Elena I. Miklyaeva

Analysis of limb use by control rats and unilateral DA-depleted rats in the Montoya staircase test : movements, impairments and compensatory strategies

The Montoya Staircase Test has been designed as a simple objective way of measuring changes in skilled movements following motor system damage. In the test, rats reach from a central platform for food pellets located on adjacent staircases and the measure of success is the number of food pellets obtained. As there has been no detailed behavioral analysis of how animals reach in this task, the present study evaluates reaching in the test by combining end point measures (success) with movement analysis based on video recordings. It is found that control rats locate food using olfaction and then reach using an identifiable sequence of movements, including (1) aiming the limb, (2) opening the digits in preparation for grasping, (3) grasping, and (4) supinating the paw, during limb withdrawal, to place food in the mouth. The nonreaching limbs adjust posture during the reaching sequence. Rats with unilateral DA-depletions show (1) severe impairments in success when using their contralateral-to-lesion limb (bad limb), (2) moderate impairments in using their ipsilateral-to-lesion limb (good limb), (3) abnormal reaching movements and posture, and (4) a variety of compensatory movements so as to enhance success. When success produced by compensatory adjustment is subtracted from total success, the DA-depleted rats show no recovery. The results confirm that the Staircase Test is a sensitive measure for motor system damage and demonstrate that when movement analysis is combined with end point measures, the test can dissociate impairment, recovery, and compensation.

Impairments and compensatory adjustments in spontaneous movement after unilateral dopamine depletion in rats

Rats with unilateral dopamine (DA) depletions (hemi-Parkinson rats) display directional biases in their locomotion in spontaneous and drug induced tests. These biases have been explained as being due either to changed responsiveness to sensory stimulation, changes in motor ability, or to central changes, but as yet their basis is not fully understood. The purpose of the present experiment is to examine the posture of immobility and the posture and strategies of locomotion in rats with unilateral DA depletions. The rats are found to display impairments in their bad limbs (contralateral-to-lesion limbs) in adjusting posture and moving. They compensate by supporting themselves mainly on their good hindlimb, using the bad hindlimb and tail for balance and by disproportionately relying upon their good limbs to turn and to walk. Thus, their center of gravity is shifted to the good side and movement is preferentially directed toward the good side, in part to maintain equilibrium and in part to remove weight from the bad limbs so that they can enter the swing phase of the stepping cycle. It is proposed that the bad limbs may be unable to apply force to adjust posture and produce movement. These results provide a basis for predicting the movements that the animals will use in various situations and they expand the test repertoire this hemi-Parkinson model provides for studying recovery processes after loss of dopamine.

HemiParkinson analogue rats display active support in good limbs versus passive support in bad limbs on a skilled reaching task of variable height

Rats with unilateral dopamine (DA) depletion (hemiParkinson analogue rats) are impaired in using the contralateral (bad) limbs for skilled movements and for postural adjustments and compensate by using their good limbs in novel ways. The present study consisted of a reaching task in which compensatory adjustments using the good limbs would not be affective, thus forcing the rats to use their bad limbs. The DA-depleted rats failed to use their bad hindlimb to extend their reach at high reaching heights and failed to lower their body with their bad forelimb to reach at low reaching heights. It is suggested that extensive DA depletion may result in the loss of the ability to apply forces with the affected limbs.

Making two movements at once: Impairments of movement, posture, and their integration underlie the adult skilled reaching deficit of neonatally dopamine-depleted rats

Adult rats depleted bilaterally of dopamine in infancy display a profound impairment in skilled forelimb use in reaching for food. This impairment was investigated using end-point measures of reaching success, movement analysis, and kinematic measures. The rats made few successful reaches in either an easy or a difficult reaching test. Their reaches were characterized by many attempts in which trajectories of the limb were irregular and the movements were slow. Their lack of success was related in part to an impairment in making component movements of the reach, including aiming, pronating, grasping, and supinating the paw and in releasing the food pellet. It was also related to an inability to adjust posture as the limb was voluntarily moved toward the food. The results are consistent with the hypotheses that the basal ganglia, including its dopamine innervation, is important for enabling voluntary movements and postural adjustments and perhaps also the simultaneous performance of two movements at the same time.

The ground reaction forces of postural adjustments during skilled reaching in unilateral dopamine-depleted hemiparkinson rats

Rats with unilateral dopamine (DA) depletions (hemiParkinson analogue rats) produced by intracerebral 6-hydroxydopamine injection are impaired in using the contralateral (bad) limbs for postural adjustments. This article examines whether the bad limbs are impaired in applying the forces required to initiate postural adjustments that anticipate and accompany voluntary movements. The rats were trained to reach for food using their good paw while standing on small platforms, each of which measured force changes produced by an individual limb. In one condition the force platforms were aligned to support the limb placement of normal rats and in the second they were aligned to permit the DA-depleted rats to use a compensatory reaching stance. It was found that the bad limbs of the DA-depleted rats produced normal supporting reactions but did not initiate adjustments in posture. Postural adjustments were initiated with the good limbs and preceded rather than accompanied the reaching movements. When constrained to use the posture of normal rats, the DA-deplete rats could not reach successfully, but when allowed to adjust their stance to increase reliance on the good limbs, reaching performance improved. Measures of ground reaction forces confirm that DA-depleted rats can support posture but cannot initiate postural adjustments with their impaired limbs.

Innate versus learned factors determining limb preference in the rat.

The basic factors determining forelimb preference in the performance of different skilled movements were studied in white rats. To analyse whether limb preference actually reflects an initial individual motor asymmetry or is a result of instrumental learning (the first successful movement becoming fixed), the method of retrograde amnesia from electroconvulsive shock was used. It was shown that limb preference is initial and not a results of learning and, evidently, is due to intrinsic factors. The preferred limb can be identified in as few as 3 successful movements. There is a gradation among animals according to the degree of initial limb preference and its resistance to rearrangement of the motor task. The differences of limb preference in different movements were also analysed. Dependence of the preference on the character of the required movement was shown. Four basic types of movement were revealed by factor analysis. As different muscular groups (distal and proximal), controlled by different descending motor systems can be involved in the performance of different movements, it is assumed that the initial motor asymmetry in each movement is a result of asymmetry of central motor structures involved in the realization of the movement. In the same animal asymmetry of different motor structures might be different. This could explain different limb preference in different movements.

Motor asymmetry of the forelimbs of rats

Conclusions1.A pronounced motor asymmetry is observed in rats in the performance of different manipulatory movements of the forelimbs. However, it is not absolute, and depends on a number of factors.2.The character of the task performed has a fundamental significance for the choice of the limb preferred. The degree of stable preference for one limb is higher in the performance of the most specialized and precise movements.3.The degree and stability of preference for a certain limb depends also on the length of training in the process of the formation of the given movement. In the process of training, the degree of preference for one limb is least stable in the performance of the most simple movements.4.Despite the diversity of factors which influence the phenomenon of motor asymmetry, true interhemispheric asymmetry probably also plays a definite role.