[Thermoregulatory activity of the intercostal muscles under a hypercapnic load].

In experiments on anesthetized cats, the reactions elicited by CO2 inhalation were studied in single motor units of the intercostal muscles activated during shivering. The excitation of the bulbar respiratory center during shivering was found to modify the activity of the respiratory and tonic motor units. Most of the respiratory motor units in a hypercapnic state increased the mean firing rate by 1.5/sec. The tonic motor units both diminished the mean firing rate and changed the pattern of activity: they began to produce bursts of spikes synchronous with the respiratory rhythm. The problems of supraspinal regulation of activity of the intercostal muscles motoneuron pool are discussed.