INFLUENCE OF TEMPERATURE UPON AFFERENT AND EFFERENT MOTOR INNERVATION OF SPINAL CORD .I. CHANGES OF AFFERENT AND EFFERENT SPONTANEOUS ACTIVITY WITH SPINAL TEMPERATURE

1. The influence of spinal cord temperature upon the spontaneous afferent and efferent activity of the spinal cord was observed in filament recordings from ventral and dorsal roots in 23 anesthetized cats. 2. No indication was found for the existence of specific extraspinal thermoreceptors within or around the vertebral canal. The temperature sensitivity of the spinal cord itself, therefore, must be responsible for the increased α- and γ-activity during spinal cord cooling. 3. The increase in γ-motoneurone activity always preceded the activation of α-motoneurones and the appearance of shivering. In many cases, the activation of the γ-motoneurones was only transient and seemed to depend on the velocity of temperature changes. At low spinal temperatures (30-33°C) γ-motoneurones were often inactivated although visible shivering persisted. 4. The height of spinal cord temperature also must be of importance for the effectiveness of supraspinal drive: at spinal temperatures below normal the responses to supraspinal stimuli were greater, at temperatures above normal the responses were less than at normal temperatures. 5. It is concluded that the thermal sensitivity of mammalian spinal motoneurones depends on their size or some factor correlated with size: the smaller the neurone the easier it can be activated and inactivated by a fall in spinal temperature. Bigger cells like α-motoneurones, therefore, are activated and inactivated at relatively low spinal temperatures. © 1969 Springer-Verlag.