Localization of acetylcholinesterase positive neurons and substance P and enkephalin positive fibers by histochemistry and immunohistochemistry in the sympathetic intermediate zone of the developing human spinal cord.

Localization of acetylcholinesterase positive neurons and substance P and enkephalin fibers were studied by histochemistry and immunohistochemistry in the intermediate sympathetic zone of the spinal cords of 39 human embryos/fetuses from gestation ages five to 40 weeks. Acetylcholinesterase positive neurons were observed in the nucleus intermediolateralis pars principalis as early as the fifth week of gestation. By the ninth to 13th weeks of gestation, positive neurons were also seen in the nuclei intermedialis pars funicularis, intercalatus spinalis and intercalatus pars paraependymalis. Increase in amount of these positive acetylcholinesterase neurons was demonstrated till term. Substance P and enkephalin fibers were initially observed by the eighth gestation week in the intermediolaterlis pars principalis nucleus and positive fibers were then detected in the nucleus intermedialis pars funicularis as well as the nucleus intercalatus spinalis by the 14th week of gestation. By the 26th week of gestation, all the major nuclei intermediolateralis par principalis, intermedialis pars funicularis, intercalatus spinalis and intercalatus pars paraependymalis has substance P and enkephalin fibers. Initial demonstration of acetylcholinesterase positive neurons appeared to be at an earlier stage than that of our substance P and enkephalin positive fibers.