The effect of acute alcohol on prefrontal cortical excitatory-inhibitory microcircuit interactions

Acute alcohol intoxication impairs cognitive function in part by affecting neuronal activity in the prefrontal cortex (PFC). However, the effect of intoxication on the in vivo activity of single and populations of PFC neurons remains understudied. Local GABAergic interneurons play an important role in orchestrating cortical activity. Whether and how alcohol modulates the in vivo activity of diverse subtypes of PFC inhibitory neurons and interactions between excitatory and inhibitory neurons are not well understood. Previous work from our lab shows that acute alcohol intoxication modulates the activity of a small subset of pyramidal (PYR) cells in the anterior cingulate cortex (ACC) subdivision of the PFC. The fact that the activity of a majority of ACC PYR neurons was unaffected is surprising, given previous work in ex vivo slices suggesting the largely suppressive effect of alcohol on cortical excitatory cells. We reconcile these differences by hypothesizing that interneurons modulate their activity to maintain net excitatory output following alcohol exposure in vivo. We tested this idea using two-photon calcium imaging of ACC activity in mice given intraperitoneal injections of 0.5, 1.5, 2.0, or 2.5 g/kg of alcohol or saline as a control. We assessed the effects of acute alcohol exposure on the activity of PYR neurons and three inhibitory interneuron subtypes, vasoactive intestinal peptide (VIP)-expressing, somatostatin (SOM)-expressing, and parvalbumin (PV)-expressing neurons. Mice were injected with AAV viruses to express the green genetically encoded calcium indicator GCaMP8s under the control of the synapsin promoter to label all ACC neurons (including the PYR cell population). We used Cre or Flp-dependent AAV viruses expressing GCaMP6s to label interneuron populations. We implanted a chronic window above the ACC region to gain optical access for two-photon calcium imaging. Alcohol decreased the average activity of GABAergic neurons (VIP, SOM, PV). Additionally, alcohol increased the coordinated activity of VIP neurons, as measured through pairwise correlations of simultaneously recorded neurons. PYR neuron activity was largely resilient to alcohol-induced changes at low to moderate doses. Our results provide a detailed account of how alcohol modulates interactions between distinct components of ACC microcircuits and lay the groundwork for a deeper understanding of the impact of alcohol on cortical computations.