Theanine, γ-glutamylethylamide, a unique amino acid in tea leaves, modulates neurotransmitter concentrations in the brain striatum interstitium in conscious rats

Abstract

Theanine (c-glutamylethylamide) is one of the major amino acid components in green tea and can pass through the blood-brain barrier. Recent studies suggest that theanine affects the mammalian central nervous system; however, the detailed mechanism remains unclear. In this study, we demonstrated the effect of theanine on neurotransmission in the brain striatum by in vivo brain microdialysis. Theanine injection into the rat brain striatum did not increase the concentration of excitatory neurotransmitters in the perfusate. On the other hand, theanine injection increased the concentration of glycine in the perfusate. Because it has been reported that theanine promotes dopamine release in the rat striatum, we investigated the glycine and dopamine concentrations in the perfusate. Co-injection of glycine receptor antagonist, strychnine, reduced theanine-induced changes in dopamine. Moreover, AMPA receptor antagonist, which regulates glycine and GABA release from glia cells, inhibited these effects of theanine and this result was in agreement with the known inhibitory effect of theanine at AMPA receptors.

Theanine is a candidate amino acid for pharmacological stabilization of mast cells

“…Recent studies have reported that theanine has various favorable physiological functions including neuroprotection in transient ischemic neuronal death (Kakuda et al 2000;Yamada et al 2005), relaxing effects under resting conditions (Abdou et al 2006;Lu et al 2004), hypolipidemic functions (Chiang et al 2005), regulation of systemic blood pressure (Yokogoshi et al 1995), suppression of the stimulatory action of caffeine (Nozawa et al 2000), modulation of neurotransmitter (Yamada et al 2009), and protection against hepatic toxicity (Sadzuka et al 2005). Additionally, studies on test rats have shown that repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects (Borzelleca et al 2006).…”

Facilitated Neurogenesis in the Developing Hippocampus After Intake of Theanine, an Amino Acid in Tea Leaves, and Object Recognition Memory

“…If ethylamine metabolized from theanine is transported into the brain, it is possible that ethylamine partially participate in the effects of theanine intake. In contrast, in vivo microdialysis experiment indicates that theanine perfusion stimulates dopamine release in the rat striatum (Yamada et al 2009). …”

Theanine Potentiates the Inhibitory Effect of (-)-epigallocatechin-3-gallate on Matrix Metalloprotease Activity in Langerhans-like Cells and on Tube Formation

“…It amounts to 1 2% dry weight of green tea, which equates to 25 60 mg per 200 ml serving of liquid tea. Green tea is therefore the major source of dietary L-theanine 37 , which is known to have a calming effect on neurotransmission and mood 38 .…”

“…It has been reported that inhibitory neurotransmitters, such as glycine and GABA, are released by activating -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid AMPA receptors, which are ionotropic glutamate receptors 38 . Theanine has been found to bind AMPA receptors, but not N-methyl-D-aspartate NMDA receptors 38 .…”

“…It has been reported that inhibitory neurotransmitters, such as glycine and GABA, are released by activating -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid AMPA receptors, which are ionotropic glutamate receptors 38 . Theanine has been found to bind AMPA receptors, but not N-methyl-D-aspartate NMDA receptors 38 . Many pharmacological agents that bind glutamate receptors have been developed primarily against NMDA and/or AMPA receptors in an attempt to combat the neuronal damage caused by the excitotoxic stress that follows global or focal ischemia 40 .…”