Abstract
Effect of histamine and other agents on the operant behaviors in rats was studied, using a commercially available apparatus. Two schedules of the food reinforcement with a fixed ratio (FR-30) and a fixed interval (FI-60) and a schedule of discriminated avoidance response (DAR) were used for the conditioned behaviors.
In the FR-30 and FI-60 schedules, histamine, 5-hydroxytryptamine (5-HT) and acetyl-choline (ACh), administered intraventricularly 5-20μg/rat, subcutaneously 5-10 mg/kg, produced the dose-related decreases in the behaviors. Although the potencies of histamine and 5-HT were almost the same, a large dose of 5-HT produced a long lasting inhibition. ACh was found to have the most potent action with a very short duration.
In avoidance schedule, histamine and ACh were less suppressive than that in the food reinforcement schedule. 5-HT showed the same potency in the both kind of the schedules.
