Early ontogeny of catecholaminergic structures in the sheep brain. Immunohistochemical study.

The localization of tyrosine hydroxylase was studied in the brain of sheep foetus during early ontogeny using immunohistochemistry. The first immunoreactive neurons appeared very early since they were found on day 30 of pregnancy in the medioventral part of the mesencephalic flexure. The distribution of the different catecholaminergic groups of neurons was similar to the adult's after 75 days of pregnancy. The latest groups to appear was the A12 group. Comparison of the development of the sheep foetus with rodents or primates, more commonly studied, is difficult because of its different development. It seems, however, that catecholaminergic structures appear earlier in sheep and rodents than in human. Considering the early appearance of these transmitters in the central nervous system, their role on brain development has to be studied in the future.