Medullary electrosensory processing in the little skate

Abstract

1. Ampullary electroreceptors in elasmobranchs are innervated by fibers of the ALLN, which projects to the dorsal octavolateralis nucleus (DON). The purpose of this study is to examine the response characteristics of ALLN fibers and DON neurons to weak D.C. and sinusoidal electric field stimuli presented as local dipole fields. 2. ALLN fibers respond to presentation of D.C. fields with a phasic burst, followed by a more slowly adapting period of firing. Ascending efferent neurons (AENs) in the DON respond to stimuli with a similar initial burst, which adapts more quickly. 3. Type 1, 2, and 3 neurons are possible local interneurons or commissural DON neurons. Type 1 neurons demonstrate response properties similar to those of AENs. Type 2 cells demonstrated slowly adapting responses to excitatory stimuli, the duration of the response increased with the amplitude of the stimulus. Type 3 neurons demonstrated an increased rate of firing, but the response lacked any specific temporal characteristics. 4. ALLN fibers typically have receptive fields consisting of a single ampulla. The receptive field sizes of DON neurons exhibited varying degrees of convergence for different cell types. 5. Responses of ALLN fibers and DON neurons to weak sinusoidal stimuli demonstrated very similar frequency response characteristics for all cell types. The peak sensitivity of electrosensory neurons was between 5-10 Hz.

Morphological variation in the electric organ of the little skate (Leucoraja erinacea) and its possible role in communication during courtship

“…Similarly, Bratton and Ayers (1987) recorded an increase in the number of times individuals discharge their organs when in contact with conspecifics. In addition, the peak discharge frequency detectable by skates adjusts at the onset of maturity to match the peak frequency of EODs generated by conspecifics (New 1990;Sisneros et al 1998;Sisneros and Tricas 2002) and reproductively active skates discharge their organs at similar peak frequencies to those detectable by other skates (Sisneros and Tricas 2002). Although this evidence is suggestive of a communicative role for skate electric organs, studies identifying sexual and ontogenetic dimorphisms in the skate EOD are needed to identify its role, if any, in gender-specific or readiness-tomate signaling during courtship.…”

Neural connections of the torus semicircularis in the adult Zebrafish

“…In most vertebrates, including teleosts, some inner ear maculae and accessory structures became specialized in reception of sounds, and land vertebrates (frogs, sauropsids, and mammals) having acquired the most specialized auditory centers and capabilities. Some fish groups (lampreys, elasmobranchs, cladistia, chondrosteans, lungfishes) present an additional sensory system based on electroreceptors (ampullary organs) located in the head region and connecting the brain through a dorsal branch of the anterior lateral line nerve with the most dorsal region of the medulla oblongata, the dorsal octavolateralis nucleus (Bullock et al., 1983; New & Bodznick, 1985; Ronan & Northcutt, 1987; New, 1990). These electrosensory ampullary organs and associated dorsal nucleus have been lost in modern ray‐finned fishes (holosteans and teleosts), although some teleosts (gymnotids, mormyrid, and some catfishes) have evolved a new and different electrosensory lateral line system that has connections with a highly specialized region of the medulla, the electrosensory lateral line lobe (Bullock et al., 1983; Boord & McCormick, 1984).…”