Theogallin and L-theanine as active ingredients in decaffeinated green tea extract: II. Characterization in the freely moving rat by means of quantitative field potential analysis

Abstract

The model Tele-Stereo-EEG (continuous recording of intracerebral field potentials in the freely moving rat to produce an electropharmacogram) has been used to see if L-theanine- and theogallin-enriched decaffeinated green tea extract would change electrical brain activity after oral administration, to provide proof of access of active components to the brain via the blood-brain barrier. Baseline recording (45 min) was followed by a 5-h recording session after oral ingestion of the extract or single components: L-theanine, theogallin and quinic acid, a suggested metabolite of theogallin. Power spectra from Fast Fourier Transformed (FFT) field potential changes were divided into six frequency bands (delta, theta, alpha1, alpha2, beta1 and beta2). No effects could be measured using a saline solution for control purposes. Oral administration of 75 mg kg(-1) total extract led to power decreases mainly in delta and alpha2 frequencies during the first hour. This pattern has been observed in the presence of stimulatory synthetic compounds. Oral administration of 30 mg kg(-1) L-theanine led to power decreases of nearly all frequencies, being more pronounced during the second and following hours in comparison with the first hour. Ingestion of 20 mg kg(-1) theogallin also showed a power decreasing effect on cortical activity. Its possible metabolite quinic acid (10 mg kg(-1), p.o.) also produced decreases in delta, alpha2 and beta1 frequencies. Measurement of motion resulted in an increase during the first hour in the presence of theogallin and L-theanine. A tendential decrease was observed in the presence of L-theanine during the last hour at its presumably highest plasma levels. The results with the administration of the total extract provided evidence for the maior involvement of L-theanine and theogallin (or its presumable metabolite quinic acid) in its action, since no other active compounds were present in the extract. These compounds could be classified by comparison with reference drugs using discriminant analysis as being antidepressive and cognition enhancing, respectively. The extract appeared among those drugs having stimulatory effects.