title: Adaptive changes in the motor cortex during and after longterm forelimb immobilization in adult rats.
abstract: Experimental and clinical studies have attempted to evaluate the changes in cortical activity seen after immobilization-induced longterm sensorimotor restriction, although results remain controversial. We used intracortical microstimulation (ICMS), which provides topographic movement representations of the motor areas in both hemispheres with optimal spatial characterization, combined with behavioural testing to unravel the effects of limb immobilization on movement representations in the rat primary motor cortex (M1). Unilateral forelimb immobilization in rats was achieved by casting the entire limb and leaving the cast in place for 15 or 30 days. Changes in M1 were bilateral and specific for the forelimb area, but were stronger in the contralateral-to-cast hemisphere. The threshold current required to evoke forelimb movement increased progressively over the period in cast, whereas the forelimb area size decreased and the non-excitable area size increased. Casting resulted in a redistribution of proximal/distal movement representations: proximal forelimb representation increased, whereas distal representation decreased in size. ICMS after cast removal showed a reversal of changes, which remained partial at 15 days. Local application of the GABAA-antagonist bicuculline revealed the impairment of cortical synaptic connectivity in the forelimb area during the period of cast and for up to 15 days after cast removal. Six days of rehabilitation using a rotarod performance protocol after cast removal did not advance map size normalization in the contralateral-to-cast M1 and enabled the cortical output towards the distal forelimb only in sites that had maintained their excitability. These results are relevant to our understanding of adult M1 plasticity during and after sensorimotor deprivation, and to new approaches to conditions that require longterm limb immobilization.
authors.affiliation: Department of Biomedical and Specialty Surgical Sciences, Section of Human Physiology, University of Ferrara, Ferrara, Italy Department of Robotics, Brain and Cognitive Sciences, Italian Institute of Technology, Genoa, Italy riccardo.viaro@unife.it.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Viaro
authors.affiliation: Department of Biomedical and Specialty Surgical Sciences, Section of Human Physiology, University of Ferrara, Ferrara, Italy.
authors.forename: Mirco
authors.initials: M
authors.lastname: Budri
authors.affiliation: Department of Biomedical and Specialty Surgical Sciences, Section of Human Physiology, University of Ferrara, Ferrara, Italy.
authors.forename: Pierantonio
authors.initials: P
authors.lastname: Parmiani
authors.affiliation: Department of Biomedical and Specialty Surgical Sciences, Section of Human Physiology, University of Ferrara, Ferrara, Italy.
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Franchi
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D005552:Forelimb / Q000502:physiology*; D019417:Hindlimb Suspension; D007103:Immobilization / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000502:physiology*