Clasper control in the round stingray,Urolapkus halleri lower sensor motor pathways

Synopsis The innervation of the clasper has been studied in the round stingray,Urolophus halleri. Several large myelinated nerves (diameters approx. 0.7 mm; # 60–64 counting from the vagus) innervate the clasper muscles and skin. Low level electrical stimulation (<100A) of the nerves evokes clasper movements including: elevation, medial and lateral extension, rotation and opening. Stimulation of the spinal cord in the area of the roots of the clasper nerves also evoked the movements (<100A). Retrograde labeling of the clasper nerves using either cobalt-lysine or horseradish peroxidase (HRP) confirmed that motor neurons and sensory components of the nerves are at the levels indicated by stimulation. The motor neurons have large multipolar cell bodies (50–70) and occupy a discrete segment of the spinal cord.