Amygdala 14-3-3ζ as a novel modulator of escalating alcohol intake in mice

Abstract

Alcoholism is a devastating brain disorder that affects millions of people worldwide. The development of alcoholism is caused by alcohol-induced maladaptive changes in neural circuits involved in emotions, motivation, and decision-making. Because of its involvement in these processes, the amygdala is thought to be a key neural structure involved in alcohol addiction. However, the molecular mechanisms that govern the development of alcoholism are incompletely understood. We have previously shown that in a limited access choice paradigm, C57BL/6J mice progressively escalate their alcohol intake and display important behavioral characteristic of alcohol addiction, in that they become insensitive to quinine-induced adulteration of alcohol. This study used the limited access choice paradigm to study gene expression changes in the amygdala during the escalation to high alcohol consumption in C57BL/6J mice. Microarray analysis revealed that changes in gene expression occurred predominantly after one week, i.e. during the initial escalation of alcohol intake. One gene that stood out from our analysis was the adapter protein 14-3-3ζ, which was up-regulated during the transition from low to high alcohol intake. Independent qPCR analysis confirmed the up-regulation of amygdala 14-3-3ζ during the escalation of alcohol intake. Subsequently, we found that local knockdown of 14-3-3ζ in the amygdala, using RNA interference, dramatically augmented alcohol intake. In addition, knockdown of amygdala 14-3-3ζ promoted the development of inflexible alcohol drinking, as apparent from insensitivity to quinine adulteration of alcohol. This study identifies amygdala 14-3-3ζ as a novel key modulator that is engaged during escalation of alcohol use.

Figure 1. Alcohol intake and preference for C57BL/6J mice that consumed alcohol for 1, 2 or 4 weeks.

A The mice show a progressive increase in alcohol intake during the first two weeks of the experiment, stabilizing thereafter. B Preference for alcohol was high throughout the experiment. C RNA for microarray analysis was isolated from 0.6 mm diameter punches (○) from serial sections through the CeA. D The majority of the gene expression changes occurred after 1 week of alcohol consumption; the bar graph shows the total numbers of up- (black) and down-regulated (grey) genes for each time-point while the Venn Diagram shows the total number of up- and down-regulated genes (marked by arrows) for each time-point and overlap between the experimental groups. E–F Analysis of the microarray data using the Short Time Series Expression Miner (STEM), revealed significant gene enrichment particularly during the early stages of escalation of alcohol intake (week 1 and/or week 2). When considering all possible time profiles for gene expression after 1 wk, 2 wk and 4 wk of alcohol consumption, relative to data from naïve control mice (exemplified by E), 6 time profiles showed significant gene enrichment: they represented more genes than expected based on chance (F). The commonality between these 6 significant time profiles is that they all show an initial change in gene expression, normalizing thereafter to baseline levels.

Figure 2. qPCR data for mice that consumed alcohol for 1 week or 2 weeks.

qPCR confirmed significant up-regulation of 4 out of 8 candidate genes when compared to naïve control mice: Gria3, 14-3-3 zeta, Gabrb3 and Prkacb. *P < 0.05, **P < 0.01 from naïve mice by Tukey HSD multiple comparisons.

Figure 3. Design and validation of 14-3-3ζ shRNA constructs

A 14-3-3ζ specific shRNA sequences (1222 and 1854 bp) were cloned into pLentiLox3.7 vectors and B western blot analysis revealed that both constructs effectively reduced 14-3-3ζ protein levels in Neuro2A cells, the 1854 construct being most effective in vitro. C In situ hybridization confirmed effective knockdown of 14-3-3ζ in the CeA after infection with the 1854 shRNA expressing lentivirus. The top panels show 14-3-3ζ expression in the CeA after infection with the control or the 1854 shRNA expressing lentivirus. The bottom panels show GFP mRNA and therefore the infection site in adjacent sections. 14-3-3ζ mRNA is completely absent in the area that is infected with the 1854 shRNA expressing lentivirus.

Figure 4. Effects of local knockdown of 14-3-3ζ in the CeA on alcohol consumption. A

Local knockdown of 14-3-3ζ in the CeA using the 1854 shRNA increased intake of a 10% alcohol solution (v/v). B Infection with the less effective 1222 shRNA also increased alcohol intake of a 10% alcohol solution (v/v), but less prominently so than the 1854 14-3-3ζ shRNA. C In a separate batch of mice, local knockdown of 14-3-3ζ in the CeA using the 1854 shRNA increased alcohol intake of a 15% alcohol solution (v/v) and D local knockdown of 14-3-3ζ in the CeA using the 1854 shRNA caused persistent preference for the alcohol solution despite adulteration with the bitter tastant quinine. In E the sites of viral infection in the brain are summarized. The black ellipses show the core of the infection site that was consistently targeted across all animals. The areas marked in grey represent less frequent infected sites that include the anterior amygdala, the basolateral amygdala and part of the caudate putamen, along the injection tract. • Control mice; ○ 14-3-3ζ-specific shRNA treated mice. * P<0.05 from controls; # P<0.05, ## P<0.01 from 0 μM quinine for mice treated with control lentivirus; $ P <0.05 from 0 μM quinine for mice treated with the 1854 14-3-3ζ shRNA expressing lentivirus by t-test.

Figure 5. Taste control experiments show that the increase in alcohol intake in mice with CeA 14-3-3ζ knockdown is not secondary to altered taste sensitivity.

Control mice and mice with CeA 14-3-3ζ knockdown showed equal intake of solutions containing A the caloric sweet tastant sucrose and B the non-caloric sweet tastant saccharin. C Aversion for the bitter tastant quinine was also not different between controls and mice with CeA 14-3-3ζ knockdown.