Electromyographic (EMG) study of cold shivering in the chronic spinal dog

Cold shivering in six chronic spinal dogs (T9-10), which became capable of weight-bearing standing and/or walking with their hindlimbs, was studied by electromyography (EMG). In the forequarters, EMG activities in the form of grouping discharges (GD) accompanied by visible tremor (VT) were induced at an ambient temperature of 15 degrees C in all the dogs. In the hindquarters, GD with VT were induced at 3 degrees C in one dog. Although GD with VT were not induced in in the remaining dogs, GD without VT were produced by additional cutaneous stimuli to the hindquarters at 3 degrees C. These stimuli never produced GD in the hindquarters at room temperature. Though the mean frequency of GD in the hindquarters was lower than that in the forequarters, the range of the frequency in the hindquarters was much the same as that in the forequarters. During the experiment, the drop in rectal temperature was less than 0.6 degrees C in all of the dogs. These findings suggest that the chronically isolated spinal cord is responsible for cold shivering, while its excitability to cold exposure is less than that of the spinal cord governed by the supraspinal center.