Cholinergic Receptor Sensitivity Following Pharmacological Modulation of the Immune System

Objective. To study the effect of immunomodulators on learning and memory and on cholinergic receptor sensitivity. Methods. Animals were initially treated for a period of 8 days with cyclosporine/levamisole/saline. They were then subjected to passive avoidance training and 48 hrs later, the retention test for the passive avoidance task was conducted. Twenty-four hours after the retention tests the animals were subjected to test for cholinergic receptor sensitivity. Oxotremorine was injected intraperitoneally in a dose of 0.46, 1.84 or 4.61 mg/kg. Rectal temperature was recorded in all the animals before administration of oxotremorine and thereafter every 15 minutes for 120 minutes. Results. Levamisole exhibited an increased latency to enter the dark compartment as compared to the control rats during the retention test. This increased latency indicates a better retrieval of learned behavior and facilitation of learning and memory processes. On the other hand in the rats treated with cyclosporine, there is a decrease in passive avoidance retention suggesting an adverse effect on learning and memory. The administration of oxotremorine exhibited an enhanced hypothermia in levamisole treated group as compared to control group suggesting hyperactivity of the cholinergic system. On the other hand oxotremorine administration failed to produce significant hypothermia in cyclosporine treated group as compared to control suggesting hypo activity of the cholinergic system. Conclusion. Levamisole causes hyperactivity and cyclosporine causes hypo activity of central cholinergic system. Central cholinergic system hypo activity impairs and hyperactivity improves the learning and memory.