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Uncrossed actions of feline corticospinal tract neurones on hindlimb motoneurones evoked via ipsilaterally descending pathways.

Journal article
Authors Katinka Stecina
Elzbieta Jankowska
Published in The Journal of physiology
Volume 580
Issue Pt 1
Pages 119-32
ISSN 0022-3751
Publication year 2007
Published at Institute of Neuroscience and Physiology, Department of Physiology
Pages 119-32
Language en
Links dx.doi.org/10.1113/jphysiol.2006.12...
https://gup.ub.gu.se/file/141048
Keywords Animals, Axons, physiology, Cats, Efferent Pathways, cytology, physiology, Electric Stimulation, Electrodes, Implanted, Excitatory Postsynaptic Potentials, physiology, Functional Laterality, physiology, Hindlimb, innervation, physiology, Motor Neurons, physiology, Neurons, physiology, Olivary Nucleus, physiology, Pyramidal Tracts, cytology, physiology, Spinal Cord, physiology, Synapses, physiology
Subject categories Physiology

Abstract

Despite numerous investigations on the corticospinal system there is only scant information on neuronal networks mediating actions of corticospinal neurones on ipsilateral motoneurones. We have previously demonstrated double crossed pathways through which pyramidal tract neurones can influence ipsilateral motoneurones, via contralaterally descending reticulospinal neurones and spinal commissural interneurones. The aim of the present study was to examine the effects of stimulation of pyramidal tract (PT) fibres mediated via ipsilaterally descending pathways and to find out which neurones relay these effects. This was done by using intracellular recordings from 96 lumbar motoneurones in deeply anaesthetized cats. To eliminate actions of fibres descending on the side contralateral to the location of the motoneurones, the spinal cords were hemisected on this side at a low-thoracic level. Stimuli that selectively activated ipsilateral PT fibres evoked EPSPs and/or IPSPs in 34/47 motoneurones tested. These PSPs were evoked at latencies indicating that the most direct coupling between PT neurones and motoneurones in uncrossed pathways is disynaptic. Occlusion and spatial facilitation between actions evoked by stimulation of ipsilateral PT and of reticulospinal tract fibres in the ipsilateral medial longitudinal fascicle (MLF) indicated that PT actions are mediated by reticulospinal neurones with axons in the MLF. However, after transection of the MLF in the caudal medulla, stimulation of the ipsilateral PT continued to evoke EPSPs and IPSPs with characteristics similar to when the MLF was intact (in 15/49 motoneurones) suggesting the existence of parallel disynaptic pathways via other relay neurones.

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