The long term objectives of the proposed research are to understand how withdrawal from chronic alcohol alters striatal learning mechanisms thereby contributing to behavioral aspects of addiction. Our central hypothesis is that withdrawal from ethanol alters the balance of synaptic plasticity from long term potentiation (LTP) to long term depression (LTD). To accomplish our goal, the proposed research employs a novel, inter-related set of experiments and model simulations to characterize both pre- synaptic mechanisms and post-synaptic signaling pathways which control striatal synaptic plasticity.
The first aim i nvestigates how spatio-temporal patterns of intracellular calcium translate different synaptic input patterns into different directions of striatal synaptic plasticity. Two-photon calcim imaging of dendrites and spines will measure the calcium dynamics in response to our recently developed, theta burst LTP induction protocol and compare this with the calcium dynamics in response to a high frequency, LTD induction protocol. Model simulations of these calcium dynamics implemented using the innovative, spatial, stochastic reaction-diffusion software NeuroRD will evaluate which calcium activated signaling pathways discriminate spatio-temporal patterns of calcium elevation.
The second aim i nvestigates how temporal patterns of neuromodulator release interact with cortical glutamatergic inputs to control the development of potentiation versus depression. One experimental component uses channelrhodopsin and halorhodopsin to control temporal patterns of acetylchloline release to test the hypotheses that a transient decrease in acetylcholine release during the 100 Hz cortico-striatal stimulation produces LTD, whereas a transient increase in acetylcholine release blocks LTD. A second experimental component measures dopamine concentration to test the hypothesis that theta burst stimulation enhances release of dopamine as compared to 100 Hz stimulation. The modeling component simulates the post-synaptic signaling pathways activated by these various temporal patterns of neuromodulator release together with calcium dynamics to identify which plasticity related kinases or phosphatases discriminate LTP from LTD induction protocols. Model predictions are tested experimentally, and the validated model will be used to evaluate spatial specificity and direction of synaptic plasticity in response to realistic cortical input trins. Future research will experimentally test our central hypothesis on the effect of alcohol withdrawal on synaptic plasticity, and will use the validated model to investigate the effect of alcohol on synaptic plasticity by simulations of a "withdrawn" model which includes the effect of alcohol on both individual molecules (e.g. adenylyl cyclase, NMDAR channels) and neuromodulator release.
One of the most disruptive and discouraging aspects of alcohol abuse is the tendency to relapse, and numerous behavioral studies have noted that cue-induced relapse shares many traits with stimulus-response learning. Just as striatal synaptic plasticity is thought to underlie habit learning, recent and converging evidence from both alcohol and drug studies point to altered striatal synaptic plasticity after withdrawal from chronic alcoho or drug use. Several molecules that are important for synaptic plasticity are altered by withdrawal and contribute to these modifications in synaptic plasticity;therefore, a complete understanding of the molecular mechanisms underlying synaptic plasticity will allow development of computer models which can simulate the abnormal synaptic plasticity produced by withdrawal from chronic alcohol use and will facilitate development of novel pharmaceuticals to treat alcohol addiction and relapse.
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