Methodology
Yellowfin tuna were implanted with a device to measure slight changes in temperature through the pineal foramen of the skull to record brain temperature, and then exposed to step changes in ambient, or surrounding, temperature and then back. The effectiveness of the carotid heat exchanger in affecting heat flux was examined by calculating the thermal rate coefficient from the rates of brain temperature change. To test for nervous control of retial efficiency, several tuna were injected with bretylium tosylate to abolish the effects of adrenergic nerve cells, or fibers of the autonomic nervous system that employ norepinephrine as their neurotransmitter.
Results
Excess brain temperatures in the yellowfin were not significant; however, rates of brain cooling during drops in ambient temperature were significantly lower than rates of heating when water temperature was increased. This difference indicates alterations in the effectiveness of the heat-exchanger to reduce heat loss during exposure to colder waters, and enhance heat gain upon return to warm waters. On average, the brain warmed about 50 percent faster than it cooled.
Conclusions
A hypothesis has developed that temperature could be regulated in tissues with retial blood supply by diverting blood through the rete or partially
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Contact: Donna Krupa
djkrupa1@aol.com
703-967-2751
American Physiological Society
26-Aug-2002