L-TheaninevsPolygala Tenuifolia

L-Theanine (gamma-glutamylethylamide) crosses the blood-brain barrier via the large neutral amino acid transporter (LAT1/SLC7A5) and exerts anxiolytic effects through multiple pathways. It increases GABA synthesis by serving as a substrate for glutamate decarboxylase (GAD), elevating inhibitory tone without directly binding GABA-A receptors — avoiding sedation. It modulates serotonin by increasing tryptophan hydroxylase (TPH2) activity and raises dopamine levels in the prefrontal cortex via inhibition of dopamine reuptake. L-Theanine antagonizes glutamate binding at AMPA and kainate receptor subtypes (GluA1-4, GluK1-5), reducing excitatory neurotransmission and excitotoxicity risk. This glutamate antagonism, combined with increased GABA, drives the characteristic increase in alpha brain wave power (8-14 Hz) in the posterior parietal and occipital cortex — the EEG signature of relaxed alertness. When co-administered with caffeine, L-theanine attenuates caffeine-induced increases in blood pressure and anxiety by modulating sympathetic nervous system activation through alpha-2 adrenergic receptor pathways, while caffeine's dopaminergic and adenosine-blocking effects on focus and attention are preserved.

The saponins (tenuigenin, polygalasaponins, onjisaponins) and oligosaccharide esters (3,6'-disinapoyl sucrose, tenuifolisides) have multiple neurological actions. They inhibit acetylcholinesterase (AChE) at the catalytic site, increasing synaptic acetylcholine and enhancing muscarinic M1/M4 and nicotinic receptor signaling. They promote BDNF and NGF expression via CREB and ERK/MAPK pathways, supporting neuroplasticity and neurogenesis in the hippocampus and subventricular zone. They modulate NMDA receptor function (possibly as positive allosteric modulators at the glycine site) and enhance long-term potentiation (LTP) via CaMKII and PKC. The anti-depressant effects involve monoaminergic modulation — increasing dopamine and norepinephrine via MAO inhibition or reuptake modulation — and HPA axis regulation (reducing CRH and cortisol). Tenuigenin may also activate TrkB receptors directly.