Do amphibians have a true locus coeruleus?

Much controversy surrounds the identity of a locus coeruleus in amphibians because although previous studies on the isthmic region of the brain of anurans and urodeles revealed the presence of noradrenergic cell bodies they failed to demonstrate their projection to the telencephalon or the spinal cord. In the present study applications of Texas Red-conjugated dextran amines to the basal telencephalon or to the spinal cord in combination with tyrosine hydroxylase immunohistochemistry revealed that the noradrenergic cell bodies in the isthmic region of anuran (Rana perezi) and urodele (Pleurodeles waltl) amphibians project to the telencephalon as well as to the spinal cord. On the basis of location, neurotransmitter content and efferent projections, the isthmic noradrenergic cell group of amphibians is, therefore, considered homologous to the locus coeruleus of amniotes.