Identification of spinal electromotoneurons in the rayRaja clavata (Rajidae)

Anatomy and motor pathways of the electric organ of skates

“…Koester and Boord's (1989) description of the segmental innervation of the electric organ of skates agrees with that of Robin (1865), but differs from that given by Baron and Sokolova (1987), Baron et al (1992), Beloborodova (1928), and Bodrova (1939). The latter authors showed that the nerves to the electric organ of R. clavata and A. radiata emanate from two trunks, called “nerve collectors,” which are formed from six spinal nerves at the base of the tail (vertebral levels 54–59).…”

“…However, in L. erinacea and R. eglanteria , there is no evidence that the electromotor nerves arise from the longitudinal nerve trunks. Moreover, the longitudinal nerve trunks in these species are formed by mixed spinal nerves from all spinal cord segments of the tail, and not by a limited number of mixed spinal nerves at the base of the tail, as described by Bodrova (1939) and Baron et al (1992) for R. clavata .…”

“…During the last three decades, studies on the development, anatomy, and physiology of the electric organ of teleosts, as well as electric rays, continued to expand our knowledge of both the functional significance of this motor system and its central nervous system control (for a comprehensive review, see Bass, 1986). Although the role of the electric organ of skates is still poorly understood, recent behavioral studies (Bratton and Ayers, 1987; Bratton et al, 1993; Hayes and Bratton, 1996) and neuroanatomical investigations (Koester, 1987; Baron et al, 1992; Koester and Boord, 1996) have provided new insight regarding its behavioral role and the central motor pathways that control it. In addition, Fox et al (1990) presented convincing evidence that the skate electric organ is an ideal model for investigating cholinergic synapses.…”

“…Descriptions of the peripheral course of the electromotor nerves that innervate the electrocytes of the electric organ, and the relationships of these nerves to other spinal nerves are conflicting (Robin, 1865; Beloborodova, 1928; Bodrova, 1939; Baron and Sokolova, 1987; Baron et al, 1992). Koester and Boord (1989) examined the tail regions of several specimens of L. erinacea and R. eglanteria that were stained with Sudan Black B or macerated in nitric acid to reveal the peripheral course of the caudal spinal nerves and the electromotor nerves.…”

“…As the nerve collectors course caudally, they give off segmental branches not only to the electric organ but also the adjacent muscle and skin. Furthermore, Baron et al (1992) stated that the electric organ also receives small branches from nerves that can be traced back to their superficial roots on the spinal cord at all levels of the electric organ. From this they inferred that two populations of electromotoneurons supply the electric organ: those that give rise to the nerve collectors, and those that form the segmental innervation of the electric organ.…”