Research Paper / Free Access
Slow periodic activity in the longitudinal hippocampal slice can self‐propagate non‐synaptically by a mechanism consistent with ephaptic coupling
Chia‐Chu Chiang
Rajat S. Shivacharan
Xile Wei
Luis E. Gonzalez‐Reyes
Dominique M. Durand
First published: 08 October 2018
https://doi.org/10.1113/JP276904
Edited by: Ole Paulsen & Matthew Nolan
C.‐C. Chiang, R. S. Shivacharan and X. Wei contributed equally to this work.
Linked articles: : This article is highlighted in a Perspectives article by Dickson. To read this article, visit
https://doi.org/10.1113/JP277233.
Abstract
Key points
- Slow periodic activity can propagate with speeds around 0.1 m s−1 and be modulated by weak electric fields.
- Slow periodic activity in the longitudinal hippocampal slice can propagate without chemical synaptic transmission or gap junctions, but can generate electric fields which in turn activate neighbouring cells.
- Applying local extracellular electric fields with amplitude in the range of endogenous fields is sufficient to modulate or block the propagation of this activity both in the in silico and in the in vitro models.
- Results support the hypothesis that endogenous electric fields, previously thought to be too small to trigger neural activity, play a significant role in the self‐propagation of slow periodic activity in the hippocampus.
- Experiments indicate that a neural network can give rise to sustained self‐propagating waves by ephaptic coupling, suggesting a novel propagation mechanism for neural activity under normal physiological conditions.
Abstract
Slow oscillations are a standard feature observed in the cortex and the hippocampus during slow wave sleep. Slow oscillations are characterized by low‐frequency periodic activity (<1 Hz) and are thought to be related to memory consolidation. These waves are assumed to be a reflection of the underlying neural activity, but it is not known if they can, by themselves, be self‐sustained and propagate. Previous studies have shown that slow periodic activity can be reproduced in the
in vitro preparation to mimic
in vivo slow oscillations. Slow periodic activity can propagate with speeds around 0.1 m s−1 and be modulated by weak electric fields. In the present study, we show that slow periodic activity in the longitudinal hippocampal slice is a self‐regenerating wave which can propagate with and without chemical or electrical synaptic transmission at the same speeds. We also show that applying local extracellular electric fields can modulate or even block the propagation of this wave in both
in silico and
in vitro models. Our results support the notion that ephaptic coupling plays a significant role in the propagation of the slow hippocampal periodic activity. Moreover, these results indicate that a neural network can give rise to sustained self‐propagating waves by ephaptic coupling, suggesting a novel propagation mechanism for neural activity under normal physiological conditions.
Discussion
In summary, the present study shows that the
in vitro slow periodic activity, mediated by the NMDA spikes, can propagate non‐synaptically by a mechanism consistent with ephaptic coupling. This study implies that ephaptic coupling could play an important role in the propagation of neural activity under normal physiological conditions as well as in pathological situations.