Simulation of Spontaneous Activity Generation in an Excitatory Network Involved in the Control of the Respiratory Rhythm

Abstract

Some neural circuits of the brainstem display a spontaneous activity even when they are isolated from their afferences (Bennett and St. John 1985, Ezure 1990). Such a spontaneous activity, related to the control of the respiratory rhythm, was observed by Fortin & Champagnat (1993) in slices of rat brainstem at the level of the Nucleus Tractus Solitarius (NTS). This spontaneous activity had a low frequency (10 to 15 synaptic events per second) and was generated by a network consisting of neurons connected only by excitatory connections. No pacemaker units were observed in this network. Fortin and Champagnat noted that Excitatory Post-Synaptic Potentials (EPSPs) were still occurring in the presence of tetrodotoxin (TTX), though action potentials were no longer generated in the cells, but with a lower frequency (1 to 1.5 EPSP per second). Fortin and Champagnat hypothesized that the spontaneous activity displayed by the brainstem slices was the result of the amplification by the excitatory connections of the low frequency background synaptic activity observed in the presence of TTX.