Complex Branching Patterns Research Articles

WIRING UP THE VISUAL SYSTEM

1. In this review we describe some of our recent studies on the developing marsupial visual pathway. The description focuses on retinal ganglion cells, considering the formation of their dendritic trees, the outgrowth of axons and the formation of connections within the brain. 2. Both dendritic trees and outgrowing axons undergo a period of exuberance, followed by one of refinement. The dendritic tree transiently develops a more complex branching pattern than is found in adults. Short side branches, referred to as spines, are a feature of immature dendrites and, to a lesser extent, of axons. These structures are mostly lost as development proceeds. However, they are retained on the dendritic trees of small-field ganglion cells and, for a proportion of axons, on that part within the nerve fibre layer of the retina. Although most axons navigate fairly direct routes towards their targets, a minority follow inappropriate courses, such as doubling back towards the eye or entering the opposite optic nerve at the chiasm. As such errant axons are not seen in the adult, we assume that their parent cell bodies die during development. 3. Throughout development, optic axons are arranged in an approximate retinotopic order along the length of the visual pathway; as a result, axons approach the visual centres aligned to form, at least, a crude retinotopic map. Axons from dorsal and ventral retina exchange locations along the optic nerve and in this way correct for the inversion of the image brought about by the lens.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer simulation of geometry and hemodynamics of canine pulmonary arteries.

Assuming that along the pulmonary arteries, mathematical expectations of branching are equal to matrix (Ei,j; i: parent branch class, j: daughter branch class number), we made computer drafts of patterns of pulmonary arterial branching trees from the published data of canine pulmonary arterial casts with the "Monte Carlo methods" by FORTRAN, calculating from these data, the numbers of branches, size and resistance of the trees. We also analyzed blood flow distribution in a pulmonary branch according to the pathlength from the entrance of the tree. The graphics of the trees were similar to the original arterial casts, and numbers of the branches were nearly the same as the previous reported values. Calculated resistance was reasonable. The rate of blood flow per unit vessel in the short pathlength group was calculated as 1.5 times that of the long pathlength group of the same diameter. We believe that our method of describing the branching pattern matrix (Ei,j) provides a reasonable simulation of complex branching patterns such as pulmonary arteries and a useful means to analyze local hemodynamics.

Fractal fingerprinting of joint and shatter-cone surfaces

The branching patterns of radiating ridges on surfaces of tensile joints and shatter cones were simulated and quantified, and their scaling properties were examined in three dimensions by means of a technique new to geology, the slit-island method. Results show that the textures are fractal over a wide range of scales. Accordingly, an algorithm simulates growth of tensile fracture-surface features by combining a set of rules with an element of randomness. The simulated surfaces are fractal and strikingly similar to natural fracture surfaces. These and other complex branching patterns observed in geology are likely due to an interplay of deterministic and random processes.

Age-related remodeling of lobster neuromuscular terminals

Multiterminal innervation of a lobster limb muscle by an identified excitor motoneuron was examined during primary development and adult growth. To keep pace with the growth in the target muscle, axonal branches proliferate by sprouting from synaptic terminals; an increasingly complex branching pattern results. Neuromuscular synapses multiply in number, enlarge in size, and become perforated. Concomitantly, synapses tend to appear on the more distal axonal branches and to disappear on more proximal branches, providing for continual remodeling of multiterminal innervation. This plasticity in an identified motoneuron occurs over a long life span of several decades.

Stability patterns and trophic structure in a Delaware Bay plankton community

Using qualitative loop analysis we have extended our examination of a Delaware Bay plankton community to include an investigation of the roles played by the various entities (population, guild or nutrient) in the community. IN an entity removal exercise, we used stability relationships as a probe into community structure. Six types of stability change are possible as a result of entity removal from the system: stable to stable (s → s); stable to unstable (s → u); stable to disconnected (s → d); unstable to stable (u → s); unstable to unstable (u → u); unstable to disconnected (u → d). Using these changes as an investigative tool, we found that in order to account for the stability-instability patterns, it was necessary to construct a refined trophic structure model. The observed connections between the entities in the larger model could be grouped into two different types of stability substructures: a simple pattern and a more complex branching pattern. These patterns map easily onto the refined trophic structure model. Using stability analysis it is also possible to model community structure in ways other than the traditional trophic approach. Patterns of system necessity and relative contribution to stability are observed. These patterns match the refined trophic structure model derived previously. The roles that the various entities play in the overall community were followed over an annual cycle. Entities were seen to change their roles as a function of time and status within a subgroup. These results show that stability determinations have the potential to be used as a valuable tool in community analysis.

Characterization and charge distribution of the asparagine-linked oligosaccharides on secreted mouse thyrotropin and free alpha-subunits.

Mouse hemipituitaries in vitro secrete TSH, composed of an alpha-beta heterodimer, as well as excess (free) alpha-subunits. By dual metabolic labeling with [35S]sulfate and [3H]mannose, we have characterized oligosaccharides from secreted TSH alpha, TSH beta, and free alpha-subunits released from the apoprotein by enzymatic deglycosylation. Oligosaccharides from each subunit displayed a distinct anion exchange HPLC profile due to a specific pattern of sialylation and sulfation. Six species were obtained from TSH alpha (with two glycosylation sites), including neutral oligosaccharides as well as those with one or two negative charges. For TSH beta (with one glycosylation site) at least eight oligosaccharide species were noted, representing nearly every permutation of sialylation and sulfation; approximately 30% contained three or more negative charges. Analysis of [3H]mannose-labeled oligosaccharides on Concanavalin-A-agarose showed 85% binding for those from TSH alpha, 70% for free alpha, and 50% for those from TSH beta. These data demonstrate that oligosaccharides from secreted TSH beta were more sialylated and sulfated, consistent with a more complex branching pattern, than those from TSH alpha. Oligosaccharides from free alpha-subunit were more sialylated than those from TSH alpha, and the net negative charge was intermediate between those of TSH alpha and TSH beta. Although great microheterogeneity is present even at the single glycosylation site on the beta-subunit of secreted TSH, a pattern of sialylation and sulfation could be discerned. If one assigns probabilities of sialylation [p(N)] and sulfation [p(S)] based on the observed distribution within monoacidic (charge -1) species, the proportion of diacidic (charge -2) oligosaccharides could be predicted for each subunit by [p(N)]2, 2[p(N)] [p(S)], [p(S)]2, corresponding to species containing two sialic acid, one sialic acid and one sulfate, and two sulfate residues, respectively. This suggests that the probability of sialylation or sulfation at a second site on these oligosaccharides is similar to that at the first and that anionic oligosaccharides in secreted TSH and free alpha are distributed binomially with regard to sialic acid and sulfate residues.

Pre-translational and post-translational regulation of TSH synthesis in normal and neoplastic thyrotrophs.

We are interested in the mechanisms by which endocrine and developmental factors regulate TSH synthesis at both pre-translational and post-translational levels. Thyroid hormone profoundly decreases transcription of the TSH-beta gene, while TRH and agents modifying cyclic AMP increase transcription. To elucidate the molecular mechanisms underlying these effects, human embryonal kidney cells were transfected with constructs of the human TSH-beta gene fused to the chloramphenicol acetyltransferase gene. The first exon of human TSH-beta, contains an element that increases basal expression and mediates T3-induced gene repression, probably through a direct interaction with c-erbA beta. This transcriptional repression by T3 appears aberrant in thyrotropic tumors. In contrast, TRH and agents modifying cyclic AMP mediate increased transcription of TSH-beta through interacting with upstream regulatory elements. Thyroid hormone, TRH and developmental factors also regulate the branching pattern and relative sialylation of TSH carbohydrate chains, which may affect TSH action in vitro and in vivo. Certain thyrotropic tumors produce TSH with more complex carbohydrate branching patterns, which may increase its biologic activity.

Transfer impedances between different regions of branched excitable cells

1. The excitable properties of branched cells were measured using a combination of voltage-clamp and frequency-domain techniques. Point impedance functions from either the soma or growth cone of NG-108 cells were curve fitted with a reduced cable model at different membrane potentials to establish kinetic parameters. 2. Transfer impedance functions between the soma and growth cone were measured and simulated with a morphologically determined model. In these experiments the membrane potential was controlled by a single-electrode voltage clamp thus allowing an estimate of transfer functions for any arbitrary input, such as a single synaptic current for differing degrees of tonic synaptic drive. Furthermore, the integration of different regional inputs was evaluated based on the transfer functions between different locations on an individual cell. 3. The activation of an outward steady-state current leads to resonating impedance functions that were used to evaluate the kinetic properties of ionic channels in different regions of branched excitable cells. For simple branching patterns the point and transfer impedances show lower resonant frequencies for active growth cones compared with active somas. 4. More complex branching patterns showed the unexpected result that the voltage-dependent resonant frequency was higher for the growth cone recording than the soma. The presence of a higher resonant frequency when the growth cone is activated does not require more rapid kinetics of the active potassium conductance, since the time constant of the active conductance can be the same in the growth cone and the soma membrane. 5. In conclusion, the resonant frequencies, as well as all other aspects of the impedance functions, are complicated interactions of the detailed branching patterns and active conductances. In general, these interactions are not predictable from a passive electrotonic analysis, especially when the voltage-dependent conductances are distributed throughout the dendritic tree.

The development, ultrastructure and synaptic connections of the mossy cells of the dentate gyrus

One of the most distinctive and common cell types in Golgi preparations of the hilus of the rat dentate gyrus is the mossy cell. We have used a variety of techniques including the Golgi method, the combined Golgi and electron microscopic (EM) method and the retrograde transport of horseradish peroxidase (HRP) to study the development, ultrastructure and synaptic connections of this cell type. The mossy cells identified in our light microscopic preparations are characterized by: triangular or multipolar shaped somata; three to four primary dendrites that arise from the soma and bifurcate once or more to produce an extensive dendritic arborization restricted, for the most part, to the hilus; numerous thorny excrescences on their somata and proximal dendrites with typical spines on distal dendrites; and axons that bifurcate and are directed toward the fimbria and the molecular layer of the dentate gyrus. The mossy cells have an immature appearance at birth and on subsequent days their maturation appears to lag somewhat behind that of the hippocampal pyramidal cells. On postnatal day 1, many of the dendrites bear growth cones primarily at their termini and have long, thin filipodia emanating from various points along their lengths. Many of the dendrites enter the molecular layer of the dentate gyrus, though this is rarely seen in the mature brain. Typical pedunculate spines are first commonly seen on the distal dendrites around postnatal day 7 while thorny excrescences are first commonly seen between postnatal days 11 and 14. By postnatal day 21, the dendrites have attained a mature appearance although the density of both typical spines and thorny excrescences is less than that found in adults. Two different retrograde transport methods were used to confirm that mossy cells give rise to the commissural projection to the contralateral dentate gyrus. The first method combined HRP histochemistry with a silver intensification procedure and the second method combined HRP histochemistry with Golgi staining. While the majority of commissurally projecting hilar neurons had the appearance of mossy cells, there were others that were smaller and either ovoid or fusiform. In EM preparations, the somata of mature mossy cells display round nuclei that lack infoldings and intranuclear rods. The perikaryal cytoplasm contains the organelles typically found in pyramidal cells of the hippocampus. Somal spines with complex shapes and branching patterns are commonly observed. The thorny excrescences on the proximal dendrites correspond to spines with long thin stalks and complex end bulbs that may appear mushroom shaped.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections of growth-cone-bearing fibers of retinal ganglion cells within co-cultured tectal explants: Early branching depends on age of target tissue

The projections of retinal ganglion cell axons within co-cultured tectal explants were analyzed in order to investigate some of the factors that determine the earliest responses of retinal axons to cues present in an isolated target tissue. Half retinas and superior colliculi (tecta) from the embryonal mouse were explanted, separated by a 0.5 mm gap. After 5 days in vitro retinal ganglion cells were labeled by extracellular ionophoresis of HRP into the optic nerve head region. Cleared co-cultures were studied as whole mounts. Growth-cone-bearing retinal fibers were studied in standard tectal co-cultures, and in cases where tectum had been explanted 2 weeks prior to retina. The heterochronously prepared cultures had a higher proportion of fibers with complex branching patterns than the synchronous explants. Cultures in which retinas were explanted 1 week after tecta exhibited intermediate proportions of such fibers. These observations suggest that older tecta facilitate branching of ingrowing retinal fibers, although other alterations during in vitro development must be evaluated. The growth patterns of axons originating in nasal and temporal hemi-retinas were analyzed in terms of possible positional cues provided by the target tecta. Axons originating in temporal hemi-retinas did not show evidence of preferential branching in, or growth toward, appropriate anterior regions of co-cultured tectal explants. In contrast, the majority of nasal retinal axons showed enhanced terminations and complex branching in, and bending towards, the posterior tectum.

Morphology of on-off direction-selective ganglion cells in the rabbit retina

On-off direction-selective ganglion cells in rabbit retina have been stained by intracellular injection of horseradish peroxidase (HRP). The dendritic ramification is basically bistratified . Global asymmetries related to the preferred direction are not apparent, but the small diameter dendrites, spines, and complex branching pattern are consistent with models based on local, non-linear mechanisms for direction-selectivity.

Stellate cells differentiate successively in the cat sensorimotor cortex during early postnatal ontogeny

Golgi and Golgi-Kopsch techniques were used to investigate maturation of stellate and pyramidal cells and development of stellate-pyramidal connections in kittens of the following ages: 2, 7, 14, 21, 28 and 34 days. By two weeks, stellate cells in layer V have become mature. Layer III stellate cells with vertical axon ramifications are differentiated by 2–3 weeks of life and in 3-week-olds the horizontal spread of axon collaterals amounts to 1300 μm. Layer II stellate cells which are poorly developed in newborns acquire the greatest number of collaterals and a complex axon branching pattern by 4 weeks of age.

PATTERNS OF CUTICULAR SCULPTURE IN THE HYBRID, CUPRESSOCYPARIS LEYLANDII (JACKSON AND DALLIMORE) DALLIMORE, AND ITS PUTATIVE PARENTS

The circumstances of the origin of X Cupressocyparis leylandii (Jackson and Dallimore) Dallimore, its subsequent propagation and comparison of morphology with its putative parents Chamaecyparis nootkatensis (D. Don) Spach and Cupressus macrocarpa Hartw., have been described by Ovens, Blight and Mitchell (1964), van de Laar (1968) and Mitchell (1972). Although its hybrid status has not yet been proved by breeding and other genetic experiments, the problem might be approached via genotypic variability of cuticular features. Increasing use has been made of cuticular characters in various taxonomic studies (e.g. Stace, 1965, Stockey and Taylor, 1978; Miranda and Chaphekar, 1980). The present study attempts to compare the leaf cuticles of X Cupressocyparis leylandii and its putative parents. The cuticles were macerated in 20 0 chromium trioxide for 16 h at room temperature for subsequent examination by scanning electron microscopy (Alvin and Boulter, 1974; Oladele, 1982). Integrity of the cuticle was not affected, although the extracuticular wax may be partly dissolved by the treatment, particularly for periods longer than 16 h. Examination of the inner surface of the cuticles isolated from the abaxial surface of the leaves, reveals sculpture patterns consisting essentially of two main features the macrorelief formed by the anticlinal or radial flanges and the microrelief of the periclinal or tangential surface (Fig. 1). The hybrid shows intermediacy in two features of the radial flanges, namely continuity of the flange and the radial flange buttress. The radial flange is sparsely interrupted in Cupressus macrocarpa [Fig. 1 (c)], highly interrupted in Charnaecyparis nootkatensis [Fig. 1 (a)] and less so in X Cupressocyparis leylandii [Fig. 1 (b)]. Along the base of radial flange is a swelling which resembles a buttress to the flange; this is absent in Cupressus macrocarpa [Fig. 1(c)], very prominent in Chamaecyparis nootkatensis [Fig. 1(a)] and intermediate in the hybrid [Fig. 1(b)]. However, the microrelief or surface sculpture of the tangential surface and of the radial surface do not show intermediacy in the hybrid. The sculpture is complex in Chamaecyparis nootkatensis, in which coarse granules predominate, with other less prominent and fewer granules. The cavities also form a complex branching pattern among the granules [Fig. 1 (d)]. In Cupressus macrocarpa, surface granulation is rather more uniform, with greater density of small elements [Fig. 1(f)]. The surface in the hybrid is comparatively smooth with only small, rather uniform widely spaced granules [Plate 1(e)]. Nor do the granules in the hybrid show intermediacy in size as they are smaller (04 4tm in diameter) than those of

Aqueductal tanycytes in the rabbit brain: A Golgi study.

Utilizing Golgi-Cox impregnation, tanycytes were found in the ependyma of the cerebral aqueduct of the neonatal and adult rabbit. These tanycyte somas showed a variety of shapes, apical projections into the aqueduct, and basal processes (shafts) projecting into the mesencephalon, particularly into the periaqueductal gray (PAG). The shafts showed a variety of branching patterns, and sometimes abutted or terminated on capillaries or on specific neuronal elements. Other shafts coiled within the PAG or terminated within the neuropil of the mesencephalon. It is possible that these tanycytes provide a route for transport of cerebrospinal-fluid-borne substances from the aqueduct to the neuronal regions and vasculature of the mesencephalon. The presence of these tanycytes with complex branching patterns in proximity to neural and vascular structures suggests a permanent, active role for these specialized ependymal cells.

Correlation between presynaptic dense bodies and tranmitter output at lobster neuromuscular terminals by serial section electron microscopy

Lobster neuromuscular terminals releasing comparatively small (low-output type) and large (high-output type) amounts of transmitter but arising from the single excitatory motor axon to the proximal accessory flexor muscle were serially sectioned for electron microscopy. The three-dimensional reconstruction showed the two types of terminals to have a complex branching pattern in which thin branches of the motor axon often enlarged into synapse bearing terminal regions. Quantitative comparison showed that the mean surface area of a synapse is similar in the two types of terminals. However, the low-output terminal has a higher synaptic density and devotes a greater part of its surface area to synapses compared to its high-output counterpart suggesting that transmitter output is not directly related to synaptic area. The mean surface area of a presynaptic dense body is not significantly different between low- and high-output synapses, but there is a significantly greater density of these active zones in the high-output terminal. This results in the ratio of mean dense body area to mean synaptic area being approximately 3 × greater in the high-output synapses than the low-output ones. This significant difference in the surface area of presynaptic dense bodies between low- and high-output synapses correlates with the difference in transmitter output at these two synapses, and implicates the dense bodies in the mechanism of transmitter release at lobster neuromuscular synapses.

Apparent prolonged evolutionary stasis in the middle Eocene hoofed mammal Hyopsodus

The stratophenetic approach to phylogeny reconstruction, developed in numerous recent papers by Gingerich, has its strongest data base in comprehensive collections from early Eocene rocks in the Big Horn Basin of northwestern Wyoming. Other examples have been criticised for lack of well-documented collection data, making suitable testing of stratophenetic interpretations of evolutionary modes virtually impossible.Study of Hyopsodus from the middle Eocene Bridger Formation of southwestern Wyoming provides new collection data. Adequate stratigraphic documentation is available, so Gingerich's graphical presentation can be essentially duplicated. In contrast to the complex branching pattern Gingerich interpreted from his data, Bridger Formation Hyopsodus data seems to show little size change through approximately one million years. This stasis or equilibrium condition, which is considered rare by Bookstein et al. (1978), is the only well developed pattern in Bridger Hyopsodus.