Thermosensitivity of the extrahypothalamic brain stem in conscious goats

In 5 conscious goats, 84 experiments with 881 perfusion periods were performed to explore the brain stem between the rostral medulla and preoptic region for thermo-sensitive structures involved in temperature regulation. The chronically implanted thermodes consisted of 24 or 27 single probes, which were arranged in 8 or 9 rows. The rows of probes were individually perfused with water of 25-46 degrees C to produce discrete temperature stimuli along the brain stem. When the animals were exposed to an air temperature of +4 degrees C, local cooling at various levels of the lower brain stem augmented shivering and increased heat production, which was not regularly followed by a rise in rectal temperature. Ongoing shivering was reduced by local warming of the same sites. In comparison to the effects of hypothalamic thermal stimuli, the magnitude of the lower brain stem responses was reduced. At an air temperature of +30 degrees C local warming of discrete areas of the lower brain stem increased panting and caused a significant rise in respiratory evaporative heat loss. However, panting and shivering were not affected by the same site, and the effective sites of the various animals were not found at corresponding anatomical positions. Thus, thermosensitive sites which are not associated with defined anatomical structures, appear to be dispersed in the lower brain stem of the goat and to interfere with the temperature regulating system.