Corticospinal and reticulospinal contacts on cervical commissural and long descending propriospinal neurons in the adult rat spinal cord; evidence for powerful reticulospinal connections

Mitchell, E. J., McCallum, S., Dewar, D. and Maxwell, D. (2016) Corticospinal and reticulospinal contacts on cervical commissural and long descending propriospinal neurons in the adult rat spinal cord; evidence for powerful reticulospinal connections. PLoS ONE, 11(3), e0152094. (doi: 10.1371/journal.pone.0152094) (PMID:26999665) (PMCID:PMC4801400)

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Abstract

Descending systems have a crucial role in the selection of motor output patterns by influencing the activity of interneuronal networks in the spinal cord. Commissural interneurons that project to the contralateral grey matter are key components of such networks as they coordinate left-right motor activity of fore and hind-limbs. The aim of this study was to determine if corticospinal (CST) and reticulospinal (RST) neurons make significant numbers of axonal contacts with cervical commissural interneurons. Two classes of commissural neurons were analysed: 1) local commissural interneurons (LCINs) in segments C4-5; 2) long descending propriospinal neurons (LDPNs) projecting from C4 to the rostral lumbar cord. Commissural interneurons were labelled with Fluorogold and CST and RST axons were labelled by injecting the b subunit of cholera toxin in the forelimb area of the primary somatosensory cortex or the medial longitudinal fasciculus respectively. The results show that LCINs and LDPNs receive few contacts from CST terminals but large numbers of contacts are formed by RST terminals. Use of vesicular glutamate and vesicular GABA transporters revealed that both types of cell received about 80% excitatory and 20% inhibitory RST contacts. Therefore the CST appears to have a minimal influence on LCINs and LDPNs but the RST has a powerful influence. This suggests that left-right activity in the rat spinal cord is not influenced directly via CST systems but is strongly controlled by the RST pathway. Many RST neurons have monosynaptic input from corticobulbar pathways therefore this pathway may provide an indirect route from the cortex to commissural systems. The cortico-reticulospinal-commissural system may also contribute to functional recovery following damage to the CST as it has the capacity to deliver information from the cortex to the spinal cord in the absence of direct CST input.

Item Type:Articles
Additional Information:: EM funded by PhD Studentship from Medical Research Council (http://www.mrc.ac.uk/). Additional support from Neurosciences Foundation, Glasgow (http://neurosciencesfoundation.org.uk/).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Dewar, Dr Deborah and Maxwell, Professor David
Authors: Mitchell, E. J., McCallum, S., Dewar, D., and Maxwell, D.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
Journal Name:PLoS ONE
Publisher:Public Library of Science
ISSN:1932-6203
ISSN (Online):1932-6203
Published Online:21 March 2016
Copyright Holders:Copyright © 2016 2016 Mitchell et al.
First Published:First published in PLoS ONE 11(3):e0152094
Publisher Policy:Reproduced under a creative commons license

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