Bacopa monniera leaf extract up-regulates tryptophan hydroxylase (TPH2) and serotonin transporter (SERT) expression: implications in memory formation

Aim of the study

To examine the effect of Bacopa monniera leaf ethanolic extract (BMEE) on the serotonergic system of postnatal rats with reference to learning and memory.

Materials and methods

From postnatal day (PND)-15-29, rats were treated with BMEE (40 mg/kg BW + 0.5% gum acacia) by oral gavage. Behavioural tests (Y-maze, hole-board and passive avoidance) were used to evaluate their learning (PND-32-37) and retention of memory (PND-47-53). Effect of BMEE on neurotransmitter system was analyzed by ELISA and semi-quantitative polymerase chain reaction (PCR).

Results

Oral administration of BMEE improved learning and retention of memory significantly in all behavioural tasks. Following BMEE treatment, the level of serotonin (5-HT) increased while dopamine (DA) decreased significantly. We also found variation in the level of acetylcholine (ACh). However, no significant changes were observed in the level of ACh and glutamate (Glu). The level of 5-HT was significantly elevated up to PND-37 and was then restored to normal level on PND-53. Interestingly, concomitant up-regulation was recorded in the mRNA expression of serotonin synthesizing enzyme tryptophan hydroxylase-2 (TPH2) and serotonin transporter (SERT) on PND-29 and PND-37, which was restored on PND-53.

Conclusions

The results suggest that BMEE treatment significantly enhances the learning and retention of memory in postnatal rats possibly through regulating the expression of TPH2, 5-HT metabolism and transport.