Uptake Of Horseradish Peroxidase Research Articles

The origins of the afferent fibers to the lingual muscles of the dog, a retrograde labelling study with horseradish peroxidase.

The origin of the afferent fibers to the lingual muscles of the dog was investigated by means of retrograde transport of horseradish peroxidase (HRP) from injection sites in the tongue and the extrinsic lingual muscles. Intralingual injections were not satisfactory because the enzyme diffused beyond the intrinsic lingual muscles to include virtually all tissues within the tongue. Thus, the resultant retrograde labeling of cell bodies of the trigeminal, geniculate, glossopharyngeal, vagal, and first cervical (C1) spinal ganglia represented a composite of lingual sensory innervation. In order to confine HRP uptake to intramuscular nerve endings, injections were limited to surgically isolated extrinsic lingual muscles, i.e., the genioglossus, hyoglossus, and styloglossus. After these intramuscular injections, labeled neurons appeared ipsilaterally in the C1 spinal ganglion, the proximal vagal (jugular) ganglion, and trigeminal ganglion. Earlier suggestions that the lingual proprioceptive neurons of the dog reside in the distal vagal (nodose) ganglion and hypoglossal ganglia were not confirmed. The mesencephalic nucleus of the trigeminal nerve failed to label after enzyme injections into the tongue or the extrinsic lingual muscles. The retrograde labeling of cell bodies in the C1 spinal ganglion was abolished when HRP injections into the extrinsic lingual muscles were preceded by surgical interruption of the ansa cervicalis or distal section of the hypoglossal nerve. Retrograde labeling of neurons in the proximal vagal ganglion persisted after hypoglossal nerve transections.

Uptake of free and liposome-entrapped horseradish peroxidase by rat intestinal sacs in vitro

FEBS LettersVolume 123, Issue 1 p. 41-44 Full-length articleFree Access Uptake of free and liposome-entrapped horseradish peroxidase by rat intestinal sacs in vitro Richard N. Rowland, Richard N. Rowland Biochemistry Research Laboratory, Department of Biological Sciences, University of Keele, Keele, Staffordshire ST5 5BG, EnglandSearch for more papers by this authorJohn F. Woodley, John F. Woodley Biochemistry Research Laboratory, Department of Biological Sciences, University of Keele, Keele, Staffordshire ST5 5BG, EnglandSearch for more papers by this author Richard N. Rowland, Richard N. Rowland Biochemistry Research Laboratory, Department of Biological Sciences, University of Keele, Keele, Staffordshire ST5 5BG, EnglandSearch for more papers by this authorJohn F. Woodley, John F. Woodley Biochemistry Research Laboratory, Department of Biological Sciences, University of Keele, Keele, Staffordshire ST5 5BG, EnglandSearch for more papers by this author First published: January 12, 1981 https://doi.org/10.1016/0014-5793(81)80015-4Citations: 15AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume123, Issue1January 12, 1981Pages 41-44 ReferencesRelatedInformation

Observations on the ultrastructure and function of the so-called "microfold" or "membraneous" cells (M cells) by means of peroxidase as a tracer.

79 NMRI mice and Wistar rats were used for ultrastructural investigations of the sequential uptake of horseradish peroxidase (HRP) by M cells. In addition the ultrastructure of the so-called tuft-cells was reported. HRP, a foreign protein antigen, was applied either by injection (Owen 1977), or by stomach tube. After variable exposure times (5 min to 3 h) segments of the distal small intestine, containing Peyer's patches, mesenteric lymph nodes and liver tissue were removed. After fixation, they were reacted with H2O2-3,3′-diaminobenzidine tetrachloride and were examined by light and electron microscopy for HRP reaction products. The uptake of HRP mainly occurs through the M cells in the dome epithelium of Peyer's patches with a continual transport of the antigenic material into lymphoid cells, macrophages, and dendritic reticulum cells. In the 3 h specimens a few single HRP-positive lymphoid cells can be observed within the efferent lymphatics of Peyer's patches. In addition, a continual uptake of HRP by necrobiotic enterocytes was observed. It has also been shown that after 3 h HRP is located inside the Kupffer cells of the liver. These findings also support the presumption that antigenic material can be transmitted via the portal circulation. However, definite, quantitatively and permanently recorded uptake of HRP by brush border cells was not be observed. To exclude a toxic effect of the applied HRP on the enterocytic epithelium additional resorptive-physiological investigations were performed using the in vivo-perfusion-recirculation method and in vitro-accumulation of L-phenylalanine.

Control of the pars intermedia of the lizard, Anolis carolinensis. V. Extravascular transfer and cellular uptake of horseradish peroxidase in the neuro-intermediate lobe.

The distribution of the tracer substance horseradish peroxidase (HRP, Mw 40,000) in the neuro-intermediate lobe of the lizard, Anolis carolinensis, was studied at various time intervals (13 min to 24 h) after vascular injection. HRP rapidly entered the extracellular lumen of the neural lobe, but did not penetrate into the third ventricle. The tracer was found in micropinocytotic vesicles (MPVs) of ependymal cells within 13 min after injection. The number of cellular inclusions containing HRP increased during the period of observation (24h). The tracer was sparsely taken up by aminergic and peptidergic nerve terminals of the external layer. After transection of the hypophysial stalk, numerous dense, labelled droplets were found in the peptidergic terminals, and the number of labelled inclusions in ependymal cells increased. MPVs were frequently found in extensions of stellate cells of the intermediate lobe, and endocytotic vacuoles (EVs) developed especially in the perikaryon. HRP was also found in large cisternae of the secretory cells, appearing predominantly towards the perivascular septum (PVS). These cisternae were found to communicate with the extracellular lumen, probably representing a system of the extracellular space extending into the secretory cell. After transection of the hypophysial stalk, there was an increase in the number of small EVs in secretory cells of the intermediate lobe. The results are discussed in terms of MSH-release regulation and possible participation of the extracellular lumen, glial and stellate cells in the transport of regulating factors and secretory material.

Pathways involved in fluid phase and adsorptive endocytosis in neuroblastoma.

The endocytosis of ricin, horseradish peroxidase (HRP), and a conjugate of ricin-HRP by monolayer cultures of murine neuroblastoma was studied using morphological and biochemical techniques. The binding of (125)I-ricin and (125)I-ricin-HRP to cells at 4 degrees C, as a function of ligand concentration, was a saturable process. The apparent affinity constants, determined at equilibrium, were 2.8 X 10(6) M(-1) for ricin and 1 x 10(6) M(-1) for ricin-HRP. The number of binding sites per cell was 8 x 10(7) and 3 x 10(7) for the lectin and the conjugate, respectively. The binding of (125)I-ricin to monolayers as not proportional to cell density. We found reduced binding at higher cell concentrations, suggesting a decrease in the accessibility of the ligand for the receptor site or fewer sites with increasing cell population. Neuroblastoma cells have an acid-phosphatase-positive network of cisternae and vesicles near the Golgi apparatus (GERL). Ricin-HRP undergoes endocytosis in vesicles and cisternae corresponding to GERL, and in residual bodies (dense bodies). The cellular uptake of ricin-HRP was 100-200 times greater than free HRP and there was no stimulation of fluid phase endocytosis by ricin. When monolayers were exposed to concentrations of native HRP 100-fold that of the conjugate, cellular uptake of peroxidase was comparable, but HRP was localized only in residual bodies and never in elements of GERL. These results support the conclusion that GERL is involved in the adsorptive endocytosis of ricin-HRP, while residual bodies are involved in the bulk uptake of HRP. In addition, the binding, uptake, and possible recycling of (125)I- subunit B (the binding subunit) of ricin and of (125)I-ricin was examined by quantitative electron microscope autoradiography. Both ricin and its binding subunit displayed similar autoradiographic grain distributions at 4 degrees C, and there was no evidence of their breakdown or recycling to the plasma membrane during endocytosis for 2 h.

The organization of projections from the olfactory bulb to the piriform cortex and olfactory tubercle in the rat.

The organization of the projection of olfactory bulb output cells was studied in the rat by injection of horseradish peroxidase (HRP) into the piriform cortex or olfactory tubercle. We made single HRP injections into small cuts in the fiber layer of the projection areas in order to enhance uptake by axons and to confine the region of HRP uptake. Following most of these injections, HRP-labeled axons could be traced in discrete fascicles through the fiber layer of the cortex or tubercle. These observations indicate that axons innervating the piriform cortex do not emit many long collaterals after they leave the lateral olfactory tract. HRP-labeled cells were generally observed throughout the ipsilateral olfactory bulb, but there were regions of greater density of labeled cells that differed in the various brains. The differences among the distributions of labeled mitral and tufted cells were analyzed statistically in 39 brains to test whether they varied systematically with injection site. In these analyses, the olfactory bulb was divided into 30 standard regions, and the labeled cells in each regions were counted. The distributions of labeled cells were similar for brains where injections were made into similar regions of the piriform cortex. The variations in density of labeled cells of the dorsal and anterior regions of the olfactory bulb were most strongly correlated with the positions of cortical injections. In contrast, the posterior medial regions of the bulb were heavily labeled after almost all injections. The ventral portions of the olfactory bulb were most heavily labeled after injections into the olfactory tubercle.

Ca2+-dependent recycling of synaptic vesicles at the frog neuromuscular junction.

Frog cutaneous pectoris muscles were treated with low doses of crude black widow spider venom (BWSV) or purified alpha-latrotoxin, and neuromuscular transmission, quantal secretion, changes in ultrastructure and uptake of horseradish peroxidase (HRP) were studied. When these agents were applied to muscles bathed in a Ca2+-free solution with 1 mM EGTA and 4 mM Mg2+, the rate of quantal secretion rose to high levels but quickly subsided; neuromuscular transmission was totally and irreversibly blocked within 1 h. The terminals became swollen and were depleted of vesicles; HRP was not taken up. When BWSV was applied to other muscles bathed in a solution with 1.8 mM Ca2+ and 4 mM Mg2+, the rate of secretion rose to high levels and then declined to intermediate levels that were sustained throughot the hour of exposure. Neuromuscular transmission was blocked in fewer than 50% of these fibers. The ultrastructure of these terminals was normal and they contained large numbers of synaptic vesicles. If HRP had been present, most of the synaptic vesicles were labeled with reaction product. These observations suggest that Ca2+ plays an important role in endocytosis at the frog neuromuscular junction.

Uptake, intra-axonal transport and fate of horseradish peroxidase in embryonic spinal neurons of the chick.

Horseradish peroxidase (HRP) was injected in ovo into the ventral muscle mass of the hind limb of 5- to 7-day-old chick embryos or into the gastrocnemius muscle of 8- to 18-day embryos and localized histochemically. HRP is extensively incorporated via endocytosis into axonal growth cones or presynaptic terminals in the proximity of the injection site. Much of the tracer is taken up in vesicles and small vacuoles. Most of these are smooth-surfaced and only a few are bristle-coated. A small amount of the tracer is also incorporated into the axon terminal through the openings between the axolemma and an intricate membrane channel. The majority of the tracer-laden vesicles and vacuoles rapidly fuse with one another to become large vacuoles, some of which are transformed into multivesicular bodies (MVBs). In axon shafts, many labeled vacuoles and MVBs are transferred to tubule-like organelles, which appear to be the primary carrier for transporting the tracer back to the cell bodies in the lumbar spinal cord. HRP arrives in the sensory ganglia about 0.5-1 hour earlier than in the motoneurons of the lateral motor column. The maximal rate of the retrograde axoplasmic transport is about 3.5 mm/hour. After arriving in the cell bodies, HRP is transferred from tubule-like organelles to discrete vacuoles of various sizes and appearance. Lysosomal dense bodies and HRP-labeled vacuoles can be distinguished ultrastructurally. A fusion of HRP-labeled vacuoles with lysosomal dense bodies or Golgi vesicles was occasionally observed and the density of HRP-labeled vacuoles diminished after 2 to 3 days. Most of the HRP-labeled organelles were found to contain acid phosphatase activity. Therefore, the complete disappearance of HRP by 4 days postinjection is most likely related to lysosomal degradation. Neuronal cell bodies diffusely labeled with HRP were only observed prior to day 6. After day 6, despite various attempts to injure the peripheral axons, only granularly labeled cell bodies were found. This difference may imply that "mature" neurons have a more efficient mechanism for the sequestration of "free" HRP in the cytoplasmic matrix into membrane-bounded organelles. A mature-like retrograde transport mechanism appears to exist at the earliest stages of axonal growth in vivo.

Effects of colchicine on endocytosis of horseradish peroxidase by rat peritoneal macrophages.

Horseradish peroxidase (HRP) was used as an exogenous marker to study the effects of microtubule-disruptive drugs on endocytosis in cultures of thioglycollate-elicited rat peritoneal macrophages. Colchicine and vinblastine, but not lumicolchicine or cytochalasin B, reduced HRP uptake by about 30-40%. However, as determined by stereological measurements, the size of the HRP-containing compartment within the cells remained unaltered. In both control cells and cells treated with colchicine or vinblastine the HRP-reactive vesicles were preferentially located close to the dictyosomes (stacks of cisternae) despite the fact that the Golgi complex was disorganized in the treated cells. These results suggest that intact cytoplasmic complex was disorganized in the treated cells. These results suggest that intact cytoplasmic microtubules are required to maintain a normal rate of fluid phase endocytosis in macrophages. On the other hand, it seems as if microtubules are not necessary for the translocation of newly formed endocytic vesicles/lysosomes to the dictyosomes, from which they probably are supplied with digestive enzymes.

Pinocytosis in human synovial cells in vitro. Evidence for enhanced activity in rheumatoid arthritis.

Human synovial tissue cells in monolayer can be shown to take up and digest a soluble protein, horseradish peroxidase (HRP). Uptake of HRP was linear with increasing concentrations of substrate and cell protein and with time for up to 4 h. Low temperature (4 degrees C), and sodium fluoride, an inhibitor of glycolysis were the most effective metabolic inhibitors of endocytosis. In addition, colchicine, an inhibitor of microtubule assembly, and yeast mannan, an inhibitor of mannose-specific receptors, reduced HRP uptake. Synovial cells from patients with rheumatoid arthritis (RSC) demonstrated a statistically significantly higher rate of endocytosis (247 +/- 107 ng HRP/100 micrograms cell protein per 2 h.) than cells from control, nonrheumatoid patients (NSC) (100 +/- 80 ng HRP/100 micrograms cell protein per 2 h). Thus, it is possible to discriminate RSC from NSC by their quantitatively different rates of endocytosis. Digestion of HRP by synovial cells is statistically significant by 6 h after uptake. A faster initial rate of digestion was seen in RSC. Over the first 6--8 h of incubation 42% of the endocytosed HRP was still cell-associated in RSC and 67% remained in NSC cultures. However, by 24 h 20--30% of endocytosed HRP was found in both types of cultures. These results indicate that endocytosed molecules may accumulate more rapidly in RSC and persist within their lysosomes for a longer time than in NSC. The quantitative determination of enhanced endocytosis by RSC compared with NSC suggests that this increased activity may have a role in the pathological function of synovial tissue in rheumatoid arthritis.

The uptake of horseradish peroxidase in rat temporomandibular joint synovium following alterations in the occlusion.

The uptake of horseradish peroxidase in rat temporomandibular joint synovium following alterations in the occlusion.

Stimulation of pinocytosis in the macrophage by lymphocyte mediators: I. Description of the phenomenon

Macrophages incubated in supernatants from antigen or concanavalin A-stimulated lymphocytes will demonstrate enhanced pinocytosis of horseradish peroxidase (HRPO) compared with macrophages incubated in control supernatants. This readily reproducible increment in HRPO uptake is seen within 12 hr in suspension culture. This enhancement may represent an early cellular change preparatory to the increased effector function of activated macrophages.

The effect of nitrogen dioxide on tracheal uptake and transport of horseradish peroxidase in the guinea pig.

The effect of 5 and 15 ppm of nitrogen dioxide (NO2) on airway transepithelial permeability to horseradish peroxidase (HRP) (molecular weight, approximately 40,000 daltons) was studied in the guinea pig. Age- and sex-matched guinea pigs (n = 34) were exposed to NO2 for 2 and for 14 days. In the control guinea pigs, 0.05% of the intratracheally instilled dosage HRP was present in the plasma within 10 min, as detected by radioimmunoassay, and increased thereafter at amean rate of 0.0016%/min. After exposure to NO2, there was a significant increase in the rate of plasma HRP accumulation (p < 0.05) with the maximal increase detected in the group exposed to 15 ppm of NO2 for 2 days. The morphologic correlates of increased permeability to HRP appear to be (a) an increase in pinocytotic activity within the hyperplastic globlet cells, and (b) transjunctional transport by leaky tight junctions that was noted only in animals exposed to 15 ppm for 14 days (p < 0.01). Our data suggests that pinocytotic vesicular transport of proteins in the secretory cells of the airway may be an important mechanism for the movement of exogenous nonlipid soluble macromolecules across the epithelial barrier.

A note on the anterograde transport of horseradish peroxidase within the olivocerebellar fibres.

In cats with unilateral injections of horseradish peroxidase in the inferior olive which were processed according to the Mesulam (1978) technique crossed olivocerebellar fibres can be followed on both sides of the brain stem into the cerebellum to the level of the granular layer. The observations indicate that perikaryal uptake of horseradish peroxidase is not a prerequisite for the visualization of the fine preterminal fibres.

Brain stem projections of the aortic nerve in the cat: A study using tetramethyl benzidine as the substrate for horseradish peroxidase

The intra-axonal transport of horseradish peroxidase (HRP) has been used to trace the nodose ganglion and brain stem projections of a physiologically distinct nerve — the aortic depressor nerve — following electrophysiological identification. Tetramethyl benzidine (TMB) has been used as the substrate for demonstrating the centrally transported HRP 15,16. This sensitive method for horseradish peroxidase histochemistry has permitted the visualization of the central projections of aortic nerve afferents and has also provided information regarding the anatomical localization of cell bodies of these sensory nerve fibers within the nodose ganglion. This study demonstrates the usefulness of using TMB as a substrate for HRP histochemistry in anatomical studies where the detection of anterogradely transported HRP is an essential prerequisite. The uptake of HRP from the cut central ends of sensory nerve fibers and the transport of this enzyme to the sensory ganglion and subsequently into the central processes of these sensory neurons have made possible this study of the central projections of a functionally distinct peripheral nerve. Information has been provided by this study that cell bodies of aortic nerve afferent fibers are localized in the rostrolateral pole of the nodose ganglion. Dense central projections of sensory terminals of aortic afferents have been found in the dorsolateral and medial subdivisions of the nucleus of the tractus solitarius. These central projections of aortic afferents extend for 6 mm rostrocaudally in the medulla with the densest projection being found at the level of the obex. These projections are bilateral at all rostrocaudal levels. This anatomical demonstration of the dorsolateral and medial subdivision of the nucleus of the tractus solitarius confirms earlier reports based on electrophysiological studies 5–8,14. Of particular interest in this study is the new observation that there exists a dense projection of aortic nerve afferents to the area postrema. The possible physiological implications of a direct input of peripheral chemoreceptor afferents to a region of central chemosensitivity are discussed. The complete absence of any retrogradely labeled cell body in the brain stem from exposure of the aortic nerve to horseradish peroxidase is noteworthy. This indicates that the aortic nerve is purely afferent in function and that reflex control of afferent activity in the aortic nerve is not mediated by brain stem neurons projecting down the same nerve.

Transganglionic demonstration of central sensory projections from skin and muscle with HRP-lectin conjugates

Transganglionic transport of horseradish peroxidase (HRP) was greatly improved by conjugating the enzyme with wheat germ agglutinin (WGA) as described by Gonatas et al. [7]. Intense dorsal horn projections from muscle groups and even discrete skin patches were labeled after peripheral injection of the HRP-WGA conjugate. These projections could not be consistently demonstrated when HRP was injected either alone or in combination with DMSO. Conjugation with WGA thus enhances the uptake and/or transport of HRP and constitutes a valuable advance in HRP technique.

Influence of the tubular flow rates on the endocytic uptake and the excretion of horseradish peroxidase by rat kidney

Summary The renal clearances of horseradish peroxidase (HRP) in diuretic and anti-diuretic rats were compared with the concentrations of HRP in the renal cortex of the same rats. The injection of mannitol, hypertonic saline, or antagonists to histamine and serotonin, together with HRP, caused diuresis. The renal clearance of HRP was 7–15% of the inulin clearance, relatively small amounts of HRP were reabsorbed into the renal cortex, and relatively large amounts were excreted in the urine. However, when HRP was injected alone causing vascular leakage and anti-diuresis, 6–10 times higher concentrations of HRP were found in the renal cortex, and only a few percent of the protein were excreted in the urine during the first 20 minutes after injection. It is suggested that the low or high endocytic uptake of HRP by the renal cortex was related to the high or low tubular flow rates during diuresis or anti-diuresis.

Uptake of horseradish peroxidase of sensory terminals of lamellated corpuscles in mouse foot pads.

Uptake of horseradish peroxidase (HRP) by sensory axon terminals was studied in lamellated corpuscles of mouse plantar foot pads after i.v. and local s.c. HRP injections. The corpuscles, considered to be rapidly adapting mechanoreceptors, are localized in dermal papillae and have discoid axon terminals enclosed in 1-5 lamellae of lamellar cells. The injected HRP diffused into interlamellar and adaxonal clefts and was taken up by sensory terminals, being incorporated in coated pits and coated vesicles formed by the axolemma. The tracer further appeared in the axoplasm in smooth vesicles, multivesicular bodies, and vacuoles. Similar incorporation of HRP into vesicles, inclusion bodies, and vacuoles was observed in the lamellae and perinuclear cytoplasm of lamellar cells. Vibratory stimulation considered to be adequate for this type of mechanoreceptors did not result in any perceptible increase in HRP uptake by sensory terminals. It is suggested that endocytosis by sensory terminals may serve for incorporation of regulatory macromolecules that presumably mediate information to the perikaryon about conditions of the distant terminals and their microenvironment.

Depletion of neurosecretory granules and membrane retrieval in the sinus gland of the crab.

Ultrastructural aspects of hormone release from the sinus gland of the crab Carcinus maenas, have been studied by incubation of glands in vitro (i) in high potassium-containing media to induce hormone release; (ii) in a high potassium-containing calcium-free medium in which depolarisation but no hormone release would be expected; and (iii) in control saline. Uptake of horseradish peroxidase into subcellular organelles was also studied. Many neurosecretory granules could be found in the nerve terminals but, in contrast to mammalian neurosecretory systems, structures resembling microvesicles were extremely scarce. High potassium stimulation in the presence of calcium caused an 18% loss of granules from the nerve terminals associated with images of single and multiple exocytosis. It further caused an increase in vacuoles which could have accounted fro 33% of the membrane of the granules exocytosed. After incubation in high potassium-containing, calcium-free media there was no evidence either of exocytosis of granules or of an increase in the vacuole population. The population of sparse microvesicle-like structures was not significantly altered by incubation in either high potassium medium. Horseradish peroxidase reaction product could be found only in vacuoles of tissues stimulated by high potassium concentrations in the presence of calcium. It is concluded that this depolarising stimulus produces, in the presence of calcium, the release by exocytosis of about one sixth of all the granules in the sinus gland, and that vacuoles are the organelle responsible for the recapture of membrane after the exocytosis.

Horseradish peroxidase localization of cardiac vagal preganglionic somata

Cardiac vagal preganglionic somata were labeled in cats by the horseradish peroxidase (HRP) technique. The anatomical characteristics of cell bodies with axons in the left and right cervicl vagi were compared. HRP was injected subepicardially in three groups of pentobarbital anesthetized animals. In two test groups, injections were made after a left and right cervical vagotomy, respectively. In a control group, peripheral cardiac parasympathectomies were performed prior to HRP injection. The controls served to determine the number of somata labeled by HRP uptake via vagal fibers innervating viscera closely approximating the myocardium. After a 48 h survival period the cats were reanesthetized, perfused and fixed. Brain stems were removed, cut in the transverse or sagittal plane and developed with 3,3′-diaminobenzidine. Control cats had 6.8% the number of labeled cell bodies identified in animals with an intact vagus. Thus, few labeled somata in test cats were associated with noncardia ti tissue. The number, distribution and sizes of labeled cell bodies in test cats were similar. Somata were located ipsilateral to the intact vagus in three regions: the nucleus ambiguus (NA), the dorsal motor nucleus of the vagus (DMN) and an intermediate zone (IZ) between the NA and DMN. The NA contained the maximum number of cell bodies while successively fewer somata were located in the DMN and IZ. Somata of the NA were heterogeneously distributed along the longitudinal neuraxis. The region of maximal cell body concentration was between 1.0 and 1.8 mm rostral to the obex. Somata of the DMN and IZ were homogeneously and sparsely distributed along the neuraxis. The long and short axes of NA somata were larger than corresponding dimensions of cell bodies in the DMN or IZ. However, the dimensions of somata in the DMN and IZ were similar. The identification of labeled cell bodies in three medullary regions and the size differences of the somata in these regions may reflect a central physiological organization of cardia vagal somata.