Effect of various calcium channel blockers on three different models of limbic seizures in rats

Voltage-dependent calcium channel-blockers were studied for their ability to modulate limbic seizures induced in rats by injection of quinolinic acid and kainic acid into the hippocampus or by hippocampal kindling. Flunarizine, at 40 mg/kg (but not 20 mg/kg), reduced the total number of seizures and total time spent in seizures induced by quinolinic acid by 75%; at 60 mg/kg, both parameters were reduced more than 90%, while at 80 mg/kg seizures induced by kainic acid were not affected. Forty and 60 mg/kg of flunarizine protected hippocampal-kindled rats from fully developed convulsions (Stage 5). Nifedipine, at 20 and 40 mg/kg, was ineffective on seizures induced by both quinolinate and kainate. However, at 20 mg/kg, 57% of the kindled animals were protected from Stage 5 and total protection was achieved at 40 mg/kg. Verapamil, at 40 mg/kg, reduced by respectively, 88% and 78%, the total number of seizures and the total time spent in seizures induced by quinolinic acid, but had no effect on seizures induced by kainate and Stage 5 seizures. The results suggest that, while seizures induced by kainic acid were refractory to all voltage-dependent calcium channel blockers, binding sites affected by flunarizine and verapamil in the brain may selectively facilitate ictal activity induced by quinolinic acid. Binding sites for dihydropyridine might contribute to the increased hippocampal excitability in kindled animals. The role of calcium entry through voltage-dependent calcium channels in the occurrence of seizures in these models of limbic epilepsy is discussed.

Role of the N-methyl-D-aspartate-type receptors in the development and maintenance of hippocampal kindling in rats

The effect of intrahippocampal infusion of 70 nmol (1 microliter/2 min) D,L-2-amino-7-phosphonoheptanoic acid (APH), a selective antagonist of N-methyl-D-aspartate (NMDA)-type receptors, was studied on behavioral seizures and afterdischarge (AD) at different stages of hippocampal kindling in rats. After completion of kindling (3 consecutive stage 5 seizures) APH infusion at the site of stimulation (granule cells of dentate gyrus) 60 min before stimulus delivery (50 Hz, 2 ms monophasic rectangular wave pulses for 1 s, current intensity 60-200 microA) suppressed the behavioral convulsions and focal AD. Four stimulations were needed after drug injection to recover stage 5 seizures and AD. When similarly injected early in kindling (stage 1-2) APH had no effect on the AD duration but significantly increased (by 37% with respect to controls) the number of stimulations needed to reach the first stage 5 seizures. Thus, it appears that NMDA-type receptors at the site of stimulation become progressively involved during the development of kindling and mediate the behavioral convulsions and focal AD observed at stage 5.

[Epithelioid sarcoma--immunohistochemical and ultrastructural study]

Five cases of epithelioid sarcoma are reported, of which four were studied by immunohistochemistry and one by electron microscopy. Immunohistochemically, the results of cytokeratin showed that these four cases were positive to different degrees by polyclonal cytokeratin and three out of four revealed positive results with low molecular weight cytokeratin monoclonal antibody. Two cases were positive with carcinoembryonic antigen and the other two were negative. The immunohistochemical stain was helpful for differential diagnosis from other sarcomas, such as malignant fibrous histiocytoma and rhabdomyosarcoma. By electron microscopy, tumor cells could be divided into light and dark cells which possessed more or less cell organelles, intermediate microfilaments in the cytoplasm and numerous pinocytic vesicles lying along the cell membrane. The occasional presence of poorly developed desmosomes or the absence of tonofibril bundles and glandular structures can rule out the diagnosis of carcinoma. One of these cases was originally diagnosed as metastatic carcinoma to the skin by light microscopy, which was refuted by electron microscopy, and the keratin positive reaction by immunohistochemistry was helpful for the diagnosis of epithelioid sarcoma. Therefore, the authors suggest that immunohistochemical and electron microscopic studies be used for diagnosing difficult cases of epithelioid sarcoma. From our observation, we consider that the cells of epithelioid sarcoma may derive from undifferentiated mesenchymal cells possessing the potentials of differentiating into synovioblasts, histiocytes or fibroblasts.

[3H]norepinephrine release from hippocampal slices is an in vitro biochemical tool for investigating the pharmacological properties of excitatory amino acid receptors

[3H]Norepinephrine ([3H]NE) efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids, with the following order of potencies: N-methyl-D-aspartate (NMDA) greater than kainic acid (KA) greater than L-glutamate greater than or equal to D,L-homocysteate greater than L-aspartate greater than quinolinic acid greater than quisqualic acid. The effect of the excitatory amino acids was blocked by physiological concentrations of Mg2+, with the exception of KA. D,L-2-Amino-7-phosphonoheptanoic acid dose-dependently inhibited the NMDA effect (ID50 = 69 microM), whereas at 1 mM it was ineffective versus KA. The release of [3H]-NE induced by quinolinic acid was blocked by 0.1 mM D,L-2-amino-7-phosphonohepatanoic acid. gamma-D-Glutamylglycine dose-dependently inhibited the KA effect with an ID50 of 1.15 mM. Tetrodotoxin (2 microM) reduced by 40 and 20% the NMDA and KA effects, respectively. The data indicate that [3H]NE release from hippocampal slices can be used as a biochemical marker for pharmacological investigations of excitatory amino acid receptors and their putative agonists and antagonists.

ATP as a marker of excitotoxin-induced nerve cell death in vivo

In an attempt to find an marker for nerve cell death in vivo, the ATP content was measured in the rat dorsal hippocampus within hours or days following in the local injection of the excitotoxins quinolinic or kainic acid. Beginning or completed neuronal degeneration is accompanied by significant decreases in ATP levels. Selective blockade of the quinolinic acid-induced decrement in ATP content by D-(-) 2-amino-7-phosphonoheptanoic acid indicates that ATP measurements may of value for the rapid in vivo screening of the anti-neurotoxic properties of pharmacologically distinct excitatory amino acid receptor antagonists.

Norepinephrine modulates seizures induced by quinolinic acid in rats: selective and distinct roles of alpha-adrenoceptor subtypes

We investigated in rats whether alterations in noradrenergic function caused by 6-hydroxydopamine or alpha- and beta-adrenoceptor agonists and antagonists would modify the susceptibility of the brain to electroencephalographic seizures induced by intrahippocampal infusion of quinolinic acid. 6-Hydroxydopamine depletion of norepinephrine facilitated the expression of seizures while alpha-adrenoceptor stimulation by clonidine had either proconvulsant (0.1 mg/kg) or anticonvulsant (from 0.5 to 2 mg/kg) effects. Clonidine's anticonvulsant activity (0.5 mg/kg) was mimicked by methoxamine given intrahippocampally (10 micrograms), and antagonized by prazosin (1 mg/kg), whereas both yohimbine (5 and 10 mg/kg) and piperoxane (5 mg/kg) had no significant effect. Seizure facilitation induced by clonidine (0.1 mg/kg) was blocked by yohimbine (10 mg/kg). Systemic (0.25 and 0.5 mg/kg) or intrahippocampal (10 and 20 micrograms) isoproterenol and propranolol (10 mg/kg) had no effect. Spiking activity and neurotoxicity induced by quinolinic acid were unaltered by treatments which protected against convulsions. Modulation of quinolinic acid-convulsive activity by alpha-adrenoceptor subtypes appears to be selective and complex, since alpha 1-type activation reduces seizures while alpha 2-type stimulation has proconvulsant effects.

Anticonvulsant drugs effective against human temporal lobe epilepsy prevent seizures but not neurotoxicity induced in rats by quinolinic acid: electroencephalographic, behavioral and histological assessments

Intrahippocampal injection of quinolinic acid (QUIN) in rats caused an epileptic-like syndrome reminiscent of human temporal lobe epilepsy. By electroencephalographic (EEG) analysis, the authors assessed whether QUIN seizures were responsive to anticonvulsants effective in the treatment of the human disease. Anticonvulsants used in clinical practice to control partial seizures, such as carbamazepine, diphenylhydantoin, sodium phenobarbital, sodium valproate and diazepam, prevented QUIN-induced EEG seizures, whereas ethosuximide, which is specifically used to control absence attacks, and chlorpromazine, a sedative with no anticonvulsant properties, were ineffective. QUIN seizures showed particular sensitivity to carbamazepine (5 mg/kg) but were resistant to diphenylhydantoin unless a relatively high dose was used (100 mg/kg). None of the effective anticonvulsants completely suppressed EEG paroxysmal events like spikes and fast activity. Animals injected with QUIN displayed chewing, sniffing and rearing; no clear correlation was found between the ability of drugs to prevent QUIN-induced EEG seizures and effects on stereotypies, suggesting that these behavioral signs are not sensitive measures of anticonvulsant activity in this model. The anticonvulsants that protected animals from QUIN seizures did not prevent nerve cell degeneration induced by the excitotoxin, thus indicating that nerve cell death can occur even in the absence of sustained seizure activity. The data show that, in this animal model of epilepsy, the EEG seizure activity is specifically sensitive to anticonvulsants effective in partial epilepsy, thus suggesting that it could be used to test potential new drugs for this human disorder.