紫叶小檗刺的形态与发生——对小檗属植物刺的重新认识

针对目前人们对小檗属植物刺的来源存在不同见解,本研究通过实体解剖及石蜡切片技术,以紫叶小檗为代表研究小檗属植物刺的形态和发生,结果表明,紫叶小檗的刺均为叶刺,而非茎刺,明确了小檗属的刺为叶的变态。     

Protracted and asynchronous accumulation of PSD95‐family MAGUKs during maturation of nascent dendritic spines

The formation and stabilization of new dendritic spines is a key component of the experience‐dependent neural circuit plasticity that supports learning, but the molecular maturation of nascent spines remains largely unexplored. The PSD95‐family of membrane‐associated guanylate kinases (PSD‐MAGUKs), most notably PSD95, has a demonstrated role in promoting spine stability. However, nascent spines contain low levels of PSD95, suggesting that other members of the PSD‐MAGUK family might act to stabilize nascent spines in the early stages of spiny synapse formation. Here, we used GFP‐fusion constructs to quantitatively define the molecular composition of new spines, focusing on the PSD‐MAGUK family. We found that PSD95 levels in new spines were as low as those previously associated with rapid subsequent spine elimination, and new spines did not achieve mature levels of PSD95 until between 12 and 20 h following new spine identification. Surprisingly, we found that the PSD‐MAGUKs PSD93, SAP97, and SAP102 were also substantially less enriched in new spines. However, they accumulated in new spines more quickly than PSD95: SAP102 enriched to mature levels within 3 h, SAP97 and PSD93 enriched gradually over the course of 6 h. Intriguingly, when we restricted our analysis to only those new spines that persisted, SAP97 was the only PSD‐MAGUK already present at mature levels in persistent new spines when first identified. Our findings uncover a key structural difference between nascent and mature spines, and suggest a mechanism for the stabilization of nascent spines through the sequential arrival of PSD‐MAGUKs. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1161–1174, 2017     

Electron microscopic 3D-reconstruction of dendritic spines in cultured hippocampal neurons undergoing synaptic plasticity

Dendritic spines are assumed to constitute the locus of neuronal plasticity, and considerable effort has been focused on attempts to demonstrate that new memories are associated with the formation of new spines. However, few studies that have documented the appearance of spines after exposure to plasticity-producing paradigms could demonstrate that a new spine is touched by a bona fida presynaptic terminal. Thus, the functional significance of plastic dendritic spine changes is not clearly understood. We have used quantitative time lapse confocal imaging of cultured hippocampal neurons before and after their exposure to a conditioning medium which activates synaptic NMDA receptors. Following the experiment the cultures were prepared for 3D electron microscopic reconstruction of visually identified dendritic spines. We found that a majority of new, 1- to 2-h-old spines was touched by presynaptic terminals. Furthermore, when spines disappeared, the parent dendrites were sometime touched by a presynaptic bouton at the site where the previously identified spine had been located. We conclude that new spines are most likely to be functional and that pruned spines can be transformed into shaft synapses and thus maintain their functionality within the neuronal network.     

Do thin spines learn to be mushroom spines that remember?

Dendritic spines are the primary site of excitatory input on most principal neurons. Long-lasting changes in synaptic activity are accompanied by alterations in spine shape, size and number. The responsiveness of thin spines to increases and decreases in synaptic activity has led to the suggestion that they are 'learning spines', whereas the stability of mushroom spines suggests that they are 'memory spines'. Synaptic enhancement leads to an enlargement of thin spines into mushroom spines and the mobilization of subcellular resources to potentiated synapses. Thin spines also concentrate biochemical signals such as Ca(2+), providing the synaptic specificity required for learning. Determining the mechanisms that regulate spine morphology is essential for understanding the cellular changes that underlie learning and memory.     

Temporal dynamics of NMDA receptor-induced changes in spine morphology and AMPA receptor recruitment to spines

Recent studies have shown that the activation of NMDA receptors can induce rapid changes in dendritic morphology and synaptic recruitment of AMPA receptors in dendritic spines. Here, we analyze the time course of NMDA receptor-induced changes in dendrite morphology and recruitment of AMPA receptors to synapses in cultured neurons. Activation of NMDA receptors causes a rapid transient increase in the size of preexisting spines and then the gradual formation of new dendritic protrusions and spines. NMDA receptor activation also induced GFP-tagged AMPA receptors to cluster in dendrites and to be inserted into the surface of dendritic spines. These results indicate that NMDA receptor activation induces several phases of dendritic plasticity, initial expansion of dendritic spines, followed by the de novo formation of spines and AMPA receptor dendritic clustering and surface expression on spines. Each of these forms of plasticity may have significant effects on the efficacy of synaptic transmission.     

The effect of cactus spines on light interception and Photosystem II for three sympatric species of Opuntia from the Mojave Desert

Cactus spines reduce herbivory, direct water toward roots and reduce the impacts of high- and low-temperature extremes. Yet, shading of stems by spines reduces incident photosynthetic photon flux density (PFD), photosynthesis and growth. This study compared spinescence, PFD interception, stem temperature, Photosystem II (PSII) photochemistry and xanthophyll pigment composition for three species of cacti from the Mojave Desert, CA. The species vary in spinescence: Opuntia basilaris , which has no central or radial spines; Opuntia erinacea , which is densely covered with spines; and Opuntia phaeacantha , which has an intermediate coverage of spines. The role of spines was tested by removing spines from stems of O. erinacea . PFD interception was similar for both O. basilaris and O. phaeacantha , and about three times that for densely spined O. erinacea ; removal of spines increased incident PFD three-fold. There were no effects of spines on stem temperatures. Steady-state light-response curves of chlorophyll a fluorescence from PSII indicated that ΦPSII, photochemical quenching (qP) and electron flux within PSII were lower, and non-photochemical quenching was higher, for O. erinacea in comparison to the other two species with less spines. After 2 months, qP was higher and electron flux lower, and xanthophyll pigment pool size was higher, for stems from which spines had been removed compared with intact stems. These three species allocate different amounts of biomass to spines, resulting in species-specific PFD interception, PSII photochemistry and xanthophyll pigment pool size, which may help maintain rates of photosynthesis during the hot, dry Mojave Desert summer.     

Evolution and losses of spines in slug caterpillars (Lepidoptera: Limacodidae)

Larvae of the cosmopolitan family Limacodidae, commonly known as “slug” caterpillars, are well known because of the widespread occurrence of spines with urticating properties, a morpho‐chemical adaptive trait that has been demonstrated to protect the larvae from natural enemies. However, while most species are armed with rows of spines (“nettle” caterpillars), slug caterpillars are morphologically diverse with some species lacking spines and thus are nonstinging. It has been demonstrated that the evolution of spines in slug caterpillars may have a single origin and that this trait is possibly derived from nonstinging slug caterpillars, but these conclusions were based on limited sampling of mainly New World taxa; thus, the evolution of spines and other traits within the family remains unresolved. Here, we analyze morphological variation in slug caterpillars within an evolutionary framework to determine character evolution of spines with samples from Asia, Australia, North America, and South America. The phylogeny of the Limacodidae was reconstructed based on a multigene dataset comprising five molecular markers (5.6 Kbp: COI, 28S, 18S, EF‐1α, and wingless) representing 45 species from 40 genera and eight outgroups. Based on this phylogeny, we infer that limacodids evolved from a common ancestor in which the larval type possessed spines, and then slug caterpillars without spines evolved independently multiple times in different continents. While larvae with spines are well adapted to avoiding generalist predators, our results imply that larvae without spines may be suited to different ecological niches. Systematic relationships of our dataset indicate six major lineages, several of which have not previously been identified.     

How predation shaped fish: the impact of fin spines on body form evolution across teleosts

It is well known that predators can induce morphological changes in some fish: individuals exposed to predation cues increase body depth and the length of spines. We hypothesize that these structures may evolve synergistically, as together, these traits will further enlarge the body dimensions of the fish that gape-limited predators must overcome. We therefore expect that the orientation of the spines will predict which body dimension increases in the presence of predators. Using phylogenetic comparative methods, we tested this prediction on the macroevolutionary scale across 347 teleost families, which display considerable variation in fin spines, body depth and width. Consistent with our predictions, we demonstrate that fin spines on the vertical plane (dorsal and anal fins) are associated with a deeper-bodied optimum. Lineages with spines on the horizontal plane (pectoral fins) are associated with a wider-bodied optimum. Optimal body dimensions across lineages without spines paralleling the body dimension match the allometric expectation. Additionally, lineages with longer spines have deeper and wider body dimensions. This evolutionary relationship between fin spines and body dimensions across teleosts reveals functional synergy between these two traits and a potential macroevolutionary signature of predation on the evolutionary dynamics of body shape.     

Dendritic spines and long-term plasticity

A recent flurry of time-lapse imaging studies of live neurons have tried to address the century-old question: what morphological changes in dendritic spines can be related to long-term memory? Changes that have been proposed to relate to memory include the formation of new spines, the enlargement of spine heads and the pruning of spines. These observations also relate to a more general question of how stable dendritic spines are. The objective of this review is to critically assess the new data and to propose much needed criteria that relate spines to memory, thereby allowing progress in understanding the morphological basis of memory.     

Functional morphology of chonetidine (Brachiopoda) spines: biomechanical tests of a potential key innovation

Chonetidine brachiopods were a significant component of Paleozoic marine life; chonetidines experienced a major adaptive radiation during the Late Silurian and Early Devonian. The Chonetidina clade is united by the presence of spines on the hingeline but the function of these spines has not been clearly demonstrated. The present study performs a biomechanical experiment, using specimens of Neochonetes granulifera with and without artificial spines in a recirculating flume, to test if the spines may have inhibited entrainment in higher energy settings. Specimens with spines were less likely to be overturned or transported than those without spines, and were overturned or transported at significantly higher velocities than specimens without spines. Performance improved with the addition of another pair of spines. In addition, spinose specimens reoriented such that their commissures faced upstream. The results suggest that chonetidines could have survived in higher-energy environments, even if the brachiopods were not physically attached to the substrate. As such, it is functionally plausible that the evolution of hinge-spines may have possibly facilitated the adaptive radiation of the clade by enabling chonetidines to inhabit previously unoccupied habitats.     

Structure and function of clypeasteroid miliary spines (Echinodermata,Echinoides)

Summary Histological and ultrastructural techniques have been used to describe the functional morphology of clypeasteroid miliary spines, with special reference to their supposed mucus-secreting role. Mucus cells were not found in the miliary spines of any members of the Arachnoididae, Fibulariidae, Laganidae, Echinarachniidae, Dendrasteridae, Astriclypeidae, or Mellitidae examined in this study. Only members of the Clypeasteridae have mucus-secreting cells in these spines. Characteristics of the skeleton, ultrastructure of the nervous system, and histology of the musculature and epithelia of the base, shaft and tip are also discussed. Miliary spines have two bands of cilia running along the entire length of opposite sides of the shaft. The geometric packing of cilium-bearing cells in these bands is described for the first time, as is the remarkable form of the sacs found at the tips of dendrasterid, astriclypeid, and mellitid miliary spines. These sacs are definitely not mucous sacs, as previously described, but are balloons of single-celled epithelium internally tethered to the skeletal tip by copious quantities of collagenous connective tissue. Miliary spines prevent obstruction of aboral nutritive and ventilatory ciliary currents caused by substrate particles falling to the test surface during burrowing. They do this in two ways: (1) they help generate ciliary currents that sweep finer material off the test, and (2) they contribute to the formation of a spine canopy that mechanically blocks larger particles from falling between the spines. Members of the Clypeasteridae secrete an interspine mucous tent that traps potentially clogging material. The miliary spine sacs of sand dollars are deformable space-fillers that plug holes between primary spines in the aboral canopy, even as the spines rock on their tubercles to push sand backwards over the test. Allometry of spines from Echinarachnius parma suggests that aboral military spines and club-shaped spines exhibit co-ordinated growth that maintains the aboral canopy throughout post-metamorphic ontogeny, and that aboral spins have an overall lower growth rate than spines on the oral surface.     

The Effect of Abdominal Spines on Female Mating Frequency and Fecundity in a Water Strider

Conflict between the sexes over mating decision may result in antagonistic coevolution in structures that increase control over copulation. In Aquarius paludum both females and males have long abdominal spines. We tested the hypothesis that abdominal spines increase female ability to resist male mating attempts and reduce the costs of mating in A. paludum. We manipulated female spine length and observed female mating and egg-production rate in two different studies. We found that females with intact spines succeeded to reject male mating attempt more often than females with removed spines. Intact females also mated less often than females with removed or shortened spines. Male presence and mating rate increased female egg number. Our results thus support the hypothesis that abdominal spines help female to reject male mating attempts but contrary to predictions, we found that A. paludum females somehow benefit from multiple matings in spite of the sexual conflict.     

Patterns of trunk spine growth in two congeneric species of acanthocephalan: investment in attachment may differ between sexes and species

Acanthocephalans have evolved a hooked proboscis and some taxa have trunk spines to attach to their definitive hosts. These structures are generated before being used, thus a key question is how investment in attachment could optimally be allocated through the ontogeny. The number and arrangement of hooks and spines are never modified in the definitive host, but it is unclear whether these structures grow during adult development. A comparison of the size of trunk spines between cystacanths and adults of Corynosoma cetaceum and C. australe indicated that spines grow in both species, but only in females, which also had significantly larger spines than males. This sexual dimorphism did not result from pure allometry because the body of females was smaller, and did not grow more than that of males. However, having a longer lifespan, females would need to withstand the extreme flow conditions prevailing in marine mammals for longer, inducing different investment and development schedules for spines. Patterns of spine growth also differed between species: fore-trunk spines grew in both species, but hind-trunk spines did only in C. cetaceum. In conclusion, investment strategies on attachment may differ, not only between congeneric species of acanthocephalan, but also between sexes of the same species.     

High speed two-photon imaging of calcium dynamics in dendritic spines: consequences for spine calcium kinetics and buffer capacity

Rapid calcium concentration changes in postsynaptic structures are crucial for synaptic plasticity. Thus far, the determinants of postsynaptic calcium dynamics have been studied predominantly based on the decay kinetics of calcium transients. Calcium rise times in spines in response to single action potentials (AP) are almost never measured due to technical limitations, but they could be crucial for synaptic plasticity. With high-speed, precisely-targeted, two-photon point imaging we measured both calcium rise and decay kinetics in spines and secondary dendrites in neocortical pyramidal neurons. We found that both rise and decay kinetics of changes in calcium-indicator fluorescence are about twice as fast in spines. During AP trains, spine calcium changes follow each AP, but not in dendrites. Apart from the higher surface-to-volume ratio (SVR), we observed that neocortical dendritic spines have a markedly smaller endogenous buffer capacity with respect to their parental dendrites. Calcium influx time course and calcium extrusion rate were both in the same range for spines and dendrites when fitted with a dynamic multi-compartment model that included calcium binding kinetics and diffusion. In a subsequent analysis we used this model to investigate which parameters are critical determinants in spine calcium dynamics. The model confirmed the experimental findings: a higher SVR is not sufficient by itself to explain the faster rise time kinetics in spines, but only when paired with a lower buffer capacity in spines. Simulations at zero calcium-dye conditions show that calmodulin is more efficiently activated in spines, which indicates that spine morphology and buffering conditions in neocortical spines favor synaptic plasticity.     

Bidirectional activity-dependent morphological plasticity in hippocampal neurons

Dendritic spines on pyramidal neurons receive the vast majority of excitatory input and are considered electrobiochemical processing units, integrating and compartmentalizing synaptic input. Following synaptic plasticity, spines can undergo morphological plasticity, which possibly forms the structural basis for long-term changes in neuronal circuitry. Here, we demonstrate that spines on CA1 pyramidal neurons from organotypic slice cultures show bidirectional activity-dependent morphological plasticity. Using two-photon time-lapse microscopy, we observed that low-frequency stimulation induced NMDA receptor-dependent spine retractions, whereas theta burst stimulation led to the formation of new spines. Moreover, without stimulation the number of spine retractions was on the same order of magnitude as the stimulus-induced spine gain or loss. Finally, we found that the ability of neurons to eliminate spines in an activity-dependent manner decreased with developmental age. Taken together, our data show that hippocampal neurons can undergo bidirectional morphological plasticity; spines are formed and eliminated in an activity-dependent way.     

Sclerotised spines in the female bursa associated with male’s spermatophore production in cantharidin-producing false blister beetles

Cantharidin is a defence chemical synthesised in only two beetle families Meloidae and Oedemeridae. In Meloidae, cantharidin is used as a defence chemical in eggs. However, in Oedemeridae the function of cantharidin remains unclear. Based on morphological comparison of female internal reproductive organs in 39 species of Oedemeridae, we found that some species have sclerotised spines in the bursa copulatrix (bursal spines), while others have no such spines. Molecular phylogenetic trees inferred from mitochondrial 16S and nuclear 28S rRNA gene sequences suggested multiple evolutionary origins of bursal spines from an ancestor without spines. In the species which lacked spines, males transferred small amounts of ejaculates to females; however, in species with spines, males transferred large spermatophores. Deposited spermatophores gradually disappeared in the bursa, probably owing to absorption. To compare the amounts of cantharidin in eggs laid by species with and without bursal spines, we constructed a new bioassay system using the small beetle Mecynotarsus tenuipes from the family Anthicidae. M. tenuipes individuals were attracted to droplets of cantharidin/acetone solution, and the level of attraction increased with cantharidin concentration. This bioassay demonstrated that the eggs of Nacerdes caudata and N. katoi, both of which species have conspicuous bursal spines, contain more cantharidin than the eggs of N. waterhousei, which lacks spines. In the former species, males transfer large spermatophores to the female, and spermatophores are eventually broken down and digested within the female’s spiny bursa. Thus, females with bursal spines may be able to provide more cantharidin to their eggs.     

Surface ultrastructure of the adult stage of Acanthotrema felis (Trematoda: Heterophyidae)

The surface ultrastructure of Acanthotrema felis (Trematoda: Heterophyidae) adults, recovered from a kitten experimentally infected with the metacercariae, was observed using a scanning electron microscope. The worm was leaf-like, ventrally concave and covered with scale-like multi-pointed tegumental spines. The spines on the anterior surface were short but broad, and had 10-12 pointed tips. The cytoplasmic processes protruded around the spines, like pockets for the spines. The ventrogenital opening was crescent, or kidney-shaped, and had protuberances with minute spines on its surrounding tegument. The spines on the posterior surface were long, but narrow, with 6-8 pointed tips. The cytoplasmic processes on this tegument were ridge-like, and elevated along the row of the spines. The surface ultrastructure of A. felis is generally similar to that of other heterophyid flukes, but some features are characteristic, and may be of taxonomic and bio-ecological significance.     

Structural and functional plasticity of dendritic spines – root or result of behavior?

Dendritic spines are multifunctional integrative units of the nervous system and are highly diverse and dynamic in nature. Both internal and external stimuli influence dendritic spine density and morphology on the order of minutes. It is clear that the structural plasticity of dendritic spines is related to changes in synaptic efficacy, learning and memory and other cognitive processes. However, it is currently unclear whether structural changes in dendritic spines are primary instigators of changes in specific behaviors, a consequence of behavioral changes, or both. In this review, we first examine the basic structure and function of dendritic spines in the brain, as well as laboratory methods to characterize and quantify morphological changes in dendritic spines. We then discuss the existing literature on the temporal and functional relationship between changes in dendritic spines in specific brain regions and changes in specific behaviors mediated by those regions. Although technological advancements have allowed us to better understand the functional relevance of structural changes in dendritic spines that are influenced by environmental stimuli, the role of spine dynamics as an underlying driver or consequence of behavior still remains elusive. We conclude that while it is likely that structural changes in dendritic spines are both instigators and results of behavioral changes, improved research tools and methods are needed to experimentally and directly manipulate spine dynamics in order to more empirically delineate the relationship between spine structure and behavior.     

Echinostoma caproni: Differential tegumental responses to growth in compatible and less compatible hosts

The topography of the tegument of Echinostoma caproni adults collected from high (mice) and low (rats) compatible hosts was compared by SEM. In the oral (OS) and the ventral sucker (VS) areas, a worm age-host species interaction was found with regard to the density of spines. There was a decrease in the density of spines in the adults collected from mice, whereas an increase occurred in the OS area in worms from rats over time. The tegumentary spines in adults from mice became larger and blunter. Some spines from the VS area in adults from mice at 4 wpi were multipointed. The spines of adults from rats were sharper, not covered by the tegument and no multipointed spines were observed. We detected a greater level of actin gene expression in the adults collected from rats. These facts suggest that the low compatible host induces an increased turnover of tegumentary spines.