Showing papers by "University of Arizona published in 1993"

Dynamics of the hippocampal ensemble code for space

Abstract: Ensemble recordings of 73 to 148 rat hippocampal neurons were used to predict accurately the animals' movement through their environment, which confirms that the hippocampus transmits an ensemble code for location. In a novel space, the ensemble code was initially less robust but improved rapidly with exploration. During this period, the activity of many inhibitory cells was suppressed, which suggests that new spatial information creates conditions in the hippocampal circuitry that are conducive to the synaptic modification presumed to be involved in learning. Development of a new population code for a novel environment did not substantially alter the code for a familiar one, which suggests that the interference between the two spatial representations was very small. The parallel recording methods outlined here make possible the study of the dynamics of neuronal interactions during unique behavioral events.

Comparison of a Standard Regimen (CHOP) with Three Intensive Chemotherapy Regimens for Advanced Non-Hodgkin's Lymphoma

Abstract: Background CHOP is a first-generation, combination-chemotherapy regimen consisting of cyclophosphamide, doxorubicin, vincristine, and prednisone that has cured approximately 30 percent of patients with advanced stages of intermediate-grade or high-grade non-Hodgkin's lymphoma in national cooperative-group trials. However, studies at single institutions have suggested that 55 to 65 percent of such patients might be cured by third-generation regimens such as ones consisting of low-dose methotrexate with leucovorin rescue, bleomycin, doxorubicin, cyclophosphamide, vincristine, and dexamethasone (m-BACOD); prednisone, doxorubicin, cyclophosphamide, and etoposide, followed by cytarabine, bleomycin, vincristine, and methotrexate with leucovorin rescue (ProMACE-CytaBOM); and methotrexate with leucovorin rescue, doxorubicin, cyclophosphamide, vincristine, prednisone, and bleomycin (MACOP-B). Methods To make a valid comparison of these regimens, the Southwest Oncology Group and the Eastern Cooperative Oncology Gro...

Suffix arrays: a new method for on-line string searches

Abstract: A new and conceptually simple data structure, called a suffix array, for on-line string searches is introduced in this paper. Constructing and querying suffix arrays is reduced to a sort and search paradigm that employs novel algorithms. The main advantage of suffix arrays over suffix trees is that, in practice, they use three to five times less space. From a complexity standpoint, suffix arrays permit on-line string searches of the type, “Is W a substring of A?” to be answered in time $O(P + \log N)$, where P is the length of W and N is the length of A, which is competitive with (and in some cases slightly better than) suffix trees. The only drawback is that in those instances where the underlying alphabet is finite and small, suffix trees can be constructed in $O(N)$ time in the worst case, versus $O(N\log N)$ time for suffix arrays. However, an augmented algorithm is given that, regardless of the alphabet size, constructs suffix arrays in $O(N)$expected time, albeit with lesser space efficiency. It is ...

Social Construction of Target Populations: Implications for Politics and Policy.

Abstract: We argue that the social construction of target populations is an important, albeit overlooked, political phenomenon that should take its place in the study of public policy by political scientists. The theory contends that social constructions influence the policy agenda and the selection of policy tools, as well as the rationales that legitimate policy choices. Constructions become embedded in policy as messages that are absorbed by citizens and affect their orientations and participation. The theory is important because it helps explain why some groups are advantaged more than others independently of traditional notions of political power and how policy designs reinforce or alter such advantages. An understanding of social constructions of target populations augments conventional hypotheses about the dynamics of policy change, the determination of beneficiaries and losers, the reasons for differing levels and types of participation among target groups, and the role of policy in democracy.

Shuffled complex evolution approach for effective and efficient global minimization

Abstract: The degree of difficulty in solving a global optimization problem is in general dependent on the dimensionality of the problem and certain characteristics of the objective function. This paper discusses five of these characteristics and presents a strategy for function optimization called the shuffled complex evolution (SCE) method, which promises to be robust, effective, and efficient for a broad class of problems. The SCE method is based on a synthesis of four concepts that have proved successful for global optimization: (a) combination of probabilistic and deterministic approaches; (b) clustering; (c) systematic evolution of a complex of points spanning the space, in the direction of global improvement; and (d) competitive evolution. Two algorithms based on the SCE method are presented. These algorithms are tested by running 100 randomly initiated trials on eight test problems of differing difficulty. The performance of the two algorithms is compared to that of the controlled random search CRS2 method presented by Price (1983, 1987) and to a multistart algorithm based on the simplex method presented by Nelder and Mead (1965).

The Place of Story in the Study of Teaching and Teacher Education

Abstract: ith increasing frequency over the past several years we, as members of a community of investigator-practitioners, have been telling stories about teaching and teacher education rather than simply reporting correlation coefficients or generating lists of findings. This trend has been upsetting to some who mourn the loss of quantitative precision and, they would argue, scientific rigor. For many of us, however, these stories capture, more than scores or mathematical formulae ever can, the richness and indeterminacy of our experiences as teachers and the complexity of our understandings of what teaching is and how others can be prepared to engage in this profession. It is not altogether surprising, then, that this attraction to stories has evolved into an explicit attempt to use the literatures on "story" or "narrative" to define both the method and the object of inquiry in teaching and teacher education. Story has become, in other words, more than simply a rhetorical device for expressing sentiments about teachers or candidates for the teaching profession. It is now, rather, a central focus for conducting research in the field. We are certainly not alone in giving formal attention to story. This term, like others from linguistics and literary theory (e.g., discourse, text, deconstruction), has caught on with considerable enthusiasm throughout the intellectual world and is beginning to appear in widely different contexts. In psychology, for example, Bruner (1985) speaks of a narrative mode of thought, and Sarbin (1986) proposes story as a "root metaphor" for the study of human conduct. Within education, scholars such as Cole and Knowles (1992); Clandinin and Connelly (1992); Elbaz (1991); Grossman (1987); Gudmundsdottir (1991); Hollingsworth (in press); and Richert (1990) have recently made story a central element in their analyses of teachers' knowledge. As Mitchell (1981) noted as early as 1981, "The study of narrative is no longer the province of literary specialists or folklorists ... but has now become a positive source of insight for all branches of human and natural science" (p. ix). Anyone with even a passing familiarity with the literatures on story soon realizes, however, that these are quite turbulent intellectual waters and quickly abandons the expectation of safe passage toward the resolution, once and for all, of the many puzzles and dilemmas we face in advancing our knowledge of teaching. Much needs to be learned about the nature of story and its value to our common enterprise, and about the wide range of purposes, approaches, and claims made by those who have adopted story as a central analytical framework. What does story capture and what does it leave out? How does this notion fit within the emerging sense of the nature of teaching and what it means to educate teachers? These and many other critical questions need to be faced if story is to become more than a loose metaphor for everything from a paradigm or worldview to a technique for bringing home a point in a lecture on a Thursday afternoon. Given both the excitement story has generated and the many issues this movement has brought to the fore, it seems appropriate to provide an analysis of the place of story in the study of teaching and teacher education. My overall purpose here is to begin the process of clarifying the arguments, mapping the intellectual terrain, and casting light on the major issues we need to consider in incorporating story into our research activities. I have no illusions that this discus-

The Genesis and Collapse of Third Millennium North Mesopotamian Civilization

Abstract: Archaeological and soil-stratigraphic data define the origin, growth, and collapse of Subir, the third millennium rain-fed agriculture civilization of northern Mesopotamia on the Habur Plains of Syria. At 2200 B. C., a marked increase in aridity and wind circulation, subsequent to a volcanic eruption, induced a considerable degradation of land-use conditions. After four centuries of urban life, this abrupt climatic change evidently caused abandonment of Tell Leilan, regional desertion, and collapse of the Akkadian empire based in southern Mesopotamia. Synchronous collapse in adjacent regions suggests that the impact of the abrupt climatic change was extensive.

The abundance and significance of a class of large, transparent organic particles in the ocean

Abstract: Polysaccharide-specific staining techniques reveal the existence and high abundance of a class of large, discrete, transparent particles in seawater and diatom cultures formed from dissolved exopolymers exuded by phytoplankton and bacteria. Transparent exopolymer particles (TEP), ranged from 28 to 5000 particles ml−1 and 3 to 100s μm in longest dimension at five coastal stations off California. A high percentage of seemingly free-living bacteria (28–68%) were attached to these transparent sheets and films, suggesting that they may alter the distributions and microenvironments of marine microbes in nature. Preliminary coagulation experiments demonstrated that TEP are major agents in the aggregation of diatoms and in the formation of marine snow. The existence of microbial exudates acting as large, discrete particles, rather than as dissolved molecules or as coating on other particles, suggests that the transformation of dissolved organic matter into particulate form in the sea can occur via a rapid abiotic pathway as well as through conventional microbial uptake. The existence of these particles has far reaching implications for food web structure, microbial processes, carbon cycling and particulate flux in the ocean.

Fire history and climate change in giant sequoia groves.

Abstract: Fire scars in giant sequoia [Sequoiadendron giganteum (Lindley) Buchholz] were used to reconstruct the spatial and temporal pattern of surface fires that burned episodically through five groves during the past 2000 years. Comparisons with independent dendroclimatic reconstructions indicate that regionally synchronous fire occurrence was inversely related to yearly fluctuations in precipitation and directly related to decadal-to-centennial variations in temperature. Frequent small fires occurred during a warm period from about A.D. 1000 to 1300, and less frequent but more widespread fires occurred during cooler periods from about A.D. 500 to 1000 and after A.D. 1300. Regionally synchronous fire histories demonstrate the importance of climate in maintaining nonequilibrium conditions.

Spatial selectivity of unit activity in the hippocampal granular layer.

Abstract: Single neuron activity was recorded in the granular layer of the fascia dentata in freely moving rats, while the animals performed a spatial “working” memory task on an eight-arm maze. Using recording methods that facilitate detection of units with low discharge rates, it was found that the majority (88%) of cells in this layer have mean rates below 0.5 Hz, with a minimum of 0.01 Hz or less. The remaining recorded cells exhibited characteristics typical of the theta interneurons found throughout the hippocampus. Based on several criteria including relative proportion and the relation of their evoked discharges to the population spike elicited by perforant path stimulation, it was concluded that the low-rate cells correspond to granule cells. Granule cells exhibited clear spatially and directionally selective discharge that was at least as selective as that of a sample of CA3 pyramidal cells recorded under the same conditions. Granule cells had significantly smaller place fields than pyramidal cells, and tended to have more discontiguous subfields. There was no spatial correlation among simultaneously recorded adjacent granule cells. Granule cells also exhibited burst discharges reminiscent of complex spikes from pyramidal cells while the animals sat quietly; however, the spike duration of granule cells was significantly shorter than CA3 pyramidal cell spike durations. Under conditions of environmental stability, granule cell place fields were stable for at least several days. Following occasional maze rotations relative to the (somewhat impoverished) visual stimuli of the recording room, granule cell place fields were maintained relative to the distal spatial cues; however, frequent rotations of the maze sometimes resulted in a shift in the reference frame to the maze itself. These observations indicate that granule cells of the fascia dentata provide their CA3 targets with a high degree of spatial information, in the form of a sparsely coded, distributed representation.

Stress protection of transgenic tobacco by production of the osmolyte mannitol.

Abstract: The accumulation of sugar alcohols and other low molecular weight metabolites such as proline and glycine-betaine is a widespread response that may protect against environmental stress that occurs in a diverse range of organisms. Transgenic tobacco plants that synthesize and accumulate the sugar alcohol mannitol were engineered by introduction of a bacterial gene that encodes mannitol 1 -phosphate dehydrogenase. Growth of plants from control and mannitol-containing lines in the absence and presence of added sodium chloride was analyzed. Plants containing mannitol had an increased ability to tolerate high salinity.

Attachment and emotion regulation during mother-teen problem solving: a control theory analysis.

Abstract: We present a control theory analysis of adolescents' attachment strategies in the Adult Attachment Interview (AAI). In Study 1, Q-sort prototypes for secure/anxious and deactivating/hyperactivating strategies were used to differentiate between Main and Goldwyn's AAI classifications. In Study 2, we examined how AAI strategies were associated with emotion regulation during mother-teen problem solving. 4 aspects of mother-teen problem solving (dysfunctional anger, support/validation, avoidance of problem solving, and maternal dominance) were used to predict teens' AAI strategies. Teens with secure strategies engaged in problem-solving discussions characterized by less dysfunctional anger and less avoidance of problem solving. In addition, attachment security showed a curvilinear relation with maternal dominance, indicating that secure teens maintained balanced assertiveness with their mothers. Teens with deactivating strategies engaged in problem-solving interactions characterized by higher levels of maternal dominance and dysfunctional anger. The contribution of attachment strategies to teens' autonomy and to transformations in mother-teen relationships is discussed.

A turnover pathway for both stable and unstable mRNAs in yeast: evidence for a requirement for deadenylation.

Abstract: To determine pathways of mRNA turnover in yeast, we have followed the poly(A) tail removal and degradation of a pulse of newly synthesized transcripts from four different genes. Before decay of both stable and unstable mRNAs initiated, there was a temporal lag during which the poly(A) tail was deadenylated to an oligo(A) length. Altering the deadenylation rate of an mRNA led to a corresponding change in the length of this lag. The rate of deadenylation and the stability of the oligo(A) species varied between mRNAs, explaining the differences in mRNA half-lives. To examine how the transcript body was degraded following deadenylation, we used the strategy of inserting strong RNA secondary structures, which can slow exonucleolytic digestion and thereby trap decay intermediates, into the 3' UTR of mRNAs. Fragments lacking the 5' portion of two different mRNAs accumulated after deadenylation as full-length mRNA levels decreased. Therefore, these results define an mRNA decay pathway in which deadenylation leads to either internal cleavage or decapping followed by 5'-->3' exonucleolytic degradation of the mRNA.

Expansion of C4 ecosystems as an indicator of global ecological change in the late Miocene

Abstract: THE most common and the most primitive pathway of the three different photosynthetic pathways used by plants is the C3 pathway, or Calvin cycle, which is characterized by an initial CO2 carboxylation to form phosphoglyceric acid, a 3-carbon acid. The carbon isotope composition (δ13C) of C3 plants varies from about −23 to −35%l–3 and averages about −26%. Virtually all trees, most shrubs, herbs and forbs, and cool-season grasses and sedges use the C3 pathway. In the C4 pathway (Hatch–Slack cycle), CO2 initially combines with phosphoenol pyruvate to form the 4-carbon acids malate or aspartic acid, which are translocated to bundle sheath cells where CO2 is released and used in Calvin cycle reactions1–4. The carbon isotope composition of C4 plants ranges from about −10 to −14%, averaging about −13% for modern plants1–3. Warm-season grasses and sedges are the most abundant C4 plants, although C4 photosynthesis is found in about twenty families5. The third photosynthetic pathway, CAM, combines features of both C3 and C4 pathways. CAM plants, which include many succulents, have intermediate carbon isotope compositions and are also adapted to conditions of water and CO2 stress. The modern global ecosystem has a significant component of C4 plants, primarily in tropical savannas, temperate grasslands and semi-desert scrublands. Studies of palaeovegetation from palaeosols and palaeodiet from fossil tooth enamel indicate a rapid expansion of C4 biomass in both the Old World and the New World starting 7 to 5 million years ago. We propose that the global expansion of C4 biomass may be related to lower atmospheric carbon dioxide levels because C4 photosynthesis is favoured over C3 photosynthesis when there are low concentrations of carbon dioxide in the atmosphere.

The Project for Intercomparison of Land-surface Parameterization Schemes

Abstract: The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) is described and the first stage science plan outlined. PILPS is a project designed to improve the parameterization of the continental surface, especially the hydrological, energy, momentum, and carbon exchanges with the atmosphere. The PILPS Science Plan incorporates enhanced documentation, comparison, and validation of continental surface parameterization schemes by community participation. Potential participants include code developers, code users, and those who can provide datasets for validation and who have expertise of value in this exercise. PILPS is an important activity because existing intercomparisons, although piecemeal, demonstrate that there are significant differences in the formulation of individual processes in the available land surface schemes. These differences are comparable to other recognized differences among current global climate models such as cloud and convection parameterizations. It is also clear that too few sensitivity studies have been undertaken with the result that there is not yet enough information to indicate which simplifications or omissions are important for the near-surface continental climate, hydrology, and biogeochemistry. PILPS emphasizes sensitivity studies with and intercomparisons of existing land surface codes and the development of areally extensive datasets for their testing and validation.

Adoption and abandonment of matrix management programs: effects of organizational characteristics and interorganizational networks.

Abstract: Organizational design theorists argue that organizations adopt matrix (departmentalized) structures for technical reasons, to solve problems of internal coordination and information processing. Research on interorganizational networks suggests that organizations adopt new structures because of mimetic forces and normative pressures. We examined the effects of both sets of factors on the adoption of matrix management in a group of hospitals. Multivariate analyses revealed that matrix adoption is influenced not only by task diversity, but also by sociometric location, the dissemination of information, and the cumulative force of adoption in interorganizational networks. Such variables exert little influence on decisions to abandon matrix programs, however.

A molecular clock in endosymbiotic bacteria is calibrated using the insect hosts

Abstract: The primary endosymbionts of aphids are maternally inherited bacteria that live only within specialized host cells. Phylogenetic analysis of the 16S ribosomal DNA sequences of aphid endosymbionts reveals that they are a monophyletic group with a phylogeny completely concordant with that of their hosts, implying long-term cospeciation. Here we show that rates of base substitution are similar in the 16.S ribosomal DNA of different endosymbiont lineages. In addition, we calibrate these rates by assigning age estimates for ancestral aphid hosts to the corresponding endosymbionts. The resulting rate estimates (1—2% per 50 Ma) are among the most reliable available for prokaryotes. They are very near values previously conjectured by using more tenuous assumptions for dating divergence events in eubacteria. Rates calibrated using dates inferred from fossil aphids imply that Asian and American species of the aphid tribe Melaphidina diverged by the early Eocene; this result confirms an earlier hypothesis based on biogeographic evidence. Based on these rate estimates, the minimum age of this endosymbiotic association and the age of aphids as a whole is estimated at 160-280 Ma.

Polymerase chain reaction detection of nonviable bacterial pathogens.

Abstract: Polymerase chain reaction (PCR) methodologies for detection of pathogens in environmental samples are currently available. However, positive amplification products for any set of primers only signal that the appropriate target nucleic acid sequences were present in the sample. The presence of the amplification products does not imply that the target organisms were viable. Here we show that PCR will detect nonviable cells, as long as intact target nucleic acid sequences are available. In an environmental water sample, nucleic acids degraded quickly and were not detectable by PCR after 3 weeks even when stored at 4 degrees C. However, these data show that there is a window of opportunity for PCR analyses to result in false positives with respect to viable cells. We further show that care must be taken in the way samples are stored for future PCR amplifications and that filter sterilization of media is not acceptable for long-term preservation of samples for PCR.

A Large Drop in Atmospheric 14C/12C and Reduced Melting in the Younger Dryas, Documented with 230Th Ages of Corals

Abstract: Paired carbon-14 ((14)C) and thorium-230((230)Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the (14)C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the (14)C and (230)Th ages suggests that the atmospheric (14)C/(12)C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric (14)C/(12)C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.

Reduced control of motor output in a human hand muscle of elderly subjects during submaximal contractions

Abstract: 1. The effect of age on the motor output of the first dorsal interosseous muscle of 22 (6 female, 16 male) human subjects was investigated. The purpose of the study was to determine the effect of age on the control of muscle force and the associated changes in the discharge behavior and mechanical properties of single motor units. 2. Each subject performed three tasks requiring isometric abduction of the left index finger: a maximum voluntary contraction (MVC), a constant-force task, and a threshold task. The ability to control force was assessed during the constant-force task by quantifying the variation in isometric force about four submaximal target forces (5, 20, 35, and 50% MVC). The threshold task involved sustaining the discharge of the isolated motor unit at a low, steady rate for approximately 3 min. 3. The discharge behavior and the mechanical properties of single motor units were determined during the threshold task by measuring the interimpulse intervals and the peak amplitude and time to peak of the spike-triggered average force. 4. The data indicated that age had an effect on the variation of force about submaximal target forces (range: 5-50% MVC), and that these force variations, when calculated relative to the target force, were greater at lower force levels in the elderly subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

The mass-luminosity relation for stars of mass 1.0 to 0.08 solar mass

Abstract: Mass-luminosity relations determined at IR wavelengths are presented for stars with masses 1.0 to 0.08 solar mass. Using IR speckle imaging techniques on a sample of nearby binaries, we have been able to concentrate on the lower main sequence, for which an accurate mass-luminosity calibration has remained problematic. In addition, the mass-visual luminosity relation for stars with 2.0-0.08 solar mass is produced by implementing new photometric relations linking V to JHK wavelengths for the nearby stars, supplemented with eclipsing binary information. These relations predict that objects with masses of about 0.08 solar mass have M(K) of about 10 and M(V) of about 18.

Model observers for assessment of image quality

Abstract: Image quality can be defined objectively in terms of the performance of some "observer" (either a human or a mathematical model) for some task of practical interest. If the end user of the image will be a human, model observers are used to predict the task performance of the human, as measured by psychophysical studies, and hence to serve as the basis for optimization of image quality. In this paper, we consider the task of detection of a weak signal in a noisy image. The mathematical observers considered include the ideal Bayesian, the nonprewhitening matched filter, a model based on linear-discriminant analysis and referred to as the Hotelling observer, and the Hotelling and Bayesian observers modified to account for the spatial-frequency-selective channels in the human visual system. The theory behind these observer models is briefly reviewed, and several psychophysical studies relating to the choice among them are summarized. Only the Hotelling model with channels is mathematically tractable in all cases considered here and capable of accounting for all of these data. This model requires no adjustment of parameters to fit the data and is relatively insensitive to the details of the channel mechanism. We therefore suggest it as a useful model observer for the purpose of assessing and optimizing image quality with respect to simple detection tasks.

A multiple criteria decision-making approach to GIS-based land suitability evaluation

Abstract: Land suitability evaluation in a raster GIS environment is conceptualized as a multiple-criteria decision-making (MCDM) problem A combination of MCDM techniques selected for implementing the methodology included value and priority assessment techniques for scaling the interval and ordinal data respectively, and compromise programming (CP) to aggregate the unidimensional evaluations The contribution of the proposed methodology to handle problems of scaling and dependence that often affect expert-based suitability analyses is discussed A case-study of habitat evaluation for the endangered Mount Graham red squirrel is presented The multiple-criteria models resulting from the CP analysis of an expert's perception of the habitat preference structure of the red squirrel are compared with data of actual habitat use The predictive power of the models is good and sensitivity analysis based on the distance-metric parameter p of CP reveals some interesting differences between alternative strategies for

Exclusive Breast-Feeding for at Least 4 Months Protects Against Otitis Media

Abstract: Objective. This study was designed to assess the relation of exclusive breast-feeding, independent of recognized risk factors, to acute and recurrent otitis media in the first 12 months of life. Methods. Records of 1220 infants who used a health maintenance organization and who were followed during their first year of life as part of the Tucson Children9s Respiratory Study were reviewed. Detailed prospective information about the duration and exclusiveness of breast-feeding was obtained, as was information relative to potential risk factors (socioeconomic status, gender, number of siblings, use of day care, maternal smoking, and family history of allergy). Acute otitis media and recurrent otitis media, defined as three or more episodes of acute otitis media in a 6-month period or four episodes in 12 months, were the outcome variables. Results. Of the 1013 infants followed for their entire first year, 476 (47%) had at least one episode of otitis and 169 (17%) had recurrent otitis media. Infants exclusively breast-fed for 4 or more months had half the mean number of acute otitis media episodes as did those not breast-fed at all and 40% less than those infants whose diets were supplemented with other foods prior to 4 months. The recurrent otitis media rate in infants exclusively breast-fed for 6 months or more was 10% and was 20.5% in those infants who breast-fed for less than 4 months. This protection was independent of the risk factors considered. Conclusion. These findings suggest that exclusive breast-feeding of 4 or more months protected infants from single and recurrent episodes of otitis media.

Age and gender influence muscle sympathetic nerve activity at rest in healthy humans.

Abstract: Muscle sympathetic nerve activity at rest increases with age in humans. The respective influences of the aging process per se and gender on this increase and whether age and gender effects on muscle sympathetic nerve activity can be identified with plasma norepinephrine concentrations, however, have not been established. To examine these issues, nine young women (aged 24 +/- 1 years; mean +/- SEM), eight young men (aged 26 +/- 1 years), seven older women (aged 63 +/- 1 years), and eight older men (aged 66 +/- 1 years) were studied. All were healthy, normotensive (blood pressure < 140/90 mm Hg), nonobese (< 20% above ideal weight), unmedicated, nonsmokers engaged in minimal to recreational levels of chronic physical activity. Arterial blood pressure (manual sphygmomanometry, brachial artery), heart rate, muscle sympathetic nerve activity (peroneal microneurography), and antecubital venous plasma norepinephrine concentrations (radioenzymatic assay) were determined during quiet supine resting conditions. Body weight was higher in men, but there were no age-related differences, whereas estimated body fat (sum of skinfolds) was higher in women and in the older groups (p < 0.05). Estimated daily energy expenditure, arterial blood pressure, and heart rate were not different among the groups. Both muscle sympathetic nerve activity burst frequency and burst incidence at rest were progressively higher in the young women, young men, older women, and older men (10 +/- 1 versus 18 +/- 2 versus 25 +/- 3 versus 39 +/- 5 bursts/min and 16 +/- 1 versus 30 +/- 4 versus 40 +/- 3 versus 61 +/- 6 bursts/100 heartbeats, respectively; all p < 0.05 versus each other).(ABSTRACT TRUNCATED AT 250 WORDS)