[Intracellular potential changes in crucian carps Mauthner cells evoked by vagal sensory inputs]

In the present experiments, microelectrode recording technique was used to explore the electrophysiological properties of Mauthner cells (M-cells) with stimuli applied to the right vagus. Direct stimulation of the right vagus evoked short-latency, long-lasting, graded, and complex postsynaptic potentials (PSPs) on both Mauthner cell bodies in crucian carp, which are stimulus strength- and frequency- dependent. The evoked PSPs reduced the amplitudes of the antidromic action potentials. After intramuscular injection of strychnine, both amplitude and averaged duration of the PSPs increased, on which two or more action potentials were superimposed. The results suggest that the afferent pathways from vagus to M-cells are mediated by several neuron chains with different numbers of relayed synapses, and they may be excitatory and/or inhibitory in nature. Therefore vagus input would modulate the excitability of the M-cells.