Localization of enkephalin immunoreactivity in the spinal cord of the long-tailed ray Himantura fai

Enkephalin‐like immunoreactivity (ENK‐LI) was found throughout the spinal cord of the long‐tailed ray Himantura fai. The densest ENK‐LI was in the superficial portion of lamina A of the dorsal horn. Lamina B and the deeper parts of lamina A contained radially oriented, labelled fibres. Laminae C, D, and E contained many longitudinally orientated fascicles which were surrounded by a reticulum of transversely orientated, labelled fibres, some of which projected into the ventral and lateral funiculi. Labelled fibres were found in the dorsal commissure and around the central canal, but the later did not cross the midline. One‐third of all enkephalinergic cells were found throughout laminae A and B, while two‐thirds were located in the medial half of C, D, and E. Occasionally a labelled cell was located in the lateral funiculus. The ventral horn (laminae F and G) contained many enkephalinergic fibres but no labelled nuclei. A few dorsal column axons contained ENK‐LI. In the lateral funiculus there were two groups of labelled axons, a superficial, dorsolateral group, and a deeper group, occupying a crescent‐shaped region. The ventral funiculus also contained many labelled axons. The central projection of the dorsal root passed through the substantia gelatinosa and divided into rostrally and caudally projecting fascicles within lamina C. The root, and these fascicles, both lacked ENK‐LI. In contrast, the fascicles in laminae D and E did contain enkephalinergic fibres. The origin of the various fibre systems and the role of enkephalin in the regulation of sensory processing and motor output are discussed. © 1996 Wiley‐Liss, Inc.