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Biomedical subjects

R A Andersen

Publications and source records attributed to R A Andersen.

At least 127 records · Page 7Linked to original sources
PubMed1987

Effects of air-curing environment on alkaloid-derived nitrosamines in burley tobacco.

Levels of nitrite and pyridine alkaloid-derived total tobacco-specific nitrosamines (TSNA) were significantly higher in tobacco leaf (normal or late harvest) air-cured at 32 degrees C/83% relative humidity (RH) than in more moderate environments, i.e., 15 degrees C/50% RH and 24 degrees C/70% RH. These constituents increased appreciably from day 10 to day 21 of the cure. The near-concurrent appearances of maximal total contents of TSNA [sum of N'-nitrosonornicotine (NNN), N'-nitrosoanatabine (NAT), N'-nitrosoanabasine (NAB) and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone) (NNK)] and nitrite supports the concept that nitrite is a limiting and proximal precursor of total TSNA during the curing of tobacco. During a long curing period (50 days) at 32 degrees C/83% RH, nicotine and anatabine contents decreased, but TSNA contents increased in leaves of all harvest dates and stalk positions. These results support the view that nicotine and anatabine are precursors of TSNA. Measurement of nitrite and individual alkaloids during post-harvest processing of tobacco leaf may provide an index of the potential accumulation of alkaloid-derived nitrosamines.

Agriculture↗
PubMed1986

Different patterns of corticopontine projections from separate cortical fields within the inferior parietal lobule and dorsal prelunate gyrus of the macaque.

Corticopontine projection patterns were studied after injections of an 3H-leucine and 3H-proline mixture into each of four distinct cortical fields within the inferior parietal lobule and dorsal prelunate gyrus. Different preferential patterns of pontine labeling were observed for each of the four cortical areas studied. Multiple injections across the dorsal aspect of the prelunate gyrus (area DP) yielded scattered patches of label limited to the dorsolateral pontine nuclear region. A single injection within the lateral intraparietal area (area LIP), located in the caudal portion of the lateral bank of the intraparietal sulcus resulted in a series of labeled patches across the dorsal tier of cells stretching across the dorsal portions of the dorsolateral, peduncular and dorsal pontine nuclei. Injection of the cortex on the caudal aspect of the inferior parietal convexity (area 7a) produced multiple patches of label along the lateral margin of the ventral, lateral, and dorsolateral nuclei. Injection of area 7b resulted in label along the lateral aspects of the ventral, lateral and dorsolateral nuclei, as seen with area 7a injections, as well as additional label in the ventromedial portions of the ventral, peduncular and paramedian pontine nuclei. These results provide supporting anatomic evidence for the functional subdivision of the inferior parietal lobule and dorsal aspect of the prelunate gyrus and provide new information about the organization of cortical projections to the primate pontine nuclei.

Animals↗
PubMed1986

Use of ethopropazine and BW 284C51 as selective inhibitors for cholinesterases from various species.

Both inhibitors tested were still able to depress the cholinesterase (ChE) for which it is not selective (BW 284C51 for pseudo ChE, ethopropazine for the true ChE) provided the concentration was high (greater than 10(-2) M). BW 284C51 totally depressed the true ChE activity from bovine erythrocytes at a concentration of 10(-6) M. This inhibitor concentration gave no depression of pseudo ChE activity from horse serum. Ethopropazine totally depressed the pseudo ChE activity from horse serum at a concentration of 5 X 10(-5) M. The true ChE was not inhibited at this concentration. For true ChE from bovine erythrocytes and pseudo ChE from horse serum BW 284C51 and ethopropazine therefore certainly have a potential as selective ChE inhibitors. Ethopropazine at a concentration of 5 X 10(-6) M completely inhibited the pseudo ChE activity in rat plasma and cortex without affecting true ChE activity. BW 284C51 at a concentration of 10(-6) M gave a total depression of the true ChE activity in these preparations. In rat plasma, however, a considerable part of the pseudo ChE activity was depressed at this concentration.

Aniline Compounds↗
PubMed1986

Antheraxanthin, a light harvesting carotenoid found in a chromophyte alga.

The pigments of the chromophyte freshwater alga, Chrysophaera magna Belcher were analyzed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) to reveal the presence of chlorophylls a and c, beta-carotene, fucoxanthin, and antheraxanthin. The presence of antheraxanthin was verified by comparison of TLC R(F) values, HPLC retention times, and absorption features to those of authentic, synthetic antheraxanthin. Antheraxanthin accounted for about 15% of the total carotenoid content of C. magna. The molar ratio of the major carotenoids was antheraxanthin:fucoxanthin:beta-carotene, 1:2.3:3.3. The whole-cell absorption spectrum revealed a broad band between 470 and 520 nanometers which was attributed to fucoxanthin and antheraxanthin in vivo. Upon extraction in hydrocarbon, this broad absorption region was lost. The in vivo fluorescence excitation spectrum for 680 nm emission revealed the energy transfer activities and light harvesting roles of chlorophylls a and c, and fucoxanthin. In addition, an excitation band was resolved at 487 nanometers which could be attributed only to antheraxanthin. Comparison of whole-cell fluorescence excitation spectra of C. magna with the diatom Phaeodactylum tricornutum, which possesses fucoxanthin but not antheraxanthin, supports the assignment of the 487 nm band to antheraxanthin. This is the first report of a photosynthetic light harvesting function of the xanthophyll, antheraxanthin. This carotenoid broadens the absorption cross-section for photosynthesis in C. magna and extends light harvesting into the green portion of the spectrum.

Journal Article↗
PubMed1985

The thalamic relations of the caudal inferior parietal lobule and the lateral prefrontal cortex in monkeys: divergent cortical projections from cell clusters in the medial pulvinar nucleus.

The thalamic relations of the caudal inferior parietal lobule and the dorsolateral prefrontal cortex in monkeys have been investigated with both anterograde and retrograde neuroanatomical tracing techniques. The results of these experiments indicate that the medial pulvinar nucleus (Pul.m.) is the principal thalamic relay to the gyral surface of the caudal inferior parietal lobule (area 7a). Within the Pul.m. there are two or three disklike aggregates of neurons which project to area 7a; these disklike neuronal aggregates are oriented from dorsomedial to ventrolateral and extend over most of the rostrocaudal extent of the nucleus. Within these disks there are rodlike clusters of neurons which are elongated in the rostrocaudal dimension of the thalamus, and which project in a topographically ordered manner to area 7a. Thus, the more rostrally located neurons within the Pul.m. disks project to more rostral parts of area 7a and, conversely, the more caudally located neurons project to the caudal part of this cortical field. Similarly, the medial part of each disk projects to the lateral part of area 7a while the laterally placed neurons project to the medial part of the cortical field. In addition to its input from the Pul.m., area 7a is also reciprocally connected with the magnocellular division of the nucleus ventralis anterior, with the nuclei which abut upon the medullary capsule of the laterodorsal nucleus, and with the suprageniculate nucleus and the nucleus limitans. The cortex on the lateral bank of the intraparietal sulcus (the so-called lateral intraparietal area, LIP) projects principally to the lateral pulvinar nucleus (Pul.l) of the thalamus rather than to Pul.m. Area LIP has been found to project to the pregeniculate nucleus, the zona incerta, the anterior pretectal nucleus, and the superior colliculus. Area 7a projects to none of these structures, but it does project to the posterior pretectal nucleus. The thalamic relations of the neighboring cortical regions, such as the prelunate gyrus and area 7b, are also distinct from those of area 7a. It thus seems that the prelunate gyrus is primarily interconnected with the Pul.l., and area 7b with the oral pulvinar nucleus. Taken together these different subcortical relationships provide further evidence for the view that the caudal inferior parietal lobule is not a homogeneous cortical area, but is composed of a number of subsidiary fields. The projection from the Pul.m. to the lateral prefrontal cortex arises from disklike aggregates of neurons, similar in their orientation to the neuronal disks that project to area 7a.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Encoding of spatial location by posterior parietal neurons.

The cortex of the inferior parietal lobule in primates is important for spatial perception and spatially oriented behavior. Recordings of single neurons in this area in behaving monkeys showed that the visual sensitivity of the retinotopic receptive fields changes systematically with the angle of gaze. The activity of many of the neurons can be largely described by the product of a gain factor that is a function of the eye position and the response profile of the visual receptive field. This operation produces an eye position-dependent tuning for locations in head-centered coordinate space.

Animals↗
PubMed1985

Callosal and prefrontal associational projecting cell populations in area 7A of the macaque monkey: a study using retrogradely transported fluorescent dyes.

The spatial interrelationship of neurons in area 7a in the inferior parietal lobule that project through the corpus callosum to the corresponding field in the contralateral hemisphere or to the ipsilateral prefrontal cortex has been analyzed in macaque monkeys by using double-labeling procedures with retrogradely transported fluorescent dyes. The populations of callosal and associational projecting neurons have similar laminar distributions and are topographically intermingled. Less than 1% of the neurons were double-labeled, thus suggesting that the two populations are largely separate. Two-dimensional reconstructions of the distribution of labeled cells made on flattened reconstructions of the inferior parietal lobule revealed that the areal distribution of the two cortico-cortical output arrays is complex. Although each pattern of labeling showed some discontinuities in density, there was no obvious periodicity within or between the spatial distributions of the two projecting populations. It was consistently observed that the cortex of the lateral wall of the intraparietal sulcus, adjacent to area 7a, projects more heavily to the prefrontal cortex than does area 7a itself.

Animals↗
PubMed1985

Visual thresholds for shearing motion in monkey and man.

A reaction-time task was used to determine the visual motion thresholds in humans and in macaque monkeys for sinusoidally modulated shearing motion of a random dot display. It was found that humans and macaques were very similar in their spatial frequency sensitivity profiles for shearing motion. These profiles were of a U-shape for all human and monkey subjects tested. Temporal frequency, varied over a wide range, did not influence the shape of the spatial frequency sensitivity curve, but only the threshold amplitudes. The above results held both for single and multiple temporal cycles of shearing motion. Previous reports for the human, using these same shearing motion stimuli, indicated no increase in threshold at the lower spatial frequencies. The reason for this discrepancy is that thresholds in the previous studies were not determined at a low enough spatial frequency to see clearly this increase in thresholds. Because of the striking similarity of the data for man and macaque, it is suggested that similar neural mechanisms underly the shearing motion sensitivity of the two species.

Animals↗
PubMed1985

Accumulation of 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone in alkaloid genotypes of burley tobacco during postharvest processing: comparisons with N'-nitrosonornicotine and probable nitrosamine precursors.

Recent work showed that 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was present in some cured tobacco and was more carcinogenic than N'-nitrosonornicotine (NNN). In the present investigation, the concentration relationships of NNK, NNN, and their probable precursors, i.e., nitrite, nitrate, and alkaloids, were determined: (a) after the growth of Ky 14 burley tobacco under different shade conditions followed by air curing; and (b) during preparation of air-cured and homogenized-leaf-cured (HLC) burley tobaccos from conventionally grown tobaccos of different alkaloid genotypes. A capillary gas chromatography-nitrogen-phosphorus detector procedure was developed and utilized for quantitative determinations of NNK and NNN. NNK contents ranged from 0.2 to 0.5 micrograms/g in air-cured Ky 14 tobacco lamina from leaves grown under 0 to 65% shade (100, 65, and 35% of natural daylight). The highest NNK concentrations were from 45% shade-grown lamina from lower leaf positions on stalks. Concentrations of NNK did not correlate significantly with those of either nitrate or total alkaloids calculated over all shade treatments and stalk positions. During HLC tobacco processing, the following significant correlations of NNK with precursor content changes were found for each of four burley alkaloid genotypes calculated over the four successive stages of processing: NNN (r = 1.0); and nitrate (r = -0.9). NNK also correlated negatively with nicotine concentration changes (r = -0.9) in the low-alkaloid and high-alkaloid isolines during processing. After a 20-h incubation period under aerobic conditions followed by a 1-h standing period without aeration, substantial increases of NNK were observed in each burley line. The increased NNK contents ranged from 9-fold for the low-alkaloid isoline to 99-fold for the nornicotine-converter line. Increases in NNK content (27 to 69%) also occurred during the air drying stage; further increases occurred during a 15-month storage period at ambient conditions. After the HLC process and prolonged storage, maximal NNK contents were observed in each tobacco genotype in the following order of increasing NNK content: Ky 14 cultivar, 79 micrograms/g; low-alkaloid line, 80 micrograms/g; nornicotine converter line, 102 micrograms/g; and high-alkaloid line, 177 micrograms/g. At the beginning of a controlled environmental storage period used for high-alkaloid and low-alkaloid isoline air-cured and HLC tobaccos, NNK contents correlated with nitrite (r = 1.0) and nitrate (r = -0.9) calculated over the two curing regimens.(ABSTRACT TRUNCATED AT 400 WORDS)

Alkaloids↗
PubMed1984

Distribution and transplacental transfer of paraquat in rats and guinea-pigs.

Radiolabelled paraquat (bis-N-(14C)methyl-4,4'-bipyridylium chloride) was administered intravenously to pregnant rats and guinea-pigs and examined by the whole body autoradiography method. Male rats were examined for comparison with the same method. The results showed that the radiolabelled compound was rapidly distributed throughout the tissues, with the highest concentrations in the cartilage, kidney, lung, spleen, salivary gland and skin. High concentrations were found in the placenta and throughout the fetuses 0.5 hr after the administration.

Animals↗
PubMed1984

Biochemical characteristics of rat superoxide dismutase and the effect caused by paraquat injection on the enzyme activity in various tissues.

Rat superoxide dismutase (SOD) prepared from the rat was not found by sedimentation in sucrose gradients or isoelectric focusing to consist of more than one molecular form. On polyacrylamide gels, however, one major and one minor activity form could be demonstrated. The sedimentation constant and corresponding molecular weight of the enzyme determined by sucrose gradient centrifugation were found to be 3.0 +/- 0.36 (34,300 +/- 4023) and the isoelectric point 4.75. These characteristics were not found to differ for SOD prepared from different rat tissues and were not affected by a single dose of 40 mg/kg paraquat given subcutaneously 48 hr prior to sacrifice. The protein contents of various tissues based on both wet and dry weight were not found to deviate from normal during 5 days following a single exposure of paraquat up to 40 mg/kg. Experiments based on SOD activity measurements in different tissues as a function of time following single exposures of paraquat, revealed the presence of a very high induction capability of the SOD protein in the rat. The results have been correlated to autoradiographic studies. A correlation between SOD induction and tissues showing high paraquat retention could be demonstrated. This was especially expressed for the lung. Due to difference in the induction pattern following exposure to 5 and 10 mg/kg paraquat, respectively, it has been suggested that the ability of the rat to bear paraquat loads might be related to the SOD induction capability in various tissues.

Animals↗
PubMed1984

Post-harvest treatment and the accumulation of nitrite and N'-nitrosonornicotine in burley tobacco.

Concentrations (dry-weight basis) of nitrate, nitrite and N'-nitrosonornicotine (NNN) in Burley tobacco were determined during successive processing stages of experimental homogenized-leaf-cured (HLC) material, after conventional air curing and during prolonged storage ('ageing') of HLC and air-cured tobaccos. During homogenized leaf curing, less than 6 micrograms/g nitrite-N and less than 10 micrograms/g NNN were found in tobacco frozen immediately after aerobic incubation of homogenates at 40 degrees C for 0, 4, 8, 20 and 25 h. Up to 550 micrograms/g nitrite-N and 850 micrograms/g NNN occurred in tobacco incubated similarly for 20 h, then allowed to stand 1 h without aeration. Samples of two genetic Burley lines of high and low alkaloid content were similarly incubated, allowed to stand 1 h, dried and 'aged' for up to one year in partially anaerobic environments. NNN contents were positively correlated with 'at-harvest' alkaloid content, and NNN increased at each subsequent stage of processing, reaching a maximum of 1 800 micrograms/g in the high-alkaloid line after one year of 'ageing'. Small increases of NNN that reached a final concentration of 50 micrograms/g occurred in tobaccos that were air-cured, then 'aged'.

Nitrites↗
PubMed1983

Contractions in bronchial musculature of rabbit and man in response to various drugs.

1. The contractile behaviour of rabbit and man bronchial musculature has been tested in response to some commonly used substrates for cholinesterase, histamine and adrenaline by the kymograph technique. 2. The sensitivity of the smooth bronchial musculature from both rabbit and man was found to be highest for acetylcholine and acetyl-beta-methylcholine (6.3 X 10(-8) M) and lowest for butyrylcholine (6.3 X 10(-6) M). 3. The smooth bronchial musculature of man was slightly more sensitive to histamine and adrenaline than that of the rabbit. 4. The results indicate that the contractile behaviour in the smooth bronchial musculature of rabbit and man is remarkably similar.

Acetylcholine↗
PubMed1983

The effect of dark adaptation on some transmitter functions in the visual pathways.

1. The high affinity uptake of GABA in optic tectum was found to be about 40% higher in frogs kept in complete darkness for 3 weeks, than in frogs in the normal condition. 2. No effects were obtained in uptake of glutamate and activity of GAD in the optic tectum. 3. The isoenzyme composition of cholinesterases in frog optic tectum and retina was not affected by dark adaptation either.

Acetylcholinesterase↗
PubMed1983

The influence of the angle of gaze upon the excitability of the light-sensitive neurons of the posterior parietal cortex.

The responses of parietal visual neurons are markedly increased during attentive fixation, as compared to those evoked in relaxed wakefulness, an effect specific for directed attention and unrelated to putative differences in the general level of arousal. Those responses are also strongly influenced by the angle of gaze, an effect observed only during directed visual attention. The change in response is smoothly graded along a meridian for about one-half the neuron population; the average spatial gradient from maximum to minimum is 78% response for a 20 degrees shift in eye position. No lateral preference was observed. For the remaining half, responses were either maximal or minimal for fixations dead ahead, and changes occurred with deviations in any direction. Angle of gaze effects were observed for neurons with foveal as well as eccentrically located receptive fields, all of which were organized in retinotopic not spatial coordinates. Control experiments showed that the effect was not produced by changes in visual background with changes in the angle of gaze, nor to changes in fixation distance, nor to variations in the intensity of stimuli viewed from different angles. The effect depends upon the position of the eye in the orbit, but is unlikely due to a direct central action of changes in nonretinal orbital afferent activity at different angles of gaze, for the effect was rarely observed with changes in the angle of gaze during relaxed wakefulness without directed visual attention. The evidence supports the interpretation that the effect is produced by a central influence of the systems controlling directed visual attention and the angle of gaze upon those linking the retinae to the parietal lobe.

Animals↗
PubMed1981

The influence of attentive fixation upon the excitability of the light-sensitive neurons of the posterior parietal cortex.

We describe the effect of behavioral state upon the excitability of light-sensitive (Ls) neurons of the inferior parietal lobule, area 7a, studied in waking monkeys. The responses of parietal LS neurons to visual stimuli are facilitated during the state of attentive fixation of a target light as compared to their responses to physically and retinotopically identical test stimuli delivered during the eye pauses of alert wakefulness. Seventy percent of the neurons tested (n = 55) showed significant increments in responses in the state of attentive fixation; the median value of the increments was 3.5 times. Only 4 of the 55 cells examined completely showed the reverse relation. Three sets of control experiments were done. The facilitation occurred when the responses evoked during the trials of a reaction task with attentive fixation of a target were compared with those evoked by identical stimuli delivered to the same retinotopic locations at the end of each intertrial interval: the facilitation of attentive fixation is not due to a shift in the general level of arousal. The facilitation occurred when the animal maintained attentive fixation of a spot of the tangent screen without a target light or when an additional light mimicking the target light was presented along with testing stimuli in the state of alert wakefulness without attentive fixation: the facilitation is not produced by a sensory-sensory interaction between target and testing lights. Finally, the facilitation was observed whether or not the test stimuli were behaviorally relevant. We conclude that the act of attentive fixation exerts a specific and powerful effect upon the excitability of the neural systems linking the retinae and the inferior parietal lobule and that the facilitation plays an important role in visually guided behavior.

Animals↗