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Newly discovered nerve cell shape allows communication without detours

In certain nerve cells, the structure that receives stimuli from other cells is directly connected with the axon, the signal-transmitting cell extension. The previously unknown nerve cell shape was discovered in a current study by a research team from Heidelberg, Mannheim and Bonn. It facilitates the signal transmissions within the nerve cell: The signal does not have to be propagated across the cell

(click on the picture for a higher resolution)

Nerve cells communicate by using electrical signals. Via widely ramified cell structures called the  dendrites, neurons receive signals from other neurons and then transmit the signal over a thin cell extension called the axon to other nerve cells. Axon and dendrites are usually interconnected by the neuron’s cell body. A team of scientists at the Bernstein Center Heidelberg-Mannheim, Heidelberg University, and the University of Bonn has now discovered neurons in which the axon arises directly from one of the dendrites. Similar to taking a bypass road, the signal transmission is thus facilitated within the cell.

 “Input signals at this dendrite do not need to be propagated across the cell body,” explains Christian Thome of the Bernstein Center Heidelberg-Mannheim and Heidelberg University, author of the study.  For their analyses, the scientists specifically colored the places of origin of axons of so-called pyramidal cells in the hippocampus. This brain region is involved in memory processes. The surprising result: “We found that in more than half of the cells, the axon does not emerge from the cell body, but arises from a lower dendrite,” Thome says.

The researchers then studied the effect of signals received at this special dendrite. For this purpose, they injected a certain form of the neural transmitter substance glutamate into the brain tissue of mice that can be activated by light pulses. A high-resolution microscope allowed the neuroscientists to direct the light beam directly to a specific dendrite. By the subsequent activation of the messenger substance, they simulated an exciting input signal. 

“Our measurements suggest that even small input stimuli in ‘axon-carrying’ dendrites are actively transmitted” says Tony Kelly a member of the SFB 1089 at the University of Bonn and author of the study. A computer simulation predicts that this effect is particularly pronounced when the information flow from other dendrites to the axon is suppressed by inhibitory input signals at the cell body.

 “That way, information transmitted by the ‘axon-carrying’ dendrite influences the behavior of the nerve cell more than input from any other dendrite,” Kelly says. In a future step, the researchers attempt to figure out which biological function is actually strengthened through the specific dendrite—and what therefore might be the reason for the unusual shape of these neurons.

The SFB 1089 ‘Synaptic Micronetworks in Health and Disease’ is a collaborative research centre in Bonn with partners in Israel.  Members of the research group investigate how neurons interact within networks, and the translation of neuronal network activity to mammalian and human behavior.  This SFB was inaugurated in October 2013 with the support of the German Research Foundation (DFG). 

 

Contact

Dr. Tony Kelly
Laboratory for Cognition Research and Experimental Epileptology, Department of Epileptology,
University of Bonn,
53127 Bonn, Germany
Tel: +49 (0) 228 6885-276
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Prof. Dr. med. Heinz Beck
Laboratory for Cognition Research and Experimental Epileptology, Department of Epileptology,
University of Bonn,
53127 Bonn, Germany
Tel: +49 (0) 228 6885-270
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Original publication:

C. Thome, T. Kelly, A. Yanez, C. Schultz, M. Engelhardt, S. B. Camebridge, M. Both, A. Draguhn, H. Beck and A. V. Egorov (2014): Axon-Carrying Dendrites Convey Privileged Synaptic Input in Hippocampal Neurons. Neuron, 83, 1418-1430.

Also see comment by P. Kaifosh and A. Losonczy in Neuron 83, 1231-1233.

Further information:

Laboratory of Cognition Research & Experimental Epileptology SFB 1089 ‘Synaptic Micronetworks in Heath & Disease‘  Institut für Physiologie und Pathophysiologie
Bernstein Center for Computational Neuroscience