The role of Calcium-induced demonic responses in co-active neurons of the ventral segmental area (VTA) in nicotine reinforcement and sensitized locomotor activity

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This project aims to identify functional ensembles of midbrain neurons and their transcriptional responses to repeated nicotine administration which underlie lasting behavioural changes associated with addiction.

Brain circuits involving dopamine neurons of the ventral tegmental area (VTA) are critical components of reward-related networks. Dopamine neurons show rhythmic pacemaker and burst activity patterns that are controlled by their connectivity within midbrain microcircuits involving acetylcholine, glutamate, GABA and other VTA dopamine containing neurons, all of which express nicotinic acetylcholine receptors.

Plasticity of synaptic connections within these circuits has been shown to occur in response to repeated nicotine administration in mice and is believed to mediate both the sensitized motor responses to nicotine and the development of intravenous self-administration of nicotine. These behaviours represent a form of plasticity within reward circuitry of the midbrain, which we wish to utilize to identify coherent activity within neuronal ensembles and investigate their nicotine-induced plasticity at a molecular and cellular level. Ensembles will be characterized with multicellular confocal calcium imaging and patch clamp electrophysiology in acute midbrain slices (ex-vivo) to assess the precise spatial and temporal dynamics of calcium signals, the sparsity of simultaneous activity, the suppression of background activity, the importance of local network connectivity and the plasticity of these circuits induced by repeated passive nicotine injections or nicotine self-administration in vivo. We will use Cre mice and fluorescent markers to identify specific cell types within ensembles during slice recordings as well as post-hoc immunohistochemical analysis. Finally, we will investigate the role of gene expression in the long-term implementation of changes in the responsiveness of midbrain neuronal ensembles to nicotine by interfering with calcium-regulated synapse-to-nucleus signalling as well as by identifying and functionally testing the role of target genes induced in co-active, ensemble forming neurons. In short, we will use live imaging in conjunction with electrophysiology and molecular signalling studies to identify and characterize neuronal ensembles in the midbrain and their nicotine-induced plasticity and to determine the role of synapse-to-nucleus communication and signal-regulated transcription in the maintenance of altered network functions and the resulting behavioural adaptations.
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Wittmann M§, Queisser G§, Eder A§, Wiegert JS§, Bengtson CP§, Hellwig A§, Wittum G, Bading
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*Principal investigators of other projects within the CRC