Temperature-sensitive ascending neurons in the spinal cord of pigeons

Summary

• 1. Ascending neuronal activity in the lateral funiculus of the spinal cord of pigeons (spinalized at about C₄, recordings at about C₆) has been studied with regard to effects of temperature changes with a thermode in the vertebral canal between Th₄ and C₈.

• 2. Both warm-sensitive (35) and cold-sensitive (14) neurons were found. According to the change in impulse frequency during steplike thermal stimuli, different reaction types could be distinguished. Twenty-four warm-sensitive and seven cold-sensitive units showed a proportional frequency change without any dynamic reaction. Three other warm-sensitive neurons had an additional dynamic reaction (excitatory overshoot during warming, inhibition during cooling). Five warmsensitive and three cold-sensitive units showed no static sensitivity but responded with outstanding dynamic frequency changes during rising or falling temperature. The activity of some neurons stopped suddenly above (4) or below (3) a critical temperature, which was always near the normal spinal temperature (about 41°C). Altogether the reaction to rapid temperature changes was consistently greatest near the normal body temperature.

• 3. The mean static sensitivity of 17 warm-sensitive units was +4.2±1.3imp./sec·°C (mean value and s. d.) and that of three cold-sensitive ones −2.3±0.3imp./sec·°C in the range 35°C–45°C (vertebral canal temperature). The temperature coefficient (Q ₁₀) which was calculated for the same neurons showed great variations with mean values of about 5 for both warm- and cold-sensitive units.