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The effects of intrahippocampally administered catechol- and indoleamines on the two types of hippocampal seizure discharges elicited by electrical and chemical stimulation were examined in unanesthetized rabbits. The catecholamines norepinephrine (NE) and dopamine (DA), injected into the hippocampus in doses of 100--200 micrograms, inhibited electrically induced hippocampal seizure discharges with a 50% increase in the stimulation threshold. However 5-hydroxytryptamine (5-HT) at doses of 50 micrograms to 100 micrograms caused no effect on electrically induced seizure discharges. On the contrary, 5-HT and 5-hydroxytryptophan (5-HTP) at a dose of 50 micrograms potentiated carbachol (5 micrograms)-induced hippocampal seizure discharges, prolonging the duration of seizure discharge three times the control. NE and DA had no effect on this chemically induced hippocampal discharges. It is therefore suggested that the effects of monoamines on hippocampal seizure discharges are very much dependent on the type of stimulation employed for the induction of this phenomenon.

We examined the effects of MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one), a novel free radical scavenger and an inhibitor of ischemia-induced brain edema, on monoamine metabolism in the brains of both normal and ischemic rats. In normal rats, 3 mg/kg i.v. MCI-186, a dose that prevents ischemic brain edema, had no significant effect on brain concentrations of dopamine, norepinephrine, 5-hydroxytryptamine, or their metabolites. After the injection of 5 microliters of 3% polyvinyl acetate into the left internal carotid artery, concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid markedly increased, but that of norepinephrine decreased, in the left telencephalon of embolized rats compared with control rats injected with vehicle; the concentration of 5-hydroxyindoleacetic acid also increased slightly. These effects were maximal 2 hours after embolization. The turnover rate of dopamine between 6 and 8 hours after embolization was significantly higher but that of norepinephrine was slightly lower than that in vehicle-treated rats. When rats were treated with 3 mg/kg i.v. MCI-186 immediately after the injection of polyvinyl acetate, the embolization-induced changes in monoamine metabolism were less marked. Our results suggest that MCI-186 attenuates ischemia-induced changes in brain monoamine metabolism, probably due to its free radical scavenging action, although it has no marked effect in normal rats.

We induced brain edema in 72 rats by injecting 5 microliters of 3.0% wt:vol polyvinyl acetate into the left internal carotid artery, producing permanent embolization in the left cerebral hemisphere, which developed ipsilateral brain edema reproducibly. Edema was assessed 24 hours after embolization by determining the brain water content and the sodium and potassium concentrations. In this model, the free radical scavenger MCI-186 at 1.0 and 3.0 mg/kg i.v. prevented brain edema in a dose-dependent manner. At 3.0 mg/kg i.v., MCI-186 significantly reduced water content by 1.5% and improved the sodium-potassium balance to within the normal range in the embolized left hemisphere. Dexamethasone at 1.0 mg/kg i.v. did but at 3.0 mg/kg i.v. did not significantly inhibit the development of brain edema. Indomethacin at 4.0 mg/kg i.p. had no effect on brain edema. We suggest that the cyclooxygenase metabolites of arachidonic acid liberated from neuronal cell membrane phospholipids are not likely to be involved in the pathogenesis of permanent brain edema induced by polyvinyl acetate. Our results suggest that MCI-186 attenuates brain edema by suppressing the production of lipoxygenase metabolites, including free radicals or lipid peroxides, and that it may prove valuable for the treatment of brain edema associated with cerebral ischemia.

The hypotensive activity of terazosin has been attributed to inhibition of postsynaptic alpha-1 adrenoceptors. The present study examined the influence of terazosin on spontaneous sympathetic outflow in anesthetize and immobilized rats. The effects on blood pressure and heart rate were also evaluated. Intravenously (i.v.) injected terazosin 0.3 mg/kg and prazosin 0.1 mg/kg increased a sympathetic outflow by 15.4 and 21.6%, respectively. These drugs produced a significant and long-lasting fall in blood pressure with slight heart rate change. On the contrary, clonidine 0.1 mg/kg, i.v. significantly inhibited the sympathetic outflow by 69.2%. The intracerebroventricularly administered 10 micrograms/kg clonidine also showed the sympathoinhibitory effect. However 3 micrograms/kg, i.c.v. of terazosin and prazosin increased the sympathetic tone by 16 and 7.2%. During these periods, in both drugs slightly decreased the blood pressure. These changes in hemodynamic parameters and nerve activities were obtained at 2 approximately 3 min after the i.c.v. administration. The 10 micrograms/kg, i.c.v. of terazosin and prazosin significantly inhibited the pressor response by phenylephrine 1 micrograms/kg, i.v. These results indicate the peripheral effect of terazosin and prazosin through the penetration of the drugs from the brain. The results provide evidence that terazosin, like prazosin, dose not affect cardiovascular regulation by a central action.