Cyclic and non-cyclic variations of spinal cord temperature related with temperature regulation in pigeons

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Abstract
The temperature of the spinal cord (T vc) was measured in unanaesthetized pigeons at different ambient temperatures (T a). In short-term experiments spontaneous or noncyclic variations ofT vc at constant (20 and 10°C) and changingT a were correlated with the amplitude of the electromyogram (EMG) which indicates shivering, i.e., heat production. At constantT a no unequivocal correlation betweenT vc (and alsoT skin) and EMG was found. During ambient cooling there was often an increase ofT vc which resulted in a positive correlation whereas there was a negative correlation toT skin. In long-term experiments (24h, LD 12∶12) cyclic variations ofT vc were measured at differentT a and correlated with O2-consumption, i.e., heat production. As with body temperatureT vc was lowered during the dark phase of the diurnal cycle. In the light phase bothT vc and heat production increased with decreasingT a which results in a positive correlation. In the dark phase there was a smaller increase in heat production but a decrease inT vc, i.e., a negative correlation. The results show that natural variations ofT vc are often positively correlated with heat production. This is in contrast to experimental changes ofT vc where a clear negative correlation to heat production can be observed.