Abstract
Carbonic anhydrase (CA) is abundant in glial cells in the brain and CA type II isoform (CA II) activity in the hippocampus plays an important role in buffering extracellular pH transients produced by neural activity. Chronic ethanol exposure results in respiratory and metabolic acidosis, producing shifts in extracellular pH in the brain and body. These neurophysiological changes by ethanol are hypothesized to contribute to the continued drinking behavior and physical withdrawal behavior in subjects consuming ethanol chronically. We explored whether chronic ethanol self-administration (ethanol drinking, 10% v/v; ED) without or under the influence of chronic intermittent ethanol vapor (CIE-ED) experience alters the expression of CA II in the hippocampus. Postmortem hippocampal tissue analyses demonstrated that CA II levels were enhanced in the hilus region of the hippocampus in ED and CIE-ED rats. We used a novel molecule—4-fluoro-N-(4-sulfamoylphenyl) benzenesulfonamide (4-FS)—a selective CA II inhibitor, to determine whether CA II plays a role in ethanol self-administration in ED and CIE-ED rats and physical withdrawal behavior in CIE-ED rats. 4-FS (20 mg/kg, i.p.) reduced ethanol self-administration in ED rats and physical withdrawal behavior in CIE-ED rats. Postmortem hippocampal tissue analyses demonstrated that 4-FS reduced CA II expression in ED and CIE-ED rats to control levels. In parallel, 4-FS enhanced GABAA receptor expression, reduced ratio of glutamatergic GluN2A/2B receptors and enhanced the expression of Fos, a marker of neuronal activation in the ventral hippocampus in ED rats. These findings suggest that 4-FS enhanced GABAergic transmission and increased activity of neurons of inhibitory phenotypes. Taken together, these findings support the role of CA II in assisting with negative affective behaviors associated with moderate to severe alcohol use disorders (AUD) and that CA II inhibitors are a potential therapeutic target to reduce continued drinking and somatic withdrawal symptoms associated with moderate to severe AUD.
Highlights
Alcohol use disorder (AUD) affects a significant population in the United States [1], and is associated with a plethora of neurological deficits
Our study demonstrates the expression of Carbonic anhydrase (CA) II in the adult rat hippocampus and corpus callosum, and that systemic 4-FS treatment reduces CA type II isoform (CA II) expression in the hippocampus
In this study we demonstrate a novel role of CA II in ethanol self-administration associated with non-dependent drinking and somatic withdrawal symptoms associated with ethanol dependence
Summary
Alcohol use disorder (AUD) affects a significant population in the United States [1], and is associated with a plethora of neurological deficits. In the context of the above hypothesis, ethanol disrupts the delicate balance between γ-aminobutyric acid (GABA) and glutamate in the hippocampus. These neuroadaptations induced by ethanol could lead to behavioral deficits, including unregulated patterns of drinking and physical withdrawal behaviors [19]. During ethanol withdrawal, glutamate release is increased in the hippocampus [26,27], and the changes in glutamate levels are associated with increased number of functional GluNs [31,32], suggesting that these effects may induce ethanol withdrawal hyperexcitability and may lead to increased susceptibility to somatic withdrawal symptoms [33]
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