephrine
J. V. Christman and C. V. Gisolfi
Bilateral stainless steel guide tubes were stereotaxically implanted above
the anterior hypothalamus (AH) of 12 male Sprague-Dawley rats (300-360 g).
Beginning 3 days postsurgery, norepinephrine (NE) was injected into the AH
each day at increasing depths below the guide tube until colonic
temperature fell at least 0.8 degrees C. Subsequently, the effects of
treadmill exercise at 21.5 m/min for 3 wk at 22 degrees C (n = 6) or 35
degrees C (n = 6) on the magnitude of the NE-induced hypothermia were
investigated. Training duration ranged from 12 to 50 min/day, depending on
the time required for colonic temperature of the heated rats to rise to a
predetermined level: 40.4 degrees C on day 1, increasing 0.1 degree C/day
to 41.5 degrees C on day 12 and thereafter. Before and after training,
bilateral injections of NE (10 micrograms) at 22 degrees C at rest and just
before exercise (21.5 m/min) caused the following mean +/- SE reductions in
colonic temperature (degree C). (Formula: See Text). These reductions in
colonic temperature were associated with sharp elevations in tail-skin
temperature, but there were no significant differences in the response
between the two groups. We conclude that repeated heat exposure increased
the sensitivity of the AH to exogenous NE.
