Location and size of carotid body-like organs (paraganglia) revealed in rats by the permeability of blood vessels to Evans blue dye

Abstract

We determined the number, distribution size, and morphology of paraganglia near the glossopharyngeal, vagus, and sympathetic nerves of rats. The location of paraganglia was revealed by a method that takes advantage of the comparatively high permeability of their blood vessels to Evans blue dye. Rats were fixed by vascular perfusion of glutaraldehyde 2 min after receiving an intravenous injection of Evans blue dye. Paraganglia appeared as circumscribed, intensely blue structures that were readily distinguished from unstained nerves associated with them. Similarly, some groups of small intensely fluorescent (SIF) cells in autonomic and sensory ganglia were surrounded by Evans blue at a time that other portions of the ganglia contained little detectable dye. An average of 92.5 (range 41-134) paraganglia and 41 (range 17-68) blue spots in ganglia were found in the neck, thorax and abdomen of each of 10 rats. Carotid bodies had a mean length of 601 +/- 123 micrometer, width of 275 +/- 65 micrometer, and volume of 25.1 +/- 11.2 micrometer 3 X 10(6). Other paraganglia had an average length of 168 +/- 108 micrometer, width of 77 +/- 41 micrometer, and volume of 0.87 +/- 1.55 micrometer 3 X 10(6). The total volume of paraganglion tissue averaged 128 micrometer 3 X 10(6) (range 62-215 micrometer 3 X 10(6)), 59% of which was due to paraganglia other than the carotid bodies. By using fluorescence microscopy, we verified that small catecholamine-containing cells, visible because of their yellow-green fluorescence induced by formaldehyde gas, were located in regions along nerves and within ganglia that contained extravascular dye, visible because of its red fluorescence. Electron-microscopic studies confirmed that blue-stained organs (presumptive paraganglia) associated with the superior laryngeal nerve and other branches of the vagus nerve contained cells morphologically similar to glomus cells of the carotid body. Celiac ganglia contained, in addition, some cells similar to chromaffin cells of the adrenal medulla. Paraganglia (but not in SIF cells in ganglia) were encapsulated by layers of perineurium, which may constitute a barrier to diffusion. Tortuous thin-walled blood vessels, some with a fenestrated endothelium, were present in all paraganglia examined and were near most groups of SIF cells in ganglia. Neural connections of the small catecholamine-containing cells varied. Most nerve terminals on cells in paraganglia resembled sensory nerve endings on glomus cells of the carotid body, although some were morphologically similar to preganglionic nerves on chromaffin cells of the adrenal medulla.

Expression of Multiple P2X Receptors by Glossopharyngeal Neurons Projecting to Rat Carotid Body O2-Chemoreceptors: Role in Nitric Oxide-Mediated Efferent Inhibition

“…Indeed, staining of whole mount of the GPN during perfusion with the largemolecular-weight Evans blue dye (supplemental Fig. 3, available at www.jneurosci.org as supplemental material) confirmed that GPN neurons were associated with an intricate network of fenestrated capillaries (McDonald and Blewett, 1981), thereby providing easy access to blood-borne substances such as ATP, present in millimolar quantities in erythrocytes (Miseta et al, 1993). (4) Hypoxia may also activate GPN neurons by inhibiting background K ϩ channels (Campanucci et al, 2003), leading to increased firing, voltage-gated Ca 2ϩ entry, nNOS activation, and NO release.…”

“…jneurosci.org as supplemental material). As described previously (McDonald and Blewett, 1981), these groups of neurons, or paraganglia, are closely related to tortuous blood vessels that seem to spiral around the area surrounding the GPN neurons (supplemental Fig. 3C, available at www.jneurosci.org as supplemental material).…”

“…Rat pups (10 -14 d old) were anesthetized by intraperitoneal administration of Somnotol (65 mg/kg), before perfusion via the aorta with PBS, followed by PBS containing 4% paraformaldehyde. Fixed animals were then perfused with filtered (0.2 m Millipore filter) Evans blue dye (100 mg of dye per milliliter of 0.9% NaCl, adjusted pH to 7.4), so as to stain paraganglia attributable to the high permeability of their blood vessels to large dye molecules (McDonald and Blewett, 1981). The carotid bifurcation was then excised, and the tissue was mounted in fresh PBS.…”

“…To confirm that the microenvironment around GPN neurons in situ has ready access even to large molecules in the circulation, we fixed and perfused rat pups with a physiological salt solution containing Evans blue dye (McDonald and Blewett, 1981). This procedure revealed the anatomical structure of blood vessels surrounding the area in which both populations of GPN neurons were concentrated (n ϭ 4) (supplemental Fig.…”

Neural Control of Respiration by the Retrotrapezoid Nucleus.

“…The majority of the cells are Type I cells (12,000 cells in the rat and upwards of 60,000 in the cat) (Verna, 1979;McDonald & Blewett, 1981). Type I cells are the major chemosensitive cell type in this organ, becoming excited when exposed to hypoxic environments.…”