SSA: Presynaptic control of subunit composition of NMDA receptors mediating synaptic plasticity in the dorsal cochlear nucleus

Presynaptic receptors are ideally suited to affect neurotransmitter release and influence the efficacy of synaptic transmission. Cellular mechanisms by which presynaptic receptors can affect neurotransmitter release are largely unknown. NMDA receptors (NMDARs) are glutamate-gated ion channels with unique biophysical, pharmacological and signalling properties. The project aims at studying the novel function of presynaptic glutamatergic NMDARs at regulating presynaptic release probability and short-term plasticity in the dorsal cochlear nucleus (DCN), an auditory brainstem structure involved in the generation of tinnitus. The study will be investigating their anatomical distribution, subunit composition, activation mechanisms as well as their downstream effects on synapse function in the mouse DCN. Anatomical evidence will come from immuno-electron microscopy experiments that will allow identifying NMDARs in presynaptic elements in the DCN. Direct monitoring of presynaptic function using calcium imaging from transgenic mice expressing fluorescent presynaptic markers and whole cell recordings of DCN principal cells will demonstrate the existence of functional presynaptic NMDARs. The role of subunit composition will be investigated using pharmacological and genetic tools. In particular, single-cell reverse transcriptase-polymerase chain reaction will be used to analyse the expression pattern of NMDAR subunits 2A, 2B, and 2C (NR2A-C) subsequent to electrophysiological characterization in presynaptic cells. Computational modelling will determine the physiological behaviour of the DCN network. Auditory brainstem response recordings will allow assessing shifts of hearing thresholds induced by acoustic over-exposure. Cochlear injections of NMDAR antagonists will allow establishing the physiological significance of presynaptic NMDARs.