Complex effects of aqueous extract of Melampyrum pratense and of its flavonoids on activity of primary cultured hippocampal neurons.

Ethnopharmacological Relevance: The aqueous extract of the plant Malmpyrum pratense (Mp), is widely used in traditional medicine as a sedative, yet the biological basis of its action is not known.

Aim Of The Study: The effects of Mp on network activity and intrinsic and synaptic properties were studied in cultured hippocampal neurons in an attempt to analyze its mode of action.

Materials And Methods: Dissociated cultures of rat hippocampal neurons were used. Spontaneous network activity was assessed by variations in intracellular [Ca(2+)] concentrations, reflecting action potential discharges. Individual neuronal synaptic activity was measured by patch clamp recordings from similar neurons. The effect of exposure to different concentrations of Mp and some of its main ingredients was measured.

Results: Mp produced complex, dose dependent, reversible effects on network activity, increasing it with low concentrations, and decreasing it at high concentrations. Individual flavonoids contained in Mp mimicked the effects of the extract, both for the facilitating and suppressing effects of the extract. Electrophysiologically, Mp caused a reduction in spontaneous activity, but did not affect membrane properties of individual patch clamped neurons, nor did it affect mEPSCs recorded from these neurons. However, a transient increase in reactivity to pulse application of GABA was evident.

Conclusions: These results suggest that a main sedative effect of Mp is on GABAergic neurotransmission in cultured hippocampal neurons.