Consumption of Reinforcing Solutions Engages Dynamic Activity of the Prelimbic Cortical Outputs.

The medial prefrontal cortex integrates information about salience and valence of stimuli, including rewarding solutions like alcohol and sucrose, and regulates aspects of alcohol seeking and consumption. However, our understanding of how cortical outputs encode alcohol consumption is limited. Using fiber photometry to measure calcium activity in putative prelimbic (PrL) glutamatergic projection neurons, we show similar but distinct patterns of activity during the peri-consummatory phase in response to consumption of water (non-deprived conditions), ethanol (20% v/v), or sucrose (1% w/v). PrL population activity appears to track hedonic value, as GCaMP6f signals ramped immediately preceding bouts for water, ethanol, and sucrose, and the signal scaled with presumed hedonic value, i.e., water<ethanol<sucrose. Further, using machine learning, population activity of PrL neurons prior to consumption was sufficient to predict both consumption of and distinguish between these different solutions. To assess valence encoding, we adulterated the ethanol solution with quinine, a bitter tastant. In non-dependent mice, calcium activity surrounding drinking bouts was reduced, paralleling the decreased consumption of quinine-adulterated ethanol. This effect was not present in ethanol dependent mice, suggesting altered hedonic value of the adulterated solution either due to reduced sensitivity to the aversiveness of quinine or increased sensitivity to the reinforcing value of ethanol. The global population of PrL glutamatergic neurons also display sustained GCaMP6f 'up-states' that last tens to hundreds of seconds, which were longer and larger when consummatory bouts occurred. Overall, our results demonstrate a functional signature in PrL neurons that differs across solutions and is disrupted by ethanol dependence.