The site of anoxic block in the spinal monosynaptic pathway.

Asphyxiation of the spinal cord for periods of 2-4 min leads to block of the monosynaptic pathway. At about the same time this blockage takes place, the afferent action potentials fail to invade the presynaptic terminals. Asphyxiation also interferes with the antidromic invasion of motoneurons, and the failure of the antidromic action potentials to invade the motoneuron dendrites coincides with the time of the disappearance of the orthodromic monosynaptic responses. During reoxygenation, both the presynaptic terminals and the dendrites recover their function, or rather their polarization, in a few seconds and yet synaptic transmission reappears only after several minutes. It is postulated that failure of synaptic transmission during asphyxia is due to depolarization of both the presynaptic terminals and the dendrites of the postsynaptic elements. However, repolarization of these elements during reoxygenation, is not sufficient to reestablish synaptic transmission, but recovery of some unidentified biochemical process is apparently necessary.