Glycine is the primary inhibitory neurotransmitter in the spinal cord and inhibits motor neurones. This effect is demonstrated by the blockage of glycine receptors in postsynaptic receptors by strychnine, which causes significant tetany and convulsions from extensive muscle contractions. The role of glycine in causing muscle relaxation in the postsynaptic motor neurones of the spinal cord can be demonstrated by the role of glycine during sleep. Glycine may play a significant role in causing atonia during sleep, and this is particularly evident during REM sleep where muscle relaxation occurs. This relaxation is a characteristic of REM sleep and may be required by the brain to allow the process of dreaming without “acting out” any movements present in the dreams. The findings of studies that glycine was important in the atonia seen during REM sleep may explain the benefits to sleep quality seen with glycine supplementation. Those with poor quality sleep may therefore benefit from taking glycine as an adjunct to other strategies to induce a deeper and more high quality sleep.
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Soja, P. J. 2008. Glycine-Mediated Postsynaptic Inhibition is Responsible for REM Sleep Atonia: Commentary on Brooks PL and Peever JH. Glycinergic and GABAA-mediated inhibition of somatic motoneurons does not mediate rapid eye movement sleep motor atonia. Journal of Neuroscience. 28: 3535–3545
