In vivo modulation of septo-hippocampal cholinergic activity in mice: relationships with spatial reference and working memory performance.

Dopaminergic afferents to the septum mediate a tonic and trans-synaptic inhibitory control on the cholinergic neurones of the septo-hippocampal pathway. Lesion of these afferents using 6-hydroxydopamine (6-OHDA) results in a chronic and specific increase of hippocampal cholinergic activity in mice. The consequence of this in vivo modulation of hippocampal cholinergic activity on the acquisition of both a spatial discrimination and a working memory (delayed non-matching to place) task in an 8-arm radial maze by C57BL/6 mice were investigated. Combined neurochemical and behavioural analyses revealed significant correlations between hippocampal sodium-dependent high-affinity choline uptake activation induced by testing and performance measures. In the first experiment 6-OHDA-treated mice compared to control and vehicle-injected mice showed a transient (day 2) but significant facilitation of their spatial discrimination performance which appears to be better related to the working but not to the reference memory component of the task. This hypothesis is strengthened by the results of the second experiment which shows an amelioration of working memory performance when the septo-hippocampal cholinergic pathway is specifically activated in vivo.