Neuroenergetics

It is increasingly recognized that energy consumption is a key constraint on neural function. To ensure optimal efficiency in synaptic transmission, plasticity and energy supply of local networks, multiple molecules are exchanged between neurons and astrocytes. A major breakthrough in the understanding of metabolic mechanisms sustaining neural activity came from the description of the neuro-astrocytic crosstalk in the tripartite excitatory synapses. In particular, glutamate uptake through astrocytic transporters coupled to lactate shuttling from astrocytes to neurons via the neural uptake system MCT2 are thought to play a central role in this crosstalk. We previously showed the implication of neuroastrocytic communication in the induction of functional signals in vivo depending on metabolic and blood flow changes. Now we want to determine whether activity-dependent metabolic mechanisms are specifically modulated and/or are permissive for the induction and maintenance of synaptic plasticity in local neural networks. Long Term Potentiation (LTP) is the prime experimental candidate for mediating learning and memory at the cellular and network level in the brain. Although LTP induction requires simultaneous activation of a large number of excitatory synapses (thus a large distribution of energy to stimulated areas), the importance of metabolic changes in LTP remains unknown. In this project our aim is to investigate the role of the neuroastrocytic crosstalk by glutamate/lactate in the hippocampal LTP in vivo. Our working hypothesis is that long term increase in synaptic strength is based on coordinated energetic input to active networks and involves an active gating role of glutamate/lactate transport between neurons and astrocytes. To explore the sustaining role of energy in LTP, we will acquire metabolic changes during LTP with local field potentials coupled to glucose, lactate and cerebral blood flow recordings. Then, to determine the gating role of GLT1 and MCT2 in synaptic plasticity, we will use mice injected with lentivirus allowing bidirectional gene-targeted regulation of these transporters. This is an experiment of high interest since bidirectional regulation of the experession of these 2 key transporters are allowed by lentiviral strategy giving the possibility to check whether intensity and duration of LTP follow variations of metabolic activity. Finally, we will check by mRNA screening and in situ hybridization transcript profiles of key metabolic molecules such as glutamate, glucose and lactate transporters in addition to key enzymes (lactate dehydrogenase, glutamine synthase) in hippocampal slices from all animals. We want to have a 'metabolic mRNA picture' before and after LTP induction to study expression changes during synaptic plasticity. Detailed technical approaches and several set of preliminary data dealing with multiple metabolic recordings and up/down regulation of transporters by lentiviral targeting are introduced in this application.