Localization of pectoral fin motoneurons (sonic and hovering) in the croaking gourami Trichopsis vittatus.
The pectoral fin of the croaking gourami, Trichopsis vittatus, has become modified as a sound-producing organ and retains its original function in locomotion and hovering. We used retrograde transport of horseradish peroxidase to localize sonic motoneurons in Trichopsis. Betta splendens, a related nonsonic gourami with unspecialized pectoral fins, served as a control. A single injection into Trichopsis epaxial muscle labeled a dorsal motor column of large cells (mean of 16.3 microns) ventrolateral to the central canal. Pectoral motoneurons formed a ventrolateral spinal motor column of smaller neurons (means from 7.7 to 11.9 microns, depending upon fish size), of about 2 mm in rostrocaudal extent, starting in the caudal medulla. Our data suggest that motoneurons for different pectoral muscles are segregated into rostrocaudal pools within the column. Distribution, morphology and size of motoneurons were similar between Trichopsis and Betta, and there was no evidence of a distinct population of neurons which might be specialized exclusively for sound production. These data suggest that a fish can evolve a specialized end organ without major reorganization of the central nervous system.
Ladich
F
F
Institute of Zoology, University of Vienna, Austria.
Fine
M L
ML
D000819:Animal Communication; D000818:Animals; D005075:Biological Evolution; D005260:Female; D005399:Fishes / Q000033:anatomy & histology*; D008124:Locomotion / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000033:anatomy & histology; D009046:Motor Neurons / Q000648:ultrastructure*; D010369:Pectoralis Muscles / Q000294:innervation*; D013045:Species Specificity; D013116:Spinal Cord / Q000033:anatomy & histology; D013550:Swimming; D014828:Vocalization, Animal / Q000502:physiology*