Responses of type A cat spinal ganglion neurons to repetitive stimulation of their central and peripheral processes.
Intracellular recordings were made from L7-S1 type A spinal ganglion neurons of anesthetized cats while electrical stimulation was delivered repetitively to their associated dorsal root and the sciatic nerve. The general response pattern of these neurons changed during stimulation at progressively higher rates. The changes were observable as jitter in onset latency of the evoked spikes, inability of evoked responses to follow electrical stimuli in a 1:1 manner (spike failure), reduction in action potential amplitude, and decomposition of the full spike into its non-myelinated and myelinated components. The frequency following ability of these spike components was in the order of full spike less than non-myelinated less than myelinated. In jitter in onset latency and inability to follow high frequency stimulation was determined only for the full spike, as is typical for antidromicity criteria, a wide frequency following spectrum was obtained for our sample of spinal ganglion neurons. Less than a third of the cells were able to follow stimulation rates in excess of 200 Hz, and about a fifth of the neurons failed to follow any rates greater than 20 Hz. Most of the neurons activated from both the dorsal root and sciatic nerve responded with the same pattern of stimulus-evoked responses. However, some of these cells exhibited strikingly different patterns to dorsal root and sciatic stimulation, including the presence of prepotentials following stimulation of one, but not the other, process. These prepotentials occurred in the depolarizing direction, at threshold stimulation were all-or-none in nature, generated spikes that varied in onset latency, and failed to occur at even low-to-moderate rates of stimulation. The results indicate that the frequency following spectrum of cat type A ganglion neurons is wide, and that it is their somata that are most vulnerable to high frequency stimulation. It is possible that some of the observed prepotentials are functional manifestations of synaptic contacts in spinal ganglia.
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Department of Comparative Biosciences, University of Wisconsin, Madison 53706.
Miletic
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D000200:Action Potentials; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D005727:Ganglia, Spinal / Q000502:physiology*; D008839:Microelectrodes; D009431:Neural Conduction; D009474:Neurons / Q000502:physiology*; D012584:Sciatic Nerve / Q000502:physiology*; D013997:Time Factors