Pilocarpine-induced reciprocal hindlimb scratching in mice

Abstract

Intrathecal (IT) administration of pilocarpine (0.25–2.0 μg) to mice produced a vigorous and dose-related reciprocal hindlimb scratching response that lasted for 10–15 minutes. Neither the intracerebroventricular administration of pilocarpine at up to 10 times the intrathecal ED90 dose nor the subcutaneous administration of 10 mg/kg pilocarpine caused as robust an effects as IT administration. The reciprocal hindlimb scratching produced by the ED90 dose of pilocarpine (2 μg, IT) was antagonised in a dose-related manner by simultaneous IT administration of atropine (ID50=0.002 μg), methysergide (ID50=1.89 μg), the substance P antagonist [D-Pro 2, D-Trp 7,9]-SP (ID50=4.94 μg), and the putative neurokinin B antagonist [D-Pro 2, D-Trp 6,8, Nle 10]-NK (ID50=3.33 μg), but not by yohimbine (5 μg), phentolamine (2 μg), or naloxone (2.5 μg). These results suggest (a) that pilocarpine-induced reciprocal hindlimb scratching is mediated spinally, (b) that the effect is produced by an action of pilocarpine on muscarinic receptors in the spinal cord, and (c) that neurokinin, and perhaps 5-HT, mechanisms might also be involved.