Physiological effects of l-theanine and theogallin enriched decaffeinated green tea extract

Green tea is known to have stimulating properties which are believed to derive from caffeine. The present project was initiated to characterize a theanine and theogallin enriched decaffeinated extract of green tea in a beverage using electrophysiological parameters in vitro, in vivo (rat) and in humans (randomized trial in comparison to placebo). Oral administration of 2.5 grams of this extract led to statistically significant changes of physiological brain activity in volunteers. Already one hour after intake of the drink containing the extract basic delta activity of the quantitatively processed electroencephalogram in frontal areas was attenuated. This decrease allows higher increases of delta power during mental work as known from earlier work. This result was indeed corroborated by higher production of delta and theta waves during reading an essay indicating better cognitive performance. Analysis of a visually evoked P300 wave revealed shorter latencies in the presence of the extract in comparison to placebo again pointing to improvement of cognitive capabilities. At the same time beta1 waves from the EEG increased compatible with a higher state of relaxation.

These findings could be backed up by analysis of field potentials from the depth of the brain of freely moving rats also showing decreases of delta, theta and alpha2 power suggesting higher activity of the cholinergic, noradrenergic and dopaminergic transmitter systems. These changes were accompanied by initial increases of locomotion which ceased during the next 4 hours. Results into the same direction were seen by administration of l-theanine, theogalline and quinic acid, a possible metabolite of theogallin alone therefore leading to the idea that these natural compounds could be responsible for the stimulatory effects of the extract.

Additional proof for the involvement of l-theanine, theogallin and possibly quinic acid in the psychotropic effects of the extract came from in vitro experiments. Hippocampal brain slices derived from adult rats were exposed to the extract and its major compounds or subfractions. Theogalline as well as quinic acid and glutamic acid increased population spike amplitudes after single and burst pattern stimuli consistent with the idea of cognitive stimulatory effects.

L-theanine attenuated the amplitudes in a concentration dependent manner antagonizing these effects to a certain degree possibly indicating relaxation. The all over net effects of the total extract consisted of increases of the population spike during single and burst pattern stimuli (induction of long term potentiation) interpreted in general as improvement of time dependent and spatial memory.

In summary the newly developed l-theanine and theogallin enriched decaffeinated green tea extract could be recognized as having a positive effect on cognitive function obviously not dependent on the presence of caffeine. The relaxing effects (increase of beta1 spectral power) observed in humans might be due the presence of l-theanine.