Adolescent Vulnerability to Alcohol Use Disorder: Neurophysiological Mechanisms from Preclinical Studies

Elevated GABAergic neurotransmission prevents chronic intermittent ethanol induced hyperexcitability of intrinsic and extrinsic inputs to the ventral subiculum of female rats

With the recent rise in the rate of alcohol use disorder (AUD) in women, the historical gap between men and women living with this condition is narrowing. While there are many commonalities in how men and women are impacted by AUD, an accumulating body of evidence is revealing sex-dependent adaptations that may require distinct therapeutic approaches. Preclinical rodent studies are beginning to shed light on sex differences in the effects of chronic alcohol exposure on synaptic activity in a number of brain regions. Prior studies from our laboratory revealed that, while withdrawal from chronic intermittent ethanol (CIE), a commonly used model of AUD, increased excitability in the ventral hippocampus (vHC) of male rats, this same treatment had the opposite effect in females. A follow-up study not only expanded on the synaptic mechanisms of these findings in male rats, but also established a CIE-dependent increase in the excitatory-inhibitory (E-I) balance of a glutamatergic projection from the basolateral amygdala to vHC (BLA-vHC). This pathway modulates anxiety-like behavior and could help explain the comorbid occurrence of anxiety disorders in individuals suffering from AUD. The present study sought to conduct a similar analysis of CIE effects on both synaptic mechanisms in the vHC and adaptations in the BLA-vHC pathway of female rats. Our findings indicate that CIE increases the strength of inhibitory neurotransmission in the vHC and that this sex-specific adaptation blocks, or at least delays, the increases in intrinsic vHC excitability and BLA-vHC synaptic transmission observed in males. Our findings establish the BLA-vHC pathway and the vHC as important circuitry to consider for future studies directed at identifying sex-dependent therapeutic approaches to AUD.

Withdrawal from chronic ethanol exposure increases postsynaptic glutamate function of insular cortex projections to the rat basolateral amygdala

A key feature of alcohol use disorder (AUD) is negative affect during withdrawal, which often contributes to relapse and is thought to be caused by altered brain function, especially in circuits that are important mediators of emotional behaviors. Both the agranular insular cortex (AIC) and the basolateral amygdala (BLA) regulate emotions and are sensitive to ethanol-induced changes in synaptic plasticity. The AIC and BLA are reciprocally connected; and the effects of chronic ethanol exposure on this circuit have yet to be explored. Here, we use a combination of optogenetics and electrophysiology to examine the pre- and postsynaptic changes that occur to AIC-BLA synapses following withdrawal from 7- or 10-days of chronic intermittent ethanol (CIE) exposure. While CIE/withdrawal did not alter presynaptic glutamate release probability from AIC inputs, withdrawal from 10, but not 7, days of CIE increased AMPA receptor-mediated postsynaptic function at these synapses. Additionally, NMDA receptor-mediated currents evoked by electrical stimulation of the external capsule, which contains AIC afferents, were also increased during withdrawal. Notably, a single subanesthetic dose of ketamine administered at the onset of withdrawal prevented the withdrawal-induced increases in both AMPAR and NMDAR postsynaptic function. Ketamine also prevented the withdrawal-induced increases in anxiety-like behavior measured using the elevated zero maze. Together, these findings suggest that chronic ethanol exposure increases postsynaptic function within the AIC-BLA circuit and that ketamine can prevent ethanol withdrawal-induced alterations in synaptic plasticity and negative affect.

Medication Development for Alcohol Use Disorder: A Focus on Clinical Studies

Compared to other medical disorders, including other brain diseases, the number of medications approved for alcohol use disorder (AUD) is very small. Disulfiram, naltrexone (oral and long-acting), and acamprosate are approved by the US Food and Drug Administration (FDA) to treat patients with AUD. These medications are also approved in other countries, including in Europe, where the European Medicines Agency (EMA) also approved nalmefene for AUD. Furthermore, baclofen was recently approved for AUD in France. These approved medications have small effect sizes, which are probably the consequence of the fact that they only work for some patients, yet a personalized approach to match the right medication with the right patient is still in its infancy. Therefore, research is needed to expand the armamentarium of medications that clinicians can use to treat their patients, as well as to better develop personalized approaches. This book chapter reviews other medications, beyond those approved by the FDA, that have shown efficacy in clinical trials, as well as medications which are still in the early stages of evaluation in human studies.