CLASPER CONTROL IN THE ROUND STINGRAY, UROLOPHUS-HALLERI - LOWER SENSORIMOTOR PATHWAYS

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 (<100 muA) of the nerves e vokes clasper movements including: elevation, medial and lateral exten sion, rotation and opening. Stimulation of the spinal cord in the area of the roots of the clasper nerves also evoked the movements (<100 mu A). Retrograde labeling of the clasper nerves using either cobalt-lysi ne or horseradish peroxidase (HRP) confirmed that motor neurons and se nsory components of the nerves are at the levels indicated by stimulat ion. The motor neurons have large multipolar cell bodies (50-70 mum) a nd occupy a discrete segment of the spinal cord.