Implication of KCC2 in the sensitization to morphine by chronic ethanol treatment in mice

Role of KCC2 in the Regulation of Brain-Derived Neurotrophic Factor on Ethanol Consumption in Rats

Alcohol use disorder (AUD) is a common and complex disorder resulting from repetitive alcohol drinking. The mesocorticolimbic dopamine (DA) system, originating from the ventral tegmental area (VTA) in the midbrain, is involved in the rewarding effect of ethanol. The γ-aminobutyric acid (GABA) neurons in VTA appear to be key substrates of acute and chronic ethanol, which regulates DA neurotransmission indirectly in the mesocorticolimbic system. Despite significant research on the relationship between brain-derived neurotrophic factor (BDNF) and reduced alcohol consumption in male rats involving tropomyosin-related kinase B (TrkB), the mechanisms of BDNF-TrkB regulating alcohol behavior remain scarce. K⁺-Cl^- cotransporter 2 (KCC2) plays a crucial role in synaptic function in GABAergic neurons by modulating intracellular chlorine homeostasis. Here, we found that 4-week intermittent alcohol exposure impaired the function of KCC2 in VTA, evidenced by a lower expression level of phosphorylated KCC2 and decreased ratio of phosphorylated KCC2 to total KCC2, especially 72 h after withdrawal from 4-week ethanol exposure in male rats. CLP290 (a KCC2 activator) reduced excessive alcohol consumption after alcohol withdrawal, whereas VU0240551 (a specific KCC2 inhibitor) further enhanced alcohol intake. Importantly, VU0240551 reversed the attenuating effects of BDNF and 7,8-dihydroxyflavone (7,8-DHF) on alcohol consumption after withdrawal. Moreover, intraperitoneal injection of 7,8-DHF upregulated KCC2 expression and phosphorylated KCC2 in VTA 72 h after withdrawal from ethanol exposure in male rats. Collectively, our data indicate that KCC2 may be critical in the regulating action of BDNF-TrkB on ethanol consumption in AUD.

Protective Role of Low Ethanol Administration Following Ischemic Stroke via Recovery of KCC2 and p75NTR Expression

A striking result from epidemiological studies show a correlation between low alcohol intake and lower incidence for ischemic stroke and severity of derived brain injury. Although reduced apoptosis and inflammation has been suggested to be involved, little is known about the mechanism mediating this effect in vivo. Increase in intracellular chloride concentration and derived depolarizing GABAAR-mediated transmission are common consequences following various brain injuries and are caused by the abnormal expression levels of the chloride cotransporters NKCC1 and KCC2. Downstream pro-apoptotic signaling through p75NTR may link GABAA depolarization with post-injury neuronal apoptosis. Here, we show that changes in GABAergic signaling, Cl- homeostasis, and expression of chloride cotransporters in the post-traumatic mouse brain can be significantly reduced by administration of 3% ethanol to the drinking water. Ethanol-induced upregulation of KCC2 has a positive impact on neuronal survival, preserving a large part of the cortical peri-infarct zone, as well as preventing the massive post-ischemic upregulation of the pro-apoptotic protein p75NTR. Importantly, intracortical multisite in vivo recordings showed that ethanol treatment could significantly ameliorate stroke-induced reduction in cortical activity. This surprising finding discloses a pathway triggered by low concentration of ethanol as a novel therapeutically relevant target.