Effects of Achillea millefolium Aqueous Extract on Electrophysiological Properties of Rat Barrel Cortex Neurons

[Background]Yarrow or Achillea millefolium (A. millefolium) is often prescribed for the treatment of nervous system-related diseases.[Objectives]This study investigated the effects of acute oral administration of A. millefolium on the responses of barrel cortex neurons in the rat.[Methods]In this experimental study, 21 male Wistar rats (body weight, 200 g - 250 g) were divided into three groups, with seven animals in each group. Aqueous extract of A. millefolium (1.4 and 2.8 mg/kg/mL) was administered by gavage, and the responses of barrel cortex neurons (i.e., the deflection of principal whiskers [PWs] and adjacent whiskers [AWs]) were recorded using tungsten microelectrodes. Computer-controlled mechanical displacement was used to deflect whiskers individually or in combination at 0, 10, 20, 30, 50, and 100 ms inter-stimulus intervals (ISIs). The ON and OFF responses of the PWs and AWs to deflection were measured. A condition-test ratio (CTR) was computed to quantify neuronal responses to whisker interactions.[Results]The evoked ON and OFF responses of PWs and AWs did not change following the treatment with the A. millefolium aqueous extract (0.5, 1, and 2 hours postapplication). The stimulation of AWs before PWs decreased ON and OFF neuronal activities. The decrement in the level of response was related to the ISI. The administration of the A. millefolium aqueous extract did not change the level of ON and OFF responses at any of the ISIs.[Conclusions]The results demonstrated that acute oral administration of A. millefolium aqueous extract did not modulate electrophysiological responses of neurons in the barrel cortex of rats.