Haloperidol exaggerates proprioceptive-tactile support reflexes and diminishes vestibular dominance over them

Rats made immobile and cataleptic by haloperidol, a dopamine receptor blocker, maintain their static stable equilibrium by employing a variety of allied postural support reflexes. Under some test conditions, competition between such reflexes occurs, and in haloperidol-treated rats, unlike undrugged controls, proprioceptive-tactile stimuli appear to be dominant over vestibular stimuli. We investigated this relationship in rats by testing their air-righting with and without simultaneous contact of the tail on a wooden platform. The rats were lightly held in a supine position by the shoulders and pelvis, with or without tail contact on a small wooden platform 47 cm above the ground. Undrugged rats showed the normal pattern of righting which involves axial rotation with cephalocaudal recruitment whether the tail is contacting the platform or not. Upon release, the haloperidol-treated rats (2.5 mg/kg) gripped the platform with their tail, which interfered with the air-righting reflex. This demonstrates that in haloperidol-treated rats, the dominance of tactile-proprioceptive postural support reflexes over those triggered vestibularly.