Histoenzymology of the developing rat spinal cord.

Using histochemical methods the activity of acetycholinesterase, acid phosphatase and various dehydrogenases was investigated in the developing rat spinal cord. At the ninth embryonic day (E9) only the activity of the lactate dehydrogenase slow-moving isoenzymes was prominent in spinal neurons. Between E13 and E15 an increase was observed in the activity of most of the dehydrogenases and of acid phosphatase in motoneurons and posterior root ganglion cells. Between E15 and E17 acetylcholinesterase activity increased markedly. On E17 and E20, this enzyme was also detectable in anterior and posterior roots and in neurons of the intermediate grey matter. On E20, although all grey matter neurons were cytologically fully differentiated, their enzymatic content was found to be still incomplete. The prominent acid phosphatase reaction within laminae I and II, which is characteristic of the adult rat, was absent in the fetal spinal cord. These findings indicate that the spinal cord metabolism is predominantly anaerobic during the first two-thirds of gestation. The histoenzymological maturation of grey-matter neurons is delayed in comparison to their cytological differentiation. Furthermore, the ontogenesis of motoneuronal acetylcholinesterase activity correlates well with the development of motor activities in the rat fetus.