Development of central catecholaminergic neuronal systems in the lizard Anolis sagrei

Catecholamines, comprising the neurotransmitters dopamine (DA), noradrenaline (NA) and adrenaline (A) are synthesized by specific enzymes (tyrosine hydroxylase (TH), dopamine ß-hydroxylase (DBH), phenylethanolamine-N-methyltransferase (PNMT)) in the central nervous system. The development and distribution of different catecholaminergic systems have been described in both the brain and retina of the lizard Anolis sagrei. The first dopaminergic neurons appear at early developmental stage 32 in the diencephalon, in the future lateral hypothalamic area (A11), followed by dopaminergic neurons in other areas of the diencephalon and in the mesencephalon. Then, dopaminergic neurons appear in the telencephalon, rhombencephalon and in the spinal cord. The last area appear just before hatching in the olfactory bulbs (dopaminergic) and in the area lining the cerebral aqueduct (L-DOPAergic). All areas with some exceptions are first immunoreactive (ir) to TH and at later stages also DA immunoreactive. The presumed noradrenergic area A6 and adrenergic area A1/C1 are both first THir and at later stages also DAir and DBHir (A6) or PNMTir (A1/C1). Dopaminergic fibers are observed in the area with dopaminergic neurons and from stage 36/37 also present in many other brain areas. PNMTir fibers appear only in the A1/C1 area during the embryonic stages, whereas DBHir fibers could not be observed during any of the embryonic stages. In juveniles and adults, no additional groups of dopaminergic neurons or fibers appear, whereas both DBHir and PNMTir are found scattered throughout the brain. The distribution of the major catecholamines have been identified in the brain of all nonmammals studied so far, including Anolis sagrei and a ?basic? temporal sequence of appearance during the embryonic development can be observed in the brain of nonmammals.

In the retina of Anolis sagrei, three types of dopaminergic amacrine cells are observed. Type 1 and 2 cells appear at late embryonic stage 34. At stage 36, a third type of dopaminergic cells appear in the retina, probably representing interplexiform cells. Both amacrine cells and interplexiform cells have been described in the retina of adult lizards, but the development of these cells have not previously been described.