Ethanol and Persistent Activity in Prefrontal Cortex

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Alcoholism is characterized by a loss of control over drinking that may result from long-lasting alterations in higher cortical circuits that normally control compulsive behaviors. Brain imaging studies show that, in alcoholics, the prefrontal cortex (PFC) displays functional alterations during abstinence or after exposure to ethanol (EtOH) or visual cues associated with drinking. Little, however, is known about the actions of EtOH on prefrontal function at the cellular level. In this project, we will investigate the effects of acute and chronic EtOH exposure on the function of excitatory pyramidal neurons of the prefrontal cortex. A hallmark of prefrontal cortical neurons is "persistent activity" characterized by spontaneous and rhythmic transitions between a hyperpolarized down-state in which firing is inhibited and a depolarized up-state that is conducive for generating action potentials. The firing activity during up-state periods is modulated by dopaminergic input from VTA neurons that synapse on layer V prefrontal cortical neurons. Persistent activity may allow the prefrontal cortex to exert higher-order control over the addiction neurocircuitry by integrating and processing sensory information derived from internal and external cues. Disruption of persistent activity states within the prefrontal cortex by EtOH may be a primary event in the loss of control over compulsive drinking behaviors. Persistent activity has been studied in anesthetized whole animals but it does not occur in reduced systems such as acutely isolated slices of cortex. To circumvent problems associated with anesthesia and to allow for precise analysis of putative mechanisms, we have adapted a slice co-culture system containing prefrontal cortex, VTA, and hippocampus. After 2 weeks in culture, prefrontal neurons in this system display robust and reproducible patterns of persistent activity that can modulated by stimulusevoked firing of VTA dopamine neurons. The major goal of this project is to determine the effects of acute and chronic ethanol exposure on persistent activity of PFC neurons using this co-culture system. Aims 1, 2 and 3 will use patch-clamp electrophysiology to analyze the effects of acute and chronic ethanol on spontaneous and VTA-evoked persistent activity in layer V prefrontal pyramidal neurons. Aim 4 will use confocal imaging techniques to assess the effects of ethanol on pyramidal cell activity at the network level. The results of these studies will yield important new information regarding ethanol's effects on brain function.