Excitatory transmitters and epilepsy-related brain damage

A systematic review and meta-analysis of ketamine in pediatric status epilepticus

OBJECTIVE

Status epilepticus (SE) is a common neurological medical emergency in the pediatric population, with 10%-40% of cases progressing to refractory SE (RSE), requiring treatment with anesthetic infusions. We present a systematic review and meta-analysis of the use of ketamine for the treatment of pediatric SE and its potential advantages over other anesthetic infusions.

METHODS

This review follows the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. Electronic databases, including PubMed, Cochrane Library, Ovid, Embase, and Google Scholar, were searched with the keywords "pediatrics," "status epilepticus," and "ketamine treatment." Randomized trials, prospective and retrospective cohort studies, and case reports were considered for inclusion.

RESULTS

Eighteen publications met the initial inclusion criteria. The 18 publications comprise 11 case reports, one nonconclusive clinical trial, two case series, and four retrospective cohorts. After excluding the case reports because of reporting bias, only the six case series and cohorts were included in the final analysis. There were 172 patients in the six included studies. The weighted age was 9.93 (SD = 10.29) years. The weighted maximum dose was 7.44 (SD = 9.39) mg/kg/h. SE cessation was attained in 51% (95% confidence interval = 43-59) of cases with the addition of ketamine. The heterogeneity was I2 = 0%, t2 = 0, χ2 (5) = 3.39 (p = .64).

SIGNIFICANCE

Pediatric RSE is difficult to treat, resulting in increased morbidity and mortality. Without strong recommendations and evidence regarding preferred agents, this review provides evidence that ketamine may be considered in managing SE in the pediatric population.

Ketamine as advanced second-line treatment in benzodiazepine-refractory convulsive status epilepticus in children

Status epilepticus (SE) is one of the most common neurological emergencies in children. To date, there is no definitive evidence to guide treatment of SE refractory to benzodiazepines. The main objectives of treatment protocols are to expedite therapeutic decisions and to use fast- and short-acting medications without significant adverse effects. Protocols differ among institutions, and most frequently valproate, phenytoin, and levetiracetam are used as second-line treatment. After failure of first- and second-line medications, admission to the intensive care unit and continuous infusion of anesthetics are usually indicated. Ketamine is a noncompetitive N-methyl-D-aspartate receptor antagonist that has been safely used for the treatment of refractory SE in adults and children. In animal models of SE, ketamine demonstrated antiepileptic and neuroprotective properties and synergistic effects with other antiseizure medications. We reviewed the literature to demonstrate the potential role of ketamine as an advanced second-line agent in the treatment of SE. Pharmacological targets, pathophysiology of SE, and the receptor trafficking hypothesis are reviewed and presented. The pharmacology of ketamine is outlined with related properties, advantages, and side effects. We summarize the most recent and relevant publications on experimental and clinical studies on ketamine in SE. Key expert opinion is also reported. Considering the current knowledge on SE pathophysiology, early sequential polytherapy should include ketamine for its wide range of positive assets. Future research and clinical trials on SE pharmacotherapy should focus on the role of ketamine as second-line medication.

Photobiomodulation improves the synapses and cognitive function and ameliorates epileptic seizure by inhibiting downregulation of Nlgn3

BACKGROUND

Temporal lobe epilepsy (TLE) remains one of the most drug-resistant focal epilepsies. Glutamate excitotoxicity and neuroinflammation which leads to loss of synaptic proteins and neuronal death appear to represent a pathogen that characterizes the neurobiology of TLE. Photobiomodulation (PBM) is a rapidly growing therapy for the attenuation of neuronal degeneration harboring non-invasiveness benefits. However, the detailed effects of PBM on excitotoxicity or neuroinflammation remain unclear. We investigated whether tPBM exerts neuroprotective effects on hippocampal neurons in epilepsy mouse model by regulating synapse and synapse-related genes.

METHODS

In an in vitro study, we performed imaging analysis and western blot in primary hippocampal neurons from embryonic (E17) rat pups. In an in vivo study, RNA sequencing was performed to identify the gene regulatory by PBM. Histological stain and immunohistochemistry analyses were used to assess synaptic connections, neuroinflammation and neuronal survival. Behavioral tests were used to evaluate the effects of PBM on cognitive functions.

RESULTS

PBM was upregulated synaptic connections in an in vitro. In addition, it was confirmed that transcranial PBM reduced synaptic degeneration, neuronal apoptosis, and neuroinflammation in an in vivo. These effects of PBM were supported by RNA sequencing results showing the relation of PBM with gene regulatory networks of neuronal functions. Specifically, Nlgn3 showed increase after PBM and silencing the Nlgn3 reversed the positive effect of PBM in in vitro. Lastly, behavioral alterations including hypoactivity, anxiety and impaired memory were recovered along with the reduction of seizure score in PBM-treated mice.

CONCLUSIONS

Our findings demonstrate that PBM attenuates epileptic excitotoxicity, neurodegeneration and cognitive decline induced by TLE through inhibition of the Nlgn3 gene decrease induced by excitotoxicity.

A companion to the preclinical common data elements and case report forms for neuropathology studies in epilepsy research. A report of the TASK3 WG2 Neuropathology Working Group of the ILAE/AES Joint Translational Task Force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force initiated the TASK3 working group to create common data elements (CDEs) for various aspects of preclinical epilepsy research studies, which could help improve the standardization of experimental designs. This article addresses neuropathological changes associated with seizures and epilepsy in rodent models of epilepsy. We discuss CDEs for histopathological parameters for neurodegeneration, changes in astrocyte morphology and function, mechanisms of inflammation, and changes in the blood-brain barrier and myelin/oligodendrocytes resulting from recurrent seizures in rats and mice. We provide detailed CDE tables and case report forms (CRFs), and with this companion manuscript, we discuss the rationale and methodological aspects of individual neuropathological examinations. The CDEs, CRFs, and companion paper are available to all researchers, and their use will benefit the harmonization and comparability of translational preclinical epilepsy research. The ultimate hope is to facilitate the development of rational therapy concepts for treating epilepsies, seizures, and comorbidities and the development of biomarkers assessing the pathological state of the disease.

Hippocampal Sclerosis in Pilocarpine Epilepsy: Survival of Peptide-Containing Neurons and Learning and Memory Disturbances in the Adult NMRI Strain Mouse

The present experiments reveal the alterations of the hippocampal neuronal populations in chronic epilepsy. The mice were injected with a single dose of pilocarpine. They had status epilepticus and spontaneously recurrent motor seizures. Three months after pilocarpine treatment, the animals were investigated with the Barnes maze to determine their learning and memory capabilities. Their hippocampi were analyzed 2 weeks later (at 3.5 months) with standard immunohistochemical methods and cell counting. Every animal displayed hippocampal sclerosis. The neuronal loss was evaluated with neuronal-N immunostaining, and the activation of the microglia was measured with Iba1 immunohistochemistry. The neuropeptide Y, parvalbumin, and calretinin immunoreactive structures were qualitatively and quantitatively analyzed in the hippocampal formation. The results were compared statistically to the results of the control mice. We detected neuronal loss and strongly activated microglia populations. Neuropeptide Y was significantly upregulated in the sprouting axons. The number of parvalbumin- and calretinin-containing interneurons decreased significantly in the Ammon’s horn and dentate gyrus. The epileptic animals displayed significantly worse learning and memory functions. We concluded that degeneration of the principal neurons, a numerical decrease of PV-containing GABAergic neurons, and strong peptidergic axonal sprouting were responsible for the loss of the hippocampal learning and memory functions.

Intranasal Therapy to Stop Status Epilepticus in Prehospital Settings

Status epilepticus (SE) is a medical emergency characterized by uncontrolled, prolonged seizures with rapid and widespread neuronal damage. Patients that suffer from longer episodes of SE are more likely to have poorer clinical outcomes and a higher cost of healthcare. Understanding novel molecular mechanisms that regulate inhibitory and excitatory neurotransmission that initiate SE and the necessary medical infrastructure to stop SE could help identify targets for early intervention. Intranasal administration of benzodiazepines may shorten the time between initiation and cessation of seizures when compared to other routes of administration. Current pharmaceutical administration guidelines are appropriate for sporadic incidences of SE, but exploring other approaches is necessary to prepare for situations involving multiple patients outside of a hospital, such as a massive chemical weapons attack. Intranasal drug delivery helps to circumvent the blood–brain barrier and offers a noninvasive way to quickly administer drugs in settings that require an immediate response, such as nerve agent exposure. In addition, examining the intranasal delivery of new drugs, such as nanotherapeutics, may lead to more effective, noninvasive, scalable, and portable methods of treating SE.

The role of excitotoxic programmed necrosis in acute brain injury

Excitotoxicity involves the excessive release of glutamate from presynaptic nerve terminals and from reversal of astrocytic glutamate uptake, when there is excessive neuronal depolarization. N-methyl-d-aspartate (NMDA) receptors, a subtype of glutamate receptor, are activated in postsynaptic neurons, opening their receptor-operated cation channels to allow Ca^2 + influx. The Ca^2 + influx activates two enzymes, calpain I and neuronal nitric oxide synthase (nNOS). Calpain I activation produces mitochondrial release of cytochrome c (cyt c), truncated apoptosis-inducing factor (tAIF) and endonuclease G (endoG), the lysosomal release of cathepsins B and D and DNase II, and inactivation of the plasma membrane Na⁺–Ca^2 + exchanger, which add to the buildup of intracellular Ca^2 +. tAIF is involved in large-scale DNA cleavage and cyt c may be involved in chromatin condensation; endoG produces internucleosomal DNA cleavage. The nuclear actions of the other proteins have not been determined. nNOS forms nitric oxide (NO), which reacts with superoxide (O₂⁻) to form peroxynitrite (ONOO⁻). These free radicals damage cellular membranes, intracellular proteins and DNA. DNA damage activates poly(ADP-ribose) polymerase-1 (PARP-1), which produces poly(ADP-ribose) (PAR) polymers that exit nuclei and translocate to mitochondrial membranes, also releasing AIF. Poly(ADP-ribose) glycohydrolase hydrolyzes PAR polymers into ADP-ribose molecules, which translocate to plasma membranes, activating melastatin-like transient receptor potential 2 (TRPM-2) channels, which open, allowing Ca^2 + influx into neurons. NADPH oxidase (NOX1) transfers electrons across cellular membranes, producing O₂⁻. The result of these processes is neuronal necrosis, which is a programmed cell death that is the basis of all acute neuronal injury in the adult brain.

Sustaining high acetylcholine levels in the frontal cortex, but not retrosplenial cortex, recovers spatial memory performance in a rodent model of diencephalic amnesia

Although the thalamus and/or mammillary bodies are the primary sites of neuropathology in cases of diencephalic amnesia such as Wernicke Korsakoff Syndrome (WKS), there is also functional deactivation of certain cortical regions that contribute to the cognitive dysfunction. Acetylcholine (ACh) is a key neurotransmitter that modulates neural processing within the cortex and between the thalamus and cortex. In the pyrithiamine-induced thiamine deficiency (PTD) rat model of WKS, there are significant reductions in cholinergic innervation and behaviorally stimulated ACh efflux in the frontal (FC) and retrosplenial (RSC) cortices. In the present study, ACh released levels were site-specifically amplified with physostigmine (0.5 μg, 1.0 μg) in the FC and the RSC, which was confirmed with in vivo microdialysis. Although physostigmine sustained high ACh levels in both cortical regions, the effects on spatial memory, assessed by spontaneous alternation, were different as a function of region (FC, RSC) and treatment (PTD, pair-fed [PF]). Higher ACh levels in the FC recovered the rate of alternation in PTD rats as well as reduced arm-reentry perseverative errors. However, higher ACh levels within the FC of PF rats exacerbated arm-reentry perseverative errors without significantly affecting alternation rates. Maintaining high ACh levels in the RSC had no procognitive effects in PTD rats, but rather impaired alternation behavior in PF rats. These results demonstrate that diverse cortical regions respond differently to intensified ACh levels-and the effects are dependent on thalamic pathology. Thus, pharmacotherapeutics aimed at enhancing cognitive functions must account for the unique features of cortical ACh stimulation and the connective circuitry with the thalamus.

Therapeutic potential of kainate receptors

Glutamate receptors are key mediators of brain communication. Among ionotropic glutamate receptors, kainate receptors (KARs) have been least explored and their relevance to pathophysiology is relatively obscure. This is in part due to the relatively low abundance of KARs, the regulatory function in network activity they play, the lack of specific agonists and antagonists for this receptor subtype, as well as to the absence of striking phenotypes in mice deficient in KAR subunits. Nonetheless, it is now well established that KARs are located presynaptically whereby they regulate glutamate and GABA release, and thus, excitability and participate in short‐term plasticity. In turn, KARs are also located postsynaptically and their activation contributes to synaptic integration. The development of specific novel ligands is helping to further investigate the contribution of KARs to health and disease. In this review, I summarize current knowledge about KAR physiology and pharmacology, and discuss their involvement in cell death and disease. In addition, I recapitulate the available data about the use of KAR antagonists and receptor subunit deficient mice in experimental paradigms of brain diseases, as well as the main findings about KAR roles in human CNS disorders. In sum, subunit specific antagonists have therapeutic potential in neurodegenerative and psychiatric diseases as well as in epilepsy and pain. Knowledge about the genetics of KARs will also help to understand the pathophysiology of those and other illnesses.

Time course and mechanism of hippocampal neuronal death in an in vitro model of status epilepticus: role of NMDA receptor activation and NMDA dependent calcium entry

The hippocampus is especially vulnerable to seizure-induced damage and excitotoxic neuronal injury. This study examined the time course of neuronal death in relationship to seizure duration and the pharmacological mechanisms underlying seizure-induced cell death using low magnesium (Mg2+) induced continuous high frequency epileptiform discharges (in vitro status epilepticus) in hippocampal neuronal cultures. Neuronal death was assessed using cell morphology and fluorescein diacetate-propidium iodide staining. Effects of low Mg2+ and various receptor antagonists on spike frequency were assessed using patch clamp electrophysiology. We observed a linear and time-dependent increase in neuronal death with increasing durations of status epilepticus. This cell death was dependent upon extracellular calcium (Ca2+) that entered primarily through the N-methyl-d-aspartate (NMDA) glutamate receptor channel subtype. Neuronal death was significantly decreased by co-incubation with the NMDA receptor antagonists and was also inhibited by reduction of extracellular (Ca2+) during status epilepticus. In contrast, neuronal death from in vitro status epilepticus was not significantly prevented by inhibition of other glutamate receptor subtypes or voltage-gated Ca2+ channels. Interestingly this NMDA-Ca2+ dependent neuronal death was much more gradual in onset compared to cell death from excitotoxic glutamate exposure. The results provide evidence that in vitro status epilepticus results in increased activation of the NMDA-Ca2+ transduction pathway leading to neuronal death in a time-dependent fashion. The results also indicate that there is a significant window of opportunity during the initial time of continuous seizure activity to be able to intervene, protect neurons and decrease the high morbidity and mortality associated with status epilepticus.

Transient postictal MRI changes in patients with brain tumors may mimic disease progression

BACKGROUND

Transient postictal imaging abnormalities in patients with non-tumor-related seizures are well documented and include fluid-attenuated inversion recovery/T2 hyperintensity and parenchymal and meningeal contrast enhancement. In contrast, transient postictal imaging abnormalities in patients with tumor-related seizures have been poorly described. Fifty percent of patients with brain tumors have a seizure during the course of their illness and are often imaged after a seizure or after a change in seizure character or frequency. Interval changes on repeat imaging can mimic disease progression or other pathologic processes.

METHODS

We describe 3 patients with brain tumors and transient postictal MRI changes that mimicked disease progression and infection.

RESULTS

Our patients demonstrated fluid-attenuated inversion recovery/T2 hyperintensity and gadolinium enhancement on MRI studies performed shortly after ictal events. These changes were suspicious for tumor progression in 2 cases and for recurrent infection in the third. Control of seizure activity resulted in resolution of these changes on scans obtained 10 to 21 days later.

CONCLUSIONS

Imaging shortly after an ictal event can potentially mislead the clinician to interpret changes as tumor or pathologic progression. Unnecessary intervention in these patients with new and suspicious imaging findings should be avoided. We recommend repeat imaging be performed in patients with brain tumors and seizures several weeks after seizure control if clinically feasible. Further research is needed to delineate the time course of seizure-induced MRI changes.

In vitro and in vivo characterization of [3H]CNS-5161—A use-dependent ligand for theN-methyl-d-aspartate receptor in rat brain

Glutamate is the major excitatory neurotransmitter in the brain. Glutamate activation of the N-methyl-D-aspartate (NMDA) receptor subtype is thought to mediate important physiological and pathological processes, including memory formation and excitotoxicity. The goal of the present work was to characterize and validate a candidate agent for noninvasive positron emission tomography (PET) imaging of this receptor. [(3)H]-labeled N-[3-(3)H]-methyl-3-(thiomethylphenyl)cyanamide (CNS-5161) was incubated with rat brain homogenates at increasing concentrations, temperatures, and times to establish the binding kinetics and affinity of the ligand in vitro. Nonspecific binding was measured with 100 microM MK-801. The compound was also injected i.v. in rats pretreated with saline, NMDA, MK801, or a combination, and organ and brain regional uptake was assessed at various times after injection by autoradiography or dissection. Blood and brain samples were assayed for metabolites by high-performance liquid chromatography. CNS-5161 binds brain membranes with high affinity (K(d) < 4 nM) and fast association and dissociation kinetics. Specific binding increased in the presence of glutamate and glycine. Intravenous administration in control rats resulted in a heterogeneous brain distribution with hippocampus and cortex > thalamus > striatum > cerebellum, and a cortex/cerebellum ratio of 1.4. Pretreatment with NMDA increased the hippocampus-to-cerebellum ratio to 1.6-1.9 while MK801 abolished this increase, resulting in ratios close to 1. Thus, CNS-5161 binds preferentially to the activated state of the NMDA receptor channel in vitro and in vivo. The high affinity and fast kinetics make it compatible with PET imaging of a carbon-11 labeled CNS-5161.

Low doses of memantine disrupt memory in adult rats

Memantine, a drug recently approved for treatment of Alzheimer's disease, has been characterized as a unique NMDA antagonist that confers protection against excitotoxic neurodegeneration without the serious side effects that other NMDA antagonists are known to cause. In the present study, we determined what dose of memantine is required to protect the adult rat brain against an NMDA receptor-mediated excitotoxic process and then tested that dose and a range of lower doses to determine whether the drug in this dose range is associated with significant side effects. Consistent with previous research, we found that memantine confers a neuroprotective effect beginning at an intraperitoneal dose of 20 mg/kg, a dose that we found, contrary to previous reports, produces locomotor disturbances severe enough to preclude testing for learning and memory effects. We then determined that, at intraperitoneal doses of 10 and 5 mg/kg, memantine disrupts both memory and locomotor behaviors. Rats treated with these doses performed at control-like levels in learning a hole-board task but were significantly impaired in demonstrating what they had learned when tested 24 h later. This impairment of memory retention was not state dependent in that it was demonstrable regardless of whether the rats were or were not exposed to memantine on the day of retention testing. We conclude that, in the adult rat, memantine behaves like other NMDA antagonists in that it is neuroprotective only at doses that produce intolerable side effects, including memory impairment.

Prolonged seizures and cellular injury: understanding the connection

Status epilepticus (SE)-induced neuronal death is morphologically necrotic and is initiated by excessive glutamate release, which activates postsynaptic N-methyl-D-aspartate (NMDA) receptors and triggers receptor-mediated calcium influx (excitotoxicity). This results in activation of intracellular proteases and neuronal nitric oxide synthase, with generation of free radicals, and damage to cellular membranes, structural proteins, and essential enzymes. Programmed cell death mechanisms, such as p53 activation, activation of cell death-promoting Bcl-2 family members, and endonuclease-induced DNA laddering, occur in SE-induced neuronal death. Caspase-independent excitotoxic mechanisms, such as NMDA-induced calpain I activation, with activation and translocation of the cell death-promoting Bcl-2 family member Bid from cytoplasm to mitochondria, and subsequent translocation of apoptosis-inducing factor and endonuclease G to nuclei (which cause large-scale and internucleosomal DNA cleavage, respectively), may be triggered by SE. Poly(ADP-ribose) polymerase-1 (PARP-1) activation and cysteinyl cathepsin and DNase II release from lysosomes may occur following SE as well, but these events await future investigation. In the future, rational combinations of central nervous system-penetrable neuroprotective agents, based on our knowledge of excitotoxic mechanisms, may be useful in refractory human SE.

Number of GABA immunonegative and GABA immunopositive neurons in human epileptic temporal cortex

The number of neurons, both GABA immunopositive and immunonegative, was determined in temporal epileptic foci of 7 patients after temporal lobectomy, and compared to neuronal numbers in temporal cortex of two controls taken from tumor operated patients. The thickness of the cortex of the epileptic cortex diminished by about 10%, while the number of nerve cells decreased to 67% of that of the control value: it was 19.000/mm(3) vs. 28.000/mm(3) found in the control. This decline was due to cell degeneration, which, however, was more severe for non-GABAergic nerve cells. Accordingly, the proportion of the GABA-positive neurons in the otherwise diminished neuronal population increased to 36.4% from the 32% control value. The number of GABAergic terminals, however, decreased even further, explaining the resulting disinhibition during epileptic seizures.

The neurophysiology of concussion

Cerebral concussion is both the most common and most puzzling type of traumatic brain injury (TBI). It is normally produced by acceleration (or deceleration) of the head and is characterized by a sudden brief impairment of consciousness, paralysis of reflex activity and loss of memory. It has long been acknowledged that one of the most worthwhile techniques for studying the acute pathophysiology of concussion is by the recording of neurophysiological activity such as the electroencephalogram (EEG) and sensory evoked potentials (EPs) from experimental animals. In the first parts of this review, the majority of such studies conducted during the past half century are critically reviewed. When potential methodological flaws and limitations such as anesthetic protocols, infliction of multiple blows and delay in onset of recordings were taken into account, two general principles could be adduced. First, the immediate post-concussive EEG was excitatory or epileptiform in nature. Second, the cortical EP waveform was totally lost during this period. In the second parts of this review, five theories of concussion which have been prominent during the past century are summarized and supportive evidence assessed. These are the vascular, reticular, centripetal, pontine cholinergic and convulsive hypotheses. It is concluded that only the convulsive theory is readily compatible with the neurophysiological data and can provide a totally viable explanation for concussion. The chief tenet of the convulsive theory is that since the symptoms of concussion bear a strong resemblance to those of a generalized epileptic seizure, then it is a reasonable assumption that similar pathobiological processes underlie them both. Further, it is demonstrated that EPs and EEGs recorded acutely following concussive trauma are indeed the same or similar to those obtained following the induction of a state of generalized seizure activity (GSA). According to the present incarnation of the convulsive theory, the energy imparted to the brain by the sudden mechanical loading of the head may generate turbulent rotatory and other movements of the cerebral hemispheres and so increase the chances of a tissue-deforming collision or impact between the cortex and the boney walls of the skull. In this conception, loss of consciousness is not orchestrated by disruption or interference with the function of the brainstem reticular activating system. Rather, it is due to functional deafferentation of the cortex as a consequence of diffuse mechanically-induced depolarization and synchronized discharge of cortical neurons. A convulsive theory can also explain traumatic amnesia, autonomic disturbances and the miscellaneous collection of symptoms of the post-concussion syndrome more adequately than any of its rivals. In addition, the symptoms of minor concussion (a.k.a. being stunned, dinged, or dazed) are often strikingly similar to minor epilepsy such as petit mal. The relevance of the convulsive theory to a number of associated problems is also discussed. These include the relationship between concussion and more serious types of closed head injury, the utility of animal models of severe brain trauma, the etiology of the cognitive deficits which may linger long after a concussive injury, the use of concussive (captive bolt) techniques to stun farm animals prior to slaughter and the question of why some animals (such as the woodpecker) can tolerate massive accelerative forces without being knocked out.

Sequential changes of brain CT and MRI after febrile status epilepticus in a 6-year-old girl

Brain CT or MRI occasionally shows transient or permanent changes in the brain after status epilepticus (SE). The mechanism for these changes has not been well elucidated. We performed repeated imaging studies on a patient with febrile SE characterized by right hemiconvulsion. CT showed transient mild edema on both hemispheres immediately after the cessation of SE. The edema improved the next day. But aphasia and right hemiparesis were observed. On day 17, CT revealed edema on left hemisphere and MRI showed a high signal intensity in cortex and subcortical white matter of the left hemisphere on T2-weighted images. Although right hemiparesis and aphasia were improved, severe atrophy of the left hemisphere was noted on CT and MRI. The results suggest that brain edema observed in several days after SE but not edema observed immediately after the cessation of SE is more pathological for the permanent brain damage. Possible mechanisms of the initial brain edema and the second edema preceded severe atrophy in left hemisphere were discussed.

Seizure activity results in increased tyrosine phosphorylation of the N-methyl-D-aspartate receptor in the hippocampus

Systemic administration of kainic acid (KA) induces status epilepticus (SE) that causes neurodegeneration and may subsequently lead to spontaneous recurrent seizures. We investigated the effects of KA-induced SE on tyrosine phosphorylation and solubility properties of the NMDA receptor. Following 1 h of SE, total protein tyrosine phosphorylation was elevated in both the hippocampus and frontal cortex relative to controls. Tyrosine phosphorylation of the NMDA receptor subunits NR2A and NR2B was also enhanced following SE. Animals that received KA but did not develop SE, did not exhibit increased tyrosine phosphorylation. SE resulted in a decrease in the solubility of NMDA receptor subunits and of PSD-95 in 1% deoxycholate. In contrast, the detergent solubility of AMPA and kainate receptors was not affected. These findings demonstrate that SE alters tyrosine phosphorylation of the NMDA receptor, and indicate that the interaction of the NMDA receptor with other components of the NMDA receptor complex are altered as a consequence of seizure activity.

Nonconvulsive Seizures Result in Behavioral but Not Electrophysiological Changes in Developing Rats

It is not known if nonconvulsive seizures lead to functional or morphological changes in immature rats. Therefore we studied consequences of such seizures induced by kainic acid (KA) on Postnatal Day (PD) 12 (2 mg/kg ip). The animals were examined electrophysiologically (cortical epileptic afterdischarges (ADs) were elicited in rats with implanted electrodes on PD 14, 18 or 25) and behaviorally (open field was studied in another group of animals on PDs 18 and 25). Hippocampal and cortical morphology was checked by light microscopy (Nissl staining) on PDs 18 and/or 25. Another group of rats was injected with a 6 mg/kg dose of KA on PD 18 and examined on PD 25. The dose of KA used induced only nonconvulsive seizures characterized by automatisms (scratching on PD 12, wet dog shakes on PD 18). Cortical ADs in animals stimulated on PD 14, 18, or 25 did not differ from those in control rats. KA-Treated rats exposed to open field two times (on PDs 18 and 25) exhibited more exploratory activities during the second exposure than control animals. A similar difference was noted in PD 25 rats injected with KA on PD 18. Qualitative histology did not reveal any obvious neuronal damage in hippocampus and cortex. These results demonstrate that nonconvulsive seizures induced at early developmental stages that do not result in observable electrophysiological and morphological changes may have delayed behavioral consequences.

Free radical production correlates with cell death in an in vitro model of epilepsy

Free radical (FR) production, a major step in calcium-dependent neurodegeneration, has been linked to the generation of epileptiform activity and seizure-induced cell death. However, direct evidence of FR production in neurons during seizures has never been presented. Using hippocampal cultured slices we demonstrate that FRs are produced in CA3 but not CA1 pyramidal neurons during the rhythmic synchronous activity induced by the GABAA receptor antagonist bicuculline. The production of FRs (measured as changes in the fluorescence emission of dihydrorhodamine 123) was correlated with an increase in the baseline levels of intracellular calcium ([Ca2+]i) estimated by fluo-3 injected into individual neurons via a patch pipette. [Ca2+]i increased during spike bursting and returned to baseline levels after the burst termination in CA1, but not in CA3, pyramidal neurons where 'interburst' calcium concentrations progressively increased. Measurement of cell death, performed with propidium iodide 48 h after a 30-min exposure to bicuculline, revealed most prominent degeneration of pyramidal neurons in the CA3 pyramidal layer. The FR scavengers vitamin E and glutathione significantly reduced the seizure-induced neurodegeneration without supressing spontaneous epileptiform activity. These observations indicate that FR overproduction is related to seizure-induced neuronal death.

Animal models of nonconvulsive status epilepticus

Nonconvulsive status epilepticus includes three clinical situations: complex partial status epilepticus; absence status epilepticus: and obtundation in the presence of electrographic status epilepticus. Animal models that provide information helpful to clinical management exist for both complex partial and absence status epilepticus. In models of complex partial status epilepticus (pilocarpine, kainic acid, and various protocols using electrical stimulation), neuronal damage in discrete neuronal populations follows an episode of status epilepticus. Hippocampal populations are particularly susceptible to neuropathologic sequelae. Although it is difficult in some cases to distinguish whether the inducing agent or the status epilepticus causes neuropathology, the similar patterns of damage caused by different inducing stimuli provide converging lines of evidence suggesting that the neuropathologic consequences stem at least in part from status epilepticus. In models of absence status epilepticus (genetic mutants, pentylenetetrazole), there is relatively scarce neuropathology that can be attributed directly to status epilepticus. Together these data from animal models suggest that neuropathologic consequences from complex partial status epilepticus may be more severe than those from absence status epilepticus. If these findings translate to patients, then nonconvulsive status epilepticus of the complex partial type should be managed more aggressively than nonconvulsive status epilepticus of the absence type.

Lithium-pilocarpine-induced status epilepticus produces necrotic neurons with internucleosomal DNA fragmentation in adult rats

Prolonged and continuous epileptic seizures [status epilepticus (SE)] produce a widespread pattern of neuronal death, primarily in limbic brain regions. Because it has been suggested that seizure-induced neuronal death may be apoptotic in nature, we tested the hypothesis that lithium-pilocarpine-induced status epilepticus (LPCSE) produces apoptotic neurons. LPCSE lasting 3 h was induced in male Wistar rats which were allowed to recover for 24 or 72 h before perfusion-fixation. Neuronal death was assessed by light microscopy with the haematoxylin-and-eosin stain (H&E), with in situ DNA nick-end labelling (TUNEL stain), by electron microscopy, and by agarose gel electrophoresis of DNA extracted from vulnerable brain regions. Ultrastructurally, acidophilic neurons identified with H&E were dark, shrunken and necrotic in appearance, exhibiting pyknotic nuclei, irregular, dispersed chromatin clumps and cytoplasmic vacuolization. No cells with apoptotic features were seen. Acidophilic neurons were found in 21 out of 23 brain regions examined, and comprised 26-45% of the total number of neurons examined. A subset of these neurons (< 10% of the total number of neurons) were TUNEL-positive at 72 h, but not 24 h, after SE. Internucleosomal DNA cleavage (DNA 'laddering') was found in the six brain regions examined ultrastructurally 24 and 72 h after SE. These results indicate that, in adult rats, LPCSE produces neuronal injury with the appearance of necrosis rather than apoptosis. The necrotic neurons show nuclear pyknosis, chromatin condensation and internucleosomal DNA fragmentation, confirming the nonspecificity of these nuclear changes. Internucleosomal DNA cleavage and other programmed cell death mechanisms can be activated by SE in neurons which become necrotic.

NMDA-receptor activity visualized with (S)-[N-methyl-11C]ketamine and positron emission tomography in patients with medial temporal lobe epilepsy

PURPOSE

To determine whether neurochemical activation of the N-methyl-D-aspartate (NMDA) receptor-gated ion channel shows quantitative changes, measured as binding of 11C-labeled (S)-[N-methyl]ketamine, in patients with medial temporal lobe epilepsy (MTLE).

METHODS

Eight patients with MTLE who were evaluated regarding epilepsy surgery underwent positron emission tomography (PET) with (S)-[N-methyl-11C]ketamine. The presurgical investigations included magnetic resonance imaging (MRI), PET with 18F-fluoro-deoxyglucose (18FDG), and seizure monitoring by using video-EEG. The uptake of (S)-[N-methyl-11C]ketamine in the temporal lobe of ictal onset was compared with the contralateral side and correlated to changes in regional glucose metabolism measured by PET with 18FDG.

RESULTS

(S)-[N-methyl-11C]ketamine rapidly reached the brain, and high radioactivities were measured in the striatum, thalamic nuclei, and cortical regions. Overall the brain uptake and regional binding potentials of (S)-[N-methyl-11C]ketamine were similar to measurements observed previously in healthy controls. However, 20 min after administration, when blood flow influence was negligible, a side-to-side comparison revealed a 9-34% reduction of tracer radioactivity in the temporal lobes of ictal onset. At earlier times, the differences in binding potentials were less pronounced, 9-21%. The magnitude and distribution of the reduction were similar to the metabolic pattern seen on PET scans with 18FDG.

CONCLUSIONS

Radioactivity uptake of intravenously administered (S)-[N-methyl-11C]ketamine was reduced in temporal lobes of ictal in patients with TLE. This may reflect reduced NMDA-receptor density, reduced perfusion, focal atrophy, or other factors.

Extratemporal atrophy in patients with complex partial seizures of left temporal origin

Total cerebral, temporal lobe, hippocampal, caudate, and lenticular nuclei volumes were quantified from magnetic resonance images of 21 patients with left temporal lobe epilepsy and medically intractable complex partial seizures. These regional brain volumes were compared with the same measures in 19 controls. No significant differences in total cerebral, left temporal lobe, right temporal lobe, or total temporal lobe volumes were found. As expected, left hippocampal volumes were significantly smaller in the patients with epilepsy than in control subjects. The left hippocampus-to-right hippocampus volume ratio was significantly lower in patients than in control subjects. In addition to left hippocampal volumes, mean left thalamic, left caudate, and bilateral lenticular volumes were significantly smaller in the patients with epilepsy than in control subjects. The left-to-right thalamic volume ratio was also significantly lower in the patients with epilepsy compared with control subjects, but there were no significant group differences in caudate or lenticular ratios. These results show that medically intractable temporal lobe epilepsy is associated with volume loss in brain structures outside the presumably involved hippocampus. The pathophysiological significance of our findings is uncertain. They could be related to the underlying cause of the disorder. However, volume loss also may reflect damage due to involvement of these structures in recurrent seizure activity.

Effects of a subconvulsant dose of kainic acid on afterdischarges elicited by cortical stimulation in rats

The aim of this study was to test the hypothesis that nonconvulsive seizures elicited by a low dose of kainic acid may induce acute as well as chronic changes in brain function. Cortical epileptic afterdischarges (ADs) characterized by spike-and-wave rhythm and clonic seizures of facial and forelimb muscles were elicited in adult male rats with chronically implanted electrodes. Four stimulations were given in each of four weekly sessions. In the second session, 26 animals were injected with kainic acid (6 mg/kg i.p.) and 19 rats received no injection. The acute effects of kainic acid were to increase the intensity of movements accompanying stimulation and abruptly prolong ADs. Epileptic ADs were followed by a depression of electrocorticographic activity in both noninjected and kainic acid groups. In addition, when kainate was administered, interictal spike activity was registered mostly in the occipital region. One and two weeks after kainate administration, i.e. in the third and fourth stimulation sessions, there was an increased incidence of transitions from spike-and-wave ADs to another, limbic type of afterdischarge. This functional change persisted although no obvious neuronal death was found in the hippocampi of 12 other rats that received the same dose of kainic acid.

Perioperative electroencephalographic seizures in infants undergoing repair of complex congenital cardiac defects

Many infants with cardiac anomalies undergo repair early in life. Both commonly used support techniques, deep hypothermic circulatory arrest (DHCA) and low-flow cardiopulmonary bypass (LFB), may be associated with adverse neurological outcomes, including seizures. In a single center study, 171 infants undergoing correction for D-transposition of the great arteries were randomized to one of these support techniques. Incidence and onset times of EEG seizures during continuous EEG-video monitoring in the first 48 h postoperatively and clinical seizures in the first postoperative week were compared. EEG seizures were characterized by time, duration, and localization of onset. Incidence of EEG seizures (20%) was more than 3 times that of clinical seizures (6%). Most infants with EEG seizures had multiple seizures beginning between 13 and 36 h postoperatively. Durations ranged from 6 s to 980 min. Onset of EEG seizures occurred most commonly in frontal and central regions. Factors associated with EEG seizures included randomization to DHCA, longer duration of circulatory arrest, and diagnosis of VSD. In this study EEG seizures were common following this type of cardiac surgery, illustrating the importance of EEG monitoring in detecting seizures. This data adds insight into mechanisms of seizures in infants undergoing cardiac surgery.

The role of excitatory neurotransmitters in seizure-induced neuronal injury in rats

Prolonged seizures have long been known to be associated with cell injury and cell death in brain. Such seizure-related neuronal injury has been assumed to be mediated by glutamate, the same excitatory amino acid in the central nervous system which propagates the seizure itself. Elevated extracellular concentrations of glutamate have not been demonstrated in brain during seizures in experimental animals. However, these studies have not been performed during status of a duration adequate to induce cell injury, a time when the putative neurotoxins might be demonstrable. We therefore induced status epilepticus (recorded both with conventional surface EEG and with deep electrodes in the area of greatest vulnerability, the piriform cortex) and lengthened the time of status to the point of cell death. Seizures were induced with intravenous kainic acid, and prolonged by injecting the NMDA antagonist AP-7 into the substantia nigra. Microdialysis probes were introduced into the piriform cortex of one hemisphere to assess the presence of extracellular glutamate. In the contralateral hemisphere the degree of neuronal injury was estimated by measurement of heat shock protein (HSP) expression and cell death quantified by acid fuchsin staining. In this model, neuronal injury correlates linearly with seizure duration; however, elevation of glutamate in the extracellular space was not seen even when neuronal injury was profound.

Functional anatomy of human hippocampal formation and related structures

Data on the internal organization, and neuronal connections of the human hippocampal formation and related structures of the limbic system are briefly reviewed. In the healthy brain, somatosensory, visual, and auditory input proceeds through neocortical core and belt fields to a variety of association areas, and from here the data is transported via long corticocortical pathways to the extended prefrontal association cortex. Tracts generated from this highest organization level of the brain guide the data via the frontal belt (premotor cortex) to the frontal core (primary motor area). The striatal and cerebellar loops provide the major routes for this data transfer. The main components of the limbic system (the hippocampal formation, the entorhinal region, and the amygdala) maintain a strategic position between the sensory and the motor association areas. Part of the stream of data from the sensory association areas to the prefrontal cortex branches off and eventually converges on the entorhinal region and the amygdala, These connections establish the afferent leg of the limbic loop. In addition, the limbic centers receive substantial input from nuclei processing viscerosensory information. The entorhinal region, the hippocampal formation, and the amygdala are densely interconnected. Important among these connections is the perforant path, which originates in the entorhinal cortex and projects to the hippocampal formation (fascia dentata, Ammon's horn, and subiculum). The subiculum projects to the amygdala, entorhinal region, mamillary nuclei, and anterior and midline thalamic nuclei. The hippocampal formation, the entorhinal region, and the amygdala generate the efferent leg of the limbic loop, which is directed toward the prefrontal cortex. Additional projections reach the key nuclei that control endocrine and autonomic functions. Furthermore, the amygdala exerts influence on all nonthalamic nuclei projecting in a nonspecific manner to the cerebral cortex (ie, the cholinergic magnocellular forebrain nuclei, the histaminergic tuberomamillary nucleus, the dopaminergic nuclei of the ventral tegmentum, the serotonergic anterior raphe nuclei, and the noradrenergic locus ceruleus). The limbic loop centers thus are in the unique strategic position to perform integration of exteroceptive sensory data of various sources with interoceptive stimuli from autonomic centers. Their efferent projections exert influence on both the prefrontal association cortex and the key centers controlling endocrine and autonomic functions.

The temporal evolution of neuronal damage from pilocarpine-induced status epilepticus

The temporal evolution of irreversible neuronal damage from pilocarpine-induced seizures was studied by light microscopy. Neuronal cell death was judged on a 0-3 scale by estimating the percentage of acidophilic neurons in each of 23 brain regions. In addition, in the dorsal dentate hilus (CA4), quantitative cell counts of normal and acidophilic neurons were also performed. A few dead neurons (grade 0.5 damage) appeared in ventral hippocampal CA1 and CA3 regions after 20-min status epilepticus (SE). Slight-to-mild damage (grades 0.5-1.5) occurred in 14 and 12 brain regions after 40-min and 1-h SE respectively, and slight-to-moderate damage (grades 0.5-2.0) was found in 15 regions after 3-h SE. Twenty-four h and 72 h after 3-h SE, there was slight-to-severe damage (grade 0.5-3.0) in 22 and 21 regions respectively. Three-h SE produced more severe damage to 7 brain regions compared to 1-h SE, and 16 regions had more pronounced neuronal injury 24 h after rather than 0-4 h after 3-h SE. Eight brain regions had less damage 72 h compared to 24 h after SE, probably because of progressive neuronal lysis and dropout, but in mediodorsal and lateroposterior thalamic nuclei damage worsened from 24 to 72 h after SE. Neuronal cell counting revealed 20% acidophilic neurons in dorsal dentate hilus after 40-min SE and no difference between the 1-h and 3-h seizure groups (31% vs. 43% acidophilic neurons respectively). Among the 3 groups of rats with 3-h SE and varying recovery periods, the 24-h and 72-h recovery groups had higher percentages of acidophilic neurons (65% and 54% respectively) than the 0-4-h group (43%). Finally, the hippocampal CA2 region and dentate granule cell layer and the caudate-putamen, considered resistant to seizure-induced cell injury, were all damaged from SE lasting 40 min or more.

Neonatal acetylcholinesterase inhibition by fasciculin 2 in rats: a model for the study of central nervous system development?

Fasciculin 2 (FAS), a potent acetylcholinesterase (AChE, EC 3.1.1.7) inhibitory peptide with affinity for the enzyme in the nanomolar range was utilized together with two other AChE inhibitors (Paroxon and BW284c51) to study the role of AChE in central nervous system development. When drugs were intracisternally injected at postnatal days 3 and 5, only FAS showed a significant inhibition of hippocampus and striatum AChE (39% and 77% inhibition, respectively). After FAS treatment, animals showed convulsive behaviour which was blocked by subcutaneous pretreatment with atropine sulfate (10 mg/kg). An assessment of developmental indices showed no alteration in neurological reflex maturation, motor behaviour or cell morphology. Body weight gain was significantly lower only in FAS-treated animals compared to controls during the preweaning period. To investigate the specificity of this effect a synthetic loop of FAS (showing no activity in vitro or in vivo) and oxidized FAS (showing a weak inhibition in vitro and no activity in vivo) were also intracisternally injected. Animals injected with the loop showed normal body weight development while those treated with oxidized FAS showed impairment in body weight. In conclusion, FAS was the most potent drug at inhibiting neonatal AChE in vivo without nonspecific brain damage. Impairment in body weight seems to be dependent on AChE involvement, although the possibility of a direct FAS effect is discussed. These results point to FAS intracisternal treatment as a useful in vivo model to study the role of AChE in the critical period of early postnatal central nervous system development.

Long-term behavioral deficits following pilocarpine seizures in immature rats

The effect of seizures on subsequent long-term behavior was studied in immature rats. A similar severity of seizures were induced in 20-day old rats (P20) and 45-day old rats (P45) by intraperitoneal injections of pilocarpine at doses of 200 mg/kg and 380 mg/kg, respectively. Immediately after injection of pilocarpine, prolonged seizures with electroencephalographic ictal discharges were observed in both groups of rats. These seizures were followed by seemingly complete neurological recovery. In rats that received pilocarpine at P45 spontaneous recurrent seizures appeared after 4-10 days and persisted until completion of the study at P100. Behavioral tests performed when the rats were fully mature demonstrated that they were more aggressive when handled, more active in open field, and had deficits in learning platform position in the water maze as compared to controls. Furthermore, flurothyl seizure latency was significantly lower in pilocarpine-treated P45 rats than controls. Histology examination showed gross cell loss in the CA3 subfield of the hippocampus in four out of six pilocarpine-treated rats while no cell loss was found in control rats. Rats that received pilocarpine at P20, despite having more severe seizures than the P45 rats, had no histological lesions, did not develop spontaneous recurrent seizures, and had no significant difference in the flurothyl seizure latency test when compared to their controls. While there was no difference between the control and pilocarpine-treated rats in the handling and open field test, P20 rats receiving pilocarpine were slower in learning platform position in the water maze than the controls. Rats receiving pilocarpine at P45 performed significantly more poorly than rats treated at P20 in the water maze. These results suggest that prolonged seizures in immature rats can cause long-term behavioral deficits. However, the severity and nature of these deficits are highly age dependent.

Seizures, brain damage and brain development

Recent evidence suggests that hippocampal damage can be both the result of seizure activity and the cause of further chronic epilepsy. A review of current models of status epilepticus-induced brain damage reveals that excitotoxic mechanisms probably mediate the lesions in most brain regions. NMDA receptors appear to play a dominant role, although non-NMDA glutamate receptors are important in several specific neuronal populations. In the immature brain, a number of unique metabolic features determine a different set of vulnerabilities, resulting in a brain which is more resistant than the adult's to certain mechanisms of brain damage, but quite vulnerable to others. The inhibition of growth by severe seizure activity has implications for the developing brain that have not yet been fully explored. The mechanisms by which seizure-induced hippocampal lesions cause chronic epilepsy have been explored in several recent animal models. A rearrangement of hippocampal circuits may result from death of selected populations of inhibitory neurons, or from misdirected regeneration by excitatory neurons. It could lead to chronic epilepsy through loss of normal inhibition, through sprouting of new excitatory connections, through conservation of excitatory connections which in a healthy brain would be pruned during development, or through facilitation of kindling by one of these mechanisms. These recent results are beginning to reconcile the pathology seen in human hippocampi ablated for intractable epilepsy with that observed in experimental animals, and offer the promise of even greater advances in the future. They suggest a mechanism for Gower's dictum that "seizures beget seizures" and highlight the importance of the interneurons of the dentate gyrus in epileptogenesis.

The competitive NMDA receptor antagonist CGP 40116 protects against status epilepticus-induced neuronal damage

We studied the efficacy of the competitive NMDA receptor antagonist CGP 40116 in protecting against seizure-induced neuronal necrosis from lithium-pilocarpine-induced status epilepticus (SE). Rats were given CGP 40116 either before SE (12 mg/kg i.p.) or 15 min after the onset of SE (4, 12 and 24 mg/kg); controls received normal saline 15 min after SE began. Diazepam and phenobarbital were given i.p. after 3 h of SE to stop the seizures. Rats were killed 24 h later, and their brains were processed for light microscopic examination. Neuronal damage occurred in 24 of 25 brain regions examined in saline-injected animals. Protection was maximal in rats given 12 and 24 mg/kg CGP 40116 after SE onset: 19 and 21 of the 24 damaged regions were protected respectively, but the 24 mg/kg group had a mortality rate comparable to saline-injected controls. No necrotic neurons were found in posterior cingulate and retrosplenial neurons at the two highest CGP 40116 doses, suggesting that the transient cytoplasmic vacuolization induced by NMDA receptor antagonists does not progress to frank necrosis. In rats given CGP 40116 seizure discharges were not eliminated, but their amplitudes were significantly reduced 2 h after SE began. The periodic epileptiform discharge (PED) EEG pattern, probably a sign of widespread neuronal damage, developed in saline-injected controls after 2-2.5 h of SE but not in rats given 12 and 24 mg/kg of CGP 40116. CGP 40116 provided widespread protection against seizure-induced neuronal necrosis, suggesting that an essential step in its production is NMDA receptor activation by endogenous glutamate. The neuroprotection provided was not simply an antiepileptic effect, since electrographic seizures persisted despite NMDA receptor blockade. CGP 40116 and NMDA receptor antagonists in general could be useful as adjunctive neuroprotectants in patients with refractory SE.

Brain parenchyma apparent diffusion coefficient alterations associated with experimental complex partial status epilepticus

The objective of this study was to evaluate whether water apparent diffusion coefficient (ADC) measurements provide more specific information than T2-weighted MRI about the evolution of brain parenchyma lesions secondary to prolonged complex partial seizures. We measured the ADC in the brain of rats exhibiting prolonged complex partial seizures induced by intraperitoneal injection of kainic acid (KA). The animals were imaged with diffusion and T2-weighted MRI at 2 T from 3 h up to 9 days after KA injection. In the piriform cortex and amygdala, the T2-weighted MRI signal intensity appeared to be uniformly increased from 24 to 72 h after KA injection, and returned to normal by 9 days. In the same regions between 24 and 72 h, the ADC first decreased and then increased. The ADC changes were consistent with the known histopathologic alterations. In this complex partial seizure model, the ADC measurement provides more specific information than T2-weighted MRI about the histopathologic evolution of the lesions. This supports the proposal that diffusion MRI may be valuable for the evaluation of the neuropathologic sequelae in patients with multiple or prolonged seizures.

Effect of temperature on kainic acid-induced seizures

The effects of body temperature on kainic acid-induced seizures and seizure-related brain damage were examined in rats. In rats with status epilepticus induced by intraperitoneal injection of 12 mg/kg of kainic acid (KA), ictal discharges were decreased by 50% when body temperature was lowered to 28 degrees C and nearly abolished when body temperature was lowered to 23 degrees C. In rats with mild hypothermia (28 degrees C), the duration of ictal discharges following KA injection was significantly lower than in rats with normal body temperature. No detectable hippocampal cell loss was observed in rats with hypothermia to 28 degrees C whereas gross cell loss in the hippocampus was observed in all rats with KA injection at normal body temperature. In contract to hypothermia, hyperthermia markedly aggravated the seizures and hippocampal damage induced by KA. Following elevation of body temperature to 42 degrees C KA (12 mg/kg) resulted in severe seizures and all rats died of tonic seizures within 2 h. Furthermore, 6 mg/kg of KA administered to rats with a body temperature of 41-42 degrees C, resulted in up to 4 h of continuous ictal discharges whereas no continuous ictal discharges were observed after the same injections in rats with normal body temperature. Histological examination in rats receiving 6 mg/kg of KA revealed severe cell loss in the hippocampus in rats with hyperthermia but not in rats with normal temperature. These results demonstrate that body temperature plays an important role in the control of epileptic seizures and seizure-related brain damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of quisqualic acid and glutamate on subsequent learning, emotionality, and seizure susceptibility in the immature and mature animal

To compare the long-term behavioral effects of chronic administration of excitatory amino acids in the mature and immature brain quisqualic acid (QA) and glutamate (GLU) were administered intraventricularly by osmotic pumps over 7 days in 20- and 60-day-old rats. Both age groups received identical dosages of QA or GLU. At age 90 days, all animals were assessed for abnormalities of learning and memory using the Morris water maze, emotionality using the handling test, and seizure threshold using flurothyl inhalation. No significant differences were found in either the water maze or handling test. However, 60-day-old rats receiving QA or GLU had more spontaneous seizures than the 20-day-old rats. In both age groups histological damage following QA and GLU was limited to the ipsilateral hippocampus, was maximum at the site of the catheter tube, and was similar in the two age groups studied. The adverse effects of long-term effects of chronic exposure to excitatory amino acids are similar in the immature and mature brain.

Brain temperature and the neuroprotective action of enadoline and dizocilpine in the gerbil model of global ischaemia

Mongolian gerbils were subjected to transient forebrain ischaemia by occluding both common carotid arteries for 7 min. Subcutaneous administration of either the kappa-opioid receptor agonist enadoline (CI-977; 1 mg kg-1), or the non-competitive NMDA receptor antagonist dizocilpine (MK-801; 3 mg kg-1), at induction of ischaemia prevented neurodegeneration of CA1-CA2 pyramidal neurones in the dorsal hippocampus. It was shown by continuously monitoring intrahippocampal temperature that brain temperature drops by approximately 4 degrees C during ischaemia, when rectal temperature is maintained normothermic. Enadoline at no time point tested affected brain temperature, whereas dizocilpine statistically lowered brain temperature following ischaemia. These findings suggest that enadoline affords neuroprotection in the absence of any hypothermic episode, whilst in the case of dizocilpine, the small transient hypothermia observed following ischaemia may act synergistically or additively with the drug to yield neuroprotection.

Cerebrospinal fluid levels of neuropeptides, cortisol, and amino acids in patients with epilepsy

We measured lumbar cerebrospinal fluid (CSF) levels of somatostatin, cholecystokinin, neurotensin, atrial natriuretic factor, vasoactive inhibitory peptide, neuropeptide Y, adrenocorticotrophic hormone, corticotropin releasing hormone, beta-endorphin, metenkephalin, cortisol, alanine, glycine, aspartate, glutamate, taurine, and gamma-aminobutyric acid in 25 inpatients with epilepsy at known interictal and postictal times and in 11 neurologically normal volunteers. There were no significant differences between interictal or postictal complex partial seizures (CPS), postictal generalized tonic-clonic seizures (GTC), and control CSF neuropeptide, cortisol, and amino acid (AA) levels. However, there were nonsignificant trends for CSF levels of several neuropeptides to be increased after CPS and GTC as compared with interictal baseline levels. There were significant correlations between levels of certain CSF neuropeptides or (AAs) and serum antiepileptic drug (AED) levels. Several correlations were noted between CSF levels of AAs, including a correlation between the excitatory neurotransmitters aspartate and glutamate identified only after CPS.

Pathophysiological mechanisms of brain damage from status epilepticus

Human status epilepticus (SE) is consistently associated with cognitive problems, and with widespread neuronal necrosis in hippocampus and other brain regions. In animal models, convulsive SE causes extensive neuronal necrosis. Nonconvulsive SE in adult animals also leads to widespread neuronal necrosis in vulnerable regions, although lesions develop more slowly than they would in the presence of convulsions or anoxia. In very young rats, nonconvulsive normoxic SE spares hippocampal pyramidal cells, but other types of neurons may not show the same resistance, and inhibition of brain growth, DNA and protein synthesis, and of myelin formation and of synaptogenesis may lead to altered brain development. Lesions induced by SE may be epileptogenic by leading to misdirected regeneration. In SE, glutamate, aspartate, and acetylcholine play major roles as excitatory neurotransmitters, and GABA is the dominant inhibitory neurotransmitter. GABA metabolism in substantia nigra (SN) plays a key role in seizure arrest. When seizures stop, a major increase in GABA synthesis is seen in SN postictally. GABA synthesis in SN may fail in SE. Extrasynaptic factors may also play an important role in seizure spread and in maintaining SE. Glial immaturity, increased electronic coupling, and SN immaturity facilitate SE development in the immature brain. Major increases in cerebral blood flow (CBF) protect the brain in early SE, but CBF falls in late SE as blood pressure falters. At the same time, large increases in cerebral metabolic rate for glucose and oxygen continue throughout SE. Adenosine triphosphate (ATP) depletion and lactate accumulation are associated with hypermetabolic neuronal necrosis. Excitotoxic mechanisms mediated by both N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors open ionic channels permeable to calcium and play a major role in neuronal injury from SE. Hypoxia, systemic lactic acidosis, CO2 narcosis, hyperkalemia, hypoglycemia, shock, cardiac arrhythmias, pulmonary edema, acute renal tubular necrosis, high output failure, aspiration pneumonia, hyperpyrexia, blood leukocytosis and CSF pleocytosis are common and potentially serious complications of SE. Our improved understanding of the pathophysiology of brain damage in SE should lead to further improvement in treatment and outcome.

Neuropathological changes during generalized seizures in newborn monkeys

The brains of four 2-week-old marmoset monkeys were perfusion-fixed immediately after bicuculline-induced seizures lasting 1.5-4.3 h and were later examined by light and electron microscopy. Mean arterial blood pressure and rectal temperature measurements during seizures did not differ significantly from baseline. Plasma glucose concentrations decreased to the 1.5 mM range at the end of seizures, and arterial pH and bicarbonate were lower than in control animals, although arterial pO2 and pCO2 were maintained. Neuropathological changes were minimal. Swollen astrocytic processes surrounded some capillaries and some neurons in cerebral cortex, hippocampus, putamen and thalamus. Almost all the neurons examined looked normal, but mitochondrial swelling was present in a few. All but the most severe mitochondrial swelling, which occurred very rarely in one of four animals, is potentially reversible. The virtual absence of neuronal necrosis in these neonatal monkeys is consistent with the resistance to seizure-induced brain damage found in immature rats, and stands in sharp contrast to the damage seen in older animals. Lack of neuronal damage, however, does not rule out potential adverse effects of prolonged seizure activity on subsequent brain growth and development.

Intracerebral microdialysis of extracellular amino acids in the human epileptic focus

Extracellular levels of aspartate (ASP), glutamate (GLU), serine (SER), asparagine (ASN), glycine (GLY), threonine (THR), arginine (ARG), alanine (ALA), taurine (TAU), tyrosine (TYR), phenylalanine (PHE), isoleucine (ILEU), and leucine (LEU) were monitored by using intracerebral microdialysis in seven patients with medically intractable epilepsy, undergoing epilepsy surgery. In association with focal seizures, dramatic increases of the extracellular ASP, GLU, GLY, and SER concentrations were observed. The other amino acids analyzed, including TAU, showed small changes. The results support the hypothesis that ASP, GLU, GLY, and possibly SER, play an important role in the mechanism of seizure activity and seizure-related brain damage in the human epileptic focus.

Seizure related elevations of extracellular amino acids in human focal epilepsy

Intracerebral microdialysis combined with electrocorticographic recordings was used in a patient subjected to epilepsy surgery. The patient developed a series of partial seizures during an 8 min period. Marked elevations of aspartate (79-fold), glycine (21-fold), glutamate (16-fold) and serine (8-fold) dialysate concentrations occurred in association with onset of the period with seizures. Recurrent seizures occurred, in spite of normalizing amino acid levels. Other amino acids analyzed (aspargine, threonine, arginine, alanine, taurine, tyrosine, phenylalanine, isoleucine and leucine) showed less pronounced changes (1-5 times the basal levels).

Hippocampal pathology in patients with intractable seizures and temporal lobe masses

The authors examined hippocampal tissue removed during surgical procedures in 17 patients with intractable epilepsy who were found by preoperative magnetic resonance imaging or computerized tomography to have intra-axial masses in the temporal lobe. Neuronal densities in the cornu ammonis (CA) fields of the hippocampus and in the dentate granule cell layer were measured in hematoxylin and eosin-stained sections and were found to be lower compared to a group of 18 autopsy controls. The neuronal densities in all hippocampal fields except CA2 were related to the patient's age at seizure onset. Patients with an earlier onset of seizures had lower neuronal densities. With the exception of CA4, neuronal densities were not significantly related to the duration of the seizure disorder. Cell counts in all fields except CA2 were also related to the location of the lesion in the temporal lobe. Patients with mesial temporal lesions had lower neuronal counts. These results suggest increased vulnerability of hippocampal cytoarchitecture to proximal lesions with early ictal manifestation.