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

1. The temperature of the spinal cord (Tvc) was measured in unanaesthetized pigeons at different ambient temperatures (Ta). 2. In short-term experiments spontaneous or noncyclic variations of Tvc at constant (20 and 10 degrees C) and changing Ta were correlated with the amplitude of the electromyogram EMG) which indicates shivering, i.e., heat production. At constant Ta no unequivocal correlation between Tvc (and also Tskin) and EMG was found. During ambient cooling there was often an increase of Tvc which resulted in a positive correlation whereas there was a negative correlation to Tskin. 3. In long-term experiments (24h, LD 12:12Y cyclic variations of Tvc were measured at different Ta and ocrrelated with O2-consumption, i.e., heat production. As with body temperature Tvc was lowered during the dark phase of the diurnal cycle. In the light phase both Tvc and heat production increased with decreasing Ta which results in a positive correlation. In the dark phase there was a smaller increase in heat production but a decrease in Tvc, i.e., a negative correlation. 4. The results show that natural variations of Tvc are often positively ocrrelated with heat production. This is in contrast to experimental changes of Tvc where a clear negative correlation to heat production can be observed.