Effect of phosphoramidon - a selective enkephalinase inhibitor - on nociception and behaviour

Phosphoramidon (100-350 micrograms i.c.v.), a selective enkephalinase inhibitor, induced in the rat a decrease of nociception to pressure stimulation without evident respiratory depression. In addition, intensive behavioural changes such as grooming (licking the fur, face washing and scratching), mounting behaviour and wet dog shakes were observed. Naltrexone pretreatment (1 mg/kg i.p.) caused a significant decrease in the phosphoramidon-induced nociception and behavioural changes. Puromycin (30 micrograms i.c.v. or 7.5 mg/kg i.p.) caused no changes in nociception or behaviour.