m-Cpp induced hypolocomotion does not interfere in the assessment of memory functions in rats

ABSTRACT

Central serotonergic system plays a critical role in the regulation of memory processes in rats. Evidence suggests that a dysfunction of serotonergic system contributes to various pathological conditions. Among the multiple classes of serotonin [5-Hydroxytryptamine, 5-HT] receptors described in CNS, much attention has been devoted to the role of 5-HT2C receptor family on memory functions. A number of studies have shown that 5-HT2C receptor agonists impair memory function and also decreased locomotor activity of rats. The present study was designed to investigate the effect of different doses of 5-HT2C receptor agonist metachlorophenylpiperazine [mCPP] on locomotion and cognitive behavior in rats. Groups of adult male rats were injected mCPP intraperitoneally at doses of 1, 3 and 5 mg/kg. The learning and memory of rats were assessed by water maze [WM] and passive avoidance [PA] tests. Locomotor activity of rats was monitored by open field test. mCPP decreased locomotor activity of rats as reported earlier. A negative correlation between memory function and 5-HT2C receptor stimulation was observed in WM. Furthermore the administration of mCPP dose dependently impaired memory functions and the impairment of memory induced by mCPP was greatest at the highest dose. PA test was also performed in the present study to confirm that the decreased locomotor activity exhibited by mCPP injected rats did not affect the memory assessment in WM. Irrespective of hypolocomotion induced by mCPP, drug injected rats took less time to enter the punishable compartment which confirmed that the impairment in memory functions following mCPP was not due its effect on locomotion. It is suggested that 5-HT2C receptors might be involved in memory function probably mediating a suppressive or constraining action by decreasing dopamine levels. It can be therefore concluded that 5-HT2C receptors have a negative influence on memory function, which raises the possibility of using 5-HT2C receptor antagonists in the improvement of memory functions