Substance P and enkephalin containing fibers in the developing nucleus dorsalis of the human spinal cord.

ABSTRACT

A peroxidase-antiperoxidase immunostaining method was employed to determine the initial stage of appearance and localization of substance P (SP) and enkephalin (ENK) in the nucleus dorsalis of the developing human spinal cord. Both SP- and ENK-positive fibers started to appear from the 10th week of gestation in regions surrounding the nucleus dorsalis. SP-positive fibers then reached the nucleus at 13 weeks and from 26 weeks to term, three strands of SP-positive fibers, which were predominantly originated from the superficial layers of the dorsal horn, penetrated into the nucleus dorsalis from its medial, median and lateral aspects. From 26 weeks onwards, ENK-positive fibers, originated from the superficial and the adjacent layers of the spinal cord, formed a thicker medial and a thinner lateral bundle projecting into the nucleus dorsalis. Our results show that both SP- and ENK-positive fibers started to appear at around 10 weeks and a consistent pattern of immunoreactivity was established by around 26-30 weeks of gestation.