Spiny Branches Research Articles

High index surface-exposed and composition-graded PtCu3@Pt3Cu@Pt nanodendrites for high-performance oxygen reduction

Alloying and nanostructuring are two strategies used to facilitate the efficient electrocatalysis of the oxygen reduction reaction (ORR) by Pt, where the high index surfaces (HISs) of Pt exhibit superior activity for ORR. Here, we report the fabrication of PtCu3 nanodendrites possessing rich spiny branches exposing n(111) × (110) HISs. The dendrites were formed through an etching-modulated seeding and growing strategy. Specifically, an oxidative atmosphere was initially applied to form the concaved nanocubes of the Pt-Cu seeds, which was then switched to an inert atmosphere to promote an explosive growth of dendrites. Separately, the oxidative or inert atmosphere failed to produce this hyperbranched structure. Electrochemical dealloying of the PtCu3 nanodendrites produced Pt3Cu shells with Pt-rich surfaces where HIS-exposed dendrite structures were maintained. The resulting PtCu3@Pt3Cu@Pt nanodendrites in 0.1 M HClO4 exhibited excellent mass and area specific activities for ORR, which were 14 and 24 times higher than that of commercial Pt/C, respectively. DFT calculations revealed that Cu alloying and HISs both contributed to the significantly enhanced activity of Pt, and that the oxygen binding energy on the step sites of HISs on the PtCu3@Pt3Cu@Pt nanodendrites approached the optimal value to achieve a near peak-top ORR activity.

A new Muricea species (Cnidaria, Anthozoa, Octocorallia) from the eastern tropical Pacific.

The genus Muricea is considered abundant and widely distributed along the eastern Pacific. Its occurrence in shallow waters has been recognised; however species from deeper than 30 m have been rarely recorded. During the 2005 R/V Urracá expedition along the north and central Pacific coast of Costa Rica several octocoral specimens were collected by bottom trawling from 30 to 150 m yielding new species and new records. Herein we describe a new species of Muricea from deeper than 30 m. The morphological characters of the species were analysed and illustrated by optic and scanning electron microscopy. Muricea subtilis sp. n. can be distinguished from the other species in the genus by its thin spiny branches, non-imbricate calyces, white colony and sclerites, and the size and composition of sclerites. Comparative character tables are provided for the closest Muricea species-group. This new species increases the number in the genus to 26, and contributes to the knowledge on the diversity and distribution of mesophotic soft corals in the eastern Pacific.

Description of two new species of Ochtodes (Rhodophyta: Gigartinales) from Caribbean Mexico on the basis of morphological and molecular evidence

Abstract The species diversity of the red algal genus Ochtodes from Caribbean Mexico is reconsidered after a new collection in this region. A combined analysis of plastid rbcL sequences together with detailed morphological studies has confirmed the presence of two undescribed species in addition to Ochtodes secundiramea. Ochtodes akumalensis sp. nov. has abundant spiny branches, especially on the main axis, and robust cystocarps densely aggregate at the branch tips. In contrast, Ochtodes maguachaveziae sp. nov. lacks spiny branches and gland cells, and bears scattered cystocarps near the branch apices. Both species develop cruciately to obliquely divided zonate tetrasporangia. The molecular analysis showed that O. maguachaveziae and O. akumalensis represent separate taxonomic entities with a 1.8% sequence divergence between them. The description of two new species of Ochtodes from Caribbean Mexico suggest that our knowledge of the regional diversity of this genus is still incomplete.

EXTENSIVE INTRASPECIFIC MORPHOLOGICAL VARIATION IN ENTEROMORPHA MUSCOIDES (CHLOROPHYTA) REVEALED BY MOLECULAR ANALYSIS

Enteromorpha muscoides (Clemente y Rubio) Cremades and E. clathrata Roth (Greville) are morphologically variable species that can easily be distinguished from other Enteromorpha species but not from each other. The key morphological character separating the two species is the presence or absence of spine‐like branches: E. muscoides has small spine‐like branches throughout the thallus, whereas E. clathrata lacks spines. The spiny branches in E. muscoides are not as obvious in summer as in winter, so summer samples may be difficult to distinguish from those of E. clathrata. In this study, molecular data were used to investigate whether these two species, as defined by morphological characters, might be conspecific. The sequences of the internal transcribed spacers ITS1 and ITS2 and the 5.8S gene differed by 0%–0.6% between all samples of both E. muscoides and E. clathrata. Phylogenetic analysis of these sequences in an alignment with 13 other representatives of both Enteromorpha and Ulva showed that this highly supported monophyletic E. muscoides/E. clathrata clade is separated by long branch lengths from other Enteromorpha and Ulva clades. Based on these results, we suggest that Enteromorpha muscoides (Clemente y Rubio) Cremades and Enteromorpha clathrata Roth (Greville) are conspecific, with the older name E. muscoides taking priority.

Effects of Paired and Unpaired Eye-Blink Conditioning on Purkinje Cell Morphology

This experiment addressed (1) the importance of conjunctive stimulus presentation for morphological plasticity of cerebellar Purkinje cells and inhibitory interneurons and (2) whether plasticity is restricted to the spiny branches of Purkinje cells, which receive parallel fiber input. These issues were investigated in naive rabbits and in rabbits that received paired or unpaired presentations of the conditioned stimulus (CS) and unconditioned stimulus (US). To direct CS input to the cerebellar cortex, pontine stimulation served as the CS. Air puffs to the cornea served as the US. Paired condition rabbits received pontine stimulation for 350 msec paired with a coterminating 100-msec air puff. Unpaired condition rabbits received the same stimuli in a pseudorandom order at 1- to 32-sec intervals. Rabbits were trained for a mean of 12 days. Naive rabbits received no treatment. In Golgi-stained Purkinje neurons in lobule HVI, total dendritic length, main branch length, total spiny branch length, and number of spiny branch arbors were all greater in the naive group than in the paired and unpaired groups, which did not differ. No differences were found between the hemispheres ipsilateral and contralateral to the trained eye. The dendritic length and number of branches for inhibitory interneurons did not differ across groups. The Purkinje cell morphological changes detected with these methods do not appear to be uniquely related to the conjunctive activation of the CS and US in the paired condition.

Spines protect plants against browsing by small climbing mammals.

The presence of spines on woody plants has been shown to limit the loss of foliage to large mammalian browsers by restricting both bite size and biting rate. We tested the hypothesis that plant spines are also an effective defense against browsing by small mammals, such as rodents, that climb within the canopy of shrubs to harvest fruits, seeds, and foliage. Tame southern plains woodrats (Neotoma micropus) were allowed to harvest raisins impaled on the branches of blackbrush shrubs (Acacia rigidula Benth.) in five categories of spinescence: naturally spineless, moderately spiny, or very spiny branches, and moderately spiny and very spiny branches with the spines removed. Plant spinescence significantly reduced the woodrats foraging efficiency (P = 0.0001). Although plant spines are generally thought to be an evolved defense against browsing by ungulate herbivores, they may also reduce browsing by small mammals.

Tree-Epiphyte-Ant Relationships in the Low Inundated Forest of Sian Ka'an Biosphere Reserve, Quintana Roo, Mexico

Research on epiphyte (9 bromeliads and 1 orchid) relationships with host trees, and with arthropods, especially ants, was undertaken in the low inundated forest of Quintana Roo, Mexico. Epiphyte association with host trees is determined by the interaction of the epiphyte seed type and dispersal mode with the bark type of the host. Airborne seeds of the Tillandsia spp. are caught on the rough-barked and small, spiny branches of Bucida spinosa; flat, ovoid seeds of Aechmea bracteata, which are disseminated by birds, germinate principally on Haematoxylum campechianum and Erythroxylum confusum, two rough-barked tree species, often in forks of major branches, and never on B. spinosa; the minute seeds of Schomburgkia tibicinis germinate generally on E. confusum, but also on Manilkara zapota and rarely on B. spinosa. Epiphyte association with non-ant arthropods is determined principally by the size and shape of the cavities. Most of the arthropods, including aquatic insects, are detritivores feeding on rotten debris which collects in the reservoirs of bromeliads. Also, some animals utilize epiphytes only as shelter. Epiphyte association with ants is largely correlated with the size and shape of the cavities. Intermediate steps between the type and the myrmecophytic type were determined in the genus Tillandsia. The best rate of occupation by ants (96% of the ramets sheltered ants) was obtained by A. bracteata of the phytotelm tank type (reservoir in peripheric cavities, but also a waterproof central cavity), while the best rate of ant diversity was observed in T. bulbosa (myrmecophytic type; 26 ant species). Ants sheltered in the bromeliads were shown to protect host trees against defoliation by an undetermined chrysomelid beetle and the leaf-cutting ant Atta cephalotes.

Beta-like ganglion cells in the South American opossum retina: a Golgi study.

Using the Golgi technique we investigated the morphology of the ganglion cells of the South American opossum retina. We focused our attention on a type of ganglion cell which has a relatively small dendritic field diameter and a medium-sized soma, making it a morphological equivalent of beta ganglion cells of cat retina. Both radial sections of the retina, where the stratification level of ganglion cells dendrites can be observed in the inner plexiform layer (IPL), and flat preparations of the retina, where the whole dendritic field of the ganglion cells can be examined and quantified, have been studied. Usually these cells have one to three primary dendrites, giving rise to short spiny branches. The dendrites of these cells are segregated in two groups, one with dendritic trees arborizing in the inner two thirds and another group arborizing in the outer third of the IPL. The two groups of beta-like cells probably represent the physiological ON- and OFF-center types of ganglion cell as found in cat retina. The mean cell body and dendritic field diameters of 47 cells were 18.5 +/- 1.6 microns, (size range 16-21 microns) and 91.5 +/- 16 microns (range 54-133 microns), respectively. Cell body and dendritic fields sizes were homogeneous across the retina of the opossum. In the opossum the relatively large dendritic fields of the beta-like ganglion cells in the area centralis are consistent with the poor visual acuity of this species.

Permanent alterations of the dendritic tree of cerebellar Purkinje neurons in the rat following postnatal exposure to cis-dichlorodiammineplatinum

The aim of this study was to characterize further the effect of cis-dichlorodiammineplatinum (cisDDP) on cerebellar Purkinje neurons of the immature rat. Ten-day-old rats were treated with cisDDP subcutaneously and killed after 1, 7, 20 or 65 days. The cerebellar vermis was impregnated by the Golgi-Cox method to evaluate the extent of morphological maturation of the Purkinje cell dendritic tree. One day after treatment, the dendritic network of Purkinje cells of treated animals was poorly developed and the cell somata still showed numerous perisomatic processes. This indicates that cisDDP interferes with the organization of microtubules and microfilaments by the cell. Later, several abnormal shapes of the Purkinje cell dendritic tree were observed. These included: (1) elongated primary dendrites; (2) asymmetrical dendrites; (3) sprouting of secondary and spiny branches in two planes of the molecular layer; and (4) damming of spiny branchlets at the pial surface. Moreover, all the dendritic networks of Purkinje cells in treated animals were of a lower Strahler order than in controls. All these data suggest that the late anomalies of the dendritic trees are secondary to the general cisDDP-induced damage of the cerebellar cortex, rather than being a primary effect of the drug on the dendritic tree growth.

Endogenous opioids regulate dendritic growth and spine formation in developing rat brain

Continuous blockade of endogenous opioid-opioid receptor interaction by opioid antagonists from birth to day 10 increased neuronal maturation in the rat brain. The lengths of oblique dendrites of pyramidal cells in the cerebral cortex and basilar dendrites of the hippocampus were increased from controls by 136 and 51%, respectively, whereas the concentrations of spines in these cells were increased 183 and 69%, respectively. Total dendritic length of spiny branches of cerebellar Purkinje neurons was 65% greater than controls, and spine concentration of granule cells in the dentate gyrus was increased by 76%. Thus, endogenous opioids exert a remarkable influence on the timetable and magnitude of dendritic elaboration and spine formation, and serve as an important trophic influence in the regulation of neuro-ontogeny.

The Purkinje neuron: I. A Golgi study of its development in the mouse and in culture

The development of the Purkinje neuron was studied in organotypic culture and compared to that occurring in the intact animal, using a modified Golgi-Cox method. The post-natal sequence of development in the intact animal occurred in five distinct stages beginning with (1) an immature state (0-3 days), (2) a stage of perisomatic dendritic processes (4-6 days), and then (3) a stage characterized by the presence of spines on the soma region (7-10 days). This stage of somatic spines has not been delineated previously in Golgi studies of the Purkinje cell during its development. There was no evidence that the lateral somatic processes resorb; rather they continue to grow and develop into dendritic branches. It is proposed that by a process of perikaryal translocation, the soma region becomes transferred "downward," resulting in an elongation of the primary, apical dendrite (stage 4, 11-14 days). Beyond 15 days (stage 5) the dendritic branches grow to the pial surface and the neuron has its full complement of secondary, tertiary, and spiny branches. In culture, the development parallels that occurring in the intact animal during the first 10 days (stages 1, 2, 3) despite the absence of extracerebellar afferents and the special conditions of the culture. However, there is an overall absence of lamination of the cortex, the Purkinje neurons do not align, and the developmental process is modified because of the failure of the process of perikaryal translocation in culture. The resultant mature neuron has an altered morphology characterized by the presence of several dendrites and spines attached to the soma, and also lacks the complete development of the smaller dendritic branches.

Effects of low-level x-irradiation on cat cerebella at different postnatal intervals. II. Changes in Purkinje cell morphology.

The whole-head of infant kittens was irradiated with fractionated doses of 150 R and 200 R at different postnatal intervals. Experimental age conditions consisted of an irradiated newborn, 1-week, 2-week, 3-week, and a 4-week age condition while the age of sacrifice remained constant at 70 days. The molecular layer thickness was reduced by 47% in the newborn, 40% in the 1-week group, 17% in the 2-week group, 19% in the 3-week group and by 9% in the 4-week group. An evaluation of Golgi impregnated material revealed that the dendritic arborizations of purkinje cells were consistently reduced the earlier the age at which radiation was begun. A reduction in spiny branchlets was seen in all of the experimental conditions. All experimental age conditions displayed the phenomenon of dendritic "damming" at the pial surface, which consisted of an excessive crowding of spiny branches at this level. An increased growth of the primary dendrite before branching tood place was seen in the newborn and 1-week group. This became less but was still significant in the 2-week group. A correlation of this phenomenon with the presence or lack of stellate cells is disclssed. Purkinje cells with two or more dendrites emerging from their soma were classified and analyzed separately. It was found that the primary dendritic branching in these cells often followed separate morphological patterns and appeared to be independent of each other. Climbing fibers were found to conform to the abnormal dendritic arborizations of the Purkinje cells, and were reduced in complexity in the early radiation treatment groups. This suggested that climbing fibers had no influence upon the dendritic growth pattern, but instead were under the influence of the Purkinje cell dendritic growth.