BDNF and GAP43 contribute to dynamic transhemispheric functional reorganization in rat brain after contralateral C7 root transfer following brachial plexus avulsion injuries

Why It Is Necessary to Use the Entire Root rather than Partial Root When Doing Contralateral C7 Nerve Transfer: Cortical Plasticity Also Matters besides the Amount of Nerve Fibers

Previous studies suggested that the mode of donor transection is a critical factor affecting the efficacy of the contralateral C7 (CC7) nerve transfer. Nevertheless, the mechanism underlying this phenomenon remains elusive. The aim of this study was to investigate the relationship between the division modes of the CC7 nerve and cortical functional reorganization of Sprague-Dawley rats. We hypothesized that different methods of CC7 nerve transection might induce differences in cortical functional reorganization, thus resulting in differences in surgery efficacy. BDNF, TNF-α/IL-6, and miR-132/134 were selected as indicators of cortical functional reorganization. No significant differences in all these indicators were noted between the entire group and the entire root+posterior division group (P > 0.05). BDNF and miR-132/134 levels in the entire group and the entire root+posterior division group were significantly increased compared with their levels in the posterior group and the blank control group (P < 0.001). In all groups, BDNF, TNF-α/IL-6, and miR-132/134 levels in both hemispheres initially increased and subsequently decreased until week 40. In conclusion, this study provided the evidence of dynamic changes in BDNF, TNF-α/IL-6, and miR-132/134 in the cortex of rats after CC7 nerve transfer using different transecting modes, demonstrating that different CC7 nerve divisions might result in different surgical effects through modulation of cortical reorganization.

Use of a Combination Strategy to Improve Morphological and Functional Recovery in Rats With Chronic Spinal Cord Injury

Immunization with neural derived peptides (INDP), as well as scar removal (SR) and the use of matrices with bone marrow-mesenchymal stem cells (MSCs), have been studied separately and proven to induce a functional and morphological improvement after spinal cord injury (SCI). Herein, we evaluated the therapeutic effects of INDP combined with SR and a fibrin glue matrix (FGM) with MSCs (FGM-MSCs), on motor recovery, axonal regeneration-associated molecules and cytokine expression, axonal regeneration (catecholaminergic and serotonergic fibers), and the induction of neurogenesis after a chronic SCI. For this purpose, female adult Sprague-Dawley rats were subjected to SCI, 60 days after lesion, rats were randomly distributed in four groups: (1) Rats immunized with complete Freund's adjuvant + PBS (vehicle; PBS-I); (2) Rats with SR+ FGM-MSCs; (3) Rats with SR+ INDP + FGM-MSCs; (4) Rats only with INDP. Afterwards, we evaluated motor recovery using the BBB locomotor test. Sixty days after the therapy, protein expression of TNFα, IL-4, IL-10, BDNF, and GAP-43 were evaluated using ELISA assay. The number of catecholaminergic and serotonergic fibers were also determined. Neurogenesis was evaluated through immunofluorescence. The results show that treatment with INDP alone significantly increased motor recovery, anti-inflammatory cytokines, regeneration-associated molecules, axonal regeneration, and neurogenesis when compared to the rest of the groups. Our findings suggest that the combination therapy (SR + INDP + FGM-MSCs) modifies the non-permissive microenvironment post SCI, but it is not capable of inducing an appropriate axonal regeneration or neurogenesis when compared to the treatment with INDP alone.

Proteomic analysis of trans-hemispheric motor cortex reorganization following contralateral C7 nerve transfer

Nerve transfer is the most common treatment for total brachial plexus avulsion injury. After nerve transfer, the movement of the injured limb may be activated by certain movements of the healthy limb at the early stage of recovery, i.e., trans-hemispheric reorganization. Previous studies have focused on functional magnetic resonance imaging and changes in brain-derived neurotrophic factor and growth associated protein 43, but there have been no proteomics studies. In this study, we designed a rat model of total brachial plexus avulsion injury involving contralateral C₇ nerve transfer. Isobaric tags for relative and absolute quantitation and western blot assay were then used to screen differentially expressed proteins in bilateral motor cortices. We found that most differentially expressed proteins in both cortices of upper limb were associated with nervous system development and function (including neuron differentiation and development, axonogenesis, and guidance), microtubule and cytoskeleton organization, synapse plasticity, and transmission of nerve impulses. Two key differentially expressed proteins, neurofilament light (NFL) and Thy-1, were identified. In contralateral cortex, the NFL level was upregulated 2 weeks after transfer and downregulated at 1 and 5 months. The Thy-1 level was upregulated from 1 to 5 months. In the affected cortex, the NFL level increased gradually from 1 to 5 months. Western blot results of key differentially expressed proteins were consistent with the proteomic findings. These results indicate that NFL and Thy-1 play an important role in trans-hemispheric organization following total brachial plexus root avulsion and contralateral C₇ nerve transfer.

Is it necessary to use the entire root as a donor when transferring contralateral C7 nerve to repair median nerve?

If a partial contralateral C₇ nerve is transferred to a recipient injured nerve, results are not satisfactory. However, if an entire contralateral C₇ nerve is used to repair two nerves, both recipient nerves show good recovery. These findings seem contradictory, as the above two methods use the same donor nerve, only the cutting method of the contralateral C₇ nerve is different. To verify whether this can actually result in different repair effects, we divided rats with right total brachial plexus injury into three groups. In the entire root group, the entire contralateral C₇ root was transected and transferred to the median nerve of the affected limb. In the posterior division group, only the posterior division of the contralateral C₇ root was transected and transferred to the median nerve. In the entire root + posterior division group, the entire contralateral C₇ root was transected but only the posterior division was transferred to the median nerve. After neurectomy, the median nerve was repaired on the affected side in the three groups. At 8, 12, and 16 weeks postoperatively, electrophysiological examination showed that maximum amplitude, latency, muscle tetanic contraction force, and muscle fiber cross-sectional area of the flexor digitorum superficialis muscle were significantly better in the entire root and entire root + posterior division groups than in the posterior division group. No significant difference was found between the entire root and entire root + posterior division groups. Counts of myelinated axons in the median nerve were greater in the entire root group than in the entire root + posterior division group, which were greater than the posterior division group. We conclude that for the same recipient nerve, harvesting of the entire contralateral C₇ root achieved significantly better recovery than partial harvesting, even if only part of the entire root was used for transfer. This result indicates that the entire root should be used as a donor when transferring contralateral C₇ nerve.

Immunization with neural derived peptides plus scar removal induces a permissive microenvironment, and improves locomotor recovery after chronic spinal cord injury

Background

Immunization with neural derived peptides (INDP) as well as scar removal—separately—have shown to induce morphological and functional improvement after spinal cord injury (SCI). In the present study, we compared the effect of INDP alone versus INDP with scar removal on motor recovery, regeneration-associated and cytokine gene expression, and axonal regeneration after chronic SCI. Scar removal was conducted through a single incision with a double-bladed scalpel along the stump, and scar renewal was halted by adding α,α′-dipyridyl.

Results

During the chronic injury stage, two experiments were undertaken. The first experiment was aimed at testing the therapeutic effect of INDP combined with scar removal. Sixty days after therapeutic intervention, the expression of genes encoding for TNFα, IFNγ, IL4, TGFβ, BDNF, IGF1, and GAP43 was evaluated at the site of injury. Tyrosine hydroxylase and 5-hydroxytryptamine positive fibers were also studied. Locomotor evaluations showed a significant recovery in the group treated with scar removal + INDP. Moreover; this group presented a significant increase in IL4, TGFβ, BDNF, IGF1, and GAP43 expression, but a decrease of TNFα and IFNγ. Also, the spinal cord of animals receiving both treatments presented a significant increase of serotonergic and catecholaminergic fibers as compared to other the groups. The second experiment compared the results of the combined approach versus INDP alone. Rats receiving INDP likewise showed improved motor recovery, although on a lesser scale than those who received the combined treatment. An increase in inflammation and regeneration-associated gene expression, as well as in the percentage of serotonergic and catecholaminergic fibers was observed in INDP-treated rats to a lesser degree than those in the combined therapy group.

Conclusions

These findings suggest that INDP, both alone and in combination with scar removal, could modify the non-permissive microenvironment prevailing at the chronic phase of SCI, providing the opportunity of improving motor recovery.

The natural product 4,10-aromadendranediol induces neuritogenesis in neuronal cells in vitro through activation of the ERK pathway

Recent studies focus on promoting neurite outgrowth to remodel the central nervous network after brain injury. Currently, however, there are few drugs treating brain diseases in the clinic by enhancing neurite outgrowth. In this study, we established an NGF-induced PC12 differentiation model to screen novel compounds that have the potential to induce neuronal differentiation, and further characterized 4,10-Aromadendranediol (ARDD) isolated from the dried twigs of the Baccharis gaudichaudiana plant, which exhibited the capability of promoting neurite outgrowth in neuronal cells in vitro. ARDD (1, 10 μmol/L) significantly enhanced neurite outgrowth in NGF-treated PC12 cells and N1E115 cells in a time-dependent manner. In cultured primary cortical neurons, ARDD (5, 10 μmol/L) not only significantly increased neurite outgrowth but also increased the number of neurites on the soma and the number of bifurcations. Further analyses showed that ARDD (10 μmol/L) significantly increased the phosphorylation of ERK1/2 and the downstream GSK-3β, subsequently induced β-catenin expression and up-regulated the gene expression of the Wnt ligands Fzd1 and Wnt3a in neuronal cells. The neurite outgrowth-promoting effect of ARDD in neuronal cells was abolished by pretreatment with the specific ERK1/2 inhibitor PD98059, but was partially reversed by XAV939, an inhibitor of the Wnt/β-catenin pathway. ARDD also increased the expression of BDNF, CREB and GAP-43 in N1E115 cells, which was reversed by pretreatment with PD98059. In N1E115 cells subjected to oxygen and glucose deprivation (OGD), pretreatment with ARDD (1-10 μmol/L) significantly enhanced the phosphorylation of ERK1/2 and induced neurite outgrowth. These results demonstrated that the natural product ARDD exhibits neurite outgrowth-inducing activity in neurons via activation of the ERK signaling pathway, which may be beneficial to the treatment of brain diseases.

Expressions of miR-132, miR-134, and miR-485 in rat primary motor cortex during transhemispheric functional reorganization after contralateral seventh cervical spinal nerve root transfer following brachial plexus avulsion injuries

The transfer of a contralateral healthy seventh cervical spinal nerve root (cC7) to the recipient nerve in the injured side is considered a promising procedure for restoration of the physiological functions of an injured hand after brachial plexus root avulsion injury (BPAI). Growing evidence shows that transhemispheric cortical reorganization plays an important role in the functional recovery of the injured arm after cC7 nerve transfer surgery. However, the molecular mechanism underlying the transhemispheric cortical reorganization after cC7 transfer remains elusive. In the present study, we investigated the expression of miR-132, miR-134, and miR-485 in the rat primary motor cortex after cC7 transfer following BPAI by quantitative PCR. The results demonstrated the dynamic alteration in the expression of miR-132, miR-134, and miR-485 in the primary motor cortex of rats after cC7 transfer following BPAI. It indicates that microRNAs are involved in the dynamic transhemispheric functional reorganization after cC7 root transfer following BPAI. Together, this study is the first to provide evidence for the involvement of microRNAs during dynamic transhemispheric functional reorganization after cC7 transfer following BPAI. The results are useful for understanding the mechanism underlying transhemispheric functional reorganization after contralateral seventh cervical spinal nerve root transfer following BPAI.

Passive exercise of the hind limbs after complete thoracic transection of the spinal cord promotes cortical reorganization

Physical exercise promotes neural plasticity in the brain of healthy subjects and modulates pathophysiological neural plasticity after sensorimotor loss, but the mechanisms of this action are not fully understood. After spinal cord injury, cortical reorganization can be maximized by exercising the non-affected body or the residual functions of the affected body. However, exercise per se also produces systemic changes – such as increased cardiovascular fitness, improved circulation and neuroendocrine changes – that have a great impact on brain function and plasticity. It is therefore possible that passive exercise therapies typically applied below the level of the lesion in patients with spinal cord injury could put the brain in a more plastic state and promote cortical reorganization. To directly test this hypothesis, we applied passive hindlimb bike exercise after complete thoracic transection of the spinal cord in adult rats. Using western blot analysis, we found that the level of proteins associated with plasticity – specifically ADCY1 and BDNF – increased in the somatosensory cortex of transected animals that received passive bike exercise compared to transected animals that received sham exercise. Using electrophysiological techniques, we then verified that neurons in the deafferented hindlimb cortex increased their responsiveness to tactile stimuli delivered to the forelimb in transected animals that received passive bike exercise compared to transected animals that received sham exercise. Passive exercise below the level of the lesion, therefore, promotes cortical reorganization after spinal cord injury, uncovering a brain-body interaction that does not rely on intact sensorimotor pathways connecting the exercised body parts and the brain.