Autoradiographic localization of D1-like dopamine receptors in the forebrain of male and female Japanese quail and their relationship with immunoreactive tyrosine hydroxylase.

The distribution of D1-like dopamine receptors was studied in the brain of male and female Japanese quail (Coturnix japonica) by means of quantitative autoradiography with 3H-labelled D1 selective antagonist, SCH 23390, serving as a ligand. A specific, saturable, high affinity binding of this ligand was demonstrated. High densities of binding sites were detected in the lobus parolfactorius, olfactory tubercle, and paleostriatum augmentatum. Medium densities were observed in the entire neostriatum and in the external layers of the optic tectum. Similar levels of binding outlined the paleostriatum primitivum, the nucleus pretecalis and the nucleus intercollicularis. Low but significant levels of receptors were also present in the medial preoptic area at the level of the sexually dimorphic medial preoptic nucleus and throughout the infundibulum, as well as in the ectostriatum, medial and lateral septum, and nucleus accumbens. At the level of the medial septum, just dorsal to the anterior commissure, two circular areas of high receptor density corresponding to the nucleus of the septal commissure were also observed. No sex difference in receptor density could be detected in any of the areas. All areas containing high densities of D1 receptors also contained high densities of tyrosine hydroxylase (TH) fibers. However, certain areas characterized by a high density of TH-immunoreactive fibers did not contain appreciable densities of D1-like dopamine receptors. The distribution of this receptor and its relationship to TH-immunoreactivity is consistent with observations made in other vertebrates, suggesting that the dopaminergic system is evolutionarily highly conserved among amniote vertebrates.