The Role of Serotonergic Antagonists on Learning and Orientation Memory in Stressed Rats

Hippocampus is full of corticosteroid and serotonergic receptors, and have an important role in memory and spatial perception. In this study, the effects of fluoxetine and cyproheptadine, were investigated on learning and orientation memory in rats.
In this study, 30 male adult rats, were divided into 5 groups, including control, under immobilization stress, treatment with fluoxetine, treatment with cyproheptadine and treatment with fluoxetine猪殢ឩ떧抝. Immobilization stress was applied by limiting polyethylene. Fluoxetine 20 and cyproheptadine (4 mg/kg bw, were injected intraperitoneally for 2 weeks. At the end of the tretment period, learning and orientation memory, were evaluated using radial arm maze and cross-maze tests. After finishing behavioral tests, serum levels of corticosterone and malondialdehyde (MDA), were measured in hippocampus tissue.
In this study, immobilization stress increased the time to find food and decreased frequency percentage compared to the control group. Administration of fluoxetine significantly increased the time to find food and significantly reduced frequency percentage compared to control and patient groups. Co-administration of cyproheptadine and fluoxetine prevented the effects of this drug. Also, in the stressed animals, MDA level increased compared to the control group, but corticosterone level decreased. While, administration of fluoxetine or cyproheptadine increased corticosterone level and decreased MDA level compared to the patient group.
The results of this study showed that immobilization stress resulted in impaired learning and orientation memory, decreased corticosterone, and increased MDA. Considering the inhibitory effects of cyproheptadine on the function of fluoxetine in impairment of learning and orientation memory, this drug probably exerts its effects through the serotonergic system.