Acute Ethanol Administration Upregulates Synaptic α4-Subunit of Neuronal Nicotinic Acetylcholine Receptors within the Nucleus Accumbens and Amygdala

Abstract

Alcohol and nicotine are two of the most frequently abused drugs, with their comorbidity well described. Previous data show that chronic exposure to nicotine upregulates high-affinity nicotinic acetylcholine receptors (nAChRs) in several brain areas. Effects of ethanol on specific brain nAChR subtypes within the mesolimbic dopaminergic (DA) pathway may be a key element in the comorbidity of ethanol and nicotine. However, it is unknown how alcohol affects the abundance of these receptor proteins. In the present study, we measured the effect of acute binge ethanol on nAChR α4 subunit levels in the prefrontal cortex (PFC), nucleus accumbens (NAc), ventral tegmental area (VTA), and amygdala (Amg) by western blot analysis using a knock-in mouse line, generated with a normally functioning α4 nAChR subunit tagged with yellow fluorescent protein (YFP). We observed a robust increase in α4-YFP subunit levels in the NAc and the Amg following acute ethanol, with no changes in the PFC and VTA. To further investigate whether this upregulation was mediated by increased local mRNA transcription, we quantified mRNA levels of the Chrna4 gene using qRT-PCR. We found no effect of ethanol on α4 mRNA expression, suggesting that the upregulation of α4 protein rather occurs post-translationally. The quantitative counting of YFP immunoreactive puncta further revealed that α4-YFP protein is upregulated in presynaptic boutons of the dopaminergic axons projecting to the shell and the core regions of the NAc as well as to the basolateral amygdala (BLA), but not to the central or lateral Amg. Together, our results demonstrate that a single exposure to binge ethanol upregulates level of synaptic α4∗ nAChRs in dopaminergic inputs to the NAc and BLA. This upregulation could be linked to the functional dysregulation of dopaminergic signalling observed during the development of alcohol dependence.

Nicotine exposure and neuronal activity regulate Golgi membrane dispersal and distribution

“…3E and F). These results correspond to the increased numbers of YFP-a4 puncta observed following alcohol exposure in YFP-a4 knock-in mice (Tarren, Lester et al 2017). There, increases also occurred in VTA dopaminergic neuron terminals in the NAc core and shell, but not in the PFC.…”

“…Previously, Tarren et al, 2017, used a YFP-tagged a4 subunit knock-in mouse to demonstrate that a4 subunit-containing puncta were localized to terminals of ventral tegmental area (VTA) dopaminergic neurons identified by tyrosine hydroxylase (TH) staining (Tarren, Lester et al 2017). Mice that were administered ethanol exhibited increased a4 subunit punctal densities at VTA dopaminergic neuron terminals in the nucleus accumbens (NAc) and amygdala, but not at other terminals such as in the prefrontal cortex (PFC).…”

Sex Specific Alterations in α4*Nicotinic Receptor Expression in the Nucleus Accumbens

“…Furthermore, exposure to alcohol alters the ability to cope with stress, such that alcoholics attempting to remain abstinent have been reported to perceive stress more intensely than non-alcoholics [ 58 , 59 , 60 , 61 , 62 ]. Consistent with this, our laboratory has recently shown, in male mice, a single sedating dose of ethanol can increase α4*nAChR expression in presynaptic bouton of dopaminergic neurons projecting to the NAc [ 63 ]. While it is likely that the altered NAc α4*nAChR expression following restraint stress in MS males would alter dopaminergic signalling, contributing to increased ethanol consumption, our recent study and this study show that exposure to ethanol or stress alone can alter NAc α4*nAChR expression, potentially disrupting dopaminergic signalling and increasing susceptibility to substance use disorders.…”

Axonal Non-segregation of the Vesicular Glutamate Transporter VGLUT3 Within Serotonergic Projections in the Mouse Forebrain

“…Mosaics of the regions of interest were acquired as depicted in A of Figure 1–7, in OIR file format. The 5-HT immunoreactive boutons were reconstructed in 3D using the surface rendering function with Imaris 9.2.1 (Bitplane), as previously described (Belmer et al, 2016; Tarren et al, 2017). All the images were processed in batch using the same surface thresholding parameters.…”