No abstract available. / Thesis (M.D.)-University of Natal, 1973.

The study of the lumbosacral plexus nerves constituents is extremely important because it relates the various evolutionary aspects of animal locomotion and posture. Considering that the femoral nerve is the largest cranial part of the lumbosacral plexus, aimed to describe the origins, distributions and ramifications of the femoral nerve in giant anteater (Myrmecophaga tridactyla), comparing with the literature described for domestic and wild animals in to establish correlations of morphological similarities and providing subsidies for similar areas. For the work three specimens were used prepared by injection of aqueous 10% formaldehyde in the femoral artery, for keeping the specimens and further dissection. The origin of the femoral nerve in the right and left sides, is the ventral brach of the lumbar spinal nerves one, two and three. As to the distributions and ramifications, the femoral nerve provides branches to the major and minor psoas muscle, lateral and medial iliac, pectineus, adductor magnus, sartorius and quadriceps. The anatomical origin of the femoral nerve in M. tridactyla shows a variation due to the difference in the number of vertebrae (L1, L2 and L3). But in most distributions and ramifications of the femoral nerve, this species has a significant degree of morphological similarities with domestic and wild animals in this study. / O estudo dos nervos constituintes do plexo lombossacral é de extrema importância, pois relaciona os diversos aspectos evolutivos de postura e locomoção dos animais. Considerando-se que o nervo femoral é o maior da parte cranial do plexo lombossacral, objetivou-se descrever as origens, distribuições e ramificações dos nervos femorais no Tamanduá bandeira (Myrmecophaga tridactyla), comparando com a literatura descrita para animais domésticos e silvestres, de modo a estabelecer correlações de similaridades morfológicas e fornecer subsídios para as áreas afins. Foram utilizadas três espécimes, preparadas através da injeção de solução aquosa de formaldeído a 10% via artéria femoral, para a conservação e posterior dissecação das mesmas. As origens nos antímeros direito e esquerdo, ocorreram dos ramos ventrais dos nervos espinhais lombares um, dois e três. As distribuições e ramificações foram observadas para os músculos psoas maior e menor, ilíacos lateral e medial, pectíneo, adutor magno, sartório e quadríceps femoral. Com base nas origens dos nervos femorais do M. tridactyla, uma reconfiguração foi observada devido à variação no número de vértebras lombares (L1, L2 e L3). Entretanto, uma similaridade morfológica parcial foi mantida quanto às distribuições e ramificações, quando comparadas aos animais domésticos e silvestres considerados neste estudo. / Mestre em Ciências Veterinárias

Neste trabalho, mostramos que a extração de veneno promove aumento na ativação dos fatores de transcrição NF<font face=\"symbol\">kB e AP-1. Noradrenalina, liberada após extração de veneno, é responsável por esse aumento. A estimulação dos adrenoceptores <font face=\"symbol\">a e <font face=\"symbol\">b estão envolvidos nessa resposta, entretanto, o grau de ativação de AP-1 é alterado dependendo do tempo. Foi verificado dimorfismo sexual na ativação dos fatores de transcrição da glândula de veneno, sendo a ativação de NF<font face=\"symbol\">kB mais rápida nas fêmeas do que nos machos e a ativação de AP-1 maior nas fêmeas. Mostramos ainda que a extração de veneno ativa a glândula de veneno através da estimulação da inervação noradrenérgica. Noradrenalina atuando em adrenoceptores <font face=\"symbol\">a e <font face=\"symbol\">b regula a síntese de proteínas da glândula de veneno e não a síntese de toxinas do veneno. Em conclusão, a estimulação da inervação noradrenérgica desencadeia o ciclo de produção de veneno regulando a síntese de proteínas da glândula que provavelmente são essenciais para sua ativação e posterior produção de veneno, através da ativação de fatores de transcrição. Thesis: Noradrenergic Innervation in activation of venom gland of Bothrops jararaca snake. / In this work we showed that venom extraction increases the activation of transcription factors like NF<font face=\"symbol\">kB and AP-1. Noradrenaline released after venom extraction is responsible for NF<font face=\"symbol\">kB and AP-1 activation. Stimulation of both <font face=\"symbol\">a- and <font face=\"symbol\">b-adrenoceptors is involved in this response, however the increase of AP-1 activation is time dependent. A sexual dimorphism has been verified in NF<font face=\"symbol\">kB and AP-1 activation. Activation of NF<font face=\"symbol\">kB occurs earlier in female than in male snakes and activation of AP-1 is greater in female than in male snakes. We also showed that venom extraction activates venom gland by stimulating noradrenergic innervation. Noradrenaline acting at both <font face=\"symbol\">a- and <font face=\"symbol\">b-adrenoceptors regulates synthesis of protein of the venom gland, but not the toxin of the venom. In conclusion, stimulation of noradrenergic innervation triggers the venom production cycle by regulating synthesis of protein that probably is essential to activate venom gland to produce venom by activating transcription factors.

INTRODUÇÃO - O câncer de próstata é a doença maligna mais diagnosticada no mundo, desconsiderando os tumores de pele. A prostatectomia radical tem sido considerada a opção terapêutica preferida no tratamento do câncer clinicamente localizado. O conhecimento da anatomia neurovascular da próstata é de extrema importância para a obtenção de resultados funcionais satisfatórios sem prejuízo aos fins oncológicos. A maioria dos estudos anatômicos já publicados utilizou próstatas removidas cirurgicamente - espécime de prostatectomia radical. Estudos realizados com próstata de cadáveres são importantes por permitir a ressecção em bloco dos órgãos pélvicos, possibilitando uma melhor avaliação da neuroanatomia periprostática. O objetivo deste estudo é avaliar detalhadamente a distribuição das fibras nervosas periprostáticas em cadáveres humanos. MÉTODOS - Foram obtidos 10 blocos viscerais de cadáveres com idade superior a 50 anos constituídos por bexiga, próstata e fáscias adjacentes, uretra proximal e reto. Após fixação em formalina, o bloco visceral foi fatiado transversalmente em fatias de aproximadamente 5 mm. Cada fatia foi dividida em quatro setores, tendo a uretra como eixo central e encaminhada para inclusão em parafina, secção com micrótomo padrão e confecção das lâminas coradas em HE. A cápsula prostática (CP) foi identificada e demarcada e áreas de avaliação foram definidas conforme distância da CP, designadas como distância D1(até 2,5 mm), D2 (2,5 a 5 mm) e D3(maior de 5 mm). Em cada região da próstata (região apical, região média e região basal) as fibras nervosas foram avaliadas de acordo com a distribuição circunferencial nos segmentos anterior, ântero-laterais direito e esquerdo, póstero-laterais direito e esquerdo e posterior e conforme a distância da CP - distâncias D1, D2 e D3. RESULTADOS - Foram identificados 29.275 fibras nervosas, das quais 3.274 (11,18%) foram detectados na região apical, 11.997 (40,98%) na região média e 14.004 (47,84%) na região basal da próstata. Na região basal, aproximadamente, 46% das fibras nervosas foram identificadas nas faces póstero-laterais, 20% na face posterior da próstata e menos de 9% na face anterior. Houve predomínio numérico de FN nas áreas mais distantes, com 46,62% delas sendo identificadas em D3. Na região média, 45% das fibras nervosas se distribuíram nos segmentos anteriores a ântero-laterais. Cerca de 45% se distribuíram igualmente nas faces póstero-laterais direita e esquerda e apenas 10% na face posterior. Nesta região, observou-se que mais de 60% das FN estavam dispostas nas áreas D1. Na região apical, também se observou predomínio de fibras nervosas nos segmentos que compõem as faces posteriores e póstero-laterais (61%). Aproximadamente, 24% das FN se distribuíram igualmente entre as faces ântero-laterais direita e esquerda e quase 15% estavam distribuídas na face anterior do ápice prostático. Mais da metade delas encontravam-se distribuídas a até 2,5 mm da cápsula prostática. Nos segmentos anteriores e ântero-laterais, o predomínio de FN nas áreas D1 foi mais acentuado do que nos outros segmentos. Na avaliação geral, a quantidade relativa de fibras nervosas identificadas nas áreas D1 variou de maneira inversamente proporcional à quantidade relativa de FN das áreas D3. Nas áreas demarcadas entre 2,5 mm e 5 mm da CP (D2), a quantidade relativa de fibras nervosas se manteve relativamente constante. CONCLUSÕES - No sentido craniocaudal, a quantidade de fibras nervosas diminui progressivamente, a distribuição circunferencial se modifica, com aumento da quantidade relativa de fibras nervosas nas faces anteriores e a distribuição em relação à distância da próstata também se modifica, com aumento da quantidade relativa de fibras nervosas nas áreas mais próximas da próstata. A quantidade relativa de fibras nervosas dispostas a uma distância mínima de 2,5 mm da cápsula prostática se mantém constante / INTRODUCTION - Prostate cancer is the most commonly diagnosed malignancy in the world, excluding skin tumors. The incidence of localized tumor increased substantially after the PSA era. Consequently, the percentage of men treated by radical surgery for clinically localized prostate cancer increased. The exact paths of periprostatic nerves have been under debate over the last decades. In the present study, the topographic distribution of nerves around the prostate and their relative distances from the prostatic capsule were analyzed in male cadaver visceral blocs. METHODS - The pelvic organs from ten fresh male cadavers were removed and serial sectioned en bloc for histological investigation. The prostatic capsule was identified, and distances of 2.5 mm and 5 mm from the prostate were demarked with lines. We quantified the number of nerve fibers present in each subsector of each slide and recorded their position relative to the prostatic capsule. RESULTS - A total of 29,275 nerve fibers were identified, of which 3,274 (11.18%) were detected in the apex, 11,997 (40.98%) in the middle and 14,004 (47.83%) in the basal area of the prostate. The majority of nerves were identified in the posterolateral and posterior surfaces of the prostate. At the apical region, the percentage of nerve fibers identified in the anterior region was higher. The nerves identified at the apex were mainly located up to 2.5 mm from the prostate. This proximity to the prostate was specifically observed in the ântero-lateral and anterior sectors. In the craniocaudal sense, the percentage of nerves identified between 2.5 and 5 mm from the prostatic capsule remained constant. CONCLUSIONS - A significant number of nerve fibers were present in the anterior and ântero-lateral positions, especially at the apex. The anterior nerves were closer to the prostate. This proximity suggests that the anterior nerves may participate in local physiology. It is likely that the safe distance of 2.5 mm from all surfaces of the prostate may be related to cavernous fiber preservation

O objetivo do presente trabalho foi avaliar a preservação da inervação de porções intestinais macroscopicamente viáveis em cães portadores de intussuscepções. Para tanto, realizou-se comparação entre segmento intestinal proveniente deste grupo de animais (G1) e segmentos intestinais de animais sem qualquer distúrbio do aparelho digestório (G2). Avaliações histológicas e imunoistoquímicas foram realizadas em sistema computadorizado (Image Pro-Plus®) além da avaliação tardia da qualidade de vida e função digestiva. As variáveis analisadas foram: densidade média das camadas musculares circular e longitudinal, relação entre as camadas musculares, número média de plexos mioentéricos, densidade celular média dos plexos mioentéricos, grau de degeneração neuronal nos plexos mioentéricos, imunoreatividade à sinaptofisina e ao NSE além de existência de distúrbios de defecação. Com exceção da densidade celular média da camada longitudinal, relação entre as camadas musculares e imunoreatividade à sinatpofisina, todos os demais parâmetros apresentaram diferença estatisticamente significativas entre os grupos testados. Foram observadas correlações entre densidade celular média dos plexos mioentéricos e densidade celular média da camada muscular circular; grau de vacuolização dos plexos mioentéricos e imunoreatividade ao NSE; além de grau de vacuolização dos plexos mioentéricos e densidade celular média dos plexos mioentéricos. Quanto aos anticorpos utilizados, o NSE apresentou melhor padrão de marcação quando comparado à sinaptofisina. Dos 13 cães pertencentes ao G1, três foram a óbito no pós-operatório inicial. No período pós-operatório tardio, três cães apresentaram alterações de consistência e freqüência de defecação, além de episódios diarréicos agudos intermitentes. O tempo de segmento foi de 6 meses após intervenção cirúrgica. Os achados deste estudo sugerem que porções intestinais macroscopicamente viáveis podem apresentar lesões de inervação eventualmente traduzidas em sintomatologia clínica futura. Assim sendo, deve-se avaliar de maneira cuidadosa a margem cirúrgica preservada durante o procedimento de enterectomia/enteroanastomose bem como realizar acompanhamento da função digestória tardia. / The purpose of this study was to evaluate the preservation of the innervation of macroscopically viable bowel segments of dogs with intussusceptions. This group (G1) was compared to bowel segment of normal dogs (G2). Histological and immunohistochemical analysis were performed using computed system (Image Pro-Plus®). Late assessment of the quality of life and digestive function were also evaluated. Analyzed variables included: mean density of circular and longitudinal muscular layers cells, ratio between muscular layers, mean of myenteric plexuses, mean density of myenteric cells, neuronal degeneration degree in myenteric plexus, synaptophysin and NSE immunoreactivity and defecatory disorders. All tested parameters, except mean density of longitudinal muscular layers cells, ratio between muscular layers and synaptophysin immunoreactivity, showed statistical differences when group G1 was compared with group G2. Correlations between mean density of myenteric cells and mean density of circular muscular layers cells; neuronal degeneration degree in myenteric plexus and NSE immunoreactivity; neuronal degeneration degree in myenteric plexus and mean density of myenteric cells were observed. Regarding the immunohistochemical antibodies, NSE showed better staining pattern than synaptophysin. Three animals of G1 (n=13) died during the initial post-operative period. During the late post-operative period, three animals presented disorders in fecal consistency, frequency of defecation and acute intermittent diarrheal episodes. The follow-up time was 6 months. These findings showed that macroscopically viable bowel segments can present innervation damage eventually translated in clinical symptoms in the future. So, a careful evaluation of the preserved surgical margin during enterectomy and enteroanastomosis must be carried out as well as monitoring of the late digestive function.

Die Recurrent airway obstruction (RAO), im deutschen auch als „Dämpfigkeit“ be-zeichnet, ist eine weltweit anerkannte und weit verbreitete Erkrankung der Luftwege beim Pferd, die durch eine hypersensitiv-vermittelte Entzündung der Atemwege und begleitende Neutrophilie charakterisiert ist. Ausgelöst durch ungünstige Umweltbedingungen umfasst der klassische Phänotyp dieses Krankheitsbildes Husten, Nasenausfluss, Dyspnoe und Leistungsabfall. Die pathophysiologischen Vorgänge äußern sich in Bronchialobstruktion, Schleimhypersekretion, Hyperreaktivität und Umbauvorgängen (Airway remodelling) der Atemwege. In der Literatur existieren bisher noch keine genaueren Daten zur sympathischen und parasympathischen Lungeninnervation beim Pferd. Die vorliegende Arbeit liefert erstmalig eine umfangreichere immunhistochemische Analyse der Nervenäste in der equinen Lunge. Durch Immunfluoreszenz-Markierungen von ChAT und TH wurden sympathische und parasympathische Fasern detektiert. Die hierfür eingesetzten hochgereinigten Antikörper haben sich hierbei als geeignete Marker für cholinerge bzw. katecholaminerge Zellstrukturen erwiesen. Hierbei gab es keinen Hinweis darauf, dass sich die Immunreaktivität im Faserverlauf ändert oder von kranial nach kaudal schwächer wird. Auffällig war die starke Immunreaktivität der ChAT in den untersuchten Gewebeschnitten eines an RAO erkrankten Pferdes, die auf eine Hochregulation des Parasympathikus im Verlauf dieser Lungenerkrankung deutet. Die zusätzliche Detektion weiterer neuronaler Marker wie z.B. MAP2 oder NF-L sowie von Mikroglia und Astrozyten erlaubte den Nachweis weiterer Veränderungen im Krankheitsverlauf. Die validierte Koexpression von katecholaminergen bzw. cholinergen Markerenzymen deutet auf eine autonome Regulationsweise mit dem Potential einer variablen Reaktion auf Umwelteinflüsse. Die in der vorliegenden Arbeit etablierte Immunfluoreszenz-Doppelmarkierung von cholinergen und katecholaminergen Zellstrukturen bildet eine solide Grundlage für weitere Untersuchungen in Pferdegeweben unter physiologischen und pathologischen Bedingungen.

Electrical stimulation of the vagus nerve attenuates tumor necrosis factor (TNF) synthesis by macrophages and reduces the systemic inflammatory response. Current evidence suggests that the α7 nicotinic acetylcholine receptor present in the celiac/superior mesenteric ganglia is a key component in vagus nerve signaling to the spleen; however, there is currently no direct anatomical evidence that the α7 receptor is present in the murine celiac/superior mesenteric ganglia. Our study addresses this deficiency by providing anatomical evidence that the α7 receptor is expressed within the celiac/superior mesenteric ganglia and splenic nerve fibers using immunohistochemistry and quantitative polymerase chain reaction (qPCR). α7 receptor mRNA is highly expressed in the celiac/superior mesenteric ganglia and at low levels in the spleen compared to the brain. Double-labeling for α7 and tyrosine hydroxylase shows that α7 receptor protein is present on noradrenergic neurons within the ganglia and prejunctionally on noradrenergic nerve fibers within the spleen. The α7 receptor in the ganglia provides a possible location for the action of α7-selective agonists, while prejunctional α7 receptor expressed on splenic nerves may induce an increase in norepinephrine release in a positive feedback system enhanced by lymphocyte-derived acetylcholine.

Our purpose was to identify and localize intrinsic cardiac ganglia innervating distinct regions of the heart using postmortem tracing of nerve projections with DiI, a method not previously used to study the intrinsic cardiac nervous system. We also investigated the possibility of collateral innervation of myocardium and intrinsic ganglia. In isolated paraformaldehyde-fixed guinea pig hearts, crystals of DiI (1,1′- dioctadecyl-3,3,3′,3′-tetramethylin-docarbocyanine perchlorate) were inserted into the posterior ventricular myocardium below the atrioventricular groove, the right atrium, or the left ventricular septum. Hearts were placed in the dark at 37°C for 2-14 weeks to allow DiI diffusion within neuronal membranes. Labeled neurons were observed in intracardiac ganglia after at least 4 weeks of dye exposure. Labeling was restricted to the inferior-most ganglia (those near the atrioventricular groove) when DiI was inserted into the posterior ventricular myocardium and to ganglia near the sinus node after right atrial DiI placement. Application of DiI to the left ventricular septum resulted in neuron labeling in ganglia primarily in the interatrial septum near the atrioventricular node. After 8 weeks, DiI-labeled nerve fibers and varicosities were seen surrounding unlabeled neurons in some ganglia, suggesting that axons terminating in or passing through the DiI application site in posterior ventricular tissue had collateral branches innervating these ganglia. These results indicate that intrinsic innervation of major cardiac subdivisions is accomplished by regionally segregated cardiac ganglia. Also, tracing with DiI has provided evidence for collateral nerve projections that could be the substrate for novel intracardiac regulatory circuits.

Résumé : Introduction : Parmi les structures anatomiques impliqués dans la statique pelvienne, la continence urinaire et anale, le muscle élévateur de l’anus (MEA), le sphincter urétral (SU) et son innervation ont un rôle déterminant. Au cours de la grossesse, de l’accouchement par voie vaginale, de la chirurgie radicale pelvienne, des lésions des muscles du plancher pelvien ou de son innervation peuvent survenir. Ces lésions sont à l’origine de dysfonctions du plancher pelvien telle que le prolapsus uro-génital ou l’incontinence urinaire. Une meilleure connaissance de l’anatomie musculaire et nerveuse pelvi-périnéale est nécessaire pour diminuer la survenue et traiter ces troubles fonctionnels. Classiquement les muscles du plancher pelvien sont décrits comme entièrement striés sous contrôle somatique (nerf du MEA et/ou nerf pudendal (NP)). La dissection Anatomique Assisté par Ordinateur (DAAO) en utilisant des marqueurs nerveux et musculaires spécifiques peut aujourd’hui compléter les données établies par la dissection conventionnelle classique de sujets anatomiques.Objectif : L’objectif était de décrire l’innervation (origine, topographie, trajet, rapports, fonction) et la structure musculaire du MEA, de décrire l’innervation (origine, topographie, trajet, rapports, fonction) du sphincter urétral pour mettre en perspective les implications potentielles dans les dysfonctions du plancher pelvien.Méthodes : Nous avons étudié 9 fœtus humains (6 féminins et 3 masculins). Des coupes histologiques sériées de 5 µm d’épaisseur ont été effectuées dans les régions pelviennes de 7 fœtus âgés de 18 à 40 semaines de gestation. Pour chaque niveau de coupe, des lames ont été colorées puis traitées en immunohistochimie pour détecter : l’ensemble des fibres nerveuses (anticorps anti-protéine S100), les fibres autonomes cholinergiques (anti-VAChT), les fibres autonomes adrénergiques (anti-TH), les fibres autonomes nitrergiques (anti-nNOS), les fibres somatiques (anti-PMP 22), les fibres sensorielles (anti-CGRP), les fibres musculaires lisses (anti-SMA) et les fibres musculaires striées (anti-MYOG). Les coupes ont ensuite été numérisées par un scanner de haute résolution optique et les images ont été reconstruites en 3D avec le logiciel Winsurf®. Un fœtus additionnel a été entièrement destiné à réaliser de la microscopie électronique afin de confirmer nos résultats au niveau architectural musculaire.Résultats : Nous avons observé une innervation à la fois autonome (plexus hypogastrique inférieur (PHI)) et somatique (nerf du MEA et NP) du MEA. Nous avons individualisé des zones de cellules musculaires lisses au sein du plancher pelvien notamment de la partie médiane sous contrôle autonome (PHI) que nous nommons « compartiment médian musculaire lisse ».Nous avons systématisé le plancher pelvien musculaire en une zone médiale lisse sous contrôle nerveux autonome réalisant une interface entre les viscères pelviens, et une zone musculaire striée latérale sous contrôle nerveux somatique.Enfin, nous avons mis en évidence une double innervation à la fois somatique et autonome du sphincter urétral.Conclusion : La DAAO a permis de mettre en évidence une innervation pelvi-périnéale complexe avec l’intrication du système nerveux somatique et autonome. La fonction du contingent musculaire lisse pelvien reste à préciser. / Abstract : Levator ani muscle (LAM), urethral sphincter (US), and their innervation play a major role in pelvic status, urinary continence and anal continence. During pregnancy, vaginal delivery, pelvic radical surgery, damage of pelvic floor muscles or of their innervation may occur. These lesions are responsible for pelvic floor dysfunction such as urogenital prolapse or urinary incontinence. Better knowledge of pelvi-perineal muscle and nerve anatomy is needed to reduce the occurrence and treat these pelvic floor dysfunctions. Classically pelvic floor muscles are described as entirely striated under somatic control (levator ani nerve (LAN) and /or pudendal nerve (PN)). Computer Assisted Anatomical Dissection (CAAD) using specific nerve and muscle markers can nowadays complete data established by conventional dissection of anatomical subjects.The objective was to describe the innervation and the muscular structure of the levator ani muscle, to describe nerve supply of the urethral sphincter in order to better understand pelvic floor dysfunction.Methods : We studied nine human fetuses (6 female and 3 male). Serial histological sections of 5 μm of thickness were performed in the lumbar and pelvic regions of seven human fetuses aged 18 to 40 weeks of gestation. For each level, slides were stained and then treated in immunohistochemistry to detect: general nerve fibers (anti-protein S100), autonomic cholinergic fibers (anti-VAChT), autonomic adrenergic fibers (anti-tyrosine hydroxylase), autonomic nitrergic fibers (anti-nNOS), somatic nerve fibers (anti-peripheral myelin protein 22), sensory fibers (anti-CGRP), smooth muscle fibers (anti-SMA) and striated muscle fibers (anti-MYOG). The slides were then digitized by a high-resolution optical scanner and the images were reconstructed in 3D using the Winsurf® software. One fetus was entirely reserved for electronic microscopy in order to confirm our results.Results: We observed that LAM innervation is supplied by both autonomic (inferior hypogastric plexus (IHP)) and somatic (LAN and PN). We have individualized areas of smooth muscle cells in the pelvic floor, particularly the median part controlled by the autonomic system that we named “smooth muscle medial compartment”.We systematized within the pelvic floor muscle a smooth medial part under an autonomic nervous control as interface between the pelvic viscera and a lateral striated muscle part under somatic nervous control.Finally, we have demonstrated a dual innervation both somatic and autonomic sphincter urethral.Conclusion : CAAD has demonstrated complex pelvic-perineal innervation with the interaction of the somatic and autonomic nervous system. The function of the pelvic smooth muscle contingent remains to be clarified.

The origin of cardiac preganglionic neurons in the rat was investigated using the retrograde transport of horseradish peroxidase (HRP). A single injection of HRP was made into the right myocardium in either a sinoatrial or mid-ventricular location. Labeled cells were found in the mid- and lower medulla primarily in and around the nucleus ambiguus (NA) 600-1800 μm above the obex. The dorsal motor nucleus of X (DMN) was sparsely labeled and a few cells were found in an intermediate zone near the level of the obex. Labeling was bilateral with slightly heavier labeling found ipsilateral to the injection site than contralateral to it. Following a unilateral vagotomy, labeled cells were only found ipsilateral to the intact vagus. Atrial and midventricular injections yielded similar results. Occasionally only 1- cells in the NA were labeled per section. Inspection of serial sections revealed that in these sparsely labeled rats, the HRP was often in the same location within the NA forming a column of cells within the nucleus. The columns sometimes extended at least 240 μm in the rostral-caudal direction. The columnar organization was most apparent in rats with few labeled cells presumably because it was obscured in nuclei that were heavily labeled. In a second group of rats, the right vagus was cut at the cervical level and dipped in HRP to determine the extent of the NA and DMN in rats. In these animals, heavier labeling was found in the DMN than in the NA. Cells in the DMN were filled from the upper spinal cord to its most rostral extent 1200 μm above the obex. Thus, although the DMN and NA send projections in the vagus nerve, those axons terminating in the myocardium primarily originate in the NA.