Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats.
Level 5 - mechanism / opinion, no new human data
Preclinical animal (rat) neurochemical study
PubMed 9566605 · doi:10.1023/a:1022490806093
What was done
Investigated the neurochemical effects of theanine (r-glutamylethylamide) in conscious rats. Theanine was administered intragastrically to assess blood-brain barrier transport via the leucine-preferring system and its effects on regional brain concentrations of norepinephrine, dopamine, serotonin, DOPAC, and 5-HIAA. In addition, direct striatal microinjection and microdialysis were performed to measure dopamine release under calcium-free conditions and following pretreatment with glutamate receptor antagonists (AP-5 and MK-801).
What was found
Intragastric theanine crossed the blood-brain barrier and significantly increased serotonin and/or dopamine concentrations in brain regions including the striatum, hypothalamus, and hippocampus, while norepinephrine, DOPAC, and 5-HIAA were unaffected except in the striatum (exact numerical concentrations not provided in the abstract). Direct microinjection of theanine into the striatum caused a significant, dose-dependent increase in dopamine release. This release was attenuated by calcium-free Ringer buffer and significantly inhibited by the NMDA receptor antagonist AP-5, but was unaffected by MK-801.
Why it matters
Provides mechanistic evidence in an animal model that theanine can cross the blood-brain barrier and modulate central monoamine neurotransmission, specifically stimulating striatal dopamine release via an NMDA receptor-dependent pathway.
Limits
Conducted entirely in rats; translatability to human neurochemistry and oral dietary doses is unproven. The abstract provides no sample size (n), baseline concentrations, or numerical effect sizes with confidence intervals. Behavioral outcomes and chronic effects were not evaluated.
Cited by
- supports L-theanine crosses the blood-brain barrier.