The Changes Of γ-aminobutyric Acid, Glutamic Acid And N-Methyl-D-Aspartate Receptors In Motor Cortex Induced By The Healthy Cervical Seventh Nerve Transfer

Objective During transhemispheric reorganization progress following total brachial plexus root avulsion and contralateral seventh cervical nerve transfer,the changes ofγ-aminobutyric acid,glutamic acid and N-Methyl-D-Aspartate receptors expression in motor cortex of adult rats were observed to explore the mechanisms underlying the plasticity.Method Two adult rat models were set up including the model of total left brachial plexus root avulsion injury and the nerve transfer model of contralateral seventh cervical nerve root to median nerve.Electromyogram was used to test the median nerve regeneration and the representation of the injured forepaw was mapped using intracortical microstimulation(ICMS).According to the ICMS results,some rats were killed and brains were removed for determination ofγ-aminobutyric acid,glutamic acid and N-Methyl-D-Aspartate receptors(NR1,NR2A,NR2B) in motor cortex by immuno-histochemical assay.Results(1) At 3rd month after the operation,the latency period and amplitude of compound muscle action potential(CAMP) were 2.26±0.11ms,1.86±0.09mV respectively.Over time,the latency period decreased and amplitude increased.At 10th month,the latency period and amplitude were 1.67ms,18.46±0.30mV respectively.(2) At 4th month,median nerve representation region of the affected forelimb appeared in the ipsilateral motor cortex in 3 rats.At 7th month,both hemispheres of cortex activated the injured forepaw in 4 rats and the representation of the injured forepaw lay in the previously silent areas of the contralateral cortex.At 10th month,the contralateral motor cortex exclusively controlled the injured forepaw.(3) According to the result from ICMS,the changes ofγ-aminobutyric acid, glutamic acid and NMDA receptors(NR1,NR2A,NR2B) in motor cortex were observed at 1h,4M,7M,10M respectively.At 1h after operation,downregulation of GABA was observed in both hemispheres of all rats from the operative groups.The GABA expression showed significant change in the normal and operative groups (P＜0.05).There was significantly difference in GABA expression between both hemispheres in operative groups(P＜0.05).At 4th month,the GABA remained down-regulation.The GABA expression still showed significant change in the normal and operative groups(P＜0.05).There was still significantly difference in GABA expression between both hemispheres in operative groups(P＜0.05).Meanwhile,the upregulation of NR1 was observed in both hemispheres of all rats from the operative groups.The NR1 expression showed significant change in the normal and operative groups(P＜0.05).NR1 expression in right cortex was significantly higher than that in left cortex(P＜0.05).At 7th month,There was a significant increase in the NR2A expression in right motor cortex in the operative groups(P＜0.05) and NR2A expression in rats following contralateral seventh cervical nerve transfer was significantly higher than that in the rats from the other operative groups(P＜0.05).At 10th month,the expression of NR2A was still up-regulate.NR2A expression in rats following contralateral seventh cervical nerve transfer was still significantly higher than that in the rats from the other operative groups(P＜0.05).Conclusion Functional recovery of the injured forepaw is clearly demonstrated in rats following contralateral seventh cervical nerve transfer.Meanwhile, transhemisphereric functional reorganization of the motor cortex is confirmed.During this process,GABA and NR1 may play an important role in the primary cortical plasticity and NR2A may be needed to continue this reorganization in later stage.In this experiment,the changes ofγ-aminobutyric acid,glutamic acid and NMDA receptors expression in motor cortex of adult rats were observed to explore the mechanisms underlying the plasticity during transhemispheric reorganization progress.These results enrich and develop the connotation of the rational study in neuroscience and traumatic surgery of peripheral nerve.Meanwhile,these findings provide an academic basis for clinic to accelerate independent control on the affected upper extremity following contralateral seventh nerve root transfer.