Neurochemical aspects of post-tetanic potentiation of monosynaptic reflexes in the cat spinal cord. I. Analysis of amino acids at maximum of potentiation.

In order to determine the chemical changes which might occur during post-tetanic potentiation, amino acids from the motor regions of the ventral horn of the spinal cord (potentiated and unpotentiated sides) of 10 different cats were analyzed. The intermittent tetanic stimulation of the Nn. gastroc. (only on the potentiated side) was carried out until a maximum of potentiation was reached (3--4 min). The monosynaptic reflexes were obtained from the ventral roots (L7 or S1) of both sides. The amino acids of the potentiated side were compared to those of the unpotentiated side (control) using a 14-C-dansyl chloride procedure. The two main amino acids considered to be excitatory neurotransmitters, glutamic acid and aspartic acid, showed a more than 20 per cent increase on the potentiated side as compared to the control side. Glycine, which plays an inhibitory role, especially in the spinal cord, reacted with 6 per cent decrease, whereas GABA which is also considered as an inhibitory neurotransmitter showed a change of + 11 per cent on the potentiated side as compared to the unpotentiated side. The importance of the potentiation time for those changes is pointed out.