It's time to revise the definition of status epilepticus.
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Adult↗
Biomedical subjects
D H Lowenstein
Publications and source records attributed to D H Lowenstein.
Increased dentate granule cell neurogenesis following amygdala kindling in the adult rat.
Structural neuronal network plasticity is associated with epileptogenesis during limbic kindling, but the full extent of network changes is not well understood. We investigated whether dentate granule cell (DGC) neurogenesis, which continues into adulthood in the rodent, is altered in the amygdala kindling model of epileptogenesis. Adult rats were stimulated to either 4-6, 9-10 or 19-20 class 4/5 (generalized) kindled seizures. 5-Bromo-2'-deoxyuridine labeling showed that cell proliferation increased in the dentate gyrus only in animals that experienced nine or more class 4/5 kindled seizures. Immunocytochemistry for neuronal markers revealed that many of the newly generated cells differentiated into DGCs in the inner aspect of the DGC layer. The lack of increased DGC neurogenesis after fewer kindled seizures or at early timepoints following kindling suggests that this process is not involved in kindling development. Instead, newly generated DGCs may be important for maintenance of the kindled state or the increased susceptibility to spontaneous recurrent seizures.
Amygdala↗
Presynaptic localization of Kv1.4-containing A-type potassium channels near excitatory synapses in the hippocampus.
Mammalian Shaker voltage-gated potassium channels that contain the Kv1.4 subunit exhibit rapid activation and prominent inactivation processes, which enable these channels to integrate brief (approximiately milliseconds) depolarizations over time intervals of up to tens of seconds. In the hippocampus, Kv1.4 immunoreactivity is detected at greatest density in two regions: (1) the middle molecular layer (MML), where perforant path axons synapse with dentate granule cells, and (2) the stratum lucidum (SL) of CA3, where the mossy fibers travel in tight fasciculi and form en passante synapses onto CA3 pyramidal cells. We have studied the localization of Kv1.4 within these regions in detail. First, we compared the distribution of Kv1.4 and synaptophysin (a synaptic vesicle protein primarily localized near termini) under confocal immunofluorescence microscopy. In the MML, Kv1.4 and synaptophysin immunofluorescence appeared to overlap. In the SL, however, Kv1.4 and synaptophysin staining was detected in nonoverlapping, irregular patches ( approximately 5-10 micro m in diameter). Ultrastructural studies of these two regions revealed that Kv1.4 immunoreactivity was absent from the surface membranes of cell bodies and dendrites and occurred prominently on axons, including axonal "necks" near termini. Small excitatory synaptic boutons also were labeled in the MML; by contrast, the mossy fiber synaptic expansions in the SL were not stained. These localizations may enable Kv1.4-containing channels to regulate the process of neurotransmitter release at these excitatory synapses.
Animals↗
The role of diversity in the health care needs of California.
Socioeconomic, racial, and ethic diversity influence many facets of health care, including access to health services, the morbidity and mortality of disease, and the process of training health care professionals. California has an increasingly diverse population, and it is essential that the University of California medical schools carefully address the role of diversity in medical education and in education for the many other professionals who have a key role in the provision of care and services to Californians. In this paper, we provide evidence in support of the belief that the University of California system must train a physician workforce that reflects the racial, ethnic, and socioeconomic characteristics of California's population in order to provide equitable health care to all segments of the state's people.
Attitude of Health Personnel↗
Dentate granule cell neurogenesis is increased by seizures and contributes to aberrant network reorganization in the adult rat hippocampus.
The dentate granule cell layer of the rodent hippocampal formation has the distinctive property of ongoing neurogenesis that continues throughout adult life. In both human temporal lobe epilepsy and rodent models of limbic epilepsy, this same neuronal population undergoes extensive remodeling, including reorganization of mossy fibers, dispersion of the granule cell layer, and the appearance of granule cells in ectopic locations within the dentate gyrus. The mechanistic basis of these abnormalities, as well as their potential relationship to dentate granule cell neurogenesis, is unknown. We used a systemic chemoconvulsant model of temporal lobe epilepsy and bromodeoxyuridine (BrdU) labeling to investigate the effects of prolonged seizures on dentate granule cell neurogenesis in adult rats, and to examine the contribution of newly differentiated dentate granule cells to the network changes seen in this model. Pilocarpine-induced status epilepticus caused a dramatic and prolonged increase in cell proliferation in the dentate subgranular proliferative zone (SGZ), an area known to contain neuronal precursor cells. Colocalization of BrdU-immunolabeled cells with the neuron-specific markers turned on after division, 64 kDa, class III beta-tubulin, or microtubule-associated protein-2 showed that the vast majority of these mitotically active cells differentiated into neurons in the granule cell layer. Newly generated dentate granule cells also appeared in ectopic locations in the hilus and inner molecular layer of the dentate gyrus. Furthermore, developing granule cells projected axons aberrantly to both the CA3 pyramidal cell region and the dentate inner molecular layer. Induction of hippocampal seizure activity by perforant path stimulation resulted in an increase in SGZ mitotic activity similar to that seen with pilocarpine administration. These observations indicate that prolonged seizure discharges stimulate dentate granule cell neurogenesis, and that hippocampal network plasticity associated with epileptogenesis may arise from aberrant connections formed by newly born dentate granule cells.
Animals↗
Mossy fiber reorganization in the epileptic hippocampus.
Reorganization of dentate granule cell axons (mossy fibers) is a prominent aspect of the pathological changes observed in human temporal lobe epilepsy. Although recent work has begun to address the significance of mossy fiber reorganization, the specific and overall functional consequences of these network changes remain poorly understood. New studies are beginning to provide insight into molecular mechanisms underlying this process. Advances in our understanding of the causes and effects of mossy fiber reorganization are likely to provide insight into the pathophysiology of temporal lobe epilepsy, as well as the larger issue of network remodeling following nervous system injury.
Animals↗
The effects of growth factors on the survival and differentiation of cultured dentate gyrus neurons.
Dentate granule cells (DGCs) are the principal cell population of the hippocampal dentate gyrus, and granule cells provide the main excitation to the hippocampus proper via their mossy fibers axons. Although it is well established that granule cells express various growth factors and growth factor receptors, the functional effects of growth factors on the normal development and response to injury of granule cells are relatively unknown. To address this question, primary cultures enriched in DGCs were prepared by microdissecting hippocampal slices from neonatal rats and growing dissociated cells in defined media with added nerve growth factor, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4/5 (NT4/5), ciliary neurotrophic factor, basic fibroblast growth factor (bFGF), or vehicle. The effects on cell survival and morphology were quantified by studying neuron-specific enolase-immunostained cells at various time points, plating densities, host ages, and growth factor concentrations. BDNF or bFGF significantly increased both neuronal survival and differentiation by 30-80% compared with control cultures. Maximal effects were observed at relatively longer time points (5-12 d), with younger cells (postnatal day 3-5) and at lowest plating densities. Addition of a trkB-IgG fusion protein that blocks the activity of BDNF or NT4/5 inhibited the effects of BDNF and attenuated the differentiation of cells cultured at high plating densities. Furthermore, treatment of cultures with the kinase inhibitor K252b specifically blocked the effects of BDNF, suggesting involvement of trkB (the high-affinity BDNF receptor) in BDNF-induced differentiation. These results show that growth properties of cultured neonatal DGCs are influenced by exogenously applied BDNF or bFGF in a time-, age-, and density-dependent manner. The effect of plating density suggests an endogenous expression of growth factors in these culture conditions, and this is mediated in part by endogenous BDNF acting via a tyrosine kinase receptor. Combined with previous work showing that various growth factors and their receptors are expressed by DGCs, these findings provide strong support for the hypothesis that BDNF and bFGF influence both the growth and development of DGCs in vivo.
Animals↗
Dentate granule cell layer collagen explant cultures: spontaneous axonal growth and induction by brain-derived neurotrophic factor or basic fibroblast growth factor.
The molecular mechanisms that underlie dentate granule cell axon (i.e., mossy fiber) growth during development and following seizure-induced hippocampal injury remain unknown. Part of this process may involve specific factors that support dentate granule cells during differentiation, and molecular cues that allow the appropriate growth of mossy fiber axons toward their targets. To study this process, we developed an in vitro assay system to measure the activity of putative trophic, chemoattractant and chemorepulsive factors. Two-hundred-micrometer-thick transverse hippocampal sections were prepared from neonatal rats and microdissected to isolate the middle one-third of the superior blade of the dentate granule cell layer. These were embedded in a three-dimensional collagen matrix either alone or with microdissected regions of the CA2 pyramidal cell layer. Cultures were maintained in a defined medium and grown for two to three days in a standard culture environment. Results showed that numerous processes grew primarily from the hilar side of explants into the collagen matrix, often in excess of 500 microns in length. These were determined to be axons based on: (i) morphological criteria including size and presence of growth cones, (ii) synaptophysin and growth-associated protein-43 immunoreactivity, (iii) lack of glial fibrillary acidic protein immunoreactivity and (iv) contiguity of biocytin-filled processes with neuronal soma within the explant. Treatment of cultures with brain-derived neurotrophic factor caused a significant increase in axon number and length, and this effect was partially reversed by the addition of a trkB-immunoglobulin fusion protein that blocks the activity of brain-derived neurotrophic factor and neurotrophin-4/5. Basic fibroblast growth factor also caused a marked increase in axon number and length, and caused a migration of neuron-like cells out of the explant into the collagen. These results show that cultured dentate granule cell layer explants are capable of growing mossy fibers into a neutral collagen matrix, and the growth of axons can be modified by the addition of exogenous growth factors. Furthermore, since target tissue and point sources of purified factors can easily be co-cultured with the explants, this new system provides a direct means for testing the molecular cues that influence mossy fiber growth.
Animals↗
Recent advances related to basic mechanisms of epileptogenesis.
A variety of clinical observations suggest that certain forms of epilepsy are due to long-term, progressive changes in neural networks that eventually provoke spontaneous and recurring seizures. This process of network transformation, known as epileptogenesis, is a potentially important therapeutic target and also serves as an extremely interesting model of central nervous system plasticity. This article reviews some of the significant, recent advances in our understanding of mechanisms underlying epileptogenesis in different forms of epilepsy. The most substantial progress has been made in work related to temporal lobe epilepsy (TLE), where the biochemical, electrophysiological and anatomical changes in the hippocampus have been intensively studied. This has led to a number of cogent and testable hypotheses, including the concept that dentate granule cell hyperexcitability in TLE is due to a selective loss of hilar neurons that renders inhibitory cells 'dormant.' Studies of other forms of focal epilepsy suggest that a seizure focus may develop as a result of axonal reorganization or immune-mediated effects on membrane channels. Epileptogenesis in generalized epilepsies remains poorly understood, although recent work using models of absence epilepsy point to the critical role of GABAB or T-type calcium channels in the thalamus. Also, new transgenic mouse lines with epilepsy phenotypes have introduced candidate genes, such as those encoding the serotonin 5-HT2C receptor or the alpha subunit of calcium/calmodulin kinase II, that may be responsible for epileptogenesis. Finally, a large amount of investigation has focused on seizure-induced gene expression and it is now clear that seizures can cause a cascade of changes in the expression of gene products that are likely to play a role in network plasticity. Progress in developing 'anti-epileptogenic' therapies will require further advances in understanding the mechanistic roles of these various biochemical and anatomical changes in the transformation of normal to hyperexcitable neural networks.
Animals↗
Eating disorder and epilepsy in mice lacking 5-HT2c serotonin receptors.
Serotonin (5-hydroxytryptamine, 5-HT) is a monoaminergic neurotransmitter that is believed to modulate numerous sensory, motor and behavioural processes in the mammalian nervous system. These diverse responses are elicited through the activation of a large family of receptor subtypes. The complexity of this signalling system and the paucity of selective drugs have made it difficult to define specific roles for 5-HT receptor subtypes, or to determine how serotonergic drugs modulate mood and behaviour. To address these issues, we have generated mutant mice lacking functional 5-HT2C receptors (previously termed 5-HT1C), prominent G-protein-coupled receptors that are widely expressed throughout the brain and spinal cord and which have been proposed to mediate numerous central nervous system (CNS) actions of serotonin. Here we show that 5-HT2C receptor-deficient mice are overweight as a result of abnormal control of feeding behaviour, establishing a role for this receptor in the serotonergic control of appetite. Mutant animals are also prone to spontaneous death from seizures, suggesting that 5-HT2C receptors mediate tonic inhibition of neuronal network excitability.
Amino Acid Sequence↗
Regional induction of c-fos and heat shock protein-72 mRNA following fluid-percussion brain injury in the rat.
To evaluate the cellular response to traumatic brain injury, the expression of mRNA for c-fos and the 72-kDa heat shock protein (hsp72) was determined using in situ hybridization following lateral fluid-percussion injury (2.2-2.4 atm) in rat brain. At 2 h after injury, induction of c-fos mRNA was observed throughout the cortex ipsilateral to the site of injury, while increased expression of hsp72 mRNA was restricted to regions of the cortex surrounding the contusion area. An increase in c-fos mRNA, but not hsp72 mRNA, was observed bilaterally in the CA3 subfield of the hippocampus and the granule cells of the dentate gyrus and in the thalamus ipsilateral to the impact site. By 6 h, increased expression of c-fos mRNA was observed only in the corpus callosum on the impact side; hsp72 mRNA persisted in the deep cortical layers and upper layers of the subcortical white matter below the site of maximal injury. By 24 h, both c-fos and hsp72 mRNA had returned to control levels in all regions of the brain. These results demonstrate that lateral fluid-percussion brain injury triggers regionally and temporally specific expression of c-fos and hsp72 mRNA, which may be suggestive of differential neurochemical alterations in neurons and glia following experimental brain injury.
Animals↗
The stress protein response and its potential relationship to prolonged seizure activity.
Recent investigations have shown that neuronal excitation can lead to a variety of changes in intracellular signaling that ultimately result in altered gene expression. In particular, the excessive neuronal activation seen with seizures leads to the induction of certain "immediate-early" genes that are transcription factors. These transcription factors presumably facilitate the subsequent expression of various "intermediate-late" or effector genes. Given the growing numbers of genes that appear to be modulated by seizures, it appears that seizures initiate a tremendous cascade of changes in gene expression over both the short and the long term. In this article, I discuss two main classes of gene products that are modulated by seizure activity: heat shock proteins and calcium binding proteins. By using both in vivo an in vitro systems, we and others are exploring the conditions that lead to altered expression of genes and the potential significance of such changes in expression. Although the functional meaning of the altered gene expression remains unknown, it seems likely that some of these changes will ultimately be related to certain components of neuronal vulnerability and epileptogenesis.
Animals↗
Selective inhibition of axon outgrowth by antibodies to NGF in a model of temporal lobe epilepsy.
The molecular basis of the axonal reorganization that follows seizure-induced brain injury is unknown. Elevations in neurotrophins following seizures suggest that growth factors may play a role in this process. After pilocarpine-induced seizures, robust axonal sprouting from dentate granule cells and cholinergic forebrain neurons was evident in the inner molecular layer of the dentate gyrus. Intraventricular infusions of an NGF-specific antibody that blocks NGF biological activity in vitro attenuated the cholinergic axonal sprouting and the increases in cell body size of basal forebrain cholinergic neurons that followed seizure-induced injury in vivo. In contrast to its effects on the cholinergic network, the NGF antibody did not decrease the sprouting of dentate granule cell axons into the inner molecular layer. These results suggest that NGF may have a functional and system-specific role in the remodeling of networks that follows repetitive seizures.
Animals↗
Persistent memory dysfunction is associated with bilateral hippocampal damage following experimental brain injury.
Memory dysfunction following head injury is a prominent feature in humans, yet the biological basis of this abnormality remains unknown. Following parasagittal fluid-percussion (FP) brain injury in the rat, we have previously observed profound spatial memory dysfunction relatively soon following injury (i.e. at 42 h). In the present study, we show that this memory dysfunction persists for at least 2 weeks following FP brain injury, and that it is associated with a selective bilateral loss of neurons in the dentate hilar region of the hippocampus. Given the important role of the hippocampus in memory, these observations may provide a potential anatomic substrate to explain, in part, the development posttraumatic memory deficits.
Animals↗
Increased expression of mRNA encoding calbindin-D28K, the glucose-regulated proteins, or the 72 kDa heat-shock protein in three models of acute CNS injury.
Changes at the level of gene expression are becoming an increasingly recognized component of the neuronal response to injury. We used Northern analysis and three in vivo models of central nervous system (CNS) injury in the rat to determine whether injury alters the expression of certain gene products related to cellular homeostasis. The three models included kainate (KA)-induced seizures, global ischemia, and lateral fluid percussion injury to the cerebral cortex. Animals were sacrificed at various times after injury, and total RNA was isolated from specific brain regions. Northern blots were hybridized with probes for calbindin-D28K, the 78 and 94 kDa glucose-regulated proteins (grp78, grp94), the inducible 72 kDa heat-shock protein (hsp72), and a control probe for the 18S ribosomal subunit. Results showed that mRNA for calbindin-D28K, grp78, and hsp72 increased in the hippocampus following seizures. Peak expression occurred 6-12 h after administration of KA, and returned towards baseline in most cases by 24 h. Changes in all four transcripts were seen in the hippocampus or cortex following global ischemia, although the return to baseline tended to exceed 24 h for the grps. In the trauma model, mRNA for hsp72 was increased in the cortex ipsilateral to the impact 12 h after injury. These results expand the repertoire of known changes in mRNA expression following CNS injury. The increases in hsp72 and grps indicate the occurrence of a generalized stress response. Furthermore, given the evidence that grp78 and grp94 are induced by calcium ionophores in vitro, and the potential role of calbindin-D28K in buffering cytoplasmic calcium, the changes observed in this study may represent a cellular response to perturbed calcium homeostasis that is known to occur in acute CNS injury.
Animals↗
Basic concepts of molecular biology for the epileptologist.
Fundamental techniques used in molecular biology can be applied toward questions of relevance to epilepsy. Many of the most common techniques used for working with nucleic acids, including DNA extraction, electrophoresis, cloning in plasmid vectors, making probes, and the polymerase chain reaction are now commonly used in basic epilepsy research. Some specific approaches that can be used to address particular questions are methods for identifying a human gene (Southern analysis and screening a library), determining whether a gene is expressed in a given brain region (Northern analysis and in situ hybridization), and expressing a gene in tissue culture or a whole organism (cell transfection and transgenic animals).
Base Sequence↗