Septo-hippocampal cholinergic system under the discrimination learning task 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 discrimination learning task, an in vivo microdialysis method with the dual-probe approach was used. Rats were trained to discriminate between lamp-on and -off states under an operant-type learning procedure. After stable discriminative behavior was established, dialysis probes were implanted into the hippocampus and the lateral septum area of each rat. The concentration of dopamine (DA) in the septum rapidly increased within 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 hippocampus was significantly enhanced during the learning session and rapidly returned to the basal value after the session, but showed a delayed and diminished increase in the non-discrimination group. These results suggest that DAergic inputs to the septum may be involved in control of the septo-hippocampal cholinergic system which is of importance for discrimination learning behavior.