LOCALIZATION OF ENKEPHALIN IMMUNOREACTIVITY IN THE SPINAL-CORD OF THELONG-TAILED RAY HIMANTURA FAI

Enkephalin-like immunoreactivity (ENK-LI) was found throughout the spi nal 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 an d the deeper parts of lamina A contained radially oriented, labelled f ibres. Laminae C, D, and E contained many longitudinally orientated fa scicles which were surrounded by a reticulum of transversely orientate d, labelled fibres, some of which projected into the ventral and later al funiculi. Labelled fibres were found in the dorsal commissure and a round 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. O ccasionally a labelled cell was located in the lateral funiculus. The ventral horn (laminae F and G) contained many enkephalinergic fibres b ut no labelled nuclei. A few dorsal column axons contained ENK-LI. In the lateral funiculus there were two groups of labelled axons, a super ficial, dorsolateral group, and a deeper group, occupying a crescent-s haped region. The ventral funiculus also contained many labelled axons . The central projection of the dorsal root passed through the substan tia gelatinosa and divided into rostrally and caudally projecting fasc icles within lamina C. The root, and these fascicles, both lacked ENK- LI. In contrast, the fascicles in laminae D and E did contain enkephal inergic fibres. The origin of the various fibre systems and the role o f enkephalin in the regulation of sensory processing and motor output are discussed. (C) 1996 Wiley-Liss, Inc.