Anatomical and physiological evidence for efficacious selective bran cooling in rats

1. To describe a mechanism of selective brain cooling (SBC), vascular structures constituting main parts of the SBC system were studied in 40 control and 13 warm-reared adult Wistar rats. Deleterious effects of invasive techniques of cerebral temperature measurement on cranial vascularization and SBC were also investigated in another group of 20 warm-reared rats. 2. There were two main venous pathways from thermolytic surfaces of the head to the intracranial cooling system, consisting of dural sinuses via the dorsal nasal and frontal veins and via the diploic network of the nasal bones conveying venous blood through the frontoparietal diploic network. 3. The diploic network covered 9.0 +/- 1.1% of the frontoparietal surface area in control rats and 12.4 +/- 1.3% in warm-reared rats. 4. Dural sinuses covered nearly 30% of dorsal cerebral surface area, a pattern unaffected by warm rearing. 5. Histological studies showed the existence of muscular sphincters in the angularis oculi and facial veins. Their contraction in hyperthermia is likely to divert cool blood, returning from the head skin to the brain. 6. Replacing an invasive measurement of cerebral temperature by a non-invasive technique increased the magnitude of SBC from 0.15 +/- 0.09 degrees C to 0.90 +/- 0.27 degrees C. 7. It is concluded that venous mechanisms of SBC in rats are well developed and efficacious.