Specialized electrophysiological properties of anatomically identified
neurons in the hilar region of the rat fascia dentata.
Joachim Lbke, Michael Frotscher and Nelson Spruston.
Anatomisches Institut, Albert-Ludwigs-Universitt Freiburg, Albertstrae
17, D-79104 Freiburg, Germany (J.L., M.F.), and Max-Planck-Institut fr
medizinische Forschung, Abteilung Zellphysiologie, D-69120 Heidelberg, Germany
and Department of Neurobiology and Physiology, Institute for Neuroscience,
Northwestern University, Evanston, IL 60208-3520, USA (N.S.).
APStracts 4:300N, 1997.
ABSTRACT
Due to their strategic position between the granule cell and pyramidal cell
layers, neurons of the hilar region of the hippocampal formation are likely to
play an important role in the information processing between the entorhinal
cortex and the hippocampus proper. Here we present an electrophysiological
characterization of anatomically identified neurons in the fascia dentata, as
studied using patch-pipette recordings and subsequent biocytin-staining of
neurons in slices. The resting potential, input resistance (RN), membrane time
constant (tm), "sag" in hyperpolarizing responses, maximum firing rate during
a one second current pulse, spike width, and fast and slow
afterhyperpolarizations (ahp) were determined for several different types of
hilar neurons. Basket cells had a dense axonal plexus almost exclusively
within the granule cell layer, and were distinguishable by their low RN, short
tm, lack of sag, and rapid firing rates. Dentate granule cells also lacked sag
and were identifiable by their higher RN, longer tm, and lower firing rates
than basket cells. Mossy cells had extensive axon collaterals within the hilus
and a few long-range collaterals to the inner molecular layer and CA3c, and
were characterized physiologically by small fast and slow ahps. Spiny and
aspiny hilar interneurons projected primarily either to the inner or outer
segment of the molecular layer and had a dense intrahilar axonal plexus,
terminating onto somata within the hilus and CA3c. Physiologically, spiny
hilar interneurons generally had higher RN values than mossy cells and a
smaller slow ahp than aspiny interneurons. The specialized physiological
properties of different classes of hilar neurons are likely to be important
determinants of their functional operation within the hippocampal circuitry.
Received 15 July 1997; accepted in final form 27 Ocotber 1997.
APS Manuscript Number J586-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 14 November 1997