Are putative dopamine-accumulating cell bodies in the hypothalamic periventricular organ a primitive brain character of non-mammalian vertebrates?

The brains of the chicken, Gallus domesticus, and two amphibians, the anuran Rana ridibunda and the urodele Pleurodeles waltlii, were investigated by means of immunohistochemical techniques with antibodies against dopamine (DA) and tyrosine hydroxylase (TH). As could be expected on the basis of the catecholamine biosynthetic pathway, cell bodies that are immunopositive for the DA antiserum also stain with the TH antibodies. However, a remarkable discrepancy is observed in the hypothalamic periventricular organ where liquor contacting cells exhibit DA- but no TH-immunoreactivity. Since similar results have been obtained in reptiles but not in mammals, it may be concluded that these putative DA-accumulating cells are a primitive brain character of non-mammalian vertebrates.