α2-adrenoceptors modulate kainic acid-induced limbic seizures

Abstract

We have tested several compounds interfering with the brain monoamine (noradrenaline, dopamine, serotonin) and acetylcholine systems for their effects on limbic seizures produced by systemically (s.c.) injected kainic acid as well as on neurochemical changes in amygdala/pyriform cortex resulting from the kainic acid treatment. The characteristic neurochemical changes induced by s.c. kainic acid were a decrease in noradrenaline and an increase in 5-hydroxyindoleacetic acid in the acute phase (3 h after kainic acid injection) suggesting strongly increased neurotransmitter turnover in noradrenergic and serotonergic neurons. This was followed by a reduction of glutamic acid decarboxylase and choline acetyltransferase activities during the chronic phase (3 days) of the kainic acid action, indicating destruction of GABAergic and cholinergic neurons. The compounds tested in this model of limbic epilepsy included l-propranolol, prazosin, clonidine, yohimbine, metergoline, atropine and haloperidol. Among these compounds the α 2-adrenergic agonist clonidine (0.1 mg/kg, i.p.) exhibited a powerful protective action on kainic acid-induced limbic seizures as well as on the neurochemical changes in the amygdala and pyriform cortex. In addition, the adrenoceptor antagonists prazosin ( α 1) and propranolol (β) as well as the dopamine receptor antagonist haloperidol had significant - but less potent - protective actions upon kainic acid-induced seizures and subsequent neurochemical changes. On the other hand, yohimbine ( α 2-antagonist) and metergoline (serotonin-antagonist) potentiated the limbic seizure syndrome and no effect was found with atropine. The experiments suggest a possible pathophysiological involvement of α-adrenergic receptors in limbic seizures induced by the excitotoxin kainic acid.