A new motor test sensitive to aging and dopaminergic function

Neurodegenerative disorders which involve motor impairment is characteristic of old age. Although there are a few tests which attempt to assess motor incapacities, many have utilized scales which have either a great deal of subjective evaluations or are subject to learning-performance complexities. This study describes a method able to measure motor impairment of aging rats which is subject to dopaminergic influences and has negligible practice effects. The test is designed so that rats have to traverse 2 meter beams of 15° inclination whose widths 3, 6, 12, 18 and 24 mm are changed on each test session using a table of random numbers. The time ceiling allowed for traversing the 2 m beams was established at 120 sec. 3-month-old rats (n = 20) and aged rats (n = 20) with a mean age of 26.5 ± 3.8 months ranging from 23 to 34 months were utilized in this study. All young rats traversed the beams, independently of beam width, while virtually none of the old rats traversed the 3 and 6 mm beams. However, as the beam width increased more and more aged rats ascended the beam. Nevertheless, there were always a few old rats who were unable to cross even on the widest beam. When young rats were fitted with a lead belt which increased their body weight by approximately 40%, they still traversed all beam widths. On the other hand, haloperidol (0.1 and 0.2 mg/kg) severly impaired the performance of young rats. Conversely, administration of amphetamine (1.0 mg/kg) or l-dopa (50 mg/kg) to old rats substantially improved their performance. The results suggest that beam taxis appears to be an effective and efficient test for screening motor dysfunction in aged rats and can be amenable to studies on changes of motor capabilities as a result of drugs and/or brain damage.