Mechanisms underlying modifications in the severity of audiogenic convulsions

Catecholamine levels were selectively decreased in peripheral sites or in brain of mice by intravenous or intraventricular injections of 6-hydroxydopamine. Brain dopamine alone was decreased by administering i.p. desmethylimipramine prior to 6 hydroxydopamine injections. A brain noradrenaline decrease does not induce mortality in a tonic strain of mice but can transform clonic audiogenic seizures into tonic seizures in a clonic mouse strain, while a dopamine depletion alone has no effect. However, a noradrenaline decrease at peripheral sites increases the number of lethal seizures in a tonic strain without modifying clonic seizures in a clonic strain. Catecholamine metabolism is neither involved in the onset of seizures in a non-sensitive strain nor involved in the change of clonus into tonus in unilaterally deafened tonic strain animals, which in this case present only clonic seizures.