Several lines of evidence suggest that cannabinoid compounds are anticonvulsant. However, the anticonvulsant potential of cannabinoids and, moreover, the role of the endogenous cannabinoid system in ...regulating seizure activity has not been tested in an in vivo model of epilepsy that is characterized by spontaneous, recurrent seizures. Here, using the rat pilocarpine model of epilepsy, we show that the marijuana extract Delta9-tetrahydrocannabinol (10 mg/kg) as well as the cannabimimetic, 4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenyl-carbonyl)-6H-pyrrolo3,2,1-i,jquinolin-6-one R(+)WIN55,212 (5 mg/kg), completely abolished spontaneous epileptic seizures. Conversely, application of the cannabinoid CB1 receptor (CB1) antagonist, N-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A), significantly increased both seizure duration and frequency. In some animals, CB1 receptor antagonism resulted in seizure durations that were protracted to a level consistent with the clinical condition status epilepticus. Furthermore, we determined that during an short-term pilocarpine-induced seizure, levels of the endogenous CB1 ligand 2-arachidonylglycerol increased significantly within the hippocampal brain region. These data indicate not only anticonvulsant activity of exogenously applied cannabinoids but also suggest that endogenous cannabinoid tone modulates seizure termination and duration through activation of the CB1 receptor. Furthermore, Western blot and immunohistochemical analyses revealed that CB1 receptor protein expression was significantly increased throughout the CA regions of epileptic hippocampi. By demonstrating a role for the endogenous cannabinoid system in regulating seizure activity, these studies define a role for the endogenous cannabinoid system in modulating neuroexcitation and suggest that plasticity of the CB1 receptor occurs with epilepsy.
Alterations in hippocampal neuronal Ca2+and Ca2+-dependent systems have been implicated in mediating some of the long-term neuroplasticity changes associated with acquired epilepsy (AE). However, ...there are no studies in an animal model of AE that directly evaluate alterations in intracellular calcium concentration ( Ca2+i) and Ca2+homeostatic mechanisms ( Ca2+dynamics) during the development of AE. In this study, Ca2+dynamics were evaluated in acutely isolated rat CA1 hippocampal, frontal, and occipital neurons in the pilocarpine model by using Ca2+iimaging fluorescence microscopy during the injury (acute), epileptogenesis (latency), and chronic-epilepsy phases of the development of AE. Immediately after status epilepticus (SE), hippocampal neurons, but not frontal and occipital neurons, had significantly elevated Ca2+icompared with saline-injected control animals. Hippocampal neuronal Ca2+iremained markedly elevated during epileptogenesis and was still elevated indefinitely in the chronic-epilepsy phase but was not elevated in SE animals that did not develop AE. Inhibiting the increase in Ca2+iduring SE with the NMDA channel inhibitor MK801 was associated in all three phases of AE with inhibition of the changes in Ca2+dynamics and the development of AE. Ca2+homeostatic mechanisms in hippocampal neurons also were altered in the brain-injury, epileptogenesis, and chronic-epilepsy phases of AE. These results provide evidence that Ca2+iand Ca2+-homeostatic mechanisms are significantly altered during the development of AE and suggest that altered Ca2+dynamics may play a role in the induction and maintenance of AE and underlie some of the neuroplasticity changes associated with the epileptic phenotype.
Purpose: Stroke is the most common cause of acquired epilepsy. The purpose of this investigation was to characterize the role of calcium in the in vitro, glutamate injury–induced epileptogenesis ...model of stoke‐induced epilepsy.
Methods: Fura‐2 calcium imaging and whole‐cell current clamp electrophysiology techniques were used to measure short‐term changes in neuronal free intracellular calcium concentration and long‐term alterations in neuronal excitability in response to epileptogenic glutamate injury (20 μM, 10 min) under various extracellular calcium conditions and in the presence of different glutamate‐receptor antagonists.
Results: Glutamate injury–induced epileptogenesis was associated with prolonged, reversible elevations of free intracellular calcium concentration during and immediately after injury and chronic hyperexcitability manifested as spontaneous recurrent epileptiform discharges for the remaining life of the cultures. Epileptogenic glutamate exposure performed in solutions containing low extracellular calcium, barium substituted for calcium, or N‐methyl‐d‐aspartate (NMDA)‐receptor antagonists reduced the duration of intracellular calcium elevation and inhibited epileptogenesis. Antagonism of non–NMDA‐receptor subtypes had no effect on glutamate injury–induced calcium changes or the induction epileptogenesis. The duration of the calcium elevation and the total calcium load statistically correlated with the development of epileptogenesis. Comparable elevations in neuronal calcium induced by non–glutamate receptor–mediated pathways did not cause epileptogenesis.
Conclusions: This investigation indicates that the glutamate injury–induced epileptogenesis model of stroke‐induced epilepsy is calcium dependent and requires NMDA‐receptor activation. Further, these experiments suggest that prolonged, reversible elevations in neuronal free intracellular calcium initiate the long‐term plasticity changes that underlie the development of injury‐induced epilepsy.
Neutrino tridents and W-Z interference MISHRA, S. R; RABINOWITZ, S. A; QUINTAS, P. Z ...
Physical review letters,
06/1991, Letnik:
66, Številka:
24
Journal Article
Recenzirano
We present a measurement of neutrino tridents, muon pairs induced by neutrino scattering in the Coulomb field of a target nucleus, in the Columbia-Chicago-Fermilab-Rochester neutrino experiment at ...the Fermilab Tevatron. The observed number of tridents after geometric and kinematic corrections, 37.0{plus minus}12.4, supports the standard-model prediction of 45.3{plus minus}2.3 events. This is the first demonstration of the {ital W}-{ital Z} destructive interference from neutrino tridents, and rules out, at 99% C.L., the {ital V}-{ital A} prediction without the interference.
Ca2+/calmodulin-dependent protein kinase II (CaM Kinase II) activity was evaluated in a well-characterized in vitro model of epileptiform activity. Long-lasting spontaneous recurrent seizure (SRS) ...activity was induced in hippocampal neuronal cultures by exposure to low Mg2+ media for 3 h. Analysis of endogenous Ca2+/calmodulin-dependent phosphorylation revealed a significant long-lasting decrease in 32P incorporation into the alpha (50 kDa) and beta (60 kDa) subunits of CaM kinase II in association with the induction of SRS activity in this preparation. Ca2+/calmodulin-dependent substrate phosphorylation of the synthetic peptides, Autocamtide-2 and Syntide II, was also significantly reduced following the induction of SRSs and persisted for the life of the neurons in culture. The decrement in CaM kinase II activity associated with low Mg2+ treatment remained significantly decreased when values were corrected for changes in levels of alpha subunit immunoreactivity and neuronal cell loss. Addition of the protein phosphatase inhibitors, okadaic acid and cyclosporin A, to the phosphorylation reaction did not block the SRS-associated decrease in substrate phosphorylation, indicating that enhanced phosphatase activity was not a contributing factor to the observed decrease in phosphate incorporation. The findings of this study demonstrate that CaM kinase II activity is decreased in association with epileptogenesis observed in these hippocampal cultures and may contribute to the production and maintenance of SRSs in this model.
We used brief bilateral carotid artery occlusion in gerbils to examine the effects of temperature on ischemia-induced inhibition of calcium/calmodulin-dependent protein kinase II activity and ...neuronal death. In normothermic (36 degrees C) gerbils, ischemia induced a severe loss of hippocampal CA1 pyramidal neurons measured 7 days after ischemia (28.4 neurons/mm, n = 10; control density in 10 naive gerbils 262.1 neurons/mm) and a significant decrease in forebrain calcium/calmodulin-dependent protein kinase II autophosphorylation measured 2 hours after ischemia (12.9 fmol/min, n = 6; control phosphorylation in six naive gerbils 23.5 fmol/min). The effect of temperature on these indicators of ischemic damage was examined by adjusting intracerebral temperature before and during the ischemic insult. Hyperthermic (39 degrees C) gerbils showed almost complete loss of neurons in the CA1 region (3.0 neurons/mm, n = 11) and extension of neuronal death into the CA2, CA3, and CA4 regions. In addition, hyperthermia exacerbated ischemia-induced inhibition of calcium/calmodulin-dependent protein kinase II activity (4.2 fmol/min, n = 6). Hypothermia (32 degrees C) protected against ischemia-induced CA1 pyramidal cell damage (257.0 neurons/mm, n = 20) and inhibition of calcium/calmodulin-dependent protein kinase II activity (26.0 fmol/min, n = 6). Our results are consistent with the hypothesis that loss of calcium/calmodulin-dependent protein kinase II activity may be a critical event in the development of ischemia-induced cell death.
We looked at FiO2, choice of anesthetic, nutritional status, and body temperature in a gerbil model of forebrain ischemia to determine their effect on data interpretation, ischemic outcome, and ...extent of pharmacologic protection. We subjected 484 gerbils to 5 minutes of forebrain ischemia under different experimental conditions. The gerbils were anesthetized with 3% halothane and inspired 21% O2, 37% O2 and 60% N2O, or 97% O2. Six groups of gerbils pretreated with 200 mg/kg phenytoin or 2 ml/kg polyethylene glycol (vehicle) underwent ischemia in the fasted or fed state. Three groups of gerbils receiving no pretreatment underwent ischemia with rectal temperatures of 32-33 degrees C, 34-35 degrees C, or 37 degrees C. We counted intact neurons in the CA1 hippocampal sector in brains fixed on Day 7 after ischemia. t tests of square-root-transformed cell counts were used to assess the effect of hypothermia, and analysis of variance of the transformed data was used to test for the effects of phenytoin, FiO2, and nutritional status. Phenytoin pretreatment provided significant protection from CA1 neuron loss in all groups tested (p less than 0.001), but the degree of protection varied from 20% to 44%. In spite of significantly higher serum glucose concentrations in fed than in fasted gerbils (173 and 118 mg/dl, respectively), we found no significant effect of nutritional status upon neuron loss in phenytoin- or vehicle-pretreated gerbils. An FiO2 of 21% significantly decreased the number of viable neurons in both vehicle- and phenytoin-pretreated groups (p less than 0.03), despite the lack of an effect of hypoxemia on arterial blood gases.
Brief bilateral carotid occlusion in the gerbil produces forebrain ischemia that results in almost complete neuronal destruction in the CA1 sector of the hippocampus. Treatment with phenytoin (200 ...mg/kg) blocked the ischemia-induced neuronal death. The average density of CA1 pyramidal neurons (cells/mm CA1) was 253.6 +/- 4.4 in the sham surgery group, 12.3 +/- 3.4 in the ischemia group, and 119.5 +/- 16.6 in the group treated with phenytoin before ischemia. Thus, phenytoin reduced ischemia-produced neuronal loss in hippocampal CA1 by 44.4% (P less than 0.001). The plasma levels of phenytoin that produced this effect ranged from 28.1 to 45.0 mg per liter, with a mean phenytoin level of 34.7 +/- 1.7 mg/l (n = 10). The results suggest that phenytoin may be a clinically useful cerebroprotective agent.
We have measured the strange-quark content of the nucleon, {eta}{sub {ital s}}={sup +0.012}{sub {minus}0.08}, and the Kobayashi-Maskawa matrix element {vert bar}{ital V}{sub {ital c}{ital d}}{vert ...bar}=0.220{sup +0.015}{sub {minus}0.018} using a sample of 1797 {nu}{sub {mu}}- and {bar {nu}}{sub {mu}}-induced {mu}{sup {minus}}{mu}{sup +} events with {ital P}{sub {mu}}{ge}9 GeV/{ital c} and 30{le}{ital E}{sub {nu}}{le}600 GeV. The data are consistent with the slow-rescaling hypothesis of charm production in {nu}-{ital N} scattering and within this formalism yield a value of the charm-quark mass parameter {ital m}{sub {ital c}}=1.31{sub {minus}0.48}{sup +0.64} GeV/{ital c}{sup 2}.
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