Evidence that reciprocal hindlimb scratching elicited in mice by intrathecal administration of muscarinic agonists is mediated through M 1 type receptors

Abstract

Intrathecal (IT) administration of pilocarpine to mice produces a vigorous and dose-related reciprocal hindlimb scratching (RHS) response (ED 50 = 0.6 μg) that is potently blocked by simultaneous IT administration of atropine (ID 50 = 0.002 μg). We now report that RHS is (1) also elicited by the more selective M 1 agonist McN-A-343-11 (ED 50 = 11.6 μg), (2) blocked by the selective M 1 antagonist pirenzepine (ID 50 = 0.001 μg), and (3) is not blocked by the selective M 2 antagonist AF-DX 116 BS at a dose up to 100 times the ID 50 dose of pirenzepine. These results extend our earlier findings and suggest that the RHS elicited in mice by IT injection of muscarinic agonists is mediated through pirenzepine-sensitive (presumably M 1) receptors and that RHS may be a convenient in vivo centrally mediated M 1 endpoint.