Aromatase immunoreactivity in the bluehead wrasse brain, Thalassoma bifasciatum: immunolocalization and co-regionalization with arginine vasotocin and tyrosine hydroxylase

Abstract

Sex steroid hormones regulate various neural functions that control vertebrate sociosexual behavior. A number of sex steroids can be synthesized de novo in the brain, including estrogens by the enzyme aromatase. Aromatase, the neuropeptides arginine vasotocin/vasopressin, and the monoamine neurotransmitter dopamine have all been implicated in the control of male sexual and aggressive behavior in a variety of vertebrates. This study examined the expression of brain aromatase in the bluehead wrasse (Thalassoma bifasciatum), a teleost fish that exhibits socially controlled behavioral and gonadal sex change. We used immunocytochemistry (ICC) to characterize distributions of aromatase-immunoreactive (ir) cells, and to examine their relationship with AVT-ir neurons and tyrosine hydroxylase-ir (TH-ir) neurons in key sensory and integrative areas of the brain of this species. Aromatase-ir appeared to be in glial cell populations, and was found in the dorsal and ventral telencephalon, the preoptic area of the hypothalamus, and the lateral recess of the third ventricle, among other brain areas. Aromatase-ir fibers are closely associated with AVT-ir neurons throughout the preoptic area, indicating the potential for functional interactions. Aromatase-ir cell bodies and fibers were also co-regionalized with TH-ir neurons, suggesting possible interaction between the dopaminergic system and neural estrogen production. The presence of aromatase in brain regions important in the regulation of sexual and aggressive behavior suggests that local estrogen synthesis could regulate sex change through effects on signaling systems that subserve reproductive behavior and function.

Figure 1

Diagram of neuroanatomical distribution of aromatase-ir positive structures on representative coronal sections (A–L) of the brain of the bluehead wrasse. Relative numbers, sizes, and locations of aromatase-ir cells and fibers are on the left side of the midline, with structures labeled on the right. See abbreviations in Table 1.

Figure 2

Aromatase immunoreactivity in the telencephalon and diencephalon. All images are fluorescently labeled with anti-aromatase in red. Arrows point to long fibers that suggest labeled cells are radial glia. Panel A, lining the telencephalic ventricle in the medial zone of the dorsal telencephalic area; B, postcommissural nucleus of ventral telencephalon; C, magnocellular preoptic area. Scale bars: 200μm.

Figure 3

Aromatase-immunoreactivity in the optic tectum and granule cell layer of the valvula of the cerebellum. All images are of aromatase immunoreactivity fluorescently labeled with anti-aromatase in red. Panel A, cell bodies in the stratum periventriculare (SPV) with fibers extending dorsally through the optic tectum (TeO); B, cell bodies and fibers in the granule cell layer of the valvula of the cerebellum; C, closeup of lower central portion of B. Scale bars: A and C, 100μm; B, 400 μm.

Figure 4

Arginine vasotocin-immunoreactivity co-regionalized with aromatase-immunoreactivity and with tyrosine hydroxylase-immunoreactivity. Panels A and B show anti-aromatase in red and anti-arginine vasopressin in green. Panel A, magnocellular preoptic area and preoptico-hypophysial tract; B, gigantocellular preoptic area. The arrows in A show ‘beading’ of arginine vasotocin-immunoreactive fibers. Panels C and D show anti-arginine vasopressin in red and anti-tyrosine hydroxylase in green. Panel C, arginine vasotocin-ir neurons in magnocellular preoptic (PM) area and TH-ir neurons ventral to the PM; D, inset of C showing TH-ir fibers co-regionalized with arginine vasotocin-ir neurons. Scale bars: A, 400μm; B, 100μm; C 200μm; D, 50 μm.

Figure 5

Aromatase-immunoreactivity (red) co-regionalized with tyrosine hydroxylase-immunoreactivity (green) in the top panel, and tyrosine hydroxylase-immunoreactivity alone (green) in the bottom panel. Panel A, posterior parvocellular preoptic nucleus; B, aromatase-ir fibers in the torus semicircularis (TS) and anti-tyrosine hydroxylase cell bodies in the stratum periventriculare (SPV) with fibers extending ventrally through the TS; C, anti-tyrosine hydroxylase cell bodies in the SPV with fibers extending dorsally into the TeO; D, absence of primary antibody eliminates staining in section adjacent to C. Scale bars: A, 200 μm; B-D, 100 μm.