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

Abstract

Transgenic rodents expressing Cre recombinase cell specifically are used for exploring mechanisms regulating behavior, including those mediated by cholinergic signaling. However, it was recently reported that transgenic mice overexpressing a bacterial artificial chromosome containing choline acetyltransferase (ChAT) gene, for synthesizing the neurotransmitter acetylcholine, present with multiple vesicular acetylcholine transporter (VAChT) gene copies, resulting in altered cholinergic tone and accompanying behavioral abnormalities. Since ChAT::Cre+ rats, used increasingly for understanding the biological basis of CNS disorders, utilize the mouse ChAT promotor to control Cre recombinase expression, we assessed for similar genotypical and phenotypical differences in such rats compared to wild-type siblings. The rats were assessed for mouse VAChT copy number, VAChT protein expression levels and for sustained attention, response control and anxiety. Rats were also subjected to a contextual fear conditioning paradigm using an unconditional fear-inducing stimulus (electrical foot shocks), with blood samples taken at baseline, the fear acquisition phase and retention testing, for measuring blood plasma markers of hypothalamic–pituitary–adrenal gland (HPA)-axis activity. ChAT::Cre+ rats expressed multiple mouse VAChT gene copies, resulting in significantly higher VAChT protein expression, revealed anxiolytic behavior, hyperlocomotion and deficits in tasks requiring sustained attention. The HPA-axis was intact, with unaltered circulatory levels of acute stress-induced corticosterone, leptin and glucose. Our findings, therefore, reveal that in ChAT::Cre+ rats, VAChT overexpression associates with significant alterations of certain cognitive, motor and affective functions. Although highly useful as an experimental tool, it is essential to consider the potential effects of altered cholinergic transmission on baseline behavior in ChAT::Cre rats.

Accumbens Cholinergic Interneurons Mediate Cue-Induced Nicotine Seeking and Associated Glutamatergic Plasticity

“…While it is important to note that these effects could affect the conclusions drawn within the current study, we have recently compared the self-administration characteristics of wildtype Long Evans rats with ChAT::cre positive Long Evans rats and found no differences in total infusions across self-administration sessions or active and inactive lever pressing (Leyrer-Jackson, Overby et al 2020). Thus, while others have reported behavioral differences of ChAT::cre rats compared to wild type (Mantanona, Alsiö et al 2019), we believe that the lack of differences in self-administration characteristics demonstrate that these groups do not differ in their nicotine-seeking behaviors. However, future studies would benefit from comparing the MSN synaptic physiology and accumbens circuitry between ChAT::cre and wildtype rats.…”

“…Recent studies have demonstrated that ChAT::cre rats display elevated levels of the vesicular acetylcholine transporter protein, as well as altered motor, anxiety and attentional task performance (Mantanona, Alsiö et al 2019). While it is important to note that these effects could affect the conclusions drawn within the current study, we have recently compared the self-administration characteristics of wildtype Long Evans rats with ChAT::cre positive Long Evans rats and found no differences in total infusions across self-administration sessions or active and inactive lever pressing (Leyrer-Jackson, Overby et al 2020).…”

Dissociable contributions of mediodorsal and anterior thalamic nuclei in visual attentional performance: A comparison using nicotinic and muscarinic cholinergic receptor antagonists

“…The 5-CSRTT is a well-validated behavioural paradigm for assessing sustained spatial visual attention in rats ( Mantanona et al, 2019 ). The rats were trained and tested in Bussey-Saksida Touch Screen chambers (Lafayette Instrument, Indiana, USA) controlled by ABET II and Whisker control software ( Cardinal and Aitken, 2010 ).…”

“…A standard touchscreen-based 5-CSRTT protocol was followed, as shown in Figure 1(a) and ( b ), and described previously ( Bharmal et al, 2015 ; Mantanona et al, 2019 ; Nilsson et al, 2016 ). Animals were trained to nose poke into a briefly illuminated, spatially random aperture.…”

Stress Regulation of Sustained Attention and the Cholinergic Attention System

“…In contrast, our approach of virally labeling cholinergic neurons in ChAT::Cre rats allows for cholinergic specificity, clear visualization of processes, and labeling of a large population of NBM cholinergic neurons. One caveat is that a recent publication found increased copies of the vesicular acetylcholine transporter gene in the prefrontal cortex of ChAT::Cre rats (41). It is not clear if this change would affect cholinergic dendritic morphology, but ChAT::Cre rats were used for both the control and VS conditions.…”