The facilitative effects of intraseptal 6-hydroxydopamine injections on time discrimination behavior in rats

Twenty one male albino rats of the Wistar strain were trained on a differential reinforcement of long latency 20 with a limited hold 36 schedule through 30 consecutive days. Six rats were injected into the medial septal area with 8 micrograms of 6-hydroxydopamine dissolved in 0.9% saline solution containing 0.1% ascorbic acid. Five rats were injected with only ascorbic acid solution and the remaining rats were not treated with any injection or surgical operation. As a result of this differential reinforcement of long latency training, the 6-hydroxydopamine-injected rats showed significantly better performance and less acceleration of lever pressing response just after nonreinforced responses (incorrect responses) compared with the other two control groups, especially in the early 10 sessions. These findings suggested that the 6-hydroxydopamine-injected rats were hardly affected by response acceleration following nonreinforcements and therefore could acquire this training schedule faster than could the controls. The authors proposed one probable hypothesis, that the catecholaminergic input to the septum mediated a frustrated emotional response such as response acceleration resulting from nonreinforcements and impaired behavioral inhibition in the time discrimination situation.