In the present study we compared the metabolic responses to selective cooling of the cervical (C9--Th1) and the thoracic (Thi--Th5) parts of the spinal cord of pigeons. To obtain selective cooling of the two parts, two thermodes (4.5 cm) were inserted into the vertebral canal through an aperture in the first thoracic vertebra. During the experiments, one of the two thermodes was perfused with water at a constant temperature for periods of 15 min. The thermosensitivity was denned as the relationship between the amount of extra heat produced and the amount of heat extracted from the stimulated area. Cooling of the thoracic part resulted in a substantially higher increase in metabolic heat production and body temperature (Tb) than did cooling of the cervical part. It is concluded that the thoracic part of the spinal cord has a greater thermosensitivity than the cervical part. In addition, it was found that the difference in elevation of Tb during cooling of the two parts was not simply a result of differences in the amount of heat produced. When the changes in Tb were related to the difference between the extra heat produced and he amount of heat extracted, the increase in Tb during thoracic cooling was greater than that recorded during cervical cooling. This indicates that cooling of the two different parts of the spinal cord also had different effects on the thermoregulatory effector mechanisms that influence thermal conductance.
The study seems to provide evidence in favour of afferent transmission of cold signals in the spinal cord.