ALTERATION OF NEURON EXCITABILITY BY RETROGRADE DEGENERATION

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Abstract
Literature review shows that physiologically, the reaction of degeneration is characterized by a loss of the proprioceptive component of the seg- mental reflex and of the antidromic cell potential, though conduction in the affected dorsal root ganglion cells and along the central portions of the cut axons of the primary motor cells is unaltered. This suggests a general increase in the threshold of excitability of the neuron. The study of the alteration of a pure cutaneous (flexor) type of reflex, the tibial-peroneal reflex, during the chromatolytic cycle confirms this interpretation. In a series of 25 cats and 14 rabbits studied for 2-102 days following section of the peroneal nerve, an increase of central latency, a simplification of the oscillographically recorded reflex potential curve, a decrease in amplitude, and, during the height of the cycle, an absence of the reflex, were noted. The subliminal fringe, as tested by a 2d shock, was relatively larger in the early part of the cycle, smaller later. All effects found are consistent with a generalized decrease in excitability of the cell. This elongated subnormal period of the chromatolyzed neuron may have its counterpart in the normal nerve cell following depletion through more "physiological" means.
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