Showing papers by "University of Virginia published in 1970"

Longitudinal Gradients in Periarteriolar Oxygen Tension

Abstract: The oxygen tension (Po2) on the external surface of arterioles between 8 and 100µ in diameter was measured with oxygen microcathodes (2 to 6µ diameter) in the suffused cheek pouch of hamsters and i...

Protein Composition of the Cell Wall and Cytoplasmic Membrane of Escherichia coli

Abstract: Envelope preparations obtained by passing Escherichia coli cells through a French pressure cell were separated by sucrose density gradient centrifugation into two distinct particulate fractions. The fraction with the higher density was enriched in fragments derived from the cell wall, as indicated by the high content of lipopolysaccharide, the low content of cytochromes, and the similar morphology of the fragments and intact cell walls. The less-dense fraction was enriched in vesicles derived from the cytoplasmic membrane, as indicated by the enrichment of cytochromes, the enzymes lactic and succinic dehydrogenase and nitrate reductase, and the morphological similarity of the vesicles to intact cytoplasmic membrane. Both fractions were rich in phospholipid. The protein composition was compared by mixing the cytoplasmic membrane-enriched fraction from a (3)H-labeled culture with the cell wall-enriched fraction from a (14)C-labeled culture and examining the resulting mixture by gel electrophoresis. Thirty-four bands of radioactive protein were resolved; of these, 27 were increased two- to fourfold in the cytoplasmic membrane-enriched fraction, whereas 6 were similarly increased in the cell wall-enriched fraction. One of the proteins which is clearly localized in the cell wall is the protein with a molecular weight of 44,000, which is the major component of the envelope. This protein accounted for 70% of the total protein of the cell wall, and its occurrence in the envelope from spheroplasts suggests that it is a structural protein of the outer membranous component of the cell wall.

Analytical gel chromatography of proteins.

Abstract: Publisher Summary This chapter describes the fundamental aspects of gel chromatography as they comprise a set of analytical techniques that a protein chemist may use. The unifying principles that underlie these techniques have been a major focus of interest. The chapter focuses on the two fundamental principles that underlie the use of gel chromatographic systems as analytical tools in protein chemistry: (1) partition coefficients depend on molecular size and shape in contrast to surface or charge properties. (2) Gel columns are linear chromatographic systems and can, therefore, be used for the analysis of nonlinear molecular phenomena such as those occurring in chemically reacting multicomponent systems. Although deviations from these two principles of ideal behavior are almost always present, their magnitude is almost always small. In addition, it is evident on both theoretical and experimental grounds that the group of techniques based on the partitioning of molecules into porous gel networks constitutes an extremely versatile and useful array of analytical tools for the studies of protein systems. It may be expected, therefore, that the application of these techniques will be extended to a much wider group of experimental systems.

Unidentified Interstellar Microwave Line

Abstract: DURING a search for H12C14N (hydrogen cyanide) and its molecular isotope H13C14N, we have detected a new molecular line. The discovery was made in June 1970 using the 36-foot telescope of the National Radio Astronomy Observatory in Tucson, Arizona. The receiver was a 3-mm mixer radiometer developed by NRAO in conjunction with Jefferts, Wilson and Penzias of the Bell Telephone Laboratories. The single sideband noise temperature of the radiometer was 3000 K and it covered frequencies from 85 to 90 GHz. At these frequencies the telescope has a beamwidth of 1′ of arc and a beam efficiency of 50 per cent under optimum conditions. The filter bank receiver used consisted of forty filters spaced 1 MHz apart covering a velocity range of 130 km s−1.

Cell proliferation, migration and differentiation in the cerebral cortex of the golden hamster

Abstract: This work was undertaken: (1) to determine the sites of cell proliferation in the cerebral cortex of the hamster during prenatal life and shortly after birth; (2) to study the migration pattern of neuroblasts before and shortly after birth; and (3) to examine the differentiation of the neuroblasts during migration and after arrival at their final location. Tritiated thymidine was injected in pregnant hamsters at various days of gestation and in newborn animals. When one hour after treatment the parietal cortex of the embryos was examined for DNA synthesis, labeled cells were found in the neuroepithelial layer but not in the cortical layers. In the newborn radioactive cells were found both in the neuroepithelial layer and in the subependymal layer, a layer consisting of polymorph cells and developing at the end of prenatal life. Hence during embryonic life cell proliferation in the parietal cortex is restricted to the neuroepithelial layer, but in the newborn the subependymal layer is also ctive in cell production. When the generation time of the neuroepithelium was determined, the DNA synthetic phase was found to be six hours, the pre-duplication and prophase about one and one-half hours and the post-duplication stage about four and one-half hours. Hence the duration of the generation time of the neuroepithelial cells during embryonic life is about 12 hours. To examine the migration pattern of the neurons formed during embryonic and postnatal life, pregnant hamsters were injected at successive days of gestation and the embryos sacrificed at the twentieth postnatal day. A similar procedure was followed for newborn animals. It was thus found that neuroblasts formed during the early stages of development occupy the deep layers of the cortex, while those formed during the later stages of intrauterine life and during the first postnatal days occupy the more superficial layers. Hence, neuroblasts produced during the final stages of development migrate through the cell layers formed at previous days to reach the surface of the cortex. The time required for this migration varied in the newborn hamster from three to five days. When newborn hamsters were injected with tritiated thymidine and the labeled cells traced during the following ten days, it was noted that the cells released by the neuroepithelial layer arrived in the deeper layer of the cortex about 48 hours after labeling. The cells were characterized by a spindle-shaped nucleus while the cytoplasm was seen to extend in peripheral direction. Shortly after arrival at the surface of the cortex the cells lost their spindle shape and the nucleus became oval-shaped with a pale nucleoplasm. Subsequently the cells were characterized by a small round pale nucleus with two or three nucleoli close to the nuclear membrane. Approximately nine days after treatment the labeled cells were clearly recognizable as advanced neuroblasts with a large, pale nucleus and one or two nucleoli.

Examination of the Protein Composition of the Cell Envelope of Escherichia coli by Polyacrylamide Gel Electrophoresis

Abstract: An envelope preparation containing the cell wall and cytoplasmic membrane of Escherichia coli was obtained by breaking the cells with a French pressure cell and sedimentating the envelope fraction by ultracentrifugation. This fraction was prepared for polyacrylamide gel electrophoresis by dissolving the protein in an acidified N,N′-dimethylformamide, removing lipids by gel filtration in the same organic solvent and removing the solvent by dialysis against aqueous urea solutions. More than 80% of the total protein of the envelope fraction was recovered in soluble form. Electrophoresis on sodium dodecyl sulfate-containing gels yielded from 20 to 30 well-resolved bands of protein. One major protein band was observed on the gels. This protein had a molecular weight of 44,000 and accounted for as much as 40% of the total protein of the envelope fraction. A double-labeling technique was used to examine the protein composition of the envelope fraction from cells grown under different sets of conditions which result in large changes in the levels of membrane-bound oxidative enzymes. These changes in growth conditions resulted in only minor alterations in the protein profiles observed on the gels, suggesting that this organism is able to adapt to changes in growth environment with only minor modifications of the major proteins of the cell envelope.

The genetics of embryogenesis in Drosophila.

Abstract: Publisher Summary This chapter describes that any study of genetic variations modify embryogenesis can be approached with two objectives in mind. On the one hand, one might emphasize the embryological aspects of such studies by concentrating on how mutation-produced modifications of particular embryological events can help to elucidate the developmental interactions involved, and aid in the search for the cellular and biochemical mechanisms that are fundamental to them. On the other hand, one might emphasize the genetic aspects of investigating such mutations. The purpose of this chapter to examine how the study of genetic variations that affect embryogenesis in drosophila has in the past contributed, and may in the future contribute, to an understanding of the precise nature of gene action in development. The ultimate goal is, of course, an understanding of the mechanisms that integrate the activities of both the genome and the cytoplasm such that development regularly proceeds from one state of determination and differentiation to the next.

Propagated vasodilation in the microcirculation of the hamster cheek pouch.

Abstract: Propagated vasodilation has been observed in the peripheral vasculature and may be significant in integrating the behavior of terminal arterioles and larger vessels. We have studied the characteristics of propagated vasodilation induced by acetylcholine in the microcirculation of the cheek pouch of the golden hamster. The technique of microionophoresis was used as a means of achieving relatively precise temporal and spatial application of drugs to single arterioles. Application of acetylcholine to an arteriole usually resulted in vasodilation which spread rapidly upstream and downstream from the point of application at a rate much greater than could be accounted for by diffusion or by other means of movement of the agent. Longitudinal propagation velocities for a series of arterioles 20 to 40µ in diameter averaged 0.02 cm/sec. The propagated response was relatively specific, being induced by acetylcholine but not by histamine, K+, H+, or eledoisin. The response was graded in both extent and magnitude, was propagated bidirectionally from the point of origin, was observed in vessels as small as 15µ o.d., and could be blocked by lidocaine.

Athletic injuries of the proximal interphalangeal joint requiring surgical treatment

Abstract: The proximal interphalangeal joint is commonly injured in vigorous sports, but often the severity of the injury is not appreciated and the onset of treatment delayed for weeks or months. In an eight-year period, 143 athletic injuries to the proximal interphalangeal joint required surgery; these cases are reviewed. The anatomy of the joint, the indications for surgery, the details of operative technique and postoperative management, and the results are discussed in the various clinical categories of injury to the joint: articular fractures, fracture-dislocations, compound dislocations, collateral-ligament ruptures, boutonniere deformities, hyperextension deformities, and pseudo-boutonniere deformities. Early surgical repair of the injuries gives good results in those young athletes who are cooperative and well motivated and who have the benefits of supervised rehabilitation. Surgical reconstruction yields satisfactory results even in the athletic injuries that receive attention late; the results are better than those following comparable industrial and occupational injuries to the proximal interphalangeal joints in older patients. The importance of this joint in future athletic competition and in later life makes the correct diagnosis and early treatment imperative.

Binding of Antibiotics to Tissue Homogenates

Abstract: Binding of metabolites and drugs, including antibiotics, to serum proteins has been extensively studied. This phenomenon has important biologic and therapeutic significance [1-3]. The ability of tissues to bind has also been explored, particularly with organic dyes and biologically active agents. In some instances, binding of drugs to specific sites in microorganisms can be linked closely with their mode of action. For example, the polymyxins owe their biologic activity to binding to polyphosphate groups of phospholipids in the bacterial cell membrane [4], and amphotericin B requires sterol binding sites in fungal cells [5]. Antitrypanosomal activity of acriflavine has been shown to depend upon binding of the drug to the parasite [6]. The receptor site theories of pharmacology and virology depend largely on evidence of specific combination between drug or virus and complementary structures on cell membranes. Some of these concepts of drug action were clearly visualized by Ehrlich and Morgenroth many years ago [7 p. 24]. Studies in this laboratory indicated that several antibiotics, particularly those in the polymyxin and aminoglycoside families, are inhibited by constituents of bacteriologic agar and various culture media [8]. The phenomenon appears to be related to the charge produced by free amino groups in the drugs and sulfate groups in the medium, since it can be overcome readily by addi-

Proteins of vesicular stomatitis virus: kinetics and cellular sites of synthesis.

Abstract: FIVE VIRAL PEPTIDES SYNTHESIZED IN L CELLS INFECTED WITH VESICULAR STOMATITIS (VS) VIRUS WERE IDENTIFIED BY POLYACRYLAMIDE GEL ELECTROPHORESIS AND DESIGNATED AS FOLLOWS: nucleoprotein N, a membrane glycoprotein G, a membrane surface protein S, and two nonstructural proteins NS1 and NS2. A slowly migrating minor structural protein L also present in infected cells is probably an aggregate. Incorporation of (3)H-amino acids into each viral protein could be detected by the 2nd hr after infection and even earlier for protein N which is synthesized in the greatest amount. There was no evidence of regulation of viral protein synthesis at the transcriptive level; nonstructural and structural proteins were synthesized throughout the cycle of infection. Short pulses of (3)H-amino acids revealed no uncleaved precursor peptides that could be chased into structural peptides. Proteins N and S were chased into released virions but protein G was apparently incorporated into virions as it was being synthesized. VS viral proteins of infected cells were released by mechanically disrupting cytoplasmic membrane by nitrogen decompression and fractionated by high-speed centrifugation. Protein NS1 was present in the nonsedimentable cytoplasmic fraction throughout the cycle of infection. The nucleoprotein N was recovered primarily from the nonsedimentable fraction early in infection but aggregated into a sedimentable component, presumably the nucleocapsid, later in infection. Proteins G and S were always present in the sedimentable fraction of mechanically disrupted infected cells, presumably in association with plasma membrane. Exposure of infected cells to the membrane-dissolving agent, digitonin, resulted in solubilization of most of protein G and all of protein S but not of protein N. These experiments are compatible with the hypothesis that VS viral proteins G and S are synthesized at and inserted into plasma membrane which envelopes a nucleocapsid core to form the VS virion.

An appraisal of the use of monoamine oxidase as an enzyme marker for the outer membrane of rat liver mitochondria

Abstract: In a recent paper we reported that monoamine oxidase (MAO) is localized on the outer membrane of rat liver mitochondria . We concluded that this enzymic activity could be used as a biochemical marker to monitor the physical separation of the outer membrane (OM), from the inner membrane plus matrix fraction (IMM), and from components housed between the membranes (6) . However, the use of MAO and rotenone-insensitive DPNH cytochrome c reductase (RIDCR) as markers for the outer membrane of rat liver mitochondria has been severely criticized by Green et al . (2) . In contrast to other workers, (1, 3-6) Green and co-workers assign enzymes of the citric acid cycle (except succinate dehydrogenase) and of fatty acid oxidation to sites on the outer membrane and MAO to the inner membrane . Green contends that, with regard to MAO localization, estimations of MAO are incorrect (a) due to errors in the spectrophotometric assay using benzylamine as substrate and (b) due to the high level of aldehyde dehydrogenase (ADH) in the mitochondria . The present paper should help to clarify this controversy as it specifically relates to the use of MAO as a marker for the OM of rat liver mito-

Factors controlling the reassembly of the microvillous border of the small intestine of the salamander.

Abstract: Hydrostatic pressure, when applied to segments of the small intestine of the salamander, causes a tremendous reduction in number of microvilli and a loss of the terminal web. The intestinal epithelium strips off from its deeper layers at the level of the basement membrane. When the pressure is released and this epithelial sheet is allowed to recover, the microvilli and its terminal web reappear. Stages in the reformation of microvilli are described. In the earliest stages, foci of dense material seem to associate with the cytoplasmic surface of the apical plasma membrane. From this material, filaments appear and their regrowth is correlated with the extension of the microvilli. We suggest that the dense material nucleates the assembly of the filaments which, in turn, appear instrumental in the redevelopment of microvilli. This concept is supported by the existing literature. Further, since neither the microvilli nor the terminal web reappear on any surface but the apical surface, even though the apical and basal surfaces are bathed with the same medium, we suggest that information in the membrane itself or directly associated with the membrane dictates the distribution of the dense material which leads to the formation of the microvilli and ultimately to the polarity of the cell.

Formation and migration of neuroblasts in the spinal cord of the chick embryo.

Abstract: To determine the origin, migration pattern and final localization of the neurons in the spinal cord, chick embryos ranging in age from two to eight days were treated with two doses of tritiated thymidine with an interval of two to four hours and sacrificed at various days thereafter. As a result of this labeling procedure, all neuroepithelial cells were labeled; hence all neuroblasts arising from the neuroepithelial cells after the treatment were labeled, while those formed earlier were unlabeled. By examining the position of the unlabeled neuroblasts at daily intervals, the migration route and final localization of these neurons could be determined. Neuroblasts formed on days two and three are initially found along the inside of the basement membrane in the ventrolateral as well as the dorsolateral region of the cord. During the following days, however, the neuroblasts found in the dorsolateral region disappear and by day 8 the majority of the two-and three-day neuroblasts is concentrated in the lateral region of the anterior horn. Since no evidence for degeneration of neuroblasts was found in the alar plate region, it is probable that „alar plate neuroblasts” migrate to the region of the anterior horn. The majority of the neuroblasts formed on days 3 and 4 finds its final position in the lateral region of the anterior horn; the majority of those formed on days 5 and 6, however, occupies a position in the medial region of the anterior horn. Hence, the majority of the motor neurons innervating the muscles of the extremities is formed earlier than those innervating the trunk musculature. The neuroblasts of the internuncial zone are formed on days 2 through 7, that is, during the entire period that neuroblast formation in the spinal cord occurs. The majority of the neuroblasts for the posterior horn arises on days 6 and 7, while the last ones are formed on day 8. Despite the fact that the majority of the neuroblasts for the anterior horn is formed before those of the internuncial zone and these in turn before those of the posterior horn, none of the cell groups in either region is formed within a sharply delineated time period.

Two-Phonon Resonances and Hybridization of the Resonance with Single-Phonon States

Abstract: Considering the anharmonic phonon-phonon interactions, two-phonon resonances are studied by Green's-function methods. The two-phonon spectrum exhibits an asymmetric peak near the top of the two-phonon continuum. In the special case of a resonance consisting of two acoustic phonons, the hybridization of the resonance with a single optical phonon is possible, in agreement with experiment.

Intraphagosomal pH of human polymorphonuclear neutrophils.

Abstract: SummaryCandida albicans were stained with one of nine different indicator dyes which encompassed a pH range of 2.5-8.0. Living polymorphonuclear neutrophils were observed microscopically, and color changes of intracellular dye-stained Candida were noted. Intraphagosomal pH decreased to the 6.0-6.5 range and this pH change was prevented by certain glycolytic inhibitors.

Repair of the external granular layer of the hamster cerebellum after prenatal and postnatal administration of methylazoxymethanol.

Abstract: The purpose of this experiment was to examine the influence of methylazoxymethanol acetate (Mam ac) on cell proliferation and regeneration of the external granular layer in the cerebellum of the hamster. Pregnant hamsters were treated with 10 mg/kg/day Mam ac on days 13–15 of gestation and youngsters on the second, third, and fourth or fourth, fifth and sixth postnatal days. In animals treated during intrauterine life and examined on the day of birth a large number of cells in the external granular layer were destroyed, but some seemingly healthy ones always remained. In those permitted to live, surviving cells formed a new external granular layer and by the 20th postnatal day no morphological differences could be detected between the treated and control animals. In animals treated on the second to fourth postnatal days practically all the cells of the external granular layer were destroyed. By the tenth day the Purkinje cells were located throughout the molecular zone. Many of them showed a cytoplasmic cone extending centrally instead of toward the periphery. The internal granular layer contained only a few cells, apparently owing to failure of the normal inflow of neurons from the external granular layer. In animals treated on the fourth to sixth postnatal days most cells in the external granular layer were destroyed. During the following days surviving cells presumably gave rise to a new external granular layer. The cells of this layer failed to migrate centrally. Instead they remained located in the molecular layer where they formed an extra layer of cells, which had the appearance of granule cells. The animals were ataxic, although retinal abnormalities may have been partially responsible for the symptoms.

A Ten-Year Study of Bacteriuria in Schoolgirls: Final Report of Bacteriologic, Urologic, and Epidemiologic Findings

Abstract: A long-term study of the epidemiology and natural history of urinary-tract infections in schoolgirls has been conducted for the past 10 years in central Virginia [1-4]. The purpose has been to develop a rational approach to early detection, treatment, and cure by defining as many characteristics as possible of the dynamics of bacteriuria in this population. It is clear, from data already presented, that among schoolgirls bacteriuria is common, often asymptomatic, and frequently recurrent. At least 596 of girls will acquire bacteriuria during the elementary and secondary school years [4]. This report will summarize the clinical, bacteriologic, and urologic characteristics of the cases detected in the epidemiologic studies and complete the description of the emergence of bacteriuria in the general population. An analysis of the natural history of recurrent infection in the population was recently published [5].

Role of Lysosomes in the Pathogenesis of Splanchnic Ischemia Shock in Cats

Abstract: Splanchnic arterial occlusion (SAO) for 2 hours followed by release of the occlusion in cats produced a lethal shock state characterized by cardiovascular collapse. Release of the occlusion resulted in a 45% fall in mean arterial blood pressure within 15 minutes; postrelease survival of these animals was 46 minutes. The plasma of cats with SAO shock exhibited a 3- to 4-fold increase in activities of the lysosomal enzymes β-glucuronidase and cathepsin, accompanied by accumulation of a myocardial depressant factor. Plasma from cats treated with methylprednisolone (20 mg/kg) prior to occlusion did not have significant levels of myocardial depressant factor nor significant increases in plasma lysosomal enzyme activity. Furthermore, the fall in mean arterial blood pressure in steroid-treated animals was significantly smaller when the occlusion was released and postrelease survival time was significantly longer. Pancreatic lysosomes from cats with SAO exhibited a marked increase in fragility as indicated by a reduction in total lysosomal enzyme activity and an increase in the percent of free enzyme activity, compared to lysosomes from cats with sham SAO or steroid-treated cats. These data indicate that the biochemical and hemodynamic alterations present in SAO-induced shock may be related to the disruption of pancreatic lysosomes and that glucocorticoids can markedly alter the course of this shock, possibly by decreasing the sensitivity of pancreatic lysosomes to splanchnic ischemia.

Linear Response of a Metal to an External Charge Distribution

Abstract: The linear response of a metal to an external-charge distribution is computed in the random-phase approximation (RPA). The surface is assumed to be perfectly reflecting and the boundary-value problem is solved by a symmetric continuation of the metal. The linear response of the metal to an external point charge is found to be described by a function $\ensuremath{ u}$ which depends only on the properties of the surface and the metal. From $\ensuremath{ u}$, we compute a surface function $S$ which fully describes the electrical properties outside the metal. Graphs of $S$ as a function of the parallel momentum $K$ are given for the quantum-mechanical RPA and for the quasiclassical RPA which is obtained by neglecting interference effects. The potential and normal fields outside the metal are well approximated by the analytic expressions which are obtained when $S(K)$ is replaced by ${e}^{\ensuremath{-}\ensuremath{\lambda}K}$, where $\ensuremath{\lambda}$ has the physical meaning of a screening length.

Human choroid plexus: Morphologic and histochemical alterations with age

Abstract: The choroid plexus was studied in 217 necropsy specimens from human beings two months to 94 years of age. With advancing age, the height of the cuboidal epithelial cell gradually decreases, many becoming squamous. Cytoplasmic vacuoles increase in number. Focal stratification is not an artefact, and is evidence of proliferation. The proliferated cells eventually desquamate, becoming round, large and foamy as they accumulate intracytoplasmic lipid and degenerate. The findings indicate that cellular desquamation occurs during life. Filaments of mucopolysac-charides are common in the choroid plexus of old people. Stromal alterations associated with increased age consist of a gradual increase in the amount of connective tissue, in number of meningocytes and psammoma bodies, and in severity of hyalinization, fibrosis, fragmentation of connective tissue fibers and calcification. Most psammoma bodies are found in the glomus choroideum. Non-lamellar calcific foci occur mainly in the matrix of the choroidal villi and fronds. Formation of psammoma bodies is associated closely with the meningocytic whorls. Lipids, mucopolysaccharides and mucins are identified in both epithelial and stromal components of the choroid plexus. Lipids appear in the stroma later in life. It is suggested that lipid in the cytoplasm of desquamated choroidal eipthelial cells is one source of lipids in the cerebrospinal fluid.

Adrenocortical function in the hamster. Sex differences and effects of gonadal hormones.

Abstract: Adrenal weight is greater in the male hamster than in the female, a sex difference opposite that in other rodent species. Prepuberal gonadectomy results in decreased adrenal weight in both sexes; testosterone or estradiol replacement restores the weight to the control level. Sex differences in adrenocortical function accompany those in weight, with the male having higher plasma corticosteroids, greater steroid output in vitro by adrenal slices or homogenates, and greater steroid secretion in vivo than the female.Hepatic metabolism of cortisol in vitro is greater and biological half-life (t½) of cortisol is shorter in the male. Prepuberal orchiectomy results in decreased plasma corticosteroids at rest and after ether stress, decreased steroid output in vitro by adrenal slices and homogenates, and decreased steroid secretion in vivo compared with the intact male. Hepatic metabolism of cortisol in vitro is decreased and the t½ of cortisol is prolonged after orchiectomy. Testosterone replacement reverses or p...

Medullary cells of origin of vagal cardioinhibitory fibers in the pigeon. I. Anatomical studies of peripheral vagus nerve and the dorsal motor nucleus.

Abstract: The organization to the dorsal motor nucleus of the vagus in the pigeon was studied in an attempt to localize the cells of origin of vagal cardioinhibitory fibers. The course of the peripheral vagus nerve is described form the intracranial rootlets to abdominal levels. Using combined microdissection and electrical stimulation techniques, the branches which mediate cardiodeceleration are found to arise from a localized segment of the vagal trunk below the thoracic ganglion, and above the level where the left and right vagi join. The dorsal motor nucleus, its cytoarchitectonic divisions, and other structures connected with vagal rootlets are described on the basis of normal material. Utilizing the above findings a series of retrograde degeneration experiments was undertaken. The distribution of chromatolytic neurons following cervical vagotomy was described to indicate the extent of the dorsal motor nucleus. Selective nerve sections (abdominal vagotomy, cardiac vagotomy, recurrent laryngeal neurotomy, or pneumonectomy) then indicated that there is an incompletely inverted topographic representation of the vagus nerve in the dorsal motor nucleus, including a representation of the recurrent laryngeal nerve; no evidence was found for the existence of a nucleus ambiguus. The vagal cardioinhibitory fibers appear to be represented throughout the rostral half of the nucleus, but they are most concentrated in the ventral portion of the nucleus, approximately three-quarters of a millimeter rostral to the obex.