Combined fetal neural transplantation and nerve growth factor infusion: effects on neurological outcome following fluid-percussion brain injury in the rat

Evaluation of combined fibroblast growth factor-2 and moderate hypothermia therapy in traumatically brain injured rats

Both the exogenous administration of fibroblast growth factor-2 (FGF-2) or the induction of moderate hypothermia have been shown to attenuate histopathology and improve functional outcome after traumatic brain injury (TBI). Since combined therapeutic strategies may be more beneficial than single therapies, we examined the potential synergistic effect of FGF-2 combined with moderate hypothermia treatment induced 10 min after TBI on functional and histological outcome following controlled cortical impact (CCI) injury. Fifty male Sprague-Dawley rats were randomized to one sham and four CCI treatment groups: Sham+vehicle (VEH); FGF-2 (45 microg/kg/h for 3 h i.v.)+Normothermia (37+/-0.5 degrees C); FGF-2+Hypothermia (32+/-0.5 degrees C for 3 h); VEH+Norm; VEH+Hypo. Vestibulomotor performance on the beam balance and beam-walk (BW) tasks on post-operative days 1-5 and spatial memory acquisition in the Morris water maze (MWM) on days 14-18 were assessed. After 4 weeks survival, histological evaluations (CA(1) and CA(3) cell counts and lesion volume) were performed. MWM performance improved in all treatment groups, but combined treatment was not more efficacious than either alone. The FGF-2+Hypo group performed significantly better than the other injured treatment groups in the BW task. Lastly, no significant group differences in beam balance or histological outcome were observed. These data suggest a suboptimal and incomplete synergy of combined FGF-2 and hypothermia treatment. These data may indicate that either our dose of FGF-2 or combination therapy was not optimized in our model.

Cell delivery to the central nervous system

A dysfunctional central nervous system (CNS) resulting from neurological disorders and diseases impacts all of humanity. The outcome presents a staggering health care issue with a tremendous potential for developing interventive therapies. The delivery of therapeutic molecules to the CNS has been hampered by the presence of the blood-brain barrier (BBB). To circumvent this barrier, putative therapeutic molecules have been delivered to the CNS by such methods as pumps/osmotic pumps, osmotic opening of the BBB, sustained polymer release systems and cell delivery via site-specific transplantation of cells. This review presents an overview of some of the CNS delivery technologies with special emphasis on transplantation of cells with and without the use of polymer encapsulation technology.

Terminally differentiated human neurons survive and integrate following transplantation into the traumatically injured rat brain

The present study evaluated the survival and integration of human postmitotic neurons (hNT) following transplantation into the traumatically injured rodent brain. Anesthetized male Sprague-Dawley rats (n = 47) were subjected to lateral fluid percussion brain injury of moderate severity (2.4-2.6 atm). Sham animals (n = 28) were surgically prepared, but did not receive brain injury. At 24 h following injury or sham surgery, the rats were re-anesthetized and approximately 100,000 hNT cells (freshly cultured or previously frozen) or vehicle were stereotactically injected into the ipsilateral cortex. Animals were examined for neuromotor function at 48 h, 7 days, and 14 days posttransplantation using a standard battery of motor tests. Animals were sacrificed at 2 weeks postinjury and viability of hNT grafts was assessed by Nissl staining and MOC-1 immunohistochemistry, which recognizes human neural cell adhesion molecules (NCAM) expressed on hNT cells. Transplanted hNT grafts remained viable in 83% of brain-injured animals at 2 weeks following transplantation of either fresh or frozen hNT cells. Glial fibrillary acidic protein (GFAP) immunohistochemistry revealed a marked increase in the number of reactive astrocytes following brain injury in both vehicle and hNT implanted animals. These reactive astrocytes appeared not to impede grafted cells from sending projections into host tissue. Despite the survival of transplanted cells in the traumatically injured brain, hNT cells had no significant effect on posttraumatic neurologic motor function during the acute posttraumatic period. Since hNT cells are transfectable, prolonged survival of these transplanted cells in the posttraumatic milieu suggests that grafted hNT cells may be a suitable means for delivery of therapeutic, exogenous proteins into the CNS for treatment of traumatic brain injury.

Survival and integration of transplanted postmitotic human neurons following experimental brain injury in immunocompetent rats

OBJECT

Limitations regarding cell homogeneity and survivability do not affect neuronlike hNT cells, which are derived from a human teratocarcinoma cell line (Ntera2) that differentiates into postmitotic neurons with exposure to retinoic acid. Because NT2N neurons survive longer than 1 year after transplantation into nude mice brains, the authors grafted these cells into the brains of immunocompetent rats following lateral fluid-percussion brain injury to determine the long-term survivability of NT2N cell grafts in cortices damaged by traumatic brain injury (TBI) and the therapeutic effect of NT2N neurons on cognitive and motor deficits.

METHODS

Seventy-two adult male Sprague-Dawley rats, each weighing between 340 and 370 g, were given an anesthetic agent and subjected to lateral fluid percussion brain injury of moderate severity (2.2-2.5 atm in 46 rats) or to surgery without TBI (shamoperation, 26 rats). Twenty-four hours postinjury, 10(5) NT2N cells (24 injured animals) or 3 microl of vehicle (22 injured and 14 control animals) was stereotactically implanted into the periinjured or control cerebral cortex. Motor function was assessed at weekly intervals and all animals were killed at 2 or 4 weeks after their posttraumatic learning ability was assessed using a Morris water maze paradigm. Viable NT2N grafts were routinely observed to extend human neural cell adhesion molecule-(MOC-1)immunoreactive processes into the periinjured cortex at 2 and 4 weeks posttransplantation, although no significant improvement in motor or cognitive function was noted. Inflammation identified around the transplant at both time points was assessed by immunohistochemical identification of macrophages (ED-1) and microglia (isolectin B4).

CONCLUSIONS

Long-term survival and integration of NT2N cells in the periinjured cortex of immunocompetent rats provides the researcher with an important cellular system that can be used to study maturation, regulation, and neurite outgrowth of transplanted neurons following TBI.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Craniocerebral trauma: protection and retrieval of the neuronal population after injury

OBJECTIVE

To review the consequences of mechanical injury to the brain with an emphasis on factors that may explain the variability of outcomes and how this might be influenced.

METHODS

Information regarding the pathophysiology of traumatic brain damage contained in original scientific reports and in review articles published in recent years was reviewed from the perspective of a clinical neurosurgeon and a neuropathologist, each with major research interests in traumatic brain damage. The information was compiled on the basis of the knowledge of and personal selection of articles that were identified through selective literature searches and current awareness profiles. A systematic literature review was not conducted.

RESULTS

Mechanical input affects neuronal and vascular elements and is translated into biological effects on the brain through a complex series of interacting cellular and molecular events. Whether these lead to permanent structural damage or to resolution and recovery is determined by the balance between processes that, on the one hand, mediate the effects of initial injury and subsequent secondary insults and, on the other, are manifestations of the brain's protective, reparative response. Experimental and clinical research has identified opportunities for altering the balance in a way that might promote recovery, but data demonstrating that this can lead to substantial clinical benefit are lacking. Recent evidence of genetically determined, individual susceptibility to the effects of injury may explain some of the puzzling variability in outcome after apparently similar insults and may also provide new opportunities for treatment.

CONCLUSION

The understanding of traumatic brain damage that is being gained from recent research is widening and broadening perspectives from the traditional focus on mechanical, vascular, and metabolic effects to encompass wider, neurobiological issues, drawn from the fields of neurodevelopment, neuroplasticity, neurodegeneration, and neurogenetics. Neurotrauma is a fascinating area of neuroscience research, with promise for the translation of knowledge to improved clinical management and outcome.

The Dorothy Russell Memorial Lecture. The molecular and cellular sequelae of experimental traumatic brain injury: pathogenetic mechanisms

The mechanisms underlying secondary or delayed cell death following traumatic brain injury (TBI) are poorly understood. Recent evidence from experimental models of TBI suggest that diffuse and widespread neuronal damage and loss is progressive and prolonged for months to years after the initial insult in selectively vulnerable regions of the cortex, hippocampus, thalamus, striatum, and subcortical nuclei. The development of new neuropathological and molecular techniques has generated new insights into the cellular and molecular sequelae of brain trauma. This paper will review the literature suggesting that alterations in intracellular calcium with resulting changes in gene expression, activation of reactive oxygen species (ROS), activation of intracellular proteases (calpains), expression of neurotrophic factors, and activation of cell death genes (apoptosis) may play a role in mediating delayed cell death after trauma. Recent data suggesting that TBI should be considered as both an inflammatory and/or a neurodegenerative disease is also presented. Further research concerning the complex molecular and neuropathological cascades following brain trauma should be conducted, as novel therapeutic strategies continue to be developed.

Intracerebral fetal raphé implants normalize hippocampal function but not cerebrovascular control in serotonin-depleted adult rat brain

The effects of hypercapnia upon local cerebral blood flow and local cerebral glucose utilization were measured by quantitative autoradiography in parallel groups of rats (six per group) which 14-16 weeks previously had been treated with the serotonergic neurotoxin, methylenedioxymethamphetamine, followed by implantation of fetal raphé or basal forebrain tissues. Following the experiments, transplants were visualized by acetylcholinesterase histochemistry, and serotonergic reinnervation assessed using [3H]paroxetine binding to serotonin reuptake sites. In methylenedioxymethamphetamine-treated rats, contralateral to the implants, [3H]paroxetine binding was reduced by between 50 and 90% in the neocortex and hippocampus. Hippocampal glucose utilization was significantly increased in these rats, and the normal increase in flow which accompanies hypercapnia was also significantly enhanced. High levels of [3H]paroxetine binding were found within the raphé transplants (308 +/- 13 fmol/mg tissue). In host brain adjacent to the implant, binding levels were normalized, and in these same areas glucose utilization was also normalized. Basal forebrain implants had no effect upon either [3H]paroxetine binding or glucose utilization. Raphé transplants did not, however, alter the enhanced cerebrovascular response to hypercapnia induced by methylenedioxymethamphetamine, even in those areas where there was evidence of serotonergic reinnervation. The transplants also showed the same enhanced response. In conclusion, intracerebral fetal raphé implants normalize hippocampal function but not cerebrovascular control in serotonin-depleted adult rat brain, and despite not sharing the serotonergic deficit, blood flow in the implants follows that of the dysfunctional host.

Central nervous system resuscitation

Traumatic injury to the central nervous system induces delayed neuronal death, which may be mediated by acute and chronic neurochemical changes. Experimental identification of these injury mechanisms and elucidation of the neurochemical cascade following trauma may provide enhanced opportunities for treatment with novel neuroprotective strategies.

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.

The status and organization of astrocytes, oligodendroglia and microglia in grafts of fetal rat cerebral cortex

Immunohistochemical methods were used to study the status and organization of astrocytes, oligodendroglia and microglia in fetal cerebral cortical tissue grafted on to the dorsal surface of the midbrain in newborn host rats. Grafts were examined 1-6 months posttransplantation. All grafts contained large numbers of hypertrophied, intensely glial fibrillary acidic protein-positive astrocytes. Microglia were also activated, displaying slightly increased levels of OX-42 immunoreactivity. The grafts consisted of lobules of gray matter which were separated by bands of myelinated fibres associated with large numbers of Rip-positive oligodendroglia. These glial cells had a relatively normal morphology. The density of astrocytes and microglia was reduced in these white matter-like regions. In association with chronic changes in glial reactivity, transplants also expressed increased levels of chondroitin sulphate proteoglycans (CS-56 antibody). The observed changes in glial cell phenotype and extracellular matrix in cortical transplants are likely to affect neuronal physiology and connectivity in a number of ways, and highlight the importance of studying both glia and neurons in order to gain a more comprehensive picture of the long-term functional potential of fetal brain grafts.

Improvement of cognitive deficits and decreased cholinergic neuronal cell loss and apoptotic cell death following neurotrophin infusion after experimental traumatic brain injury

This study explores the effects of infusion of nerve growth factor (NGF) on behavioral outcome and cell death in the septal region using the clinically relevant model of fluid-percussion brain injury in the rat. Animals were subjected to fluid-percussion brain injury and 24 hours later a miniosmotic pump was implanted to infuse NGF (12 animals) or vehicle (12 animals) directly into the region of maximum injury for 2 weeks. Four weeks postinjury the animals were tested for cognitive function using a Morris Water Maze paradigm. Neurological motor function was evaluated over a 4-week postinjury period. The rats receiving NGF infusions had significantly higher memory scores than vehicle-treated animals. Examination of the cholinergic neurons in the medial septal region using choline acetyltransferase immunohistochemistry demonstrated significant cell loss after injury. Infusion of NGF significantly attenuated loss of these cholinergic neurons. A second group of animals was subjected to fluid-percussion brain injury alone (23 rats) or injury followed by NGF infusion (18 rats). These animals were killed between 24 hours and 2 weeks postinjury and the septal region was examined for the presence of apoptotic cells using the terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridinetriphosphate nick-end labeling technique. Apoptotic cells were identified as early as 24 hours postinjury; their numbers peaked at 4 and 7 days, and then declined by 14 days. The NGF-treated animals had some apoptotic cells; however, even at 7 days there were significantly fewer of these cells. No significant motor differences were observed between the NGF- and vehicle-treated groups. These data indicate that NGF administration beginning 24 hours after fluid-percussion brain injury has a beneficial effect on cognition and results in sparing of cholinergic septal neurons. These improvements persist after cessation of NGF administration. The beneficial effects of NGF may be related to its ability to attenuate traumatically induced apoptotic cell death.

Fluid percussion injury causes disruption of the septohippocampal pathway in the rat

Fluid percussion injury (FPI) causes memory deficits, loss of hippocampal neurons, and basal forebrain cholinergic immunoreactivity in rats. Basal forebrain septohippocampal projections terminate in specific hippocampal regions. The purpose of this study was to examine the effects of FPI on the septohippocampal pathway (SHP). Halothane-anesthetized rats received either a sham injury or a parasagittal FPI. To characterize the anatomical effects of FPI on the SHP, silver stains were performed on brains of animals at 1, 5, and 10 days following FPI and were compared to sham-injured preparations. To characterize the effects of FPI on retrograde transport in the SHP, a separate group of FPI and sham-injured animals with survival times of 2, 5, and 10 days received bilateral WGA-HRP injections into the hippocampal formation 24 h prior to sacrifice. Argyrophilic CA3 neurons were present 1 day following FPI. Five days following FPI, terminal degeneration was present in the inner third of the molecular layer of the dentate gyrus bilaterally that was not present 1 day after injury. Fiber and terminal degeneration was not observed in the basal forebrain until 10 days after FPI. WGA-HRP-labeled septal neurons decreased significantly (P < 0.05) ipsilateral to injury in animals sacrificed 5 and 10 days following FPI but not 2 days after injury. This investigation demonstrated that FPI produces focal injury in the hippocampal formation. In addition, the appearance of terminal degeneration in the dentate molecular layer correlated with the significant reduction in axonal transport 5 days following injury. This correlation illustrates the secondary processes that structurally damage the SHP up to 10 days after injury.