Dr. Peter Jonas

1. 2012-13 SEMINAR SERIES Dr. Peter Jonas “Hippocampal GABAergic Interneurons: From Somata to Dendrites and Axons” Thursday, March 21, 2013 11:00 am – 12:00 pm MPFI Auditorium Hosted by Jason Christie, PhD Peter Jonas, MD, PhD Professor, Dept. of Neuroscience IST Austria (Institute of Science and Technology) Abstract: Fast-spiking, parvalbumin-expressing basket cells (BCs) play a key role in the function of hippocampal microcircuits. They are involved in fast feedforward and feedback inhibition, generation of high-frequency network oscillations, and coding of information in principal neuron ensembles. However, the functional properties of the subcellular processes of this important class of GABAergic interneuron are largely unknown. To study BC axons and dendrites directly, we made subcellular patch-clamp recordings, combining nanophysiology with confocal imaging. Direct recordings revealed that the action potential was initiated in the axon and propagated back into the dendrites with marked amplitude attenuation. The action potential initiation site was located close to the soma, at approximately 20 µm distance. Analysis of active conductances revealed that BC showed a unique spatial profile of conductance distribution. Na+ channel density was very low in the dendrites, low at the soma, but uniformly high in the axon. Cable modeling suggested that the high axonal Na+ channel density was necessary not only for reliability, but particularly to ensure speed of propagation. Thus, the high degree of BC polarity contributes to the fast signaling properties of hippocampal interneurons. Furthermore, the uniformly high axonal Na+ channel density suggests a novel mechanism for increasing conduction velocity in unmyelinated axons.