Thursday, April 13, 2017

Journal club: The role of electrical coupling in generating and modulating oscillations in a neuronal network

by Christina Mouser, Amitabha Bose and Farzan Nadim
Mathematical Biosciences 278 (2016) 11–21

Melissa Coleman showed in her 1995 Nature paper that there is an electrical connection between MCN1 and LG. I was a grad student back then. I really liked that paper, but I have forgotten about this electrical connection.  This electrical synapse is voltage-sensitive. It gets stronger when LG was depolarized. It looks opposite to regular EPSPs which usually become smaller when depolarized. This voltage-sensitive electrical synapse seems to act as a positive feedback to LG activity.

   In this paper, Mouser et al. showed that this electrical coupling is very important for LG bursting by using a mathematical model. LG forms a Half-Center Oscillator with Int1 by forming mutually inhibitory synapses. This HCO configuration itself can generate a rhythm, which is influenced by periodic inhibition from pyrolic pacemaker (AB). However, the major finding in this paper is that the LG oscillation can also be generated without the reciprocal inhibition, but with the voltage-dependent electrical coupling between MCN1 and LG. This also indicates that the half-center configuration is not the main element that produces the rhythm; rather it is to form a pattern of activity in left-right alternation. For rhythmogenesis, some sorts of positive feedback system seems more important than mutual inhibition.

   I don't know how electrical coupling gets voltage-sensitive. I assume it not caused by changes in the coupling coefficient, but rather by overall depolarization at dendrites, which may trigger Ca influx and hence enhancing spike width.

No comments: