Distinct but overlapping populations of commissural and GABAergic neurons in the dorsal nucleus of the little skate, Raja erinacea.

ABSTRACT

In the little skate, Raja erinacea, the electrosensory primary afferents are responsive to electrical potentials created during the animal's own ventilation, while second-order electrosensory cells in the dorsal nucleus of the medulla suppress the responses to ventilatory potentials but retain their extreme sensitivity to important environmental electric signals. Previous electrophysiological studies indicate a role for a commissural pathway between the bilateral dorsal nuclei in ventilatory noise suppression. In the present study, retrograde tracers were used to label dorsal nucleus commissural cells. Large round or triangular and thin elongate commissural cells occur in the central zone of the dorsal nucleus where the primary afferent fibers terminate. Elongate commissural cells also occur in the peripheral zone which is the cell body area of the major efferents of the dorsal nucleus. Immunohistochemical studies indicate that stellate cells of the molecular layer and round or triangular cells of the central zone comprise the GABA-immunoreactive cell groups of the dorsal nucleus. A subpopulation of the round commissural cells in the central zone are GABA-immunoreactive and may be candidates for mediators of common-mode noise rejection in the dorsal nucleus of skates. The non-GABAergic commissural cells may mediate crossed inhibition through an inhibitory transmitter other than GABA or may supply crossed excitation to the dorsal nucleus.