How Galvanic Electrical Stimulation Modulate Glial Cells & Boost Brain Function
Introduction:
The human brain is an intricate and awe-inspiring organ, consisting of billions of neurons working in harmony to facilitate various cognitive functions. While neurons often steal the spotlight in discussions about brain function, an equally important player often remains in the shadows – glial cells. Recent research has shed light on the exciting role glial cells play in enhancing brain function, challenging the conventional view that neurons are solely responsible for cognitive processes.
Galvanic electrical stimulation, also known as transcranial direct current stimulation (tDCS), is a non-invasive neuromodulation technique that involves applying a low electrical current to the scalp to modulate neuronal activity. While the majority of research on tDCS has focused on its effects on neurons, there is evidence to suggest that galvanic electrical stimulation can also influence glial cells, particularly astrocytes.
Non-invasive electrical brain stimulation by application of direct current (DCS) promotes plasticity in neuronal networks in vitro and in in vivo. This effect has been mainly attributed to the direct modulation of neurons. Glia represents approximately 50% of cells in the brain. Glial cells are electrically active and participate in synaptic plasticity. Despite that, effects of DCS on glial structures and on interaction with neurons are only sparsely investigated. In this perspective article we review the current literature, present our own dose response data and provide a framework for future research from two points of view: first, the direct effects of DCS on glia and second, the contribution of glia to DCS related neuronal plasticity.[1]
The Glorious World of Glial Cells:
Glial cells, once considered mere supporting structures for neurons, are gaining recognition for their multifaceted roles in maintaining brain health and function. Comprising about 90% of the brain's cells, glia consist of various types, including astrocytes, microglia, and oligodendrocytes. Each type contributes uniquely to the brain's overall well-being.
Astrocytes: The Versatile Support System:
Astrocytes are star-shaped cells that provide crucial support to neurons. They regulate the brain's chemical environment by controlling the concentration of neurotransmitters and ions. Astrocytes play a vital role in synapse formation and plasticity, influencing learning and memory. Additionally, astrocytes play a crucial role in regulating the concentration of calcium ions in the brain. Studies have indicated that galvanic electrical stimulation can impact astrocytic calcium activity. Changes in calcium levels within astrocytes are associated with alterations in their function, including the release of gliotransmitters, which can influence neuronal activity.
Microglia: Guardians of Brain Health:
Microglia act as the brain's immune system, protecting it from infections and injuries. Microglia not only safeguard the brain from potential threats but also actively participate in repair processes. By removing damaged cells and debris, microglia contribute to the maintenance of a healthy neural environment, preventing cognitive decline and supporting overall brain function. Recent studies suggest that microglia also play a role in synaptic pruning, refining the connections between neurons and optimizing the efficiency of neural circuits. This process is essential for learning and memory consolidation.
Oligodendrocytes: Speeding up Information Processing:
Oligodendrocytes produce myelin, a fatty substance that wraps around neuronal axons. Myelin acts as an insulator, facilitating faster transmission of electrical signals between neurons. This accelerated communication enhances overall cognitive processing speed and efficiency. This not only improves the efficiency of information processing but also enhances cognitive functions such as problem-solving and motor coordination. Galvanic electrical stimulation has shown potential effects on myelination processes, which could influence the speed of signal transmission between neurons. This may contribute to improved cognitive processing. Electrical stimulation of the CNS has been impactful not only on the treatment of neurological disorders, but also in the exploration of the neural circuitry involved in their pathologies as well as in the normal functioning of the healthy brain. The delivery of electrical current to the brain can cause direct or indirect excitation and inhibition of neuronal firing as well as induce changes in non-neuronal cell types. This review provides a survey of common clinically relevant stimulation approaches, focusing on what is known about their effect on non-neuronal cells including microglia, astrocytes, oligodendrocytes, and endothelial cells.[2]
Neurotransmitter Regulation:
Astrocytes actively regulate the levels of neurotransmitters such as glutamate and GABA in the synapses. By maintaining an optimal chemical environment, astrocytes contribute to efficient communication between neurons, ultimately enhancing cognitive functions like attention and decision-making. Astrocytes are involved in the regulation of neurotransmitters such as glutamate, the primary excitatory neurotransmitter in the brain. Galvanic electrical stimulation has been shown to affect glutamate release and uptake by astrocytes. This modulation of glutamate levels can have downstream effects on synaptic transmission and plasticity.
Synaptic Plasticity:
Astrocytes are involved in the modulation of synaptic plasticity, the ability of synapses to strengthen or weaken over time. This process is crucial for learning and memory formation, and astrocytes play a dynamic role in shaping and optimizing these synaptic connections. Galvanic electrical stimulation has been associated with increased levels of brain-derived neurotrophic factor (BDNF), a key neurotrophin. Elevated BDNF levels can promote neuroplasticity and synaptic plasticity, potentially enhancing cognitive functions.[3]
Influence on Neuroinflammation:
Glial cells, including astrocytes and microglia, are integral components of the brain's immune system. Galvanic electrical stimulation has been investigated for its potential anti-inflammatory effects, and studies suggest that it may modulate the activity of microglia and reduce neuroinflammation. This anti-inflammatory action could contribute to a more supportive environment for neuronal function. Non-invasive electrical stimulation (ES) employing a low-intensity electric current presents a potential therapeutic modality that can be applied for treating retinal and brain neurodegenerative disorders. As neurons are known to respond directly to ES, the effects of ES on glial cells are poorly studied. A key question is if ES directly mediates microglial function or modulates their activity merely via neuron-glial signaling.[4]
Conclusion:
It's important to note that while there is evidence supporting the influence of galvanic electrical stimulation on glial cells, the mechanisms involved and the outcomes are complex and may vary depending on the specific parameters of stimulation, such as current intensity, duration, and electrode placement. In the evolving landscape of neuroscience, glial cells are emerging as key players in shaping the brain's incredible capabilities. Beyond their traditional roles as support cells, astrocytes, microglia, and oligodendrocytes actively contribute to optimizing synaptic connections, regulating neurotransmitters, and speeding up information processing. Understanding and harnessing the potential of glial cells could pave the way for innovative therapies and interventions to enhance brain function, offering new hope for individuals facing cognitive challenges. As research in this field continues to unfold, the profound impact of glial cells on brain function promises to be one of the most exciting frontiers in neuroscience.
References:
1.AUTHOR=Gellner Anne-Kathrin, Reis Janine, Fritsch Brita TITLE=Glia: A Neglected Player in Non-invasive Direct Current Brain Stimulation JOURNAL=Frontiers in Cellular Neuroscience VOLUME=10 YEAR=2016 URL=https://www.frontiersin.org/articles/10.3389/fncel.2016.00188 DOI=10.3389/fncel.2016.00188 ISSN=1662-5102
2.AUTHOR=Williams Nathaniel P., Kushwah Neetu, Dhawan Vaishnavi, Zheng Xin Sally, Cui Xinyan Tracy TITLE=Effects of central nervous system electrical stimulation on non-neuronal cells JOURNAL=Frontiers in Neuroscience VOLUME=16 YEAR=2022 URL=https://www.frontiersin.org/articles/10.3389/fnins.2022.967491 DOI=10.3389/fnins.2022.967491 ISSN=1662-453X
3.Saad Javeed, Amir H. Faraji, Christopher Dy, Wilson Z. Ray, Matthew R. MacEwan,
Application of electrical stimulation for peripheral nerve regeneration: Stimulation parameters and future horizons, Interdisciplinary Neurosurgery, Volume 24, 2021, 101117, ISSN 2214-7519,
https://doi.org/10.1016/j.inat.2021.101117.
(https://www.sciencedirect.com/science/article/pii/S2214751921000293)
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