AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 577-R581, Copyright © 1982 by American Physiological Society
Regulation of brain temperature in pigeons: effects of corneal convection
B. Pinshow, M. H. Bernstein, G. E. Lopez and S. Kleinhaus
The effect of direct ventilation of the eyes on cooling in the brain was
investigated in domestic pigeons (Columba livia, mean mass 0.27 kg) with
thermocouples chronically implanted in the hypothalamus and anterior eye
chamber. During conductive heating in still air body-brain temperature
difference (delta T) was 2.6 degrees C. During exclusive ventilation of
ocular surfaces, with air flowing at about flight speed, delta T increased
to 3.5 degrees C and returned to preventilation values on cessation of
ventilation. When the eyes were sealed then ventilated, delta T was not
different from that in still air. Administration of phenylephrine caused
iridial vasoconstriction and a significant decrease in intraocular
temperature, but no changes in brain temperature. This suggests that
compensation may occur via other evaporating cranial surfaces. Our findings
suggest that the eyes contribute to the control of brain temperature by
dissipating heat. Blood cooled while flowing through the ocular vasculature
apparently contributes to the venous flow through the ophthalmic rete,
serving as a heat sink for arterial blood flowing to the brain.
