Spinal Nerve Innervation to the Sonic Muscle and Sonic Motor Nucleus in Red Piranha, Pygocentrus nattereri (Characiformes, Ostariophysi)Onuki A. · Ohmori Y. · Somiya H.
Laboratories of aFish Biology, and bAnimal Morphology and Function, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
The red piranha, Pygocentrus nattereri, produces sounds by rapid contractions of a pair of extrinsic sonic muscles. The detailed innervation pattern of the sonic muscle of the red piranha was investigated. The sonic muscle is innervated by branches (sonic branches) of the third (S3so), fourth (S4so), and fifth (S5so) spinal nerves. The average total number of nerve fibers contained in the right sonic branches (n = 5; standard length, SL, 71–85 mm) was 151.8 (standard deviation, SD, 28.3). The occipital nerve did not innervate the sonic muscle. The sonic motor nucleus (SMN) in the piranha was identified by tracer methods using wheat germ agglutinin-conjugated horseradish peroxidase; labeled sonic motor neurons were only observed on the side ipsilateral to the sonic muscle injected with the tracer. In the transverse sections, the labeled sonic motor neurons were located in the dorsal zone (mainly large and medium neurons) and in the ventral zone (mainly small neurons) of the ventral horn. In the horizontal sections, the labeled neurons formed a rostrocaudally elongated SMN from the level of the caudal part of the second spinal nerve root to the intermediate region between the fifth and sixth spinal nerve roots. The average number of the labeled neurons (n = 5; SL, 64–87 mm) was 152.6 (SD, 7.3). We conclude that the sonic muscles of the piranha are innervated by approximately 300 sonic motor neurons located only in the spinal cord.
Laboratory of Fish Biology, Graduate School of Bioagricultural Sciences
Nagoya University, Furo-cho, Chikusa-ku
Nagoya, Aichi 464-8601 (Japan)
Tel./Fax +81 52 789 4083, E-Mail firstname.lastname@example.org
Received: March 29, 2005
Accepted after revision: June 27, 2005
Returned for revision: May 27, 2005
Published online: October 24, 2005
Number of Print Pages : 12
Number of Figures : 9, Number of Tables : 2, Number of References : 25
Brain, Behavior and Evolution
Vol. 67, No. 2, Year 2006 (Cover Date: January 2006)
Journal Editor: Wilczynski, W. (Atlanta, Ga.)
ISSN: 0006–8977 (print), 1421–9743 (Online)
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