Adjusting the thickness and internodal length of the myelin sheath is a mechanism for tuning the conduction velocity of axons to match computational needs. Interactions between oligodendrocyte precursor cells (OPCs) and developing axons regulate the formation of myelin around axons. We now show, using organotypic cerebral cortex slices from mice expressing eGFP in Sox10-positive oligodendrocytes, that endogenously released GABA, acting on GABAA receptors, greatly reduces the number of oligodendrocyte lineage cells. The decrease in oligodendrocyte number correlates with a reduction in the amount of myelination but also an increase in internode length, a parameter previously thought to be set by the axon diameter or to be a property intrinsic to oligodendrocytes. Importantly, while TTX block of neuronal activity had no effect on oligodendrocyte lineage cell number when applied alone, it was able to completely abolish the effect of blocking GABAA receptors, suggesting that control of myelination by endogenous GABA may require a permissive factor to be released from axons. In contrast, block of AMPA/KA receptors had no effect on oligodendrocyte lineage cell number or myelination. These results imply that, during development, GABA can act as a local environmental cue to control myelination and thus influence the conduction velocity of action potentials within the CNS.
GABA is the major inhibitory neurotransmitter and blocks signals from excitatory nerves such as glutamate. A few years ago, it was found that oligodendrocyte precursors have glutamate receptors and when these get stimulated it probably acts as a signal to the oligodendrocyte precursor cells to change into an oligodendrocyte and to start myelination. The glutamate is essentially a calcium channel making the inside of the cell more electrically positive. however blocking this made no infuence on cell numbers. However, if you stimulate with GABA A which is a chloride channel meaning the inside becomes more electrically negative you get less oligos and less myelination. Is there any evidence that benzodiazepines block or stimulate myelination ? Don’t think so, but have people looked ?.