IMMUNOLOCALIZATION OF AROMATIC L-AMINO-ACID DECARBOXYLASE, TYROSINE-HYDROXYLASE, DOPAMINE, AND SEROTONIN IN THE FOREBRAIN OF AMBYSTOMA-MEXICANUM

To improve basic knowledge about the neurochemical organization of the urodele brain, and to study discrepancies in the localization of mono aminergic markers, we immunohistochemically charted the distribution o f four such markers (tyrosine hydroxylase, aromatic L-amino acid decar boxylase, dopamine, and serotonin) in the axolotl (Ambystoma mexicanum ) forebrain. Catecholaminergic and serotoninergic systems were found i n similar locations to those seen in other Urodela. As seen in other v ertebrates, the localization of the different monoaminergic markers re veals some inconsistencies. Cells that are exclusively tyrosine hydrox ylase-immunoreactive are observed in the olfactory bulb, anterior olfa ctory nucleus/nucleus accumbens region, the epichiasmatic portion of t he preoptic nucleus, and in the pars intercalaris thalami, whereas cel ls that are only labelled by aromatic L-amino acid decarboxylase are s een in the anterior olfactory nucleus/nucleus accumbens region, the be d nuclei of the anterior commissure, the posterior portion of the preo ptic nucleus, the ventral hypothalamus, and the pars intercalaris thal ami. The presence of cells solely serotonin (5-HT)-immunoreactive is s uggested for the nucleus infundibularis dorsalis. Conversely, there we re no areas that appeared to be exclusively immunoreactive for dopamin e. Double-labelling for aromatic L-amino acid decarboxylase/tyrosine h ydroxylase and aromatic L-amino acid decarboxylase/serotonin, together with cell counting, confirmed the existence of neurons that express o nly one monoaminergic marker in amphibian, supporting the hypothesis t hat these cells are universally present in the central nervous system of vertebrates. (C) 1998 Wiley-Liss, Inc.