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Biomedical subjects

M Chen

Publications and source records attributed to M Chen.

At least 847 records · Page 47Linked to original sources
PubMed1988

Development of a smoking prevention mass media program using diagnostic and formative research.

The process of developing a mass media campaign to prevent smoking among adolescents is described in detail. This campaign supplements a school smoking prevention program and shares educational objectives with the school program but is otherwise independent. It comprises various television and radio 30- and 60-sec "spot" messages. The campaign development process includes identifying educational objectives and strategies for appealing to young people; conducting diagnostic surveys and focus groups to determine target audience interests and perceptions about smoking and media content; suggesting approaches to producers to create preliminary television and radio messages for testing; conducting formative pretests with target groups to select optimal messages and suggest improvements to those messages; producing final messages for media presentation; and developing a media exposure plan to place messages in local media at optimal times for reception by target audiences. The media campaign is being evaluated in a 5-year project with 5,500 adolescents in four communities to determine the additional effect of mass media over a school program alone in preventing smoking.

Adolescent↗
PubMed1988

Anaerobic biodegradation of polychlorinated biphenyls by bacteria from Hudson River sediments.

Anaerobic biodegradation of monochlorobiphenyls; a tetrachlorobiphenyl; Aroclor 1221, a polychlorinated biphenyl (PCB) mixture; and sediment PCBs was investigated by using mixed bacterial populations from Hudson River sediments obtained by PCB enrichment. When the bacteria were incubated with Aroclor 1221, the disappearance of congeners was in general inversely related to GC retention time and thus indirectly to the octanol/water partition coefficient. When incubated with 14C-labeled monochlorobiphenyls, 14CO2 was detected, but methane was not. Radioactivity was also found in the cell material and the aqueous fraction. 2,4,2',4'-Tetrachlorobiphenyl produced little evidence of biodegradation or reductive dechlorination. Inoculation of anaerobic sediments from the Hudson River with the mixed population produced a marked decrease in sediment PCBs, whereas uninoculated sediments were observed to have little change. This decrease was also related to the partition coefficient.

Anaerobiosis↗
PubMed1988

Visual split brain and monocular deprivation in kittens: differentiation between the effects of disuse and of binocular competition in visual cortex cells.

To differentiate between the resulting effect of disuse, developmentally induced by deprivation, and the binocular competition effect on cortical cells, visual split brain was performed concurrently with monocular deprivation in kittens. In the experienced hemisphere of the split brain deprived cats (ipsilaterally to the non-deprived eye), there were twice as many visually responsive cortical cells than found in their inexperienced hemisphere (ipsilaterally to the deprived eye); however, these cells were equal in number to that found in the split brain controls. In the monocularly deprived control cats a relation of 3.2 was found between cells driven by the non-deprived and the deprived eye. Visual disuse, therefore, resulting from monocular deprivation, affects cortical cells under complete absence of binocular competition but is greatly enhanced by the latter.

Animals↗
PubMed1988

Interleukin 1 prevents loss of corticotropic responsiveness to beta-adrenergic stimulation in vitro.

Corticotropin (ACTH) secretion by the anterior pituitary is stimulated by catecholamines in vivo and in vitro. The nature of the response in vivo is controversial but appears to be mediated by beta-adrenergic receptors, whereas the response is dependent on alpha-adrenergic receptors in cultured anterior pituitary cells. In the present studies, by using a superfusion technique, we demonstrate that catecholamine stimulation of ACTH release from rat anterior pituitaries changes with time from a predominantly beta-adrenergic-mediated event to a predominantly alpha-adrenergic-mediated event. From 0 to 2 hr after initiating the superfusion, release of ACTH from anterior pituitary glands is stimulated up to 2.4-fold by the beta-adrenergic agonist l-isoproterenol. However, the ACTH secretory response to the alpha-adrenergic agonist l-phenylephrine is less than or equal to 5% of that to l-isoproterenol during the same time period. Beginning 2 hr after the start of the superfusion, the responsiveness to the beta-adrenergic agonist declines, and the response to the alpha-adrenergic agonist increases until, 10 hr after removal, greater than 95% of the catecholamine-inducible ACTH release is mediated by an alpha-adrenergic pathway. The addition of interleukin 1 alone to the medium from the beginning of the superfusion does not modify basal ACTH secretion rates and does not affect the acquisition of the response to phenylephrine. However, the presence of interleukin 1 does allow the maintenance of the full ACTH secretory response to isoproterenol. This effect of interleukin 1 is reversed by an interleukin 1 antagonist. These observations suggest an additional way in which immune regulators might interact with the hypothalamic-pituitary-adrenal axis.

Adrenergic alpha-Agonists↗
PubMed1988

Long-term sensitization in Aplysia increases the number of presynaptic contacts onto the identified gill motor neuron L7.

We have used the gill and siphon withdrawal reflex of Aplysia to study the morphological basis of the persistent synaptic plasticity that underlies long-term sensitization. One critical locus for storage of the memory for sensitization is the set of monosynaptic connections between identified siphon sensory neurons and gill and siphon motor neurons. To complement previous morphological studies of the presynaptic terminals of identified sensory neurons, we examined the effects of long-term sensitization on the structure of an identified postsynaptic target--the gill motor neuron L7. We found an increase in the frequency, size, and vesicle complement of presynaptic contacts onto L7 processes in sensitized compared to control animals. Combined, these data indicate a striking increase in the percentage of the surface area of L7 that is occupied by synaptic contacts after long-term training. These results are consistent with our observations that sensitization produces an increase in the synapses that the sensory neurons make on their target cells and provide additional support for the hypothesis that changes in synapse number may represent a mechanism underlying long-term memory.

Animals↗
PubMed1988

Long-term memory in Aplysia modulates the total number of varicosities of single identified sensory neurons.

The morphological consequences of long-term habituation and sensitization of the gill withdrawal reflex in Aplysia california were explored by examining the total number of presynaptic varicosities of single identified sensory neurons (a critical site of plasticity for the biochemical and biophysical changes that underlie both types of learning) in control and behaviorally trained animals. Sensory neurons from habituated animals had 35% fewer synaptic varicosities than did sensory neurons from control animals. In contrast, sensory neurons from sensitized animals had twice as many varicosities per sensory neuron compared to controls, as well as enlarged neuropil arbors. These changes suggest that modulation of synapse number may play a role in the maintenance of long-term memory.

Animals↗
PubMed1988

Efficacy of S26308 against guinea pig cytomegalovirus infection.

Prophylactic use of antiviral agents against cytomegalovirus (CMV) is particularly indicated for the immunocompromised host because morbidity and mortality due to CMV occur most frequently following immunosuppression. We have evaluated the new Riker compound S26308 for its therapeutic and prophylactic antiviral activity against CMV in guinea pigs. The efficacy of the compound was assessed in vitro in guinea pig embryo cells and in vivo in both immunocompetent and immunocompromised guinea pigs. Guinea pig CMV plaque formation was reduced only in cells treated with S26308 prior to virus infection. The antiviral activity remained even when the compound was removed after virus absorption and was due to neither virus destruction nor inhibition of cell growth. The frequency of viremia was reduced in guinea pigs for which S26308 therapy was initiated 24 h prior to virus inoculation compared with sham-treated animals. This reduction in the frequency of viremia did not prevent virus spread to target tissues but did result in a reduction of the severity of CMV-induced disease in immunocompromised guinea pigs. Low levels of interferon were detected in supernatants of S26308-treated cells, and interferon was detected in the serum of guinea pigs given S26308. These results indicate that S26308 can induce interferon and reduce CMV infectivity in vivo and in vitro when used prophylactically. This antiviral activity, although modest, was accompanied by beneficial effects on CMV-induced morbidity and mortality. Prophylactic use of S26308 in combination with other therapeutic agents may be a useful strategy against CMV infections.

Aminoquinolines↗
PubMed1988

Sequence and genetic organization of adenovirus type 35 early region 3.

The early transcription region 3 (E3) of group B adenovirus type 35 (Ad35), a serotype isolated primarily from patients with acquired immunodeficiency syndrome and other immunodeficiency disorders, has been partially sequenced. We had previously identified an Ad35 29-kilodalton (kDa) early glycoprotein which, analogous to group C Ad2 E3-19K, associated with major histocompatibility complex class I antigens in the endoplasmic reticulum of infected cells. The open reading frame (ORF) of the Ad35 29-kDa protein has now been identified within a 2-kilobase-pair cloned Ad35 E3 fragment. The predicted amino acid sequence was very similar to that of group B Ad3 E3-19K. In contrast, homology between the Ad35 and Ad2 glycoproteins was limited to five cysteines in identical positions and a 20-amino-acid region proximal to the transmembrane domain. In addition, 20.3- and 20.6-kDa ORFs have been identified downstream from the ORF for the Ad35 glycoprotein. Analogous 20-kDa ORFs are present in the Ad3 E3 region but are not present in Ad2 and Ad5. In contrast, the region analogous to an Ad2 11.6-kDa ORF, which is 9 kDa in size in Ad3, was absent from the expected position within the Ad35 E3 region. Because the E3 region is likely to play an important role in the interaction between virus and host, analysis of the function of the Ad35 E3 proteins should further our understanding of adenovirus pathogenesis.

Adenoviruses, Human↗
PubMed1988

Naloxone attenuates development of hypertension in two-kidney one-clip Goldblatt rats.

The present experiments were designed to determine if an opiate antagonist affects blood pressure in two-kidney one-clip Goldblatt rats. Male Sprague-Dawley rats were divided into three groups. Group 1 received an infusion of saline intraperitoneally via an osmotic pump and left renal artery constriction (RAC). In group 2, rats were treated the same as group 1, except that they received an intraperitoneal infusion of naloxone (100 micrograms/h). Group 3 received the same infusion of naloxone without RAC. Naloxone-infused Goldblatt rats showed a significantly lower systolic blood pressure (SBP) than saline-infused Goldblatt rats (132 +/- 7 vs. 160 +/- 9 mmHg at day 14), but a higher SBP than control (132 +/- 7 vs. 106 +/- 1 mmHg). Infusion of naloxone did not significantly change SBP in normotensive rats. Renal renin activity in the clipped kidney was higher than in the nonclipped kidney in groups 1 and 2. Plasma renin activity (PRA) in both groups of Goldblatt rats was higher than in group 3, but no significant difference was found between the two groups of Goldblatt rats (groups 1 and 2). Naloxone (1.5 microM) did not affect the basal secretion of renin by isolated cortical slices from untreated rats. The present data demonstrate that naloxone significantly attenuates the development of hypertension in two-kidney one-clip rats. The attenuation of blood pressure was not associated with the changes in PRA, renal renin activity, or plasma aldosterone concentrations. The data support the hypothesis that the endogenous opioid system may be involved in the development of renovascular hypertension.

Aldosterone↗
PubMed1988

Insulin resistance and beta-cell dysfunction in aging: the importance of dietary carbohydrate.

Aging is associated with a progressive decrease in glucose tolerance. This decrease is associated with insulin resistance and beta-cell dysfunction. This study was performed to evaluate the possible role of dietary factors in the glucose intolerance of aging. Two groups of men were studied: one young (Y; n = 8; age range, 18-36 yr) and one elderly (E; n = 10; age range, 65-82 yr). Frequently sampled iv glucose tolerance tests were performed in random order: 1) during ad libitum home dietary conditions; 2) after a 3- to 5-day regimen of very high (85%) carbohydrate intake; and 3) after a 3- to 5-day regimen of low (30%) carbohydrate intake (Y only). From the frequently sampled iv glucose tolerance test data, we calculated the glucose disappearance rate (Kg) and metabolic parameters according to the minimal model method, including the insulin sensitivity index (S1) and the first and second phase beta-cell responsivity to glucose (phi 1 and phi 2). The elderly men, while eating an ad libitum diet, were less tolerant to glucose than the young [mean Kg: E = 1.5 +/- 0.2% (+/- SE) min-1; Y = 2.3 +/- 0.3% min-1; P less than 0.025], had relative insulin resistance (mean Si: Y = 6.1 +/- 1.1; E = 2.4 +/- 0.7 min-1 10(-4)/(microU/mL) [0.85 +/- 0.15 vs. 0.33 +/- 0.10 min-1 10(-4)/(pmol/L)]; P less than 0.01), and lesser second phase beta-cell responsiveness to glucose (mean phi 2: Y = 18.5 +/- 3.6; E = 8.7 +/- 2.7 (microU/mL).min-2/(mg/dL) [2390 +/- 465 vs. 1120 +/- 349 (pmol/L).min-2/(mmol/L)]; P less than 0.05). A maximum improvement in Kg and S1 occurred at 41% carbohydrate feeding in the young men, whereas in the elderly men there was a significant increase in both of these parameters while eating the very high (85%) carbohydrate diet. Thus, the difference in glucose tolerance between groups was corrected by the very high carbohydrate diet (mean Kg: Y = 2.2 +/- 0.2%; E = 2.0 +/- 0.3%/min; P greater than 0.05), as was the age-related difference in insulin sensitivity (mean S1: Y = 5.6 +/- 1.2; E = 4.4 +/- 1.3 min-1 10(-4)/(microU/mL) [0.78 +/- 0.17 vs. 0.61 +/- 0.18 min-1 10(-4)/(pmol/L)]; P greater than 0.5).(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1988

Modulation of rat granulocyte traffic by a surface active agent in vitro and bleomycin injury.

Pluronic F68 (F68) is a nonionic surfactant which has been reported to inhibit the in vitro adherence and migration of polymorphonuclear leukocytes (PMN) obtained from some species. We demonstrated similar effects on PMN obtained from rats, with diminished adherence to nylon wool and diminished chemotaxis toward zymosan-activated serum. We then examined the in vivo effects of 12-hr F68 infusion on the injury induced by intratracheal bleomycin instillation (ITB) in rats. When sacrificed 24 hr following injury, rats demonstrated neutrophilia, neutrophil-prominent lung lavage cellularity, and increased lung weights. F68 decreased lavage leukocyte counts and lung weight gain in ITB-injured animals. Lung weights of ITB-injured animals correlated (r = 0.81, P less than 0.001) with logarithmic values of lavage PMN. F68 also enhanced neutrophilia and decreased spleen weight gain in injured animals. The acute effects of F68 on circulating leukocyte counts, osmolality, and total complement were also examined. The data demonstrate that F68 can affect PMN traffic both in vitro and in vivo. The data also confirm the prominence of PMN in lavage fluid early in ITB injury, and suggest that an influx of relatively few PMN is associated with lung weight gain in this model.

Animals↗
PubMed1988

Temperature response of Antarctic cryptoendolithic photosynthetic microorganisms.

Growth responses to temperatures between 12.5 [degrees] C and 25 degrees C were determined for five photosynthetic microorganisms isolated from the Ross Desert cryptoendolithic community. Among eukaryotic algae, two strains of Trebouxia sp. have an upper temperature limit of 20 degrees C, and two strains of Hemichloris antarctica of 25 degrees C. The cyanobacterium Chroococcidiopsis sp., in contrast, grows at temperatures above 25 degrees C. These and earlier studies suggest that the eukaryotic algae of the Antarctic cryptoendolithic community have an upper temperature limit near 25 degrees C.

Antarctic Regions↗
PubMed1988

Morphological basis of short-term habituation in Aplysia.

We have explored the morphological basis of the synaptic depression that underlies short-term habituation of the gill-withdrawal reflex in Aplysia by examining the fine structure of the presynaptic terminals of identified sensory neurons--a critical site of plasticity for the biochemical and biophysical changes that underlie this elementary form of learning. The structure of sensory neuron synapses from control (unstimulated) cells was compared with that of sensory neuron synapses from cells in which synaptic transmission had been depressed by repeated activation. We focused our analysis, as we had in an earlier study of long-term memory (Bailey and Chen, 1983), on the morphology of active zones at sensory neuron synapses. We found that both the incidence and size of serially reconstructed active zones were not changed in cells exposed to short-term habituation. This contrasts sharply with the reduction in both the frequency and surface area of sensory neuron active zones that accompanies long-term habituation, and suggests that modulation of active zone number and size may be an anatomical correlate that lies in the long-term domain. A quantitative analysis of the relationship between the active zone and nearby vesicle populations revealed a possible morphological substrate for the homosynaptic depression that underlies short-term habituation. Habituation leads to a depletion of synaptic vesicles immediately adjacent to the active zone. The ratio of this readily releasable pool of vesicles to the total population of vesicles associated with the active zone is 28% for control terminals, but only 11.5% for habituated terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Split brain acutely and chronically induced in cats causes ipsilateral eye dominance and reduced excitability of cells in the visual cortex.

The ocular dominance distribution and the excitability level of single cells in the callosal projection zone of the visual cortex (area 17-18 boundary), were electrophysiologically studied in acute and in chronic cats following simultaneous (OCX-CCX) and separate transections of the optic chiasm (OCX) and corpus callosum (CCX). Except for a few cells (3.4%) in the acute OCX-CCX cats showing an interhemispheric transfer, as expressed by their contralateral eye response, all other cells had a monocular response to the ipsilateral eye. An ipsilateral monocular response was found in the chronic OCX-CCX cats, even for long survival periods (17.0 months). The result for the OCX cats was similar, as indicated by the major ipsilateral response and the small proportion of cells showing an interhemispheric transfer. No improvement was found with postoperative time; acute OCX cats had 5.0% cells with contralateral input and 1-7 months chronic cats had 1.7-6.5% of these cells. These animals have thus split brain from point of view of the visual cortex; each hemisphere is therefore independent of the other one as far as neuronal functions are concerned. A remarkable reduction in binocularity was found following callosal transection (CCX) both in acute (41.4% binocularly driven cells) and in 3-39 months chronic cats (45.5% cells), in comparison to the control cats (74.2%). This indicates that elimination of the corpus callosum as itself enhances the binocularity diminution in split brain cats. The reduction found in visual responsiveness in our split brain cats (total: 63.2% unresponsive cells), is attributed to the summation of the individual effects of the optic chiasm and corpus callosum transections. A consistent tendency was found in the long chronic in comparison to the acute OCX-CCX, OCX, and CCX cats for a decrease in the responsiveness level with survival time; however, the short chronic OCX-CCX and CCX cats had the maximal proportion of unresponsive cells. It was concluded that the split brain induced in adult cats has a permanent effect on interhemispheric transfer to visual cortex cells. The absence of interhemispheric interaction under these conditions is not compensated by either transfer through anterior parts of the corpus callosum or through other commissures.

Animals↗
PubMed1988

A novel method for measurement of triglyceride lipase activity: suitable for microgram and nanogram quantities of tissue.

The measurement of triglyceride lipase activity in microgram and nanogram quantities of tissue is reported. The method involves quantitation of glycerol released from a triglyceride substrate, which is shown to provide a value of approximately one-third of that obtained by quantitation of free fatty acid release. Influences on glycerol release, including pH optimum, NaCl inhibition, and activation by serum and heparin are characterized. Two separate assays are described for the measurement of glycerol that yield identical results with nanogram quantities of tissue. The advantage of one assay is its simplicity, while the advantage of the other is that it can be adjusted to measure very small tissue samples (nanogram) with the use of microanalytical procedures (i.e., enzymatic amplification of the NAD+ product of glycerol analysis). Sensitivity of the method is demonstrated by the analysis of triglyceride lipase activity in nanogram samples of single soleus muscle fibers. Measurement of picomole quantities of glycerol produced by lipase activity in single muscle fibers represents at least a 1,000-fold increase in sensitivity compared to currently available methods.

Animals↗