Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institute, Retzius väg 8, A3:5, SE-171 77 Stockholm, Sweden.
A novel role for MNTB neuron dendrites in regulating action potential amplitude and cell excitability during repetitive firing
Article first published online: 28 JUN 2008
© The Authors (2008). Journal Compilation © Federation of European Neuroscience Societies and Blackwell Publishing Ltd
European Journal of Neuroscience
Volume 27, Issue 12, pages 3095–3108, June 2008
How to Cite
Leão, R. N., Leão, R. M., Da Costa, L. F., Rock Levinson, S. and Walmsley, B. (2008), A novel role for MNTB neuron dendrites in regulating action potential amplitude and cell excitability during repetitive firing. European Journal of Neuroscience, 27: 3095–3108. doi: 10.1111/j.1460-9568.2008.06297.x
- Issue published online: 28 JUN 2008
- Article first published online: 28 JUN 2008
- Received 19 March 2008, revised 23 April 2008, accepted 27 April 2008
- active dendrite;
- repetitive firing;
- sodium currents;
- sodium imaging
Principal cells of the medial nucleus of the trapezoid body (MNTB) are simple round neurons that receive a large excitatory synapse (the calyx of Held) and many small inhibitory synapses on the soma. Strangely, these neurons also possess one or two short tufted dendrites, whose function is unknown. Here we assess the role of these MNTB cell dendrites using patch-clamp recordings, imaging and immunohistochemistry techniques. Using outside-out patches and immunohistochemistry, we demonstrate the presence of dendritic Na+ channels. Current-clamp recordings show that tetrodotoxin applied onto dendrites impairs action potential (AP) firing. Using Na+ imaging, we show that the dendrite may serve to maintain AP amplitudes during high-frequency firing, as Na+ clearance in dendritic compartments is faster than axonal compartments. Prolonged high-frequency firing can diminish Na+ gradients in the axon while the dendritic gradient remains closer to resting conditions; therefore, the dendrite can provide additional inward current during prolonged firing. Using electron microscopy, we demonstrate that there are small excitatory synaptic boutons on dendrites. Multi-compartment MNTB cell simulations show that, with an active dendrite, dendritic excitatory postsynaptic currents (EPSCs) elicit delayed APs compared with calyceal EPSCs. Together with high- and low-threshold voltage-gated K+ currents, we suggest that the function of the MNTB dendrite is to improve high-fidelity firing, and our modelling results indicate that an active dendrite could contribute to a ‘dual’ firing mode for MNTB cells (an instantaneous response to calyceal inputs and a delayed response to non-calyceal dendritic excitatory postsynaptic potentials).