Aim: In the primary motor cortex (M1) of adult mammals, electrophysiological changes which are behind the interhemispheric diaschisis remain unclear. In the present study we aimed to demonstrate rapid changes in the M1 forelimb movement representation as the effect of inactivation of the homotopic cortical region. Methods: Five adult rats underwent three injections of Lidocaine (L-group) within the FM1 of one hemisphere (10μL delivered through a Hamilton syringe at a depth of 1mm from the pial surface). After injections, rats underwent intracortical microstimulation (ICMS) for M1 mapping in both hemispheres. Under ketamine anaesthesia (50mg\Kg i.p.), ICMS (30ms trains of 0.2ms cathodal pulses at 300Hz, stimulation current ≤ 60μA ) was delivered at a depth of 1.5mm from the pial surface using glass-insulated tungsten microelettrodes (impedance:0.6-1.2 ΩM). Other 5 rats were used as Sham-group and 5 rats were used as Control-group. Results: The cortical area that elicits forelimb movement was analyzed in the hemisphere contralateral to lidocaine injections. We observed significant increase in the forelimb area in the L-group as compared to Sham and Control- group (P<0.005, ANOVA). The forelimb area in L-group expanded in the medial direction overlapping the lateral portion of the vibrissa representation. In this part of M1, the ICMS evoked forelimb and vibrissa movement at the same current threshold. These dual movement sites increase significantly in L-group rats relative to Control and Sham- group of rats (P<0.001, ANOVA). Conclusions: Our results suggest that FM1 inactivation leads to shaping and size changes of forelimb movement representation in the contralateral hemisphere. We conclude that the loss of the inhibitory interhemispheric input induces the loss of the sharp border between vibrissa and forelimb representation.
SHORT-TERM FORELIMB MOTOR CORTEX (FM1) PLASTICITY AFTER INACTIVATION OF THE CORRESPONDING CORTEX IN THE OPPOSITE HEMISPHERE
MAGGIOLINI, Emma;VIARO, Riccardo;FRANCHI, Gianfranco
2006
Abstract
Aim: In the primary motor cortex (M1) of adult mammals, electrophysiological changes which are behind the interhemispheric diaschisis remain unclear. In the present study we aimed to demonstrate rapid changes in the M1 forelimb movement representation as the effect of inactivation of the homotopic cortical region. Methods: Five adult rats underwent three injections of Lidocaine (L-group) within the FM1 of one hemisphere (10μL delivered through a Hamilton syringe at a depth of 1mm from the pial surface). After injections, rats underwent intracortical microstimulation (ICMS) for M1 mapping in both hemispheres. Under ketamine anaesthesia (50mg\Kg i.p.), ICMS (30ms trains of 0.2ms cathodal pulses at 300Hz, stimulation current ≤ 60μA ) was delivered at a depth of 1.5mm from the pial surface using glass-insulated tungsten microelettrodes (impedance:0.6-1.2 ΩM). Other 5 rats were used as Sham-group and 5 rats were used as Control-group. Results: The cortical area that elicits forelimb movement was analyzed in the hemisphere contralateral to lidocaine injections. We observed significant increase in the forelimb area in the L-group as compared to Sham and Control- group (P<0.005, ANOVA). The forelimb area in L-group expanded in the medial direction overlapping the lateral portion of the vibrissa representation. In this part of M1, the ICMS evoked forelimb and vibrissa movement at the same current threshold. These dual movement sites increase significantly in L-group rats relative to Control and Sham- group of rats (P<0.001, ANOVA). Conclusions: Our results suggest that FM1 inactivation leads to shaping and size changes of forelimb movement representation in the contralateral hemisphere. We conclude that the loss of the inhibitory interhemispheric input induces the loss of the sharp border between vibrissa and forelimb representation.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
