Valerian extract prepared with methanol but not with ethanol or ethyl acetat inhibits the postsynaptic potentials in rat cortical neurons indicating an adenosine like action

Valerian binds to adenosine receptors and acts as a partial agonist thereon. Investigation on brain slices revealed an agonistic activity on the central adenosine A1 receptors which can be blocked by an adenosine A1 receptors antagonist. Manufacturing the extract by means of different solvents might influence the extract composition and alter its biological action. Therefore, the aim of the present experiments was to compare the central action of an ethanolic (EtOH 63%) and a methanolic extract (MeOH 45%, Ze 911) prepared from the identical starting material. For that purpose the brain slice technique was used again. Coronal slices were cut with a vibratome from a block of rat brain including the cingulated cortex. Intracellular recordings were obtained from pyramidal cells of the cingulated cortex in layer V. Post-synaptical potentials (PSP) were evoked by electrical stimulation (0.2Hz, 1–2 ms, 20–120 V) with a concentric bipolar tungsten electrode placed in layer I. The stimulation voltage was adjusted individually for each slice to yield PSP amplitudes which were approximately 80% of maximum. The ethanolic extract did not modulate the PSP. However, the methanolic extract clearly inhibited the PSP in a dose related manner (range: 0.1–15mg) with an IC₅₀ value of 0.8mg/mL. The maximal inhibition induced by 10mg Ze911/mL was completely antagonized by 0.1µM of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), an adenosine A1 blocker indicating that adenosine A1 receptors mediate the pharmacological action of the methanolic valerian extract Ze911. The extraction solvent is important for extract composition and influences the pharmacological action. Exclusively, the methanolic extract Ze 911 acts at central adenosine A1 receptors whilst an ethanolic extract failed in this respect.