Distribution of DARPP-32 immunoreactive structures in the quail brain: anatomical relationship with dopamine and aromatase

We recently demonstrated that dopamine (DA) as well as different DA recepto r agonists and antagonists are able to decrease within a few minutes the ar omatase activity (AA) measured in vitro in homogenates or in explants of th e quail preoptic area hypothalamus. In addition, DA also appears to regulat e AA, in vivo presumably by modifying enzyme synthesis. The cellular mechan isms and the anatomical substrate that mediate these controls of AA by DA a re poorly understood. Tyrosine hydroxylase-immunoreactive (TH-ir) fibers an d punctate structures have been previously observed in close vicinity of ar omatase-immunoreactive (ARO-ir) cells in the quail medial preoptic nucleus (POM) and bed nucleus striae terminalis (BST) but these fibers could reflec t a noradrenergic innervation. We also do not know whether aromatase cells are dopaminoceptive. The main goal of the present study was therefore to br ing more information on the anatomical relationships between aromatase expr essing neurons and the dopaminergic system in the quail brain. The visualiz ation by immunocytochemistry of DA and of the D1 receptor associated protei n DARPP-32 was used to address these questions. DA-ir fibers were observed in the quail forebrain and overlapped extensively with nuclei that contain high densities of ARO-ir cells such as the POM and BST. This confirms that the previously reported TH-ir innervation of ARO-ir cells is, at least in p art, of dopaminergic nature. DARPP-32-immunoreactive cells were found in pe riventricular position throughout the hypothalamus. DARPP-32-ir cells were also observed in telencephalic and mesencephalic areas (hyperstriatum acces sorium, paleostriatum, nucleus intercollicularis, optic tectum). DARPP-32-i r fibers were widespread in tel-, di-, and mes-encephalic areas. The highes t densities of immunoreactive fibers were detected in the lobus parolfactor ius, paleostriatum augmentatum and substantia nigra/area ventralis of Tsai. In double-labeled sections, appositions between DARPP-32 fibers and ARO-ir cells were present in the dorsolateral POM and BST but DARPP-32 immunoreac tivity was not detected in the ARO-ir perikarya (no colocalization). These data confirm the presence of a dopaminoceptive structures within the main c ell clusters of ARO-ir cells in the quail brain but provide no evidence tha t these ARO-ir cells are themselves dopaminoceptive. Because DARPP-32 is no t present in all types of cells expressing DA receptors, the presence of DA receptors that would not be associated with DARPP-32 in ARO-ir cells still remains to be investigated (C) 2001 Elsevier Science B.V. All rights reser ved.