Organization Of Nervous System Research Articles

The central nervous system of sea cucumbers (Echinodermata: Holothuroidea) shows positive immunostaining for a chordate glial secretion.

BackgroundEchinoderms and chordates belong to the same monophyletic taxon, the Deuterostomia. In spite of significant differences in body plan organization, the two phyla may share more common traits than was thought previously. Of particular interest are the common features in the organization of the central nervous system. The present study employs two polyclonal antisera raised against bovine Reissner's substance (RS), a secretory product produced by glial cells of the subcomissural organ, to study RS-like immunoreactivity in the central nervous system of sea cucumbers.ResultsIn the ectoneural division of the nervous system, both antisera recognize the content of secretory vacuoles in the apical cytoplasm of the radial glia-like cells of the neuroepithelium and in the flattened glial cells of the non-neural epineural roof epithelium. The secreted immunopositive material seems to form a thin layer covering the cell apices. There is no accumulation of the immunoreactive material on the apical surface of the hyponeural neuroepithelium or the hyponeural roof epithelium. Besides labelling the supporting cells and flattened glial cells of the epineural roof epithelium, both anti-RS antisera reveal a previously unknown putative glial cell type within the neural parenchyma of the holothurian nervous system.ConclusionOur results show that: a) the glial cells of the holothurian tubular nervous system produce a material similar to Reissner's substance known to be synthesized by secretory glial cells in all chordates studied so far; b) the nervous system of sea cucumbers shows a previously unrealized complexity of glial organization. Our findings also provide significant clues for interpretation of the evolution of the nervous system in the Deuterostomia. It is suggested that echinoderms and chordates might have inherited the RS-producing radial glial cell type from the central nervous system of their common ancestor, i.e., the last common ancestor of all the Deuterostomia.

A multi-scale spatial and semantic knowledge framework for neuroanatomy

Event Abstract Back to Event A multi-scale spatial and semantic knowledge framework for neuroanatomy Stephen Larson1*, Christopher Aprea1, Sarah Maynard1, Fahim Imam1, Mark H. Ellisman1 and Maryann Martone1 1 UCSD, United States Cellular networks in the brain are fundamentally multi-scale with relevant data derived from subcellular junctional connectivity, cytoarchitectural local connectivity, and long-range topographical connectivity. Experimental limitations make it difficult to study all these scales simultaneously. Consequently, experimental methodologies tend to reveal only a limited aspect of nervous system organization. However, to generate hypotheses across scales, we must analyze the nervous system across spatial dimensions spanning several orders of magnitude. Experimental technologies are now able to reveal organization within these scales, yet the development of tools to synthesize these data into more coherent models of brain structure and function is lagging behind.An ideal knowledge framework for neuroanatomy would provide researchers the ability to 1) upload their data into a common data environment where it can be easily discovered and retrieved, 2) contextualize their data by superimposing and combining related data from multiple scales, and 3) create hypothetical, synthetic views of structures of interest by stitching data together or generalizing patterns found in data. The framework would allow researchers to deal with their data in both spatially, placing it in register in a location in a common brain space, and semantically, annotating and tagging it with standard labels drawn from shared ontologies for neuroscience. These two dimensions of data, spatial and semantic, create a key basis for organizing the heterogenous, scattered knowledge of the brain's structure into a cohesive whole.We have taken a step towards the construction of such a knowledge framework by creating a platform that can serve as its foundation. This platform consists of the following elements 1) a spatial registration workflow for images that allows large 2D data to be registered to a brain atlas 2) a 3D game engine that allows real-time rendering and interaction with 2D and 3D multi scale data, 3) an online collaborative ontology manipulation, maintenance, and retrieval system populated from the Neuroscience Information Framework's NIF Standard Ontology, 4) a backend web services and data management layer that ties these elements together.We have created an existance proof prototype of this platform that allows data from brain regions to molecules to be represented in a common space. It allows researchers to upload their data into this framework in forms such as 3D meshes of subcellular scenes and of brain region territories, large 2D image data sets from both EM and light level microscopy, NeuroML / Neurolucida neuronal reconstructions, and PDB protein structures. Researchers can annotate their data with tags from the ontology system, and manipulating their data within the prototype causes knowledge links to be made between the data in an exportable formal structure (OWL). We feel that this platform can scale up as the beginning of a shared knowledge environment for neuroanatomy that can handle the multiple scales and modalities of data within this complex domain. Conference: Neuroinformatics 2009, Pilsen, Czechia, 6 Sep - 8 Sep, 2009. Presentation Type: Poster Presentation Topic: Digital atlasing Citation: Larson S, Aprea C, Maynard S, Imam F, Ellisman MH and Martone M (2019). A multi-scale spatial and semantic knowledge framework for neuroanatomy. Front. Neuroinform. Conference Abstract: Neuroinformatics 2009. doi: 10.3389/conf.neuro.11.2009.08.015 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 May 2009; Published Online: 09 May 2019. * Correspondence: Stephen Larson, UCSD, San Diego, United States, stephen.larson@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Stephen Larson Christopher Aprea Sarah Maynard Fahim Imam Mark H Ellisman Maryann Martone Google Stephen Larson Christopher Aprea Sarah Maynard Fahim Imam Mark H Ellisman Maryann Martone Google Scholar Stephen Larson Christopher Aprea Sarah Maynard Fahim Imam Mark H Ellisman Maryann Martone PubMed Stephen Larson Christopher Aprea Sarah Maynard Fahim Imam Mark H Ellisman Maryann Martone Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Gene regulatory networks underlying the compartmentalization of theCionacentral nervous system

The tripartite organization of the central nervous system (CNS) may be an ancient character of the bilaterians. However, the elaboration of the more complex vertebrate brain depends on the midbrain-hindbrain boundary (MHB) organizer, which is absent in invertebrates such as Drosophila. The Fgf8 signaling molecule expressed in the MHB organizer plays a key role in delineating separate mesencephalon and metencephalon compartments in the vertebrate CNS. Here, we present evidence that an Fgf8 ortholog establishes sequential patterns of regulatory gene expression in the developing posterior sensory vesicle, and the interleaved ;neck' region located between the sensory vesicle and visceral ganglion of the simple chordate Ciona intestinalis. The detailed characterization of gene networks in the developing CNS led to new insights into the mechanisms by which Fgf8/17/18 patterns the chordate brain. The precise positioning of this Fgf signaling activity depends on an unusual AND/OR network motif that regulates Snail, which encodes a threshold repressor of Fgf8 expression. Nodal is sufficient to activate low levels of the Snail repressor within the neural plate, while the combination of Nodal and Neurogenin produces high levels of Snail in neighboring domains of the CNS. The loss of Fgf8 patterning activity results in the transformation of hindbrain structures into an expanded mesencephalon in both ascidians and vertebrates, suggesting that the primitive MHB-like activity predates the vertebrate CNS.

Extensive presence of serotonergic cells and fibers in the peripheral nervous system of lampreys

Lampreys are suitable animal models for studying the evolution of the vertebrate nervous system because they belong to the earliest group of extant vertebrates, the agnathans. The general organization of the serotonergic central nervous system is well known in lampreys, but information about its peripheral organization is lacking. In the present study, high-performance liquid chromatography and immunohistochemistry with an antibody against serotonin were used to study the presence and peripheral distribution of serotonergic elements in the head of larval sea lampreys. Adult lampreys were also analyzed in order to compare the organization of the system in larval and postmetamorphic stages. Serotonergic cells were observed in the cranial nerve ganglia, the musculature, the taste buds, and in the gills. Serotonergic fibers were extensive in all tissues except the epidermis. Possible roles were proposed for the different cell types observed in relation to their location, structure, and innervation patterns. The serotonergic cells appear to be involved in the oxygen and taste chemoreception processes, the modulation of musculature contraction, and in the regulation of cilia beat frequency and mucus secretion in lampreys. The extensive presence of serotonergic elements in the peripheral nervous system of lampreys suggests a close relationship with the organization of this system in invertebrate groups.

Temporal identity in axonal target layer recognition

The segregation of axon and dendrite projections into distinct synaptic layers is a fundamental principle of nervous system organization and the structural basis for information processing in the brain. Layer-specific recognition molecules that allow projecting neurons to stabilize transient contacts and initiate synaptogenesis have been identified. However, most of the neuronal cell-surface molecules critical for layer organization are expressed broadly in the developing nervous system, raising the question of how these so-called permissive adhesion molecules support synaptic specificity. Here we show that the temporal expression dynamics of the zinc-finger protein sequoia is the major determinant of Drosophila photoreceptor connectivity into distinct synaptic layers. Neighbouring R8 and R7 photoreceptors show consecutive peaks of elevated sequoia expression, which correspond to their sequential target-layer innervation. Loss of sequoia in R7 leads to a projection switch into the R8 recipient layer, whereas a prolonged expression in R8 induces a redirection of their axons into the R7 layer. The sequoia-induced axon targeting is mediated through the ubiquitously expressed Cadherin-N cell adhesion molecule. Our data support a model in which recognition specificity during synaptic layer formation is generated through a temporally restricted axonal competence to respond to broadly expressed adhesion molecules. Because developing neurons innervating the same target area often project in a distinct, birth-order-dependent sequence, temporal identity seems to contain crucial information in generating not only cell type diversity during neuronal division but also connection diversity of projecting neurons.

EvoD/Vo: the origins of BMP signalling in the neuroectoderm

The genetic systems controlling body axis formation trace back as far as the ancestor of diploblasts (corals, hydra, and jellyfish) and triploblasts (bilaterians). Comparative molecular studies, often referred to as evo-devo, provide powerful tools for elucidating the origins of mechanisms for establishing the dorsal-ventral and anterior-posterior axes in bilaterians and reveal differences in the evolutionary pressures acting upon tissue patterning. In this Review, we focus on the origins of nervous system patterning and discuss recent comparative genetic studies; these indicate the existence of an ancient molecular mechanism underlying nervous system organization that was probably already present in the bilaterian ancestor.

Cortical reorganization in children with cochlear implants

Congenital deafness leads to atypical organization of the auditory nervous system. However, the extent to which auditory pathways reorganize during deafness is not well understood. We recorded cortical auditory evoked potentials in normal hearing children and in congenitally deaf children fitted with cochlear implants. High-density EEG and source modeling revealed principal activity from auditory cortex in normal hearing and early implanted children. However, children implanted after a critical period of seven years revealed activity from parietotemporal cortex in response to auditory stimulation, demonstrating reorganized cortical pathways. Reorganization of central auditory pathways is limited by the age at which implantation occurs, and may help explain the benefits and limitations of implantation in congenitally deaf children.

Microelectrodes, Microelectronics, and Implantable Neural Microsystems

Lithographically defined microelectrode arrays now permit high-density recording and stimulation in the brain and are facilitating new insights into the organization and function of the central nervous system. They will soon allow more detailed mapping of neural structures than has ever before been possible, and capabilities for highly localized drug-delivery are being added for treating disorders such as severe epilepsy. For chronic neuroscience and neuroprosthesis applications, the arrays are being used in implantable microsystems that provide embedded signal processing and wireless data transmission to the outside world. A 64-channel microsystem amplifies the neural signals by 60 dB with a user-programmable bandwidth and an input-referred noise level of 8 muVrms before processing the signals digitally. The channels can be scanned at a rate of 62.5 kS/s, and signals above a user-specified biphasic threshold are transmitted wirelessly to the external world at 2 Mbps. Individual channels can also be digitized and viewed externally at high resolution to examine spike waveforms. The microsystem dissipates 14.14 mW from 1.8 V and measures 1.4 1.55 cm2.

On the key role played by altered protein conformation in Parkinson’s disease

On the basis of the previously proposed hierarchic organisation of the central nervous system (CNS) and of its syntropic behaviour, a view of neurodegenerative diseases focusing on the assemblage of abnormal multimeric proteins (pathologic protein mosaics (PMs)) is proposed. Thus, the main focus of the present paper is on Parkinson's disease (PD) as a neurodegenerative disease, which has as crucial feature protein conformational alterations and formation of pathological PMs. Two interconnected cellular dysfunctions are discussed as main pathogenic factors of PD syndromes, namely mitochondrial deficits (i.e. energy failure, especially critical for Substantia Nigra DA neurons) and conformational protein alterations (due to genetic or environmental causes). Conformational protein alterations can trigger pathological phenomena via the loss and/or the gain of new functions. In particular, altered proteins can lead to the formation of abnormal PMs, which can, inter alia, cause distortion of cellular structures, toxic functions and/or formation of improper membrane ion channels. In view of the fact that disordered proteins can easily acquire unwanted conformation, the "disorder index" (DI) for proteins involved in PD has been evaluated. It has been found that both alpha-synuclein and tau-protein have high DI. This datum is in agreement with the observation that these two proteins synergistically promote polymerisation of each other into amyloid fibrils, favouring the formation of Lewy bodies.

The enteric nervous system: normal functions and enteric neuropathies

Most aspects of the normal organisation and functioning of the enteric nervous system have been resolved in recent years, especially for the small and large intestines, where the ENS has essential roles in controlling bowel movement and transmucosal fluid exchange. The roles of the ENS in the esophagus are not understood, and the relative roles of intrinsic reflexes in relation to extrinsic control of the stomach require clarification. In the small intestine and colon, it needs to be understood how neural activity is orchestrated to subserve different functional outcomes, for example propulsion, mixing and retrograde movement. However, the most important future challenges are to properly understand the molecular and cellular changes that underlie enteric neuropathies, to utilise knowledge of the normal neurochemistry, pharmacology and physiology of the ENS to devise strategies to treat disorders of motility and secretion, and to develop effective therapeutic compounds. It is suggested that ion channels of enteric neurons have been under-investigated as therapeutic targets. Other future challenges lie in the identification of biomarkers for functional bowel disorders and in the use of neural stem cells for restitution of ENS function.

Visual prediction: Psychophysics and neurophysiology of compensation for time delays

A necessary consequence of the nature of neural transmission systems is that as change in the physical state of a time-varying event takes place, delays produce error between the instantaneous registered state and the external state. Another source of delay is the transmission of internal motor commands to muscles and the inertia of the musculoskeletal system. How does the central nervous system compensate for these pervasive delays? Although it has been argued that delay compensation occurs late in the motor planning stages, even the earliest visual processes, such as phototransduction, contribute significantly to delays. I argue that compensation is not an exclusive property of the motor system, but rather, is a pervasive feature of the central nervous system (CNS) organization. Although the motor planning system may contain a highly flexible compensation mechanism, accounting not just for delays but also variability in delays (e.g., those resulting from variations in luminance contrast, internal body temperature, muscle fatigue, etc.), visual mechanisms also contribute to compensation. Previous suggestions of this notion of "visual prediction" led to a lively debate producing re-examination of previous arguments, new analyses, and review of the experiments presented here. Understanding visual prediction will inform our theories of sensory processes and visual perception, and will impact our notion of visual awareness.

Retention of Memory through Metamorphosis: Can a Moth Remember What It Learned As a Caterpillar?

Insects that undergo complete metamorphosis experience enormous changes in both morphology and lifestyle. The current study examines whether larval experience can persist through pupation into adulthood in Lepidoptera, and assesses two possible mechanisms that could underlie such behavior: exposure of emerging adults to chemicals from the larval environment, or associative learning transferred to adulthood via maintenance of intact synaptic connections. Fifth instar Manduca sexta caterpillars received an electrical shock associatively paired with a specific odor in order to create a conditioned odor aversion, and were assayed for learning in a Y choice apparatus as larvae and again as adult moths. We show that larvae learned to avoid the training odor, and that this aversion was still present in the adults. The adult aversion did not result from carryover of chemicals from the larval environment, as neither applying odorants to naïve pupae nor washing the pupae of trained caterpillars resulted in a change in behavior. In addition, we report that larvae trained at third instar still showed odor aversion after two molts, as fifth instars, but did not avoid the odor as adults, consistent with the idea that post-metamorphic recall involves regions of the brain that are not produced until later in larval development. The present study, the first to demonstrate conclusively that associative memory survives metamorphosis in Lepidoptera, provokes intriguing new questions about the organization and persistence of the central nervous system during metamorphosis. Our results have both ecological and evolutionary implications, as retention of memory through metamorphosis could influence host choice by polyphagous insects, shape habitat selection, and lead to eventual sympatric speciation.

Aneuploid mosaicism in the developing and adult cerebellar cortex

Neuroprogenitor cells (NPCs) in several telencephalic proliferative regions of the mammalian brain, including the embryonic cerebral cortex and postnatal subventricular zone (SVZ), display cell division "defects" in normal cells that result in aneuploid adult progeny. Here, we identify the developing cerebellum as a major, nontelencephalic proliferative region of the vertebrate central nervous system (CNS) that also produces aneuploid NPCs and nonmitotic cells. Mitotic NPCs assessed by metaphase chromosome analyses revealed that 15.3% and 20.8% of cerebellar NPCs are aneuploid at P0 and P7, respectively. By using immunofluorescent analysis of cerebellar NPCs, we show that chromosome segregation defects contribute to the generation of cells with an aneuploid genomic complement. Nonmitotic cells were assessed by fluorescence-activated cell sorting (FACS) coupled with fluorescence in situ hybridization (FISH), which revealed neuronal and nonneuronal aneuploid populations in both the adult mouse and human cerebellum. Taken together, these results demonstrate that the prevalence of neural aneuploidy includes nontelencephalic portions of the neuraxis and suggest that the generation and maintenance of aneuploid cells is a widespread, if not universal, property of central nervous system development and organization.

Alexia and agraphia

To evaluate 19th-century concepts of cerebral localization for complex mental activities, focusing on alexia and agraphia in published writings of Jean-Martin Charcot (1825-1893) and John Hughlings Jackson (1835-1911). In the early 1860 s, Broca's reports on a special role for the left frontal lobe in articulate language ignited frenetic interest in cerebral localization. Disorders of written language (alexia and agraphia) were enmeshed in ensuing discussions of how the brain was organized for language and other complex behaviors. Focused review and analysis of Charcot's and Hughlings Jackson's publications on aphasia, alexia, and agraphia. In the wake of Broca's observations, the extent to which language functions in general--or such specialized functions as reading and writing--might involve focal cerebral representation was controversial. Based on his clinical-pathologic approach to "regional diagnosis," Charcot came to value insights provided by "partial isolated aphasias." He described patients with isolated alexia and agraphia, and he proposed a functional-anatomic framework to accommodate these disorders. Adopting a hierarchical model of nervous system organization, Hughlings Jackson argued that reading and writing could not be dissociated from other aspects of "intellectual language." Charcot's reductionism was typical of his era, but Hughlings Jackson's more holistic approach was to gain ascendancy in early decades of the 20th century. Charcot's and Hughlings Jackson's positions on alexia and agraphia reflected contrasting philosophical approaches to the study of brain disorders. Their views informed the opinions of their contemporaries and neurologic heirs in important debates on cerebral organization.

Distribution of serotonin in the trunk of Metaperipatus blainvillei (Onychophora, Peripatopsidae): Implications for the evolution of the nervous system in Arhropoda

Onychophora ("velvet worms") are a key taxon in the discussion of arthropod phylogeny. Studies that analyze neuroanatomical characters against a phylogenetic background have recently provided new insights into this debate. However, to date only a few studies on nervous system organization, particularly in the trunk, are available in Onychophora. To close this gap and to compare the onychophoran nervous system with that of other bilaterians, we have analyzed the pattern of serotonin-like immunoreactivity in Metaperipatus blainvillei (Peripatopsidae). In addition to confirming previous histological observations, our experiments revealed many new aspects of nervous system organization in Onychophora. The serotonergic nervous system of M. blainvillei consists of five longitudinal nerve strands (the paired dorsolateral nerves, the heart nerve, and the paired ventral cords), which are interconnected at regular intervals by ring commissures as well as median commissures. The ring commissures are absent in the leg-bearing regions. In addition to the main nerve tracts, there are several extensive fiber networks innervating the integument, the nephridial organs, and the body musculature. The leg nerves and nephridial nerves represent the only strictly segmental neuronal structures. We conclude that the general architecture of the onychophoran nervous system in the trunk closely resembles the orthogonal organization that is present in various other groups of Bilateria, which suggests that the arthropod nervous system is derived from such an orthogonal pattern. This finding implies that the "rope ladder-like" nervous system may have arisen independently in Panarthropoda and Annelida and does not represent a synapomorphy of these groups.

Extensions of the Brain Architecture Management System

Event Abstract Back to Event Extensions of the Brain Architecture Management System Mihail Bota1*, Arshad Khan1, Alan Watts1 and Larry Swanson1 1 University of Southern California, United States The Brain Architecture Management System (BAMS; http://brancusi.usc.edu/bkms/) is an online neuroinformatics system that handles data related to brain parts defined in neuroanatomical nomenclatures, and across four levels of organization of the mammalian central nervous system. BAMS contains four interrelated modules: Brain Parts, Molecules, Cell Types, and Connections, and Relations between brain parts defined in different neuroanatomical nomenclatures. The backend database structure of BAMS and its web interface were described in detail elsewhere (Bota et al. 2005; Bota & Swanson 2006, 2007). We present here several new extensions of the database structure of BAMS, and its web interface: a) an extension of the Brain Parts module, which allows insertion of fiber endings reports, marked with different chemicals; b) an extension of the Relations module, which registers metadata relevant to methods used in defining brain parts, and relations between those, as inserted from the literature c) an extension of the Connections web interface, which adds the sets of molecules expressed in brain regions to each of layers of networks constructed by users. In terms of populating the system, we concentrated our efforts to provide a systematic account of the molecular makeup of the rat periventricular hypothalamic nucleus (PVH), and of the relations between terms associated with the rat bed nuclei of the stria terminalis (BST). We will present the structure of BAMS, describe its new extensions demonstrate its main functionalities with We will present the structure of BAMS, describe its new extensions, and demonstrate its main functionalities to the neuroscience with emphasis on the rat PVH and BST.

Control of multidendritic neuron differentiation in Drosophila: The role of Collier

Proper sampling of sensory inputs critically depends upon neuron morphogenesis and expression of sensory channels. The highly stereotyped organisation of the Drosophila peripheral nervous system (PNS) provides a model to study neuronal determination and morphogenesis. Here, we report that Collier/Knot (Col/Kn), the Drosophila member of the COE family of transcription factors, is transiently expressed in the subset of multidendritic arborisation (da) sensory neurons that display an highly branched dendritic arborisation, class IV neurons. When lacking Col activity, class IV da neurons are formed but display a reduced dendrite arborisation. Col control on dendrite branching is distinct from that exerted by Cut, another transcription factor expressed in class IV neurons and necessary for proper dendrite morphogenesis. Col is also required for the class IV da-specific expression of pickpocket ( ppk), which encodes a degenerin/epithelial sodium channel subunit required for larval locomotion. Characterisation of the col upstream region identified a 9-kb cis-regulatory region driving col expression in all class IV md neurons, even though these originate from two types of sensory precursor cells. Altogether, these findings indicate that col is required in at least two distinct programs that control the morphological and sensory specificity of Drosophila md neurons.

Three-dimensional reconstruction of the central nervous system of Macrobiotus hufelandi (Eutardigrada, Parachela): implications for the phylogenetic position of Tardigrada

The morphology of the central nervous system of the tardigrade species Macrobiotus hufelandi was analysed with anti α-tubulin immunostaining in combination with confocal-laser-scanning-microscopy and computer aided three-dimensional reconstruction. The brain anatomy is unexpectedly complex with distinct tracts and highly intermingled nerve fibres. In contrast to older descriptions, we could not detect a suboesophageal ganglion. Furthermore, we found no evidence for a tripartite/three-segmented brain organisation. The median part of the brain is directly connected to the first pair of trunk ganglia via circumoesophageal connectives. Surprisingly, the four paired ventral ganglia do not show segmental commissures typical for the ladder-like nervous system of arthropods. Our findings constrain the phylogenetic position of Tardigrada. The much simpler organisation of the central nervous system of Tardigrada compared to that of Onychophora and Euarthropoda and some similarities to the nervous system of Cycloneuralia support a phylogenetic position of Tardigrada outside an Onychophora/Euarthropoda clade. This means that Tardigrada might be either the sister group to all other Arthropoda or they are more closely related to Cycloneuralia.

Central Nervous System ofChaetoderma japonicum(Caudofoveata, Aplacophora): Implications for Diversified Ganglionic Plans in Early Molluscan Evolution

The organization of the central nervous system of an "aplacophoran" mollusc, Chaetoderma japonicum, is described as a means to understand a primitive condition in highly diversified molluscan animals. This histological and immunocytochemical study revealed that C. japonicum still retains a conservative molluscan tetra-neural plan similar to those of neomenioids, polyplacophorans, and tryblidiids. However, the ventral and lateral nerve cords of C. japonicum are obviously ganglionated to various degrees, and the cerebral cord-like ganglia display a lobular structure. The putative chemosensory networks are developed, being composed of sensory cells of the oral shield, eight precerebral ganglia, and eight neuropil compartments that form distinct masses of neurites. In the cerebral cord-like ganglia, three anterior, posterior, and dorsal lobes are distinguished with well-fasciculated tracts in their neuropils. Most neuronal somata are uniform in size, and no small globuli-like cell clusters are found; however, localized serotonin-like immunoreactivity and acetylated tubulin-containing tracts suggest the presence of functional subdivisions. These complicated morphological features may be adaptive structures related to the specialized foraminiferan food in muddy bottoms. Based on a comparative scheme in basal molluscan groups, we characterize an independent evolutionary process for the unique characters of the central nervous systems of chaetoderms.

The Spotted Hyena (Crocuta crocuta) as a Model System for Study of the Evolution of Intelligence

Large brains and great intelligence are metabolically costly, but the social complexity hypothesis suggests that these traits were favored nonetheless in primates by selection pressures associated with life in complex societies. If so, then cognitive abilities and nervous systems with primatelike attributes should have evolved convergently in nonprimate mammals living in large, elaborate societies in which social dexterity enhances individual fitness. Societies of spotted hyenas (Crocuta crocuta) are remarkably similar to those of cercopithecine primates with respect to size, structure, and patterns of competition and cooperation. These similarities set an ideal stage for comparative analysis of social intelligence and nervous system organization. As in cercopithecine primates, spotted hyenas use multiple sensory modalities to recognize their kin and other conspecifics as individuals, they know that some group-mates are more valuable social partners than others, they recognize 3rd-party kin and rank relationships among their clan-mates, and they use this knowledge adaptively during social decision-making. Examination of the available data strongly suggests convergent evolution of intelligence between spotted hyenas and primates. Evidence that less gregarious members of the family Hyaenidae lack some of the cognitive abilities found in spotted hyenas would provide further support for the idea that social complexity favors enhancement of intelligence in mammals.