Altered Baseline and Nicotine-Mediated Behavioral and Cholinergic Profiles in ChAT-Cre Mouse Lines

Abstract

The recent development of transgenic rodent lines expressing cre recombinase in a cell-specific manner, along with advances in engineered viral vectors, has permitted in-depth investigations into circuit function. However, emerging evidence has begun to suggest that genetic modifications may introduce unexpected caveats. In the current studies, we sought to extensively characterize male and female mice from both the ChAT-Cre mouse line, created with the bacterial artificial chromosome (BAC) method, and ChAT-Cre mouse line, generated with the internal ribosome entry site (IRES) method. ChAT-Cre transgenic and wild-type mice did not differ in general locomotor behavior, anxiety measures, drug-induced cataplexy, nicotine-mediated hypolocomotion, or operant food training. However, ChAT-Cre transgenic mice did exhibit significant deficits in intravenous nicotine self-administration, which paralleled an increase in vesicular acetylcholine transporter and choline acetyltransferase (ChAT) hippocampal expression. For the ChAT-Cre line, transgenic mice exhibited deficits in baseline locomotor, nicotine-mediated hypolocomotion, and operant food training compared with wild-type and hemizygous littermates. No differences among ChAT-Cre wild-type, hemizygous, and transgenic littermates were found in anxiety measures, drug-induced cataplexy, and nicotine self-administration. Given that increased cre expression was present in the ChAT-Cre transgenic mice, as well as a decrease in ChAT expression in the hippocampus, altered neuronal function may underlie behavioral phenotypes. In contrast, ChAT-Cre hemizygous mice were more similar to wild-type mice in both protein expression and the majority of behavioral assessments. As such, interpretation of data derived from ChAT-Cre rodents must consider potential limitations dependent on the line and/or genotype used in research investigations. Altered baseline and/or nicotine-mediated behavioral profiles were discovered in transgenic mice from the ChAT-Cre and ChAT-Cre lines. Given that these cre-expressing mice have become increasingly used by the scientific community, either independently with chemicogenetic and optogenetic viral vectors or crossed with other transgenic lines, the current studies highlight important considerations for the interpretation of data from previous and future experimental investigations. Moreover, the current findings detail the behavioral effects of either increased or decreased baseline cholinergic signaling mechanisms on locomotor, anxiety, learning/memory, and intravenous nicotine self-administration behaviors.

Exercise enhances motor skill learning by neurotransmitter switching in the adult midbrain

“…12). The ChAT-Cre line ( 26,27 ) demonstrated the same running-dependent transmitter switch as wild-type mice, even with expression of control constructs (AAV-DIO-mRuby2, Fig. 6c; AAV-DIO-shScr, Fig.…”

“…To seek more direct evidence for neurotransmitter switching, we selectively tagged cholinergic neurons with genetic markers to reveal their change in transmitter identity following the exercise challenge. We used a well-characterized ChAT-Cre transgenic mouse line ( 26,27 ) that exhibited the same running-dependent loss of ChAT and gain of GAD1 expression as wild-type mice (Supplementary Fig. 8).…”

Synaptic Inhibition of Medial Olivocochlear Efferent Neurons by Neurons of the Medial Nucleus of the Trapezoid Body

“…4C, experiments) mice of either sex resulting from a cross between ChAT-IRES-Cre transgenic mice on either a C57BL/6J (The Jackson Laboratory 028861) or a C57BL/6N (The Jackson Laboratory 018957) background strain, with tdTomato reporter mice (Ai14, Cre reporter allele inserted into Rosa 26 locus; catalog #007914, The Jackson Laboratory). Hemizygotes were used to prevent deleterious effects noted in ChAT-IRES-Cre homozygotes (Chen et al, 2018). As noted in the mouse line descriptions, these two ChAT-IRES-Cre strains are occasionally prone to ectopic expression of Cre due to the presence of the neo cassette.…”

The Novel CYP2A6 Inhibitor, DLCI-1, Decreases Nicotine Self-Administration in Mice

“…Subjects were food trained and then surgically catheterized as previously described Chen et al, 2018b). Briefly, mice were anesthetized with an isoflurane…”

“…The open field chamber was composed of Plexiglas (35 cm L × 35 cm W × 31 cm H) as described previously (Chen et al, 2018b). Following testing in the intravenous nicotine selfadministration session, mice (Cohort 1, n=5) were immediately transferred to the open field chamber.…”