Prominent Constriction Research Articles

Morphometric Studies on the Skull of the Australian Domestic Cat (F. catus) and its Clinical Implications for Regional Anesthesia

Understanding of orbital and periorbital anatomy is critical to the diagnosis and therapy of orbital disorders. Twenty-six cat heads were obtained from the dissecting room in the Discipline of Veterinary Sciences, College of Public Health and Veterinary Sciences, James Cook University, Townsville, Australia for use in this study. After macerating the heads and cleaning the skulls they were grouped by morphology into 15 round-headed and 11 flat-headed skulls. In the flat-headed group, the skulls were elongated with a prominent constriction between the cranium and facial bones and a prominent external sagittal crest, which extended from the nuchal crest. Furthermore, complete to nearly complete fusion of the zygomatic process of the frontal bone with the zygomatic arch resulted in a complete bony orbit. The skulls were radiographed, and a total of 32 parameters measured for each group: the skull, cranium, face, orbit and mandible were compared and analyzed. The sites of injecting the infra-orbital, mandibular alveolar and mental nerves were confirmed in both groups of cat skulls. We conclude that old age plays a major role in forming the skull shape (rounded versus flattened) and clo- sure of the orbital rim.

Khetoceras (Craspeditidae, ammonoidea)—A new genus from the Volgian stage of northern Middle Siberia, and parallel evolution of Late Volgian boreal ammonites

A new ammonite genus, Khetoceras (Craspeditinae), is proposed, showing an atypical combination of features for the subfamily (arrowlike cross-section and prominent constrictions). A new subfamily Subcraspeditinae is proposed within the family Craspeditidae. An increase in whorl overlap was the major trend in the evolution of the Late Volgian subfamilies belonging to Craspeditidae (Craspeditinae, Garniericeratinae, and Subcraspeditinae) leading to the appearance of discoid morphotypes with a narrow (or acute) cross-section in all these subfamilies. However, while this evolutionary trend dominated the evolution of Garniericeratinae and less so Subcraspeditinae, it was not so prominent in the Volgian Craspeditinae, in which this morphotype only developed in northern Siberia (genus Khetoceras), where at that time the other two subfamilies were absent.

Probing the Pore Dimensions of Bacterial Nicotinic Receptor-Like Channels with Open-Channel Blockers

ELIC and GLIC, two bacterial nicotinic receptor-like channels, are remarkably amenable to both structural and functional studies. This observation, along with the notion that the overall structure and functional properties of these channels are very similar to those of their metazoan counterparts, amply justifies the use of ELIC and GLIC as models for the entire superfamily. At the level of the transmembrane pore, the structural model of ELIC shows a prominent constriction around the 16' position of the M2 alpha-helices, whereas that of GLIC displays a much wider, semi-conical cavity with helices tilted away from the long axis of the pore. As a result, the structural models of ELIC and GLIC are often considered to represent the closed-channel and open-channel conformations, respectively, of all members of the superfamily, a notion that assumes that the end states of the gating conformational change are conserved across orthologs. Thus far, attempts to capture the different physiologically relevant conformations of each of these channels in well-diffracting crystals have failed. Here, as an alternative approach to probe the transmembrane-pore domain in the open-channel conformation, we studied the interaction of ELIC, GLIC and the muscle nicotinic acetylcholine receptor (AChR) with pore blockers. From the comparative analysis of these results, it appears as though the muscle AChR and GLIC have very similar open-channel pore structures, whereas the open-channel pore of ELIC seems much narrower, and thus, closer to the structural model of ELIC in its closed state. Hence, it is likely that the closed-to-open conformational change of ELIC at the level of the pore domain is subtler than the one that could be predicted if ELIC were to adopt a GLIC-like structure in the open state.

Crystal Structure of a Voltage-gated K+ Channel Pore Module in a Closed State in Lipid Membranes

Voltage-gated K(+) channels underlie the electrical excitability of cells. Each subunit of the functional tetramer consists of the tandem fusion of two modules, an N-terminal voltage-sensor and a C-terminal pore. To investigate how sensor coupling to the pore generates voltage-dependent channel opening, we solved the crystal structure and characterized the function of a voltage-gated K(+) channel pore in a lipid membrane. The structure of a functional channel in a membrane environment at 3.1 Å resolution establishes an unprecedented connection between channel structure and function. The structure is unique in delineating an ion-occupied ready to conduct selectivity filter, a confined aqueous cavity, and a closed activation gate, embodying a dynamic entity trapped in an unstable closed state.

Description of a New Species of the GenusKrisna(Hemiptera: Cicadellidae: Iassinae) from India

A new species, Krisna pampadumparaensis, is described from Pampadumpara, Kerala, India collected from Ficus exasperata. It is distinguished by its deeply transversely carinate vertex and without any anterior transverse black spot. Three prominent constrictions at the ventral lower margin of aedeagal shaft, hind margin of male eighth sternite medially slightly concave and its lateral angles slightly rounded are the other distinguishing characters. Aedeagus in caudal aspects with shallow concavity in the apical region, second pair of gonapophyses with a smooth area between basal and median teeth, margin between median and apical prominent teeth with denticles and margin beyond apical prominent teeth serrated up to tip, apex with undulated margin and ventral margin with subapical notch, make it distinct from K. varia Viraktamath with which it is closely related.

Early tooth development, gestation, and season of birth in mammoths

The Yamal mammoth calf “Lyuba” and the Oimyakon mammoth calf are two recently collected, mummified woolly mammoth calves both dating to around 41 ka. They offer opportunities to study the earliest parts of mammoth life history through microstructural and compositional analyses of tooth dentin. Understanding mammoth paleobiology is critical for assessing how populations might have responded to ecological changes in the late Pleistocene, and such assessment will aid in determining the likely cause(s) of extinction.The state of tooth eruption and wear in Lyuba suggests that she died quite young. Prominent constrictions in the roots of the dP2s and dP3 correspond to neonatal lines in the dentin of each tooth, marking the time of birth. The neonatal line in dP2 allowed us to estimate the duration of prenatal development, determine Lyuba’s age at death, and place birth in the context of variation in isotopic and elemental composition of the dentin.Growth increments and seasonal variation in δ15N indicate that Lyuba’s dP2 records over a year of prenatal development, suggesting duration of gestation was similar to that observed in elephants. Death occurred at about 30–35 days, and birth appears to have occurred in spring.The Oimyakon specimen represents an individual older (biologically) than Lyuba. The dP2s have been lost, and most plates of the dP3s are in wear. An unerupted permanent tusk is present, but no deciduous tusk is present in the single recovered premaxilla. The tusk exhibits a circumferential ridge at mid-length that represents the surface expression of a prominent growth line in the dentin. Based on its prominence and elevated dentin Zn/Ca in its vicinity, this is interpreted as a neonatal line. Its occurrence in the tusk is of interest because this implies initiation of permanent tusk mineralization months before birth— yet permanent tusks are not present in Lyuba. Differences in timing of tusk development may result from individual, population, or sexual variation.Growth increments in the tusk indicate death at an age of about 7 months with both δ15N and δ13C generally declining postnatally. The increment-based age at death is less than an estimate based on the state of cheek tooth eruption and wear (using extant elephants as references), implying that ages based on comparisons to elephants may be inaccurate. Counts of dentin growth increments combined with identification of seasonally varying aspects of dentin composition could be used to calibrate the cheek tooth aging system for Mammuthus primigenius.

Toxoplasma gondii: Ultrastructure study of the entry of tachyzoites into mammalian cells

Toxoplama gondii (Apicomplexa: Coccidia), an obligatory intracellular parasite with a unique capacity to invade virtually all nucleated cell type from warm-blooded vertebrate hosts. Despite the efficiency with which Toxoplasma enters its host cell, it remains unresolved if invasion occurs by direct penetration of the parasite or through phagocytosis. In the present work, electron microscopic study was designed to examine the entry process of Toxoplasma (RH strain) into macrophages and non phagocytic-host cells (Hela cells) and to observe the ultrastructure changes associated with intracellular parasitism. The results showed that both active invasion and phagocytosis were occurred and revealed that invasion is an ordered process that initiates with binding of the parasite at its apical end followed by tight-fitting invagination of the host cell membrane and a prominent constriction in the parasite at the site of penetration. The process ended by the professional parasitophorous vacuole that is distinct at the outset from those formed by phagocytosis in which once Toxoplasma triggered, phagocytic uptake can proceed by capture of the parasite within a loose fitting vacuole formed by localized membrane ruffling. The cytopathic effects of the parasite on macrophages and Hela cells were demonstrated within 5–15 h post-inoculation in the form of degenerative mitochondria, swelling Golgi apparatus and widening of endoplasmic reticulum indicating intracellular oedema. These changes were exaggerated and several cells were found dead after 48–72 h.

Vegetative Cell Division and Nuclear Translocation in Three Algae Species of Netrium (Zygnematales, Chlorophyta)

Three species of Netrium oblongum, N. digitus v. latum, and N. interruptum were studied for their mode in the vegetative cell division and nuclear translocation during mitosis using light and fluorescence microscopy. The process of cell division in the three species began with the prominent constriction at the chloroplast in both semicells about half way from the apex. The constriction of chloroplast was mostly visible in N. digitus v. latum. Soon after nucleus divided, septum was formed across the cell and cytokinesis occurred. Observation with fluorescence microscope showed that the movement of nucleus moved back into the center of daughter cells was not always synchronous. Division of chloroplast in N. oblongum and N. digitus v. latum were different with that of N. interruptum. Chloroplast division in two former species occured following the movement of the nucleus down semicell. However, in N. interruptum, chloroplast divided later after nucleus occupied the position at the center of the daughter cells. Cell restoration started after the completion of mitosis and cytokinesis. Key words: Cell division, conjugating alga, mitosis, Netrium

Evolving force balance at Columbia Glacier, Alaska, during its rapid retreat

Changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats. We describe changes in geometry, velocity, and strain rate and present a top‐down force balance analysis performed over the lower reach of Columbia Glacier. Our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001, while assuming depth‐independent strain. Sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters. Spatial distributions of ice speed show little correspondence with driving stress. Instead, spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag. Primary resistance to flow comes from basal drag, but lateral drag becomes increasingly more important throughout the retreat, which may account for observed increases in speed. Maximum basal drag is always located in a prominent constriction located ∼12 km upstream from the preretreat terminus. Once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent, the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream. An increase in both ice velocity and calving resulted, initiating what appears to be an irreversible retreat.

In vivo visualization of angiotensin II- and tubuloglomerular feedback-mediated renal vasoconstriction

A noninvasive technique to monitor renal microcirculation would be a useful tool for investigation of renal disease and the effects of drugs on the renal system. We have developed a novel, less invasive technique to visualize renal microcirculation in vivo using an intravital tapered-tip (1 mm phi) lens-probe (pencil lens-probe) videomicroscopy, which only requires insertion of the probe into superficial renal cortex in situ. To assess validity of this technique, the effects of angiotensin II (Ang II) and intrarenal sodium chloride loading (activator of tubuloglomerular mechanism) were examined. The renal microvasculature was successfully visualized and monitored. Administration of Ang II (1, 3, 10 and 30 ng/kg/min) produced a dose-dependent constriction of afferent and efferent arterioles in similar degrees; at 30 ng/kg/min, Ang II elicited 52 +/- 3 (N = 9) and 53 +/- 3% decreases in diameter (N = 9), respectively. The Ang II-induced arteriolar constriction was completely prevented by losartan, an Ang II type 1 (AT1) antagonist. The intrarenal hypertonic saline administration elicited transient increments (from 98 +/- 8 to 122 +/- 7 mL/min, N = 6, P < 0.05), followed by a marked reduction in renal blood flow (RBF; 78 +/- 7 mL/min, P < 0.05). This response was accompanied by prominent constriction of afferent (from 15.0 +/- 1.1 to 8.5 +/- 1.1 microm, N = 6, P < 0.05), but not efferent (from 14.3 +/- 1.2 to 13.8 +/- 1.0 microm, N = 3) arterioles. Furthermore, this response was completely inhibited by furosemide, a tubuloglomerular feedback inhibitor. : The intravital pencil lens-probe videomicroscopy can be a powerful tool for in vivo observation of renal microcirculation, with intact renal microvascular responses to two important renal homeostatic mechanisms, angiotensin II and tubuloglomerular feedback.

Early stages of channel formation in a short-gap breakdown

A description and analysis of the solution of a two-dimensional model for a HV breakdown of a short gap is presented. The model consists of the electron, ion, and excited-atom conservation and Poisson equations and is applied to a plane-parallel gap with an electrode separation of 0.48 mm in helium gas at atmospheric pressure and a temperature of 293 K subjected to an electrical field of 10 kV cm−1. Two-dimensional plots of the charged and excited-particle densities and electric field components are presented and discussed. It is shown that in the first, diffusion-controlled, stage density profiles are close to a Gaussian distribution with an effective radius increasing in time. The subsequent stage is controlled by the space-charge field, causing prominent constriction of the electron density channel. In consequence, a high ionization near the discharge axis results in a virtual narrowing of the ion and excited-atom profiles as well, and the forming conductive chanel exhibits a tendency towards constriction. Calculations were conducted up to a maximum time of t=1139 ns, when maximum electron, ion, and excited-atom densities reached values of 3.1×1010, 3.7×1011, and 2.5×1012 cm−3. Among the ionization processes the direct and Penning interactions are dominant, accounting at average for approximately 70% and 30% of the total at time t=1139 ns; ionization frequencies are substantially affected by space-charge field and vary considerably in time and space near the end of calculations.

Chromosome studies of the lethal hybrid Rana pipiens ♀ × Rana catesbeiana ♂

Developmental arrest of amphibian interspecific hybrids about the time of gastrulation may be causally related to chromosomal breakage and loss during cleavage. This paper presents the karyotypes of white blood cells of adult Rana pipiens and Rana catesbeiana, and evidence that hybrids between Rana pipiens ♀ × Rana catesbeiana ♂ retain complete haploid chromosome sets from both parental species shortly before arrest at the early gastrula stage. Both species have 13 pairs of homomorphic chromosomes. Individual real and relative chromosome lengths are very similar in both species, as are centromere positions in the two karyotypes. Two chromosome pairs in Rana catesbeiana (Nos. 7 and 10) contain prominent constrictions; the constrictions are present only in chromosomes of pair No. 10 in Rana pipiens. Metaphase figures from hybrid blastulae contained no ring chromosomes or acentric fragments; no anaphase bridges were seen. Most figures in which chromosomes could be counted contained 26 chromosomes, and the frequency of figures with abnormal chromosome numbers was less than that from control Rana pipiens blastulae. Relative lengths of individual chromosomes from hybrid karyotypes were the same as those from controls. Karyotypes from hybrid embryos contained three chromosomes with prominent constrictions, one falling into pair No. 7—for which there was no homolog with a constriction—and two into pair No. 10. The lengths of the longer chromosome segments of hybrid pair No. 10 were significantly different from one another; those of controls were not. The conclusion that functional inadequacy of nucleocytoplasmic interactions during cleavage can account for early developmental arrest without associated karyotypic abnormality is discussed. The relationship of chromosomal damage to blastula and gastrula arrest in other experimental systems is considered, and the Rana pipiens ♀ × Rana catesbeiana ♂ hybrid is suggested as a system amenable to further study of genetic dysfunction before gastrulation.