Overexpression of the vesicular acetylcholine transporter increased acetylcholine release in the hippocampus

Abstract

Cholinergic neurotransmission in the hippocampus is involved in cognitive functions, including learning and memory. Strategies to enhance septohippocampal cholinergic neurotransmission may therefore be of therapeutic value to limit cognitive decline during cholinergic dysfunction. In addition to current strategies being developed, such as the use of acetylcholinesterase inhibitors, enhancing acetylcholine (ACh) release may be critical for optimal cholinergic neurotransmission. Vesicular acetylcholine transporter (VAChT) activity limits the rate of formation of the readily releasable ACh pool. As such, we sought to determine the influence of increased VAChT expression on the septohippocampal cholinergic system. To do this, we used the B6.eGFPChAT congenic mouse, which we show contains multiple gene copies of VAChT. In this transgenic mouse, the increased VAChT gene copy number led to an increase in VAChT gene expression in the septum and a corresponding enhancement of VAChT protein in the hippocampal formation. VAChT overexpression enhanced the release of ACh from ex vivo hippocampal slices. From these findings, we conclude that VAChT overexpression is sufficient to enhance ACh release in the hippocampal formation. It remains to be established whether, in cases of cholinergic deficits, increasing VAChT expression would re-establish adequate levels of cholinergic neurotransmission, thereby providing a valid therapeutic target.