Characterization of the Dopaminergic System in the Brain of an African Cichlid Fish, Astatotilapia burtoni

Catecholamines, such as dopamine, are evolutionarily ancient neurotransmitters that play an essential role in mediating behavior. In vertebrates, dopamine is central to the nigrostriatal motor and mesolimbic reward systems. Despite its importance, the distribution of the dopaminergic system has not been well studied in the teleost brain. The African cichlid fish Astatotilapia burtoni has become an important model system in social neuroscience and lends itself to uncovering how social decisions are implemented in the brain. To understand better where dopamine acts to regulate social behavior in this species, we have determined the distribution of putative dopaminergic cells and fibers (by tyrosine hydroxylase immunohistochemistry) and dopamine receptors (by in situ hybridization for the D-1A and D-2 dopamine receptor subtypes) throughout the forebrain and part of the mesencephalon of A. burtoni. Tyrosine hydroxylase immunoreactivity was evident in several regions of the fore-and midbrain, in support of putative homologies to tetrapods. Additionally, the D-1A and D-2 receptors were identified in brain regions known to modulate social behavior in other vertebrates, including the proposed teleost homologues of the mammalian amygdalar complex, hippocampus, striatum, preoptic area, anterior hypothalamus, ventromedial hypothalamus, and ventral tegmental area/substantia nigra pars compacta. Tyrosine hydroxylase-immunoreactive fibers as well as D-1A and D-2 receptor expression overlap almost completely in their distribution. These results significantly extend our understanding of the distribution of the dopaminergic system in the teleost brain and suggest a conserved role of dopamine in modulating behavior across vertebrates. J. Comp. Neurol. 519:75-92, 2011. (C) 2010 Wiley-Liss, Inc.