CRCNS: Spatio-temporal Dynamics of Dopamine Activated 2nd Messenger Pathway

George Mason University, Fairfax VA

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Abstract

DESCRIPTION (provided by applicant): 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 investigates 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 investigates 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.