Diffusion-Weighted Imaging of Edema following Traumatic Brain Injury in Rats: Effects of Secondary Hypoxia

Hypoxia and edema are frequent and serious complications of traumatic brain injury (TBI). Therefore, we examined the effects of hypoxia on edema formation after moderate lateral fluid percussion (LFP) injury using NMR diffusion-weighted imaging (DWI). Adult Sprague-Dawley rats were separated into four groups: sham uninjured (S), hypoxia alone (H), trauma alone (T), and trauma and hypoxia (TH). Animals in Groups T and TH received LFP brain injury, with Groups H and TH undergoing 30 min of moderately severe hypoxia (FiO2 = 0.11) immediately after surgery or TBI (respectively). DWIs were obtained at 2, 4, and 24 h and at 1 week post injury, and apparent diffusion coefficient (ADC) maps were constructed. Animals in Groups T and TH showed an early decrease (p < 0.001) in ADC values in the cortex ipsilateral to TBI 4 hr post injury, followed by elevated ADCs 1 week later (p < 0.05). No significant differences in ADC values were seen between T and TH groups in the ipsilateral cortex. In contrast, the ipsilateral hippocampus for Group TH showed only increasing ADC values. This hyperintensity in the ADC map began at 2 h after TBI, was significant by 24 h (p < 0.05), and reached a maximum at 1 week. This hyperintensity was not observed in Group T. Histopathology seen in TBI animals corresponded well with the pathology observed with MRI. Midline shifts reflecting edema were only observed in TBI animals with little difference between normoxic (T) and hypoxic animals (TH). In sum, this study demonstrates that the development and extent of brain edema following TBI can be examined in vivo in rats using DWI technology. TBI resulted in an early decrease in ADC values indicating cytotoxic edema in the cortex that was followed at 1 week by an increase in the ADC that was associated with decreased tissue cellularity. Histopathology corresponded well to the regions of brain injury and edema visualized by T2 and DWI procedures. Overall, the addition of hypoxia to brain injury resulted in a small increase in the magnitude of edema in hippocampus and cortex over that seen with trauma alone.

The effect of groups II and III metabotropic glutamate receptor activation on neuronal injury in a rodent model of traumatic brain injury

OBJECTIVE

The role of metabotropic glutamate receptor activation after traumatic brain injury (TBI) is not well understood. In vitro studies suggest that activation of Groups II and III metabotropic glutamate receptors may provide some degree of neuroprotection and may be potential targets for the development of therapeutic strategies. Thus, we examined the effects of Group II and Group III selective agonists on neuronal degeneration after in vivo TBI.

METHODS

Fifty male Sprague-Dawley rats were subjected to lateral fluid percussion brain injury immediately followed by an intracranial injection of 2-(2',3')-dicarboxycyclopropylglycine (DCG-IV) (Group II) or (R,S)-4-phosphonophenylglycine (Group III) in the CA2 and CA3 areas of the hippocampus. DCG-IV was injected at doses of 20 fmol, 100 fmol, and 500 fmol, and (R,S)-4-phosphonophenylglycine was injected at 8 nmol, 40 nmol, and 200 nmol. Vehicle injection control groups were used for comparison with each drug group. All animals were killed 24 hours after TBI was induced. Four 50-microm brain sections were obtained from each animal and stained for degenerating neurons with the fluorochrome Fluoro-Jade. Two independent, blinded investigators counted the number of degenerating (Fluoro-Jade-positive) neurons in the CA2 and CA3 areas of the hippocampus of each brain section.

RESULTS

Compared with vehicle, the 500-fmol dose of DCG-IV significantly reduced the number of Fluoro-Jade-positive degenerating neurons (P < 0.001). Lower doses of DCG-IV were associated with a decreased but not statistically significant number of Fluoro-Jade-positive neurons. In contrast, (R,S)-4-phosphonophenylglycine had no significant effect on the number of degenerating neurons.

CONCLUSION

Administration of selective Group II metabotropic glutamate receptor agonists protects neurons against in vivo TBI. These receptors may thus be a promising target for future neuroprotective drugs.

Group I metabotropic glutamate antagonist reduces acute neuronal degeneration and behavioral deficits after traumatic brain injury in rats

Recent studies indicate that acute activation of Group I mGluRs following traumatic brain injury (TBI) contributes to the ensuing pathophysiology. The present study examined the effects of post-TBI administration of the selective mGluR1 antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) on acute neuronal degeneration in the hippocampus and long-term sensorimotor and learning/memory outcome. In Experiment 1, 26 rats received 0.4, 2.0, or 10.0 nmol AIDA or artificial CSF vehicle infusion into the hippocampus starting 5 min postinjury. At 24 h after TBI characteristic pyramidal cell degeneration was observed in Fluoro-Jade-stained coronal sections of the CA2/3 sectors of the dorsal hippocampus. The mean (+/-SEM) number of Fluoro-Jade-positive neurons in the 10 nmol AIDA group (184 +/- 32) was significantly less (P < 0.05) than the vehicle group (310 +/- 47). In Experiment 2, 20 rats were trained on sensorimotor and memory tasks prior to parasagittal fluid percussion TBI. Rats were administered 10 nmol AIDA or vehicle as in Experiment 1. Rats were assessed on beam walking and radial arm maze (RAM) performance weekly for 6 weeks after TBI. Acquisition of a Morris water maze (MWM) task was assessed on days 11-15 after TBI. The AIDA-treated group had significantly reduced deficits in beam walk, MWM, and RAM performance compared to the vehicle-treated group. These data indicate that injury-induced acute activation of mGluR1 receptors contributes to both the cellular pathology and the behavioral morbidity associated with TBI.

Subtle alterations in NMDA-stimulated cyclic GMP levels following lateral fluid percussion brain injury

This study examined whether NMDA-stimulated cyclic GMP levels were altered at two different time points following lateral fluid percussion injury. At 60 min and 15 days postinjury, the left and right hippocampi were dissected and chopped into mini-prisms. Each hippocampus was divided into five equal parts and incubated with either the phosphodiesterase inhibitor IBMX (3-isobutyl-1-methylxanthine, 500 microM) alone, IBMX and N-methyl-D-aspartic acid (NMDA) OR IBMX, NMDA, and glycine (10 MM). Two concentrations of NMDA were used: 500 or 1,000 microM. Tissues were then assayed for levels of cyclic GMP. Results indicated that there were no changes in basal levels of cyclic GMP at either postinjury time point. At 60 min postinjury, there were no significant main effects for injury or drug concentration. There was a significant injury x side interaction effect with increased levels of NMDA-stimulated cyclic GMP in the hippocampus ipsilateral to the injury impact and decreased cyclic GMP levels in the contralateral hippocampus. There were no significant alterations in NMDA-stimulated cyclic GMP levels at 15 days postinjury. The data from this study indicated that NMDA-stimulated cyclic GMP accumulation is differentially altered in the hippocampus ipsilateral and contralateral to the site of the injury at 1 h after injury, but is normalized by 15 days postinjury. These findings implicate NMDA-mediated intracellular signaling processes in the acute excitotoxic response to injury.

Dicyclomine, an M1 muscarinic antagonist, reduces infarct volume in a rat subdural hematoma model

The rat subdural hematoma (SDH) model produces a zone of ischemic brain damage within the hemisphere beneath the SDH. Previous studies have measured large increases in extracellular acetylcholine during cerebral ischemia in the rat. We examined infarct volume after selectively blocking muscarinic M1 receptors with dicyclomine during SDH. Rats were anesthetized with isoflurane (2%), intubated, and femoral artery and vein cannulated. Autologous blood (0.375 ml) was injected (0.05 ml/min) under the dura of the right parietal cortex. Dicyclomine (5 mg/kg, i.v.) was injected at 5 min after and again at 2 h after completion of the subdural blood infusion. Blood pressure and intracranial pressure (ICP) were continuously measured. At 4 h after SDH rats were euthanized, brains sectioned, and immunoreacted with glia fibrillary acidic protein. Cortical infarct volume was quantified in coronal brain sections at 0.7-mm intervals from +1.0 mm to -3.9 mm relative to bregma. Infarct volume in drug-treated rats (n = 10) 22.1 +/- 6.99 mm3 was significantly smaller (p < 0.02) than vehicle treated rats (n = 10) 56.7 +/- 9.59 mm3. ICP, blood pressure and cerebral perfusion pressure were not significantly different between groups. These data suggest that activation of M1 muscarinic receptors during an ischemic event may contribute to the development of subsequent pathology.

ICP monitoring in the rat: comparison of monitoring in the ventricle, brain parenchyma, and cisterna magna

Various methods of continuous intracranial pressure (ICP) monitoring during experimental procedures in the rat have been described. However, no systematic comparison of ICP monitoring in the ventricle, brain parenchyma, and cisterna magna has been reported. Since accurate and reliable ICP measurements are important in experimental models of traumatic brain injury, the present study was conducted to compare simultaneous ICP measurements from ventricular, cisterna magna, and intraparenchymal monitors during ICP changes. Subdural hematoma was produced by infusion of 0.3 ml of autologous blood into the subdural space over 6 min. The ventricular and the intraparenchymal fiberoptic catheter produced reliable and comparable pressure recordings, that did not statistically differ (p = 0.4), throughout the one hour monitoring time. In contrast, the cisterna magna catheter was less reliable and produced significantly lower readings throughout the monitoring time (p<0.001). The intraparenchymal device produced greater cortical damage than the ventricular catheter. In conclusion, ventricular ICP monitoring is the preferred method under these circumstances, since it is accurate and induces least brain damage.

Metabotropic glutamate receptor protein alterations after traumatic brain injury in rats

Glutamate toxicity, mediated via ion channel-linked receptors, plays a key role in traumatic brain injury (TBI) pathophysiology. Excessive glutamate release after TBI also activates protein G-linked metabotropic glutamate receptors (mGluRs). We performed Western blot and immunohistochemical analysis with antibodies for group 1 and 2 mGluRs in hippocampal and cortex tissue at 7 and 15 days after lateral fluid-percussion TBI in rats. Protein homogenates of brain tissue were separated on 7.5% sodium dodecyl sulfate (SDS)-polyacrylamide gels, transferred to nitrocellulose, and incubated with either antibodies recognizing both mGluR2 and mGluR3 or antibodies against mGluR5. Equivalent protein loading of lanes was confirmed by using beta-actin antibody. Immunoreactive proteins were revealed with enhanced chemiluminescence and relative optical density of Western blots quantified by computerized image analysis. At 7 days after TBI, mGluR2/3 immunobinding ipsilateral to the fluid-percussion injury was reduced by 28% in hippocampus and 25% in cortex in comparison with the contralateral hemisphere (p < .05). mGluR5 immunobinding ipsilateral to the fluid-percussion injury was reduced by 20% in hippocampus and 27% in cortex (p < .05). At 15 days after TBI, the decreases in immunobinding were no longer significant. Immunohistochemical staining with the same antibodies revealed density changes congruent with the Western blot results. These data suggest that TBI produces an alteration in receptor protein expression that spontaneously recovers by 15 days after injury.

Current status of neuroprotection trials for traumatic brain injury: lessons from animal models and clinical studies

Laboratory studies have identified numerous potential therapeutic interventions that might have clinical application for the treatment of human traumatic brain injury. Many of these therapies have progressed into human clinical trials in severe traumatic brain injury. Numerous trials have been completed, and many others have been prematurely terminated or are currently in various phases of testing. The results of the completed Phase III trials have been generally disappointing, compared with the expectations produced by the successes of these interventions in animal laboratory studies. In this review, we summarize the current status of human traumatic brain injury clinical trials, as well as the animal laboratory studies that led to some of these trials. We summarize criteria for conducting clinical trials in severe traumatic brain injury, with suggestions for future improvements. We also attempt to identify factors that might contribute to the discrepancies between animal and human trials, and we propose recommendations that could help investigators avoid certain pitfalls in future clinical trials in traumatic brain injury.

Combined therapy affects outcomes differentially after mild traumatic brain injury and secondary forebrain ischemia in rats

Muscarinic and NMDA receptors contribute to post-traumatic hypersensitivity to secondary ischemia. However, the effect of these receptor antagonists on behavior and CA1 neuronal death after traumatic brain injury (TBI) with acute (1 h after TBI) forebrain ischemia has not been systematically assessed. We examined cognitive and motor dysfunction and the relationship of behavior deficits to neuronal death in this model using muscarinic and NMDA antagonists. Three behavioral groups (n=10/group) of Wistar rats were subjected to mild TBI and 6 min of forebrain ischemia imposed 1 h after TBI with 45 days survival. Motor and spatial memory performance were assessed using the rotarod task and Morris water maze. Seven additional groups (n=6/group) were evaluated only for CA1 death after 7 days survival following sham, individual or combined injury with and without drug treatments. Rats were given 0.3 mg/kg MK-801 (M) and 1.0 mg/kg scopolamine (S) alone or combined (M-S) before or 45 min after TBI. Rotarod performance was tested at days 1-5 and maze performance on days 11-15 and 40-44 after M-S treatment. The 7-day studies showed M-S treatment (p<0.01) reduced CA1 neuronal death better than either S or M alone. Behavioral groups had inadvertent post-ischemic hypothermia that decreased CA1 death and likely influenced behavioral morbidity. M-S given before TBI (p<0.01) decreased memory deficits on day 15, while M-S treatment given after TBI was ineffective. Unexpectedly, M-S treatment before or after TBI produced transient motor deficits (p<0. 01). Memory improvement occurred independent of CA1 death.

Status epilepticus causes long-term NMDA receptor-dependent behavioral changes and cognitive deficits

PURPOSE

The role of N-methyl-D-aspartate (NMDA)-receptor activation on behavioral and cognitive changes after status epilepticus (SE) is unknown. In this study, behavioral and cognitive changes after SE were evaluated in the short and long term and in rats in which the NMDA receptor was inactivated during SE.

METHODS

Pilocarpine (350 mg/kg) was injected to induce SE. Inhibition of the NMDA receptor during SE was achieved with MK-801 (4 mg/kg). Seizure intensity during SE was monitored by electroencephalography (EEG). After SE, behavioral studies were performed to identify abnormal behavior by using behavioral tests adapted from Moser's functional observational battery. Cognitive changes were assessed by using the Morris Water Maze (MWM).

RESULTS

Pilocarpine-treated animals scored significantly higher on two of the behavioral tests: the Touch test and the Pick-Up test. These behavioral changes occurred very soon after SE, with the earliest changes observed 2 days after SE and persisting for the life of the animal. Inhibition of the NMDA receptor with MK-801 completely inhibited these behavioral changes under conditions that did not alter the duration of SE. In addition, pilocarpine-treated animals exhibited cognitive deficits as determined by using the MWM. Six weeks after SE, the animals displayed significantly longer latencies to locate the hidden platform on this test. The impaired performance on the MWM also occurred as early as 5 days after SE. These cognitive deficits were prevented in animals treated with MK-801 during SE.

CONCLUSIONS

The results indicate that behavioral and cognitive changes occur soon after SE, are permanent, and are dependent on NMDA-receptor activation during SE. NMDA-receptor activation may play an important role in causing cognitive and behavioral morbidity after recovery from SE.

Glutamate antagonism during secondary deafferentation enhances cognition and axo-dendritic integrity after traumatic brain injury

The combination of central fluid percussion traumatic brain injury (TBI) followed 24 h later by a bilateral entorhinal cortical deafferentation (BEC) produces profound cognitive morbidity. We recently showed that MK-801 given prior to TBI in this insult improved spatial memory for up to 15 days. In the present study we examine whether MK-801 treatment of the BEC component in the combined insult model affects cognitive recovery. Two strategies for drug treatment were tested. Fifteen minutes prior to the BEC lesion in the combined insult, rats were given i.p. doses of either 3 mg/kg (acute group) or 1 mg/kg (chronic group) MK-801. The acute group received no further injections, whereas the chronic group received 1 mg/kg MK-801 i.p. twice a day for 2 days post-BEC lesion. Two additional groups of animals received BEC lesion alone and either acute or chronic MK-801 treatment identical with the combined insult cases. Each group was then assessed for spatial memory deficits with the Morris water maze at days 11-15 and 60-64 postinjury. Both acute and chronic MK-801 treatment in the combined insult group significantly reduced spatial memory deficits at 15 days postinjury relative to untreated injured cases (P < .01). This reduction appeared more robust at 15 days and persisted for up to 64 days in the chronically treated group (P < .05). By contrast, neither acute nor chronic MK-801 treatment affected memory performance with the BEC insult alone. Immunocytochemical localization of parvalbumin showed that chronic administration of MK-801 in the combined insult cases attenuated the injury-induced dendritic atrophy of inhibitory neurons in the dentate gyrus and area CA1. Synaptophysin immunobinding revealed that chronic MK-801 treatment of the BEC component of the combined insult normalized the distribution of presynaptic terminals within the dentate gyrus. These results suggest that cognitive deficits produced by head trauma involving both neuroexcitation and deafferentation can be attenuated with chronic application of glutamatergic antagonists during the period of deafferentation injury and that this attenuation is correlated with axo-dendritic integrity.

Effect of tetrahydroaminoacridine, a cholinesterase inhibitor, on cognitive performance following experimental brain injury

An emerging literature exists in support of deficits in cholinergic neurotransmission days to weeks following experimental traumatic brain injury (TBI). In addition, novel cholinomimetic therapeutics have been demonstrated to improve cognitive outcome following TBI in rats. We examined the effects of repeated postinjury administration of a cholinesterase inhibitor, tetrahydroaminoacridine (THA), on cognitive performance following experimental TBI. Rats were either injured at a moderate level of central fluid percussion TBI (2.1+/-0.1 atm) or were surgically prepared but not delivered a fluid pulse (sham injury). Beginning 24 h after TBI or sham injury, rats were injected (IP) daily for 15 days with an equal volume (1.0 ml/kg) of either 0.0, 1.0, 3.0, or 9.0 mg/kg THA (TBI: n = 8, 8, 10, and 7, respectively, and Sham: n = 5, 7, 8, 7, respectively). Cognitive performance was assessed on Days 11-15 after injury in a Morris water maze (MWM). Analysis of maze latencies over days indicated that chronic administration of THA produced a dose-related impairment in MWM performance in both the injured and sham groups, with the 9.0 mg/kg dose producing the largest deficit. The 1.0 and 3.0 mg/kg doses of THA impaired MWM performance without affecting swimming speeds. Thus, the results of this investigation do not support the use of THA as a cholinomimetic therapeutic for the treatment of cognitive deficits following TBI.

Effect of prior receptor antagonism on behavioral morbidity produced by combined fluid percussion injury and entorhinal cortical lesion

We have used an animal model of traumatic brain injury (TBI) that incorporates both the neurotransmitter toxicity of fluid percussion TBI and deafferentation of bilateral entorhinal cortical (BEC) lesion to explore whether administration of muscarinic cholinergic or N-methyl-D-aspartate glutamatergic antagonists prior to injury ameliorates cognitive morbidity. Fifteen minutes prior to moderate central fluid percussion TBI, rats were given intraperitoneal injections of either scopolamine (1.0 mg/kg) or MK-801 (0.3 mg/kg) and 24 hr later underwent BEC lesion. Body weight was followed for 5 days postinjury, as was beam balance and beam walk performance to assure motor recovery prior to spatial memory testing. Each group was assessed for spatial memory deficits with the Morris water maze at short term (days 11-15) and long-term (60-64 days) postinjury intervals and then compared with untreated combined insult and sham-injured controls. Results showed that each drug significantly elevated body weight relative to untreated injured cases. Both scopolamine and MK-801 reduced beam balance deficits, whereas neither drug had a significant effect on beam walk deficits. Interestingly, short-term cognitive deficits assessed on days 11-15 were differentially affected by the two drugs: MK-801 pretreatment enhanced the recovery of spatial memory performance, whereas scopolamine pretreatment did not. Long-term (days 60-64) deficits in spatial memory were not altered by pretreatment with either drug. Our results suggest that, unlike fluid percussion TBI alone, behavioral impairment may require more select intervention when deafferentation is part of the head trauma pathology.

The effects of traumatic brain injury on inhibition in the hippocampus and dentate gyrus

Changes in inhibitory neuronal functioning may contribute to morbidity following traumatic brain injury (TBI). Evoked responses to orthodromic paired-pulse stimulation were examined in the hippocampus and dentate gyrus at 2 and 15 days following lateral fluid percussion TBI in adult rats. The relative strength of inhibition was estimated by measuring evoked paired pulses in three afferent systems: the CA3 commissural input to the CA1 region of the hippocampus; the entorhinal cortical input to the ipsilateral CA1 area (temporoammonic system); and the entorhinal input to the ipsilateral dentate gyrus (perforant path). In addition to quantitative electrophysiological estimates of inhibitory efficacy, levels of gamma-aminobutyric acid (GABA) were qualitatively examined with immunohistochemical techniques. Effects of TBI on paired-pulse responses were pathway-specific, and dependent on time postinjury. At 2 days following TBI, inhibition of population spikes was significantly reduced in the CA3 commissural input to CA1, which contrasted with injury-induced increases in inhibition in the dentate gyrus seen at both 2 and 15 days postinjury. Low-level stimulation, subthreshold for population spikes, also revealed changes in paired-pulse facilitation of field extracellular postsynaptic potentials (fEPSPs), which depended on fiber pathway and time postinjury. Significant injury-induced electrophysiological changes were almost entirely confined to the hemisphere ipsilateral to injury. Intensity of GABA immunobinding exhibited a regional association with electrophysiological indices of inhibition, with the most pronounced increases in GABA levels and inhibition found in the dentate gyrus. TBI-induced effects showed a regional pattern within the hippocampus which corresponds closely to inhibitory changes reported to follow ischemia and kindling. This degree of similarity in outcome following dissimilar injuries may indicate common mechanisms in the nervous system response to injury.

Inhibition of nitric oxide synthase potentiates hypertension and increases mortality in traumatically brain-injured rats

We examined the effects of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), on mortality, morbidity, and cardiovascular parameters following traumatic brain injury (TBI) in the rat. Rats were anesthetized with 2% isoflurane prior to moderate (2.0 atmosphere), central fluid percussion TBI. Temporalis muscle temperature was maintained at 37 +/- 0.5 degrees C. L-NAME (10 mg/kg iv) was administered once at either 5 min before, 5 min after, or 15 min after TBI. Sensorimotor deficits and spatial learning/ memory deficits were assessed after injury. Separate groups of rats were monitored for cardiovascular parameters. Preinjury administration of L-NAME significantly increased mortality from 13 (vehicle) to 70% (associated with pulmonary edema), whereas postinjury, L-NAME had no effect on mortality (14 and 25%). L-NAME administered at 5 or 15 min after injury had no significant effect on motor performance or cognitive performance deficits associated with TBI. L-NAME in uninjured rats increased arterial blood pressure by 25 mmHg within 2 min. L-NAME injected 5 min before TBI greatly prolonged the hypertensive episode associated with TBI (1 min in vehicle vs 60 min in L-NAME). L-NAME injected 5 min after TBI caused a sustained 35 mmHg increase in blood pressure. These findings suggest that acute inhibition of NOS has detrimental consequences on mortality that may be owing to its cardiovascular effects.

Effects of muscarinic receptor antagonism on the phosphatidylinositol bisphosphate signal transduction pathway after experimental brain injury

Hippocampal levels of fatty acids extracted from phosphatidylinositol 4,5-bisphosphate (PIP2), free fatty acids (FFA), and lactate were measured after central fluid percussion traumatic brain injury (TBI) in rats. At 5 min after injury, there was a decrease in fatty acids extracted from PIP2 suggesting a decrease in PIP2. At the same time point, total FFA increased in saline-treated TBI rats. Levels of arachidonic acid were significantly decreased in PIP2, while at the same time arachidonic and stearic acids increased in FFA in saline-treated TBI rats. No significant alterations in PIP2-derived fatty acids or FFA were observed at 20 min after TBI. Hippocampal concentrations of lactate were significantly elevated at 5 and 20 min after injury in saline-treated rats. In general, these alterations were blunted by preinjury administration of the muscarinic antagonist, scopolamine. These results suggest that the PIP2 signal transduction pathway is activated in the hippocampus at the onset of central fluid percussion TBI and that the enhanced phospholipase C-catalyzed phosphodiestric breakdown of PIP2 is a major mechanism of liberation of FFA in these sites immediately after such injury. The blunting of PIP2 and FFA alterations in animals treated with scopolamine suggests that activation of muscarinic receptors significantly contributes to the phospholipase C (PLC) signal transduction pathophysiology in TBI. The attenuation of lactate accumulation in scopolamine-treated rats suggests that TBI-induced muscarinic receptor activation also contributes to increased glycolytic metabolism and/or ionic imbalances.

Brain injury-induced enhanced limbic epileptogenesis: anatomical and physiological parallels to an animal model of temporal lobe epilepsy

Traumatic brain injury (TBI) is a leading cause of symptomatic epilepsy in young adults. This study examined physiological and anatomical epileptogenic consequences of a prior incident of TBI in rats. Rats were subjected to a fluid percussion brain injury one week prior to experimentation, and in vitro electrophysiological recording studies were conducted using combined hippocampal-entorhinal cortical slices (HEC slices). Results were compared to sham operated controls and rats in which a condition of chronic temporal lobe epilepsy was induced by a 2 h bout of pilocarpine-induced status epilepticus 2 months prior to recording (PILO). In field potential recording, PILO HEC slices evidenced a greater degree of disinhibition in Ca1 than did TBI or control slices. TBI slices showed greater disinhibition in the dentate gyrus than did PILO or control rats. In in vitro kindling experiments, 86% of TBI HEC slices generated self-sustaining epileptic activity within 9 stimulus trains. This type of activity was never triggered in control slices. HEC slices prepared from PILO animals generated self-sustaining epileptic activity with fewer stimulus trains than did TBI slices. In anatomical studies, both TBI and PILO hippocampi evidenced significant loss of neurons within the hilar region. TBI induces a series of changes within the limbic system of rats, which are qualitatively similar in many aspects but quantitatively less severe than changes seen in rats with chronic temporal lobe epilepsy. These physiological and anatomical TBI-associated alterations in the limbic system may contribute to the development of epilepsy following head trauma.

Voltage-dependent Na+/K+ ion channel blockade fails to ameliorate behavioral deficits after traumatic brain injury in the rat

Traumatic brain injury (TBI) induces massive, transient ion flux, after impact. This may be via agonist gated channels, such as the muscarinic, cholinergic or NMDA receptor, or via voltage-dependent channels. Pharmacological blockade of the former, is neuroprotective in most TBI models, but the role of voltage-dependent Na+/K+ channels has not been tested. We have therefore tested the hypothesis that intraventricular tetrodotoxin (TTX) (20 microliters, 5 mM) induced blockade of post-TBI ion flux will prevent cytotoxic cell swelling, Na+ and K+ flux, and behavioral deficit. Microdialysis demonstrated blockade of [K+]d flux in the TTX group compared to controls. Behavioral evaluation of motor (days 1-5) and memory function (days 11-15) after TBI revealed no beneficial effect in the TTX group compared to controls. Thus, although evidence of reduced ionic flux was demonstrated in the TTX group, memory and behavior were unaffected, suggesting that agonist-operated channel-mediated ion flux is more important after TBI.

Working memory deficits following traumatic brain injury in the rat

This study was designed to examine working memory following fluid-percussion traumatic brain injury (TBI) using the Morris water maze (MWM). Rats were injured (n = 9) at a moderate level of central fluid percussion injury (2.1 atm) or were prepared for injury but did not receive a fluid pulse (sham injury) (n = 10). On days 11-15 postinjury, working memory was assessed using the MWM. Each animal received 8 pairs of trials per day. For each pair of trials, animals were randomly assigned to one of four possible starting points and one of four possible escape platform positions. On the first trial of each pair, rats were placed in the maze facing the wall and were given 120 sec to locate the hidden escape platform. After remaining on the goal platform for 10 sec, they were placed back into the maze for the second trial of the pair. The platform position and the start position remained unchanged on this trial. After the second trial, the animal was given a 4 min intertrial rest. Between pairs of trials, both the start position and the goal location were changed. Analyses of the latency to reach the goal platform indicated that sham-injured animals performed significantly better on the second trial than on the first trial of each pair. However, injured animals did not significantly differ between first and second trial goal latencies on any day. These results indicate that injured animals have a profound and enduring deficit in spatial working memory function on days 11-15 after TBI.

Exposure to environmental complexity promotes recovery of cognitive function after traumatic brain injury

This study was designed to determine whether exposure to a complex environment after traumatic brain injury (TBI) would promote the recovery of cognitive function. Rats were injured at a moderate level of fluid percussion injury (2.1 atm) or were prepared for injury but were not injured (sham injury). Immediately after the injury or sham injury, the injured/complex (n = 8) and the sham/complex (n = 7) groups were placed into a complex environment. The complex environment was a 89 x 89-cm enclosure with different types of bedding and objects that provided motor, olfactory, tactile, and visual stimulation. The injured/standard (n = 8) and the sham/standard (n = 8) groups were returned to the animal vivarium where they were housed individually in standard wire mesh cages (24 x 20 x 18 cm). On days 11-15 (postinjury), performance in the Morris water maze was assessed. Analysis of the latency to reach the goal platform indicated that injured animals recuperating in the complex environment performed significantly better than injured animals recovering in the standard environment (p < 0.01). In fact, injured animals in the complex environment performed as well as both sham-injured groups. The improved performance of injured rats recovering in the enriched environment occurred in the absence of environmentally induced alterations in brain weight. These results indicate that exposure to environmental complexity enhances recovery of cognitive function after TBI.

Differential consequences of lateral and central fluid percussion brain injury on receptor coupling in rat hippocampus

We have identified alterations in the responses of muscarinic and metabotropic receptors in rat hippocampus that persist for at least 15 days after central fluid percussion injury. This study compares the effect of lateral fluid percussion and central fluid percussion on these responses. Moderate injury was obtained by displacement and deformation of the brain within the closed cranial cavity using a fluid percussion device positioned either centrally or laterally. Carbachol and (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated polyphosphoinositide (PPI) hydrolysis was assayed in hippocampus from injured and sham-injured controls at 15 days following injury. At 15 days after central fluid percussion traumatic brain injury (TBI), the response to carbachol was enhanced by 30% and the response to trans-ACPD was enhanced by 75% compared to sham-injured animals. At 15 days after lateral fluid percussion TBI the response to trans-ACPD was enhanced by 40% both ipsilateral and contralateral to the side of injury. In contrast, the response to carbachol was enhanced by 29% contralateral to the side of injury but was diminished by 12% ipsilateral to the side of injury. Cresyl violet staining shows no hippocampal cell death after central fluid percussion injury or on the side contralateral to lateral fluid percussion injury but on the ipsilateral side cell death was identified in hippocampal area CA3. Thus, abnormal hippocampal cell signaling through the phosphoinositide pathway occurs in the absence of cell death and may contribute to cognitive impairment.

The effect of postinjury kindled seizures on cognitive performance of traumatically brain-injured rats

The purpose of this experiment was to examine the consequences of postinjury seizures on cognitive performance after experimental traumatic brain injury (TBI). Rats either were injured at a moderate (2.1 atm) level of central fluid percussion TBI (n = 16) or were surgically prepared but did not receive a fluid pulse (sham-injured control, n = 16). Beginning 24 h after TBI, injured animals were injected (ip) once daily (Days 1-24 postinjury) with either saline (n = 8) or 25 mg/kg pentylenetetrazol (PTZ) (n = 8). Sham-injured rats were injected with an equal volume of saline (n = 8) or PTZ (n = 8). In both injured and sham-injured animals, daily injections of PTZ resulted in an increase in the severity of behavioral seizures over days. On Days 25-29 after injury or sham injury, all animals were tested in the Morris water maze (MWM). Analysis of maze performance indicated that in sham-injured animals PTZ-produced seizures had a detrimental effect on performance. In injured animals, however, PTZ-treated animals exhibited significantly faster acquisition and better terminal performance in the MWM than did untreated injured animals. These results show that posttraumatic kindled seizures do not exacerbate behavioral deficits after TBI and may, in fact, improve recovery following injury. The findings of this experiment are consistent with the hypothesis that post-TBI neuronal depression may contribute to behavioral morbidity following injury.

Metabotropic glutamate antagonist, MCPG, treatment of traumatic brain injury in rats

The metabotropic glutamate receptor (mGluR) antagonist, alpha-methyl-4-carboxyphenylglycine (MCPG) was administered into the left lateral ventricle 5 min prior to fluid percussion traumatic brain injury (TBI) in the rat. A single 5.0 microliters ventricular infusion of the active isomer. (+)-MCPG (0.2 mumol), significantly reduced beam walking motor deficits on days 1-5 after injury and learning/memory deficits measured on days 11-15 after injury. Neither a lower dose of (+)-MCPG (0.2 mumol) affected behavioral outcome. (+)-MCPG (0.2 mumol) did not affect systemic hemodynamic responses to injury. These results suggest that TBI induced activation of mGluRs contributes to behavioral morbidity and that blockade of certain mGluR subtypes (mGluR1, mGluR5 and/or mGluR2) may reduce these pathophysiological responses.

Effects of mu opioid agonist and antagonist on neurological outcome following traumatic brain injury in the rat

We examined the effects of an exogenous mu opioid agonist and antagonist on systemic physiology and neurological outcome following TBI in the rat. Experiment I: [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) (0.1 nMol or 0.3 nMol in 5 microliters) (n = 10) or artificial CSF (n = 10) was administered 5 min prior to fluid-percussion brain injury (2.1 atmospheres). Motor performance was assessed on days 1-5 after TBI. The mu receptor agonist, DAMGO significantly reduced both beam-walking latency and body weight loss after injury (p < 0.05). DAMGO-treated rats (n = 5) did not differ from CSF-treated rats (n = 5) on either systemic arterial blood pressure or heart rate responses to injury. Experiment II: Beta-funaltrexamine (beta-FNA) (20.0 nMol in 5.0 microliters) (n = 10) or artificial CSF (n = 10) was administered (icv) to rats 5 min prior to fluid-percussion brain injury (1.8 atmospheres). Motor performance was assessed on days 1-5 after TBI. The mu receptor antagonist, beta-FNA, significantly increased beam-walking latency after injury (p < 0.05). beta-FNA-treated rats (n = 5) did not differ from CSF-treated rats (n = 5) on either systemic arterial blood pressure or heart rate responses to injury. Experiment III: Neither beta-FNA nor DAMGO affected motor performance in uninjured rats. These results suggest that activation of mu opioid receptors by exogenous agonists may provide protection against deficits in motor performance produced by fluid percussion brain injury.

Impaired gustatory neophobia following traumatic brain injury in rats

To investigate the function of the amygdala following traumatic brain injury (TBI), rats were tested on a gustatory neophobia task that is sensitive to amygdala and hippocampal damage. Rats were either injured at a moderate level of fluid percussion injury (2.1 atm) or surgically prepared but not injured (sham-injury). Seven days after injury (n = 8) or sham injury (n = 9), rats were habituated to the testing chamber without food items present for 30 min. All rats were then food deprived. Twenty-four hours later, rats were placed in the testing chamber for 30 min and allowed to eat freely from four dishes of different foods: rat chow, raisins, potatoes, and cookies. Results showed that injured and sham-injured rats did not differ in their ability to find hidden food, suggesting that TBI does not produce an enduring impairment of olfaction. There was also no difference in the total amount of food eaten between injured and sham groups (p > 0.05). The percentage of each type of food consumed did differ between the two groups with sham controls consuming more familiar food (rat chow) compared to the unfamiliar foods (p < 0.01). The injured animals distributed their eating evenly among the four foods with no particular preference for any one food (p < 0.05). This pattern of eating behavior in injured animals is similar to animals that have lesions to both the hippocampus and amygdala (Sutherland and McDonald, 1990). Therefore, the results of this experiment suggest that, in addition to the hippocampus, the amygdala may also contribute to the behavioral changes observed following TBI.

Differential modulation of carbachol and trans-ACPD-stimulated phosphoinositide turnover following traumatic brain injury

In the fluid percussion model of traumatic brain injury (TBI), we examined muscarinic and metabotropic glutamate receptor-stimulated polyphosphoinositide (PPI) turnover in rat hippocampus. Moderate injury was obtained by displacement and deformation of the brain within the closed cranial cavity using a fluid percussion device. Carbachol and (+/-)-1-Aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated PPI hydrolysis was assayed in hippocampus from injured and sham-injured controls at both 1 hour and 15 days following injury. At 1 hour after TBI, the response to carbachol was enhanced in injured rats by up to 200% but the response to trans-ACPD was diminished by as much as 28%. By contrast, at 15 days after TBI, the response to carbachol was enhanced by 25% and the response to trans-ACPD was enhanced by 73%. The ionotropic glutamate agonists N-methyl-D-aspartate (NMDA), and alpha-amino-3 hydroxy-5-methyl-4-isoxazolepropionate (AMPA), did not increase PPI hydrolysis in either sham or injured rats and injury did not alter basal hydrolysis. Thus, hippocampal muscarinic and metabotropic receptors linked to phospholipase C are differentially altered by TBI.

The effect of acute cocaine or lidocaine on behavioral function following fluid percussion brain injury in rats

One of the goals of our laboratory is to examine how the presence of drugs of abuse will influence traumatic brain injury. Previous studies in our laboratory have shown that cocaine or lidocaine treatment before experimental fluid percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if pretreatment with cocaine or lidocaine is also associated with changes in trauma-induced suppression of reflexes and motor and cognitive dysfunction that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug pretreatment group, cocaine (0.5, 2, or 5 mg/kg) or lidocaine (2 mg/kg), which was injected via the tail vein. None of the drug pretreatments worsened injury. Lidocaine and cocaine decreased the duration of suppression of some neurological reflexes and reduced posttraumatic body weight losses. Lidocaine and cocaine both decreased postinjury motor deficits. Lidocaine and cocaine did not affect cognitive function on days 11-15 postinjury. The mechanism by which lidocaine improves acute neurological and motor function following brain injury is unknown, but may involve improved posttraumatic cortical blood flow, as seen in our previous study. Our results, along with other studies showing lidocaine to be neuroprotective in animal models of ischemia, suggest that studies of the effect of posttraumatic administration of lidocaine are warranted.

Long-term potentiation deficits and excitability changes following traumatic brain injury

The effects of traumatic brain injury (TBI) on hippocampal long-term potentiation (LTP) and cellular excitability were assessed at postinjury days 2, 7, and 15. TBI was induced using a well-characterized central fluid-percussion model. LTP of the Schaffer collateral/commissural system was assessed in vivo in urethane-anesthetized rats. Significant LTP of the population excitatory postsynaptic potential (EPSP) slope was found only in controls, and no recovery to control levels was observed for any postinjury time point. Four measurement parameters reflecting pyramidal cell discharges (population spike) indicated that TBI significantly increased cellular excitability at postinjury day 2: (1) pretetanus baseline recording showed that TBI reduced population spike threshold and latency; (2) tetanic stimulation (400 Hz) increased population spike amplitudes to a greater degree in injured animals than in control animals; (3) tetanus-induced population spike latency shifts were greater in injured cases; and (4) tetanic stimulation elevated EPSP to spike ratios (E-S potentiation) to a greater degree in injured animals. These parameters returned to control levels, as measured on postinjury days 7 and 15. These results suggest that TBI-induced excitability changes persist at least through 2 days postinjury and involve a differential impairment of mechanisms subserving LTP of synaptic efficacy and mechanisms related to action potential generation.

Combined fluid percussion brain injury and entorhinal cortical lesion: a model for assessing the interaction between neuroexcitation and deafferentation

Laboratory studies suggest that excessive neuroexcitation and deafferentation contribute to long-term morbidity following human head injury. Because no current animal model of traumatic brain injury (TBI) has been shown to combine excessive neuroexcitation and significant levels of deafferentation, we developed a rat model combining the neuroexcitation of fluid percussion TBI with subsequent entorhinal cortical (EC) deafferentation. In this paradigm, moderate fluid percussion TBI was induced in each rat, followed 24 h later by bilateral EC lesion (BEC). Six conditions were examined: (1) fluid percussion TBI followed 24 h later by bilateral EC lesion (TBEC), (2) fluid percussion TBI (TBI), (3) bilateral EC lesion (BEC), (4) sham fluid percussion TBI (SHAM), (5) TBI followed 24 h later by unilateral EC lesion (TUEC), and (6) unilateral EC lesion (UEC). The first four groups were assessed for motor (with beam-balance and beam-walk testing) and cognitive deficits (with the Morris water maze) and hippocampal morphology (with immunocytochemistry and electron microscopy). The TUEC and UEC groups were assessed for cognitive deficits alone. Motor deficits were greater in the TBEC injury than in TBI or sham alone; however, no significant difference was observed between the TBEC and BEC conditions in motor performance. Cognitive deficits were of a greater magnitude in the combined TBEC injury model relative to each individual insult. These cognitive deficits appeared to be additive for the two experimental injuries, BEC deafferentation producing deficits intermediate between TBI and TBEC insults. Morphologic analysis of the dentate gyrus molecular layer at 15 days after TBEC showed that the distribution of synaptophysin-positive presynaptic terminals was distinct from that observed after either TBI or BEC alone. Specifically, the laminar pattern of presynaptic rearrangement induced by BEC lesion did not occur after TBEC injury. The present results show that axonal injury and its attendant deafferentation, when coupled with traumatically induced neuroexcitation, produce an enhancement of the morbidity associated with TBI. Moreover, they indicate that this model can effectively be used to study the interaction between neuroexcitation and synaptic plasticity.

Traumatic brain injury causes a decrease in M2 muscarinic cholinergic receptor binding in the rat brain

Numerous studies indicate that an acute, excessive activation of muscarinic acetylcholine receptors (mAChR) contributes to the pathophysiological sequela of TBI. The present study examined the effect of moderate fluid percussion traumatic brain injury (TBI) on binding to M1 and M2 mAChR subtypes in the hippocampal formation and adjacent cortex using quantitative autoradiography. Injured animals along with concurrent controls were sacrificed by in situ freezing at 3 h or 24 h following TBI. Slide-mounted tissue sections were incubated in either [3H]pirenzepine (23 nM) for M1 or [3H]AFDX384 (9 nM) for M2 mAChR subtype labeling. Binding of [3H]pirenzepine to the M1 mAChR subtype was not significantly altered by TBI when compared to sham-injured animals. [3H]AFDX384 binding to the M2 mAChR subtype was significantly decreased at 24 h in hippocampal CA2-3 region and dorsal blade of the dentate gyrus (P < 0.05). The differences observed between M1 and M2 subtypes suggests that these muscarinic subtypes may differentially contribute to the pathophysiology of TBI.

Traumatic brain injury enhances the amnesic effect of an NMDA antagonist in rats

The authors have examined the effect of experimental traumatic brain injury on the amnesia produced by the N-methyl-D-aspartate (NMDA) antagonist MK-801. Rats were either subjected to a moderate level of fluid-percussion injury or prepared for injury but not injured ("sham injury"). Nine days following injury or sham injury, the rats were injected either with saline (sham/saline group, nine rats; injured/saline group, nine rats) or with 0.1 mg/kg of MK-801 (sham/MK-801 group, nine rats; injured/MK-801 group, eight rats) 30 minutes before being trained on a passive-avoidance task. Twenty-four hours later, the rats were tested for retention of the passive-avoidance task. Results revealed that the low dose of MK-801 did not significantly affect retention of the passive-avoidance task in the sham-injured group. In injured animals, administration of MK-801 produced a profound amnesia in contrast to the sham-injured animals treated with MK-801 and the injured animals treated with saline. To further investigate this enhanced sensitivity to the amnesic effects of MK-801 exhibited by the injured animals, nine injured and eight sham-injured rats were injected with 0.3 mg/kg of MK-801 15 minutes before injury. Results indicated that the animals treated with MK-801 before injury did not significantly differ from the sham-injured animals in retention of the passive-avoidance task. In addition, test results in the animals treated with MK-801 before injury and reinjected with MK-801 before passive-avoidance testing did not differ from those in untreated injured animals reinjected with saline before passive-avoidance testing. These findings indicate that MK-801 treatment before injury prevented the enhanced sensitivity to MK-801-induced amnesia that follows traumatic brain injury.

Muscarinic cholinergic receptor binding in rat brain at 15 days following traumatic brain injury

Laboratory studies indicate that activation of muscarinic cholinergic receptors (mAChRs) at or soon after traumatic brain injury (TBI) significantly contributes to behavioral morbidity. Recent research has demonstrated that pre-injury treatment with the muscarinic antagonist scopolamine significantly reduces spatial memory deficits at 11-15 days post-TBI. In the present study, we examined mAChR binding kinetics in brain regions at 15 days after moderate (1.95 atm) fluid percussion TBI in untreated and scopolamine-treated rats. Three groups were examined: untreated TBI (n = 8), TBI with pre-injury scopolamine treatment (1.0 mg/kg, i.p., 15 min prior to injury) (n = 11), and sham-injury (n = 7). The affinity (Kd) and maximum number of binding sites (Bmax) of mAChRs in hippocampus, neocortex, and brainstem were determined by [3H]QNB binding. Bmax values in TBI animals were significantly higher in hippocampus (4061 +/- 494 fmol/mg protein) and neocortex (4272 +/- 640 fmol/mg protein), but not in brainstem (833 +/- 39 fmol/mg protein) compared to sham-injured controls (hipp. 2812 +/- 218 fmol/mg/protein; neoctx. 2850 +/- 129 fmol/mg protein; brainstem 794 +/- 26 fmol/mg protein) (P < 0.05). At 15 days after injury, Bmax values of mAChRs in TBI animals with pre-injury scopolamine treatment (hipp. 2850 +/- 129 fmol/mg protein; neoctx. 2948 +/- 123 fmol/mg protein) did not differ from control. In all brain regions, Kd values did not differ between groups. These results demonstrate that TBI significantly alters the binding sites of mAChRs in hippocampus and neocortex for as long as 15 days after TBI. Furthermore, these results indicate that a pharmacological treatment that improves motor and memory function outcome also normalizes aspects of mAChRs physiology. These data suggest that excessive activation of mAChRs at or soon after TBI impact contributes to long-term pathophysiological processes in TBI.

The rotarod test: an evaluation of its effectiveness in assessing motor deficits following traumatic brain injury

The purpose of the present experiment was to examine the effectiveness of a modified rotarod test in detecting motor deficits following mild and moderate central fluid percussion brain injury. In addition, this investigation compared the performance of the rotarod task with two other commonly used measures of motor function after brain injury (beam-balance and beam-walking latencies). Rats were either injured with a mild (n = 14) or moderate (n = 8) level of fluid percussion injury or were surgically prepared but not injured (n = 8). All rats were assessed on all tasks for 5 days following their respective treatments. Results revealed that both the mild and moderate injury levels produced significant deficits in the ability of the animals to perform the rotarod task. Performance on the beam-balance and beam-walking tasks were not significantly impaired at the mild injury level. It was only at the moderate injury level that the beam-balance and beam-walking tasks detected deficits in motor performance. This result demonstrated that the rotarod task was a sensitive index of injury-induced motor dysfunction following even mild fluid percussion injury. A power analysis of the three tasks indicated that statistically significant group differences could be obtained with the rotarod task with much smaller sample sizes than with the beam-balance and beam-walking tasks. Performance on the rotarod, beam-walk, and beam-balance tasks were compared and evaluated by a multivariate stepdown analysis (multiple analysis of variance followed by univariate analyses of covariance). This analysis indicated that the rotarod task measures aspects of motor impairment that are not assessed by either the beam-balance or beam-walking latency. These findings suggest that compared to the beam-balance and beam-walking tasks, the rotarod task is a more sensitive and efficient index for assessing motor impairment produced by brain injury.

Muscarinic cholinergic receptor binding in rat brain following traumatic brain injury

Recent evidence suggests that excessive activation of muscarinic cholinergic receptors (mAChRs) contributes significantly to the pathophysiological consequences of traumatic brain injury (TBI). To examine possible alterations in mAChRs after TBI, the affinity (Kd) and maximum number of binding sites (Bmax) of mAChRs in hippocampus, neocortex, brain stem and cerebellum were determined by [3H]QNB binding. Three groups of rats were examined: 1 h post-TBI (n = 21), 24 h post-TBI (n = 21) and sham-injured rats (n = 21). Kd values were significantly higher in hippocampus and brain stem at 1 but not 24 h post-TBI compared with sham-injured controls (P < 0.05). Kd values did not significantly differ in neocortex and cerebellum at 1 or 24 h post-TBI compared with sham-injured controls. Bmax values did not significantly differ in any brain areas at 1 or 24 h post-TBI compared with sham-injured controls. These results show that TBI significantly decreases the affinity of mAChRs in hippocampus and brain stem at an early stage post-TBI, which may contribute to desensitization of mAChRs after TBI. The findings of no change in Bmax values are consistent with a transient elevation in ACh concentrations after TBI.

Protective effect of galanin on behavioral deficits in experimental traumatic brain injury

The magnitude of behavioral deficits in traumatic brain injury (TBI) has been shown to be partly related to alterations in the balance between excitatory and inhibitory neurotransmitter release. Previous studies have demonstrated that extracellular excitatory neurotransmitter concentrations dramatically increase following experimental TBI. We examined the effects of a neuromodulatory peptide, galanin (GAL), on behavioral morbidity, as measured by sensory motor and memory performance tasks, associated with experimental TBI in the rat. A single intraventricular injection of GAL (1.0 micrograms, n = 8 or 10.0 micrograms, n = 10) or cerebrospinal fluid (CSF) vehicle (n = 10) was administered 5 minutes prior to central fluid percussion TBI in rats. Performance on sensory motor tasks was assessed prior to injury and for 5 days after TBI with beam-balance, beam-walking, and rotarod tasks. Memory performance was assessed on days 11-15 after TBI with the Morris water maze. TBI produced significant motor and memory deficits in the CSF-treated group. GAL-treated rats had significantly less magnitude of deficits compared to CSF-treated rats on beam-balance, beam-walking, and rotarod performance. The 1.0 micrograms GAL dose produced slightly greater protection than the 10.0 micrograms GAL dose. Neither GAL dose affected body weight loss or Morris water maze performance. These results suggest that the physiologic effects of GAL may reduce certain components of TBI morbidity, possibly by modulating neuronal excitability.

Selective cognitive impairment following traumatic brain injury in rats

Impairment of cognitive abilities is a frequent and significant sequelae of traumatic brain injury (TBI). The purpose of this experiment was to examine the generality of the cognitive deficits observed after TBI. The performance of three tasks was evaluated. Two of the tasks (passive avoidance and a constant-start version of the Morris water maze) were chosen because they do not depend on hippocampal processing. The third task examined was the standard version of the Morris water maze which is known to rely on hippocampal processing. Rats were either injured at a moderate level (2.1 atm) of fluid percussion brain injury or surgically prepared but not injured (sham-injured control group). Nine days after fluid percussion injury, injured (n = 9) and sham-injured rats (n = 8) were trained on the one-trial passive avoidance task with retention assessed 24 h later. On days 11-15 following injury, injured (n = 9) and sham-injured (n = 8) rats were trained on a constant-start version of the Morris water maze that has the animals begin the maze from a fixed start position on each trial. Additional injured (n = 8) and sham-injured (n = 8) animals were trained on days 11-15 after injury on the standard (i.e. using variable start positions) version of the Morris water maze. The results of this experiment revealed that performance of the passive avoidance and the constant-start version of the Morris water maze were not impaired by fluid percussion TBI.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive impairment following traumatic brain injury: the effect of pre- and post-injury administration of scopolamine and MK-801

In order to examine the effectiveness of pre- and post-injury administration of muscarinic cholinergic and NMDA antagonists in reducing cognitive deficits following traumatic brain injury (TBI), rats were injected with either scopolamine (1 mg/kg) or MK-801 (0.3 mg/kg) 15 min prior to or 15 min after fluid percussion TBI. Cognitive performance was assessed with the Morris water maze procedure on days 11-15 after TBI or sham injury. When scopolamine and MK-801 were injected 15 min before injury, Morris water maze deficits were significantly reduced (P < 0.01 and P < 0.05, respectively). When scopolamine and MK-801 were injected 15 min after TBI, neither drug was effective in attenuating Morris water maze deficits. Consistent with other research, these results suggest that the cognitive deficits produced by TBI are the consequence of a brief period of excessive excitation of cholinergic and NMDA receptor systems. The results of this experiment also suggest that the temporal therapeutic window for the treatment of cognitive dysfunction with receptor antagonist intervention appears to be quite brief (< 15 min) in the rat.

Combined scopolamine and morphine treatment of traumatic brain injury in the rat

Previous studies have indicated that either scopolamine (1.0 mg/kg) or morphine (10.0 mg/kg) administered to rats prior to or soon after moderate fluid percussion traumatic brain injury (TBI) reduces behavioral deficits associated with injury. In this study, a series of experiments examined the effects of a combination of these drugs, as well as each drug individually, on behavioral outcome, brain temperature, and systemic physiological responses to TBI. Experiment I: a single systemic bolus injection of scopolamine (n = 10), morphine (n = 11), scopolamine plus morphine (n = 11), or saline (n = 10) was administered to rats 15 min prior to TBI. Animals were assessed on beam-walking behavioral performance for 5 days after injury. Scopolamine alone or morphine alone significantly reduced (P < 0.05) deficits produced by injury. Treatment with a combination of scopolamine and morphine provided greater protection on beam-walking behavioral measures than either drug alone. Experiment II: morphine raised brain temperature in uninjured rats (n = 5) to a mean of 39.3 degrees C +/- 0.3 by 60 min post-injection. Neither scopolamine (n = 5) nor scopolamine plus morphine (n = 5) altered brain temperature. Experiment III: scopolamine (n = 7) significantly raised heart rate for 5 min after injury. Saline (n = 8), morphine (n = 9) and scopolamine plus morphine (n = 7) significantly lowered heart rate after injury. All four groups had similar hypertensive responses to TBI which peaked at 10 s after injury. The results confirm that pharmacological blockade of muscarinic receptors or stimulation of mu opioid receptors reduces functional deficits associated with TBI.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothermia blunts acetylcholine increase in CSF of traumatically brain injured rats

Activation of muscarinic acetylcholine (ACh) receptors contributes to the pathophysiological consequences of moderate experimental traumatic brain injury (TBI). Hypothermia (30 degrees C) provides protection in experimental TBI. We measured ACh levels in CSF and plasma 5 min after moderate fluid percussion TBI under normothermic or hypothermic conditions, because ACh in the CSF has been correlated with the severity of behavioral deficits after TBI. Three groups were examined: TBI with hypothermic brain (30 degrees C), TBI with normothermic brain (37 degrees C), or sham TBI with normothermic brain (37 degrees C). ACh concentrations in CSF were significantly higher in 37 degrees C TBI rats, but not in 30 degrees C TBI rats compared to shams. ACh concentrations in plasma did not differ between groups. These results suggest that a contributing factor to the neuroprotective effects of moderate hypothermia in TBI may be related to the reduction of excessive ACh levels in the central nervous system following injury.

Behavioral protection by moderate hypothermia initiated after experimental traumatic brain injury

The effects of postinjury hypothermia on behavioral outcome following moderate fluid percussion traumatic brain injury (TBI) were examined. In Experiment I, three groups of rats were examined. The first group was normothermic (37.5 degrees C); and hypothermia (30 degrees C) was initiated 15 min and 30 min postinjury in the second and third groups, respectively. Whole body cooling was achieved by ventral ice pack. Cooling of the brain to 30 degrees C was achieved in 25 min and maintained for 60 min. Brain temperature was measured indirectly by a probe in the temporalis muscle. Behavioral outcome was assessed by beam-balance performance, beam-walking performance, and body weight loss measured daily for 5 days after TBI. Both the normothermic group and the 30-min postinjury hypothermic group exhibited significant (p < 0.05) beam-balance and beam-walking deficits on days 1 through 5 after TBI. In contrast, the 15-min postinjury hypothermic group exhibited significant (p < 0.05) beam-walking deficits only on day 1 after TBI and significant (p < 0.05) beam-balance deficits on days 1, 3, and 4 after TBI. In Experiment II, subcortical brain temperature was compared to temporalis muscle temperature in normothermic (37.5 degrees C) and hypothermic (30 degrees C) rats subjected to TBI. In both groups brain temperature tracked within 0.4 degree C of temporalis muscle temperature. These results are similar to post-TBI excitatory receptor antagonist studies and indicate a therapeutic window for moderate hypothermia of less than 30 min after moderate fluid percussion TBI in the rat.

The effect of age on motor and cognitive deficits after traumatic brain injury in rats

Age is one of the most important predictors of outcome after human traumatic brain injury. This study used fluid percussion brain injury to investigate the effects of aging on outcome after brain injury in rats. Three-month-old (n = 8) and 20-month-old (n = 11) rats were injured at a low level (1.7-1.8 atm) of fluid percussion brain injury or received a sham injury (n = 6 for both age groups). Body weight and motor function (beam balance and beam walking) were assessed before injury and for the first 5 days after injury. Cognitive outcome was assessed with the Morris water maze on Days 11 to 15 after injury. Injury did not produce significant weight loss in either age group. At the low level of brain injury used in this study, the 3-month-old rats did not demonstrate any significant motor deficits on the beam-balance or beam-walking tasks. However, the 20-month-old rats displayed significant beam-balance deficits on each of the 5 postinjury test days and significant beam-walking deficits for the first 3 postinjury days. Although Morris water maze performance was impaired in both age groups, the magnitude of impairment was greater in the aged animals. These data demonstrate that traumatic brain injury in the aged animal is marked by increased motor and cognitive deficits, in the absence of pronounced compromise of the animal's general health.(ABSTRACT TRUNCATED AT 250 WORDS)

Moderate hypothermia reduces blood-brain barrier disruption following traumatic brain injury in the rat

The effects of moderate hypothermia on blood-brain barrier (BBB) permeability and the acute hypertensive response after moderate traumatic brain injury (TBI) in rats were examined. TBI produced increased vascular permeability to endogenous serum albumin (IgG) in normothermic rats (37.5 degrees C) throughout the dorsal cortical gray and white matter as well as in the underlying hippocampi as visualized by immunocytochemical techniques. Vascular permeability was greatly reduced in hypothermic rats cooled to 30 degrees C (brain temperature) prior to injury. In hypothermic rats, albumin immunoreactivity was confined to the gray-white interface between cortex and hippocampi with no involvement of the overlying cortices and greatly reduced involvement of the underlying hippocampi. The acute hypertensive response in normothermic rats peaked at 10 s after TBI (187.3 mm Hg) and returned to baseline within 50 s. In contrast, the peak acute hypertensive response was significantly (P < 0.05) reduced in hypothermic rats (154.8 mm Hg, 10 s after TBI) and returned to baseline at 30 s after injury. These results demonstrate that moderate hypothermia greatly reduces endogenous vascular protein-tracer passage into and perhaps through the brain. This reduction may, in part, be related to hypothermia-induced modulation of the systemic blood pressure response to TBI.

Enduring suppression of hippocampal long-term potentiation following traumatic brain injury in rat

This study investigated changes in synaptic responses (population spike and population EPSP) of CA1 pyramidal cells of the rat hippocampus to stimulation of the Schaffer collateral/commissural pathways 2-3 h after traumatic brain injury (TBI). TBI was induced by a fluid percussion pulse delivered to the parietal epidural space resulting in loss of righting responses for 4.90-8.98 min. Prior to tetanic stimulation, changes observed after the injury included: (1) decreases in population spikes threshold but not EPSP thresholds; (2) decreases in maximal amplitude of population spikes as well as EPSPs. TBI also suppressed long-term potentiation (LTP), as evidenced by reductions in post-tetanic increases in population spikes as well as EPSPs. Since LTP may reflect processes involved in memory formation, the observed suppression of LTP may be an electrophysiological correlate of enduring memory deficits previously demonstrated in the same injury model.

Cholinergic and opioid mediation of traumatic brain injury

There is considerable evidence for the involvement of cholinergic and opioid systems in the pathophysiological responses associated with traumatic brain injury (TBI). To some extent, interest in this area has been eclipsed by a strong focus on, and rapid progress in, studies of the role of excitatory amino acids in TBI. We present evidence that both cholinergic and opioid systems are important modulators of the pathophysiological response to TBI, potentially equally as important as excitatory amino acids. There is a relatively large body of experimental data documenting the involvement of these systems in TBI that has yielded important principles with general significance for laboratory studies of the neuropharmacology of TBI. In fact, the first demonstration of excitotoxic mechanisms of TBI involved studies of the role of acetylcholine in experimental TBI. There also are clinical data suggesting that modulation of opioid and cholinergic systems could benefit patients.

Neurotransmitter-mediated mechanisms of traumatic brain injury: acetylcholine and excitatory amino acids

Research into traumatic brain injury (TBI), focusing on changes in energy metabolism, cerebrovascular dysfunction, and brain parenchymal morphology, has not produced complete descriptions of mechanisms mediating the pathophysiology of TBI. New studies indicate that neurochemical alterations mediate important components of brain physiology associated with TBI, and these alterations may be responsive to pharmacologic therapy. We discuss rodent models of TBI, review current experimental evidence of muscarinic cholinergic and excitatory amino acid (EAA) receptor involvement in its pathophysiology, and address issues relevant to the interpretation of these data.

Effects of traumatic brain injury in rats on binding to forebrain opiate receptor subtypes

Sprague-Dawley rats were subjected to a moderate level (2.2 atm) of traumatic brain injury (TBI) using fluid percussion. Injured animals were allowed to survive posttrauma for periods of 5 min, 3 h, and 24 h. The effect of TBI on binding to forebrain opiate receptors was assessed using quantitative receptor autoradiography, and compared to a sham control group. Binding of [3H]DAGO to mu receptors in neocortex and the CA1 pyramidal layer of the hippocampus was significantly decreased in the 24-h group (p less than 0.05). [3H]Bremazocine binding to kappa receptors was unchanged at 5 min and 24 h, but showed large decreases 3 h after TBI in the CA1 pyramidal layer (65%, p less than 0.05) and dentate gyrus (43%, p less than 0.05). Levels of delta binding (measured with [3H]DSLET) and lambda binding (measured with [3H]naloxone) were unaffected by TBI. These data support previous suggestions of a role for endogenous opioids in TBI, and provide further evidence that mu and kappa opioid receptor subtypes in neocortex and hippocampus may have different functions in TBI.

Postinjury scopolamine administration in experimental traumatic brain injury

A single bolus dose of scopolamine (1.0 mg/kg) or saline (equal volume) was injected (i.p.) at 15, 30 or 60 min after fluid percussion traumatic brain injury in the rat. Scopolamine administered at 15 min postinjury significantly reduced beam walking deficits and body weight loss assessed for 5 days after injury. Scopolamine treatment at 30 or 60 min postinjury had no effect on behavioral outcome assessed for 5 days after injury. Plasma concentrations of scopolamine were measured with a radioreceptor assay. The plasma half-life for scopolamine was 21.6 min in injured rats and 17.3 min in normal rats (P less than 0.05). These results, along with evidence from previous studies, suggest that a brief period of excessive neuronal excitation can produce relatively long-lasting behavioral deficits. The temporal effectiveness of receptor antagonist intervention in this process appears to be brief.

Cognitive deficits following traumatic brain injury produced by controlled cortical impact

Traumatic brain injury produces significant cognitive deficits in humans. This experiment used a controlled cortical impact model of experimental brain injury to examine the effects of brain injury on spatial learning and memory using the Morris water maze task. Rats (n = 8) were injured at a moderate level of cortical impact injury (6 m/sec, 1.5-2.0 mm deformation). Eight additional rats served as a sham-injured control group. Morris water maze performance was assessed on days 11-15 and 30-34 following injury. Results revealed that brain-injured rats exhibited significant deficits (p less than 0.05) in maze performance at both testing intervals. Since the Morris water maze task is particularly sensitive to hippocampal dysfunction, the results of the present experiment support the hypothesis that the hippocampus is preferentially vulnerable to damage following traumatic brain injury. These results demonstrate that controlled cortical impact brain injury produces enduring cognitive deficits analogous to those observed after human brain injury.

The effect of age on outcome following traumatic brain injury in rats

Age of the patient is one of the most important predictors of outcome following human traumatic brain injury. This study employs the fluid-percussion model to investigate the effects of aging on outcome following traumatic brain injury in rats. The results revealed that there was an age-associated increase in mortality rate following both low (1.7 to 1.8 atm) and moderate (2.00 to 2.25 atm) levels of traumatic brain injury. Age-related changes in systemic physiological, neurological, and histopathological indexes of brain injury were also examined following a low level of traumatic brain injury. Traumatic brain injury produced equivalent acute hypertension and increased plasma glucose levels in both young adult and aging rats. Injury produced an acute increase in heart rate in the young adult rat group, while the heart rate decreased in the aged rats. At low levels of brain injury, no significant gross histopathological alterations were produced in either age group. Neurological outcome was assessed by measuring the duration of suppression of a number of nonpostural and postural reflexes and more complex somatomotor functions (righting, escape, head support). Except for head support, there was a significant age-related increase in the duration of the suppression of these reflexes following brain injury. These data demonstrate that aging is associated with an increased mortality rate and greater acute neurological deficits following traumatic brain injury. These data also demonstrate the usefulness of the fluid-percussion model for studying the mechanisms responsible for the age-related increase in vulnerability to brain injury.

Relationship between body and brain temperature in traumatically brain-injured rodents

Recent work has shown that mild to moderate levels of hypothermia may profoundly reduce the histological and biochemical sequelae of cerebral ischemic injury. In the present study, the authors examined the effect of fluid-percussion injury on brain temperature in anesthetized rats and the effect of anesthesia on brain temperature in uninjured rats. The relationship between the brain, rectal, and temporalis muscle temperatures during normothermia, hypothermia, and hyperthermia was studied following a moderate magnitude of fluid-percussion brain injury (2.10 to 2.25 atmospheres) in rats. The results showed that mean brain temperature in 10 anesthetized injured rats, in 21 anesthetized uninjured rats, and in 10 unanesthetized uninjured rats was a mean (+/- standard error of the mean) of 36.04 degrees +/- 0.20 degrees C, 36.30 degrees +/- 0.08 degrees C, and 37.95 degrees +/- 0.09 degrees C, respectively. There was no significant difference in temperature under general anesthesia between injured and uninjured rats (p greater than 0.05). In the absence of brain injury, mean brain temperature was significantly lower in anesthetized rats than in unanesthetized rats (p less than 0.001). In anesthetized brain-injured rats, temporalis muscle temperature correlated well with brain temperature over a 30 degrees to 40 degrees C range, even when brain temperature was rapidly changed during induction of hypothermia or hyperthermia (r = 0.9986, p less than 0.0001). In contrast, rectal temperature varied inconsistently from brain temperature. These observations indicated that: 1) brain injury itself does not influence brain temperature in this model; 2) anesthesia alone decreases brain temperature to levels producing cerebral protection in this model; and 3) external monitoring of temporalis muscle temperature can provide a reliable indirect measure of brain temperature in the course of experimental brain injury. The authors believe that it is essential to monitor or control brain temperature in studies of experimental brain injury.