Effect of cooling on latency of monosynaptic discharges evoked in motoneurons of the frog.

Cold produced increase in latency of the dorsal root evoked monosynaptic ventral root reflex was investigated in frog lumbar spinal cord. Attempts were made to separate changes in the synaptic transmission time from changes in the conduction velocity of axons involved in the reflex pathway. Reduction of the temperature by 10 degrees C from the initial values of about 17-19 degrees C produced a 50-60 per cent increase in reflex latency, similar to the degree of slowing down of the axonal conduction velocity. The finding fails to conclusively support the chemical synaptic transmission mechanism of the ventral root discharges studied and calls for more detailed investigation of the phenomenon.