The effect of Medial Septum Stimulation on Hippocampal Electrophysiology and Behaviour of Freely Moving Rats

Abstract

This study focuses on the interaction between the medial septum and hippocampus in freely moving animals. To investigate this circuit, we used electrophysiological techniques combined with behavioural tasks. The medial septum exerts a modulatory effect on the entire hippocampal and parahippocampal formation. However, the role of the medial septum in spatial processing is still poorly understood. Here, we explore the septohippocampal circuit, focusing on electrophysiology, spatial processing and behaviour. Our results suggest that nonselective optogenetic stimulation of the medial septum induces inhibition of intra-septal neurons and consequently, disinhibition of hippocampal CA1 interneurons. We also demonstrated that firing rate of medial septal neurons is inversely proportional to the animal's speed. Transgenic models were used to investigate the contribution of septal GABAergic and cholinergic neurons in reward-related behaviour. We showed for the first time that the firing of medial septal GABAergic neurons can mediate place preference behaviour. To investigate if medial septum neurons can modulate hippocampal spatial processing, we recorded CA1 place cells during septal stimulation. We showed that medial septum stimulation induces place field remapping. We also showed that the medial septum stimulation restricted to a region of the arena was able to induced place preference and shifted the place field assembly towards this region.