Mechanisms underlying reward-related synaptogenesis

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DESCRIPTION (provided by applicant): Addictive drugs have numerous effects on the brain but among the most significant is the powerful effect of drug-related stimuli on mnemonic processes. The research outlined in present proposal explores the mechanisms underlying these processes during amphetamine-induced conditioning. Since the amygdala is important for emotional learning, the expression of conditioned behavior may require structural changes in circuits located here. These alterations could take the form of increased or remodeled synapses, and our preliminary studies show that repeated amphetamine exposure is associated with increased density of synaptophysin- and serotonergic- immunoreactive terminals in the basolateral (BL) nucleus of the amygdala. We have also demonstrated long-lasting changes in the expression and production of the neurotrophin, BDNF and its tyrosine kinase B receptor. This enhanced BDNF signaling could lead to the synaptic strengthening. As shown elsewhere, interneurons in this nucleus are innervated by collaterals of pyramidal cells and serotonergic terminals, and so we postulate that psychostimulant-enhanced excitation of BL output pathways results in compensatory changes in the inhibitory regulation of the projection neurons resetting their firing synchrony, an adaptation that may be fundamental to the conditioned response. This application will focus on the role of BDNF and trkB in changing synaptic structure and the resetting of BL neuron function. We will use a conditioned place preference paradigm and determine whether synaptic changes are precipitated by altered expression of BDNF acting through its trk B receptors. We will further explore the physiological consequences of an increased synaptic covering. The work is designed around three aims. Specifically, in Aim 1, we will test whether in BL amphetamine-induced conditioning is associated with synaptogenesis and enhanced neuronal excitability. This work will involve unbiased stereological measurement of synaptic organization and an analysis of FOS induction after amphetamine conditioning. In Aim 2, we will further test whether synaptic strengthening is glutamate receptor-mediated, by studying AMPA and NMDA receptor expression and function in BL. Finally, in Aim 3, we will examine the influence of BDNF on synaptic strength in BL by chronically infusing this factor and studying the physiological and anatomical synaptic responses.