The pruritogenic effect of Anaphe venata extracts in rats: the role of cholinergic, GABAergic and opioid systems

Abstract

This study sought to investigate the effect of the crude aqueous and phosphate buffer saline (PBS) extracts of Anaphe venata on body scratching behaviour in rat in a novel environment and also to determine the neural mechanism(s) involved. Aqueous and PBS extracts of Anaphe venata were prepared and their effects on body scratching behaviour were evaluated in rats. Animals were divided into four groups (n = 6-12 per group) and graded doses of extracts (100-400 mg/kg) were administered (dissolved in normal saline) intraperitoneally (i.p.) to each animal in the experimental groups. The control group received an equivalent volume of normal saline. Behavioural scores were recorded for a period of 30 minutes after the administration of normal saline or extract. The role of various receptors in the extract induced pruritus was evaluated using known receptor agonist/antagonists. Results showed that aqueous Anaphe extract induced dose-dependent increase in body scratching behaviour (p<0.05) compared to the saline control. This effect was attenuated by scopolamine (3 mg/kg, i.p), flumazenil (2 mg/kg, i.p), and thiamine (1 mg/kg, i.p) while naloxone (2.5 mg/kg, i.p) attenuated body scratching with complete blockade seen at 100 and 200 mg/kg dose levels (p<0.05). PBS extract did not alter body scratching behaviour in the rats. Only the aqueous extract was significantly pruritogenic which was mediated via the muscarinic cholinergic, GABAergic and opioid pathways, while PBS extract did not alter
body scratching behaviour. © 2010 International Formulae Group. All rights reserved.

Keywords: Behaviour, body scratching, extract, intraperitoneal, receptors, rat