Electrical excitability of motoneurones in early local tetanus.

1. After injection of tetanus toxin into the gastrocnemius muscle of the cat non-synaptic excitability of motoneurones was studied in early local tetanus. Antidromic stimulation of motoneurones was performed onthe toxin-treated side and on the control side of the same cat. 2. The mean resting membrane potential of the motoneurones on the toxin-treated side did not differ from that on the control side. 3. Similarly, no differences were found as to the amplitude of the action potential and its rate of rise as well as to the size and time course of the after-hyperpolarization. 4. The mean input resistance of the motoneurones of the toxintreated side did not differ from that of the motoneurones of the control side. 5. Tetanus toxin did not change the mean refractory period and latency of antidromic responses. 6. It is concluded that the action of tetanus toxin the spinal cord cannot be explained by an action of the toxin on the electrically excitable membrane elements of the motoneurones.