ResearchQuantitative evaluation of motor function before and after engraftment of dopaminergic neurons in a rat model of Parkinson ' s disease

Although gait change is considered a useful indicator of severity in animal models of Parkinson's disease, systematic and extensive gait analysis in animal models of neurological deficits is not well established. The CatWalk-assisted automated gait analysis system provides a comprehensive way to assess a number of dynamic and static gait parameters simultaneously. In this study, we used the Catwalk system to investigate changes in gait parameters in adult rats with unilateral 6-OHDA-induced lesions and the rescue effect of dopaminergic neuron transplantation on gait function. Four weeks after 6-OHDA injection, the intensity and maximal area of contact were significantly decreased in the affected paws and the swing speed significantly decreased in all four paws. The relative distance between the hind paws also increased, suggesting that animals with unilateral 6-OHDA-induced lesions required all four paws to compensate for loss of balance function. At 8 weeks post-transplantation, engrafted dopaminergic neurons expressed tyrosine hydroxylase. In addition, the intensity, contact area, and swing speed of the four limbs increased and the distance between the hind paws decreased. Partial recovery of methamphetamine-induced rotational response was also noted. Introduction Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. The worldwide prevalence is estimated to be 200 per 100,000 population [1]. Degeneration of dopamine neurons in the substantia nigra (SN) and the consequent deficit of dopamine release in the striatum and other target areas appear to be responsible for the characteristic manifestations of PD. Common parkinsonian symptoms are rest tremor, bradykinesia, rigidity, and loss of postural reflexes [2]. Gait disturbances are one of the most common motor problems in Parkinson's disease. Patients with PD often present with a stooped posture and shuffling gait, decreased stride length and overall velocity, increased double-limb support, reduced foot clearance during swing phase, and increased cadence leading to the potential for falls [3-5]. Progressive gait disturbance combined with posture instability finally deprives patients of locomotor ability and activities of daily living [6]. In typical cases, however, the onset of symptoms is asymmetrical, with tremor and rigidity affecting limbs on one side of the body first. Although the limbs on the contralateral side of the body will eventually be affected, it can often be several years before the symptoms manifest. Although systematic gait analyses have been widely used in the clinical setting as important indices to evaluate the severity of PD, the extent of gait changes after unilateral 6OHDA-induced lesions in rats remains to be explored. One of the methods of analyzing gait and ambulation in animal models of PD includes the treadmill locomotion test to evaluate walking velocity, swing and stance time [7]. Other methods include the cylinder test to assess forelimb-use asymmetry and the forelimb akinesia test to measure movement initiation in animals with 6-OHDA-induced lesions [8,9]. These tests, however, measure only dynamic or static changes in gait. Therefore, multiple methods are necessary to evaluate dynamic and static gait parameters simultaneously. A computer-assisted gait analysis, called the CatWalk method, provides an automated way to assess gait function with the benefit of measuring a large number of both dynamic and static gait parameters simultaneously [10]. The CatWalk method can also detect the spatial and * Correspondence: 26602@cch.org.tw 1 Department of Neurology, Changhua Christian Hospital, Changhua City 500,