Neuronal Organization of the Corticorubral System
EPSPs evoked in rubrospinal neurons by stimulation of the sensorimotor cortex were studied in pentobarbitonized cats with the intracellular recording technique. Participation of corticospinal inputs in initiating the above-mentioned EPSPs was determined by selectively activating of corticospinal fibres at the level of the medullary pyramids and by studying peculiarities of their interaction with effects of cortical stimulation. Convergence of excitatory influences from the sensorimotor cortex and medullary pyramids was observed in 94.2% of the rubrospinal neurons studied. In some neurons (8.1%), the summation of cortical and pyramidal inputs was 100%, which suggests that the corticorubral neurons played a predominant role in the genesis of cortical EPSPs. In the majority of cells, the summation of inputs tested was less than 100%, proving that both corticospinal and corticorubral neurons participated in initiating the EPSPs evoked by cortical stimulation. A collision component consisting of the difference between the algebraic and experimental sum of the EPSPs and reflecting that part of the depolarization which “dropped out” of the summed EPSP as a result of impulse collision in pyramidal fibres carrying stimulation effects from both the sensorimotor cortex and the medullary pyramids, was distinguished when studying interactions between the inputs mentioned above. From this analysis, it was possible to separately assess pyramidal and extrapyramidal participation in corticofugal control. It was found that slow-conducting corticospinal and corticorubral neurons participated equally in initiating the first two components of complex EPSPs. Cell composition and the mechanisms underlying corticofugal influences on the red nucleus neurons are discussed.
KeywordsSensorimotor Cortex Spinal Cord Stimulation Cortical Stimulation Rubrospinal Tract Medullary Pyramid
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