FGF-2-induced functional improvement from neonatal motor cortex injury via corticospinal projections

Sensitive Periods for Recovery from Early Brain Injury

The developing brain is remarkably plastic as it changes in response to a wide range of experiences including sensory and motor experience, psychoactive drugs, peer relationships, parent-infant interactions, gonadal hormones, intestinal flora, diet, and injury. There are sensitive periods for many of these experiences, including cerebral injury. Comparisons across mammalian species (humans, monkeys, cats, rats, mice) show a sensitive period for good outcomes from cerebral injury around the time of intense synaptogenesis. This period is postnatal in humans, cats, and rats, but prenatal in monkeys, reflecting the differences in neuronal development at birth across species. In addition, there appears to be a sensitive period prenatally during the time of maximum cortical neurogenesis and possibly during adolescence as well, although these periods are not as well studied as the period related to synaptogenesis and to date only examined in rats. Here we review the evidence for sensitive periods related to brain injury across species and propose mechanisms that may underlie the plasticity during these periods.

Developmental and Interventional Plasticity of Motor Maps after Perinatal Stroke

Within the perinatal stroke field, there is a need to establish preclinical models where putative biomarkers for motor function can be examined. In a mouse model of perinatal stroke, we evaluated motor map size and movement latency following optogenetic cortical stimulation against three factors of post-stroke biomarker utility: (1) correlation to chronic impairment on a behavioral test battery; (2) amenability to change using a skilled motor training paradigm; and (3) ability to distinguish individuals with potential to respond well to training. Thy1-ChR2-YFP mice received a photothrombotic stroke at postnatal day 7 and were evaluated on a battery of motor tests between days 59 and 70. Following a cranial window implant, mice underwent longitudinal optogenetic motor mapping both before and after 3 weeks of skilled forelimb training. Map size and movement latency of both hemispheres were positively correlated with impaired spontaneous forelimb use, whereas only ipsilesional hemisphere map size was correlated with performance in skilled reaching. Map size and movement latency did not show groupwise changes with training; however, mice with the smallest pretraining map sizes and worst impairments demonstrated the greatest expansion of map size in response to skilled forelimb training. Overall, motor map size showed utility as a potential biomarker for impairment and training-induced modulation in specific individuals. Future assessment of the predictive capacity of post-stroke motor representations for behavioral outcome in animal models opens the possibility of dissecting how plasticity mechanisms contribute to recovery following perinatal stroke.SIGNIFICANCE STATEMENT We investigated the utility of two cortical motor representation measures (motor map size and movement onset latency) as potential biomarkers for post-stroke motor recovery in a mouse model of perinatal stroke. Both motor map size and movement latency were associated with functional recovery after perinatal stroke, with map size showing an additional association between training responsiveness and severity of impairment. Overall, both motor map size and movement onset latency show potential as neurophysiological correlates of recovery. As such, future studies of perinatal stroke rehabilitation and neuromodulation should include these measures to help explain neurophysiological changes that might be occurring in response to treatment.

Plasticity and Reorganization in the Rehabilitation of Stroke

Abstract. This paper outlines some actual developments in the behavioral treatment and rehabilitation of stroke and other brain injuries in post-acute and chronic conditions of brain lesion. It points to a number of processes that demonstrate the enormous plasticity and reorganization capacity of the human brain following brain lesion. It also highlights a series of behavioral and neuroscientific studies that indicate that successful behavioral rehabilitation is paralleled by plastic changes of brain structures and by cortical reorganization and that the amount of such plastic changes is obviously significantly determining the overall outcome of rehabilitation.

Harnessing the power of neuroplasticity for intervention

A fundamental property of the brain is its capacity to change with a wide variety of experiences, including injury. Although there are spontaneous reparative changes following injury, these changes are rarely sufficient to support significant functional recovery. Research on the basic principles of brain plasticity is leading to new approaches to treating the injured brain. We review factors that affect synaptic organization in the normal brain, evidence of spontaneous neuroplasticity after injury, and the evidence that factors including postinjury experience, pharmacotherapy, and cell-based therapies, can form the basis of rehabilitation strategies after brain injuries early in life and in adulthood.

Searching for the principles of brain plasticity and behavior

An important development in behavioral neuroscience in the past 25 years has been the demonstration that the brain is far more flexible in structure and function than was previously believed. Studies of laboratory animals have provided an important tool for understanding the nature of brain plasticity and behavior at many levels ranging from detailed behavioral paradigms, electrophysiology, neuronal morphology, protein chemistry, and epigenetics. Here we seek a synthesis of the multidisciplinary work on brain plasticity and behavior to identify some general principles on how the brain changes in response to a wide range of experiences over the lifetime.

Basic fibroblast growth factor increases the transplantation‑mediated therapeutic effect of bone mesenchymal stem cells following traumatic brain injury

Basic fibroblast growth factor (bFGF) has proven useful for neural stem and progenitor cells during the transplantation‑mediated therapeutic effect of bone mesenchymal stem cells (BMSCs). Endogenous bFGF expression levels increase during brain development and gradually diminish with aging. To date, few studies have been conducted on exogenous bFGF promoting BMSC transplantation‑mediated functional recovery in adult rats following traumatic brain injury (TBI). The results of the present study showed that BMSCs in the TBI cortex and dentate gyrus showed differentiation along the glial and neuronal lines, which are possibly enhanced by bFGF. The neuronal differentiation rate was not consistent with neurological functional recovery rate over time. bFGF may promote the transplantation‑mediated therapeutic effect of BMSCs more significantly and rapidly in rats following TBI, with a small proportion of differentiated neurons. In conclusion, exogenous bFGF functions as a booster of the transplantation‑mediated therapeutic effect of BMSCs following TBI.

Brain plasticity in the developing brain

The developing normal brain shows a remarkable capacity for plastic change in response to a wide range of experiences including sensory and motor experience, psychoactive drugs, parent-child relationships, peer relationships, stress, gonadal hormones, intestinal flora, diet, and injury. The effects of injury vary with the precise age-at-injury, with the general result being that injury during cell migration and neuronal maturation has a poor functional outcome, whereas similar injury during synaptogenesis has a far better outcome. A variety of factors influence functional outcome including the nature of the behavior in question and the age at behavioral assessment as well as pre- and postinjury experiences. Here, we review the phases of brain development, how factors influence brain, and behavioral development in both the normal and perturbed brain, and propose mechanisms that may underlie these effects.

Brain plasticity and recovery from early cortical injury

Neocortical development represents more than a simple unfolding of a genetic blueprint: rather, it represents a complex dance of genetic and environmental events that interact to adapt the brain to fit a particular environmental context. Most cortical regions are sensitive to a wide range of experiential factors during development and later in life, but the injured cortex appears to be unusually sensitive to perinatal experiences. This paper reviews the factors that influence how normal and injured brains (both focal and ischemic injuries) develop and adapt into adulthood. Such factors include prenatal experiences in utero as well as postnatal experiences throughout life. Examples include the effects of sensory and motor stimulation, psychoactive drugs (including illicit and prescription drugs), maternal and postnatal stress, neurotrophic factors, and pre- and postnatal diet. All these factors influence cerebral development and influence recovery from brain injury during development.

Factors influencing frontal cortex development and recovery from early frontal injury

BACKGROUND

Neocortical development represents more than a simple unfolding of a genetic blueprint but rather represents a complex dance of genetic and environmental events that interact to adapt the brain to fit a particular environmental context. Although most cortical regions are sensitive to a wide range of experiential factors during development and later in life, the prefrontal cortex appears to be unusually sensitive to perinatal experiences and relatively immune to many adulthood experiences relative to other neocortical regions.

METHODS AND RESULTS

One way to examine experience-dependent prefrontal development is to conduct studies in which experiential perturbations are related neuronal morphology. This review of the research reveals both pre- and post-natal factors have important effects on prefrontal development and behaviour. Such factors include psychoactive drugs, including both illicit drugs and prescription drugs, stress, gonadal hormones and sensory and motor stimulation. A second method of study is to examine both the effects of perinatal prefrontal injury on the development of the remaining cerebral mantle and correlated behaviours as well as the effects of post-injury rehabilitation programmes on the anatomical and behavioural measures.

CONCLUSIONS

Prefrontal injury alters cerebral development in a developmental-stage dependent manner with perinatal injuries having far more deleterious effects than similar injuries later in infancy. The outcome of perinatal injuries can be modified, however, by rehabilitation with many of the factors shown to influence prefrontal development in the otherwise normal brain.

Hitting a moving target: Basic mechanisms of recovery from acquired developmental brain injury

Acquired brain injuries represent a major cause of disability in the pediatric population. Understanding responses to developmental acquired brain injuries requires knowledge of the neurobiology of normal development, age-at-injury effects and experience-dependent neuroplasticity. In the developing brain, full recovery cannot be considered as a return to the premorbid baseline, since ongoing maturation means that cerebral functioning in normal individuals will continue to advance. Thus, the recovering immature brain has to 'hit a moving target' to achieve full functional recovery, defined as parity with age-matched uninjured peers. This review will discuss the consequences of developmental injuries such as focal lesions, diffuse hypoxia and traumatic brain injury (TBI). Underlying cellular and physiological mechanisms relevant to age-at-injury effects will be described in considerable detail, including but not limited to alterations in neurotransmission, connectivity/network functioning, the extracellular matrix, response to oxidative stress and changes in cerebral metabolism. Finally, mechanisms of experience-dependent plasticity will be reviewed in conjunction with their effects on neural repair and recovery.

Basic fibroblast growth factor-enhanced neurogenesis contributes to cognitive recovery in rats following traumatic brain injury

Stem/progenitor cells reside throughout the adult CNS and are actively dividing in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus. This neurogenic capacity of the SVZ and DG is enhanced following traumatic brain injury (TBI) suggesting that the adult brain has the inherent potential to restore populations lost to injury. This raises the possibility of developing strategies aimed at harnessing the neurogenic capacity of these regions to repair the damaged brain. One strategy is to enhance neurogenesis with mitogenic factors. As basic fibroblast growth factor (bFGF) is a potent stem cell mitogen, we set out to determine if an intraventricular administration of bFGF following TBI could affect the levels of injury-induced neurogenesis in the SVZ and DG, and the degree to which this is associated with cognitive recovery. Specifically, adult rats received a bFGF intraventricular infusion for 7 days immediately following TBI. BrdU was administered to animals daily at 2-7 days post-injury to label cell proliferation. At 1 or 4 weeks post-injury, brain sections were immunostained for BrdU and neuronal or astrocytic markers. We found that injured animals infused with bFGF exhibited significantly enhanced cell proliferation in the SVZ and the DG at 1 week post-TBI as compared to vehicle-infused animals. Moreover, following bFGF infusion, a greater number of the newly generated cells survived to 4 weeks post-injury, with the majority being neurons. Additionally, animals infused with bFGF showed significant cognitive improvement. Collectively, the current findings suggest that bFGF-enhanced neurogenesis contributes to cognitive recovery following TBI.

The problem of relating plasticity and skilled reaching after motor cortex stroke in the rat

The plasticity of the nervous system is illustrated in the many new neuronal connections that are formed during the acquisition of behavioral skills, loss of function after brain injury, and subsequent recovery of function. The present review describes the acquisition of skilled reaching, the act of reaching for food with a forelimb, and the changes that take place in skilled reaching following motor cortex stroke. The review then discusses the difficulty in associating plastic changes with specific aspects of behavioral change. Skilled reaching behavior is complex and consists of a number of oppositions (stimulus response relationships), between the rat and the food target, a number of forelimb gestures (non-weight supporting movements), which are performed to obtain food, and a complex series of segmental movements (of the limb, head, and trunk), all of which influence the success of the act. Measures of these four aspects of skilled reaching behavior following motor cortex stroke reveal that there are a number of learned changes that take place at different times, including learned nonuse, learned bad-use, and forgetting. The widespread dendritic proliferation, axonal growth, and synaptic formation that take place both before and after stroke are difficult to precisely relate to these behavioral changes. Whereas plasticity is usually proposed to be associated with improved performance it is suggested that future work should attempt to better relate plastic changes to the details of behavioral changes.