Head displacement and bracing in haloperidol-treated rats compared to rats with lateral hypothalamic damage

A characteristic of catecholamine-depletion-induced catalepsy is that such animals resist horizontal displacement, forward, backward or sideward, by bracing, i.e., pushing against the displacing force rather than stepping away as do normal animals. In this report the bracing responses of two cataleptic preparations were compared: (1) intact rats given haloperidol, a dopamine antagonist, and (2) rats with large lesions of the lateral hypothalamus (LH). Although both preparations exhibited exaggerated bracing responses when pushed, the LH rats acted in a non-cataleptic manner when pushed backward by the head; they retreated backward. The backward walking was a head-elicited response, because pushing the body backwards by the shoulders elicited bracing, not walking. Other forms of head displacement elicited body bracing if the body's stability was challenged: as when the head (and thus the body) was pulled forward; or no strong bracing responses if the head was displaced without affecting the body's stability, i.e., when as the head was pushed laterally. Therefore, retreating rather than bracing was elicited by one specific form of head displacement: backward. In contrast, haloperidol-treated rats braced whenever the body's stability was challenged, including when the head was pushed backward.