Scyliorhinin-I and -II induce reciprocal hindlimb scratching in mice: differentiation of spinal and supraspinal neurokinin receptors in vivo

Scyliorhinin-I amide (SCY-I) (selective for NK-1 and NK-2 receptors) or scyliorhinin-II amide (SCY-II) (selective for NK-3 receptors) were injected either spinally (i.t.; intrathecally) or supraspinally (i.c.v.; intracerebroventricularly) to mice. Following i.c.v. administration, SCI-I and SCY-II produced potent, dose-related reciprocal hindlimb scratching about equipotently (ED50 = 0.05 and 0.08 nmol, respectively). However, following i.t. administration, only SCY-I elicited greater than 50% response (ED50 = 0.07 nmol). Reciprocal hindlimb scratching is a behavioral response that has not been associated previously with neurokinins. These results might provide the first functional in vivo correlate for the differential localization of Neurokinin Receptor types within the mammalian central nervous system.