Tramadol hydrochloride, a synthetic opioid, acts via a multiple mechanism of action. Tramadol can potentially change the behavioral phenomena. The present study evaluates the effect of tramadol after single or multiple dose/s on the spatial memory of rat using object recognition task (ORT). Tramadol, 20 mg/kg, was injected intraperitoneally (i.p) as a single dose or once a day for 21 successive days considered as acute or chronic treatment respectively. After treatment, animals underwent two trials in the ORT. In the first trial (T1), animals encountered with two identical objects for exploration in a five-minute period. After 1 h, in the T2 trial, the animals were exposed to a familiar and a nonfamiliar object. The exploration times and frequency of the exploration for any objects were recorded. The results showed that tramadol decreased the exploration times for the nonfamiliar object in the T2 trial when administered either as a single dose (P<0.001) or as the multiple dose (P<0.05) compared to the respective control groups. Both acute and chronic tramadol administration eliminated the different frequency of exploration between the familiar and nonfamiliar objects. Our findings revealed that tramadol impaired memory when administered acutely or chronically. Single dose administration of tramadol showed more destructive effect than multiple doses of tramadol on the memory. The observed data can be explained by the inhibitory effects of tramadol on the wide range of neurotransmitters and receptors including muscarinic, N-methyl D-aspartate, AMPA as well as some second messenger like cAMP and cGMP or its stimulatory effect on the opioid, gama amino butyric acid, dopamine or serotonin in the brain.
Keywords: Acute; Chronic; Memory; ORT; Tramadol.