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The nervous system as a three-dimensional map

A Freiburg research team has created the first complete map of special connections of nerve cells in zebrafish. The data identify all projection possibilities (“projectome”) of nerve cells in a particular class of messengers in the nervous system that is of great importance for medicine. The data were published in Nature Communications on 25th January.

It would be difficult to understand how a city is organised without knowing the layout of its streets. Scientists are faced with the same problem when they attempt to understand how the brain functions. In the case of vertebrates, we only have fragmentary knowledge of which nerve cells send their connections, so-called axons, into certain regions of the brain.

Such knowledge is particularly important for understanding the functioning of groups of nerves that send out axons to modulate the activity of neural circuits in remote regions of the brain. One of these groups consists of nerve cells that use the tiny molecule dopamine as a messenger to control many types of behaviour. It is precisely these neurons which die off in people suffering from Parkinson’s disease, which demonstrates just how central a role they play in medicine.

A team of neurobiologists from the University of Freiburg led by Prof. Dr. Wolfgang Driever from the Faculty of Biology and including Dr. Olaf Ronneberger from the Department of Computer Science and Dr. Roland Nitschke from the Centre for Biological Systems Analysis (ZBSA), has now succeeded in creating the first complete map of all axons which use dopamine as a messenger in a vertebrate, in this case using zebrafish, which are a popular laboratory model. The data identify all projection possibilities, the so-called “projectome,” of every nerve cell for a class of messengers in the nervous system that is of great importance for medicine. The researchers worked in close cooperation with the university’s Centre for Biological Systems Analysis (ZBSA) and BIOSS, Centre for Biological Signalling Studies. The results were published on 25th January 2011 in the new journal “Nature Communications” published by the renowned Nature Publishing Group (NPG).

Overall view of a zebrafish nervous system in colour. © Driever and Ruy

The scientists were able to create the first three-dimensional projectome map of the intact brain of the zebrafish by combining the selective genetic labelling of individual nerve cells with high-resolution microscopy available at the ZBSA. The new map uncovers important information on ways that the brain functions. For instance, it illustrates that dopaminergic neurons of the diencephalon connect distant regions of the brain in previously unimagined ways - regions that are responsible for higher brain functions in the telencephalon, physiological control in the hypothalamus, coordination of movement in the hindbrain and execution of movement in the spinal cord. These neurons are variously involved in effecting changes in basic behavioural states following stress: active reactions like fight or flight or passive reactions like freezing all activity. In the same study, the scientists describe a new dopaminergic system in another region of the zebrafish brain, the corpus striatum, in which the loss of dopaminergic connections in Parkinson patients is particularly severe. The authors speculate that this system might compensate for the small number of dopaminergic neurons in fish. In conjunction with further neurobiological studies, the "projectome" map opens up possibilities for a new understanding of neural circuits in the brains of simple vertebrates like the zebrafish.

Prof. Dr. Wolfgang Driever
Faculty of Biology
University of Freiburg
BIOSS - Centre for Biological Signalling Studies
Freiburg Institute for Advanced Studies (FRIAS) 
Centre for Biological Systems Analysis (ZBSA)
Tel.: +49 (0)761/203-2587
Fax: +49 (0)761/203-2597
E-mail: driever(at)biologie.uni-freiburg.de

Website address: https://www.gesundheitsindustrie-bw.de/en/article/press-release/the-nervous-system-as-a-three-dimensional-map