Alcohol Enhances Responses to High Frequency Stimulation in Hippocampus from Transgenic Mice with Increased Astrocyte Expression of IL-6

Impact of Elevated Brain IL-6 in Transgenic Mice on the Behavioral and Neurochemical Consequences of Chronic Alcohol Exposure

Alcohol consumption activates the neuroimmune system of the brain, a system in which brain astrocytes and microglia play dominant roles. These glial cells normally produce low levels of neuroimmune factors, which are important signaling factors and regulators of brain function. Alcohol activation of the neuroimmune system is known to dysregulate the production of neuroimmune factors, such as the cytokine IL-6, thereby changing the neuroimmune status of the brain, which could impact the actions of alcohol. The consequences of neuroimmune-alcohol interactions are not fully known. In the current studies we investigated this issue in transgenic (TG) mice with altered neuroimmune status relative to IL-6. The TG mice express elevated levels of astrocyte-produced IL-6, a condition known to occur with alcohol exposure. Standard behavioral tests of alcohol drinking and negative affect/emotionality were carried out in homozygous and heterozygous TG mice and control mice to assess the impact of neuroimmune status on the actions of chronic intermittent alcohol (ethanol) (CIE) exposure on these behaviors. The expressions of signal transduction and synaptic proteins were also assessed by Western blot to identify the impact of alcohol-neuroimmune interactions on brain neurochemistry. The results from these studies show that neuroimmune status with respect to IL-6 significantly impacts the effects of alcohol on multiple levels.

IL-6, but not TNF-α, response to alcohol cues and acute consumption associated with neural cue reactivity, craving, and future drinking in binge drinkers

Objective and design

Preclinical studies suggest learned immune system responses to alcohol cues and consumption may contribute to alcohol's pharmacodynamic properties and/or Alcohol Use Disorder (AUD) pathogenesis. Mechanistically, these immune alterations may be associated with increased craving and alcohol consumption, both acutely and over time. We sought to characterize this relationship in a randomized, counter-balanced, crossover neuroimaging experiment which took place between June 2020-November 2021.

Methods

Thirty-three binge drinkers (BD) and 31 non-binge, social drinkers (SD), matched for demographic and psychological variables, were exposed to alcohol cues and water cues in two separate 7 T functional magnetic resonance imaging (fMRI) scans. Each scan was followed by the Alcohol Taste Test (ATT) of implicit motivation for acute alcohol. Craving measures and blood cytokine levels were collected repeatedly during and after scanning to examine the effects of alcohol cues and alcohol consumption on craving levels, Tumor necrosis factor alpha (TNF-α), and Interleukin 6 (IL-6) levels. A post-experiment one-month prospective measurement of participants' "real world" drinking behavior was performed to approximate chronic effects.

Results

BD demonstrated significantly higher peak craving and IL-6 levels than SD in response to alcohol cues and relative to water cues. Ventromedial Prefrontal Cortex (VmPFC) signal change in the alcohol-water contrast positively related to alcohol cue condition craving and IL-6 levels, relative to water cue condition craving and IL-6 levels, in BD only. Additionally, peak craving and IL-6 levels were each independently related to ATT alcohol consumption and the number of drinks consumed in the next month for BD, again after controlling for craving and IL-6 repones to water cues. However, TNF-α release in the alcohol cue condition was not related to craving, neural activation, IL-6 levels, immediate and future alcohol consumption in either group after controlling for water cue condition responses.

Conclusions

In sum, BD show greater craving and IL-6 release in the alcohol cue condition than SD, both of which were associated with prefrontal cue reactivity, immediate alcohol consumption, and future alcohol consumption over the subsequent 30 days. Alcohol associated immune changes and craving effects on drinking behavior may be independent of one another or may be indicative of a common pathway by which immune changes in BD could influence motivation to consume alcohol.

Trial registration

Clinical Trials NCT04412824.

Modulation of neuronal excitability by binge alcohol drinking

Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.

Alcohol Enhances Responses to High Frequency Stimulation in Hippocampus from Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies show that alcohol exposure can induce glial production of neuroimmune factors in the CNS. Of these, IL-6 has gained attention because it is involved in a number of important physiological and pathophysiological processes that could be affected by alcohol-induced CNS production of IL-6, particularly under conditions of excessive alcohol use. For example, IL-6 has been shown to play a role in hippocampal behaviors and synaptic plasticity (long-term potentiation; LTP) associated with memory and learning. Surprisingly, in our in vitro studies of LTP at the Schaffer collateral to CA1 pyramidal neuron synapse in hippocampus from transgenic mice that express elevated levels of astrocyte produced IL-6 (TG), LTP was not altered by the increased levels of IL-6. However, exposure to acute alcohol revealed neuroadaptive changes that served to protect LTP against the alcohol-induced reduction of LTP observed in hippocampus from non-transgenic control mice (WT). Here we examined the induction phase of LTP to assess if presynaptic neuroadaptive changes occurred in the hippocampus of TG mice that contributed to the resistance of LTP to alcohol. Results are consistent with a role for IL-6-induced neuroadaptive effects on presynaptic mechanisms involved in transmitter release in the resistance of LTP to alcohol in hippocampus from the TG mice. These actions are important with respect to a role for IL-6 in physiological and pathophysiological processes in the CNS and in CNS actions of alcohol, especially when excessive alcohol used is comorbid with conditions associated with elevated levels of IL-6 in the CNS.