The Rehabilitation Potential of Neurostimulation for Mild Traumatic Brain Injury in Animal and Human Studies.

Neurostimulation carries high therapeutic potential, accompanied by an excellent safety profile. In this review, we argue that an arena in which these tools could provide breakthrough benefits is traumatic brain injury (TBI). TBI is a major health problem worldwide, with the majority of cases identified as mild TBI (mTBI). MTBI is of concern because it is a modifiable risk factor for dementia. A major challenge in studying mTBI is its inherent heterogeneity across a large feature space (e.g., etiology, age of injury, sex, treatment, initial health status, etc.). Parallel lines of research in human and rodent mTBI can be collated to take advantage of the full suite of neuroscience tools, from neuroimaging (electroencephalography: EEG; functional magnetic resonance imaging: fMRI; diffusion tensor imaging: DTI) to biochemical assays. Despite these attractive components and the need for effective treatments, there are at least two major challenges to implementation. First, there is insufficient understanding of how neurostimulation alters neural mechanisms. Second, there is insufficient understanding of how mTBI alters neural function. The goal of this review is to assemble interrelated but disparate areas of research to identify important gaps in knowledge impeding the implementation of neurostimulation.

Sustained ICP Elevation Is a Driver of Spatial Memory Deficits After Intraventricular Hemorrhage and Leads to Activation of Distinct Microglial Signaling Pathways.

The mechanisms of cognitive decline after intraventricular hemorrhage (IVH) in some patients continue to be poorly understood. Multiple rodent models of intraventricular or subarachnoid hemorrhage have only shown mild or even no cognitive impairment on subsequent behavioral testing. In this study, we show that intraventricular hemorrhage only leads to a significant spatial memory deficit in the Morris water maze if it occurs in the setting of an elevated intracranial pressure (ICP). Histopathological analysis of these IVH + ICP animals did not show evidence of neuronal degeneration in the hippocampal formation after 2 weeks but instead showed significant microglial activation measured by lacunarity and fractal dimensions. RNA sequencing of the hippocampus showed distinct enrichment of genes in the IVH + ICP group but not in IVH alone having activated microglial signaling pathways. The most significantly activated signaling pathway was the classical complement pathway, which is used by microglia to remove synapses, followed by activation of the Fc receptor and DAP12 pathways. Thus, our study lays the groundwork for identifying signaling pathways that could be targeted to ameliorate behavioral deficits after IVH.

Moderate and severe TBI in children and adolescents: The effects of age, sex, and injury severity on patient outcome 6 months after injury.

The interaction of age, sex, and outcomes of children with head injury remains incompletely understood and these factors need rigorous evaluation in prognostic models for pediatric head injury. We leveraged our large institutional pediatric TBI population to evaluate age and sex along with a series of predictive factors used in the acute care of injury to describe the response and outcome of children and adolescents with moderate to severe injury. We hypothesized that younger age at injury and male sex would be associated with adverse outcomes and that a novel GCS-based scale incorporating pupillary response (GCS-P) would have superior performance in predicting 6-month outcome. GCS and GCS-P along with established CT scan variables associated with neurologic outcomes were retrospectively reviewed in children (age birth to 18 years) with moderate or severe head injury. GOS-E was prospectively collected 6 months after injury; 570 patients were enrolled in the study, 520 with TBI and 50 with abusive head trauma, each analyzed separately. In the TBI cohort, the median age of patients was 8 years and 42.7% had a severe head injury. Multiple predictors of outcome were identified in univariate analysis; however, based on a multivariate analysis, the GCS was identified as most reliable, outperforming GCS-P, pupil score, and other clinical and CT scan predictors. After stratifying patients for severity of injury by GCS, no age- or sex-related effects were observed in our patient population, except for a trend toward worse outcomes in the neonatal group. Patients with abusive head trauma were more likely to have severe injury on presentation, increased mortality rate, and unfavorable outcome. Additionally, there was clear evidence that secondary injuries, including hypoxia, hypotension, and hypothermia were significantly associated with lower GCS and higher mortality in both AHT and TBI populations. Our findings support the use of GCS to guide clinical decision-making and prognostication in addition to emphasizing the need to stratify head injuries for severity when undertaking outcome studies. Finally, secondary injuries are a clear predictor of poor outcome and how we record and manage these events need to be considered moving forward.

Combined Inhibition of Fyn and c-Src Protects Hippocampal Neurons and Improves Spatial Memory via ROCK after Traumatic Brain Injury.

Our previous studies demonstrated that traumatic brain injury (TBI) and ventricular administration of thrombin caused hippocampal neuron loss and cognitive dysfunction via activation of Src family kinases (SFKs). Based on SFK localization in brain, we hypothesized SFK subtypes Fyn and c-Src, as well as SFK downstream molecule Rho-associated protein kinase (ROCK), contribute to cell death and cognitive dysfunction after TBI. We administered nanoparticle wrapped small interfering RNA (siRNA)-Fyn and siRNA-c-Src, or ROCK inhibitor Y-27632 to adult rats subjected to moderate lateral fluid percussion (LFP)-induced TBI. Spatial memory function was assessed from 12 to 16 days, and NeuN stained hippocampal neurons were assessed 16 days after TBI. The combination of siRNA-Fyn and siRNA-c-Src, but neither alone, prevented hippocampal neuron loss and spatial memory deficits after TBI. The ROCK inhibitor Y-27632 also prevented hippocampal neuronal loss and spatial memory deficits after TBI. The data suggest that the combined actions of three kinases (Fyn, c-Src, ROCK) mediate hippocampal neuronal cell death and spatial memory deficits produced by LFP-TBI, and that inhibiting this pathway prevents the TBI-induced cell death and memory deficits.

Transcriptional Pathology Evolves over Time in Rat Hippocampus after Lateral Fluid Percussion Traumatic Brain Injury.

Traumatic brain injury (TBI) causes acute and lasting impacts on the brain, driving pathology along anatomical, cellular, and behavioral dimensions. Rodent models offer an opportunity to study the temporal progression of disease from injury to recovery. Transcriptomic and epigenomic analysis were applied to evaluate gene expression in ipsilateral hippocampus at 1 and 14 days after sham (n = 2 and 4, respectively per time point) and moderate lateral fluid percussion injury (n = 4 per time point). This enabled the identification of dynamic changes and differential gene expression (differentially expressed genes; DEGs) modules linked to underlying epigenetic response. We observed acute signatures associated with cell death, astrocytosis, and neurotransmission that largely recovered by 2 weeks. Inflammation and immune signatures segregated into upregulated modules with distinct expression trajectories and functions. Whereas most down-regulated genes recovered by 14 days, two modules with delayed and persistent changes were associated with cholesterol metabolism, amyloid beta clearance, and neurodegeneration. Differential expression was paralleled by changes in histone H3 lysine residue 4 trimethylation at the promoters of DEGs at 1 day post-TBI, with the strongest changes observed for inflammation and immune response genes. These results demonstrate how integrated genomics analysis in the pre-clinical setting has the potential to identify stage-specific biomarkers for injury and/or recovery. Though limited in scope here, our general strategy has the potential to capture pathological signatures over time and evaluate treatment efficacy at the systems level.

Sex-specific acute and chronic neurotoxicity of acute diisopropylfluorophosphate (DFP)-intoxication in juvenile Sprague-Dawley rats.

Preclinical efforts to improve medical countermeasures against organophosphate (OP) chemical threat agents have largely focused on adult male models. However, age and sex have been shown to influence the neurotoxicity of repeated low-level OP exposure. Therefore, to determine the influence of sex and age on outcomes associated with acute OP intoxication, postnatal day 28 Sprague-Dawley male and female rats were exposed to the OP diisopropylfluorophosphate (DFP; 3.4 mg/kg, s.c.) or an equal volume of vehicle (∼80 µL saline, s.c.) followed by atropine sulfate (0.1 mg/kg, i.m.) and pralidoxime (2-PAM; 25 mg/kg, i.m.). Seizure activity was assessed during the first 4 h post-exposure using behavioral criteria and electroencephalographic (EEG) recordings. At 1 d post-exposure, acetylcholinesterase (AChE) activity was measured in cortical tissue, and at 1, 7, and 28 d post-exposure, brains were collected for neuropathologic analyses. At 1 month post-DFP, animals were analyzed for motor ability, learning and memory, and hippocampal neurogenesis. Acute DFP intoxication triggered more severe seizure behavior in males than females, which was supported by EEG recordings. DFP caused significant neurodegeneration and persistent microglial activation in numerous brain regions of both sexes, but astrogliosis occurred earlier and was more severe in males compared to females. DFP males and females exhibited pronounced memory deficits relative to sex-matched controls. In contrast, acute DFP intoxication altered hippocampal neurogenesis in males, but not females. These findings demonstrate that acute DFP intoxication triggers seizures in juvenile rats of both sexes, but the seizure severity varies by sex. Some, but not all, chronic neurotoxic outcomes also varied by sex. The spatiotemporal patterns of neurological damage suggest that microglial activation may be a more important factor than astrogliosis or altered neurogenesis in the pathogenesis of cognitive deficits in juvenile rats acutely intoxicated with OPs.

Early Intervention via Stimulation of the Medial Septal Nucleus Improves Cognition and Alters Markers of Epileptogenesis in Pilocarpine-Induced Epilepsy.

Over one-third of patients with temporal lobe epilepsy are refractory to medication. In addition, anti-epileptic drugs often exacerbate cognitive comorbidities. Neuromodulation is an FDA treatment for refractory epilepsy, but patients often wait >20 years for a surgical referral for resection or neuromodulation. Using a rodent model, we test the hypothesis that 2 weeks of theta stimulation of the medial septum acutely following exposure to pilocarpine will alter the course of epileptogenesis resulting in persistent behavioral improvements. Electrodes were implanted in the medial septum, dorsal and ventral hippocampus, and the pre-frontal cortex of pilocarpine-treated rats. Rats received 30 min/day of 7.7 Hz or theta burst frequency on days 4-16 post-pilocarpine, prior to the development of spontaneous seizures. Seizure threshold, spikes, and oscillatory activity, as well as spatial and object-based learning, were assessed in the weeks following stimulation. Non-stimulated pilocarpine animals exhibited significantly decreased seizure threshold, increased spikes, and cognitive impairments as compared to vehicle controls. Furthermore, decreased ventral hippocampal power (6-10 Hz) correlated with both the development of spikes and impaired cognition. Measures of spikes, seizure threshold, and cognitive performance in both acute 7.7 Hz and theta burst stimulated animals were statistically similar to vehicle controls when tested during the chronic phase of epilepsy, weeks after stimulation was terminated. These data indicate that modulation of the septohippocampal circuit early after pilocarpine treatment alters the progression of epileptic activity, resulting in elevated seizure thresholds, fewer spikes, and improved cognitive outcome. Results from this study support that septal theta stimulation has the potential to serve in combination or as an alternative to high frequency thalamic stimulation in refractory cases and that further research into early intervention is critical.

Aneurysmal subarachnoid hemorrhage survivors show long-term deficits in spatial reference memory in a pilot study of a virtual water maze paradigm.

BACKGROUND: Limited data exists on the long-term effects of aneurysmal subarachnoid hemorrhage (SAH) on spatial memory. Herein, we used a computerized virtual water maze to evaluate the feasibility of spatial memory testing in pilot cohort of ten patients who survived previous SAH. METHODS: Ten SAH survivors (5.8 ± 5.1 years after initial hemorrhage) and 7 age-matched controls underwent testing in a virtual water maze computer program. Additional subgroup analyses were performed to evaluate spatial reference memory correlation for ventricular size on admission, placement of an external ventricular drain and placement of a shunt. RESULTS: With respect to the spatial memory acquisition phase, there was no significant difference of pathway length traveled to reach the platform between SAH survivors and control subjects. During the probe trial, control subjects spent significantly longer time in target quadrants compared to SAH survivors (F(3, 24) = 10.32, p = 0.0001; Target vs. Right: Mean percent difference 0.16 [0-0.32], p = 0.045; Target vs. Across: Mean percent difference 0.35 [0.19-0.51], p < 0.0001; Target vs. Left: Mean percent difference 0.21 [0.05-0.37], p = 0.0094). Furthermore, patients who initially presented with smaller ventricles performed worse that those patients who had ventriculomegaly and/or required surgical management of hydrocephalus. CONCLUSIONS: Our data demonstrate that SAH survivors have persistent spatial reference memory deficits years after the hemorrhage. Hydrocephalus at presentation and external ventricular drainage were not found to be associated with poor spatial memory outcomes in this pilot cohort. Therefore, other causes such as global cerebral edema or magnitude of initial ICP spike, need to be considered to be examined as root cause as well in subsequent studies. The protocol described in this manuscript is able to demonstrate a spatial reference memory deficit and can be used to study risk factors for spatial memory impairment on a larger scale.

Recovery of Theta Frequency Oscillations in Rats Following Lateral Fluid Percussion Corresponds With a Mild Cognitive Phenotype.

Whether from a fall, sports concussion, or even combat injury, there is a critical need to identify when an individual is able to return to play or work following traumatic brain injury (TBI). Electroencephalogram (EEG) and local field potentials (LFP) represent potential tools to monitor circuit-level abnormalities related to learning and memory: specifically, theta oscillations can be readily observed and play a critical role in cognition. Following moderate traumatic brain injury in the rat, lasting changes in theta oscillations coincide with deficits in spatial learning. We hypothesized, therefore, that theta oscillations can be used as an objective biomarker of recovery, with a return of oscillatory activity corresponding with improved spatial learning. In the current study, LFP were recorded from dorsal hippocampus and anterior cingulate in awake, behaving adult Sprague Dawley rats in both a novel environment on post-injury days 3 and 7, and Barnes maze spatial navigation on post-injury days 8-11. Theta oscillations, as measured by power, theta-delta ratio, peak theta frequency, and phase coherence, were significantly altered on day 3, but had largely recovered by day 7 post-injury. Injured rats had a mild behavioral phenotype and were not different from shams on the Barnes maze, as measured by escape latency. Injured rats did use suboptimal search strategies. Combined with our previous findings that demonstrated a correlation between persistent alterations in theta oscillations and spatial learning deficits, these new data suggest that neural oscillations, and particularly theta oscillations, have potential as a biomarker to monitor recovery of brain function following TBI. Specifically, we now demonstrate that oscillations are depressed following injury, but as oscillations recover, so does behavior.

Mechanical injury and blood are drivers of spatial memory deficits after rapid intraventricular hemorrhage.

Aneurysmal intraventricular hemorrhage (IVH) survivors may recover with significant deficits in learning and memory. The goal of this study was to investigate the mechanism of memory decline after intraventricular aneurysm rupture. We developed an aneurysmal IVH rat model by injecting autologous, arterial blood over the period of two minutes into the right lateral ventricle. We also evaluated the effects of a volume-matched artificial cerebrospinal fluid (CSF) control, thrombin and the mode of delivery (pulsed hand injection versus continuous pump infusion). We performed magnetic resonance brain imaging after 1 and 5 weeks to evaluate for hydrocephalus and histological analysis of the dentate gyrus after 6 weeks. Only animals which underwent a whole blood pulsed hand injection had a spatial memory acquisition and retention deficit 5 weeks later. These animals had larger ventricles at 1 and 5 weeks than animals which underwent a continuous pump infusion of whole blood. We did not find a decline in dentate gyrus granule cell neurons or an impairment in dentate gyrus neurogenesis or differentiation 6 weeks after IVH. Rapid injections of blood or volume resulted in microglial activation in the dentate gyrus. In conclusion, our results point to mechanical injury as the predominant mechanism of memory decline after intraventricular aneurysmal rupture. However, volume-matched pulsed injections of artificial CSF did not create a spatial memory deficit at 5 weeks. Therefore, whole blood itself must play a role in the mechanism. Further research is required to evaluate whether the viscosity of blood causes additional mechanical disruption and hydrocephalus through a primary injury mechanism or whether the toxicity of blood causes a secondary injury mechanism that leads to the observed spatial memory deficit after 5 weeks.

From adagio to allegretto: The changing tempo of theta frequencies in epilepsy and its relation to interneuron function.

Despite decades of research, our understanding of epilepsy, including how seizures are generated and propagate, is incomplete. However, there is growing recognition that epilepsy is more than just the occurrence of seizures, with patients often experiencing comorbid deficits in cognition that are poorly understood. In addition, the available therapies for treatment of epilepsy, from pharmaceutical treatment to surgical resection and seizure prevention devices, often exacerbate deficits in cognitive function. In this review, we discuss the hypothesis that seizure generation and cognitive deficits have a similar pathological source characterized by, but not limited to, deficits in theta oscillations and their influence on interneurons. We present a new framework that describes oscillatory states in epilepsy as alternating between hyper- and hypo-synchrony rather than solely the spontaneous transition to hyper-excitability characterized by the seizures. This framework suggests that as neural oscillations, specifically in the theta range, vary their tempo from a slowed almost adagio tempo during interictal periods to faster, more rhythmic allegretto tempo preictally, they impact the function of interneurons, modulating their ability to control seizures and their role in cognitive processing. This slow wave oscillatory framework may help explain why current therapies that work to reduce hyper-excitability do not completely eliminate seizures and often lead to exacerbated cognitive deficits.

Medial septal stimulation increases seizure threshold and improves cognition in epileptic rats.

BACKGROUND: Temporal lobe epilepsy is most prevalent among focal epilepsies, and nearly one-third of patients are refractory to pharmacological intervention. Persistent cognitive and neurobehavioral comorbidities also occur due to the recurrent nature of seizures and medication-related side effects. HYPOTHESIS: Electrical neuromodulation is an effective strategy to reduce seizures both in animal models and clinically, but its efficacy to modulate cognition remains unclear. We hypothesized that theta frequency stimulation of the medial septum would increase septohippocampal oscillations, increase seizure threshold, and improve spatial learning in a rat model of pilocarpine-induced epilepsy. METHODS: Sham and pilocarpine rats were implanted with electrodes in the medial septum, hippocampus and prefrontal cortex. EEG was assessed days prior to and following stimulation. Sham and pilocarpine-treated rats received either no stimulation, continuous (throughout each behavior), or pre-task (one minute prior to each behavior) 7.7 Hz septal stimulation during the Barnes maze spatial navigation test and also during assessment of flurothyl-induced seizures. RESULTS: Both continuous and pre-task stimulation prevented epilepsy-associated reductions in theta oscillations over time. Additionally, both stimulation paradigms significantly improved spatial navigation in the Barnes maze, reducing latency and improving search strategy. Moreover, stimulation led to significant increases in seizure threshold in pilocarpine-treated rats. There was no evidence of cognitive enhancement or increased seizure threshold in stimulated sham rats. CONCLUSION: These findings have profound implications as theta stimulation of the septum represents a single frequency and target that has the potential to both improve cognition and reduce seizures for patients with refractory epilepsy.

Stimulation of the medial septum improves performance in spatial learning following pilocarpine-induced status epilepticus.

Temporal lobe epilepsy often leads to hippocampal sclerosis and persistent cognitive deficits, including difficulty with learning and memory. Hippocampal theta oscillations are critical in optimizing hippocampal function and facilitating plasticity. We hypothesized that pilocarpine-induced status epilepticus would disrupt oscillations and behavioral performance and that electrical neuromodulation to entrain theta would improve cognition specifically in injured rats. Rats received a pilocarpine (n=30) or saline injection (n=27) and unilateral bi-polar electrodes were implanted into the medial septum and hippocampus the following day. Hippocampal and septal theta were recorded in a Plexiglas box over the first week following implantation. Control and pilocarpine-treated rats were split into stimulation (continuous 7.7Hz, 80µA, 1ms pulse width) and non-stimulation groups for behavioral analysis. Continuous stimulation was initiated one-minute prior to and throughout an object exploration task (post-injury day seven) and again for each of six trials on the Barnes maze (post-injury days 12-14). There was a significant reduction in hippocampal theta power (p<0.05) and percentage of time oscillating in theta (p<0.05). In addition there was a significant decrease in object exploration in rats post-pilocarpine (p<0.05) and an impairment in spatial learning. Specifically, pilocarpine-treated rats were more likely to use random search strategies (p<0.001) and had an increase in latency to find the hidden platform (p<0.05) on the Barnes maze. Stimulation of the medial septum at 7.7Hz in pilocarpine-treated rats resulted in performance similar to shams in both the object recognition and Barnes maze tasks. Stimulation of sham rats resulted in impaired object exploration (p<0.05) with no difference in Barnes maze latency or strategy. In conclusion, pilocarpine-induced seizures diminished hippocampal oscillations and impaired performance in both an object exploration and a spatial memory task in pilocarpine-treated rats. Theta stimulation at 7.7Hz improved behavioral outcome on the Barnes maze task; this improvement in function was not related to a general cognitive enhancement, as shams did not benefit from stimulation. Therefore, stimulation of the medial septum represents an exciting target to improve behavioral outcome in patients with epilepsy.

Making Waves in the Brain: What Are Oscillations, and Why Modulating Them Makes Sense for Brain Injury.

Traumatic brain injury (TBI) can result in persistent cognitive, behavioral and emotional deficits. However, the vast majority of patients are not chronically hospitalized; rather they have to manage their disabilities once they are discharged to home. Promoting recovery to pre-injury level is important from a patient care as well as a societal perspective. Electrical neuromodulation is one approach that has shown promise in alleviating symptoms associated with neurological disorders such as in Parkinson's disease (PD) and epilepsy. Consistent with this perspective, both animal and clinical studies have revealed that TBI alters physiological oscillatory rhythms. More recently several studies demonstrated that low frequency stimulation improves cognitive outcome in models of TBI. Specifically, stimulation of the septohippocampal circuit in the theta frequency entrained oscillations and improved spatial learning following TBI. In order to evaluate the potential of electrical deep brain stimulation for clinical translation we review the basic neurophysiology of oscillations, their role in cognition and how they are changed post-TBI. Furthermore, we highlight several factors for future pre-clinical and clinical studies to consider, with the hope that it will promote a hypothesis driven approach to subsequent experimental designs and ultimately successful translation to improve outcome in patients with TBI.

Septohippocampal Neuromodulation Improves Cognition after Traumatic Brain Injury.

Traumatic brain injury (TBI) often results in persistent attention and memory deficits that are associated with hippocampal dysfunction. Although deep brain stimulation (DBS) is used to treat neurological disorders related to motor dysfunction, the effectiveness of stimulation to treat cognition remains largely unknown. In this study, adult male Harlan Sprague-Dawley rats underwent a lateral fluid percussion or sham injury followed by implantation of bipolar electrodes in the medial septal nucleus (MSN) and ipsilateral hippocampus. In the first week after injury, there was a significant decrease in hippocampal theta oscillations that correlated with decreased object exploration and impaired performance in the Barnes maze spatial learning task. Continuous 7.7 Hz theta stimulation of the medial septum significantly increased hippocampal theta oscillations, restored normal object exploration, and improved spatial learning in injured animals. There were no benefits with 100 Hz gamma stimulation, and stimulation of sham animals at either frequency did not enhance performance. We conclude, therefore, that there was a theta frequency-specific benefit of DBS that restored cognitive function in brain-injured rats. These data suggest that septal theta stimulation may be an effective and novel neuromodulatory therapy for treatment of persistent cognitive deficits following TBI.

Intracerebroventricular opiate infusion for refractory head and facial pain.

AIM: To study the risks and benefits of intracerebroventricular (ICV) opiate pumps for the management of benign head and face pain. METHODS: SSix patients with refractory trigeminal neuralgia and/or cluster headaches were evaluated for implantation of an ICV opiate infusion pump using either ICV injections through an Ommaya reservoir or external ventricular drain. Four patients received morphine ICV pumps and two patientS received a hydromorphone pump. Of the Four patients with morphine ICV pumps, one patient had the medication changed to hydromorphone. Preoperative and post-operative visual analog scores (VAS) were obtained. Patients were evaluated post-operatively for a minimum of 3 mo and the pump dosage was adjusted at each outpatient clinic visit according to the patient's pain level. RESULTS: All 6 patients had an intracerebroventricular opiate injection trial period, using either an Ommaya reservoir or an external ventricular drain. There was an average VAS improvement of 75.8%. During the trial period, no complications were observed. Pump implantation was performed an average of 3.7 wk (range 1-7) after the trial injections. After implantation, an average of 20.7 ± 8.3 dose adjustments were made over 3-56 mo after surgery to achieve maximal pain relief. At the most recent follow-up (26.2 mo, range 3-56), VAS scores significantly improved from an average of 7.8 ± 0.5 (range 6-10) to 2.8 ± 0.7 (range 0-5) at the final dose (mean improvement 5.0 ± 1.0, P < 0.001). All patients required a stepwise increase in opiate infusion rates to achieve maximal benefit. The most common complications were nausea and drowsiness, both of which resolved with pump adjustments. On average, infusion pumps were replaced every 4-5 years. CONCLUSION: These results suggest that ICV delivery of opiates may potentially be a viable treatment option for patients with intractable pain from trigeminal neuralgia or cluster headache.

NAAG peptidase inhibitor improves motor function and reduces cognitive dysfunction in a model of TBI with secondary hypoxia.

Immediately following traumatic brain injury (TBI) and TBI with hypoxia, there is a rapid and pathophysiological increase in extracellular glutamate, subsequent neuronal damage and ultimately diminished motor and cognitive function. N-acetyl-aspartyl glutamate (NAAG), a prevalent neuropeptide in the CNS, is co-released with glutamate, binds to the presynaptic group II metabotropic glutamate receptor subtype 3 (mGluR3) and suppresses glutamate release. However, the catalytic enzyme glutamate carboxypeptidase II (GCP II) rapidly hydrolyzes NAAG into NAA and glutamate. Inhibition of the GCP II enzyme with NAAG peptidase inhibitors reduces the concentration of glutamate both by increasing the duration of NAAG activity on mGluR3 and by reducing degradation into NAA and glutamate resulting in reduced cell death in models of TBI and TBI with hypoxia. In the following study, rats were administered the NAAG peptidase inhibitor PGI-02776 (10mg/kg) 30 min following TBI combined with a hypoxic second insult. Over the two weeks following injury, PGI-02776-treated rats had significantly improved motor function as measured by increased duration on the rota-rod and a trend toward improved performance on the beam walk. Furthermore, two weeks post-injury, PGI-02776-treated animals had a significant decrease in latency to find the target platform in the Morris water maze as compared to vehicle-treated animals. These findings demonstrate that the application of NAAG peptidase inhibitors can reduce the deleterious motor and cognitive effects of TBI combined with a second hypoxic insult in the weeks following injury.

A comparative study of human and rat hippocampal low-frequency oscillations during spatial navigation.

Rhythmic oscillations within the 3-12 Hz theta frequency band manifest in the rodent hippocampus during a variety of behaviors and are particularly well characterized during spatial navigation. In contrast, previous studies of rhythmic hippocampal activity in primates under comparable behavioral conditions suggest it may be less apparent and possibly less prevalent, or even absent, compared with the rodent. We compared the relative presence of low-frequency oscillations in rats and humans during spatial navigation by using an oscillation detection algorithm ("P-episode" or "BOSC") to better characterize their presence in microelectrode local field potential (LFP) recordings. This method quantifies the proportion of time the LFP exceeds both a power and cycle duration threshold at each frequency, characterizing the presence of (1) oscillatory activity compared with background noise, (2) the peak frequency of oscillatory activity, and (3) the duration of oscillatory activity. Results demonstrate that both humans and rodents have hippocampal rhythmic fluctuations lasting, on average, 2.75 and 4.3 cycles, respectively. Analyses further suggest that human hippocampal rhythmicity is centered around ∼3 Hz while that of rats is centered around ∼8 Hz. These results establish that low-frequency rhythms relevant to spatial navigation are present in both the rodent and human hippocampus, albeit with different properties under the behavioral conditions tested.

Evaluation of metric, topological, and temporal ordering memory tasks after lateral fluid percussion injury.

Impairments in learning and memory occur in as many as 50% of patients following traumatic brain injury (TBI). Similar impairments occur in rodent models of TBI, and the development of new memory testing procedures provides an opportunity to examine how TBI affects memory processing in specific neural memory systems. Specifically, metric, topological, and temporal ordering tasks are object-based tests for memory of spatial orientation and temporal sequencing working memory developed for use in rodents. Previous studies demonstrated that specific lesions of the dentate gyrus/CA3 of the hippocampus and the parietal cortex resulted in deficits in the metric and topological spatial orientation tasks, respectively. Lesions of the CA1 impaired a rat's ability to recall the temporal order of odors. The purpose of the following study was to determine whether moderate lateral fluid percussion TBI would generate deficits in these working memory tasks, and whether observed deficits were associated with cell loss in the CA2/3 and/or CA1 of the hippocampus. Two weeks following a moderate lateral fluid percussion TBI, adult rats demonstrated significant deficits in both the metric and temporal ordering tasks (p<0.05) but not in the topological task. Stereological analysis identified a significant reduction in neurons in the CA2/3 (p<0.05) but not the CA1 of the hippocampus. These data demonstrate the utility of three object-based tasks to expand our understanding of how different neural memory systems are affected by TBI.

Neuroprotective effects of SNX-185 in an in vitro model of TBI with a second insult.

PURPOSE: Second insults following traumatic brain injury (TBI), such as ischemia and hypoxia, significantly worsen outcome in patients and in experimental models of TBI. Following TBI there is a pathological increase in intracellular calcium, triggering cellular mechanisms of dysfunction and death. N-type specific voltage gated calcium channel (VGCC) blockers reduce cell death in both in vitro mechanical strain injury (MSI) and in vivo models of TBI, but they have not been previously explored in a model of TBI followed by a second insult. METHODS: In the following studies, cortical neurons and astrocytes experienced MSI followed by incubation in 20% CO2. Cultures were treated with the N-type VGCC blocker, ω-conopeptide SNX-185 (1 µM), 5-minutes post-injury and intracellular calcium accumulation was assessed at 3, 6 and 24 h. Neuronal viability was assessed 24 h after MSI. RESULTS: Increasing incubator CO2 to 20% significantly increased calcium accumulation and cell death regardless of MSI severity. Treatment with 1 µM of SNX-185 significantly reduced the accumulation of calcium 3 hours following injury and increased the number of viable neurons 24 h post-injury and incubation in 20% CO2. CONCLUSIONS: In vitro models provide a critical tool for identifying roles of cell specific mechanisms involved in neuronal dysfunction and death following injury. These data demonstrate the potential of N-type VGCC blockers in reducing the damaging effects of TBI and second insults.