Contrasting sex-dependent adaptations to synaptic physiology and membrane properties of prefrontal cortex interneuron subtypes in a mouse model of binge drinking

Abstract

Alcohol use disorder (AUD) affects all sexes, however women who develop AUD may be particularly susceptible to cravings and other components of the disease. While many brain regions are involved in AUD etiology, proper function of the prefrontal cortex (PFC) is particularly important for top-down craving management and the moderation of drinking behaviors. Essential regulation of PFC output is provided by local inhibitory interneurons, yet the effects of chronic drinking on interneuron physiology remain poorly understood, particularly in female individuals. To address this gap, we generated fluorescent reporter transgenic mice to label the two major classes of interneuron in deep layer prelimbic PFC, based on expression of parvalbumin (PV-IN) or somatostatin (SST-IN). We then interrogated PV-IN and SST-IN membrane and synaptic physiology in a rodent model of binge drinking. Beginning in late adolescence, mice received 3-4 weeks of intermittent access (IA) ethanol. One day after the last drinking session, adaptations to PV-IN and SST-IN intrinsic physiology were observed in male mice but not in female mice. Furthermore, IA ethanol precipitated diametrically opposing changes to PV-IN synaptic physiology based on sex. IA ethanol decreased excitatory synaptic strength onto PV-INs from female mice and potentiated excitatory transmission onto PV-INs male mice. In contrast, decreased synaptic strength onto SST-INs was observed following IA ethanol in all groups of mice. Together, these findings illustrate novel sex differences in drinking-related PFC pathophysiology. Discovering means to restore PV-IN and SST-IN dysfunction following extended drinking provides opportunities for developing new treatments for all AUD patients.

Bi-directional control of a prelimbic somatostatin microcircuit decreases binge alcohol consumption

“…Here we observed that the effects of DID on neuronal intrinsic excitability and synaptic transmission in the PL extends to SST neurons, in which SST neurons displayed a state of hypoactivity with diminished intrinsic excitability and a disrupted excitatory/inhibitory transmission dynamic in both sexes. Similar effects were observed in an intermittent-access model of alcohol drinking (39). Of note, despite a reduction in sEPSC frequency on SST neurons in both sexes, there is an increase in evoked GABA release probability, as evidenced by reduced IPSC paired-pulse ratio (39), suggesting that there could be a compensatory mechanism on a whole-circuit level to counteract the effects on excitatory transmission in single neurons.…”

“…Similar effects were observed in an intermittent-access model of alcohol drinking (39). Of note, despite a reduction in sEPSC frequency on SST neurons in both sexes, there is an increase in evoked GABA release probability, as evidenced by reduced IPSC paired-pulse ratio (39), suggesting that there could be a compensatory mechanism on a whole-circuit level to counteract the effects on excitatory transmission in single neurons. Alterations in sEPSC frequency indicate the effects of DID on a presynaptic locus, which could arise from a wide array of glutamatergic sources such as the basolateral amygdala (BLA), the ventral hippocampus, the thalamus as well as within the medial prefrontal cortex itself (12,40,41).…”

“…Ethanol exposure has been shown to modify expression of key modulators of neuronal excitability, including ionotropic glutamate receptors (20,38), inward-rectifying potassium channel (45), voltage-gated calcium channels (46), and hyperpolarization-activated cation channels (HCN; (47). Intermittent access to alcohol increased medium afterhyperpolarization in PL SST neurons (39), which might be mediated by M-type potassium channels and HCN channels (48). Notably, in females following DID, PL SST neurons displayed highly depolarized resting membrane potential yet could not efficiently produce action potentials, suggesting a state of depolarization block.…”

“…One interpretation is that the population-wide, optically-evoked IPSC transmission from SST neurons (Figure 3) does not reflect the changes on a single-neuron level in the intrinsic excitability experiments (Figure 1). Population-wide increase in SST-mediated inhibitory outputs may occur to compensate the reduction in excitation of single neurons, which bears resemblance to the discrepancy between spontaneous and evoked EPSC on SST neurons in the intermittent-access model (39). In addition, assessments of raw optogenetically evoked IPSC amplitudes must be interpreted with caution, as mouse-to-mouse variability in ChR2 injection may drive changes in overall results.…”

Constitutive Genetic Deletion of Hcn1 Increases Alcohol Preference during Adolescence

“…Another major limitation is that sex was not used as a biological variable in this study but should be in the future. Female mice are known to drink more in the IA EtOH procedure [31] and display divergent adaptations to chronic alcohol [43] and female rodents have higher Hcn1 expression in the medial PFC [37].…”