Rachel P. Allred

Motor Skill Training, but not Voluntary Exercise, Improves Skilled Reaching After Unilateral Ischemic Lesions of the Sensorimotor Cortex in Rats

Background and Purpose . Exercise and rehabilitative training each have been implicated in the promotion of restorative neural plasticity after cerebral injury. Because motor skill training induces synaptic plasticity and exercise increases plasticity-related proteins, we asked if exercise could improve the efficacy of training on a skilled motor task after focal cortical lesions. Methods . Female young and middle-aged rats were trained on the single-pellet retrieval task and received unilateral ischemic sensorimotor cortex lesions contralateral to the trained limb. Rats then received both, either, or neither voluntary running and/or rehabilitative training for 5 weeks beginning 5 days postlesion. Motor skill training consisted of daily practice of the impaired forelimb in a tray-reaching task. Exercised rats had free access to running wheels for 6 h/day. Reaching function was periodically probed using the single-pellet retrieval task. Results. In young adults, motor skill training significantly enhanced skilled reaching recovery compared to controls. However, exercise did not significantly enhance performance when administered alone or in combination with skill training. There was also no major benefit of exercise in older rats. Additionally, there were no effects of exercise in a measure of coordinated forelimb placement (the foot-fault test) or in immunocytochemical measures of several plasticity-related proteins in the motor cortex. Conclusions. In young and middle-aged animals, exercise did not improve motor skill training efficacy following ischemic lesions. Practicing motor skills more effectively improved recovery of these skills than did exercise. It remains possible that an alternative manner of administering exercise would be more effective.

The Vermicelli Handling Test: A Simple Quantitative Measure of Dexterous Forepaw Function in Rats

Loss of function in the hands occurs with many brain disorders, but there are few measures of skillful forepaw use in rats available to model these impairments that are both sensitive and simple to administer. Whishaw and Coles previously described the dexterous manner in which rats manipulate food items with their paws, including thin pieces of pasta [Whishaw IQ, Coles BL. Varieties of paw and digit movement during spontaneous food handling in rats: postures, bimanual coordination, preferences, and the effect of forelimb cortex lesions. Behav Brain Res 1996;77:135-48]. We set out to develop a measure of this food handling behavior that would be quantitative, easy to administer, sensitive to the effects of damage to sensory and motor systems of the CNS and useful for identifying the side of lateralized impairments. When rats handle 7 cm lengths of vermicelli, they manipulate the pasta by repeatedly adjusting the forepaw hold on the pasta piece. As operationally defined, these adjustments can be easily identified and counted by an experimenter without specialized equipment. After unilateral sensorimotor cortex (SMC) lesions, transient middle cerebral artery occlusion (MCAO) and striatal dopamine depleting (6-hydroxydopamine, 6-OHDA) lesions in adult rats, there were enduring reductions in adjustments made with the contralateral forepaw. Additional pasta handling characteristics distinguished between the lesion types. MCAO and 6-OHDA lesions increased the frequency of several identified atypical handling patterns. Severe dopamine depletion increased eating time and adjustments made with the ipsilateral forepaw. However, contralateral forepaw adjustment number most sensitively detected enduring impairments across lesion types. Because of its ease of administration and sensitivity to lateralized impairments in skilled forepaw use, this measure may be useful in rat models of upper extremity impairment.

Remodeling the Brain With Behavioral Experience After Stroke

Background and Purpose— Behavioral experience can drive brain plasticity, but we lack sufficient knowledge to optimize its therapeutic use after stroke. Methods— We outline recent findings from rodent models of cortical stroke of how experiences interact with postinjury events to influence synaptic connectivity and functional outcome. We focus on upper extremity function. Results— After unilateral cortical infarcts, behavioral experiences shape neuronal structure and activity in both hemispheres. Experiences that matter include interventions such as skill training and constraint-like therapy as well as unguided behaviors such as learned nonuse and behavioral compensation. Lateralized behaviors have bihemispheric influences. Ischemic injury can alter the sensitivity of remaining neocortical neurons to behavioral change and this can have positive and negative functional effects. Conclusions— Because experience is ongoing in stroke survivors, a better understanding of its interaction with brain reorganization is needed so that it can be manipulated to improve function and prevent its worsening.

Unilateral ischemic sensorimotor cortical damage in female rats: forelimb behavioral effects and dendritic structural plasticity in the contralateral homotopic cortex.

Previous studies in male rats with unilateral sensorimotor cortical (SMC) damage have demonstrated dendritic structural plasticity in the contralateral homotopic cortex and an enhancement of skilled reaching performance in the forelimb ipsilateral to the lesion compared to sham-operated rats. The purpose of this study was to determine if these findings could be replicated in an ischemic lesion model in female rats. Female rats were given sham operations or unilateral ischemic (endothelin-1 induced) damage in the forelimb representation area of the SMC opposite their preferred forelimb. Animals then received either 20 consecutive days of training on a skilled reaching task with the non-preferred/unimpaired forelimb or no-training control procedures. The surface density of dendrites immunoreactive (IR) for microtubule-associated protein 2 (MAP2) was then measured in the motor cortex opposite the trained limb and/or lesion. Female rats with sufficiently large, but not very small, lesions performed better with the unimpaired forelimb than sham-operated rats on the reaching task. The post-lesion reaching performance was not found to be significantly dependent upon estrous stage at the time of surgery, in agreement with previous studies that failed to find sex or sex-hormone effects after other types of SMC damage. Additionally, there were major laminar-dependent increases in the surface density of MAP2 IR dendrites in the cortex opposite lesions and trained limbs. These findings in female rats are consistent with the dendritic and behavioral changes previously found in male rats. They extend these previous findings by indicating that lesion size is an important variable in the enhancement of reaching performance.

The vermicelli and capellini handling tests: simple quantitative measures of dexterous forepaw function in rats and mice.

Previous characterizations of rodent eating behavior have revealed that they use coordinated forepaw movements to manipulate food pieces. We have extended upon this work to develop a simple quantitative measure of forepaw dexterity that is sensitive to lateralized impairments and age-dependent changes. Rodents learn skillful forepaw and digit movements to manage thin pasta pieces, which they eagerly consume. We have previously described methods for quantifying vermicelli handling in rats and showed that the measures are very sensitive to forelimb impairments resulting from unilateral ischemic lesions, middle cerebral artery occlusions and unilateral striatal dopamine depletion [Allred, R.P., Adkins, D.L., Woodlee, M.T., Husbands, L.C., Maldonado M.A., Kane, J.R., Schallert, T. & Jones, T.A. The Vermicelli Handling Test: a simple quantitative measure of dexterous forepaw function in rats. J. Neurosci. Methods 170, 229-244 (2008)]. Here we present a more detailed protocol for this test in rats and compare it with a newly developed version for mice, the Capellini Handling Test. Rats and mice are videotaped while handling short lengths of uncooked vermicelli or capellini pasta, respectively, with a camera positioned to optimize the view of paw movements. Slow motion video playback allows for the identification of forepaw adjustments, defined as any distinct removal and replacement of the paw, or of any number of digits, on the pasta piece after eating commences. Forepaw adjustments per piece are averaged over trials per each testing session. Repeated testing permits sensitive quantitative analysis of changes in forepaw dexterity over time. Protocols for pre-testing habituation and handling practice, as well as procedures for characterizing atypical handling patterns, are described. Because rats and mice perform the pasta handling tests slightly differently, species-specific differences in administration and scoring of these tests are highlighted. All animal use was in accordance with protocols approved by the University of Texas at Austin Animal Care and Use Committee.

Experience with the “Good” Limb Induces Aberrant Synaptic Plasticity in the Perilesion Cortex after Stroke

Following unilateral stroke, the contralateral (paretic) body side is often severely impaired, and individuals naturally learn to rely more on the nonparetic body side, which involves learning new skills with it. Such compensatory hyper-reliance on the “good” body side, however, can limit functional improvements of the paretic side. In rats, motor skill training with the nonparetic forelimb (NPT) following a unilateral infarct lessens the efficacy of rehabilitative training, and reduces neuronal activation in perilesion motor cortex. However, the underlying mechanisms remain unclear. In the present study, we investigated how forelimb movement representations and synaptic restructuring in perilesion motor cortex respond to NPT and their relationship with behavioral outcomes. Forelimb representations were diminished as a result of NPT, as revealed with intracortical microstimulation mapping. Using transmission electron microscopy and stereological analyses, we found that densities of axodendritic synapses, especially axo-spinous synapses, as well as multiple synaptic boutons were increased in the perilesion cortex by NPT. The synaptic density was negatively correlated with the functional outcome of the paretic limb, as revealed in reaching performance. Furthermore, in animals with NPT, there was dissociation between astrocytic morphological features and axo-spinous synaptic density in perilesion motor cortex, compared with controls. These findings demonstrate that skill learning with the nonparetic limb following unilateral brain damage results in aberrant synaptogenesis, potentially of transcallosal projections, and this seems to hamper the functionality of the perilesion motor cortex and the paretic forelimb.

Use it and/or lose it—experience effects on brain remodeling across time after stroke

The process of brain remodeling after stroke is time- and neural activity-dependent, and the latter makes it inherently sensitive to behavioral experiences. This generally supports targeting early dynamic periods of post-stroke neural remodeling with rehabilitative training (RT). However, the specific neural events that optimize RT effects are unclear and, as such, cannot be precisely targeted. Here we review evidence for, potential mechanisms of, and ongoing knowledge gaps surrounding time-sensitivities in RT efficacy, with a focus on findings from animal models of upper extremity RT. The reorganization of neural connectivity after stroke is a complex multiphasic process interacting with glial and vascular changes. Behavioral manipulations can impact numerous elements of this process to affect function. RT efficacy varies both with onset time and its timing relative to the development of compensatory strategies with the less-affected (nonparetic) hand. Earlier RT may not only capitalize on a dynamic period of brain remodeling but also counter a tendency for compensatory strategies to stamp-in suboptimal reorganization patterns. However, there is considerable variability across injuries and individuals in brain remodeling responses, and some early behavioral manipulations worsen function. The optimal timing of RT may remain unpredictable without clarification of the cellular events underlying time-sensitivities in its effects.

Motor System Plasticity in Stroke Models: Intrinsically Use-dependent, Unreliably Useful

Functional impairment is a powerful incentive for behavioral change. The natural response to disability in one limb is to learn new ways of using the other limb. Animals, including humans, with upper extremity impairments spontaneously learn to use the less-affected (nonparetic) hand in novel ways to perform daily activities.1–3 In intact brains, the acquisition of manual skills depends on practice-dependent synaptic structural and functional reorganization of motor cortex (MC).4,5 After stroke, this skill acquisition overlaps with ongoing degenerative and regenerative responses to the injury, many of which are also neural activity dependent6,7 and sensitive to behavioral manipulations.8–10 When they converge on the same circuits, ischemia-induced and experience-driven remodeling responses interact.3 Learning to rely on the nonparetic hand is a particularly prevalent and profound form of poststroke behavioral compensation, but compensatory strategies can be found across different impairment modalities, body sides, and injury loci.11–13 Their development is among the most reliable consequences of brain injury survival. The implication is that understanding the brain’s typical adaptation to stroke will require understanding its interactions with compensatory behavioral changes. The compensatory reliance on the better functioning limb after stroke has long been thought to contribute to persistent dysfunction in the affected (paretic) limb by encouraging its disuse (ie, learned nonuse).14 Our recent findings suggest that it can go well beyond this to directly disrupt the neural substrates paretic limb functional improvements. Here we overview these findings, as revealed in rodent models of chronic upper extremity impairments using precise control and manipulation of forelimb experiences to understand bilateral and interhemispheric contributions to motor functional outcome. After unilateral ischemic MC damage in rats, a relatively subtle variation in behavioral experience—learning a single new motor skill with the nonparetic limb—reduces …

Breeder and batch-dependent variability in the acquisition and performance of a motor skill in adult Long-Evans rats

Reaching tasks are popular tools for investigating the neural mechanisms of motor skill learning and recovery from brain damage in rodents, but there is considerable unexplained variability across studies using these tasks. We investigated whether breeder, batch effects, experimenter, time of year, weight and other factors contribute to differences in the acquisition and performance of a skilled reaching task, the single pellet retrieval task, in adult male Long-Evans hooded rats. First, we retrospectively analyzed task acquisition and performance in rats from different breeding colonies that were used in several studies spanning a 3 year period in our laboratory. Second, we compared reaching variables in age-matched rats from different breeders that were trained together as a batch by the same experimenters. All rats had received daily training on the reaching task until they reached a criterion of successful reaches per attempt. We found significant breeder-dependent differences in learning rate and final performance level. This was found even when age-matched rats from different breeders were trained together by the same experimenters. There was also significant batch-to-batch variability within rats from the same breeder trained by the same experimenter. Other factors, including weight, paw preference and the experimenter, were not as strong or consistent in their contributions to differences across studies. The breeder and batch effects found within the same rat strain may reflect genetic and environmental influences on the neural substrates of motor skill learning. This is an important consideration when comparing baseline performance across studies and for controlling variability within studies.