Projects within the BCCN:
The main objectives of this project were the optical manipulation and electrophysiological recording of defined dopaminergic neurons and PFC neurons, respectively, in vivo.
The dopaminergic system is frequently affected in psychiatric disorders. In this project, we established tools for an optogenetic mapping of the dopaminergic system in the rat. We have generated BAC -transgenic rat lines for the expression of cre recombinase in dopaminergic (DAT-cre) and dopaminoceptive (D1-cre) (Schonig et.al 2012). Those transgenic cre-driver lines were first characterized by mating them to a reporter line, expressing eGFP after cre mediated recombination (CAG-loxP.EGFP, Weber et al.). We identified functional D1-cre and DAT-iCre lines. Animals of both transgenic lines were used for viral injections with Adeno-associated viruses (AAV). These viruses carry a double floxed inverse open reading frame (DIO) of a red fluorescent protein, which gets expressed only in cre producing cells. AAV mediated expression confirmed our initial analyses with the cre reporter line.
Similarly cre dependent AAV harbouring a DIO with ChR2 were injected in DAT-iCre animals, for targeting ChR2 expression to the dopaminergic system. AAV mediated expression of ChR2 in dopaminergic cells was shown using co- immunohistochemistry.
In collaboration with the Kelsch and Durstewitz groups (B5/ D2), successful stimulation of DA fibers into the PFC could be demonstrated in prefrontal slices in vitro. In this collaborative project (supported partly by DFG), the DAT-iCre rats were used to explore dopamine D1/D2 receptor modulation of cortico-cortical spike-timing-dependent plasticity (STDP) in adult rat prefrontal cortex, where DA was shown to further boost LTD at negative and convert LTP into LTD at positive pairing lags, through the combined D1/D2 receptor action.
The original application proposed the generation of the conditional NpHR/ChR2 allele in transgenic rats, using the CAGS promoter and FLEX/double loxP technology. While we have generated the rat transgenic line, the expression of opsins was not sufficient for optogenetic stimulation. We have therefore generated DAT-cre and D1-cre rats and combined them with AAV-driven expression of opsins. The DAT-cre and D1-cre rat mutants generated in our laboratory are available and distributed to other labs for further research.
Sculfort SA, Bartsch D, Enkel T (2016) Dopamine antagonism does not impair learning of Pavlovian conditioned approach to manipulable or non-manipulable cues but biases responding towards goal tracking Behav Brain Res 314:1-5 .
Schonig K, Weber T, Frommig A, Wendler L, Pesold B, Djandji D, Bujard H, Bartsch D (2012) Conditional Gene Expression Systems in the Transgenic Rat Brain BMC Biol 10:77 .