Myelination determines the nerve cell power of inhibition, study finds


Date:
February 18, 2022
Source:
Netherlands Institute for Neuroscience - KNAW
Summary:
Researchers shed new light on how myelin loss might underpin
aberrant brain activity which have been observed in people with
multiple sclerosis. The study suggests that myelination, however
patchy on specific interneurons, is required to reach their full
inhibitory potential.



FULL STORY ========================================================================== Researchers from the Netherlands Institute for Neuroscience (NIN) shed
new light on how myelin loss might underpin aberrant brain activity
which have been observed in people with multiple sclerosis. This study, published in eLife, suggests that myelination, however patchy on specific interneurons, is required to reach their full inhibitory potential.


========================================================================== Impact of losing myelin The brain contains billions of nerves that
connect with each other via cable- like structures called axons. Axons
transmit electrical impulses and are often wrapped in a fatty substance
called myelin. This substance increases the speed of nerve impulses
and reduces the energy lost over long distances. Loss or damage of
the myelin layer -- which is the case for multiple sclerosis- can cause
serious disability. Although myelinated axons play pivotal roles in brain function, only little is understood about their role in the electrical architecture of local circuits where experiences are processed, and
memories are stored.

However, a fast-firing neuron within the brain, called the PV+
interneuron, has short, sparsely myelinated axons. Even so, PV+
interneurons are powerful inhibitors that regulate important brain rhythms
and cognitive processes in gray matter areas of the brain. Recent findings
have shown that also axons of PV+ interneurons are insulated by myelin
sheaths. Yet it remains unclear how the unusual, patchy myelination
affects their function.

Epileptic spikes as indicator To study the impact on interneurons and
slow brain waves, researcher Mohit Dubey, from the NIN, together with colleagues from the Erasmus Medical Centre used genetically engineered
mice either lacking or losing myelin. "As mice progressively lost
myelin, the speed of inhibitory signals from PV+ interneuron did not
change but their signal strength decreased" says Dubey. As a result of
being no longer inhibited by PV+ interneurons, the power of slow brain
waves dramatically increased. These waves also triggered brief spikes resembling signals seen in epilepsy, only when the mice were inactive
and quiet. Restoring the activity of PV+ interneurons helped to reverse
the epileptic spikes.

"These results expand our understanding of the importance of myelin in
gray matter and its clinical relevance to demyelinating disorders such
as multiple sclerosis" says Maarten Kole, group leader at the NIN. More research is needed to determine whether these brief epileptic spikes could
be a biomarker of multiple sclerosis and/or a target for developing new therapeutic strategies to limit cognitive impairments.

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========================================================================== Journal Reference:
1. Mohit Dubey, Maria Pascual-Garcia, Koke Helmes, Dennis D Wever,
Mustafa S
Hamada, Steven A Kushner, Maarten HP Kole. Myelination synchronizes
cortical oscillations by consolidating parvalbumin-mediated phasic
inhibition. eLife, 2022; 11 DOI: 10.7554/eLife.73827 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220218100650.htm

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