Intrathecal application of cyproheptadine impairs locomotion in intact rats

In intact adult rats, cyproheptadine, a 5-HT2 antagonist, administered intrathecally at the midlumbar segments was found to impair hindlimb locomotor movements during overground locomotion. These effects were dose-dependent; they varied from transient complete hindlimb paraplegia seen at doses of 300 μg/20 μl, to short-lasting trunk instability at doses of 100 μg/20 μl. After the return of overground locomotion, transient abduction of one of the hindlimbs was observed in some animals. These findings demonstrate that the blockade of 5-HT2 receptors affects locomotion in intact rats. Our results provide support for the hypothesis of serotonergic involvement in rat locomotion, which, so far, has been based mainly on the effects of 5-HT2 agonists on the recovery of locomotion in spinal rats.