Journal article
5-HT2 antagonism indirectly increases motor unit discharge rate and cervicomedullary motor evoked potential amplitude during submaximal elbow flexions
The Journal of physiology, Vol.603(16), pp.4573-4591
17/07/2025
PMID: 40674385
Appears in Recent Faculty of Health Publications
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Abstract
Spinal motoneurone excitability is heavily regulated by serotonin via somatodendritic 5-HT2 receptors. However, the effects of these receptors on the excitability of motoneurones in the upper limb are not clearly understood. Therefore, the purpose of this study was to assess the effects of 5-HT2 antagonism on motor unit discharge characteristics of the biceps brachii and evoked responses to cervicomedullary stimulation. Twelve healthy individuals (aged 24 +/- 3 years) participated in this double-blind, placebo-controlled, two-way crossover trial and were administered the 5-HT2 antagonist cyproheptadine. high-density surface EMG (HDsEMG) was used to examine motor unit activity in the biceps brachii during trapezoidal contractions of 10%, 20% and 30% maximal voluntary contraction (MVC). Cervicomedullary stimulation was used to produce small and large cervicomedullary motor evoked potentials (CMEPs) in the elbow flexors during these submaximal contractions. Cyproheptadine reduced maximal elbow flexion torque (similar to 5%, P = 0.003), and increased EMG amplitude (similar to 2%, P = 0.037), motor unit discharge rates (similar to 1.5 pulses/s, P = 0.001) and CMEP amplitude from low (similar to 25%, P = 0.002) and high (similar to 15%, P = 0.026) intensity stimulation during submaximal contractions. This is the first study to examine the effects of 5-HT2 antagonism on motoneurone excitability using both HDsEMG and cervicomedullary stimulation in a single experiment. The results of this study provide novel evidence that 5-HT2 receptor antagonism increases both motor unit discharge rates and CMEP amplitude during elbow flexions when torque targets remain unchanged from baseline.Key points Animal models have revealed that serotonin can heavily regulate motoneurone gain via 5-HT2 receptors. Recently, it has been revealed that 5-HT2 receptors can modulate motor unit firing characteristics in humans. However, the effect of these receptors on motoneurone excitability of the upper limb is not clearly understood. This study paired high-density surface EMG with cervicomedullary stimulation to provide a novel insight to the effects of 5-HT2 antagonism on motoneurone excitability. 5-HT2 antagonism reduced maximal elbow flexor torque, and increased motor unit discharge rates and cervicomedullary motor evoked potential amplitudes during submaximal contractions. These findings suggest that compensatory voluntary drive is required to achieve the same torque level with 5-HT2 receptor antagonism, indirectly enhancing motoneurone activity and excitability of the motoneurone pool.
Details
- Title
- 5-HT2 antagonism indirectly increases motor unit discharge rate and cervicomedullary motor evoked potential amplitude during submaximal elbow flexions
- Creators
- Tyler T. Henderson - Charles Darwin UniversityJanet L. Taylor - Neuroscience Research AustraliaJacob R. Thorstensen - Bond UniversityJustin J. Kavanagh - Griffith University
- Publication Details
- The Journal of physiology, Vol.603(16), pp.4573-4591
- Publisher
- Wiley
- Number of pages
- 19
- Grant note
- Open access publishing facilitated by Griffith University, as part of the Wiley - Griffith University agreement via the Council of Australian University Librarians.
- Identifiers
- 991013386139902368
- Copyright
- © 2025 The Author(s).
- Academic Unit
- Faculty of Health
- Language
- English
- Resource Type
- Journal article