NITRIC-OXIDE MEDIATES CERULEIN-INDUCED SUPPRESSION OF LOCOMOTOR-ACTIVITY

Caerulein, a non-selective agonist of cholecystokinin (CCK) receptors, is shown to suppress locomotor activity in rodents via stimulation of CCKA receptors. In the present study we examined the possible involve ment of nitric oxide (NO) in caerulein-induced hypolocomotion in rats. Caerulein (10 mu g/kg) markedly decreased the horizontal and vertical components of locomotor activity in rats measured in dark motility bo xes. Pretreatment with a nitric oxide synthase inhibitor N-G-nitro-L-a rginine methyl ester (L-NAME), at 5 mg/kg i.p., abolished the inhibiti ng action of caerulein on the horizontal activity, but did not affect the reduced frequency of rearing. The other doses of L-NAME (1, 10 and 20 mg/kg) were ineffective against caerulein. As L-NAME at this dose range does not stimulate locomotor activity, ii is likely that NO is i nvolved in the motor suppressant effect of systemically administered c aerulein.