Sexually dimorphic postural adjustments during vertical behaviour are altered in a unilateral 6-OHDA rat model of Parkinson's disease

The study of sex differences in the onset, progression and symptoms of Parkinson's disease, in humans, has led to mixed results. In this study, we used a unilateral 6-hydroxydopamine (6-OHDA) lesion animal model of Parkinson's disease, to address whether there are sex differences in the composition of the movements used during vertical exploration within a confined cylinder. Tyrosine hydroxylase staining and apomorphine induced rotation were used to confirm lesion magnitude. There were no sex differences or lesion effects in the frequency of occurrence of a vertical bout or the average time spent vertical. Both male and female 6-OHDA animals exhibited equal impairments in the use of the forelimbs during vertical exploration. 6-OHDA males, as compared to 6-OHDA females, however, had a significant reduction in the use of their hindlimbs. An analysis of hindlimb step direction revealed that while sham females were more likely to step forward, sham males were more likely to step backwards during a vertical bout. This sex difference was no longer present in the 6-OHDA animals. Finally, 6-OHDA males were significantly more likely to place their dorsal surface in contact with the wall of the cylinder to maintain an upright posture during a vertical bout than animals in any other condition. These results demonstrate that the use of a confined cylinder task is appropriate for the kinematic analysis of sex differences in vertical behaviour and show that there are sex differences in motor behaviour in an animal model of human Parkinson's disease.