B6eGFPChAT mice overexpressing the vesicular acetylcholine transporter exhibit spontaneous hypoactivity and enhanced exploration in novel environments

Abstract

Cholinergic innervation is extensive throughout the central and peripheral nervous systems. Among its many roles, the neurotransmitter acetylcholine (ACh) contributes to the regulation of motor function, locomotion, and exploration. Cholinergic deficits and replacement strategies have been investigated in neurodegenerative disorders, particularly in cases of Alzheimer's disease (AD). Focus has been on blocking acetylcholinesterase (AChE) and enhancing ACh synthesis to improve cholinergic neurotransmission. As a first step in evaluating the physiological effects of enhanced cholinergic function through the upregulation of the vesicular acetylcholine transporter (VAChT), we used the hypercholinergic B6eGFPChAT congenic mouse model that has been shown to contain multiple VAChT gene copies. Analysis of biochemical and behavioral paradigms suggest that modest increases in VAChT expression can have a significant effect on spontaneous locomotion, reaction to novel stimuli, and the adaptation to novel environments. These observations support the potential of VAChT as a therapeutic target to enhance cholinergic tone, thereby decreasing spontaneous hyperactivity and increasing exploration in novel environments.

Transgenic overexpression of the presynaptic choline transporter elevates acetylcholine levels and augments motor endurance

“…Models that achieve conditional, region specific changes to expression of CHT are needed to dissect the contributions of individual components of corticostriatal circuitry, as well as to evaluate potential compensatory changes that may arise from constitutive transporter overexpression. Finally, we note that VAChT-overexpressing transgenic mice demonstrate hypoactivity in the open field paradigm (Nagy and Aubert, 2013), in contrast to the present findings. The reason for the difference in locomotor activity between this model of cholinergic hyperfunction and the BAC–CHT model is presently unclear, but may reflect a differential contribution of each transporter to cholinergic signaling capacity.…”

“…The lack of a change in grip strength or performance on the wire hang task in BAC–CHT mice indicates that the factors assessed in the treadmill test are independent of a change in strength per se . We also note that CHT +/− mice (Bazalakova et al, 2007), VAChT knock-down animals (Martins-Silva et al, 2011), and VAChT overexpressers (Nagy and Aubert, 2013) fail to display any phenotype in this task, indicating that grip strength is not affected by changes to cholinergic signaling capacity. As with studies of sustained attention in CHT +/− mice (Parikh et al, 2013), our findings of sustained motor function in the BAC–CHT mice indicate that phenotypes dependent on CHT are most likely to be revealed under conditions that are taxing to cholinergic transmission.…”

Altered motor, anxiety-related and attentional task performance at baseline associate with multiple gene copies of the vesicular acetylcholine transporter and related protein overexpression in ChAT::Cre+ rats

“…This result suggests that modest levels of VAChT overexpression at both the gene and protein level, previously shown to increase ACh release and, therefore, render animals hypercholinergic (Sugita et al 2016; Janickova et al 2017), associate with an anxiolytic behavioral profile in the ChAT::Cre+ rats. The findings reflect those from another hypercholinergic mouse model that also overexpresses VAChT at the gene and protein level, with such mice that showed enhanced exploration of novel environments and, therefore, anxiolytic-like behavior, when compared to C57BL/6J (B6) control mice (Nagy and Aubert 2013). In this work, use was made of the B6eGFPChAT congenic mouse model that contains four genomic copies of the cholinergic gene locus, which encompasses the promoter and coding regions of both VAChT and ChAT (Tallini et al 2006; Nagy and Aubert 2012).…”

Orexin Receptor Activation Generates Gamma Band Input to Cholinergic and Serotonergic Arousal System Neurons and Drives an Intrinsic Ca2+-Dependent Resonance in LDT and PPT Cholinergic Neurons

“…Use of the ChAT-IRES-Cre mice also avoids a problem discovered with recent BAC transgenics developed for visualizing (ChAT-GFP) and manipulating (ChAT-ChR2-EYFP) cholinergic neurons, where additional copies of the vesicular ACh transporter (VAChT) were introduced in the BAC construct. This results in over-expression of VAChT in these mice and a hypercholinergic phenotype ( 43 – 45 ). Thus, ChAT-IRES-Cre mice are highly suitable for studies in which LDT/PPT cholinergic neurons need to be visualized or manipulated with Cre/Lox approaches.…”