Sex differences in catalepsy: evidence for hormone-dependent postural mechanisms in haloperidol-treated rats

Catalepsy, a symptom of Parkinson's disease and related disorders can be produced in rats and other laboratory animals by the blockade of nigrostriatal dopamine using dopaminergic antagonists such as haloperidol. When haloperidol-induced cataleptic rats are placed facing downward on an inclined plane, they will brace against the resulting downward force by pushing backwards, and if they lose postural stability, or their position on the inclined plane, they will jump forward. Females, however, jump from the inclined plane at a significantly lower angle than do males. Frame-by-frame analysis of the jumping sequences revealed that females and males use a different combination of postural adjustments to maintain their position on the inclined plane prior to jumping. Furthermore, gonadal hormone manipulations at birth and in adulthood reveal that these sex differences in postural adjustments are dependent on the organizational effects of gonadal hormones in the perinatal period. These results provide evidence for sex differences in postural support mechanisms and suggest that the sex of subjects, or their hormonal state, must be considered when studying the behavioral aspects of neurological disorders such as Parkinson's disease which include a postural component.