A mixed methods exploration of the emergence of goal orientation in medical students' individualized learning plans.

PURPOSE: Goal orientation (GO) describes an individual's approach to different achievement situations. Understanding the motivations and approach to achieving goals of medical students is vital with the increasing emphasis on self-directed learning. The purpose of this study was to identify themes in self-improvement reflections that relate to each GO dimension (learning, performance-prove, and performance-avoid). METHODS: A sequential explanatory mixed methods design was used. GO data was used to categorize students into groups aligning with the GO dimension identified in the previous stage of quantitative analysis. Individualized learning plans (ILPs) for each GO dimension group were coded inductively to identify emergent themes related to goal setting and achievement. RESULTS: The learning GO group was the largest of the three GOs. Five themes were identified from inductive analysis: importance of practice, identifying elements that helped, identifying structural barriers, opportunities for improvement, and acknowledging experience. While these themes occur across GO, patterns exist within their ILPs based on GO. CONCLUSIONS: We identified common themes for motivations of medical students, and these motivations might differ depending on their GO. Further exploration into the themes over the course of their training will provide additional insights on what factors may be involved in student motivations towards learning and achievement. Educators can use this information to individualize feedback and students can better understand their motivations towards achieving goals.

Crashing from cadaver to computer: Covid-driven crisis-mode pedagogy spawns active online substitute for teaching gross anatomy.

In early 2020, the Covid-19 crisis forced medical institutions worldwide to convert quickly to online platforms for content delivery. Although many components of medical education were adaptable to that format, anatomical dissection laboratory lost substantial content in that conversion, including features of active student participation, three-dimensional spatial relationships of structures, and the perception of texture, variation, and scale. The present study aimed to develop and assess online anatomy laboratory sessions that sought to preserve benefits of the dissection experience for first-year medical students. The online teaching package was based on a novel form of active videography that emulates eye movement patterns that occur during processes of visual identification, scene analysis, and learning. Using this video-image library of dissected materials, content was presented through asynchronous narrated laboratory demonstrations and synchronous/active video conference sessions and included a novel, video-based assessment tool. Data were obtained using summative assessments and a final course evaluation. Test scores for the online practical examination were significantly improved over those for previous in-person dissection-based examinations, as evidenced by several measures of performance (Mean: 2015-2019: 82.5%; 2020: 94.9%; P = 0.003). Concurrently, didactic test scores were slightly, but not significantly, improved (Mean: 2015-2019: 88.0%; 2020: 89.9%). Student evaluations of online sessions and overall course were highly positive. Results indicated that this innovative online teaching package can provide an effective alternative when in-person dissection laboratory is unavailable. Although this approach consumed considerable faculty time for video editing, further development will include video conference breakout rooms to emulate dissection small-group teamwork.

Cadaver Rounds: A Comprehensive Exercise That Integrates Clinical Context Into Medical Gross Anatomy.

PROBLEM: The purpose of medical schools is to train students to care for patients; however, the temporal and conceptual gap between course work and patient care may induce students to undervalue preclinical course work, thereby decreasing learning and retention. Bringing clinical context into preclinical courses reduces this problem, and many preclinical programs incorporate "cameo" appearances of clinical material. In contrast, the authors describe a comprehensive program at Virginia Commonwealth University School of Medicine that uses the cadaver as the students' first patient to embed clinical context within preclinical anatomy. APPROACH: As the students' first patient, cadavers undergo modified physical exams, whole-body computed tomography scans, and pathology sample analysis. Students log daily dissection observations onto a "patient chart." Group findings are integrated, on a self-directed basis, into a final grand rounds-style presentation ("Cadaver Rounds") requiring students to synthesize longitudinally collected observations into a plausible clinical condition likely experienced by the cadaver-patient when alive. The entire exercise uses few additional contact hours (about six) and runs concurrently with the existing medical curriculum. OUTCOMES: According to course surveys used to assess students' perceptions of the relevance and effectiveness of Cadaver Rounds (2015-2017), the students' experience was highly positive. Participation by faculty and clinicians has been enthusiastic. NEXT STEPS: The authors hope both to identify additional authentic clinical tasks to import into the dissection lab and to partner with other programs to adopt and evaluate this clinically centered approach to anatomy.

Pathophysiology of Traumatic Brain Injury.

This article provides a concise overview, at the structural and functional level, of those changes evoked by traumatic brain injury across the spectrum of the disease. Using data derived from animals and humans, the pathogenesis of focal versus diffuse brain damage is presented for consideration of its overall implications for morbidity. Emphasis is placed on contusion and its potential expansion in concert with diffuse changes primarily assessed at the axonal level. Concomitant involvement of neuroexcitation and its role in global and focal metabolic changes is considered. Lastly, the influence of premorbid factors including age, genetics, and socioeconomic background is discussed.

Cellular and molecular mechanisms of injury and spontaneous recovery.

Until recently, most have assumed that traumatic brain injury (TBI) was singularly associated with the overt destruction of brain tissue resulting in subsequent morbidity or death. More recently, experimental and clinical studies have shown that the pathobiology of TBI is more complex, involving a host of cellular and subcellular changes that impact on neuronal function and viability while also affecting vascular reactivity and the activation of multiple biological response pathways. Here we review the brain's response to injury, examining both focal and diffuse changes and their implications for post-traumatic brain dysfunction and recovery. TBI-induced neuronal dysfunction and death as well as the diffuse involvement of multiple fiber projections are discussed together with considerations of how local axonal membrane changes or channelopathy translate into local ionic dysregulation and axonal disconnection. Concomitant changes in the cerebral microcirculation are also discussed and their relationship with the parallel changes in the brain's metabolism is considered. These cellular and subcellular events occurring within neurons and their blood supply are correlated with multiple biological response modifiers evoked by generalized post-traumatic inflammation and the parallel activation of oxidative stress processes. The chapter closes with considerations of recovery following focal or diffuse injury. Evidence for dynamic brain reorganization/repair is presented, with considerations of traumatically induced circuit disruption and their progression to either adaptive or in some cases, maladaptive reorganization.

Traumatic brain injury-induced axonal phenotypes react differently to treatment.

Injured axons with distinct morphologies have been found following mild traumatic brain injury (mTBI), although it is currently unclear whether they reflect varied responses to the injury or represent different stages of progressing pathology. This complicates evaluation of therapeutic interventions targeting axonal injury. To address this issue, we assessed axonal injury over time within a well-defined axonal population, while also evaluating mitochondrial permeability transition as a therapeutic target. We utilized mice expressing yellow fluorescent protein (YFP) in cortical neurons which were crossed with mice which lacked Cyclophilin D (CypD), a positive regulator of mitochondrial permeability transition pore opening. Their offspring were subjected to mTBI and the ensuing axonal injury was assessed using YFP expression and amyloid precursor protein (APP) immunohistochemistry, visualized by confocal and electron microscopy. YFP(+) axons initially developed a single, APP(+), focal swelling (proximal bulb) which progressed to axotomy. Disconnected axonal segments developed either a single bulb (distal bulb) or multiple bulbs (varicosities), which were APP(-) and whose ultrastructure was consistent with ongoing Wallerian degeneration. CypD knock-out failed to reduce proximal bulb formation but decreased the number of distal bulbs and varicosities, as well as a population of small, APP(+), callosal bulbs not associated with YFP(+) axons. The observation that YFP(+) axons contain several pathological morphologies points to the complexity of traumatic axonal injury. The fact that CypD knock-out reduced some, but not all, subtypes highlights the need to appropriately characterize injured axons when evaluating potential neuroprotective strategies.

Mild traumatic brain injury in the mouse induces axotomy primarily within the axon initial segment.

Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI), and is associated with much of its morbidity. Increasingly, it has also been recognized as a major pathology of mild TBI (mTBI). In terms of its pathogenesis, numerous studies have investigated the susceptibility of the nodes of Ranvier, the paranode and internodal regions to TAI. The nodes of Ranvier, with their unique composition and concentration of ion channels, have been suggested as the primary site of injury, initiating a cascade of abnormalities in the related paranodal and internodal domains that lead to local axonal swellings and detachment. No investigation, however, has determined the effect of TAI upon the axon initial segment (AIS), a segment critical to regulating polarity and excitability. The current study sought to identify the susceptibility of these different axon domains to TAI within the neocortex, where each axonal domain could be simultaneously assessed. Utilizing a mouse model of mTBI, a temporal and spatial heterogeneity of axonal injury was found within the neocortical gray matter. Although axonal swellings were found in all domains along myelinated neocortical axons, the majority of TAI occurred within the AIS, which progressed without overt structural disruption of the AIS itself. The finding of primary AIS involvement has important implications regarding neuronal polarity and the fate of axotomized processes, while also raising therapeutic implications, as the mechanisms underlying such axonal injury in the AIS may be distinct from those described for nodal/paranodal injury.

Aging- and injury-related differential apoptotic response in the dentate gyrus of the hippocampus in rats following brain trauma.

The elderly are among the most vulnerable to traumatic brain injury (TBI) with poor functional outcomes and impaired cognitive recovery. Of the pathological changes that occur following TBI, apoptosis is an important contributor to the secondary insults and subsequent morbidity associated with TBI. The current study investigated age-related differences in the apoptotic response to injury, which may represent a mechanistic underpinning of the heightened vulnerability of the aged brain to TBI. This study compared the degree of TBI-induced apoptotic response and changes of several apoptosis-related proteins in the hippocampal dentate gyrus (DG) of juvenile and aged animals following injury. Juvenile (p28) and aged rats (24 months) were subjected to a moderate fluid percussive injury or sham injury and sacrificed at 2 days post-injury. One group of rats in both ages was sacrificed and brain sections were processed for TUNEL and immunofluorescent labeling to assess the level of apoptosis and to identify cell types which undergo apoptosis. Another group of animals was subjected to proteomic analysis, whereby proteins from the ipsilateral DG were extracted and subjected to 2D-gel electrophoresis and mass spectrometry analysis. Histological studies revealed age- and injury-related differences in the number of TUNEL-labeled cells in the DG. In sham animals, juveniles displayed a higher number of TUNEL(+) apoptotic cells located primarily in the subgranular zone of the DG as compared to the aged brain. These apoptotic cells expressed the early neuronal marker PSA-NCAM, suggestive of newly generated immature neurons. In contrast, aged rats had a significantly higher number of TUNEL(+) cells following TBI than injured juveniles, which were NeuN-positive mature neurons located predominantly in the granule cell layer. Fluorescent triple labeling revealed that microglial cells were closely associated to the apoptotic cells. In concert with these cellular changes, proteomic studies revealed both age-associated and injury-induced changes in the expression levels of three apoptotic-related proteins: hippocalcin, leucine-rich acidic nuclear protein and heat shock protein 27. Taken together, this study revealed distinct apoptotic responses following TBI in the juvenile and aged brain which may contribute to the differential cognitive recovery observed.

Increased intracranial pressure after diffuse traumatic brain injury exacerbates neuronal somatic membrane poration but not axonal injury: evidence for primary intracranial pressure-induced neuronal perturbation.

Increased intracranial pressure (ICP) associated with traumatic brain injury (TBI) is linked to increased morbidity. Although our understanding of the pathobiology of TBI has expanded, questions remain regarding the specific neuronal somatic and axonal damaging consequences of elevated ICP, independent of its impact on cerebral perfusion pressure (CPP). To investigate this, Fischer rats were subjected to moderate TBI. Measurements of ICP revealed two distinct responses to injury. One population exhibited transient increases in ICP that returned to baseline levels acutely, while the other displayed persistent ICP elevation (>20 mm Hg). Utilizing these populations, the effect of elevated ICP on neuronal pathology associated with diffuse TBI was analyzed at 6 hours after TBI. No difference in axonal injury was observed, however, rats exhibiting persistently elevated ICP postinjury revealed a doubling of neurons with chronic membrane poration compared with rats exhibiting only transient increases in ICP. Elevated postinjury ICP was not associated with a concurrent increase in DNA damage; however, traditional histological assessments did reveal increased neuronal damage, potentially associated with redistribution of cathepsin-B from the lysosomal compartment into the cytosol. These findings indicate that persistently increased ICP, without deleterious alteration of CPP, exacerbates neuronal plasmalemmal perturbation that could precipitate persistent neuronal impairment and ultimate neuronal death.

Age-related proteomic changes in the subventricular zone and their association with neural stem/progenitor cell proliferation.

In the mammalian central nervous system, generation of new neurons persists in the subventricular zone (SVZ) throughout life. However, the capacity for neurogenesis in this region declines with aging. Recent studies have examined the degree of these age-related neurogenic declines and the changes of cytoarchitecture of the SVZ with aging. However, little is known about the molecular changes in the SVZ with aging. In this study, we dissected the SVZs from rats aged postnatal day 28, 3 months, and 24 months. The SVZ tissues were processed for 2-D gel electrophoresis to identify protein changes following aging. Protein spots were subsequently subjected to mass spectrometry analysis to compare age-related alterations in the SVZ proteome. We also examined the level of cell proliferation in the SVZ in animals of these three age groups by using bromodeoxyuridine labeling. We found significant age-related changes in the expression of several proteins that play critical roles in the proliferation and survival of neural stem/progenitor cells in the SVZ. Among these proteins, glial fibrillary acidic protein, ubiquitin carboxy terminal hydrolase 1, glutathione S-transferase omega, and preproalbumin were increased with aging, whereas collapsin response-mediated protein 4 (CRMP-4), CRMP-5, and microsomal protease ER60 exhibited declines with aging. We have also observed a significant decline of neural stem/progenitor cell proliferation in the SVZ with aging. These alterations in protein expression in the SVZ with aging likely underlie the diminishing proliferative capacity of stem/progenitor cells in the aging brain.

Diffuse traumatic axonal injury in the mouse induces atrophy, c-Jun activation, and axonal outgrowth in the axotomized neuronal population.

Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI) and is associated with much of its morbidity. Little is known regarding the long-term retrograde neuronal consequences of TAI and/or the potential that TAI could lead to anterograde axonal reorganization and repair. To investigate the repertoire of anterograde and retrograde responses triggered by TIA, Thy1-YFP-H mice were subjected to mild central fluid percussion injury and killed at various times between 15 min and 28 d post-injury. Based upon confocal assessment of the endogenous neuronal fluorescence, such injury was found to result in diffuse TAI throughout layer V of the neocortex within yellow fluorescent protein (YFP)-positive axons. When these fluorescent approaches were coupled with various quantitative and immunohistochemical approaches, we found that this TAI did not result in neuronal death over the 28 d period assessed. Rather, it elicited neuronal atrophy. Within these same axotomized neuronal populations, TAI was also found to induce an early and sustained activation of the transcription factors c-Jun and ATF-3 (activating transcription factor 3), known regulators of axon regeneration. Parallel ultrastructural studies confirmed that these reactive changes are consistent with atrophy in the absence of neuronal death. Concurrent with those events ongoing in the neuronal cell bodies, their downstream axonal segments revealed, as early as 1 d post-injury, morphological changes consistent with reactive sprouting that was accompanied by significant axonal elongation over time. Collectively, these TAI-linked events are consistent with sustained neuronal recovery, an activation of a regenerative genetic program, and subsequent axonal reorganization suggestive of some form of regenerative response.

The effect of epidermal growth factor in the injured brain after trauma in rats.

Epidermal growth factor (EGF) is a known mitogen for neural stem and progenitor cells (NS/NPCs) in the central nervous system (CNS). In vitro, EGF maintains NS/NPCs in the proliferative state, whereas in the normal rodent brain it promotes their proliferation and migration in the subventricular zone (SVZ). Additionally, EGF administration can augment neuronal replacement in the ischemic-injured adult striatum. Recently we found that the SVZ and the hippocampus display an injury-induced proliferative response following traumatic brain injury (TBI) that is linked to increased EGF expression. As adult neurogenesis is associated with cognitive function, we hypothesized that post-TBI administration of EGF could affect neurogenesis and cognitive recovery. Adult rats were intraventricularly infused with EGF or vehicle for 7 days following TBI. 5-Bromo-2-deoxyuridine (BrdU) was administered to label proliferating cells and the animals were sacrificed at 1 or 4 weeks post-injury. Using immunohistochemistry and stereology, we found that at 1 week post-injury, compared to vehicle-infused animals EGF-infused animals had significantly more BrdU-positive cells in the SVZ and hippocampus concomitant with enhanced EGF receptor expression. At 4 weeks post-injury, the number of BrdU-positive cells in the hippocampus was similar in both groups, suggesting that EGF does not support long-term survival of newly generated cells. Furthermore, we found that the EGF-induced proliferative population differentiated preferentially toward astroglial phenotype. Nevertheless, animals treated with EGF showed significant improvement in cognitive function, which was accompanied by reduced hippocampal neuronal cell loss. Collectively, the data from this study demonstrate that EGF exerts a neuroprotective rather than neurogenic effect in protecting the brain from injury.

Biochemical, structural, and biomarker evidence for calpain-mediated cytoskeletal change after diffuse brain injury uncomplicated by contusion.

Calpain-mediated degradation of the cytoskeletal protein alpha-II-spectrin has been implicated in the pathobiology of experimental and human traumatic brain injury (TBI). Spectrin proteolysis after diffuse/widespread TBI uncomplicated by either subtle or overt contusion and/or mass lesions, (i.e. mild to moderate TBI), has not been previously evaluated. To determine the spatiotemporal pattern and cellular localization of calpain-mediated spectrin proteolysis after diffuse/widespread TBI and the extent to which parenchymal changes in calpain-mediated spectrin proteolysis are reflected in the cerebrospinal fluid, adult rats were subjected to a moderate midline fluid percussion injury and allowed to survive for 3 hours to 7 days postinjury. Light and electron microscopic immunocytochemical and Western blot analyses were performed to identify the calpain-specific 145-kDa breakdown product of alpha-II-spectrin (SBDP145). After diffuse TBI, enhanced levels of SBDP145 immunoreactivity were observed in the neocortex, subcortical white matter, thalamus, and hippocampus, peaking between 24 and 48 hours postinjury. Immunoreactivity was localized almost exclusively to damaged axons and axonal terminal debris. Heightened levels of SBDP145 were also observed in the cerebrospinal fluid at 24 hours postinjury. These results confirm the widespread occurrence of calpain-mediated spectrin proteolysis after diffuse TBI without contusion and support the potential utility of SBDPs as biomarkers of a diffusely injured brain.

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.

Utilizing X-irradiation to selectively eliminate neural stem/progenitor cells from neurogenic regions of the mammalian brain.

Neural stem/progenitor cells residing in the mammalian CNS provide a potential endogenous source for replenishing neurons that are lost due to aging, trauma or disease. However, little is known about their functional potential due to the lack of methodologies that allow for the reproducible alteration of stem cell numbers in vivo. Accordingly, we describe a methodology that utilizes targeted X-irradiation to experimentally generate neural stem/progenitor cell-depleted rat models. We show that, by virtue of their mitotic activity, proliferating neural stem/progenitor cells can be selectively eliminated from either the subventricular zone (SVZ) or dentate gyrus of a rat by treating it to an (unilateral or bilateral) exposure of X-irradiation. Utilizing BrdU incorporation, it was found that a single 15 gray (Gy) exposure to the SVZ resulted in the elimination of 85% of the proliferating cell population for up to 3 months. Immunohistochemistry, ultrastructural analysis and proteomics were employed to confirm that the cells eliminated following X-irradiation were neural stem/progenitor cells. Similar depletions of the stem/progenitor cell population in the dentate gyrus were achieved by targeting the hippocampus with a single 15Gy exposure. The reproducibility, versatility and ease of generation make these experimental animal models a valuable tool to aid in our understanding of the properties and functions of neural stem/progenitor cells.

Anatomical integration of newly generated dentate granule neurons following traumatic brain injury in adult rats and its association to cognitive recovery.

The hippocampus is particularly vulnerable to traumatic brain injury (TBI), the consequences of which are manifested as learning and memory deficits. Following injury, substantive spontaneous cognitive recovery occurs, suggesting that innate repair mechanisms exist in the brain. However, the underlying mechanism contributing to this is largely unknown. The existence of neural stem cells in the adult hippocampal dentate gyrus (DG) and their proliferative response following injury led us to speculate that neurogenesis may contribute to cognitive recovery following TBI. To test this, we first examined the time course of cognitive recovery following lateral fluid percussion injury in rats. Cognitive deficits were tested at 11-15, 26-30 or 56-60 days post-injury using Morris Water Maze. At 11-15 and 26-30 days post-injury, animals displayed significant cognitive deficits, which were no longer apparent at 56-60 days post-TBI, suggesting an innate cognitive recovery at 56-60 days. We next examined the proliferative response, maturational fate and integration of newly generated cells in the DG following injury. Specifically, rats received BrdU at 2-5 days post-injury followed by Fluorogold (FG) injection into the CA3 region at 56 days post-TBI. We found the majority of BrdU+ cells which survived for 10 weeks became dentate granule neurons, as assessed by NeuN and calbindin labeling, approximately 30% being labeled with FG, demonstrating their integration into the hippocampus. Additionally, some BrdU+ cells were synaptophysin-positive, suggesting they received synaptic input. Collectively, our data demonstrate the extensive anatomical integration of new born dentate granule neurons at the time when innate cognitive recovery is observed.

Characterizing the mitogenic effect of basic fibroblast growth factor in the adult rat striatum.

The limited regenerative capacity of the adult central nervous system (CNS) renders it unable to fully recover from injury or disease. Although stem and progenitor cells have been shown to reside throughout the brain, in most regions they exist as quiescent cell populations and do not divide sufficiently to replace damaged or destroyed cells. In an effort to stimulate the proliferative capacity of these multipotent cells, we sought to determine the in vivo response of the adult CNS to an exogenous application of basic fibroblast growth factor (bFGF), a known mitogen to stem and progenitor cells. Specifically, we administered bFGF to the striatum of adult rats at varying concentrations (1, 10, 100, 1,000, or 10,000 ng/mL in saline) so as to establish a dose response curve for bFGF-induced cell proliferation. Forty-eight hours following bFGF administration, animals were injected with 5-bromodeoxyuridine to label dividing cells. Of the doses assessed, we found that 1,000 ng/mL bFGF generated the greatest proliferative response over that observed in animals given a control saline injection. Further, the proliferative response of the striatum to bFGF administration could be enhanced twofold by supplementing this growth factor with heparin sulfate, a factor that facilitates the binding of bFGF to its receptors. By determining the maturational fate of the proliferating cell population, we found that a significant proportion of newly generated cells resulting from bFGF administration differentiated into astrocytes. Collectively, these studies demonstrate the potential of bFGF to promote proliferation in the adult brain, which can be exploited to facilitate cell replacement therapies.

Enhanced hippocampal neurogenesis by intraventricular S100B infusion is associated with improved cognitive recovery after traumatic brain injury.

Evidence of injury-induced neurogenesis in the adult hippocampus suggests that an endogenous repair mechanism exists for cognitive dysfunction following traumatic brain injury (TBI). One factor that may be associated with this restoration is S100B, a neurotrophic/mitogenic protein produced by astrocytes, which has been shown to improve memory function. Therefore, we examined whether an intraventricular S100B infusion enhances neurogenesis within the hippocampus following experimental TBI and whether the biological response can be associated with a measurable cognitive improvement. Following lateral fluid percussion or sham injury in male rats (n = 60), we infused S100B (50 ng/h) or vehicle into the lateral ventricle for 7 days using an osmotic micro-pump. Cell proliferation was assessed by injecting the mitotic marker bromodeoxyuridine (BrdU) on day 2 postinjury. Quantification of BrdU-immunoreactive cells in the dentate gyrus revealed an S100B-enhanced proliferation as assessed on day 5 post-injury (p < 0.05), persisting up to 5 weeks (p < 0.05). Using cell-specific markers, we determined the relative numbers of these progenitor cells that became neurons or glia and found that S100B profoundly increased hippocampal neurogenesis 5 weeks after TBI (p < 0.05). Furthermore, spatial learning ability, as assessed by the Morris water maze on day 30-34 post-injury, revealed an improved cognitive performance after S100B infusion (p < 0.05). Collectively, our findings indicate that an intraventricular S100B infusion induces neurogenesis within the hippocampus, which can be associated with an enhanced cognitive function following experimental TBI. These observations provide compelling evidence for the therapeutic potential of S100B in improving functional recovery following TBI.

Cell proliferation and neuronal differentiation in the dentate gyrus in juvenile and adult rats following traumatic brain injury.

It is well known that the cognitive functions of juveniles recover to a greater extent than adult patients following traumatic brain injury (TBI). The exact mechanisms underlying this age-related disparity are unknown; however, we speculate that this improved recovery in juveniles following TBI may be associated with an endogenous neurogenic response in the hippocampus. We, therefore, examined the effects of TBI on cellular proliferation and differentiation in the dentate gyrus (DG) of the hippocampus in juvenile and adult rats following lateral fluid percussion injury (FPI). The temporal profile of the injury-induced proliferative response was determined using BrdU labeling at varying survival times. The differentiation of these newly generated cells was investigated using cell-type specific markers. We found that, following injury, there was a significant increase in cell proliferation in the DG in both injured juveniles and adults at 2 days post injury when compared to shams. When comparing the extent of cell proliferation between juveniles and adults following TBI, the absolute number of cells generated in the subgranular zone (SGZ) was far greater in the juveniles. Moreover, the percentage of newly generated cells in the SGZ that differentiated into neurons was nearly two times higher in the juveniles as compared to adults. Conversely, more glial differentiation was observed in the DG of adult rats. These findings provide compelling evidence that age-related differences in the neurogenic response to injury may underlie the differences observed in cognitive recovery in juvenile mammals as compared to adults following TBI.

Epidermal growth factor-induced cell proliferation in the adult rat striatum.

Current strategies for repairing the adult CNS following injury include cell transplantation and/or the use of viral vectors to deliver therapeutic agents. Although promising, both techniques are limited in their usefulness due to the immunological response triggered in the brain as a result of the introduction of foreign antigens. An alternative method to repair the damaged CNS is to stimulate endogenous cells within the brain to divide thereby replacing cells lost to injury. Since it has been shown that growth factors such as epidermal growth factor (EGF) are potent mitogens to CNS cells in vitro, we sought to assess the mitogenic effect of an in vivo application of EGF to the adult mammalian brain. Accordingly, varying doses of human recombinant EGF were administered to the striatum of adult rats, followed 48 h later by intraperitoneal injections of 5-bromodeoxyuridine (BrdU), a marker for cell proliferation. Of four doses assessed, 0.05 ng of EGF induced the highest levels of cell proliferation. To determine the cellular identity of these proliferating cells, animals were injected with (3)H-thymidine 48 h following EGF administration to label dividing cells. Sections were subsequently immunostained for markers to astrocytes, microglia, oligodendrocytes, neural precursors, and mature neurons. Compared to controls, a significant proportion of the newly generated cells resulting from EGF administration were identified as immature and mature astrocytes. Collectively, these results provide valuable information for utilizing a growth factor administration approach to mobilize the proliferative response of endogenous cells to replace those lost to injury or disease.