EXCITATION OF LATERAL VESTIBULAR NEURONES.
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Biomedical subjects
Publications and source records attributed to V J WILSON.
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Recurrent facilitation in the cat's spinal cord has been studied in deep peroneal and quadriceps motoneurons with the use of intracellular recording. The presence of facilitation was indicated by several criteria, among them increased firing index of the cells or decreased latency of firing. In many, but not all, facilitated cells the conditioning volley caused a small visible depolarization. Subthreshold synaptic potentials were frequently increased in magnitude by the conditioning volley, which also increased the effectiveness of a stimulus applied through the microelectrode. Facilitation was found in a large percentage of the motoneurons investigated and was clearly able to bring about pronounced changes in the excitability and firing behavior of these cells.
The action of cumulative doses of meprobamate on antidromic conditioning has been studied in spinal cats. Recurrent facilitation is greatly reduced or completely abolished by total doses ranging from 210 to 400 mg./kg. The depth of recurrent inhibition is not affected in a consistent manner by meprobamate, but the duration of inhibition is markedly increased in all experiments. This differential action of meprobamate on facilitation and inhibition can be utilized to study conditioning effects consisting of combined inhibition and facilitation. If conditioning starts with an inhibitory phase, variable in duration, followed by facilitation, meprobamate depresses the facilitation and reveals an extended inhibitory curve. Facilitation, however, is not always accompanied by inhibition, since in some cases facilitation is depressed and no inhibition is uncovered. The results of these experiments are discussed in relation to the various types of conditioning that have been produced by antidromic stimulation.
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Prominent monosynaptic and disynaptic reflex discharges characterize ipsilateral reflex transmission in the third sacral segment. Convergence upon the motoneurons from the two sides of the body is inhibitory, that through disynaptic paths excitatory. The relative latencies of excitation and inhibition of reflex responses, of excitatory and inhibitory synaptic potentials, and of various aspects of impulse discharge in motoneurons are considered. It is concluded: (1) that a direct (i.e. monosynaptic) action of primary afferent collaterals upon motoneurons is responsible for inhibition of monosynaptic reflex discharge of antagonist motoneurons within a myotatic unit; (2) that the inhibitory postsynaptic potential as described is not the primary agency for monosynaptic reflex inhibition of monosynaptic reflex discharge; (3) that, however, a common causal agent may be responsible for inhibition of reflex discharge and for generation of an inhibitory postsynaptic potential; and (4) that the inhibitory post-synaptic potential may be linked with, or be the agent for, inhibition of soma response.
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