Descending supraspinal effect in tetanus intoxication of the spinal cord

Abstract

In experiments performed on cats under Nembutal-chloralose anesthesia it was established that in development of local tentanus there occurs a strengthening of facilitatory and weakening of inhibitory descending effects on the side of toxin injection. At stimulation of facilitatory structures of the medulla oblongata (parvocellular and ambigus nuclei) strengthening of extensor and flexor monosynaptic reflexes and appearance of polysynaptic activity were observed. Stimulation of structures which in the normal state evokes inhibition (gigantocellular and raphe nuclei) in local tetanus produced facilitation instead of inhibition of extensor and flexor monosynaptic reflexes and appearance of polysynaptic activity on the side of toxin injection. On the contralateral side at stimulation of the same nuclei usual inhibitory effects are observed. The intracellular recording of motoneurones potentials showed abolishment of IPSP in tetanus at stimulation of different brain stem structures and their replacement with EPSP. The study of temporal course of suprasegmental inhibition of monosynaptic and early polysynaptic reflexes in normal state and on the side of toxin injection has shown that there are two components. The first short-lasting component (20–60 msec) and the second-later with a maximum about 160 msec. In local tetanus the short-lasting inhibition which is apparently of postsynaptic origin was abolished. The late inhibition was maintained, but slightly weakened. Inhibition of late polysynaptic relfexes belonging by their characteristics to spinobulbo-spinal ones were not abolished but even strengthened in local tetanus. The possible mechanism of appearance of excitatory responses instead of inhibitory ones in local tetanus are discussed.