The prefrontal cortex (PFC) is of critical importance for higher order cognitive functions and the organization of complex behaviors, including those related to addiction. In spite of clear clinical evidence that chronic alcohol consumption alters the activity and function of the PFC, surprisingly little is known about the underlying changes at the molecular and cellular level. Although altered glutamatergic neurotransmission in prefrontal- limbic circuits has been implicated in the development of addiction, virtually nothing is known regarding how chronic alcohol may induce aberrant plasticity within the PFC. An understanding of the alcohol-induced changes in PFC function requires knowledge of the changes in the properties of excitatory synaptic transmission and specifically NMDA receptor function. The over-arching hypothesis of this application is that chronic ethanol exposure induces homeostatic increases in NMDA receptors, which will affect the interplay between backpropagating action potentials and localized Ca2+-spikes that are required for spike timing-dependent plasticity, a physiologically relevant model of synaptic plasticity. Such changes could alter integrative properties and synaptic plasticity and may represent pathological neuroadaptations of PFC pyramidal neurons underlying alcohol dependence. Thus, the increased NM.D.AR activity after prolonged ethanol exposure may result in aberrant plasticity, which could contribute to a loss of response inhibition in the PFC that may underlie alcohol drinking behavior. We provide preliminary data that supports this idea. In the current exploratory R21 application, we will examine ethanol-induced changes in the synaptic plasticity of the PFC in acute brain slices from adult drug-naive mice and mice chronically exposed to alcohol. Alcohol consumption of mice will be measured in a limited-access paradigm and dependence will be induced by exposing animals to alcohol vapor in a chronic-intermittent fashion.
Aim 1 will use current-clamp recordings to assess the effects of the homeostatic changes at the NMDA receptor on synaptic plasticity. Therefore, we will study spike-timing dependent plasticity (STDP;plasticity induced by pairing EPSPs with backpropagating action potentials) to study changes in the magnitude and induction threshold of long term potentiation (LTP) or depression (LTD).
Aim 1. 1 will establish the main effect (i.e., alterations in STDP in alcohol exposed animals) and its persistence over 1 week of withdrawal.
Aim 1. 2 will test whether changes at NMDA receptors shift the frequency dependence of the induction of STDP.
In Aim 2 we will use a combination of current clamp recordings and high resolution Ca2+ imaging to investigate whether altered Ca2+ influx through NMDA receptors in basal dendrites (dendritic Ca2+ spikes) provides a mechanism for the hypothesized changes in STDP.
Aim 2. 2 tests the alternative hypothesis that voltage-gated Ca2+ channels are a main target of alcohol responsible for the hypothesized changes in STDP in Aim 1.
The prefrontal cortex is critically involved in the regulation of higher order cognitive functions and disturbances in these processes may underlie a loss of control over alcohol drinking behavior. The experiments in this project will use an animal model of alcohol addiction to study changes in glutamatergic synaptic transmission and NMDA receptor function in the prefrontal cortex. These studies will provide insights into the mechanisms that underlie synaptic plasticity during the development and maintenance of addiction to alcohol.
| Mulholland, Patrick J; Spencer, Kathryn B; Hu, Wei et al. (2015) Neuroplasticity of A-type potassium channel complexes induced by chronic alcohol exposure enhances dendritic calcium transients in hippocampus. Psychopharmacology (Berl) 232:1995-2006 |
| Hu, Wei; Morris, Brett; Carrasco, Angelique et al. (2015) Effects of acamprosate on attentional set-shifting and cellular function in the prefrontal cortex of chronic alcohol-exposed mice. Alcohol Clin Exp Res 39:953-61 |
