Recurrent depression of postsynaptic responses in the frog motoneurons at low temperature.

Recurrent depression of responses evoked in motoneurons by sciatic nerve volleys was studied at 1-3 degrees C body temperature in Rana esculenta. Gross recordings from the ventral root axons and intracellular recordings from the motoneurons were made. In accord previous data obtained from the same species using the same techniques at room temperature, recurrent volleys depressed the responses of motoneurons to sciatic nerve impulses also at low temperature. The latency and duration of the depression was increased by a factor of about two with cooling. The short latency components of the evoked responses suffered more than the late ones. Intracellularly was indicated depression by delay or blockage of postsynaptic discharge and diminution of epsp in motoneurons. The data are considered as evidence for the operation of simple polysynaptic pathways in the central nervous system of poikilothermic animals at temperatures near 0 degrees C. Properties of the interaction are in accord with those found at higher temperature and undergo the expected modifications with cooling.