Locomotor activity and one-way active avoidance after intrahippocampal injection of neurotransmitter antagonists

Sixty-three rats with previous training in a T-maze, bilaterally implanted with cannulae directed toward the dorsal hippocampus, were used in this study. All rats received bilateral 1-microliter injections 20 min before testing for locomotor activity (day 1) and one-way active avoidance (day 3). The following drugs were injected into groups of 4 to 8 animals: scopolamine (9 or 18 micrograms/microliters), propranolol (5 or 10 micrograms/microliters), cimetidine (0.75 or 1.5 micrograms/microliters), sulpiride (5 or 10 micrograms/microliters), or vehicle (Krebs-Ringer). Locomotor activity was not changed by injection of any drug. However, intrahippocampal injections of scopolamine (9 micrograms/microliters) and sulpiride (10 micrograms/microliters) impaired avoidance behavior, particularly during the last five trials of the task. We conclude that muscarinic-cholinergic and D2-dopaminergic, but not beta-adrenergic or H2-histaminergic, mechanisms in the hippocampus are involved in the performance of one-way active avoidance behavior.