Chronic ethanol exposure inhibits dopamine release via effects on the presynaptic actin cytoskeleton in PC12 cells

An increase in nucleus accumbens dopamine release appears to mediate the "rewarding" properties of drugs of abuse. Using PC12 cells, it has been shown that chronic ethanol exposure can significantly reduce nicotine-stimulated dopamine release. Here, a novel mechanism of ethanol in regulating presynaptic dopamine release is demonstrated. In neuronal cells, a layer of filamentous actin beneath the cell surface regulates the movement and release of synaptic vesicles. Upon stimulation, there is a protein kinase C (PKC)-dependent breakdown of this actin cytoskeleton, allowing vesicles to move near the nerve terminal membrane for release. Chronic ethanol alters PKC signaling, thus the hypothesis that chronic ethanol inhibits presynaptic actin cytoskeleton breakdown in response to stimulation was tested. PC12 cells were chronically exposed to ethanol and then acutely exposed to multiple forms of stimulation (nicotine, sucrose, potassium, and ionophore). In ethanol-treated cells, dopamine release was inhibited following stimulation by forms of release shown to be PKC-dependent (nicotine, sucrose, and potassium). In contrast, dopamine release was not altered following stimulation by PKC-independent forms of release (ionophore). Actin cytoskeleton breakdown was also inhibited following stimulation with PKC-dependent forms of stimulated release but not by PKC-independent (ionophore) forms. Further, cytochalasin B, an agent which depolymerizes actin, reversed the effects of chronic ethanol on both actin depolymerization and dopamine release. These data suggest that chronic ethanol inhibits presynaptic actin breakdown, likely resulting in decreased neurotransmitter release.