Convulsant action of naloxone in the rat amygdala

Increasing doses of naloxone hydrochloride (100-1000 nmol) were micro-injected unilaterally into the rat amygdala and the behavioral, neuropathological and electrographic responses were studied. Microinjections of low doses of naloxone (100-250 nmol) produced staring, gustatory automatisms and wet shakes whereas higher doses additionally resulted in motor limbic seizures and status epilepticus. The electroencephalogram showed a sequence of alterations characterised by high voltage fast activity, spiking, bursts of polyspiking, electrographic seizures and postictal depression which first appeared in the amygdala and rapidly spread to hippocampal and cortical areas. The neuropathological analysis of frontal forebrain sections by means of light microscopy revealed seizure-related brain damage in amygdala, olfactory cortex, thalamus, hippocampal formation, substantia nigra and neocortex. Diazepam, 10 mg/kg i.p., when given prior to the microinjection of naloxone into the amygdala, abolished the epileptogenic and neurotoxic effects of the drug. The results suggest that naloxone, when microinjected into rat amygdala elicits electrographic and motor limbic seizures followed by seizure-related brain damage.