What question did this study set out to answer?

This research aims to investigate how the size of motor neurons affects their expression of TrkB mRNA.

February 11, 2026Journal of Neurochemistry1 citations

Motor Neuron Size‐Dependent Differences in m RNA Expression of Tropomyosin‐Related Kinase Receptor B in Adult Rats

RMR C MartinezMayo Clinic SRS RanaMayo Clinic HGH M GranseeMayo Clinic

Key Points

This research aims to investigate how the size of motor neurons affects their expression of TrkB mRNA.
Examined individual phrenic motor neurons from the cervical spinal cord of adult male rats.
Used Alexa Fluor 488-conjugated cholera toxin for retrograde labeling of motor neurons.
Applied fluorescence in situ hybridization to assess TrkB mRNA transcripts.
Classified motor neurons into tertiles based on somal surface area for analysis.
Larger phrenic motor neurons expressed significantly more TrkB mRNA transcripts compared to smaller ones.
Average TrkB mRNA transcripts per larger neuron were approximately threefold higher than in smaller neurons.
Somal surface area varied significantly among the 287 motor neurons analyzed.

Abstract

ABSTRACT Motor neuron plasticity and survival depend on several trophic factors, with signaling via the tropomyosin receptor kinase B (TrkB) receptor being particularly important beyond development and across the lifespan. We hypothesized that differences in motor neuron properties may reflect differential trophic influences across motor units within a single motor unit pool. Based on extensive previous characterization of rat phrenic motor neurons (PhMN), somal surface area was used as an indicator of motor unit type (smaller neurons innervating slow‐twitch, fatigue‐resistant units versus larger neurons innervating fast‐twitch, fatigable units). To examine whether TrkB expression reflects these size‐related properties, TrkB mRNA transcripts were studied in individual PhMNs labeled retrogradely with Alexa Fluor 488‐conjugated cholera toxin subunit β from five adult male Sprague–Dawley rats. Longitudinal sections of the cervical C3–C5 spinal cord (10 μm thick) were processed using fluorescence in situ hybridization (RNAscope) and imaged using confocal microscopy to measure individual PhMN size and full‐length TrkB mRNA transcripts in nuclear and cytoplasmic compartments. Across 287 PhMNs, significant size variation existed both within and between animals. Across all animals, somal surface area averaged 4385 ± 1627 μm 2 with mean values per animal ranging from 3544 to 5461 μm 2 . PhMNs were classified into tertiles within each animal based on somal surface area. Individual PhMNs averaged 1070 ± 685 TrkB mRNA transcripts per motor neuron. Larger PhMNs in the upper tertile by size expressed a greater total number of TrkB mRNA transcripts per motor neuron, with values on average threefold higher compared to smaller motor neurons in the lower tertile ( p < 0.001). Cytoplasmic and nuclear TrkB mRNA density (transcripts/volume) displayed no significant effect of PhMN somal surface area tertile. Overall, the greater TrkB mRNA levels in larger motor units responsible for higher force, expulsive motor behaviors may underlie their functional adaptations and resilience to injury or disease. image

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Cite This Study

Martinez et al. (Sun,) studied this question.

synapsesocial.com/papers/698c1bb8267fb587c655d943 https://doi.org/https://doi.org/10.1111/jnc.70381

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