Ventilatory behavior and carotid body morphology of Brown Norway and Sprague Dawley rats

Abstract

Differences in acute ventilatory behavior are associated with carotid body (CB) structural and immunohistologic profiles in some, but not all, reports. Brown Norway (BN) rats exhibit lower acute ventilatory responses to hypoxia and hypercapnia compared to Sprague Dawley (SD) rats. We hypothesized that BN rats possess CB with fewer glomus cells. Ventilation was recorded in 6-month-old BN and SD rats exposed to hypoxia-reoxygenation and hypercapnia. Extracted CBs were examined using H&E staining, and immunohistochemistry with antibodies specific for tyrosine hydroxylase (TH), neural nitric oxide synthase (nNOS), and pyruvate dehydrogenase (PD). Sections were analyzed for cell and immunostaining density. SD displayed greater hypoxic and hypercapnic responses, and post-hypoxic short term potentiation, whereas BN exhibited post-hypoxic frequency decline. Contrary to our hypothesis, BN demonstrated a denser arrangement of glomus cells with a larger TH stained area (31.7% BN, 22.6% SD; p<0.0001), and nNOS stained area (37.3% BN, 32.1%; SD; p=0.01). Hence, respiratory phenotype does not correlate intuitively with these anatomic features.

Figure 1

Bar graphs of f (top), VT (middle), and VE (bottom) for each strain. B- Baseline, IH-Isocapnic Hypoxia, PH- Poikilocapnic Hypoxia, R-Reoxygenation, HC-Hypercapnia. Error bars represent ± standard error. *-p < 0.05, **-p<0.01, ***-p<0.001.

Figure 2

Photomicrographs of representative BN carotid body stained with H&E at 10x and 20x magnification. Location of 20x image is outlined in black on the 10x image. Internal Carotid Artery (ICA) and Carotid Sinus Nerve (CSN) are labeled in 10x image. Scale bar (0.5 mm) is present in lower right lower corner of images.

Figure 3

Photomicrographs of representative SD carotid body stained with H&E at 10x and 20x magnification. Location of 20x image is outlined in black on the 10x image. Internal Carotid Artery (ICA) and Carotid Sinus Nerve (CSN) are labeled in 10x image. Scale bar (0.5 mm) is present in lower right lower corner of images.

Figure 4

Photomicrographs of BN (left column) and SD (right column) carotid bodies stained against TH (top row), nNOS (center row), and PD (bottom row) and counterstained with hematoxylin at 40x magnification. Scale bar (0.1 mm) is present in the right lower corner of all images.