Sonic Motor Pathways in Teleost Fishes: A Comparative HRP Study

Abstract

Among marine teleost fishes, one neuroeffector pathway for sonic communication consists of two components: a peripheral effector organ that consists of a swimbladder with associated 'drum' muscles, and a swimbladder or 'sonic' motor nucleus (SMN) located at the junction of the spinal cord and the medulla oblongata. Here, the organization of the SMN is compared in two unrelated groups of teleosts, the midshipmen, Porichthys notatus and P. myriaster, and the sea robin, Prionotus carolinus. Horseradish peroxidase (HRP), used as a retrograde tracer, revealed the position of the SMN in each species. While the SMN is a fused midline structure in midshipmen, it is bilateral in sea robins. The functional significance of these two contrasting patterns of organization remains to be explored. A third study group included mormyrid freshwater electric fish, which are also sonic. Mormyrids were included in part because an earlier study identified androgen-binding cells at a brain level comparable to that of the SMN of marine fishes. Using HRP methods, a swimbladder motor nucleus was identified at the caudal pole of the vagal motor column. However, the nucleus in mormyrids lies dorsal to the fourth ventricle and central canal, not ventral as it does in midshipmen and sea robins. Its position corresponds to the steroid-concentrating cells identified in a previous study.

Sonic / Vocal Motor Pathways in Catfishes: Comparisons with Other Teleosts

“…This report now demonstrates a similar dendritic branching pattern for biocytin-labeled sonic motoneurons in sculpin; a previous HRP study only labeled motoneuron somata and their proximal dendrites [Bass and Baker, 1991]. In both searobins and sculpin, sonic motor axons exit the medulla via occipital nerves [Bass, 1985;Bass and Baker, 1991;this report]. We propose that all scorpaeniforms possess ventral sonic motoneurons, despite the diversity in peripheral end organs.…”

“…The different sonic mechanisms in sculpins (pectoral girdle vibration) and searobins (intrinsic swimbladder muscles) are not linked to different locations for sonic motor nuclei; sonic motoneuron somata are always situated lateral to the ventral fasciculus, close to the ventral surface of the medulla and spinal cord within the ventral motor column [Bass and Baker, 1991; also see Bass, 1985;Finger and Kalil, 1985]. Intracellular labeling of sonic motoneurons in searobins shows that their dendrites extend far dorsolaterally [Bass and Baker, 1991].…”

“…Experimental neuroanatomical studies have identified sonic motoneurons among Osteoglossomorpha [the weakly electric mormyrid, Brienomyrus -Bass, 1985;Bass et al, 1986], Paracanthopterygii [batrachoidids;review: in Bass and Baker, 1991], Acanthopterygii [triglids and cottids; Bass, 1985;Bass and Baker, 1991], Perciformes [anabantoids; Ladich and Fine, 1992] and Ostariophysi [pimelodid and mochokid catfish; Ladich and Fine, 1994;Ladich and Bass, 1996a]. Premotoneurons have also been identified among batrachoidids and mochokid catfish [Bass and Baker, 1991;Bass et al, 1994;Ladich and Bass, 1996a].…”

Sonic Motor Nucleus and Its Connections with Octaval and Lateral Line Nuclei of the Medulla in a Rockfish, <i>Sebastiscus marmoratus</i>

“…Previous authors have focused on stridulatory and swimbladder sound-producing mechanisms, and have identified the sound-producing muscles and their motor nuclei in the medulla and spinal cord in several species [Fine et al, 1984;Bass, 1985;Finger and Kalil, 1985;Fine, 1989;Fine and Mosca, 1989;Bass and Baker, 1991;Ladich and Fine, 1994;Bass, 1996, 1998]. So far, four groups of motor nuclei related to sound-production in teleosts have been described.…”

“…An additional group is the pectoral motor nucleus which innervates the abductor and adductor muscles of the pectoral fin spine [Ladich and Bass, 1996]. The toadfish and midshipman (Batrachoididae) have paired midline sonic motor nuclei [Fine et al, 1984;Bass, 1985;Fine, 1989;Fine and Mosca, 1989;Bass and Baker, 1991;Ladich and Fine, 1994], and the sculpin and sea robin (Scorpaeniformes) have paired ventrally located sonic motor nuclei [Bass, 1985;Finger and Kalil, 1985;Bass and Baker, 1991;Ladich and Fine, 1994;Ladich and Bass, 1998]. Mochokid catfishes have a midline sonic motor nucleus and paired pectoral motor nuclei [Ladich and Bass, 1996].…”