Functional connection from Mauthner cell to homologous reticulospinal neurons in the goldfish hindbrain

Abstract

Crossed vestibular inhibition first described in mammals, also occurs in many species ranging from reptiles to mammals, but was nct observed in frog and toadfish. During a study of the inhibitory pathways of the Mauthner cell (M-cell) of a teleost, two classes of interneurons were individualized. Their identification was made possible by intracellular injection of horseradish peroxidase (HRP) after they had been physiologicaIly identified by the presence of an intracellularly recorded passive hyperpolarizing potential induced by the firing of their adjacent M-cell. Interneurons of the first group are part of the recurrent collateral network of the M-cell; they have some similarities with the Renshaw cells. The second group is composed of commissural vestibule-vestibular neurons. In a recent study of the neurons inhibiting the M-cell of teleosts, it was demonstrated that each bouton established on the M-cell by the commissural and recurrent collateral interneurons functions as an independent all-or-none unit. This result has prompted the investigation of the ultrastructure of these endings to determine if they were morphologically different from those found at other central chemically transmitting synapses.This chapter deals with deals with the relation that was found between the morphology and the function of a set of neurons that are known to inhibit the M-cell, in this case second order vestibulo-vestibular interneurons.