Regional and temporal profiles of c-fos and nerve growth factor mRNA expression in rat brain after lateral cortical impact injury

Pudendal nerve stretch reduces external urethral sphincter activity in rats

PURPOSE

Most animal models of stress urinary incontinence simulate maternal injuries of childbirth since delivery is a major risk factor but they do not reproduce the nerve stretch known to occur during human childbirth. We hypothesized that pudendal nerve stretch produces reversible dysfunction of the external urethral sphincter.

MATERIALS AND METHODS

Female virgin Sprague-Dawley® rats were anesthetized with urethane. Bilateral pudendal nerve stretch or sham injury was performed for 5 minutes. External urethral sphincter electromyography and leak point pressure were recorded immediately before and after, and 10, 30, 60 and 120 minutes after pudendal nerve stretch. Post-pudendal nerve stretch results were compared to prestretch values and to values in sham injured animals. The pudendal nerves underwent qualitative histological assessment. The nucleus of Onuf was evaluated by immunohistochemistry and polymerase chain reaction for β-APP and c-Fos expression as markers of neuronal activity and injury.

RESULTS

A total of 14 rats underwent bilateral pudendal nerve stretch (9) or sham injury (5). Each nerve was stretched a mean ± SEM of 74% ± 18% on the left side and 63% ± 13% on the right side. Electromyography amplitude decreased significantly immediately after stretch compared to before stretch and after sham injury (p = 0.003) but it recovered by 30 minutes after stretch. There was no significant change in leak point pressure at any time. Two hours after injury histology showed occasional neuronal degeneration. β-APP and c-Fos expression was similar in the 2 groups.

CONCLUSIONS

Acute pudendal nerve stretch produces reversible electrophysiological dysfunction but without leak point pressure impairment. Pudendal nerve stretch shows promise in modeling injury. It should be tested as part of a multi-injury, chronic, physiological model of human childbirth injury.

Gabapentin decreases epileptiform discharges in a chronic model of neocortical trauma

Gabapentin (GBP) is an anticonvulsant that acts at the α2δ-1 submit of the L-type calcium channel. It is recently reported that GBP is a potent inhibitor of thrombospondin (TSP)-induced excitatory synapse formation in vitro and in vivo. Here we studied effects of chronic GBP administration on epileptogenesis in the partial cortical isolation ("undercut") model of posttraumatic epilepsy, in which abnormal axonal sprouting and aberrant synaptogenesis contribute to occurrence of epileptiform discharges. Results showed that 1) the incidence of evoked epileptiform discharges in undercut cortical slices studied 1 day or ~2 weeks after the last GBP dose, was significantly reduced by GBP treatments, beginning on the day of injury; 2) the expression of GFAP and TSP1 protein, as well as the number of FJC stained cells was decreased in GBP treated undercut animals; 3) in vivo GBP treatment of rats with undercuts for 3 or 7 days decreased the density of vGlut1-PSD95 close appositions (presumed synapses) in comparison to saline treated controls with similar lesions;4) the electrophysiological data are compatible with the above anatomical changes, showing decreases in mEPSC and sEPSC frequency in the GBP treated animals. These results indicate that chronic administration of GBP after cortical injury is antiepileptogenic in the undercut model of post-traumatic epilepsy, perhaps by both neuroprotective actions and decreases in excitatory synapse formation. The findings may suggest the potential use of GBP as an antiepileptogenic agent following traumatic brain injury.

Temporal and regional changes in IGF-1/IGF-1R signaling in the mouse brain after traumatic brain injury

Although neurotrophic factors such as nerve growth factor, basic fibroblast growth factor, brain-derived neurotrophic factor, and neurotrophin 4/5 are elevated after traumatic brain injury (TBI), little is known about the endogenous response of insulin-like growth factor-1 (IGF-1). We evaluated IGF-1, IGF-1 receptor (IGF-1R), and total and phosphorylated Akt (p-Akt), a known downstream mediator of IGF-1 signaling, using ELISA, Western blotting, and immunohistochemistry at 1, 6, 24, 48, and 72 h following 0.5-mm controlled cortical impact brain injury in adult mice. IGF-1 was transiently upregulated in homogenates of injured cortex at 1 h, and cells with increased IGF-1 immunoreactivity were observed in and around the cortical contusion site up to 48 h. IGF-1R and total Akt levels in cortical homogenates were unchanged, although immunohistochemistry revealed regional changes. In contrast, serine p-Akt levels increased significantly in homogenates at 6 h post-injury. Interestingly, delayed increases in vascular IGF-1R, total Akt, and p-Akt immunostaining were observed in and around the cortical contusion. IGF-1 and its downstream mediators were also upregulated in the subcortical white matter. Our findings indicate that moderate TBI results in a brief induction of IGF-1 and its signaling components in the acute post-traumatic period. This may reflect an attempt at endogenous neuroprotection or repair.

Protective effects of bone marrow stromal cell transplantation in injured rodent brain: synthesis of neurotrophic factors

Several groups have suggested that transplantation of marrow stromal cells (MSCs) promotes functional recovery in animal models of brain trauma. Recent studies indicate that tissue replacement by this method may not be the main source of therapeutic benefit, as transplanted MSCs have only limited ability to replace injured central nervous system (CNS) tissue. To gain insight into the mechanisms responsible for such effects, we systematically investigated the therapeutic potential of MSCs for treatment of brain injury. Using in vitro studies, we detected the synthesis of various growth factors, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), and neurotrophin-3 (NT-3). Enzyme-linked immunosorbent assay (ELISA) demonstrated that MSCs cultured in Dulbecco's modified Eagle medium (DMEM) produced substantial amounts of NGF for at least 7 weeks, whereas the levels of BDNF, GDNF and NT-3 remained unchanged. In studies in mice, after intraventricular injection of MSCs, NGF levels were increased significantly in cerebrospinal fluid by ELISA, confirming our cell culture results. Further studies showed that treatment of traumatic brain injury with MSCs could attenuate the loss of cholinergic neuronal immunostaining in the medial septum of mice. These studies demonstrate for the first time that by increasing the brain concentration of NGF, intraventricularly transplanted MSCs might play an important role in the treatment of traumatic brain injury.

Ex VivoGene Therapy Using Targeted Engraftment of NGF-Expressing Human NT2N Neurons Attenuates Cognitive Deficits Following Traumatic Brain Injury in Mice

Infusion of nerve growth factor (NGF) has been shown to be neuroprotective following traumatic brain injury (TBI). In this study, we tested the hypothesis that NGF-expressing human NT2N neurons transplanted into the basal forebrain of brain-injured mice can attenuate long-term cognitive dysfunction associated with TBI. Undifferentiated NT2 cells were transduced in vitro with a lentiviral vector to release NGF, differentiated into NT2N neurons by exposure to retinoic acid and transplanted into the medial septum of mice 24 h following controlled cortical impact (CCI) brain injury or sham injury. Adult mice (n = 78) were randomly assigned to one of four groups: (1) sham-injured and vehicle (serum-free medium)-treated, (2) brain-injured and vehicle-treated, (3) brain-injured engrafted with untransduced NT2N neurons, and (4) brain-injured engrafted with transduced NGF-NT2N neurons. All groups were immunosuppressed daily with cyclosporin A (CsA) for 4 weeks. At 1 month post-transplantation, animals engrafted with NGF-expressing NT2N neurons showed significantly improved learning ability (evaluated with the Morris water maze) compared to brain-injured mice receiving either vehicle (p < 0.05) or untransduced NT2N neurons (p < 0.01). No effect of NGF-secreting NT2N cells on motor function deficits at 1-4 weeks post-transplantation was observed. These data suggest that NGF gene therapy using transduced NT2N neurons (as a source of delivery) may selectively improve cognitive function following TBI.

Differential gene expression in hippocampus following experimental brain trauma reveals distinct features of moderate and severe injuries

Microarray technology was employed to determine the differential pattern of gene expression within the hippocampus as a result of traumatic brain injury (TBI). The validity of the microarray data was confirmed using real-time RT-PCR. Following either moderate or severe lateral fluid percussion injury, rats were studied 0.5, 4, and 24 h after injury. In general, animals exhibited mRNA up or down regulation of approximately 10% of the genes studied. However, it was clear that the pattern of gene expression was influenced by both the severity of injury and the time after injury at which animals were studied. For example, genes encoding molecules for cellular signaling, synaptic plasticity, metabolism, ion channels and transporters were up regulated following severe injury, but down regulated following moderate injury. Furthermore, moderate injury was associated with an increasing number of responsive genes as a function of time post-injury. However, animals sustaining a severe level of injury exhibited decreasing number of responsive genes during the same post-injury period. The different patterns of gene expression between injury severity and across time after the insult suggests that the pathophysiological cascade induced by TBI is accompanied by a molecular response which, like the other aspects of the cellular response for survival, may indicate a "molecular window" that may offer an opportunity for therapeutic interventions involving gene therapy. Our results also suggest that fundamentally different pathophysiological processes or cascades may be induced by different severities of injury.

A critical period for prevention of posttraumatic neocortical hyperexcitability in rats

Penetrating cortical trauma frequently results in delayed development of epilepsy. In the rat undercut model of neocortical posttraumatic hyperexcitability, suppression of neuronal activity by exposing the injured cortex to tetrodotoxin (TTX) in vivo for approximately 2 weeks prevents the expression of abnormal hypersynchronous discharges in neocortical slices. We examined the relationship between neuronal activity during the latent period after trauma and subsequent expression of hyperexcitability by varying the timing of TTX treatment. Partially isolated islands of rat sensorimotor cortex were treated with Elvax polymer containing TTX to suppress cortical activity and slices obtained for in vitro experiments 10 to 15 days later. TTX treatment was either started immediately after injury and discontinued after a variable number of days or delayed for a variable time after the lesion was placed. Immediate treatment lasting only 2 to 3 days and treatment delayed up to 3 days prevented hyperexcitability. Thus, there is a critical period for development of hyperexcitability in this model that depends on cortical activity. We propose that the hyperexcitability caused by partial cortical isolation may represent an early stage of posttraumatic epileptogenesis. A hypothetical cascade of events leading to subsequent pathophysiological activity is likely initiated at the time of injury but remains plastic during this critical period.

Liposome-mediated transfer of vascular endothelial growth factor cDNA augments survival of random-pattern skin flaps in the rat

Tissue engineering is an application for gene therapy that is in its infancy. We show that simple liposomal-mediated gene transfer could result in a potentially useful biological effect in the field of wound healing. cDNA encoding the 165 amino acid form of vascular endothelial growth factor complexed to commercially available liposomes was injected into rat skin 1 week before raising a random pattern 3 x 10 cm flap. The flap survival was enhanced by 14 percent, and was accomplished without accessing the arterial inflow of the territory. These results were statistically significant (p<0.002) and reproducible. No adverse effects were seen. Histological analysis of the angiogenesis localized much of the new vessel formation to the area around the hair follicles. Polymerase chain reaction amplification of extracted flap tissue confirmed the presence of the transgene.

Time Course Analysis of Hippocampal Nerve Growth Factor and Antioxidant Enzyme Activity following Lateral Controlled Cortical Impact Brain Injury in the Rat

Gradual secondary injury processes, including the release of toxic reactive oxygen species, are important components of the pathogenesis of traumatic brain injury (TBI). The extent of oxidative stress is determined in part by the effectiveness of the antioxidant response, involving the enzymes glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD). Since nerve growth factor (NGF) may be involved in the initiation of antioxidant activity, we employed a controlled cortical impact injury model in rats to produce secondary hippocampal damage and determined the subsequent time course of changes in NGF production and GPx, CAT, and SOD activity in this brain region. Hippocampal NGF production showed a rapid increase with a biphasic response after TBI. NGF protein was increased at 6 h, plateaued at 12 h, declined by 7 days, and exhibited a second rise at 14 days after injury. Similar to NGF, hippocampal GPx activity also showed a biphasic response, increasing by 12 h, declining at 24 h, and exhibiting a second peak at 7 days. In contrast, increased CAT activity occured steadily from 1 day through 7 days after injury. SOD activity was decreased at 6 h after injury, and continued to decline through 14 days. The initial rise in NGF preceded that of CAT, and coincided with an increase in GPX and a drop in SOD activity. These data demonstrate a complex temporal spectrum of antioxidant enzyme activation following secondary brain injury in the hippocampus, and suggest a selective regulatory role for NGF in this response.

Chronic intermittent cold stress activates ovarian sympathetic nerves and modifies ovarian follicular development in the rat

We studied the effects of a chronic intermittent cold stress regime on sympathetic nerve activation and ovarian physiology. This paradigm (4 degrees C for 3 h/day, Monday-Friday, for 3 or 4 wk) does not affect basal plasma levels of corticosterone. After 3 wk of stress, we detected a decrease in noradrenaline (NA) in the ovary, but after 4 wk, this ovarian neurotransmitter concentration increased over that of unstressed control rats. To analyze whether this effect on NA is preceded by an activation of the neurotrophic factor system responsible for growth and survival of sympathetic neurons, we measured both nerve growth factor (NGF) (by enzyme immunoassay) and the intraovarian levels of its low affinity receptor mRNA (by reverse transcription-polymerase chain reaction). The activation of sympathetic nerves was followed by an increase in NGF concentration without affecting the ovarian levels of either NGF or the mRNA of its receptor. Interestingly, follicular development changed during the stress procedure; after 3 or 4 wk of stress, we found a decrease in preantral healthy follicles without a compensatory increase in atresia. Concomitantly with the increase in NA and NGF in the ovary, we observed that a new population of follicles with hypertrophied thecal cell layers appeared after 4 wk of stress. These results suggest that chronic stress, through an intraovarian neurotrophin-mediated sympathetic activation, produces changes in follicular development that could lead to an impairment of reproductive function.

Altered expression of randomly selected genes in mouse hippocampus after traumatic brain injury

Using a cDNA microarray method, we analyzed gene expression profiles in mouse hippocampus after traumatic brain injury (TBI). Of 6,400 randomly selected arrayed genes and expressed sequence tags from a mouse cDNA library, 253 were found to be differentially expressed (106 increased and 147 decreased). Genes involved in cell homeostasis and calcium signaling were primarily up-regulated while those encoding mitochondrial enzymes, metabolic molecules, and structural proteins were predominantly down-regulated. Equal numbers of genes related to inflammatory reactions showed increased or decreased expression. Importantly, a large proportion of the dysregulated genes we identified have not been reported as differentially expressed in TBI models. Semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) analyses of representative genes confirmed the validity of the corresponding microarray findings. Thus, our microarray-based evaluation of gene expression in traumatically injured hippocampus identified both known and novel genes that respond to TBI. Further investigation of these candidate molecules may suggest new ways to attenuate the traumatic effects of brain injury.

Traumatic brain injury-induced acute gene expression changes in rat cerebral cortex identified by GeneChip analysis

Proper CNS function depends on concerted expression of thousands of genes in a controlled and timely manner. Traumatic brain injury (TBI) in mammals results in neuronal death and neurological dysfunction, which might be mediated by altered expression of several genes. By employing a CNS-specific GeneChip and real-time polymerase chain reaction (PCR), the present study analyzed the gene expression changes in adult rat cerebral cortex in the first 24 hr after a controlled cortical impact injury. Many functional families of genes not previously implicated in TBI-induced brain damage are altered in the injured cortex. These include up-regulated transcription factors (SOCS-3, JAK-2, STAT-3, CREM, IRF-1, SMN, silencer factor-B, ANIA-3, ANIA-4, and HES-1) and signal transduction pathways (cpg21, Narp, and CRBP) and down-regulated transmitter release mechanisms (CITRON, synaptojanin II, ras-related rab3, neurexin-1beta, and SNAP25A and -B), kinases (IP-3-kinase, Pak1, Ca(2+)/CaM-dependent protein kinases), and ion channels (K(+) channels TWIK, RK5, X62839, and Na(+) channel I). In addition, several genes previously shown to play a role in TBI pathophysiology, including proinflammatory genes, proapoptotic genes, heat shock proteins, immediate early genes, neuropeptides, and glutamate receptor subunits, were also observed to be altered in the injured cortex. Real-time PCR analysis confirmed the GeneChip data for many of these transcripts. The novel physiologically relevant gene expression changes observed here might explain some of the molecular mechanisms of TBI-induced neuronal damage.

Expression profiling following traumatic brain injury: a review

Traumatic brain injury (TBI) elicits a complex sequence of putative autodestructive and neuroprotective cellular cascades. It is hypothesized that the genomic responses of cells in the injured brain serve as the basis for these cascades. Traditional methods for analyzing differential gene expression following brain trauma demonstrate that immediate early genes, cytokines, transcription factors, and neurotrophic factors can all participate in the brain's active and directed response to injury, and may do so concurrently. It is this complexity and multiplicity of interrelated molecular mechanisms that has demanded new methods for comprehensive and parallel evaluation of putative as well as novel gene targets. Recent advances in DNA microarray technology have enabled the simultaneous evaluation of thousands of genes and the subsequent generation of massive amounts of biological data relevant to CNS injury. This emerging technology can serve to further current knowledge regarding recognized molecular cascades as well as to identify novel molecular mechanisms that occur throughout the post-traumatic period. The elucidation of the complex alterations in gene expression underlying the pathological sequelae following TBI is of central importance in the design of future therapeutic agents.

The association between neuronal nitric oxide synthase and neuronal sensitivity in the brain after brain injury

Injury to the central nervous system is the leading cause of disability in the United States. Neuronal death is one of the causes of disability. Among patients who survive this type of injury, various degrees of recovery in brain function are observed. The molecular basis of functional recovery is poorly understood. Clinical observations and research using experimental injury models have implicated several metabolites in the cascade of events that lead to neuronal degeneration. The levels of intracellular ATP (energy source) and pH are decreased, whereas levels of extracellular glutamate, intracellular calcium ions, and oxidative damage to RNA/DNA, protein, and lipid are increased. These initiating events can be associated with energy failure and mitochondrial dysfunction, resulting in functional or structural brain damage. The injured brain is known to express immediate early genes. Recent studies show that reactive oxygen species (ROS) cause lesions in genes from which mRNA is transcribed as part of the endogenous neuroprotective response. Although degenerating proteins and lipids may contribute to necrosis significantly after severe injury, abnormalities in genetic material, if not repaired, disturb cellular function at every level by affecting replication, transcription, and translation. These lesions include abnormal nucleic acids, known as oxidative lesions of DNA (ODLs) or of RNA (ORLs). In this review, we focus on our current understanding of the various effects of neuronal nitric oxide synthase on the formation of modified bases in DNA and RNA that are induced in the brain after injury, and how ODLs and ORLs affect cell function.

Genes preferentially induced by depolarization after concussive brain injury: effects of age and injury severity

Fluid percussion (FP) brain injury leads to immediate indiscriminate depolarization and massive potassium efflux from neurons. Using Northern blotting, we examined the post-FP expression of primary response/immediate early genes previously described as induced by depolarization in brain. RNA from ipsilateral and contralateral hippocampus was harvested from immature and adult rats 1 h following mild, moderate, or severe lateral fluid percussion injury and compared against age-matched sham animals. C-fos gene expression was used as a positive control and showed marked induction in both pups (6-25-fold with increasing severity) and adults (9.7-17.1-fold). Kinase-induced-by-depolarization-1 (KID-1) and salt-inducible kinase (SIK) gene expression was increased in adult (KID-1 1.5-1.6-fold; SIK 1.3-3.9-fold) but not developing rats. NGFI-b RNA was elevated after injury in both ages (pups 1.8-6.1-fold; adults 3.5-5-fold), in a pattern similar to that seen for c-fos. Secretogranin I (sec I) demonstrated no significant changes. Synaptotagmin IV (syt IV) was induced only following severe injury in the immature rats (1.4-fold). Our results reveal specific severity- and age-dependent patterns of hippocampal immediate early gene expression for these depolarization-induced genes following traumatic brain injury. Differential expression of these genes may be an important determinant of the distinct molecular responses of the brain to varying severities of trauma experienced at different ages.

N-methyl-D-aspartate receptors: transient loss of NR1/NR2A/NR2B subunits after traumatic brain injury in a rodent model

Hippocampal N-methyl-D-aspartate (NMDA) receptor subunits, by virtue of their involvement in excitotoxic injury as well as memory association, may play an important role in the pathophysiologic mechanisms of traumatic brain injury (TBI). In this study, temporal changes in NMDA receptor subunit (NR1, NR2A, and NR2B) levels in rat hippocampus after TBI were investigated by Western blot and mRNA expression levels by RT-PCR methods. Sprague-Dawley rats (250-350 g) were employed, and a controlled cortical impact injury device was used to produce the TBI in rodents. At different postinjury time points (2, 6, 12, 24, and 48 hr), the rat hippocampi were dissected out for protein and RNA preparation. Western blot analysis revealed significant decreases of NR1, NR2A, and NR2B subunit proteins at 6 and 12 hr postinjury in rat hippocampus. Complete recovery of NR1, NR2A, and NR2B subunit protein to the levels of sham controls was observed at 24 hr postinjury. However, RT-PCR analysis did not show any significant change in the mRNA levels at 2, 6, and 12 hr postinjury in comparison with sham controls, suggesting nontranscriptional change in the levels of these subunits. Thus, TBI can produce transient degradation of NMDA receptor subunits in the hippocampus, which might contribute to temporary memory impairment after injury.

Therapeutic success and efficacy of nonviral liposomal cDNA gene transfer to the skin in vivo is dose dependent

It is well documented that responses to growth factor treatment typically display bell-shaped dose responses that can significantly affect efficacy. Here we tested the hypothesis that nonviral liposomal gene delivery also displays this characteristic. We chose two different growth factors, keratinocyte growth factor (KGF) and insulin-like growth factor-I (IGF-I) CMV-driven transfecting constructs at three different concentrations and assessed efficacy on several physiological parameters that are descriptive of wound healing progress in a burn-wound healing model. Rats were given a 60% TBSA scald burn and randomly divided into one of seven groups to receive weekly subcutaneous injections of liposomes containing the cDNA for KGF (0.2 microg, 2.2 microg, or 22.2 microg), or liposomes containing the cDNA for IGF-I (0.2 microg, 2.2 microg, or 22.2 microg) at various concentrations, but constant liposome:DNA ratios and a LacZ gene (0.2 microg) CMV-driven construct for beta-galactosidase as vehicle and marker gene. Transfection was confirmed by histology for beta-galactosidase. Physiological efficacy was evaluated by measuring the wound healing parameters that define dermal and epidermal regeneration. Transfection products were found in the cytoplasm of rapidly dividing cells of the granulation tissue. Different doses of the nonviral cDNA gene transfer coding for KGF or IGF-I resulted in different outcomes for dermal and epidermal regeneration. There was a dose-dependent response to both growth factor gene transfers that was not dissimilar from that typically displayed by treatment with growth factor proteins. Both concentrations below and above the optimal concentration of DNA:liposomal preparations did not yield the results observed at the optimal concentration.

Neuroprotective and behavioral efficacy of nerve growth factor-transfected hippocampal progenitor cell transplants after experimental traumatic brain injury

OBJECT

Immortalized neural progenitor cells derived from embryonic rat hippocampus (HiB5), were transduced ex vivo with the gene for mouse nerve growth factor (NGF) to secrete NGF (NGF-HiB5) at 2 ng/hr/10(5) cells in culture.

METHODS

Fifty-nine male Wistar rats weighing 300 to 370 g each were anesthetized with 60 mg/kg sodium pentobarbital and subjected to lateral fluid-percussion brain injury of moderate severity (2.3-2.4 atm, 34 rats) or sham injury (25 rats). At 24 hours postinjury, 2 microl (150,000 cells/microl) of [3H]thymidine-labeled NGF-HiB5 cells were transplanted stereotactically into three individual sites in the cerebral cortex adjacent to the injury site (14 rats). Separate groups of brain-injured rats received nontransfected (naive [n])-HiB5 cells (12 animals) or cell suspension vehicle (eight animals). One week postinjury, animals underwent neurological evaluation for motor function and cognition (Morris water maze) and were killed for histological, autoradiographic, and immunocytochemical analysis. Viable HiB5 cell grafts were identified in all animals, together with reactive microglia and macrophages located throughout the periinjured parenchyma and grafts (OX-42 immunohistochemistry). Brain-injured animals transplanted with either NGF-HiB5 or n-HiB5 cells displayed significantly improved neuromotor function (p < 0.05) and spatial learning behavior (p < 0.005) compared with brain-injured animals receiving microinjections of vehicle alone. A significant reduction in hippocampal CA3 cell death was observed in brain-injured animals receiving transplants of NGF-HiB5 cells compared with those receiving n-HiB5 cells or vehicle (p < 0.025).

CONCLUSIONS

This study demonstrates that immortalized neural stem cells that have been retrovirally transduced to produce NGF can markedly improve cognitive and neuromotor function and rescue hippocampal CA3 neurons when transplanted into the injured brain during the acute posttraumatic period.

Time course of Fos and Fras expression in the hypothalamic supraoptic neurons during chronic osmotic stimulation

The Fos family comprises Fos and several subtypes of Fos-related proteins (Fras) such as FosB, Fra-1, Fra-2, DeltaFosB, and chronic Fras. Changes in the expression of Fos family proteins with time are not well elucidated, particularly during chronic stimulation. In the present experiments, we investigated quantitatively the time course changes in Fos, FosB and Fras immunoreactivity in the magnocellular neurons of the supraoptic nucleus (SON) during acute and chronic osmotic stimulation. A small number of Fos- and FosB-positive neurons were observed in the SON of control rats, while many Fras-positive neurons were seen in control animals. Significant increases in the numbers of Fos-, FosB-, and Fras-positive neurons were observed 2 h after acute osmotic stimulation by intraperitoneal (i.p.) injection of 3% NaCl solution. Although the number of Fos-positive neurons returned to the control level 4 h after i.p. injection, a significant number of FosB- and Fras-positive neurons were still observed 8 h after i.p. injection. During chronic osmotic stimulation by giving 2% NaCl solution for 2 and 5 days, a large number of Fos-positive neurons were observed, but the cessation of chronic osmotic stimulation by normal water drinking immediately decreased the number of Fos-positive neurons to the control level within 2 h. The number of FosB-positive neurons was increased with period of chronic osmotic stimulation, and a significant number were observed 2-8 h after the cessation of the stimulation. The number of Fras-positive neurons was also significantly higher during chronic osmotic stimulation, and this number was significantly high 2-8 h after the cessation of the stimulation. RT-PCR analysis demonstrated the persistent expression of c-fos mRNA in the SON during chronic osmotic stimulation. These results suggest that c-fos mRNA and Fos protein are constitutively elevated during chronic osmotic stimulation and the time course changes in Fos are different from those seen in FosB and Fras.

Traumatic brain injury alters the molecular fingerprint of TUNEL-positive cortical neurons In vivo: A single-cell analysis

The cerebral cortex is selectively vulnerable to cell death after traumatic brain injury (TBI). We hypothesized that the ratio of mRNAs encoding proteins important for cell survival and/or cell death is altered in individual damaged neurons after injury that may contribute to the cell's fate. To investigate this possibility, we used amplified antisense mRNA (aRNA) amplification to examine the relative abundance of 31 selected candidate mRNAs in individual cortical neurons with fragmented DNA at 12 or 24 hr after lateral fluid percussion brain injury in anesthetized rats. Only pyramidal neurons characterized by nuclear terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling (TUNEL) reactivity with little cytoplasmic staining were analyzed. For controls, non-TUNEL-positive neurons from the cortex of sham-injured animals were obtained and subjected to aRNA amplification. At 12 hr after injury, injured neurons exhibited a decrease in the relative abundance of specific mRNAs including those encoding for endogenous neuroprotective proteins. By 24 hr after injury, many of the mRNAs altered at 12 hr after injury had returned to baseline (sham-injured) levels except for increases in caspase-2 and bax mRNAs. These data suggest that TBI induces a temporal and selective alteration in the gene expression profiles or "molecular fingerprints" of TUNEL-positive neurons in the cerebral cortex. These patterns of gene expression may provide information about the molecular basis of cell death in this region after TBI and may suggest multiple avenues for therapeutic intervention.

Dynamic mechanical stretch of organotypic brain slice cultures induces differential genomic expression: relationship to mechanical parameters

Although the material properties of biological tissues are reasonably well established, recent studies have suggested that the biological response of brain tissue and its constituent cells may also be viscoelastic and sensitive to both the magnitude and rate of a mechanical stimulus. Given the potential involvement of changes in gene expression in the pathogenic sequelae after head trauma, we analyzed the expression of 22 genes related to cell death and survival and found that a number of these genes were differentially regulated after mechanical stretch of an organotypic brain slice culture. Twenty-four hours after stretch, the expression of BDNF, NGF, and TrkA was significantly increased, whereas that of bcl-2, CREB, and GAD65 was significantly decreased (MANOVA followed by ANOVA, p < 0.05). Expression of CREB and GAD65 was negatively correlated with strain, whereas expression of APP695 was negatively correlated with strain rate (all p < 0.05). This study demonstrates that a subset of genes involved in cell death and survival are differentially regulated after dynamic stretch in vitro and that the expression of specific genes is correlated with mechanical parameters of that stretch.

Traumatic injury induces differential expression of cell death genes in organotypic brain slice cultures determined by complementary DNA array hybridization

The expression of a large panel of selected genes hypothesized to play a central role in post-traumatic cell death was shown to be differentially altered in response to a precisely controlled, mechanical injury applied to an organotypic slice culture of the rat brain. Within 48 h of injury, the expression of nerve growth factor messenger RNA was significantly increased whereas the levels of bcl-2, alpha-subunit of calcium/calmodulin-dependent protein kinase II, cAMP response element binding protein, 65,000 mol. wt isoform of glutamate decarboxylase, 1beta isoform of protein kinase C, and ubiquitin messenger RNA were significantly decreased. Because the expression levels of a number of other messenger RNAs such as the neuron-specific amyloid precursor protein, beta(2) microglobulin, bax, bcl(xl), brain-derived neurotrophic factor, cyclooxygenase-2, interleukin-1beta, interleukin-6, tumor necrosis factor-alpha, receptor tyrosine kinase A, and receptor tyrosine kinase B were unaffected, these selective changes may represent components of an active and directed response of the brain initiated by mechanical trauma. Interpretation of these co-ordinated alterations suggests that mechanical injury to the central nervous system may lead to disruption of calcium homeostasis resulting in altered gene expression, an impairment of intracellular cascades responsible for trophic factor signaling, and initiation of apoptosis via multiple pathways. An understanding of these transcriptional changes may contribute to the development of novel therapeutic strategies to enhance beneficial and blunt detrimental, endogenous, post-injury response mechanisms.

Regional changes in the expression of neurotrophic factors and their receptors following acute traumatic brain injury in the adult rat brain

We have analyzed the effect of severe traumatic brain injury (TBI) on the levels of mRNA expression of neurotrophic factors (NTFs): brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), ciliary neurotrophic factor (CNTF) and their respective receptors: trkB, trkA and CNTFRalpha. The expression was examined in the region of the lesion as well as a region remote from the lesion at 12, 24, and 36 h following the injury. Our data suggest that after the brain injury, the expression of NGF and BDNF mRNAs were early, transiently and significantly upregulated while that of CNTF was a slow and less amplified response in both areas of the brain. We also found that trkA mRNA expression was only upregulated significantly in the remote area; trkB mRNA showed no significant change in either area except an upregulation at 12 h in the remote area. CNTFRalpha was downregulated significantly by 24-36 h in the lesion area and by 24 h in the remote area. These changes suggest that TBI regulates the expression of NTFs and their receptors. These alterations in expression may be involved in modulating the neuronal response after brain injury.

Expression of brain-derived neurotrophic factor, nerve growth factor, and heat shock protein HSP70 following fluid percussion brain injury in rats

Traumatic brain injury can induce the expression of stress-related and neurotrophic genes both within the injury site and in distant regions. These genes may affect severity of damage and/or be neuroprotective. We used in situ hybridization to assess the alterations in expression of the heat shock protein HSP70, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) genes in rat brain following moderate fluid-percussion (F-P) injury at various survival times. HSP70 gene expression was induced at and surrounding the injury site as early as 30 min after trauma. This elevated signal spread ventrally and laterally through the ipsilateral cortex and into the underlying white matter over the next few hours. In addition, there was elevated expression in the temporal hippocampus. BDNF was strongly upregulated in the granular cells of the dentate gyrus and in the CA3 hippocampus 2-6 h after injury. Cortical regions at and near the injury site showed no response at the mRNA level. NGF mRNA increased over the granular cells of the dentate gyrus at early time points. There was also a weaker secondary induction of the NGF gene in the contralateral dentate gyrus of some animals. Cortical response was observed in the entorhinal cortex, bilaterally, but not at the injury site. All three of the studied genes responded quickly to injury, as early as 30 min. The induction of gene expression for neurotrophins in regions remote from areas with histopathology may reflect coupling of gene expression to neuronal excitation, which may be associated with neuroprotection and plasticity.

Expression of c-fos, junB, c-jun, MKP-1 and hsp72 following traumatic neocortical lesions in rats--relation to spreading depression

The effects of a traumatic neocortical lesion on c-fos, junB, c-jun, MKP-1 and hsp72 expression were examined by in situ hybridization and immunocytochemistry 1-6 h following transcranial cold injury. The direct current potential was recorded in the injury-remote cortex to evaluate the role of transient direct current shifts, i.e. spreading depressions, in gene expression. In 14 out of 21 injured rats, spreading depression-like depolarizations of the direct current potential were noticed, which were accompanied by a transient decrease in electroencephalographic activity and increase in laser Doppler flow. In seven injured animals, no spontaneous spreading depressions were seen. In animals without spreading depressions, only a short-lasting response of c-fos, junB, c-jun and MKP-1 messenger RNAs as well as c-Fos protein was bilaterally found in the piriform cortex, and--with ipsilateral dominance--the dentate gyrus and hippocampal CA3/4 fields at 1 h after lesioning. In injured animals with spreading depressions however, a strong elevation was seen in layers II-IV and VI of the injury-remote ipsilateral cerebral cortex, which persisted over as long as 6 h. Messenger RNA levels for c-fos, junB and MKP-1 were closely related to the time interval between the last depolarization and the end of experiment. Levels were highest shortly after transient direct current shifts, and decreased thereafter mono-exponentially with half-lives of 48, 75 and 58 min for c-fos, junB and MKP-1 messenger RNAs, respectively. In 6 h animals with spreading depressions, hsp72 messenger RNA was slightly elevated in layer II of the injury-remote cortex, but heat shock protein 72 was not increased. The present results demonstrate that spreading depression is the most prominent factor influencing the trauma-related gene response in the lesion-remote cortical tissue.

Astrocytes are the major source of nerve growth factor upregulation following traumatic brain injury in the rat

Previous studies from our group have demonstrated an upregulation in nerve growth factor (NGF) RNA and protein in the cortex 24 h following traumatic brain injury (TBI) in a rat model. This increase in NGF is suppressed if rats are subjected to 4 h of whole-body hypothermia following TBI. In the present study we used in situ hybridization to extend our initial RNA gel-blot (Northern) hybridization findings by demonstrating that NGF RNA is increased in the cortex following TBI and that hypothermia diminishes this response. Further, by combining in situ hybridization with immunocytochemistry for glial fibrillary acidic protein we demonstrate that astrocytes are the major cellular source for the upregulation in NGF and that this upregulation can be observed in the hippocampus as early as 3 h posttrauma. The predominantly astrocytic origin suggests that the NGF upregulation is not related primarily to cholinotrophic activities. We hypothesize that its function is to stimulate upregulation of antioxidant enzymes, as part of an injury-induced cascade, and that supplementation of NGF or antioxidants may be warranted in hypothermic therapies for head injury.

Transforming growth factor-beta response and expression in junctional and oral gingival epithelial cells

The junctional (JE) and oral gingival (OGE) epithelium show distinct morphological phenotypes and express different cell surface and keratin markers. Transforming growth factor-beta (TGF-beta) has been shown to stimulate extracellular matrix formation and inhibit proteolytic matrix degradation in periodontal wound healing. To elucidate potential roles of TGF-beta in gingival epithelial regeneration and reattachment, the present study examined the effects of TGF-beta on JE and OGE cell growth and determined the patterns of expression of mRNAs for the TGF-beta isotypes beta 1, beta 2 and beta 3 and TGF-beta receptor types I, II and III. Primary cell cultures were initiated from JE and OGE and the cell phenotypes confirmed using monoclonal antibodies to specific keratins. TGF-beta induced a significant growth inhibition in OGE cells derived from 6 different patients with a mean inhibition of 46% and a range of 16-70% (p = 0.031). Although responses varied between patients, in general maximum inhibition occurred at 10 ng/ml TGF-beta. JE cells from 5 patients showed no significant growth inhibition by TGF-beta (p = 0.125). Greater expression of TGF-beta 2 and receptor type I mRNA was found in OGE than JE cells and thus appeared to be associated with differentiating epithelial cells. JE cells expressed more TGF-beta type II receptor specific mRNA than did OGE cells, but TGF-beta 1 mRNA expression was similar in JE and OGE cells. JE or OGE cultures derived from 2 of 3 patients showed expression of mRNA for the TGF-beta type III receptor. TGF-beta 3 mRNA was not detected in any of the JE or OGE samples examined. The greater sensitivity of OGE than JE to the growth inhibiting effects of TGF-beta correlated with higher expression of receptor type I mRNA which, together with the type II receptor, is required for sensitivity to growth inhibition by TGF-beta. The results suggest that, in addition to structural differences, the development of functional differences in the responses of JE and OGE to TGF-beta may be associated with the formation of JE from OGE cells and the reformation of attachment after periodontal surgery.

Nerve growth factor attenuates cholinergic deficits following traumatic brain injury in rats

Traumatic brain injury (TBI) results in chronic derangements in central cholinergic neurotransmission that may contribute to posttraumatic memory deficits. Intraventricular cannula (IVC) nerve growth factor (NGF) infusion can reduce axotomy-induced spatial memory deficits and morphologic changes observed in medial septal cholinergic neurons immunostained for choline acetyltransferase (ChAT). We examined the efficacy of NGF to (1) ameliorate reduced posttraumatic spatial memory performance, (2) release of hippocampal acetylcholine (ACh), and (3) ChAT immunoreactivity in the rat medial septum. Rats (n = 36) were trained prior to TBI on the functional tasks and retested on Days 1-5 (motor) and on Day 7 (memory retention). Immediately following injury, an IVC and osmotic pump were implanted, and NGF or vehicle was infused for 7 days. While there were no differences in motor performance, the NGF-treated group had significantly better spatial memory retention (P < 0.05) than the vehicle-treated group. The IVC cannula was then removed on Day 7, and a microdialysis probe was placed into the dorsal hippocampus. After a 22-h equilibration period, samples were collected prior to and after administration of scopolamine (1 mg/kg), which evoked ACh release by blocking autoreceptors. The posttraumatic reduction in scopolamine-evoked ACh release was completely reversed with NGF. Injury produced a bilateral reduction in the number and cross-sectional area of ChAT immunopositive medial septal neurons that was reversed by NGF treatment. These data suggest that cognitive but not motor deficits following TBI are, in part, mediated by chronic deficits in cholinergic systems that can be modulated by neurotrophic factors such as NGF.

Neuronal cell loss in the CA3 subfield of the hippocampus following cortical contusion utilizing the optical disector method for cell counting

Unilateral cortical contusion in the rat results in cell loss in both the cortex and hippocampus. Pharmacological intervention with growth factors or excitatory neurotransmitter antagonists may reduce cell loss and improve neurological outcome. The window of opportunity for such intervention remains unclear because a detailed temporal analysis of neuronal loss has not been performed in the rodent cortical contusion model. To elucidate the time course of hippocampal CA3 neuronal death ensuing cortical contusion, we employed the optical disector method for assessing the total number of CA3 neurons at 1 and 6 hours, 1, 2, 10, and 30 days following injury. This stereological technique allows reporting of total cell numbers within a given region and is unaffected by change in the volume of the structure or cell size. A rapid and significant reduction in neurons/mm3 in the ipsilateral CA3 field was observed by 1 h following trauma. However, a significant increase in neurons/mm3 was seen at 30 days postinjury. This surprising finding is a result of CA3 volume shrinkage and redistribution of CA3 neurons. Utilization of the optical disector reveals that regardless of an increase in neurons/mm3 at 30 days following injury, CA3 cell loss reaches 41% of control animals by 1 day posttrauma and remains near that level at all subsequent time points examined. It is estimated that there are about 156,000 neurons in the CA3 region in control animals. By 1 h following cortical contusion the cell population decreases to 93,000 neurons indicating a very rapid cell loss. This suggests a window of less than 24 h for pharmacological intervention in order to save CA3 neurons following cortical contusion.

Differential effects of Th1 and Th2 derived cytokines on NGF synthesis by mouse astrocytes

During the course of brain injury and inflammation there is an increased secretion of neurotrophic substances by astrocytes. We have examined the effect of the Th2-derived cytokine IL-10 and the Th1-derived cytokines Il-2 and IFN-gamma on the secretion of NGF by mouse astrocytes. IL-10 induced a dose-dependent increase in NGF secretion which was blocked by anti-IL-10 antibody. In contrast, the Th1-derived cytokines IFN-gamma and IL-2 did not induce NGF synthesis. Moreover, INF-gamma completely inhibited the increase in NGF secretion induced by IL-10 whereas it had no effect on the induction of NGF by TNF-alpha. These results indicate that IL-10 similarly to other Th2-derived cytokines may provide a neurotrophic support to injured neurons via the induction of NGF synthesis, whereas the Th1-derived cytokine IFN-gamma antagonizes this effect.

Increased expression of brain-derived neurotrophic factor but not neurotrophin-3 mRNA in rat brain after cortical impact injury

Levels of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) mRNA expression were measured in a rodent model of traumatic brain injury (TBI) following unilateral injury to the cerebral cortex. To obtain reliable data on the co-expression of neurotrophin genes, adjacent coronal sections from the same rat brains were hybridized in situ with BDNF and NT3 cRNA probes. BDNF mRNA increased at 1,3, and 5 hr after unilateral cortical injury in the cortex ipsilateral to the injury site and bilaterally in the dorsal hippocampus. NT3 mRNA did not change significantly following injury. Our results suggest that TBI produces rapid increases in BDNF mRNA expression in rat brain without changes in NT3 mRNA expression, a finding which differs from studies of ischemia and seizures. It is possible that increased levels of BDNF mRNA rather than NT3 are important components of pathophysiological responses to TBI.