Absence Of Spines Research Articles

Transient compartmentalization of interneuron dendrites

Much of our understanding of the delicate interplay between synaptic input, dendritic voltage-gated channels and spike backpropagation comes from a relatively small sampling of cortical or hippocampal principal cell types, whose large diameter apical dendrites permit electrophysiological manipulation combined with imaging approaches (Stuart et al. 1999). Although the dendrites of local circuit interneurons possess voltage-gated channels influential in action potential (AP) initiation and timing (Martina et al. 2000; Kaiser et al. 2001), their functional properties are poorly understood. In this issue of The Journal of Physiology, Goldberg et al. (2003a,b) combine two-photon imaging with whole-cell recording and anatomical reconstruction to examine calcium dynamics during AP backpropagation and subthreshold synaptic stimulation in dendrites of three types of primary visual cortex (V1) supragranular interneurons: multipolar parvalbumin positive ‘fast spikers’ (FS), bipolar calretinin-positive ‘irregular spikers’ (IS) and a heterogeneous group of ‘adapting cells’ (AD). In all interneurons, somatically generated APs actively backpropagated into the dendrites and evoked instantaneous calcium transients confirming the presence of voltage-gated sodium, potassium and calcium channels. However, in contrast to neighbouring pyramidal neurons, single APs rarely evoked detectable calcium signals and only when trains of stimuli were applied were appreciable calcium transients detected. The calcium signal in interneuron dendrites during a 10 AP (40 Hz) train was comparable to that activated by a single pyramidal cell backpropagating spike. Consistent with the high endogenous buffering capacity of interneurons (Kaiser et al. 2001) the decay time constant of the interneuron calcium transients was also significantly slower (IS > FS) than in pyramidal cells. The spatial extent of calcium transients was not uniform across the interneuron dendritic trees and they were typically observed only at proximal dendritic locations (< 100 μm) despite the confirmed presence of voltage-gated calcium channels throughout their dendrites. This spatial control was mediated by A-type transient outward potassium currents and was mitigated by previous synaptic activity in a manner reminiscent of that described for principal cells (Hoffman et al. 1997). Interestingly, blockade of transient A-type potassium channels was without effect on proximal calcium transients and suggests that like pyramidal cells, the transient potassium channel density in V1 interneurons increases with distance from the soma. This contrasts with the uniform density of 4-AP/TEA-sensitive channels observed on hippocampal somatostatin-positive interneurons (Martina et al. 2000) and underscores that few general assumptions can be applied to the diverse population of inhibitory interneurons. K+ currents on interneurons are important in regulating both synaptic activation and spike initiation (Fricker & Miles 2000) and these data suggest that A-type transient currents on V1 interneurons regulate both spike initiation and propagation. The present data highlight a hitherto unrecognized functional compartmentalization of interneuron dendrites: a perisomatic domain where backpropagating APs influence propagation of both electrical and calcium signals perhaps via gap junctions, and a distal compartment which backpropagating spikes reach only following inactivation of dendritic potassium channels. Given the afferent-specific innervation of proximal versus distal dendritic locations by thalamic and intracortical glutamatergic afferents respectively, the functional compartmentalization of interneuron dendrites may serve to additionally increase their computational prowess. Turning their attention to subthreshold synaptic stimuli, Goldberg et al. report that the predominant dendritic calcium signal in IS and AD cells arises via activation of synaptic NMDA receptors following AMPA receptor-driven depolarization. However, in FS cells, blockade of NMDA receptors removed only a small (and variable) calcium component to reveal a kinetically distinct calcium signal generated by Ca2+-permeable (CP-) AMPA receptors. CP-AMPA receptor-mediated synaptic events possess rapid kinetics and enable tight coincidence detection in interneuron populations. Accordingly, calcium influx kinetics in FS cells was more rapid than either IS and AD cells. Of particular note, in all three cell types synaptic activation generated calcium signals typically restricted to ≈10-20 μm of dendritic space, suggesting that despite the absence of spines, the synaptic calcium signal will remain highly localized. How this is achieved is unclear but this functional compartmentalization is probably highly significant given that kinetically distinct afferent projections can target overlapping dendritic domains of interneuron dendrites (Walker et al. 2002). Thus, the present papers demonstrate yet another tantalizing aspect of interneuron physiology and suggest that FS cells (and other cells that possess CP-AMPA receptors) may sustain multiple spatially isolated calcium domains that are independent of the background depolarization required for NMDA receptor-mediated calcium signals. Moreover, the different requirements for calcium entry via NMDA versus CP-AMPA receptors may provide the discriminatory mechanism for activation of downstream molecular targets and the plastic processes currently being studied in interneuron populations.

Zoeal stages and megalopa of Leucippa pentagona H. Milne Edwards, 1833 (Decapoda: Brachyura: Majoidea: Epialtidae) obtained from laboratory culture and a comparison with other epialtid and majoid larvae

Summary Leucippa pentagona H. Milne Edwards, 1833 is a small epialtid majoid crab occurring on sandy or muddy bottoms in shallow waters of the eastern Pacific and southwest Atlantic. Larvae of this monotypic genus obtained from Brazilian waters are described and illustrated for the first time. Larval development consists of two zoeal stages and a megalopa. The duration of the zoeal stages at 24°±1°C was 5–9 (6.4±0.5) and 5–7 (3.5±0.5) days for the first and second zoea, respectively, the megalopa phase appearing 10–13 (11±1) days after hatching. Larvae of L. pentagona are compared to those of other known epialtid larvae in particular and other majoids in general. The zoeal stages are characterized by a relatively long unarmed dorsal spine and a very small rostral spine that set them apart from other epialtid zoeae. Characteristic features of the megalopa include the absence of spines on the carapace and pereiopods and the presence of four plumose setae on the first abdominal somite.

STEPHANODISCUS KOMOROENSIS SP. NOV., A NEW PLEISTOCENE DIATOM FROM CENTRAL JAPAN

Stephanodiscus komoroensis sp. nov. is described from a lacustrine diatomite of the Uryuzaka Formation which is inferred to be Lower Pleistocene. The new species is characterized by rimoportulae with triangular tips at the tops of externally elongated, thick tubes, a complete absence of spines, and mantle fultoportulae that lack any vestiges of external tubuli. Stephanodiscus komoroensis is morphologically most similar to S. niagarae Ehrenberg and S. rotula (Kültzing) Hendey.

THE DISTRIBUTION AND CLASSIFICATION OF THE PROBLEMATICFRAGILARIA(VIRESCENSV.)EXIGUAGRUN./FRAGILARIA EXIGUIFORMIS(GRUN.) LANGE-BERTALOT: A NEW SPECIES OR A NEW GENUS?

The nomenclature of the taxon first recorded as Fragilaria (virescens) v. exigua by Grunow in Cleve & Moeller (1878) is examined with regard to the current botanical name, F. exiguiformis Lange-Bertalot. The distribution of this taxon in relation to pH is described from surface sediment samples collected from more than 200 soft-water lakes in both NW Europe and Antarctica. The optimum pH requirement is shown to be different in the two regions with a lower optimum (pH 5.7) for the European data set. One reason for this difference is the lack of moderately acid sites in the Antarctic data set. Another is that SEM investigation of F. exiguiformis from several localities shows that at least two taxa, characterized inter alia by presence or absence of spines, are present within this species. Lack of a rimoportula indicates that taxa in the F. exiguiformis complex should be transferred elsewhere. Also, the recognition of a non-spinose taxon within F. exiguiformis indicates that a new species description is requ...

Further Observations on the Genus Lissodinium Matz., (Dinophyceae), with Descriptions of Seventeen New Species

The morphology of the dinoflagellate genus Lissodinium Matz., emend. Carbonell-Moore was studied from cells collected in different parts of the world's oceans. The type species, Lissodinium schilleri, is redefined seventeen new species are described. No variation in the plate tabulation pattern was found. The apical pore complex consists of three platelets: a pore plate, a cover plate and a canal plate. The genus Lissodinium may also present an antapical spine. This feature was found in two of the new species. The differences between the species are based on cell size and shape, plate size and shape, presence or absence of spines, and on the kind of thecal pores

Evaluation of Characters to Distinguish Fitchia aptera and F. spinosula (Heteroptera: Reduviidae)

Presence or absence of spines, and number of spines (4), on the posterior margin of the pronotum were found to be an unreliable character to distinguish Fitchia aptera and F. spinosula. The morphology of the male parameres and female terminalia, and the color of the abdominal spiracular peritreme, are diagnostic. Other characters were found that, as a group and in combination with presence of spines, are useful in distinguishing the two species but are not diagnostic. These include the lateral anteocular length, lengths and ratios of antennal segments, and width of the lateral abdominal stripe. Brachypterous and macropterous adults are found in both species; brachyptery is more common in F. spinosula than in F. aptera.

Inheritance of reduction, loss, and asymmetry of the pelvis in Pungitius pungitius (ninespine stickleback)

The pelvis of Pungitius pungitius (ninespine stickleback) is normally a robust, bilaterally symmetrical structure with stout spines. In some populations it is reduced in size, sometimes to complete absence. The first sign of reduction is loss of the spines, which is accompanied by a reduction in the size of the pelvic bones (vestiges) and an increase in bilateral asymmetry. Further reduction in the size of the vestiges leads to their eventual loss. In a pelvis-reduced population the propensity to spine asymmetry is highly heritable (h2 = 0.85 ± 0.14) but asymmetry of the bony vestiges in fish without spines is not heritable. The absence of spines is heritable, as is size of the bony vestiges (h2 = 0.49 ± 0.12). Crosses of spineless fish from a reduced population with spined fish from either of two normal populations produce only spined progeny. The inter-population heritability of pelvis size is h2 = 0.26 ± 0.10, but that of bilateral asymmetry is zero. The expression of spines and vestiges is influenced relatively little by variation in pH, calcium, and salinity. We propose a polygenic model of inheritance with two phenotypic thresholds, the upper for the presence of spines and the lower for complete absence of the pelvis. Canalization breaks down between the thresholds. This genetic system probably predates divergence of the stickleback genera. We discuss its relevance to understanding the dynamics of pelvis reduction in extant and fossil stickleback populations.

Echinobothrium clavatum n. sp. (Cestoda, Diphyllidea) from the spiral valve of Raja clavata L., 1758, including a note on its ultrastructure and a key to species of the genus

Echinobothrium clavatum n. sp. from the spiral valve of the thornback ray Raja clavata from the Irish Sea is described and illustrated. On the basis of the number of apical hooks it resembles most closely E. musteli but can be distinguished from it by the absence of spines on the rostellum and the different number of spines on the cephalic peduncle. A generic diagnosis together with a key to species of the genus is given. Transmission and scanning electron microscopy of the scolex indicates that the tegument of the rostellum is capable of taking up food by pinocytosis.

The morphology and life-cycle of Trichobilharzia arcuata n. sp. (Schistosomatidae: Bilharziellinae) a nasal schistosome of water whistle ducks (Dendrocygna arcuata) in Australia

The morphology and life-cycle of Trichobilharzia arcuata n. sp. from the nasal blood vessels of Dendrocygna arcuata from northern Australia are described. T. arcuata is distinguished from all species of Trichobilharzia except T. australis and African nasal schistosomes by its location in the nasal blood vessels and by the cercariae having 16 flame cells with a formula 2[(3)+(4+1)] against 14 with a formula 2[(3)+(3+1)], or 12 with a formula 2[(3)+(2+1)] in the case of T. corvi. T. arcuata differs from the five African nasal schistosomes in the nature of the tegument, the position of the male genital papilla and the shape of the eggs and from T. australis in the position of the caecal reunion, the number of testes, the absence of spines on the ventral tegument between the ovary and the seminal receptacle, the shape of the eggs and the presence of two germinal masses in the miracidium. Lymnaea lessoni exposed to miracidia of T. arcuata developed patent infection in 22 to 41 days. Intramolluscan development of T. arcuata is similar to T. stagnicolae and T. physellae. Domestic Muscovy ducks and pigeons developed patent infections in 22 and 12 days respectively. Chickens, a black duck and a grey teal did not become infected. ac]19840616

The green algal genera Rhipiliopsis A. &amp; E.S. Gepp and Rhipiliella gen. nov. (Udoteaceae, Bryopsidales) in Australia and the Philippines

Abstract Four new species of Rhipiliopsis from eastern (R. gracilis, R. howensis, R. millarii) and western (R. multiplex) Australia and one new species (R. carolyniae) from the Philippines are described and compared anatomically with the type of the genus, R. peltata (J. Agardh) A. & E.S. Gepp. Rhipiliopsis echinocaulos (Cribb) Farghaly comb. nov. from eastern Australia has also been studied. All are characterized by corticated or spinous mono- or multisiphonous stalks, polystromatic blades, and siphons which either cohere directly at scattered localized sites or form lateral attachment processes. Distinguishing features include habit, number of siphon layers composing the blade, presence or lack ofblade differentiation into distinct medullary and cortical regions, siphon diameter and shape, degree of constriction above siphon dichotomies, presence (and distribution) or absence of spines on blade siphons, and stalk anatomy. Rhipiliopsis multiplex is unique in producing branching erect axes with tiers of p...

Carnoya kermarreci n.sp. (Rhigonematidae: Nematoda) from Anadenobolus politus (Porat) (Rhinocricidae: Diplopoda) from Guadeloupe

Carnoya kermarreci n.sp. (Rhigonematidae; Nematoda) is described from Anadenobolus politus (Porat) (Rhinocricidae; Diplopoda) from Guadeloupe. The new species most closely resembles C. martiniquensis Adamson, 1984 from A. politus in Martinique and C. venezuelensis Adamson, 1984 from Rhinocricus flavocinctus from Venezuela in that the lips in the male are broad and the arrangement of caudal papillae is almost identical in the three species. Males of C. kermarreci are easily distinguished by the absence of spines, by the form of the cuticular projections at the base of the buccal cavity and by the fact that the most anterior pair of caudal papillae are located very close together. Females are distinguished by the presence of three pairs of somatic papillae near the level of the vulva. The nematode fauna of A. politus includes species from two distinct orders and presumably reflects the fact that diplopods are among the most ancient hosts of nematodes.

Scanning electron microscopic studies of the body surface and external genitalia of a dicrocoeliid trematode,Concinnum epomopis Sandground 1973

A detailed study of the surface topography ofConcinnum epomopis (Dicrocoeliidae) was carried out with a scanning electron microscope. The ultrastructural observations demonstrate the absence of spines on the body surface; however, the tegument is complex, exhibiting distinct, minute, lateral undulations, predominantly on the ventral side. The pattern of the tegumentary lamellae in different regions of the body is described. Two types of sensory papillae, the pit-type and the aciliate dome-type exhibit a uniform and distinct pattern of distribution on the surface of the worm. The pit-type is limited to the ventral depression anterior to the oral sucker. The pre-acetabular ventral genital opening, the posterior terminal excretory pore and pre-equatorial opening of the Laurer's canal are devoid of structural specialization and sensory papillae. The cylindrical, everted cirrus is covered with anastomosing, longitudinal lamellae of tegument, between which lie minute aggregates of protuberances forming the cirral papillae.

Planktonic foraminifera: factors controlling sinking speeds

Sinking speeds of 330 specimens belonging to 10 extant species of planktonic foraminifera were determined in a sinking column device filled with 3°C seawater. The sinking speed is governed primarily by shell weight and presence/absence of spines. For example, preserved planktonic specimens of Orbulina universa, whose shell weight ranged from 2 to 21 μg, sank 122 to 583 m day −1, with a correlation coefficient of 0.92 on log-log scale. Progressive shell thickening during foraminiferal growth accounts for some of the higher sinking speeds. In addition, shells from sediment on the average sink about three times faster than shells (of equivalent size and species) of planktonic foraminifera collected in near-surface waters. These high values are in part due to the shells often being encrusted with clay and nannoplankton remains. In contrast, the sinking speeds of the spinose species are approximately 3-fold slower than those of the non-spinose species. Based on data from plankton tows, most planktonic foraminifera > 150 μm reach the mean ocean depth of 3800 m in 3 to 12 days depending upon shell weight and presence or absence of spines. Estimated Reynolds numbers range from 0.05 to 24.85 and most exceed a value of 0.5 which is an upper for limit Stokes' Law range, suggesting that foraminifera are out of Stokes' sinking range. The Reynolds number and drag coefficients are negatively well correlated, indicating that drag is one of the important controlling factors in the sinking regime. The presence of spines is significant in increasing drag, decreasing the Reynolds number, and hence reducing the sinking speed.

The role of spines in preventing structural damage to echinoid tests

Living echinoids provide a structural analogue to the rigid thecae of many extinct echinoderms and are here used to examine some consequences of the increased rigidity and decreased number of plates which occurred in several lineages of echinoderms. A special feature of the echinoids is the large spines which protect the echinoid tests from failure under impact. The spines absorb energy or spread loads because the spines break or the tissue connecting the spine to the test is stretched or torn. Spines that absorb impacts might be superfluous in echinoderms encased in a rigid test or theca if they have flexible stems or are in low energy habitats, but spines should be useful to stemless thecate echinoderms on hard substrata. In the absence of spines, a flexible theca of overlapping plates might be superior to a rigid theca. Greater rigidity does not necessarily provide greater protection.Tracts of podial pores are sites of weakness in all tests examined [Eucidaris tribuloides(Lamarck),Echinometra viridisAgassiz,Diadema antillarumPhilippi,Lytechinus variegatus(Lamarck),Tripneustes ventricosus(Lamarck)]. Therefore arrangement of pores affects strength of rigid thecae. Sutures are stronger than plates in most species examined, but cracks cross sutures, and tests ofE. tribuloidesfrequently break along sutures. It is not yet proven that sutures increase toughness of rigid tests by relieving stress on plates or stopping cracks. If resisting failure under impact is important, then preconditions for acquiring rigidity are life in a low energy habitat or accessory structures which absorb or spread impacts.

Sobre uma nova espécie do gênero Acanthocolpus Lühe, 1906

Os autores, na presente nota, propõem Acanthocolpus brasiliensis sp. n. sendo este gênero pela primeira vez referido no Brasil. A espécie aqui descrita difere das demais do gênero pela ausência de espinhos na vagina e no ducto hermafrodita e pela presença de vitelinos em quase toda extensão da metade posterior do corpo.

A STUDY OF THE PROPOSED GENUS OBREGONIA (CACTACEAE)

The monotypic genus Obregonia Frič was compared with Ariocarpus, Lophophora, Strombocactus, and certain other cactus genera. Obregonia and Ariocarpus are similar in characters of seeds, seedlings, habitat, fruits, and general habit. They differ in time of flowering, point of flower origin, areole structure, presence or absence of druses and a mucilage system, and presence or absence of spines. Obregonia and Lophophora are similar in characters of seeds, habitat, basic areole structure, and fruits. They differ in seedling form, habit of adult plants, presence or absence of spines, and chemical analysis. Strombocactus resembles Obregonia in few ways except in basic areole structure and some aspects of anatomy. The author concludes that Obregonia is an intermediate form between Ariocarpus and Lophophora and deserves generic rank. A formal taxonomic treatment of the genus follows the conclusions.

Raja richardsoni from the continental slope off south-west England

A pair of rays caught by line from 1300fm westward of the English Channel have been identified as Raja richardsoni Garrick known only from the type specimen also taken by line in New Zealand waters from about the same depth. The Plymouth rays agree well with the New Zealand fish in proportional measurements, in bearing denticles on both surfaces, and in the absence of spines but differ slightly in colour, in their smaller number of teeth, and in the greater development of a lateral process on the nasal flap.

THE ORIGIN OF THE FAMILY HORRIDONIIDAE MUIR-WOOD ET COOPER

The late Paleozoic genus Praehorridonia and its type species is described, differing from Horridonia by presence of radial and concentric sculpture and by absence of spines on the brachial valve. The author believes the large Praehorridonia possessing traces of semireticulate structure, descended from the strongly semireticulate Antiquatonia in Middle Carboniferous and evolved into Horridonia, thus representing an intermediate stage between Antiquatonia and Horridonia. The family was confined to the Arctic throughout its history and became extinct in the middle of the Upper Permian. -- G. A. Cooper.

Notes on the Species of Capillaria Zeder, 1800 Known from Gallinaceous Birds

The species of the nematode genus, Capillaria Zeder, 1800, present many taxonomic difficulties. The most important of more recent studies regarding species in birds are those of Orosz (1931), Morgan (1932), Freitas & Almeida (1935a-b), Cram (1936) and Read (1949). Based upon large collections from gallinaceous and anatine game birds the present author (1945) tried to clear up the difficulties and confusions in the very scattered literature on these species. Since then I have found several new features especially concerning the species in gallinaceous birds. I consider it, therefore, of some use to summarize the results, and give a revised list of the species from these birds. The genus Capillaria comprises a large number of species. It would, therefore, be useful if it could be split into several genera. Some attempts have been made in this respect, beginning with Dujardin (1845). Baylis (1931) showed that the attempts up to that time had been futile, and this point of view was accepted by the above mentioned authors. Recently, L6pex-Neyra (1947), in a very comprehensive paper, revived some of the genera discarded by Baylis (1931), and erected some new ones. As principal characters for segregating the genera he used the ratio between the length of the esophagus, and of the entire body, and the presence or absence of spines on the spicule sheath. It is already doubtful to use differences in size, and even more ratios taxonomically. This is the more objectionable since he did not compute this ratio on the individual ratios, but took the first and last figure in the range of the length of the esophagus and of the posterior part of the body, respectively, computing the range of the ratio on these figures. For instance, in a table, p. 43, quoting measurements by Wehr (1939), on Capillaria obsignata, he found a range of the said ratio of 1.23-1.59; whereas the range, computed on the indivudal measurements is actually 1.20-1.88. For the main grouping in his key, p. 46-47, he used the feature, whether the esophagus constitutes less or more than one-third of the total length, and as subgrouping in both groups, spiny or non-spiny spicule sheath. If this key is strictly followed it should be possible to place, e.g. my specimens of Capillaria caudinflata in no less than four of his genera! (cf. Holger Madsen (1945, p. 15 and fig. 4)). I cannot, therefore, find an attempt at erecting subgenera or genera justified, when based upon the characters known at present, and prefer to adopt the opinion of Baylis. In the synopsis given by L6pez-Neyra, and by me in 1945, species described by Yamaguti (1941) and Johnston & Mawson (1941, 1945) are not included. In the following list the new points of view will be given under the heading of the individual species.

A Method for Determining the Presence or Absence of Spines in Pocket-Mice

A Method for Determining the Presence or Absence of Spines in Pocket-Mice