SEPTOHIPPOCAMPAL CHOLINERGIC SYSTEM UNDER THE DISCRIMINATION-LEARNINGTASK IN THE RAT - A MICRODIALYSIS STUDY WITH THE DUAL-PROBE APPROACH

To investigate regulation of the septo-hippocampal cholinergic system by dopaminergic inputs to the septum in rats which performed a discrim ination learning task, an in vivo microdialysis method with the dual-p robe approach was used. Rats were trained to discriminate between lamp -on and -off states under an operant-type learning procedure. After st able discriminative behavior was established, dialysis probes were imp lanted into the hippocampus and the lateral septum area of each rat. T he concentration of dopamine (DA) in the septum rapidly increased with in 20 min after the beginning of a learning session. However, another group of rats trained on a similar but non-discriminative task showed no such increase. The concentration of acetylcholine (ACh) in the hipp ocampus was significantly enhanced during the learning session and rap idly returned to the basal value after the session, but showed a delay ed and diminished increase in the non-discrimination group. These resu lts suggest that DAergic inputs to the septum may be involved in contr ol of the septo-hippocampal cholinergic system which is of importance for discrimination learning behavior.