Showing papers by "National Autonomous University of Mexico published in 1984"
TL;DR: Lipid bilayers Lateral diffusion Membrane proteins Fluorescent probes Photobleaching
191 citations
TL;DR: The feeding preferences of howler monkeys at their northernmost distribution in the Neotropics are reported for an annual cycle and a remarkable selectivity for 27 species representing 15 families was observed.
Abstract: The feeding preferences of howler monkeys at their northernmost distribution in the Neotropics are reported for an annual cycle. A remarkable selectivity for 27 species representing 15 families was observed. The Moraceae and Lauraceae plant families were the most important in the diet. The howlers spent an almost equal proportion of their feeding time eating leaves and fruit, and displayed a marked preference for young leaves and mature fruit. The consumption of different plant parts was markedly seasonal and the howlers’ ranging behavior was closely associated with the availability of young leaves and mature fruit. Their home range was unusually large (ca. 60 ha) for howlers and the food species exploited occur at very low densities (93%, ≤ 4 ind/ha). They chose food items richer in protein and energy. Alkaloid compounds, present in some of the leaves, play a secondary role in their dietary selectivity.
158 citations
Journal Article•
158 citations
TL;DR: The results show that grafts allow animals to recover lost functional properties due to lesions, and further support the notion that the SCN is a pacemaker for certain behaviors.
156 citations
TL;DR: Howling monkeys created diverse seed shadows in the vicinity of their leaf and fruit sources, and while they dispersed the seeds of some plant species, they also produced a great deal of fruit and seed waste for others.
Abstract: The frugivory and ranging habits of howling monkeys living in the rain forest of Los Tuxtlas, Veracruz, Mexico, were studied for 5 consecutive years with the aim of investigating the role of seed dispersal agents played by the howling monkeys. The howling monkeys' consumption of fruit occupied half of their feeding time, and 80% of this time was spent feeding on mature fruit. Observations confirmed use of 19 tree species and a preference for a few species of Moraceae and Lauraceae. Fruit exploitation was very seasonal; only two species provided fruit year-round. Home range size was about 60 ha, and animals in the troop (N = 16) showed a day range of 10-893 m. Monthly collection of fecal samples during 2 years indicated that 90% of the seeds (N = 7,928) in the samples belonged to eight tree species and to one liana; the rest belonged to 15 unidentified species of vines. Germination success for the seeds in the feces was about 60% and for control seeds was 35%. Howling monkeys created diverse seed shadows in the vicinity of their leaf and fruit sources, and while they dispersed the seeds of some plant species, they also produced a great deal of fruit and seed waste for others.
145 citations
TL;DR: A study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeo- graphica, indicates major environmental influences on the hatchling sex ratio in map turtles.
Abstract: Incubation temperature is known to determine the sex of hatchlings in many species of turtles, including the map turtles, Graptemys ouachitensis, G. pseudogeographica, G. geographica, and painted turtle, Chrysemys picta. This paper presents a study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeo- graphica. Nesting was monitored during June, and hatchlings were obtained from 236 nests during August and September 1980. The distribution of nest sex ratios in samples of the two common species was bimodal, tending to be all-female or all-male within a nest, with an overall excess of females. Nests with males were located amid vegetation, with cool temperatures, and nests with females were located in open sand exposed to the sun, with high temperatures. The sex ratio differed significantly between nesting beaches, apparently because of differences in the availability of warm vs. cool nest sites. All-female nests hatched in less time than all-male nests, and the sex ratio of emerging hatchlings consequently changed from nearly all female early in August to all male in September. The data indicate major environmental influences on the hatchling sex ratio in map turtles.
113 citations
TL;DR: The results suggest that VIP may participate in the regulation of REM sleep and that it did not protect the animals from the specific REM inhibiting properties of CAP.
112 citations
TL;DR: The El Chichon volcano in SE Mexico erupted explosively during the months of March and April, 1982 as mentioned in this paper, and three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 March at 0515 GMT and on 4 April at 0139 and 1110 GMT.
108 citations
TL;DR: The potencies of the different phorbol esters used in this study suggests that the inhibitory effects of these agents may be due to activation of protein kinase C, which seems to occur at an early step of the alpha 1-adrenergic action.
99 citations
TL;DR: It is proved that every vertex in an R^--digraph is contained in an even directed cycle not containing special pseudodiagonals and any digraph in which every odd directed cycle has two pseudodiagonsals with consecutive terminal endpoints is an R-digraph.
98 citations
TL;DR: The boundaries and relative sensitivity of brain stimulation reward were mapped in relation to the dopamine (DA) terminal fields of the striatum and adjacent limbic structures and reward sites in the olfactory tubercle and amygdala went against the view that direct activation of dopamine terminals or their efferent targets accounts for the rewarding quality of stimulation in these regions.
TL;DR: The initial velocity patterns for the amination reaction were obtained under conditions of hyperbolic kinetics produced by GlcNAc6 P; the Km values for the allosteric substrates were determined under the same conditions, and their dependence upon pH was studied.
TL;DR: The data suggest the presence of isoenzymes or conformers of GDH, specific for each tissue, whose activities vary depending on the nutritional requirements of the tissue and the state of differentiation.
Abstract: Both calli and plantlets of maize (Zea mays L. var Tuxpeno 1) were exposed to specific nitrogen sources, and the aminative (NADH) and deaminative (NAD+) glutamate dehydrogenase activities were measured at various periods of time in homogenates of calli, roots, and leaves. A differential effect of the nitrogen sources on the tissues tested was observed. In callus tissue, glutamate, ammonium, and urea inhibited glutamate dehydrogenase (GDH) activity. The amination and deamination reactions also showed different ratios of activity under different nitrogen sources. In roots, ammonium and glutamine produced an increase in GDH-NADH activity whereas the same metabolites were inhibitory of this activity in leaves. These data suggest the presence of isoenzymes or conformers of GDH, specific for each tissue, whose activities vary depending on the nutritional requirements of the tissue and the state of differentiation.
01 Jan 1984
TL;DR: In this paper, the authors show that delayed germination and enforced dormancy are frequent among light-gap adapted trees and species with hard-coated seeds in tropical forests. But they do not consider the effect of light gap on the survival of trees.
Abstract: Most forest tree seeds from the humid tropics germinate soon after dispersal forming carpets of semi-dormant seedlings. Delayed germination and enforced dormancy is frequent among light- gap adapted species, some emergent trees and species with hard-coated seeds. Dormancy is more important as an adaptative trait in marked seasonal forests.
TL;DR: It is concluded that taurine and zinc protect ROS membranes from ion and/or water entry occurring as a consequence of membrane lipid peroxidation.
Abstract: Exposure of isolated frog rod outer segments (ROS) to ferrous sulfate in a Krebs-bicarbonate medium causes a time-dependent disruption of the membrane organization of the discs. Ferrous sulfate also causes ROS swelling and aggregation. Addition of taurine (5-20 mM) and zinc sulfate (250 microM) to the incubation medium markedly protected ROS from the disrupting effect of ferrous sulfate. Of other amino acids tested, only beta-alanine had a protective effect on ROS structure. Ferrous sulfate caused an increase in lipid peroxidation, measured by malonaldehyde formation. The protective effect of taurine and zinc is not accompanied by a reduction of lipid peroxidation. Water accumulation occurs as a consequence of the peroxidative action of ferrous sulfate, and this effect was counteracted by taurine and zinc. Ferrous sulfate did not cause damage to ROS structure when incubation was carried out in sucrose-HEPES. Sodium, chloride, and bicarbonate ions caused ferrous sulfate to disrupt ROS structure. It is concluded that taurine and zinc protect ROS membranes from ion and/or water entry occurring as a consequence of membrane lipid peroxidation.
TL;DR: In this paper, a theory of macroscopic systems which takes as independent variables the slow (conserved) ones plus the fast dissipative fluxes is carefully analyzed at three levels of description.
Abstract: A theory of macroscopic systems which takes as independent variables the slow (conserved) ones plus the fast dissipative fluxes is carefully analyzed at three levels of description: macroscopic (thermodynamic), microscopic (projection operators) and mesoscopic (fluctuation theory). Such a description is compared with the memory function approach based only on the conserved variables. We find that the first theory is richer and wider than the second one, and some misunderstandings in this connection are clarified and discussed.
TL;DR: In this article, the interior of El Chichon Volcano was mapped and sampled by the explosion of the 1982 explosion crater, which exposed volcanic domes, talus breccias, plinian airfall deposits and pyroclastic-flow deposits.
TL;DR: The U( 6 12 ) dynamical supersymmetry of the Interacting Boson-Fermion Model, appropriate for nuclei where the odd nucleon can occupy the single-particle orbits J = 1 2, 3 2, and 5 2 is analyzed in this paper.
TL;DR: A series of thrust sheets, with a minimum linear shortening of 3 to 4 km each and 10 to 12 km in total, formed where the platform edge was approximately normal to the greatest principal stress trajectories, as deduced from fold axes as discussed by the authors.
Abstract: The eastern margin of the Cretaceous Valles–San Luis Potosi carbonate platform (Hidalgo, Queretaro, and San Luis Potosi States) became activated during the formation of the Sierra Madre Oriental fold-thrust belt. A series of thrust sheets, with a minimum linear shortening of 3 to 4 km each and 10 to 12 km in total, formed where the platform edge was approximately normal to the greatest principal stress trajectories, as deduced from fold axes. A tear fault developed where the platform edge formed an acute angle with the same stress trajectories. The overthrusts cut across the competent layers of the Lower Cretaceous on tectonic ramps that dip >10° and became partly steepened by subsequent imbrication or folding. In the mechanically weak Upper Cretaceous rocks, the thrust faults are nearly parallel to bedding for several kilometres. The location of the thrusts is controlled mainly by the lithological and thickness change of the middle Cretaceous rocks from an orthotropically layered basin facies into a two to five times thicker homogeneous platform–edge assemblage. The bank margin was a zone of stress concentration. The magnitude of the horizontal tectonic components which caused the deformation may have changed by a factor of two to five across the platform margin, due to the change in cross-sectional area. Oblique and layer-parallel discrete shears and subordinate tectonic stylolites appear to have been the dominant deformational mechanisms. The rocks did not suffer any measurable penetrative ductile deformation; ooids present at the base of the Xilitla Thrust are unflattened but are marked by a closely spaced stylolitic cleavage perpendicular to bedding. The deformations are bracketed by the paleontological age of the youngest strata affected by the overthrusts (Globotruncana contusa planktonic foraminiferal zone) and by the isotopic age of a post-tectonic pluton (62.2 Ma) and are thus of late Maastrichtian/Paleocene age.
TL;DR: In this paper, the state of Guanajuato has provided much needed stratigraphic control relevant to collected fossils, such as the Cedazo (Pleistocene), Las Tunas, Las Ocote, Coecillo, and Rancho Viejo (Pliocene).
Abstract: Historically, the knowledge of late Cenozoic mammals from central Mexico has been slow in developing. Most early studies did not include stratigraphic controls or meaningful correlations. At present the geology is incompletely known at most fossil-yielding localities. However, research in the past several years, especially in the State of Guanajuato, has provided much needed stratigraphic control relevant to collected fossils. Of the eleven faunas identified in this paper, only the Cedazo (Pleistocene), Las Tunas, Rancho El Ocote, Coecillo, and Rancho Viejo (Pliocene) have this control. These faunas, then, with several taxa reported here for the first time, are considered most important. They provide significant information about changing climates, a trend from humid, warm conditions in the Pliocene to drier and cooler conditions in the Pleistocene, and mammalian dispersals. Most fossils can be derived from North American ancestors; however, South American constituents can be identified beginning...
01 Jan 1984
TL;DR: In this article, a Monte-Carlo calculation was carried out to obtain the energy distribution of ions and neutrals at the cathode of a glow discharge, assuming charge exchange collisions in different fields.
TL;DR: The role of Western medicine in Totonac life is analyzed in this article, where the authors report on their herbal remedies and briefly discuss their traditional medicine and the role of western medicine in their life.
TL;DR: A 2.3-kb PstI- ClaI chromosomal DNA segment, carrying the complete coding region of the glutamate dehydrogenase (GDH) structural gene from Escherichia coli K-12, has been sequenced.
TL;DR: The data suggest that rewarding brain stimulation in these regions is not due to direct activation of either the dopaminergic terminals or the cells that they innervate, and there was no special relation between goodness of self-stimulation and density of dopamine terminal innervation.
TL;DR: To the authors' knowledge, this is the first reported somatostatinoma occurring in the extrahepatic biliary tract.
Abstract: An unusual tumor of the cystic duct in a 28-year-old woman is described. The patient presented with a painful distended gallbladder due to a small tumor occluding the cystic duct. Microscopically the tumor cells showed a nesting pattern suggestive of endocrine differentiation, but contained numerous lipid vacuoles and were argentaffin and argyrophil negative. Ultrastructurally, there were relatively few dense granules measuring 135 to 475 nm. Immunoperoxidase staining showed that the tumor cells contained somatostatin but did not contain immunoreactive ACTH, gastrin, calcitonin, glucagon, insulin, parathyroid hormone, or carcinoembryonic antigen. To the authors' knowledge, this is the first reported somatostatinoma occurring in the extrahepatic biliary tract.
TL;DR: The radiation-chemical approach to chemistry in the cometary nucleus is examined in this article, where the inventory of absorbed doses in the core and icy surface layers is made after considering the contribution of cosmic rays and some radionuclides imbedded in the material during accretion.
TL;DR: The results indicate the possibility of a slow exchange of cholesterol between the tightly bound lipid surrounding the (Ca2+ + Mg2+)-ATPase and the bulk lipid of the sarcolemma.
TL;DR: A much larger increase in cAMP levels seemed to be required for the stimulation of hepatocyte metabolism by forskolin than by glucagon or THG, which may suggest the existence of a functional compartmentation of cAMP in rat hepatocytes.
TL;DR: In this paper, a linear relationship between frequencies of micronuclei and cadmium concentrations was found: at 1.5, and 10 mg/liter micron nuclei numbers were always the lowest.