Targeted Delivery of TrkB Receptor to Phrenic Motoneurons Enhances Functional Recovery of Rhythmic Phrenic Activity after Cervical Spinal Hemisection

Sieck

et al. 2015

Journal of Neurotrauma

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113

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), are important in modulating neuroplasticity and promoting recovery after spinal cord injury. Intrathecal delivery of BDNF enhances functional recovery following unilateral spinal cord hemisection (SH) at C2, a well-established model of incomplete cervical spinal cord injury. We hypothesized that localized delivery of BDNF-expressing mesenchymal stem cells (BDNF-MSCs) would promote functional recovery of rhythmic diaphragm activity after SH. In adult rats, bilateral diaphragm electromyographic (EMG) activity was chronically monitored to determine evidence of complete SH at 3 days post-injury, and recovery of rhythmic ipsilateral diaphragm EMG activity over time post-SH. Wild-type, bone marrow-derived MSCs (WT-MSCs) or BDNF-MSCs (2 · 10 5 cells) were injected intraspinally at C2 at the time of injury. At 14 days post-SH, green fluorescent protein (GFP) immunoreactivity confirmed MSCs presence in the cervical spinal cord. Functional recovery in SH animals injected with WT-MSCs was not different from untreated SH controls (n = 10; overall, 20% at 7 days and 30% at 14 days). In contrast, functional recovery was observed in 29% and 100% of SH animals injected with BDNF-MSCs at 7 days and 14 days post-SH, respectively (n = 7). In BDNF-MSCs treated SH animals at 14 days, root-mean-squared EMG amplitude was 63 -16% of the pre-SH value compared with 12 -9% in the control/WT-MSCs group. We conclude that localized delivery of BDNF-expressing MSCs enhances functional recovery of diaphragm muscle activity following cervical spinal cord injury. MSCs can be used to facilitate localized delivery of trophic factors such as BDNF in order to promote neuroplasticity following spinal cord injury.

Section: Primary Antibody Validationmentioning

confidence: 92%

“…14,21,[42][43][44][45][46] The uninsulated portion was embedded within the diaphragm. The wires were tunneled subcutaneously to the dorsum of the animal and externalized.…”

Section: Chronic Diaphragm Electromyographic (Emg) Recordingsmentioning

confidence: 99%

Section: Emg Analysesmentioning

confidence: 99%

“…Retrogradely labeled phrenic motoneurons in rats injected with CTB had a staining pattern identical to previous studies. 12,46,48,49 186 GRANSEE ET AL.…”

Section: Primary Antibody Validationmentioning

confidence: 99%

Section: Proportion Of Animals Displaying Functional Recovery After Shmentioning

confidence: 99%

See 3 more Smart Citations

Localized Delivery of Brain-Derived Neurotrophic Factor-Expressing Mesenchymal Stem Cells Enhances Functional Recovery following Cervical Spinal Cord Injury

Sieck

et al. 2015

Journal of Neurotrauma

Self Cite

113

Motoneuron glutamatergic receptor expression following recovery from cervical spinal hemisection

Porras

J of Comparative Neurology

et al. 2016

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Cervical spinal hemisection at C2 (SH) removes premotor drive to phrenic motoneurons located in segments C3–C5 in rats. Spontaneous recovery of ipsilateral diaphragm muscle activity is associated with increased phrenic motoneuron expression of glutamatergic N-methyl-D-aspartate (NMDA) receptors and decreased expression of α-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) receptors. Glutamatergic receptor expression is regulated by tropomyosin related kinase receptor subtype B (TrkB) signaling in various neuronal systems and increased TrkB receptor expression in phrenic motoneurons enhances recovery post-SH. Accordingly, we hypothesized that recovery of ipsilateral diaphragm muscle activity post-SH, whether spontaneous or enhanced by adeno-associated virus (AAV)-mediated upregulation of TrkB receptor expression, is associated with increased expression of glutamatergic NMDA receptors in phrenic motoneurons. Adult male Sprague-Dawley rats underwent diaphragm EMG electrode implantation and SH surgery. Rats were injected intrapleurally with AAV expressing TrkB or GFP at 3 weeks before SH. At 14 days post-SH, the proportion of animals displaying recovery of ipsilateral diaphragm activity increased in AAV-TrkB treated (9/9) compared to untreated (3/5) or AAV-GFP treated animals (4/10; p < 0.027). Phrenic motoneuron NMDA NR1 subunit mRNA expression was ~4-fold greater in AAV-TrkB vs. AAV-GFP treated SH animals (p < 0.004) and in animals displaying recovery vs. those not recovering (p < 0.005). Phrenic motoneuron AMPA GluR2 subunit mRNA expression decreased after SH and albeit increased in animals displaying recovery vs. those not recovering, levels remained lower than control. We conclude that increased phrenic motoneuron expression of glutamatergic NMDA receptors is associated with spontaneous recovery after SH and enhanced recovery following AAV-TrkB treatment.

Phrenic motoneuron structural plasticity across models of diaphragm muscle paralysis

Mantilla

J of Comparative Neurology

et al. 2018

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Structural plasticity in motoneurons may be influenced by activation history and motoneuron-muscle fiber interactions. The goal of this study was to examine morphological adaptations of phrenic motoneurons following imposed motoneuron inactivity while controlling for diaphragm muscle inactivity. Well-characterized rat models were used including unilateral C2 spinal hemisection (SH; ipsilateral phrenic motoneurons and diaphragm muscle are inactive) and tetrodotoxin phrenic nerve blockade (TTX; ipsilateral diaphragm muscle is paralyzed while phrenic motoneuron activity is preserved). We hypothesized that inactivity of phrenic motoneurons would result in a decrease in motoneuron size, consistent with a homeostatic increase in excitability. Phrenic motoneurons were retrogradely labeled by ipsilateral diaphragm muscle injection of fluorescent dextrans or cholera toxin subunit B. Following 2 weeks of diaphragm muscle paralysis, morphological parameters of labeled ipsilateral phrenic motoneurons were assessed quantitatively using fluorescence confocal microscopy. Compared to controls, phrenic motoneuron somal volumes and surface areas decreased with SH, but increased with TTX. Total phrenic motoneuron surface area was unchanged by SH, but increased with TTX. Dendritic surface area was estimated from primary dendrite diameter using a power equation obtained from 3D reconstructed phrenic motoneurons. Estimated dendritic surface area was not significantly different between control and SH, but increased with TTX. Similarly, TTX significantly increased total phrenic motoneuron surface area. These results suggest that ipsilateral phrenic motoneuron morphological adaptations are consistent with a normalization of motoneuron excitability following prolonged alterations in motoneuron activity. Phrenic motoneuron structural plasticity is likely more dependent on motoneuron activity (or descending input) than muscle fiber activity.