Impaired Arpeggio Movement in Skilled Reaching by Rubrospinal Tract Lesions in the Rat: A Behavioral/Anatomical Fractionation

Abstract

Spinal cord injury damaging the rubrospinal tract (RST) interferes with skilled forelimb movement, but identification of the precise role of the RST in this behavior is impeded by the difficulty of surgically isolating the RST from other pathways running within the lateral funiculus (LF). The present study used a skilled reaching task and a behavioral/anatomical dissection method to identify the contribution of the RST to skilled forelimb movement. Rats were trained on the skilled reaching task and subjected to lesions of the LF. Based on histological evaluation, the animals were assigned to large, medium, or small LF lesion size groups. End point and arm/hand/digit movements were subsequently identified for each group. Success was impaired in all groups, but the impairment was not related to lesion size. Frame-by-frame qualitative analysis of the video recordings revealed that large LF lesions abolished the elements of digits close, digits open, arpeggio, grasp, supination 2, and release. Medium LF lesions interfered with a subset of the movement elements that were shown to be affected by the large LF lesions, namely arpeggio and grasp. Only the arpeggio movement was compromised after small LF lesions. The results show that not only does the LF contribute to skilled reaching, but because the RST was likely to have been damaged in all lesion groups, the RST is more involved in hand rotation than in digit use. The results are discussed in relation to the fiber tracts that are likely to be damaged in the different LF lesion groups.

A Cervical Hemi-Contusion Spinal Cord Injury Model for the Investigation of Novel Therapeutics Targeting Proximal and Distal Forelimb Functional Recovery

“…In addition to being responsible for more proximally dependent functions like the CatWalk, the RST also has been shown to play a strong role in controlling more distal forelimb functions, like pellet reaching tasks [32][33][34][35] and staircase pellet reaching tasks. 34,36 While these tasks were not assessed in the current study, the IBB task involves comparable distal forelimb functions.…”

Dorsolateral Funiculus Lesioning of the Mouse Cervical Spinal Cord at C4 but Not at C6 Results in Sustained Forelimb Motor Deficits

“…34,35 In particular, DLF lesioning indicates the RST's importance for arpeggio movement; that is, pronation of the paw and positioning of the digits with wrist movement when grasping for food. 36 We found a significant reduction in the number of pellets eaten in the staircase pellet test with the ipsilesional forepaw after C4 dorsolateral crush. In the cat, Alstermark and colleagues have shown that ablation of the DLF at C5/C6 resulted in complete loss of food-taking ability.…”

Skilled Reaching and Grasping in the Rat: Lacking Effect of Corticospinal Lesion

“…It was shown that lesions of the nucleus ruber resulted in defective control of reaching and paw movements (14), especially the searching (arpeggio) component during pronation (17) and the importance of the rubrospinal tract in the control of grasping was demonstrated in the cat (4). Interestingly, Whishaw et al (14) found that even following combined lesions of the pyramid and of nucleus ruber, the rats could still reach and grasp despite their deficits.…”