Biomedical subjects

C G Wasterlain

Publications and source records attributed to C G Wasterlain.

At least 19 recordsLinked to original sources

PubMed1995

The effect of urethane anesthesia on evoked potentials in dentate gyrus.

We examined the effect of urethane (1000 mg/kg, followed by 50 mg/kg per h, i.v.), an anesthetic commonly used by physiologists, on evoked potentials recorded in dentate gyrus in adult Wistar rats by stimulating the ipsilateral perforant path, via chronically implanted electrodes. Urethane decreased paired-pulse inhibition. Under urethane, with paired-pulse stimulation, the ratio of the second population spike amplitude to the first increased by 11.1-20.7% at 25-60 ms interstimulus interval (n = 18, P < 0.05). At 25 ms, the proportion was 3.6 +/- 1.6 while awake, and 14.7 +/- 3.5 under urethane. Urethane depressed granule cell excitability and strength of synaptic responses. Under urethane, the ratio of the population spike amplitude obtained at 250 microA stimulation to the maximal response in the same input/output response examination decreased by 20%, and the ratio of the excitatory postsynaptic response slopes fell by 10%. These results indicate that urethane affects neurotransmission in the hippocampus, and suggest that its effect may be exerted in part on excitatory neurotransmission.

Analysis of Variance↗

PubMed1995

Nitric oxide mediates the increase in local cerebral blood flow during focal seizures.

The role of nitric oxide (NO) in the increase in local cerebral blood flow (LCBF) elicited by focal cortical epileptic seizures was investigated in anesthetized adult rats. Seizures were induced by topical bicuculline methiodide applied through two cranial windows drilled over homotopic sites of the frontal cortex, and LCBF was measured by quantitative autoradiography by using 4-iodo[N-methyl-14C]antipyrine. Superfusion of an inhibitor of NO synthase, N omega-nitro-L-arginine (NA; 1 mM), for 45 min abolished the increase of LCBF induced by topical bicuculline methiodide (10 mM) [164 +/- 18 ml/100 g per min in the artificial cerebrospinal fluid (aCSF)-superfused side and 104 +/- 12 ml/100 g per ml in the NA-superfused side; P < 0.005]. This effect was reversed by coapplication of an excess of L-arginine substrate (10 mM) (218 +/- 22 ml/100 g per min in the aCSF-superfused side and 183 +/- 31 ml/100 g per min in the NA + L-Arg-superfused side) but not by 10 mM D-arginine, a stereoisomer with poor affinity for NO synthase (193 +/- 17 ml/100 g per min in the aCSF-superfused side and 139 +/- 21 ml/100 g per min in the NA + D-Arg-superfused side; P < 0.005). Superfusion of the guanylyl cyclase inhibitor methylene blue attenuated the LCBF increase elicited by topical bicuculline methiodide by 25% +/- 16% (P < 0.05). The present findings suggest that NO is the mediator of the vasodilation in response to focal epileptic seizures.

Amino Acid Oxidoreductases↗

PubMed1995

Inhibition of regulated catecholamine secretion from PC12 cells by the Ca2+/calmodulin kinase II inhibitor KN-62.

When stimulated by the cholinergic agonist carbachol, PC12 cells rapidly secrete a large fraction of the intracellular catecholamines by exocytotic release from the large dense-core secretory vesicles in a Ca(2+)-dependent manner. To investigate whether Ca2+/calmodulin kinase II plays a role in the regulated secretion of catecholamines, we examined the effect of the specific Ca2+/calmodulin kinase II inhibitor KN-62 on the carbachol-induced release of norepinephrine from PC12 cells. Approximately 50% of the regulated release of norepinephrine, stimulated either by carbachol or direct depolarization, was inhibited by pretreatment with KN-62, while the remaining 50% was resistant to KN-62 and therefore independent of Ca2+/calmodulin kinase II. In contrast, H7, an inhibitor of protein kinase C, had no effect on any of the stimulated release. FURA 2 imaging experiments demonstrated that KN-62 does not act by blocking the stimulation-induced increase in intracellular [Ca2+]. The most likely model consistent with these data is that all the dense-core vesicles fuse with the plasma membrane in a Ca(2+)-dependent process, but that approximately 50% of the vesicles require an additional step that is dependent on the action of Ca2+/calmodulin kinase II. This step occurs between the influx of Ca2+ and the fusion of vesicle membranes with the plasma membrane, and may be analogous to the Ca2+/calmodulin kinase II phosphorylation of synapsin which mobilizes small, clear synaptic vesicles for exocytosis at the synapse.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1994

Chronic epileptogenicity following focal status epilepticus.

We examined chronic epileptogenicity in the perforant path stimulation model of focal status epilepticus. After 24 h of perforant path stimulation, every stimulation elicited multiple population spike discharges, and this phenomenon persisted more than 2-3 months after stimulation. Short (10-100 ms) interstimulus interval-dependent paired-pulse inhibition was almost completely lost right after stimulation, but recovered progressively over the following month. Long (200-1000 ms) interstimulus interval-dependent paired-pulse inhibition decreased, and in spite of a partial recovery, remained significantly reduced 4 weeks after stimulation. Frequency-dependent paired-pulse inhibition was lost immediately after stimulation. One month later, inhibition at 2 Hz remained significantly reduced, although in individual rats recovery ranged from poor to complete. Input/output response curves showed increased population spike amplitude but no change of the slope of excitatory postsynaptic potentials. 3-4 weeks after stimulation, spontaneous generalized motor convulsions were observed in half of the stimulated rats. In all of the stimulated rats, the kindling phenomenon was significantly accelerated compared with non-stimulated controls, and class 5 convulsions were elicited in 3.3 +/- 1.0 trials in stimulated rats, against 11.0 +/- 2.5 trials in controls.

Animals↗

PubMed1994

Nitric oxide mediates the sustained opening of NMDA receptor-gated ionic channels which follows transient excitotoxic exposure in hippocampal slices.

In the rat hippocampal slice, a brief exposure to glutamate and glycine increased MK-801 binding to 246% of controls. Increased binding persisted 90 min after removal of those amino acids from the incubation medium. Posttreatment with the competitive substrate inhibitor of nitric oxide synthase, N omega-nitro-L-arginine or with hemoglobin, which binds NO extracellularly, inhibited this postexcitotoxic increase in MK-801 binding. L-Arginine reversed this inhibitory effect but D-arginine did not. The combination of tetrodotoxin and low Ca2+, which blocks transmitter release prevented the poststimulation increase in MK-801 binding, suggesting a presynaptic component. These findings suggest that the sustained opening of NMDA receptor-gated ionic channels seen after transient glutamate/glycine stimulation is mediated by NO.

Animals↗

PubMed1994

Nitric oxide participates in excitotoxic mechanisms induced by chemical hypoxia.

Changes in the activity of the NMDA receptor-gated ionic channels induced by potassium cyanide were studied in rat hippocampal slices utilizing a [3H]MK-801 binding technique. A 30-min exposure of slices to potassium cyanide (KCN) increased MK-801 binding by 252%. Co-application of N omega-nitro-L-arginine (NNLA), a competitive antagonist of nitric oxide (NO) synthase, reduced this increase by 72%. This inhibition by NNLA was completely reversed by an excess of L-arginine, a substrate for NO synthase, suggesting that the KCN-induced increase in MK-801 binding is mediated by NO synthase activity. KCN had no effect on MK-801 binding in synaptic membranes. In Ca(2+)-containing medium, KCN increased the release of glutamate, aspartate and glycine by 4- to 5-fold, and this was blocked by application of NNLA. NNLA inhibition was reversed by an excess of L-arginine, indicating that KCN-stimulated release of these amino acids is mediated by NO synthase activity. In Ca(2+)-free medium, a KCN-induced increase in MK-801 binding and in excitatory amino acid release was also observed, however, this increase was not influenced by NO-related agents, suggesting that these changes were not mediated by NO synthase activation. NNLA given after the end of exposure to KCN did not reverse the increase in MK-801 binding. These findings suggest that NO is involved in the initial activation of NMDA receptor-gated ionic channels and in the enhanced amino acid transmitter release induced by KCN, but that KCN can also induce some of these effects by a Ca(2+)- and NO-independent mechanism.

Amino Acids↗

PubMed1994

Selective protection of neuropeptide containing dentate hilar interneurons by non-NMDA receptor blockade in an animal model of status epilepticus.

We used a 24 h perforant path stimulation model of status epilepticus to study the role of non-NMDA receptors in the loss of hilar interneurons and paired pulse inhibition associated with the model. In one experiment, NBQX administered i.v. at 1.0 mg/kg/h significantly reduced the loss of hematoxylin and eosin-stained hilar neurons from 360.2 to 125.3 but failed to protect against the loss of paired pulse inhibition. In a second experiment, i.v. NBQX at 1.5 mg/kg/h significantly protected against loss of SS- and NPY-positive hilar interneurons but also failed to protect against loss of paired pulse inhibition. These results demonstrate that the neuronal loss associated with sustained stimulation of this excitatory pathway is mediated in part through non-NMDA receptors. The lack of protection against loss of paired pulse inhibition suggests that SS- and NPY-immunoreactive interneurons may not be responsible for frequency-dependent paired-pulse inhibition of dentate granule cells.

Animals↗

PubMed1994

Novel rat cardiac arrest model of posthypoxic myoclonus.

We describe the time course of and pharmacology associated with auditory-induced muscle jerks following cardiac arrest in rats. The data indicate that several key features of this model mimic those of human posthypoxic myoclonus. Similar to the human form, the muscle jerks appear in the rats following an acute hypoxic episode (cardiac arrest). Initially, it is known that both spontaneous and auditory-induced myoclonus are present in these animals; some cardiac-arrested rats also exhibit seizures. Over the first few days after the arrest, episodes of both the seizure activity and spontaneous myoclonus disappear. The auditory-induced myoclonus continues to worsen, reaches a peak about 2 weeks after the arrest, then declines over time to subnormal levels. The auditory-induced muscle jerks exhibited by the cardiac arrested animals are attenuated by the typical antimyoclonic drugs 5-hydroxytryptophan, valproic acid, and clonazepam. In addition, the novel anticonvulsant felbamate was found to have antimyoclonic properties. The data suggest that this rat cardiac arrest model may be a valuable tool for investigating the pathophysiologic mechanisms of posthypoxic myoclonus and for developing new therapeutic strategies for treating the disorder.

5-Hydroxytryptophan↗

PubMed1994

Prevalence of detectable carotid artery calcifications on panoramic radiographs of recent stroke victims.

Cerebrovascular accidents are responsible for killing or disabling half a million Americans every year and are the third leading cause of death in this country. Finding cost-effective means of decreasing stroke mortality and morbidity is of great humanitarian and economic importance. Panoramic dental radiography was done on 19 white men who had a recent cerebrovascular accident and who were hospitalized at a Department of Veteran Affairs medical center. Inclusion criteria included clinical suspicion or imaging study evidence that the stroke arose from atheroembolic disease of the carotid artery bifurcation. Women were omitted from the study because of their paucity in the patient pool, and African-Americans and Asian-Americans were omitted because strokes in those groups usually develop as a result of disease of intracranial vessels. Carotid arterial calcifications appearing as a radiopaque nodular mass adjacent to the cervical vertebrae at or below intervertebral space C3-4 were noted in seven persons (37%). These patients had an average age of 65 years and demonstrated multiple risk factors (prior transient ischemic attacks, prior stroke, hypertension, obesity, tobacco and alcohol abuse, hyperlipidemia) associated with occurrence of a stroke. We concluded that some white men at risk for a cerebrovascular accident may be identified in the dentist's office by appropriate review of the panoramic dental radiograph and medical history. The presence of carotid artery calcifications demands an expeditious referral to an appropriate practitioner who can assist in the control of risk factors and arrange prophylactic surgical removal of the carotid arterial plaque, which are both safe and reliable methods of reducing the incidence of stroke.

Aged↗

PubMed1993

Neuroprotection against nitric oxide injury with inhibitors of ADP-ribosylation.

We investigated the effect of nitric oxide (NO) upon CA1 neurons of the hippocampal slice. NO was given via perfusate without oxygen and with glucose concentration increased to 10 mM to prevent hypoxic injury. Exposure to NO for 10 min produced severe neuronal injury, with CA1 orthodromic and antidromic population spike regaining only 3 +/- 3% and 9 +/- 3% of initial amplitude after 1 h recovery. Hypoxic controls in contrast, showed orthodromic and antidromic recovery of 98 +/- 5% and 93 +/- 7%. Good protection from NO-induced injury was seen with 10 mM nicotinamide, an inhibitor of poly-ADP-ribosylation, with CA1 PS recovering to 116 +/- 10% orthodromically, and 96 +/- 4% antidromically. Protection was also seen with 3'-aminobenzamide, another poly-ADP-ribosylation inhibitor, suggesting that poly-ADP-ribosylation may play an important role in NO-mediated neuronal injury.

Adenosine Diphosphate Ribose↗

PubMed1993

Calbindin-D28k immunoreactivity and selective vulnerability to ischemia in the dentate gyrus of the developing rat.

Hippocampal dentate granule cells normally express the calcium-binding protein calbindin-D28k and, in the adult, are the hippocampal neurons least vulnerable to an ischemic insult. We evaluated hippocampal structure 2-3 days after hypoxic/ischemic insult at postnatal day 7-10, and discovered that, unlike adult granule cells, developing granule cells were irreversibly injured. Localization of calbindin-D28k-like immunoreactivity (LI) revealed that the vulnerable cells were the immature granule cells at the base of the cell layer that were not yet calbindin-immunoreactive. Adjacent granule cells that did not die in response to the hypoxic/ischemic insult were calbindin-immunoreactive. Whether the lack of calbindin-LI in immature granule cells is causally related to their vulnerability, or is a coincidental reflection of cellular immaturity, remains to be determined.

Animals↗

PubMed1993

GABA metabolism in the substantia nigra, cortex, and hippocampus during status epilepticus.

The metabolism of GABA and other amino acids was studied in the substantia nigra, the hippocampus and the parietal cortex of rats following microinjections of GAMMA-vinyl-GABA during status epilepticus induced by lithium and pilocarpine. GABA metabolism showed striking regional variations. In controls, both GABA concentration and rate of GABA synthesis were highest in the substantia nigra and lowest in cortex, as expected. In substantia nigra, status epilepticus resulted in a 2 1/2 fold decline in the rate of GABA synthesis and in a 307% increase in the turnover time of the GABA pool. In hippocampus, the rate of GABA synthesis was not altered significantly, but the turnover time of the GABA pool was 284% of controls, and the size of that pool increased to 208% of controls. By contrast, in cortex, where seizure activity is limited in this model, the rate of GABA synthesis increased to 230% of controls while pool size and turnover time did not change. Aspartate concentration decreased in all three brain regions. These data suggest that the observed reduction of the rate of GABA synthesis in substantia nigra could play a key role in seizure spread in this model of status epilepticus.

Amino Acids↗

PubMed1993

Determination of serum and brain concentrations of neuroprotective and non-neuroprotective doses of MK-801.

We developed a sensitive and reliable gas chromatographic (GC) technique for the quantitative analysis of MK-801 in brain and serum and applied the technique to investigate tissue concentrations of neuroprotective and non-neuroprotective doses of MK-801 in a neonatal rat model of hypoxic-ischemia. Brain concentrations of MK-801 were a linear function of dose over 4 orders of magnitude. After administration of a neuroprotective dose of MK-801 (29.6 mumol/kg) to control rats, both serum and brain concentrations rose rapidly to approximately 300 nM and approximately 2000 nM, respectively, within 30 min. Approximately 60% of serum and 90% of brain MK-801 were bound leaving the free concentrations in both blood and brain at approximately 100-200 nM. After hypoxic-ischemia, serum MK-801 concentrations were not different from controls but brain concentrations were lowered by 32%. Free brain concentrations of MK-801 after hypoxic-ischemic were 124 nM after 29.6 mumol/kg while after 8.9 mumol/kg (the non-neuroprotective dose) they were 39 nM. In view of the slow kinetics of MK-801 channel blockade, which never reaches equilibrium during the current experiment, this difference in concentration would be expected to result in an 80-fold (or greater) difference in the current flux through NMDA receptor-operated ion-channels as the rate of NMDA receptor-operated ion-channel blockade is concentration dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

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.

Animals↗

PubMed1993

Posthypoxic treatment with felbamate is neuroprotective in a rat model of hypoxia-ischemia.

Felbamate, a novel dicarbamate anticonvulsant that blocks the glycine site of the N-methyl-D-aspartate receptor and protects the hippocampal slice from hypoxic damage, shows remarkably low toxicity in animals and in humans. Since most treatment of human cerebral ischemia will have to be delivered after the insult, we investigated the neuroprotective potency of post hoc felbamate in rat pups with bilateral carotid ligations exposed to an atmosphere of 6.5% O2 for 1 hour. Brain temperature was unaffected by surgery, hypoxia, or felbamate. Neuroprotection was greatest at 300 mg/kg, less effective at 200 and 400 mg/kg, and ineffective at 100 mg/kg. Post hoc felbamate (300 mg/kg) reduced the volume of infarction from 67% +/- 7% of neocortex in unmedicated rats to 32% +/- 8%, 51% +/- 12%, 38% +/- 19%, and 53% +/- 10% when given 0, 1, 2, and 4 hours after hypoxic exposure, respectively. By 6 hours, post hoc protection was no longer significant. Delayed neuronal necrosis in hippocampal granule cells was reduced from 156 +/- 33 neurons to 12 +/- 7 (0 hours, p < 0.01) and 37 +/- 17 (1 hour, p < 0.05). These effects were obtained at plasma concentrations (60 to 120 mg/ml) that have occasionally been reached without serious toxicity in human anticonvulsant trials. These data suggest that, in this animal model, felbamate given after a hypoxic-ischemic insult is effective in reducing cerebral infarction and extremely effective in preventing delayed neuronal necrosis, but that the window of opportunity for post hoc treatment is only 1 to 4 hours.

Animals↗

PubMed1993

Dextromethorphan and its combination with phenytoin facilitate kindling.

We implanted 20 rats with bipolar electrodes and randomly distributed them into four groups that received intraperitoneal injections of phenytoin (PHT) (20 mg/kg), dextromethorphan (DM) (50 mg/kg), PHT+DM (20 and 50 mg/kg, respectively), or saline (C), 15 minutes before each daily stimulation. The number of stimulations needed to reach stage 3 seizures was 14.4 +/- 1.7 (C); 28 +/- 12 (PHT, p < 0.001); 6.2 +/- 3.9 (DM, p < 0.05); and 7.6 +/- 3.4 (PHT+DM, p < 0.05), suggesting that DM accelerated the expression of kindled seizures. Daily injections of DM and of DM+PHT without stimulation resulted in progressive seizure buildup to stage 3 in 4.8 +/- 6.2 (DM) or in 8 +/- 4.8 (DM+PHT) trials. We demonstrated savings in six kindled animals reinjected after 1 month. These results and previous experimental and clinical data suggest that DM may be epileptogenic when given repeatedly in high doses.

Animals↗

PubMed1993

Evidence for anticonvulsant and neuroprotectant action of felbamate mediated by strychnine-insensitive glycine receptors.

Felbamate (2-phenyl-1,3-propanediol dicarbamate) is a novel agent effective against maximal electroshock, pentylenetetrazol and other chemically induced seizures in mice and rats. Felbamate has been proposed as a novel anticonvulsant for the treatment of generalized tonic-clonic and complex partial seizures. In addition, felbamate has been shown to have neuroprotectant effects (in vitro and in vivo) in neonate models of cerebral ischemia. However, few existing studies have contributed to the elucidation of the mechanism of anticonvulsant and neuroprotectant action of felbamate. Because glycinergic mechanisms have been demonstrated to be involved with seizure disorders and neuroprotection, we investigated the binding interaction of felbamate with strychnine-insensitive glycine receptors and compared these findings with brain and plasma levels of felbamate after drug treatment. Inhibition of [3H]5,7-dichlorokynurenic acid (a high-affinity glycine receptor antagonist) binding by felbamate (IC50 = 374 microM) corresponded well with peak felbamate concentrations found in brain (683 and 759 microM) and plasma (679 and 807 microM) 8 hr after 300 (i.p.) or 500 mg/kg (p.o.) doses, respectively. Chemically diverse anticonvulsants tested and MK 801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine maleate] did not modulate [3H]5,7-dichlorokynurenic acid binding. Additional studies have shown that felbamate does not interact with other sites associated with the N-methyl-D-aspartate receptor complex. Thus, the data presented in this report strongly indicate a mechanism of action for felbamate through strychnine-insensitive glycine receptor interaction.

Animals↗

PubMed1992

Low sodium injury in the hippocampal slice is mediated through NMDA receptors.

Perfusion of hippocampal slices with normoxic medium containing no added sodium resulted in a rapid loss of the CA1 population spike, with only 35 +/- 10% (S.E.M.) (P < 0.001) recovery after a 15 min exposure. This injury was prevented by the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801 (93 +/- 4% recovery, P < 0.001), suggesting that low sodium injury may be mediated by opening of the NMDA receptor-associated ionic channels, possibly secondary to the well known sodium dependency of transmitter uptake systems. By contrast, slice perfusion with a medium moderately low in sodium (26 mM) produced only slight injury to the CA1 population spike under normoxic conditions (76 +/- 8% recovery) and provided no protection against hypoxic injury. Low chloride medium also provided no protection against hypoxic injury.

Animals↗