Neuroanatomical association of hypothalamic HSD2-containing neurons with ERα, catecholamines, or oxytocin: implications for feeding?

Abstract

This study used immunohistochemical methods to investigate the possibility that hypothalamic neurons that contain 11-β-hydroxysteroid dehydrogenase type 2 (HSD2) are involved in the control of feeding by rats via neuroanatomical associations with the α subtype of estrogen receptor (ERα), catecholamines, and/or oxytocin (OT). An aggregate of HSD2-containing neurons is located laterally in the hypothalamus, and the numbers of these neurons were greatly increased by estradiol treatment in ovariectomized (OVX) rats compared to numbers in male rats and in OVX rats that were not given estradiol. However, HSD2-containing neurons were anatomically segregated from ERα-containing neurons in the Ventromedial Hypothalamus and the Arcuate Nucleus. There was an absence of OT-immunolabeled fibers in the area of HSD2-labeled neurons. Taken together, these findings provide no support for direct associations between hypothalamic HSD2 and ERα or OT neurons in the control of feeding. In contrast, there was catecholamine-fiber labeling in the area of HSD2-labeled neurons, and these fibers occasionally were in close apposition to HSD2-labeled neurons. Therefore, we cannot rule out interactions between HSD2 and catecholamines in the control of feeding; however, given the relative sparseness of the appositions, any such interaction would appear to be modest. Thus, these studies do not conclusively identify a neuroanatomical substrate by which HSD2-containing neurons in the hypothalamus may alter feeding, and leave the functional role of hypothalamic HSD2-containing neurons subject to further investigation.

Keywords: arcuate nucleus; lateral hypothalamic area; paraventricular hypothalamic nucleus; sex differences; ventromedial hypothalamic nucleus.

Figure 1

ERα neurons in the hypothalamus. (A) Atlas drawing (adapted from Paxinos and Watson, 1998) showing approximate location of ERα-containing neurons (green shading) in the Arcuate nucleus (ARC) of the hypothalamus and the Ventromedial hypothalamus (VMH); (B) digital photomicrograph (scale bar = 100 μm) of ERα-immunolabeled neurons in the ARC and VMH. Graphs showing mean numbers of ERα-immunolabeled neurons in (C) the VMH and (D) ARC of male rats (white bars; n = 5–6), and of ovariectomized (OVX) rats given the oil vehicle (OIL; gray bars; n = 5–6) or estradiol benzoate (EB; black bars; n = 7). **significantly greater than Male (p < 0.01). ***significantly greater than Male (p < 0.001).

Figure 2

HSD2 neurons in the hypothalamus. (A) High magnification digital photomicrographs (scale bars = 20 μm) showing the morphology of HSD2-immunolabeled neurons in the hypothalamus; (B) digital photomicrograph (scale bar = 50 μm) of HSD2-immunolabeled neurons in the hypothalamus of an OVX rat given estradiol-benzoate and (C) atlas drawing (adapted from Paxinos and Watson, 1998) showing approximate location of HSD2-containing neurons (red shading) and ERα-containing cells (green shading) in the hypothalamus. (D) Graph showing mean number of HSD2-immunolabeled neurons in the hypothalamus of male rats (white bars; n = 5), and of OVX rats given oil vehicle (OIL; gray bars; n = 3) or estradiol benzoate (EB; black bars; n = 7). ***significantly greater than Male and OIL (both ps < 0.001).

Figure 3

Catecholamines in the hypothalamus. (A) Atlas drawing (adapted from Paxinos and Watson, 1998) showing approximate locations of catecholamine neurons and fibers (green shading) in the hypothalamus. Digital photomicrographs (scale bars = 100 μm) of tyrosine hydroxylase (TH)-immunolabeled neurons in (B) the A13 region of the hypothalamus and (C) the Arcuate Nucleus (ARC), and TH-immunolabeled fibers (D) in the medial forebrain bundle (MFB). Merged digital photomicrographs (scale bars = 50 μm, 20 μm) of immunolabeling for HSD2 (red) and TH (TH; green). (E) TH-immunolabeled fibers within a population of HSD2-immunolabeled neurons. Area in box on left is shown at higher magnification on the right (E’). (F) HSD2- and TH-immunolabeled neurons in close proximity.

Figure 4

Oxytocin (OT) in the hypothalamus. (A) Atlas drawing (adapted from Paxinos and Watson, 1998) showing approximate locations of OT neurons (green shading) in the hypothalamus. Digital photomicrographs (scale bars = 50 μm, 100 um) of OT immunolabeled neurons in (B) the Paraventricular nucleus (PVN), (C) the Nucleus Circularis, (D) the Supraoptic nucleus (SON). (E) Merged digital photomicrograph (scale bar = 50 μm) of immunolabeling for HSD2 (red) and OT (green).