Neuropathologic asymmetries in the brain of a patient with a unilateral status epilepticus

The bidirectional relationship between the cerebellum and seizure networks: a double-edged sword

Epilepsy is highly prevalent and notoriously pharmacoresistant. New therapeutic interventions are urgently needed, both for preventing the seizures themselves as well as negative outcomes and comorbidities associated with chronic epilepsy. While the cerebellum is not traditionally associated with epilepsy or seizures, research over the past decade has outlined the cerebellum as a brain region that is uniquely suited for both therapeutic needs. This review discusses our current understanding of the cerebellum as a key node within seizure networks, capable of both attenuating seizures in several animal models, and conversely, prone to altered structure and function in chronic epilepsy. Critical next steps are to advance therapeutic modulation of the cerebellum more towards translation, and to provide a more comprehensive characterization of how the cerebellum is impacted by chronic epilepsy, in order to subvert negative outcomes.

The cerebellum's understated role and influences in the epilepsies

Approximately 1 in 26 people will develop epilepsy in their lifetime, but current treatment options leave as many as half of all epilepsy patients with uncontrolled seizures. In addition to the burden of the seizures themselves, chronic epilepsy can be associated with cognitive deficits, structural changes, and devastating negative outcomes such as sudden unexpected death in epilepsy (SUDEP). Thus, major challenges in epilepsy research surround the need to both develop new therapeutic targets for intervention as well as shed light on the mechanisms by which chronic epilepsy can lead to comorbidities and negative outcomes. Despite not being traditionally associated with epilepsy or seizures, the cerebellum has emerged as not only a brain region that can serve as an important target for seizure control, but one that may also be profoundly impacted by chronic epilepsy. Here, we discuss targeting the cerebellum for potential therapeutic intervention and discuss pathway insights gained from recent optogenetic studies. We then review observations of cerebellar alterations during seizures and in chronic epilepsy, as well as the potential for the cerebellum to be a seizure focus. Cerebellar alterations in epilepsy may be critical to patient outcomes, highlighting the need for a more comprehensive understanding and appreciation of the cerebellum in the epilepsies.

Increases in GFAP immunoreactive astrocytes in the cerebellar molecular layer of young adult CBA/J mice

Background

CBA/J mice are standard experimental animals in auditory studies, and age-related changes in auditory pathways are well documented. However, changes in locomotion-related brain regions have not been systematically explored.

Results

We showed an increase in immunoreactivity for glial fibrillary acidic protein (GFAP) in the cerebellar molecular layer associated with Purkinje cells in mice at 24 weeks of age but not in the younger mice. Increased GFAP immunoreactivity appeared in the form of clusters and distributed multifocally consistent with hyperplasia of astrocytes that were occasionally associated with Purkinje cell degeneration. Three out of 12 animals at 16 and 24 weeks of age exhibited pre-convulsive clinical signs. Two of these 3 animals also showed increased GFAP immunoreactivity in the cerebellum. Rotarod behavioral assessments indicated decreased performance at 24 weeks of age.

Conclusions

These results suggest minimal to mild reactive astrocytosis likely associated with Purkinje cell degeneration in the cerebellum at 24 weeks of age in CBA/J mice. These findings should be taken into consideration prior to using this mouse strain for studying neuroinflammation or aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-021-00100-5.

The cerebellum and epilepsy

Epilepsy is the fourth most common neurological disorder, but current treatment options provide limited efficacy and carry the potential for problematic adverse effects. There is an immense need to develop new therapeutic interventions in epilepsy, and targeting areas outside the seizure focus for neuromodulation has shown therapeutic value. While not traditionally associated with epilepsy, anatomical, clinical, and electrophysiological studies suggest the cerebellum can play a role in seizure networks, and importantly, may be a potential therapeutic target for seizure control. However, previous interventions targeting the cerebellum in both preclinical and clinical studies have produced mixed effects on seizures. These inconsistent results may be due in part to the lack of specificity inherent with open-loop electrical stimulation interventions. More recent studies, using more targeted closed-loop optogenetic approaches, suggest the possibility of robust seizure inhibition via cerebellar modulation for a range of seizure types. Therefore, while the mechanisms of cerebellar inhibition of seizures have yet to be fully elucidated, the cerebellum should be thoroughly revisited as a potential target for therapeutic intervention in epilepsy. This article is part of the Special Issue "NEWroscience 2018.

Modulating neuroinflammation and oxidative stress to prevent epilepsy and improve outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in young adults worldwide. TBI survival is associated with persistent neuropsychiatric and neurological impairments, including posttraumatic epilepsy (PTE). To date, no pharmaceutical treatment has been found to prevent PTE or ameliorate neurological/neuropsychiatric deficits after TBI. Brain trauma results in immediate mechanical damage to brain cells and blood vessels that may never be fully restored given the limited regenerative capacity of brain tissue. This primary insult unleashes cascades of events, prominently including neuroinflammation and massive oxidative stress that evolve over time, expanding the brain injury, but also clearing cellular debris and establishing homeostasis in the region of damage. Accumulating evidence suggests that oxidative stress and neuroinflammatory sequelae of TBI contribute to posttraumatic epileptogenesis. This review will focus on possible roles of reactive oxygen species (ROS), their interactions with neuroinflammation in posttraumatic epileptogenesis, and emerging therapeutic strategies after TBI. We propose that inhibitors of the professional ROS-generating enzymes, the NADPH oxygenases and myeloperoxidase alone, or combined with selective inhibition of cyclooxygenase mediated signaling may have promise for the treatment or prevention of PTE and other sequelae of TBI. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Time course of the effect of status epilepticus induced in the developing rat on γ-amino butyric acid and glutamate cerebellar concentration

INTRODUCTION

Status epilepticus (SE) is an epileptic condition that can cause cerebellar atrophy and loss of Purkinje cells in both humans and research animals. Cerebellum is a region rich in γ-aminobutyric acid (GABA) and glutamate, and some studies have shown that their concentrations may be altered after convulsions. However, there are no studies showing the effect of seizures on different cerebellar regions in developing rats. Time course of the effect of status epilepticus induced in the developing rat on γ-amino butyric acid and glutamate cerebellar concentration.

METHODS

SE was induced using the lithium-pilocarpine model; control rats were injected with saline solution. At 6h, 24h, and 1 month after SE o saline injection, rats were anaesthetised with pentobarbital and decapitated, and cerebella were extracted. The vermis and hemispheres were dissected and homogenised in 0.1M perchloric acid containing 4mM sodium bisulfite. Homogenates were centrifuged and supernatant was used to quantify GABA, and glutamate tissue concentrations by HPLC coupled with fluorometric detection.

RESULTS

SE did not alter GABA and glutamate tissue concentration in the cerebellar vermis and hemispheres.

CONCLUSION

The developing rat cerebellum is resistant to both short- and long-term neurochemical changes induced by SE.

Cognitive Collaborations: Bidirectional Functional Connectivity Between the Cerebellum and the Hippocampus

There is a growing recognition that the utility of the cerebellum is not limited to motor control. This review focuses on the particularly novel area of hippocampal-cerebellar interactions. Recent work has illustrated that the hippocampus and cerebellum are functionally connected in a bidirectional manner such that the cerebellum can influence hippocampal activity and vice versa. This functional connectivity has important implications for physiology, including spatial navigation and timing-dependent tasks, as well as pathophysiology, including seizures. Moving forward, an improved understanding of the critical biological underpinnings of these cognitive collaborations may improve interventions for neurological disorders such as epilepsy.

Increased neurokinin-1 receptor availability in temporal lobe epilepsy: a positron emission tomography study using [(11)C]GR205171

PURPOSE

Activation of the neurokinin-1 (NK1) receptor by neuropeptide substance P (SP) induces and maintains epileptic activity in various experimental models of epilepsy. The primary objective of this study was to investigate whether neurobiological changes linked to NK1-SP receptor system are associated with hyperexcitability in patients with temporal lobe epilepsy (TLE). A secondary objective was to investigate the relationship between seizure frequency and NK1 receptor availability.

METHODS

A positron emission tomography study was conducted with the selective NK1 receptor antagonist [(11)C]GR205171 in nine patients with TLE and 18 healthy control participants. Parametric PET images were generated using the Patlak graphical method, with cerebellum as reference region. Data analyses including group comparisons were performed using statistical parametric mapping.

RESULTS

Patients with TLE showed increased NK1 receptor availability in both hemispheres with the most pronounced increase in anterior cingulate gyrus ipsilateral to seizure onset. A positive correlation between NK1 receptor availability and seizure frequency was observed in the medial temporal lobe and in the lentiform nucleus ipsilateral to the seizure onset.

CONCLUSION

Our results suggest that there is an intrinsic network using the NK1-SP receptor system for synaptic transmission and epileptiform activity in TLE.

A single episode of neonatal seizures alters the cerebellum of immature rats

PURPOSE

to test whether a single episode of early-life seizures may interfere with the development of the cerebellum. The cerebellum is particularly vulnerable in infants, since it is characterized by an important postnatal histogenesis that leads to the settling of adult circuitry.

METHODS

seizures were induced in 10-day-old Wistar rats with a single convulsive dose (80μg/g b.w., s.c.) of pentylentetrazole (PTZ). Immediately after rats were treated with (3)H-thymidine ((3)HTdR, 2.5μCi/g b.w, s.c.). Rats were killed 4h later and paraffin sections of the cerebellar vermis were processed for (3)HTdR autoradiography and immunocytochemistry for 2/3 subunits of AMPA glutamate receptor (GluR2/3), glutamate transporter 1 (GLT1) and calbindin.

RESULTS

seizures reduced the proliferation rate of cells in the external germinal layer. Purkinje cells showed increased GluR2/3 immunoreactivity. However, some Purkinje cells were unstained or lost. Increased GLT1 immunoreactivity was present in glial cells surrounding Purkinje cells. Calbindin immunoreaction confirmed that some Purkinje cells were missed. The remaining Purkinje cells showed large spheroids along the course of their axon.

CONCLUSIONS

data indicate that seizures lead to a loss and alteration of Purkinje cells in the cerebellum of immature rats. Since at 10 days of life Purkinje cells are no more proliferating, the loss of Purkinje cells should be permanent.

Parvalbumin immunoreactivity and protein content alter in the hippocampus after adrenalectomy in seizure sensitive gerbils

OBJECTIVES

Neurons containing parvalbumin (PV), a calcium-binding protein, in the hippocampus, play an important role in hippocampal excitability in epilepsy. In this study, we examined temporal and spatial changes of PV immunoreactivity and protein content in the hippocampus after adrenalectomy (ADX) in seizure sensitive (SS) gerbils, which are hereditarily seizure-prone.

METHODS

PV distribution and change in SS gerbils after ADX were examined in the hippocampal CA1 region and in the dentate gyrus (DG) using immunohistochemistry and Western blot analysis.

RESULTS

PV immunoreactivity in sham-operated SS gerbils was detected in many CA1 pyramidal cells. Three hours after ADX, PV immunoreactivity significantly decreased in CA1 pyramidal cells and thereafter PV immunoreactivity began to increase by 4 days after ADX. Four days after ADX, PV immunoreactivity was significantly higher than that in the sham-operated SS gerbils. In the DG of sham-operated SS gerbils, PV immunoreactivity was mainly detected in polymorphic cells. Three hours after ADX, PV immunoreactivity in the DG significantly decreased in the polymorphic layer. Thereafter, PV-immunoreactive neurons decreased with time after ADX. Western blot analysis showed that change in PV protein content was similar to immunohistochemical data after ADX in SS gerbils.

CONCLUSION

Our results indicate that PV is changed in hippocampus after ADX and PV may be associated with the regulation of seizure activity.

Childhood status epilepticus and excitotoxic neuronal injury

This report describes the case of an 11-year-old girl with a prior history of epilepsy and multiple episodes of status epilepticus who presented with generalized convulsive status epilepticus and left hemiclonic seizures. Magnetic resonance imaging, including diffusion-weighted sequences and spectroscopy, and neuropathology at autopsy were consistent with excitotoxic neuronal injury to the hippocampus, cortex, thalamus, mammillary bodies, and cerebellum. Review of the literature revealed 11 similar cases that support the hypothesis of excitotoxic neuronal cell death after status epilepticus.

Differential Expression of Cerebellar Metabotropic Glutamate Receptors mGLUR2/3 and mGLUR4a after the Administration of a Convulsant Drug and the Adenosine Analogue Cyclopentyladenosine

Metabotropic glutamate receptors (mGluR) play a role in synaptic transmission, neuronal modulation and plasticity but their action in epileptic activity is still controversial. On the other hand adenosine acts as a neuromodulator with endogenous anticonvulsive properties. Since cerebellum from epileptic patients has shown neuronal damage, sometimes associated with Purkinje cells loss, we have explored the effect of repetitive seizures on two types of mGluR in the cerebellum. Seizures were induced by the convulsant drug 3-mercaptopropionic acid (MP) and the effect of the adenosine analogue cyclopentyladenosine (CPA) alone or before MP administration (CPA+MP) were also evaluated. The expression of the receptors subtypes 2/3 (mGluR2/3) and 4a (mGluR4a) was assessed by immunocitochemistry. Granular cell layer was labeled with mGluR2/3 antibody and increased immunoreactivity was observed after MP (60%), CPA (53%) and CPA + MP (85%) treatments. Control cerebellum slices showed mGluR4a reactivity around Purkinje cells, while MP, CPA and CPA+MP treatment decreased this immunostaining. Repetitive administration of MP and CPA induces an increased cerebellar mGluR2/3 and a decreased mGluR4a immunostaining, suggesting a distinct participation of both receptors that may be related to the type of cell involved. A protective action and /or an apoptotic effect may not be discarded. CPA repetitive administration although increase seizure latency, cannot prevent seizure activity.

Elevated substance P (NK-1) receptor immunoreactivity in the cerebellum of seizure prone gerbil

In the present study, we performed a comparative analysis of the distribution of substance P (SP) receptor (NK-1) immunoreactivity in order to determine the characteristics of the SP system in the cerebelli of rat and gerbils. In the rat cerebellar cortex, only a few Purkinje cells exhibited weak NK-1 receptor immunoreactivity. Similar to the case of rat, NK-1 receptor immunoreactivity in the cerebellar cortex of seizure resistant (SR) gerbils was rarely detected. In contrast, in the cerebellar cortex of seizure sensitive (SS) gerbils, dendrites and cell bodies of Purkinje cell showed strong NK-1 receptor immunoreactivity. Similar to the cerebellar cortex, little NK-1 receptor immunoreactivity in deep cerebellar nuclei was observed in the rat. In SR gerbils, however, deep cerebellar nuclei showed weak NK-1 receptor immunoreactivity. NK-1 receptor immunoreactivity in the deep cerebellar nuclei of SS gerbils was markedly increased, as compared with SR gerbils. Based on the present data, we suggest that the SP system of cerebellar circuit in gerbil are different from rat, and over-expression of NK-1 receptor immunoreactivity in Purkinje cells of SS gerbils may be relevant to Purkinje cell loss induced by seizure activity.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Activation of neurokinin-1 receptors promotes GABA release at synapses in the rat entorhinal cortex

We have previously shown that activation of neurokinin-1 receptors reduces acutely provoked epileptiform activity in rat entorhinal cortex in vitro, and suggested that this may result from an increase in GABA release from inhibitory interneurones. In the present study we have made whole cell patch clamp recordings of spontaneous GABA-mediated inhibitory postsynaptic currents as an indicator of GABA release in slices of rat entorhinal cortex, and determined the effects of neurokinin receptor activation on this release. The neurokinin-1 receptor agonists septide and GR73632 provoked a robust increase in the frequency of GABA-mediated currents, and an increase in mean amplitude. The effects were mimicked by substance P, and blocked by a neurokinin-1 receptor antagonist. High concentrations of neurokinin A had similar effects, which were also blocked by the neurokinin-1 receptor antagonist, but agonists at neurokinin-2 or neurokinin-3 receptors were ineffective. The increases in amplitude and frequency of events provoked by septide were prevented by prior blockade of action potential-dependent release with tetrodotoxin. In current clamp recordings from putative interneurones, GR73632 evoked depolarisation and a prolonged discharge of action potentials. Finally, recordings from pyramidal neurones and oriens-alveus interneurones in CA1 of the hippocampus showed that application of GR73632 caused an increase in frequency and amplitude of GABA-mediated inhibitory postsynaptic currents in the former and persistent firing of action potentials in the latter. The results demonstrate that neurokinin-1 receptor activation promotes the release of GABA at synapses on principal neurones in both entorhinal cortex and hippocampus. The abolition of this effect by tetrodotoxin and the excitatory responses seen in interneurones clearly suggest that the neurokinin-1 receptor is localised on the soma-dendritic domain of the inhibitory neurones. Thus, substance P inputs to inhibitory neurones may have a widespread influence on cortical network excitability and could play a role in epileptogenesis and its control.

Neurokinin-receptor-mediated depolarization of cortical neurons elicits an increase in glutamate release at excitatory synapses

Using whole-cell patch-clamp recordings of spontaneous synaptic activity, we have previously shown that activation of neurokinin-1 (NK1) but not NK3 receptors leads to increased GABA release onto principal cells in the rat entorhinal cortex. In the present study, we examine the effect of activation of these receptors on spontaneous excitatory synaptic responses mediated by glutamate. Both neurokinin B (NKB) and the specific NK3 receptor agonist, senktide, increased the spontaneous release of glutamate, and a similar effect was also seen with substance P (SP) and other NK1 receptor agonists. The increased release induced by either SP or senktide was absent in the presence of tetrodotoxin, demonstrating that it was likely to occur via activation of presynaptic excitatory neurons. Current-clamp recordings confirmed that principal neurons were depolarized by both NK3 and NK1 agonists. However, the response to the former but not the latter persisted in tetrodotoxin, allowing us to conclude that NK3 receptor activation provoked glutamate release via recurrent collaterals between principal neurons, whereas the NK1 receptors may be localized to excitatory interneurons. Finally, the increased release induced by senktide, but not SP, was reduced by an antagonist of group III metabotropic glutamate receptors. Thus, glutamate release from recurrent collaterals is facilitated by a presynaptic group III autoreceptor [Evans, D.I.P., Jones, R.S.G. & Woodhall, G.L. (2000) J. Neurophysiol.,83, 2519-2525], whereas the terminals of neurons responsible for the NK1-receptor induced glutamate release may not bear these receptors. These results have implications for control of activity and epileptogenesis in cortical networks.

The decreases in calcium binding proteins and neurofilament immunoreactivities in the Purkinje cell of the seizure sensitive gerbils

In previous studies, it has been reported that Purkinje cell degeneration during seizure is evoked by excitotoxicity due to an increase in the intracellular Ca(2+) level, though calbindin D-28k (CB) and parvalbumin (PV), intracellular free calcium buffers, are abundantly colocalized in these cells. In the present study, we investigated the expressions of CB, PV, neurofilament (NF) 68, 150, 200, and polyphosphorylated epitope in NF (RT 97), in the cerebellum of gerbils to identify the mechanism of Purkinje cell damages induced by seizure. In seizure resistant gerbils, nearly all the Purkinje cells showed CB, PA, NF 150, NF 200 and RT 97 immunoreactivity. In SS gerbils, however, a clear decrease in the number of CB(+) and PV(+) Purkinje cells was observed. The NF and RT 97 immunoreactivities, in the Purkinje cells was also lower (except NF 68), but not absent. These results suggest several points. First, the decrease in the concentrations of CB and PV may render the Purkinje cells more susceptible to intermittent Ca(2+) fluctuations and more prone to accumulating intolerable quantities of Ca(2+). Second, during the Ca(2+)-PV interaction PV plays an important role in facilitating donations of Mg(2+), which is a potent enzyme activator in phosphorylation. Thus the decline in PV concentration also implicated the defects of phosphorylation in the NF. Third, increases in both the intracellular Ca(2+) level and dephosphorylation trigger the degradation of the NF, particularly NF 200. Finally, these degradations in the NF induce the functional defects in Purkinje cell, which then cause Purkinje cell degeneration.

High level of adenosine A1 receptor-like immunoreactivity in the CA2/CA3a region of the adult rat hippocampus

We describe the immunocytochemical distribution of adenosine A1 receptors in the rat hippocampus. Adenosine A1 receptor-like immunoreactivity was seen on the cell soma and dendrites of pyramidal cells and the cell soma and proximal part of dendrites of granule cells, but not on glial cells. Developmentally, adenosine A1 receptor-like immunoreactivity was diffuse on postnatal day 7 and increased in intensity in individual cells by day 21. In the CA2/CA3a region, the adult pattern of A1 receptor distribution was established by day 28. In the adult rat hippocampus, rostrocaudal inspection revealed that immunoreactivity in CA2/CA3a was greatest. Confocal microscopy revealed differences in the staining patterns for the adenosine A receptor and synaptophysin, a marker of presynaptic terminals. This result suggests that the adenosine A1 receptor might have postsynaptic physiological functions. Double-labeling of adenosine A1 receptors and anterogradely-labeled fibers from the supramammillary nucleus showed that the fibers from the supramammillary nucleus terminate directly on the cell soma of the A1 receptor-immunopositive neurons in CA2/CA3a and the dentate gyrus. These results indicate that the adenosine A 1 receptor in CA2/CA3a and the dentate gyrus are in a position to regulate hippocampal theta activity and that resultant strong synaptic depression in CA2/CA3a could play a role in regulating the intrinsic signal flow between CA3 and CA1.

Neuroprotective effects of early vs. late administration of dantrolene in experimental status epilepticus

We examined the effects of dantrolene, an inhibitor of intracellular calcium release, on hippocampal neuronal damage associated with 140 min of limbic status epilepticus in the rat. Dantrolene (10 mg/kg i.p.) was administered after either 30 min or 140 min of status epilepticus. Early administration was associated with a significant reduction in the amount of neuronal injury in all hippocampal subregions, while late administration was associated with less neuronal injury in area CA3 only. These findings suggest that a substantial portion of seizure-induced hippocampal injury is associated with release of calcium from intracellular stores, and that early administration of dantrolene may be a useful adjunct to anticonvulsant treatment of status epilepticus.

Topiramate reduces neuronal injury after experimental status epilepticus

Prolonged seizures are associated with injury to vulnerable neurons, particularly in the hippocampus. Identification of compounds that attenuate injury after prolonged seizures could be of value in the management of refractory status epilepticus. We hypothesized that topiramate, an anticonvulsant with multiple mechanisms of action, would attenuate hippocampal neuronal injury when given after experimental status epilepticus. Limbic status epilepticus was induced in adult male Wistar rats for 140 min by unilateral hippocampal electrical stimulation. Rats then received intraperitoneal injections of either vehicle (n=6) or topiramate at 20 mg/kg (n=6), 40 mg/kg (n=7) or 80 mg/kg (n=7). Three days later, hippocampal sections were processed for neuronal degeneration using a silver impregnation stain. Seizure-induced damage was assessed by measuring the density of silver staining in hippocampal regions CA1, CA3 and dentate hilus. Administration of topiramate at each dose was associated with a significant reduction in staining density bilaterally in area CA1 and the dentate hilus. Reduction in staining density in area CA3 was seen contralateral to the side of stimulation at the two higher topiramate doses only. The results indicate that administration of topiramate after experimental status epilepticus can attenuate seizure-induced hippocampal neuronal injury.

Tachykinins may modify spontaneous epileptiform activity in the rat entorhinal cortex in vitro by activating GABAergic inhibition

The effects of substance P and related tachykinins on intrinsic membrane properties and synaptic responses of neurons in cortical slices were determined. Substance P had no detectable effect on membrane properties of principal neurons in layer II or V of the rat medial entorhinal cortex or on neurons in either layer of the anterior cingulate cortex. Specific agonists at the neurokinin1-receptor were also without effect as were agonists at both neurokinin1- and neurokinin3-receptors. Substance P hyperpolarized a small number of principal neurons. These responses were weak and desensitized with repeated applications. Similar effects were seen with other neurokinin1-receptor agonists. Excitatory synaptic potentials mediated by either alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate- or N-methyl-D-aspartate-receptors in principal neurons of the entorhinal cortex were unaffected by substance P. Responses of entorhinal neurons to iontophoretically applied glutamate and N-methyl-D-aspartate were also unaffected. Inhibitory synaptic potentials mediated by either GABA(A)- or GABA(B)-receptors in entorhinal neurons were slightly but consistently enhanced by substance P. Neurons identified as interneurons on the basis of their firing characteristics were consistently depolarized by substance P. These responses also desensitized with repeated applications. Spontaneous epileptiform discharges evoked in entorhinal cortex by perfusion with a GABA(A)-receptor antagonist (bicuculline), were reduced in frequency and, sometimes, in duration by substance P. This effect was mimicked by other neurokinin1-receptor agonists and blocked by neurokinin1-receptor antagonists. It was also mimicked by neurokinin A but not by a specific neurokinin1-receptor agonist. The reduction in frequency of discharges was also mimicked by a GABA(B)-receptor agonist, L-baclofen, and blocked by the GABA(B)-receptor antagonist, CGP55845A. Neurokinin B, and a specific neurokinin1-receptor agonist (senktide), increased the frequency and (sometimes) duration of epileptiform discharges. Substance P could also increase frequency but this usually succeeded or preceded a decrease in frequency. The effect of neurokinin B was reduced by a metabotropic glutamate receptor antagonist. Substance P appears to have little direct effect on principal neurons of the entorhinal cortex but may hyperpolarize them indirectly by activating interneurons and releasing GABA. This indirect inhibition may be responsible for the ability of substance P to reduce the frequency of epileptiform discharges in the entorhinal cortex and may suggest that neurokinin1-receptor agonists have potential as anticonvulsant drugs.

Kainic acid-induced sprouting of dynorphin- and enkephalin-containing mossy fibers in the dentate gyrus of the rat hippocampus

This study utilized Timm histochemistry and immunocytochemistry to determine the prolonged effects of kainic acid on the distribution of dynorphin- and enkephalin-containing mossy fibers in the rat dentate gyrus at progressive time points following kainic acid injection. Beginning 1-2 weeks after kainic acid administration, a progressive increase in the distribution and intensity of staining for supragranular zinc, dynorphin and enkephalin was observed in the dentate gyrus. The kainic acid-induced sprouting of mossy fibers containing dynorphin and enkephalin strongly resembles the pattern observed in the dentate gyrus of humans with temporal lobe epilepsy.

Myocyte-specific enhancer binding factor 2C expression in human brain development

Myocyte-specific enhancer binding factor 2C (MEF2C) activates transcription by binding to the myocyte-specific enhancer binding factor 2 (MEF2) regulatory element and has been shown previously to be expressed in muscle and in the brain. We have now studied MEF2C expression in human brain using an antiserum raised against amino acids 140-238 of MEF2C. Western blotting demonstrated that, in fetal brain, MEF2C-immunoreactive bands have the same apparent molecular weight as those in extracts of COS cells transfected with MEF2C complementary DNA. In adult brain, however, MEF2C-immunoreactive bands have a higher molecular weight. In the cerebral cortex, MEF2C immunoreactivity is present in the cortical plate, and is not found in the intermediate zone or ventricular zone. At 14 weeks of gestation, the earliest age examined, MEF2C immunoreactivity is present in cell nuclei throughout the cortical plate. Subsequently, MEF2C immunoreactivity develops a bilaminate and then a trilaminate distribution, and ultimately is expressed preferentially in layers II, IV and VI of mature neocortex. MEF2C immunoreactivity is also found in entorhinal cortex, hippocampus, claustrum, cerebellum and amygdala, and in scattered cells in the thalamus. These findings suggest a role for MEF2C in postmitotic neuronal differentiation, in particular, in the development of certain cortical layers, but also in differentiation of other neurons as well.

Increase in enkephalin-like immunoreactivity in hippocampi of adults with generalized epilepsy

The changes of opioid peptide reactivity in seizure activity have been well studied in animals. Increased enkephalin and dynorphin immunoreactivity in the hippocampi of animals are interpreted as the result of seizure induced mossy fibre sprouting. We studied the hippocampi of six patients with a history of long-standing grand mal seizures and six age-matched control patients with no history of epilepsy or neurologic disease, using frozen sections which were immunostained with antibodies against Leu-enkephalin and Met-enkephalin. The staining intensity in the CA3, CA4 and internal molecular layer of the dentate fascia in each case was quantified using optical densitometry image analysis. The CA3 and CA4 of the epileptic hippocampi showed highly significant increase in Leu-enkephalin-like immunoreactivity compared to the controls (P < 0.005) while the inner molecular layer showed only significant increase (P < 0.05). Met-Enkephalin-like immunoreactivity was only significantly increased in CA4 of the epileptic hippocampi (P < 0.05).

Status epilepticus may be caused by loss of adenosine anticonvulsant mechanisms

The inhibitory neuromodulator adenosine is an endogenous anticonvulsant that terminates brief seizures in the brain and it has been proposed that loss of adenosine or adenosine-mediating systems may play a major role in the development of status epilepticus, a seizure condition characterized by prolonged and/or recurrent seizures that last by definition, at least 20 min. In this study, the effect of specific A1-adenosine agonists and antagonists were tested for their ability to prevent and cause status epilepticus in two electrical stimulation models in rats. In a recurrent electrical stimulation model, whereas no vehicle-treated animals developed status epilepticus after 20 recurrent electrical stimulations, rats injected with 10 mg/kg of the specific A1-adenosine antagonist 8-cyclopentyl-1,3-dimethylxanthine intraperitoneally developed status epilepticus after stimulation. 8-(p-Sulphophenyl)-theophylline, which has limited penetrability into the brain when administered peripherally, did not cause status epilepticus when injected intraperitoneally. However, when 200 micrograms of 8-(p-sulphophenyl)-theophylline were administered intracerebroventricularly, status epilepticus developed in all animals, suggesting status epilepticus developed as a result of central adenosine receptor antagonism. In the second study, whereas all vehicle-treated animals developed status epilepticus after constant electrical stimulation, administration of N6-cyclohexyladenosine and N6-cyclopentyladenosine prior to stimulation suppressed the development of status epilepticus. N6-Cyclohexyladenosine was also effective in terminating status epilepticus after it had progressed for 20 min. The effects of a selective A2-agonist was also tested on both stimulation models and had no anticonvulsant effects. An electrical stimulus given to rats pretreated three days prior to stimulation with pertussis toxin, a compound which inactivates Gi-proteins, also resulted in generalized status epilepticus, suggesting that impairment of G-protein-linked receptors is involved in the development of status epilepticus. The effects of a GABAB antagonist, phaclofen, and a GABAB agonist, baclofen, were also tested in the recurrent stimulation model, as GABAB receptors are also coupled to the same subset of K+ channels as the A1-receptor. Rats given phaclofen did not develop status epilepticus after recurrent electrical stimulation, although baclofen was effective at preventing the induction of status epilepticus in the constant stimulation model. These results, together with some preliminary data obtained showing that the GABAA antagonist picrotoxin did not cause status epilepticus after recurrent stimulation, suggest that loss of GABAergic inhibition only has a minor role in status epilepticus development in our models. Brains from all animals were also assessed for brain injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Transient expression of calbindin-D28k immunoreactivity in layer V pyramidal neurons during postnatal development of kitten cortical areas

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric acid inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (P0) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to layer I, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas postnatally. Transient staining in extrastriate visual cortical areas disappeared first from the lateral suprasylvian areas, and persisted longest in area 7. Pyramidal neurons in the cingulate gyrus expressed calbindin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.