Motor skill recovery in rats with various forelimb preference subjected to lesions in the caudate nucleus

Rats were trained for retrieving a sunflower seed from a tube using a forelimb. In the process of training, all the animals were divided in two groups: with the right- and left-limb preference. The period of learning was divided in two emotional (after the period of anxiety the animal takes a sunflower seed from the flow of a chamber) and three motor stages (different degrees of dexterity and precision in reaching a seed in the tube and grasping it). After a rat learned the skilled movement, the caudate nucleus was lesioned contralaterally to the preferred limb. After surgery, the animals were tested for recovery of the motor skill. The stages of recovery were the same as during learning. "Right-" and "left-handed" rats were compared in the percentage of animals performing each stage, duration of each stage, the depth of the tube reached by the animal's forelimb, and time required for obtaining the best results. The "right-handed" rats dominated in the percentage of animals performing the emotional stages and later began to recover the skilled movement (the crucial motor stage) but faster acquired their individual maximal depth of reaching a seed in the tube than the "left-handed" animals. The recovery of the skilled movement in the "left-handed" animals was a more gradual process than that in the "right-handed" ones.     

Different recovery of a skilled movement after destruction of the caudate nucleus in rats with right- or left-forelimb preference]

Recovery of the motor skill of taking a sunflower seed from a tube after the electrolytic destruction of the caudate nucleus was studied in Wistar rats with left- (n = 27) and right-forelimb (n = 22) preference. The reaching performance was divided in 5 stages. The first two stages characterize the emotional condition of an animal, the following three were immediately related with the skilled movement. After preliminary testing, the head of the caudate nucleus contralateral to the preferred limb was electrolytically damaged. After surgery, rats were tested during 20 weeks, and in every test the following indices were measured: percent of rats which perform the movement characteristic for the given stage, stage duration, depth of reaching a flower seed from the tube, time necessary to obtain the best results etc. It was found that at the "emotional" stages, higher percent of the right-handed animals perform the characteristic movements, but they spend more time to complete these stages than the left-handed rats. In rats with the left-limb dominance the recovery of the specialized movement is positively correlated with the time of the recovery onset at all the stages, while there is no such correlation in rats with right-limb dominance. Both groups of animals reach the same depth of the tube in the course of recovery, but the left-handed rats attain these results later and gradually, while the right-handed animals attain the maximal extent of recovery spontaneously and earlier than left-handed ones.     

Recovery of motor skills after the caudate lesion in rats with the different prefered forelimb: the role of intense retraining

Rats were trained for instrumental reaching (17 mm) of a sunflower seed from a horizontal tube 12 mm in diameter. After training, rats were divided into groups, "right-" and "left-handers", by the forelimb preference. Unilateral electrolytic lesions of the head of the caudate nucleus contralateral to the prefered forelimb were performed. After surgery, animals were retrained to perform the food-retrieval reaction by the same forelimb (reaching reaction by the "intact" forelimb was prohibited by a special bracelet). Both right- and left-handers were divided into groups of rare and intense retraining. Over the course of five months, animals of the groups of rare training were tested once a week, whereas the intense retraining was performed three or four times a week. Rats with right and left forelimb preference were shown to recover the reaching skill with different rates. In general, animals with left-side caudate lesion (right-handers) recovered the skill better both under condition of spontaneous recovery (rare testing) and intense retraining. The results suggest different mechanism of skill recovery after the right- and left-side brain lesion.     

Effect of apomorphine injection into the nucleus accumbens on the limb preference in manipulation movements in rats

The concentration of dophamine and its derivates is known to correlate with the degree of handedness in manipulative movements in rodents. In this work we studied a possibility to changing handedness in rats by injection of a dopamine agonist into the nucleus accumbens. Retrieving food from a horizontal tube was used to determine the limb preference (10 food retrievals by the preferred limb). Then apomorphine was injected into the n. accumbens ipsilateral to the preferred limb in the course of 7 days. The same volume of buffer solution was injected into the contralateral n. accumbens. Just after the last injection the limb preference was tested. It was shown that the chronic injection of the non-specific agonist of dophamine receptors significantly changed the limb preference.     

Asymmetry in the dopamine content in the nucleus accumbens and the motor preference in rats

A number of published studies reported a correlation between the paw preference in mice and asymmetry of tissue concentrations of dopamine (DA) and DA metabolites measured in the nucleus accumbens (NAcb) the DA concentration being higher in the nucleus ipsylateral to a preferred paw. This study aimed to investigate whether such asymmetry existed in rats. The paw preference was defined by reaching into a small horizontal tube for a food pellet. Tissue concentration of DA was measured by high-performance liquid chromatography with electrochemical detection. It was shown that the DA concentration in the left NAcb was significantly higher in "left-handed" rats than in "right-handed" animals. Within the group of "right-handers", the DA concentration was significantly higher in the right NAcb than in the left NAcb. The results confirm in part the experimental data obtained in mice and support the hypothesis that the paw preference is paralleled by elevated tissue DA in the ipsylateral NAcb of rodents.