Cascading influence of inorganic nitrogen sources on DOM production, composition, lability and microbial community structure in the open ocean.

Nitrogen frequently limits oceanic photosynthesis and the availability of inorganic nitrogen sources in the surface oceans is shifting with global change. We evaluated the potential for abrupt increases in inorganic N sources to induce cascading effects on dissolved organic matter (DOM) and microbial communities in the surface ocean. We collected water from 5 m depth in the central North Pacific and amended duplicate 20 liter polycarbonate carboys with nitrate or ammonium, tracking planktonic carbon fixation, DOM production, DOM composition and microbial community structure responses over 1 week relative to controls. Both nitrogen sources stimulated bulk phytoplankton, bacterial and DOM production and enriched Synechococcus and Flavobacteriaceae; ammonium enriched for oligotrophic Actinobacteria OM1 and Gammaproteobacteria KI89A clades while nitrate enriched Gammaproteobacteria SAR86, SAR92 and OM60 clades. DOM resulting from both N enrichments was more labile and stimulated growth of copiotrophic Gammaproteobacteria (Alteromonadaceae and Oceanospirillaceae) and Alphaproteobacteria (Rhodobacteraceae and Hyphomonadaceae) in weeklong dark incubations relative to controls. Our study illustrates how nitrogen pulses may have direct and cascading effects on DOM composition and microbial community dynamics in the open ocean.

Refractory dissolved organic nitrogen accumulation in high-elevation lakes.

The role of dissolved organic matter (DOM) as either a sink for inorganic nutrients or an additional nutrient source is an often-neglected component of nutrient budgets in aquatic environments. Here, we examined the role of DOM in reactive nitrogen (N) storage in Sierra Nevada (California, USA) lakes where atmospheric deposition of N has shifted the lakes toward seasonal phosphorus (P)-limitation. Nuclear magnetic resonance (NMR) spectroscopy and isotope analyses performed on DOM isolated from Lake Tahoe reveal the accumulation of refractory proteinaceous material with a 100-200-year residence time. In contrast, smaller lakes in the same watershed contain DOM with typical terrestrial characteristics, indicating that proteins in Lake Tahoe are autochthonously produced. These data support the role of DOM as a possible sink for reactive N in these lake ecosystems and identify a potential role for DOM in affecting the inorganic nutrient stoichiometry of these environments.

Long time-constant behavior of the oculomotor plant in barbiturate-anesthetized primate.

The mechanics of the extraocular muscles and orbital tissue ("oculomotor plant") can be approximated by a small number of viscoelastic (Voigt) elements in series. Recent analysis of the eye's return from displacement in lightly anesthetized rhesus monkeys has suggested a four-element plant model with time constants (TCs) of approximately 0.01, 0.1, 1, and 10 s. To demonstrate directly the presence of long (1,10 s) TC elements and to assess their contribution quantitatively, horizontal eye displacement was induced in Cynomolgus monkeys under deep barbiturate anesthesia that prevented interference from spontaneous eye movements. The displacement was maintained for either a prolonged (30 s) or brief (0.2 s) period before release. Return to resting position took 20-30 s after prolonged displacement but only 1-2 s after brief displacement, consistent with the presence of long TC elements that would only be substantially stretched in the former condition. Quantitative fitting of the release curves after prolonged displacement indicated that the two long TC elements contribute a substantial proportion (approximately 30%) of the total plant compliance. A model based on the estimated compliance values is shown to account quantitatively both for our release data and for Goldstein and Robinson's data on hysteresis of ocular motoneuron firing rates measured after centripetal saccades following prolonged eccentric fixation. Long time-constant elements in the plant thus make a substantial contribution to some types of eye movement, and their inclusion in plant models can help interpret the firing patterns of single units in the oculomotor system.

Effects of electrode penetrations into the abducens nucleus of the monkey: eye movement recordings and histopathological evaluation of the nuclei and lateral rectus muscles.

Two adult rhesus monkeys that had undergone 2 years of electrode penetrations into their abducens and vestibular nuclei, for chronic eye movement studies, were examined histologically. An analysis of their VIth nucleus neurons and lateral rectus muscles revealed the following. Twenty-two percent of the large neurons (approximately 30 microm in diameter), on average, were missing and extensive neuropil disruption and gliosis was evident in the experimental side abducens nuclei as compared with the control side in each animal. While the lateral rectus muscles showed small, but inconsistent, changes in total fiber number, the muscle fiber diameters were altered, leading to a more homogenous muscle and making the typical orbital and global subdivisions of the muscle less distinct. Eye movement records from before and after the electrophysiological studies were comparable. We discuss how the complex architecture of the extraocular muscles as well as the possibility of polyneuronal innervation of single muscle fibers could explain our results.

ANCA-associated vasculitis in Greek siblings with chronic exposure to silica.

We present the case of two siblings with similar environmental exposure to silica. Both of them developed perinuclear antineutrophil cytoplasmic antibody (p-ANCA)-associated vasculitis with pulmonary-renal syndrome. p-ANCAs were present with antimyeloperoxidase specificity on capture enzyme-linked immunosorbent assay. Treatment with corticosteroids and cyclophosphamide resulted in resolution of the clinical picture. Chronic exposure to silica is the leading environmental factor associated with ANCA-positive vasculitis. Several clusters of systemic vasculitis have been described. Positive and negative human leukocyte antigens (HLA) have been reported in systemic vasculitis. Affected brothers in our case shared one parental HLA haplotype. To the best of our knowledge, this is the first report of a family cluster of silica-induced, ANCA-associated systemic vasculitis with members sharing some of their HLA antigens.

Colorectal cancer in Russian-speaking Jewish emigrés: community-based screening.

OBJECTIVES: Colorectal cancer (CRC) screening by fecal occult blood testing and flexible sigmoidoscopy is recommended by many authorities for those older than age 50. Ashkenazi Jews have been shown to have a higher level of CRC and polyps than the general population. A subset of Ashkenazi Jews, Russian-speaking Jewish immigrants to the United States (RJIs), have not been studied extensively for CRC and may have additional risk factors not found in other Ashkenazi populations. METHODS: A retrospective chart review was undertaken of fecal occult blood tests, endoscopy reports, and pathology reports of 132 RJIs and 124 non-RJI controls over age 50 between 1987 and 1999 at the Jewish Hospital of Cincinnati Medical Outpatient Clinic. RESULTS: Mean ages at the time of diagnosis or flexible sigmoidoscopy were 68 yr for RJIs and 66 yr for the non-RJI patients. Of the RJI patients, 38.7% had positive findings: 37 (28.0%) with lesions < 2 cm, five (3.8%) with lesions > 2 cm, and nine (6.8%) with CRC. Of the non-RJI control group patients, 16.9% had positive findings: 16 (12.9%) with lesions < 2 cm, three (2.4%) with lesions > 2 cm, and two (1.6%) with CRC. Age- and sex-matched statistical analysis revealed significantly greater CRC and significantly more polyps > 2 cm for the RJI patients (p < 0.003). This is higher than in other studies of Ashkenazis, which show a 2.3% incidence, and in statistics from the National Cancer Institute, which reveal a national CRC incidence rate for those over age 65 to be 0.30%. CONCLUSIONS: RJIs in our study have polyps > 2 cm and CRC at a rate of 10.6%, as compared with 4.0% for in-clinic controls and a national average of 0.30% for patients over age 65. This suggests a need for more aggressive screening of this patient population for CRC.

Motoneurons of the lateral and medial rectus extraocular muscles in squirrel monkey and cat.

The goal of this study was to examine and compare the number and size of motoneurons in the cat and squirrel monkey abducens nucleus. We also examined medial rectus muscle motoneuron compartmentalization in the squirrel monkey oculomotor nucleus and compared those cells to abducens nucleus motoneurons. Retrograde labeling of the motoneurons, using cholera toxin conjugate of horseradish peroxidase (CTHRP) injected into cat and monkey lateral or medial rectus muscles, was observed after 24 h. The CTHRP was histochemically localized with tetramethylbenzidine. The slide-mounted sections were analyzed using a computerized imaging system. Cat abducens nucleus motoneurons showed a wide range of cell sizes (26.0-66.0 microm, mean = 37.2 +/- 6.2 microm), four or more dendrites per cell and an average of 1,418 cells within a relatively loosely packed nucleus. Squirrel monkey abducens nucleus motoneurons were significantly smaller than those in the cat with a narrower range of cell sizes (20.0-44.0 microm, mean = 31.7 +/- 3.8 microm), four or more dendrites per cell and an average of 2,473 cells densely packed within the nucleus. Squirrel monkey medial rectus muscle motoneurons were organized into MRa, MRb and MRc subgroups. MRa motoneurons comprise the primary innervation for the medial rectus muscle and were similar in size to abducens nucleus motoneurons while the MRc subgroup cells were significantly smaller in size. Similar relationships among medial rectus motoneurons have been seen in rhesus monkeys. The relationship of these anatomical findings to previous physiological results regarding the generation of extraocular muscle force in the squirrel monkey is discussed.

Functional anatomy of the hypoglossal innervated muscles of the rat tongue: a model for elongation and protrusion of the mammalian tongue.

This anatomical investigation in the rat was designed to illustrate the detailed organization of the tongue's muscles and their innervation in order to elucidate the actions of the muscles of the higher mammalian tongue and thereby clarify the protrusor subdivision of the hypoglossal-tongue complex. The hypoglossal innervated, extrinsic styloglossus, hyoglossus, and genioglossus and the intrinsic transversus, verticalis and longitudinalis linguae muscles were observed by microdissection and analysis of serial transverse-sections of the tongue. Sihler's staining technique was applied to whole rat tongues to demonstrate the hypoglossal nerve branching patterns. Dissections of the tongue demonstrate the angles at which the extrinsic muscles act on the base of the tongue. The Sihler stained hypoglossal nerves demonstrate branches to the styloglossus and hyoglossus emanating from its lateral division while branches to the genioglossus muscle exit from its medial division. The largest portions of both XIIth nerve divisions can be seen to enter the body of the tongue to innervate the intrinsic muscles. Transverse sections of the tongue demonstrate the organization of the intrinsic muscle fibers of the tongue. Longitudinal muscle fibers run along the entire circumference of the tongue. Alternating sheets of transverse lingual and vertical lingual muscles can be observed to insert into the circumference of the tongue. Most importantly in clarifying tongue protrusion, we demonstrate the transversus muscle fibers enveloping the most superior and inferior portions of the longitudinalis muscles. Longitudinal muscle fascicles are completely encircled and thus are likely to be compressed by transverse muscle fascicles resulting in elongation of the tongue. We discuss our findings in relation to biomechanical studies, that describe the tongue as a muscular hydrostat and thereby define the "elongation-protrusion apparatus" of the mammalian tongue. In so doing, we clarify the functional organization of the hypoglossal-tongue complex.

Contractile properties of the tongue's genioglossus muscle and motor units in the rat.

The contractile characteristics of individual mammalian tongue muscles have rarely been investigated, in contrast to spinal cord-innervated and extraocular muscles. Therefore, whole muscle and motor unit contractile forces, plus muscle fiber types, were studied in the genioglossus, the major protrusor muscle, of the rat tongue. The muscle, exclusively composed of fast-contracting units, could be activated from rostroventral hypoglossal nucleus sites only. The following figures represent the means of the contractile measures. Whole muscle twitch tension was 7.02 g, contraction time was 14.22 ms, fusion frequency was 104 Hz, maximum tetanic tension was 37.22 g, and fatigue index was 0.72. Single motor unit twitch tension was 45. 9 mg, contraction time was 11.7 ms, fusion frequency was 94.8 Hz, maximum tetanic tension was 241.95 mg, and fatigue index was 0.68. The genioglossus muscle appeared qualitatively similar to the rat styloglossus muscle, one of the two major retractor muscles of the tongue. The delineation of motor unit contractile characteristics in tongue muscle is important in our understanding of the control of tongue movement.

Hemodynamic and electrophysiologic effects of acute chocolate ingestion in young adults.

The purpose of this study was to determine the hemodynamic and electrophysiologic effects of acute chocolate, and hence theobromine, ingestion on the hearts of young adults. Theobromine was not found to have any cardiovascular effects on subjects in this study.

Whole-muscle and motor-unit contractile properties of the styloglossus muscle in rat.

Investigations of whole muscle and motor-unit contractile properties have provided valuable information for our understanding of the spinal cord and extraocular motor systems. However, no previous investigation has examined these properties in an isolated tongue muscle. The purpose of this study was to determine the contractile properties and muscle fiber types of the rat styloglossus muscle. The styloglossus is one of three extrinsic tongue muscles and serves to retract the tongue within the oral cavity. Adult male Sprague-Dawley rats (n = 19) were used in these experiments. The contractile characteristics of the whole styloglossus muscle (n = 9) were measured in response to stimulation of the hypoglossal nerve branch to the muscle. The average twitch tension produced was 3.30 g with a mean twitch contraction time of 13.81 ms. The mean maximum tetanic tension was 19.66 g and occurred at or near the fusion frequency, which averaged 109 Hz. The styloglossus muscle was resistant to fatigue [fatigue index (F. I.) = 0.76]. In separate experiments (n = 7), the contractile characteristics of 37 single motor units were measured in response to extracellular stimulation of hypoglossal motoneurons. The twitch tension generated by styloglossus motor units averaged 35.7 mg, and the mean twitch contraction time was 12.46 ms. The mean fusion frequency was 92 Hz. Maximum tetanic tension averaged 177.8 mg. Styloglossus single motor units were resistant to fatigue (F. I. = 0.74). The sites of stimulation that yielded a contractile response in the styloglossus muscle were consistent with the location of the styloglossus motoneuron pool reported in earlier anatomy studies. Muscle fiber typing was determined in three animals based on the myofibrillar ATPase reaction at pH 9.8, 4.6, and 4.3. The styloglossus muscle was composed of approximately 99% type IIA fibers with a few scattered type I fibers present in the study sample. On the basis of the combined findings of the physiology and histochemistry experiments, the styloglossus muscle appeared to be a homogeneous muscle composed almost exclusively of fast, fatigue-resistant motor units. These properties of the styloglossus muscle and its motor units were compared with findings in other rat skeletal muscles.

Organization of motoneurons in the dorsal hypoglossal nucleus that innervate the retrusor muscles of the tongue in the rat.

This anatomical investigation was prompted by the incomplete knowledge of the myotopic organization of the dorsal subdivison of the hypoglossal nucleus. Intrinsic muscle motoneurons were not segregated and labeled previously with regard to the lateral division of the hypoglossal nerve. Also, motoneuron number and cell size, in relation to the individual retrusor tongue musculature, were rarely addressed previously. Retrograde labeling ofretrusor muscle motoneurons in the dorsal subdivision of the rat hypoglossal nucleus was done. Cholera toxin conjugate horseradish peroxidase (CTHRP) was injected into the retrusor tongue muscles with only the lateral division of the hypoglossal nerve intact. The dorsal subdivision of the hypoglossal nucleus contained approximately 800 motoneurons ranging in cell body size from 19 to 41 microm. When either the styloglossus, hyoglossus, superior longitudinal, or inferior longitudinal muscle was isolated and injected with CTHRP, a separate motoneuron pool for each muscle was seen. The extrinsic muscle motoneurons, styloglossus and hyoglossus, were found rostrolateral and caudolateral respectively. In contrast, the intrinsic superior and inferior longitudinal muscle motoneurons were found more central and medial in the nucleus. Extrinsic muscle motoneurons were larger (approximately 30 microm) than intrinsic muscle motoneurons (approximately 26 microm; P < .0001). Intrinsic muscle motoneurons account for a great majority of the motoneurons in the dorsal aspect of the hypoglossal nucleus and their axons have been shown to be contained in the lateral (retrusor) division of the hypoglossal nerve. This study revealed the myotopic organization of the retrusor subdivision of the rat hypoglossal nucleus.

Extraocular motor unit and whole-muscle responses in the lateral rectus muscle of the squirrel monkey.

Because primate studies provide data for the current experimental models of the human oculomotor system, we investigated the relationship of lateral rectus muscle motoneuron firing to muscle unit contractile characteristics in the squirrel monkey. Also examined was the correlation of whole-muscle contractile force with the degree of evoked eye displacement. A force transducer was used to record lateral rectus whole-muscle or muscle unit contraction in response to abducens whole-nerve stimulation or stimulation of single abducens motoneurons or axons. Horizontal eye displacement was recorded using a magnetic search coil. (1) Motor units could be categorized based on contraction speed (fusion frequency) and fatigue. (2) The kt value (change in motoneuronal firing necessary to increase motor unit force by 1.0 mg) of the units correlated with maximum tetanic tension. (3) There was some tendency for maximum tetanic tension of this unit population to separate into three groups. (4) At a constant frequency of 100 Hz, 95% of the motor units demonstrated significantly different force levels dependent on immediately previous stimulation history (hysteresis). (5) A mean force change of 0.32 gm/ degrees and a mean frequency change of 4.7 Hz/ degrees of eye displacement were observed in response to whole-nerve stimulation. These quantitative data provide the first contractile measures of primate extraocular motor units. Models of eye movement dynamics may need to consider the nonlinear transformations observed between stimulation rate and muscle tension as well as the probability that as few as two to three motor units can deviate the eye 1 degrees.

Acute effects of caffeine ingestion on signal-averaged electrocardiograms.

BACKGROUND: Although moderate caffeine ingestion has not been shown to be arrhythmogenic, caffeine toxicity can cause severe cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. Atrial fibrillation and ventricular tachycardia have been associated with prolongation of P-wave and QRS complex durations on signal-averaged electrocardiograms. This study investigated acute effects of caffeine ingestion on signal-averaged P-wave and QRS complexes. METHODS AND RESULTS: Signal-averaged electrocardiograms were obtained from 12 normal subjects (6 men, 6 women; ages 21 to 26 years) before and after ingestion of caffeine (5 mg/kg body weight) or placebo in a randomized, double-blind, crossover fashion. Electrocardiograms for signal averaging were recorded from electrodes left in a constant location. After bandpass filtering (30 to 300 Hz) and amplification, signals were sampled over 7.2 minutes at 2000 Hz. Signal-averaged P-wave and QRS complex durations did not significantly change after placebo ingestion. After caffeine ingestion QRS duration prolonged in 9 of 11 subjects at 90 minutes (mean +/- SEM = 0.8+/-0.3 ms, P< .02) and in 8 of 9 after 3 hours (1.1+/-0.2 ms, P< .001). No significant change in P-wave duration or heart rate was found after caffeine ingestion at any test interval. Average caffeine level in saliva 90 minutes after ingestion was 6.6+/-1.6 (SD) microg/dL. CONCLUSIONS: Although probably not arrhythmogenic in normal subjects, moderate caffeine ingestion does produce a small but statistically significant prolongation of signal-averaged QRS complexes. Further prolongation caused by excessive caffeine intake may be a factor in the genesis of arrhythmias associated with caffeine toxicity.

Cardiac teratogenicity of trichloroethylene metabolites.

OBJECTIVES: The hypothesis of this study was that metabolites of trichloroethylene (TCE), dichloroethylene (DCE) and related compounds were responsible for fetal cardiac teratogenic effects seen when TCE or DCE is consumed by pregnant rats during organogenesis. Identification of teratogenic metabolites would allow more accurate assessment of environmental contaminants and public health risks from contaminated water or possibly municipal water supplies which, when chlorinated, may produce these potentially dangerous chemicals. BACKGROUND: Human epidemiologic studies and previous teratogenic studies using chick embryos and fetal rats have shown an increased incidence of congenital cardiac lesions in animals exposed to TCE and DCE. METHODS: Metabolites and compounds studied in drinking water exposure included: trichloroacetic acid (TCAA), monochloroacetic acid (MCAA), trichloroethanol (TCEth), carboxy methylcystine (CMC), trichloroacetaldehyde (TCAld), dichloroacetaldehyde (DCAld), and dichlorovinyl cystine (DCVC). Compounds were administered to pregnant rats during fetal heart development. RESULTS: Fetuses of rats receiving 2,730 ppm TCAA in drinking water were the only group that demonstrated a significant increase in cardiac defects (10.53%) compared with controls (2.15%) on a per fetus basis (p = 0.0001, Fischer's exact test), and a per litter basis (p = 0.0004, Wilcoxon and p = 0.0015, exact permutation tests). Trichloroacetic acid also demonstrated an increased number of implantation and resorption sites (p < 0.05) over controls. Other maternal and fetal variables showed no statistically significant differences between treated and untreated groups. CONCLUSIONS: Of the metabolites tested, only TCAA appeared to be a specific cardiac teratogen in the fetus when imbibed by the maternal rat.

A review: trichloroethylene metabolites: potential cardiac teratogens.

This review is a a series of the authors' studies designed to test the hypothesis that administration of trichloroethylene (TCE), dichloroethylene (DCE), their metabolites, and related compounds are responsible for fetal cardiac teratogenesis when given to pregnant rats during organogenesis. Identification of teratogenic compounds will allow more accurate assessment of environmental contaminants and public health risks. Epidemiologic studies and previous teratogenic studies using chick embryos and fetal rats have reported an increased number of congenital cardiac defects when exposed to TCE or DCE during fetal development. Metabolites of TCE and DCE studied in the drinking-water exposure study include trichloroacetic acid TCAA), monochloroacetic acid, trichloroethanol, carboxymethylcysteine, trichloroacetaldehyde, dichloroacetaldehyde, and dichlorovinyl cysteine. Varying doses of each were given in drinking water to pregnant rats during the period of fetal heart development. Rats receiving 2730 ppm TCAA in drinking water were the only metabolite group demonstrating a significant increase in the number of cardiac defects in fetuses on a per-litter basis (p = 0.0004 Wilcoxon test and p =0.0015 exact permutation test). Maternal and fetal variables showed no statistically significant differences between treated and untreated groups. When treated with TCAA the increased cardiac defects, as compared to controls, do not preclude the involvement of other metabolites as cardiac teratogens, but indicates TCAA as a specific cardiac teratogen. Further studies of drinking-water exposure and potential mechanisms of action on the developing heart are proceeding.

Summation of extraocular motor unit tensions in the lateral rectus muscle of the cat.

Contractile measures on 67 single muscle units in the cat lateral rectus muscle were made in response to motoneuron stimulation. Simultaneous activation of four to five additional units, using muscle nerve stimulation, allowed an examination of unit force summation. Linear force addition was found in 73% of the units, while 25% added only about half of their twitch force to the twitch force of the nerve-activated units. "Nonadditive" units had significantly weaker twitch tensions than the units which added linearly. Lengthening or shortening the whole muscle, from maximal isometric settings, reduced whole muscle twitch tension as well as muscle unit tension. Injury to the lateral rectus muscle did not significantly alter whole muscle tension. These findings suggest that the known serial and branching arrangement of these muscle fibers, as well as the complex interfiber matrix, may help explain the force reduction in some muscle units and the whole muscle's resistance to insult.