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Traumatic brain injury (TBI) produces a wide range of motor and cognitive changes. While some neurological symptoms may respond to therapeutic intervention during the initial recovery period, others may persist for many years after the initial insult, and often have a devastating impact on quality of life for the TBI victim. The aim of the current study was to develop neurobehavioral testing parameters designed to provide a longitudinal assessment of neurofunctional deficits in a rodent model of penetrating ballistic-like brain injury (PBBI). We report here a series of experiments in which unilateral frontal PBBI was induced in rats, and motor/cognitive abilities were assessed using a battery of tests ranging from 30 min to 10 weeks post-injury. The results showed that PBBI produced consistent and significant (1) neurological deficits (neuroscore examination: 30 min to 10 weeks post-PBBI), (2) sensorimotor dysfunction in the contralateral forelimb (forelimb asymmetry task: 7 and 21 days), (3) motor dysfunction (balance beam task: 3-7 days; and fixed-speed rotarod task: 3-28 days), and (4) spatial learning deficits in the Morris water maze (MWM) task out to 10 weeks post-injury. Overall, the results of this study demonstrate that PBBI produces enduring motor and cognitive deficits, and identifies the optimal task and testing parameters for facilitating longitudinal screening of promising therapeutic interventions in this brain injury model.

IntroductionHuntington’s disease (HD) is an autosomal dominant disorder caused by an expanded CAG repeat on the short arm of chromosome 4 resulting in cognitive decline, motor dysfunction, and death, typically occurring 15 to 20 years after the onset of motor symptoms. Neuropathologically, HD is characterized by a specific loss of medium spiny neurons in the caudate and the putamen, as well as subsequent neuronal loss in the cerebral cortex. The transgenic R6/2 mouse model of HD carries the N-terminal fragment of the human HD gene (145 to 155 repeats) and rapidly develops some of the behavioral characteristics that are analogous to the human form of the disease. Mesenchymal stem cells (MSCs) have shown the ability to slow the onset of behavioral and neuropathological deficits following intrastriatal transplantation in rodent models of HD. Use of MSCs derived from umbilical cord (UC) offers an attractive strategy for transplantation as these cells are isolated from a noncontroversial and inexhaustible source and can be harvested at a low cost. Because UC MSCs represent an intermediate link between adult and embryonic tissue, they may hold more pluripotent properties than adult stem cells derived from other sources.MethodsMesenchymal stem cells, isolated from the UC of day 15 gestation pups, were transplanted intrastriatally into 5-week-old R6/2 mice at either a low-passage (3 to 8) or high-passage (40 to 50). Mice were tested behaviorally for 6 weeks using the rotarod task, the Morris water maze, and the limb-clasping response. Following behavioral testing, tissue sections were analyzed for UC MSC survival, the immune response to the transplanted cells, and neuropathological changes.ResultsFollowing transplantation of UC MSCs, R6/2 mice did not display a reduction in motor deficits but there appeared to be transient sparing in a spatial memory task when compared to untreated R6/2 mice. However, R6/2 mice receiving either low- or high-passage UC MSCs displayed significantly less neuropathological deficits, relative to untreated R6/2 mice.ConclusionsThe results from this study demonstrate that UC MSCs hold promise for reducing the neuropathological deficits observed in the R6/2 rodent model of HD.