The Primary Projections of the Lateral-Line Nerves of the Florida Gar, <i>Lepisosteus platyrhincu</i><i>s</i>; pp. 38–50

Abstract

Gars, like most other ray-finned fishes, possess lines of superficial and canal neuromasts that form highly ordered spatial arrays on the head and trunk. These neuromasts are innervated by three pairs of cranial nerves: anterior, middle and posterior lateral-line nerves. Application of horseradish peroxidase to the roots of these nerves indicates that the afferent fibers of each nerve terminate throughout the rostrocaudal extent of the ipsilateral octavolateralis column, composed of medial and caudal octavolateralis nuclei, as well as rostrally in the eminentia granularis of the cerebellum. The afferents of each nerve terminate within different regions of these nuclei, thus preserving a rostrocaudal somatotopy of the peripheral receptors. The individual rami of these nerves innervate peripheral receptors in a dorsoventral sequence; however, application of horseradish peroxidase to these rami indicates an almost total overlap of the terminal fields of adjacent rami and, thus, little or no preservation of dorsoventral somatotopy of the peripheral receptors. Similarly, the terminal fields of fibers that innervate canal and superficial neuromasts overlap extensively, and there is no evidence for separate maps of canal and superficial neuromasts. Furthermore, the position of the terminal fields of superficial neuromasts is not consistent with a hypothesis that these receptors may have evolved into electroreceptors in some teleosts. However, these experiments do indicate that superficial neuromasts, like canal neuromasts, are innervated by efferent fibers of rostral and caudal efferent nuclei, but there is no evidence of a diencephalic efferent nucleus as occurs in teleosts.