Influence of 5-HT2 Receptor Blockade on Motor Unit Firing and Persistent Inward Currents in Humans during Voluntary Muscle Contraction

Benjamin Kavanagh^*
*Correspondence: Benjamin Kavanagh, Department of Physiology and Pharmacology, Griffith University, QLD 4222, Australia, Email:

Keywords

Dendrites • Antagonism • Motoneurones

Introduction

The intricate interplay between the nervous and muscular systems governs our ability to perform voluntary movements. One key neurotransmitter involved in this process is serotonin (5-HT), which acts on various receptors, including the 5-HT2 receptor subtype. Recent research has shed light on the role of 5-HT2 receptors in modulating motor unit firing and the estimation of persistent inward currents during voluntary muscle contraction in humans. Understanding these mechanisms could have significant implications for unraveling the complexities of neuromuscular control and potentially lead to therapeutic advancements in motor function-related disorders. Serotonin, commonly known as the "feel-good" neurotransmitter, plays a multifaceted role in the nervous system. In addition to its involvement in mood regulation, sleep, and appetite, serotonin also exerts influence on motor function. The 5-HT2 receptor subtype, a member of the G-protein coupled receptor family, has garnered particular interest due to its presence in both the central nervous system and peripheral tissues, including skeletal muscles [1-3].

Description

Motor unit firing and voluntary muscle contraction

Motor units are fundamental components of the neuromuscular system, comprising a motor neuron and the muscle fibers it innervates. Voluntary muscle contractions involve the recruitment and firing of motor units to generate force and produce movement. The firing rate of motor units is a critical factor in determining the strength and precision of muscle contractions [4].

Persistent Inward Currents (PICs)

Persistent Inward Currents (PICs) are subthreshold currents that can contribute to the excitability of motor neurons. These currents are implicated in various neuromuscular disorders and can significantly impact motor unit behavior. PICs are thought to play a role in sustaining motor neuron firing during weak synaptic input, contributing to the generation of rhythmic motor patterns and influencing muscle tone [5].

The link between 5-HT2 receptors and motor unit firing

Recent studies have begun to unravel the intricate relationship between 5-HT2 receptors and motor unit firing. Blockade of 5-HT2 receptors has been shown to suppress motor unit firing during voluntary muscle contractions. This suggests that serotonin, acting through the 5-HT2 receptor subtype, modulates the excitability of motor neurons, potentially affecting motor unit recruitment and force production.

Role of 5-HT2 receptor blockade in persistent inward currents

Emerging evidence also points to the involvement of 5-HT2 receptors in regulating PICs. Blockade of 5-HT2 receptors appears to influence the magnitude of PICs, which could have implications for motor unit firing patterns and the overall control of muscle contraction. The exact mechanisms underlying this relationship are still being investigated, but it is becoming increasingly clear that serotonin and 5-HT2 receptors play a significant role in shaping PICs.

Clinical implications

The insights gained from studying the blockade of 5-HT2 receptors and its effects on motor unit firing and PICs hold promise for potential clinical applications. Understanding these mechanisms could lead to novel therapeutic strategies for conditions characterized by altered neuromuscular control, such as neuromuscular disorders, movement disorders, and even rehabilitation after injuries. Targeted interventions that modulate 5-HT2 receptor activity could help fine-tune motor unit firing patterns and enhance muscle function [6].

Conclusion

The blockade of 5-HT2 receptors has emerged as a key player in modulating motor unit firing and persistent inward currents during voluntary muscle contraction in humans. As our understanding of these intricate processes continues to evolve, the potential for therapeutic interventions to optimize neuromuscular control becomes increasingly promising. This research not only sheds light on the fundamental mechanisms of motor function but also paves the way for innovative treatments that could significantly impact the lives of individuals with motor-related disorders.

Acknowledgement

None.

Conflict of Interest

None.

References

1. Afsharipour, Babak, Nagib Manzur, Jennifer Duchcherer and Keith F Fenrich, et al. "Estimation of self-sustained activity produced by persistent inward currents using firing rate profiles of multiple motor units in humans." J Neurophys (2020).

Google Scholar, Crossref, Indexed at

2. Bennett, David J., Hans Hultborn, Brent Fedirchuk and Monica Gorassini. "Synaptic activation of plateaus in hindlimb motoneurons of decerebrate cats." J Neurophys 80 (1998): 2023-2037.

Google Scholar, Crossref, Indexed at

3. Berger, Albert J and Tomoyuki Takahashi. "Serotonin enhances a low-voltage-activated calcium current in rat spinal motoneurons." J Neurosci 10 (1990): 1922-1928.

Google Scholar, Crossref, Indexed at

4. Boess, FG and IL Martin. "Molecular biology of 5-HT receptors." Neuropharmacol 33 (1994): 275-317.

Google Scholar, Crossref, Indexed at

5. Bräcklein, Mario, Deren Y Barsakcioglu, Alessandro Del Vecchio and Jaime Ibáñez, et al. "Reading and modulating cortical β bursts from motor unit spiking activity." J Neurosci 42 (2022): 3611-3621.

Google Scholar, Crossref, Indexed at

6. Cotel, Florence, Richard Exley, Stephanie J Cragg and Jean-François Perrier. "Serotonin spillover onto the axon initial segment of motoneurons induces central fatigue by inhibiting action potential initiation." Proceed Nat Acad Sci 110 (2013): 4774-4779.

Google Scholar, Crossref, Indexed at