Locomotor activity and one-way active avoidance after intrahyppocampal 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-microngl 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 microng/micronl), propranolol (5 or 10 microng/micronl), cimetidine (0.75 or 1.5 microng/micronl), sulpiride (5 or 10 microng/micronl), or vehicle (Krebs-ringer). Locomotor activity was not changed by injection of any drug. However, intrahippocampal injections of scolpolamine (9 microng/micronl) and sulpiride (10 microng/micronl) impoaired avoidance bahavior, 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

The cholinergic and dopaminergic systems of the prelimbic sector of frontal cortex and memory in the rat

Rats were trained to perform delayed non-matching to sample (a working/representational memory task) and visual discrimination(a reference/dispositional memory task) in a T-maze, and implanted bilaterally with cannulae in the prelimbic cortex. The rats were tested postoperatively after bilateral 1 - micronl injections of vehicle (Krebs-Ringer), sulpiride (10 microng/micronl) or scopolamine (18 microng/micronl). Sulpiride had no effect on the performance of either task, whereas scopolamine interfered only with the performance of delayed non-matching to sample. We conclude that dopaminergic mechanisms in the prelimbic cortex are not involved in either type of memory and that cholinergic, but not dopaminergic, mechanisms are important for working/representational memory process