EMG activity in pectoral and femoral muscles during spinal cord cooling in exercising pigeons

Abstract

Adult domestic pigeons, with thermodes chronically implanted in the vertebral canal, were trained to walk on a treadmill. In the first series of experiments, EMG activity in a pectoral (M. pectoralis) and a femoral muscle (M. biceps femoris) was measured to determine if shivering could occur during exercise. When the spinal cord was cooled (36.2±0.5°C) during exercise (0.6 km/h), pectoral muscle EMG activity increased by 80%, while femoral muscle EMG activity did not change significantly. EMG activity remained unchanged during exercise in control experiments where the spinal cord was not cooled.

In the second series of experiments, the spinal cord was first cooled (36.1±0.5°C) for 5 min in resting pigeons and then the treadmill was started. Spinal cord cooling during rest significantly increased pectoral muscle EMG activity but not that of the femoral muscle. Within 1 s after the onset of exercise, EMG activity in the pectoral muscle decreased by 74%.

In both series of experiments, shivering was not induced in the femoral muscle. The level of pectoral muscle EMG activity stimulated by spinal cord cooling during exercise in the first series of experiments corresponded to the level to which EMG activity was reduced by exercise during spinal cord cooling in the second series of experiments (192% and 186% in relation to the post-cooling level, respectively).

It is concluded that shivering can be induced in the pectoral muscle by spinal cord cooling during exercise in the pigeon. The level of shivering induced in the pectoral muscle is well balanced according to the degree of spinal cord cooling (thermal information) and the running speed of exercise (non-thermal information possibly from active muscles and joints).