We investigated the effects of silymarin, a component of the extract from milk thistle (Silybum marianum) on the level of anxiety in rats and also the potential role of the serotonergic system in the modulatory influences of silymarin on anxiety-related behavior. The elevated plus-maze test was used for testing the above level. Oral administrations of silymarin (35, 70, 140, and 280 mg per rat) for 2 weeks induced an anxiolytic-like effect shown by specific increases in normalized values of the open arm time (OAT) and open arm entries (OAE) in the elevated plus-maze. Intraventricular infusion of a 5-HT1A receptor agonist, 8-OH-DPAT (5, 10, and 25 ng per rat), increased the OAT and OAE, indicating that this agent also possesses an anxiolytic effect. Similar injections of a 5-HT1A receptor antagonist, NAN190 (0.25, 0.5, and 1.0 μg per rat), intensified anxiety-related behavior. The least effective dose of intraventricularly injected 8-OH-DPAT (5 ng per rat), when co-administered with silymarin (35, 70, and 140 mg per rat, pretreatment for 2 weeks), decreased the anxiety-related behavior significantly. An effective dose of NAN190 (0.5 μg per rat) combined with silymarin in the above-mentioned dosage provided significant decreases in the OAT and OAE. These results demonstrate that the effects of silymarin on anxiety are mediated, at least partly, by 5-HT1A receptors of serotonin.
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Solati, J., Yaghmaei, P. & Mohammdadi, K. Role of the 5-HT1A Serotonergic System in Anxiolytic-Like Effects of Silymarin. Neurophysiology 44, 49–55 (2012). https://doi.org/10.1007/s11062-012-9266-0
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DOI: https://doi.org/10.1007/s11062-012-9266-0