In humans, damage to the orbitofrontal cortex (OFC) often results in poor judgment that is characterized by behavioral inflexibility and an inability to anticipate consequences of one's actions. Human alcoholics also exhibit a similar behavioral profile characterized by deficits in inhibition and measures of impulsivity/perseverations. In rodents, lesions of the lateral and ventral portions of the OFC disrupt attentional set-shifting by slowing acquisition rates and increasing the number of errors made during a reversal learning task (Bissonette et al, 2008). These observations suggest that chronic exposure to alcohol produces alterations in OFC function that reduces behavioral flexibility. To date, few studies have investigated the direct effects of ethanol (EtOH) on OFC neuron function and related behavioral consequences. The present proposal will address this issue.
Aim 1 will test the hypothesis that acute and chronic alcohol exposure disrupts OFC- dependent cognitive function in adult mice. These studies will use a well-established model of alcohol dependence and a behavioral set-shifting assay recently shown to require an intact OFC. A baseline of set- shifting behavior and reversal learning will be established in all mice prior to alcohol exposure and the effects of an acute injection of EtOH (0.5, 1.0, 1.75 g/kg, ip) or saline will be determined. Mice will then be exposed to chronic intermittent EtOH exposure [multiple cycles of voluntary EtOH drinking and EtOH (or air) vapor inhalation] to induce alcohol dependence. To determine how long effects of EtOH dependence on set-shifting persist, testing will be conducted during the first (days 4-9) or second (days 11-16) week following the last bout of EtOH (or air) inhalation exposure. It is expected that alcohol dependent mice will show dose-dependent deficits in set-shifting and reversal learning.
Aim 2 will test the hypothesis that deficits in behavioral flexibility in EtOH dependent mice are associated with changes in the excitability and synaptic properties of OFC neurons. These studies will use acute brain slices and whole-cell patch clamp electrophysiology to investigate changes in OFC neuron function in EtOH-dependent mice. To determine how long effects of EtOH dependence on OFC neuronal excitability and synaptic transmission persist, OFC neurons will be recorded at 0, 5 or 12 days post alcohol exposure with the later two time points corresponding to reversal learning training days. Synaptic efficacy will be determined by measuring evoked synaptic responses in the presence of selective pharmacological agents in order to isolate NMDA, AMPA, and GABA mediated events. We will also determine the effects of acute EtOH on glutamatergic and GABAergic synaptic events in alcohol dependent and non- dependent mice. It is expected that NMDA receptors will be inhibited by concentrations of EtOH (22, 44 or 66 mM) that are associated with behavioral signs of intoxication. These results will address an important gap in our knowledge regarding the effects of alcohol on cognitive function in the OFC and will provide an avenue for the further investigation of mechanisms underlying behavioral inflexibility in alcohol dependent subjects.
These studies will examine the long term effects of alcohol dependency on the adult male mouse brain (orbitofrontal cortex) and their ability to alter attention.
|Badanich, Kimberly A; Mulholland, Patrick J; Beckley, Jacob T et al. (2013) Ethanol reduces neuronal excitability of lateral orbitofrontal cortex neurons via a glycine receptor dependent mechanism. Neuropsychopharmacology 38:1176-88|
|Badanich, Kimberly A; Becker, Howard C; Woodward, John J (2011) Effects of chronic intermittent ethanol exposure on orbitofrontal and medial prefrontal cortex-dependent behaviors in mice. Behav Neurosci 125:879-91|