Threshold and slope of selective brain cooling

Area of Science:

• Physiology
• Thermoregulation

Background:

• Selective brain cooling (SBC) is a thermoregulatory mechanism observed in some mammals.
• Understanding the factors influencing SBC is crucial for comprehending whole-body thermal balance.

Purpose of the Study:

• To determine the threshold and slope of selective brain cooling (SBC) in conscious goats.
• To analyze the thermal inputs affecting SBC, including head and trunk temperatures.

Main Methods:

• Experiments were conducted on three conscious goats in a thermoneutral environment.
• Animals were surgically fitted with carotid loops and an arteriovenous shunt to independently control head and trunk temperatures.
• Measurements included brain temperature, carotid blood temperature, trunk temperature, metabolic rate, and respiratory heat loss.

Main Results:

• The mean SBC threshold was 38.75°C carotid blood temperature (Tcarotis), independent of trunk temperature (Ttrunk).
• The mean SBC slope was 0.78 and increased with rising Ttrunk.
• SBC was largely independent of respiratory heat loss, with high heat loss occurring without SBC and significant SBC observed at low heat loss levels.
• The SBC threshold was reached before metabolic rate minimum or cutaneous vasodilation during hyperthermia.

Conclusions:

• Selective brain cooling in goats operates at a specific threshold and is modulated by trunk temperature.
• SBC plays a role in smoothing the onset of shivering and panting, creating a stable internal temperature range.
• This mechanism contributes to efficient thermoregulation by minimizing metabolic and respiratory heat loss around normothermia.