The effect of dehydration on brain temperature regulation in Japanese quail (Coturnix coturnix japonica).

1. The effect of dehydration and heat exposure on body and brain temperature was studied in quail exposed to increasing ambient temperatures within the range of 25-40 degrees C. 2. The body-to-brain temperature difference was not affected by increasing ambient temperature or hydration state. A mean body-to-brain temperature difference of 0.96 +/- 0.64 degrees C and 0.85 +/- 0.65 degrees C was found in normally hydrated and dehydrated quail, respectively. 3. The slope of the relation between brain temperature to body temperature (0.77) was significantly lower than 1.0 (P less than 0.001), when the results of the two hydration states were pooled. This indicates increased brain cooling with increased body temperature. 4. Body and brain temperatures of water-deprived quail were significantly higher (P less than 0.05) than those of hydrated birds during exposure to ambient temperatures of 35 and 40 degrees C. 5. Respiration frequency increased during exposure to 35 (four birds) and 40 degrees C (six birds) in the normally hydrated quail, while in the dehydrated quail, respiration frequency increased only in three birds during exposure to 35 degrees C, and four birds during exposure to 40 degrees C, the frequencies were lower during dehydration. 6. Plasma osmolality and chloride concentration were significantly higher in the dehydrated quail (P less than 0.05). 7. The present findings show that dehydration and heat exposure resulted in a relative hyperthermy, and thus implying a reduced evaporative cooling. The quail appears to be well adapted to dehydrating conditions.