Anatomical relationships between aromatase and tyrosine hydroxylase in the quail brain: Double-label immunocytochemical studies

Abstract

The activation of male sexual behavior in Japanese quail (Coturnix japonica) requires the transformation of testosterone to 17beta-estradiol by the enzyme aromatase (estrogen synthetase). There are prominent sex differences in aromatase activity that may be regulated in part by sex differences in catecholaminergic activity. In this study, we investigate, with double-label immunocytochemistry methods, the anatomical relationship between the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH) and aromatase (ARO) in the quail brain. The immunoreactivity observed for each antigen generally matched the previously described distribution. One exception is the observation that cells weakly labeled for aromatase were found widely distributed throughout the telencephalon. The presence of telencephalic aromatase was confirmed independently by radioenzymatic assays. There was an extensive overlap between the distribution of the two antigens in many brain areas. In all densely labeled aromatase-immunoreactive (ARO-ir) cell groups, including the preoptic medial nucleus, nucleus of the stria terminalis, mediobasal hypothalamus, and paleostriatum ventrale, ARO-ir cells were found in close association with TH-ir fibers. These TH-ir fibers often converged on an ARO-ir cell, and one or more TH-ir punctate structure(s) were found in close contact with nearly every densely labeled ARO-ir cell. In the telencephalon (mostly the neostriatum), all TH-ir fibers were found to be part of fiber groups that surrounded weakly immunoreactive aromatase cells. The few cells exhibiting an intracellular colocalization were detected in the anteroventral periventricular nucleus. These results are consistent with the hypothesis that catecholaminergic inputs regulate brain aromatase.

Local modulation of steroid action: rapid control of enzymatic activity

“…It should be noted that dopaminergic signaling could also be involved in the rapid modulation of AA. Double immunocytochemistry highlighted a close interaction between dopaminergic fibers (tyrosine hydroxylase-positive structures) and aromatase-positive cells in the hypothalamus of Japanese quail (Balthazart et al, 1998 ). More importantly, several dopaminergic drugs rapidly inhibited AA in homogenates and in vitro explants obtained from the preoptic area hypothalamus of male Japanese quail (Baillien and Balthazart, 1997 ; Balthazart et al, 2002 ).…”

The avian subpallium: New insights into structural and functional subdivisions occupying the lateral subpallial wall and their embryological origins

“…As true of the mammalian medial amygdala, the avian subpallial medial amygdala is reciprocally connected with the hippocampal formation (Atoji et al, 2002; Atoji and Wild, 2004). Importantly, the avian subpallial medial amygdala is enriched in sex-steroid concentrating neurons possessing estrogen and androgen receptors and the enzyme aromatase (Martinez-Vargas et al 1976; Balthazart et al, 1998; Foidart et al, 1999). Their abundance is more striking in males (Watson and Adkins-Regan, 1989), and reflects the role of the steroid receptors and the neurons that contain them in male sexual behavior (Panzica et al, 1996; Thompson et al, 1998; Absil et al, 2002).…”

Review: neuroestrogen regulation of socio-sexual behavior of males

“…Immunohistochemical studies have demonstrated that there are dense networks of tyrosine hydroxylase (TH)-ir fibers in brain areas that contain aromatase-ir neurons, such as the sexually dimorphic MPOA or the bed nucleus striae terminalis (BNST) in quail. Double-labeling has confirmed that aromatase-ir cells are in close association with TH-ir fibers in quail (Balthazart et al, 1998 ). Therefore, the possible existence of a direct modulation of aromatase activity by dopamine and/or norepinephrine was systematically investigated by in vitro incubations of quail hypothalamic homogenates (Balthazart et al, 2002 ).…”