Comparative aspects of cerebellar organization. From mormyrids to mammals.

Recent progress in the comparative analysis of the vertebrate cerebellar organization shows that the cerebella of different tetrapods have a basically similar intrinsic organization, whereas the cerebellum of fishes displays a number of fundamental differences in this respect. Clear examples of teleostean cerebellar specializations are present in the gigantocerebellum of mormyrids, including a valvula cerebelli, the absence of a parasagittal zonal organization, the presence of eurydendroid projection neurons instead of deep cerebellar nuclei, a precerebellar nucleus lateralis valvulae, olivocerebellar fibers that do not climb into the molecular layer, uni- and bilateral locations of granule cells, parallel fibers without a T-shaped bifurcation and with a coextensive distribution in the transverse plane, and different Purkinje cell arrangements including a dendritic palisade pattern. A theoretical exploration of the possible significance of these configurations suggests that they all might be involved in a single main cerebellar function, i.e. coincidence detection of parallel fiber activity by Purkinje cells.     

Functional origins of the vertebrate cerebellum from a sensory processing antecedent

The structure of the cerebellar cortex is remarkably similar across vertebrate phylogeny. It is well developed in basaljawed fishes, such as sharks and rays with many of the same cell types and organizational features found in other vertebrategroups, including mammals. In particular, the lattice-like organization of cerebellar cortex (with a molecular layer of parallel fibres,interneurons, spiny Purkinje cell dendrites, and climbing fires) is a common defining characteristic. In addition to the cerebell...     

The yellow stingray, Urobatis jamaicensis, as a model for studying cerebellar function in vertebrates

Fishes, in general, have several advantages as vertebrate models for basic brain function. They are phylogenetically closer than mammals to the basic vertebrate blueprint and thus allow behavioural and neurological studies of fundamental brain systems without the interaction of more recently evolved functions. Further, the absence of a highly developed telencephalon allows ready access to many structures without cerebral interference. A disadvantage of working with most fishes is, however, the relatively small size of the brain that often hinders or precludes the use of many standard neurological techniques. In contrast, a group of chondrichthians, the stingrays, Dasyatoidea, has a brain size rivaling mammalian rodent models. Of particular interest to our research, stingrays, like mammals, have a large, complex, three‐lobed cerebellum. However, in the yellow stingray these lobes are completely separated. Thus, the lobes can be individually manipulated to examine behavioural correlates of specific lobes. For example, ablation of the centre lobe (also known as anterior caudal lobule) causes a fixed‐pattern hyperactivity. Yellow stingrays are abundant in many areas, they are hardy, and tolerate anaesthesia and the surgical procedures well. A more complete elucidation of cerebellar function awaits further physical and pharmacological ablative studies but the potential for these animals as vertebrate models of cerebellar‐controlled behaviour is clear.     

The somatotopic organization of the olfactory bulb in elasmobranchs

The olfactory bulbs (OBs) are bilaterally paired structures in the vertebrate forebrain that receive and process odor information from the olfactory receptor neurons (ORNs) in the periphery. Virtually all vertebrate OBs are arranged chemotopically, with different regions of the OB processing different types of odorants. However, there is some evidence that elasmobranch fishes (sharks, rays, and skates) may possess a gross somatotopic organization instead. To test this hypothesis, we used histological staining and retrograde tracing techniques to examine the morphology and organization of ORN projections from the olfactory epithelium (OE) to the OB in three elasmobranch species with varying OB morphologies. In all three species, glomeruli in the OB received projections from ORNs located on only the three to five lamellae situated immediately anterior within the OE. These results support that the gross arrangement of the elasmobranch OB is somatotopic, an organization unique among fishes and most other vertebrates. In addition, certain elasmobranch species possess a unique OB morphology in which each OB is physically subdivided into two or more “hemi‐olfactory bulbs.” Somatotopy could provide a preadaptation which facilitated the evolution of olfactory hemibulbs in these species. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Co-occurrence of ectoparasites of marine fishes: a null model analysis

We used null model analysis to test for nonrandomness in the structure of metazoan ectoparasite communities of 45 species of marine fish. Host species consistently supported fewer parasite species combinations than expected by chance, even in analyses that incorporated empty sites. However, for most analyses, the null hypothesis was not rejected, and co-occurrence patterns could not be distinguished from those that might arise by random colonization and extinction. We compared our results to analyses of presence–absence matrices for vertebrate taxa, and found support for the hypothesis that there is an ecological continuum of community organization. Presence–absence matrices for small-bodied taxa with low vagility and/or small populations (marine ectoparasites, herps) were mostly random, whereas presence–absence matrices for large-bodied taxa with high vagility and/or large populations (birds, mammals) were highly structured. Metazoan ectoparasites of marine fishes fall near the low end of this continuum, with little evidence for nonrandom species co-occurrence patterns.     

Angiotensin and angiotensin receptors in cartilaginous fishes

In mammals, a principal bioactive component of the renin-angiotensin system (RAS), angiotensin II (ANG II), is known to be vasopressor, dipsogenic, a stimulant of adrenocortical secretion and to control glomerular and renal tubular function. Historically, a RAS analogous to that found in mammals was thought to have first evolved in the bony fishes. Recent research has identified the unusually structured elasmobranch [Asp(1)-Pro(3)-Ile(5)] ANG II. Physiological studies have demonstrated that ANG II in elasmobranchs is vasopressor, and stimulates interrenal gland production of the elasmobranch corticosteroid 1alpha-hydroxycorticosterone. The specific binding of ANG II in elasmobranchs has been reported in gills, heart, interrenal gland, gut and rectal gland. The precise osmoregulatory role ANG II plays in cartilaginous fishes is not yet known; however, putative evidence is emerging for a role in the control of drinking rate, rectal gland secretion, and kidney function.     

Early Evolution of Immunoglobulin Genes

Considerable progress has been made in the characterizationof immunoglobulin genes from several lower vertebrate taxa.Isolation and identification of immunoglobulin genes in phylogeneticallyprimitive species is based predominantly on heterologous crosshybridization.The unit, clustered organization of heavy chain segmental elementsobserved in the germline of the horned shark (Hinds and Litman,1986) has also been found in another elasmobranch. Studies todetermine whether the clustered organization is universal throughoutthe entire cartilaginous fish assemblage are ongoing. In contrast,the ray-finned (bony)fishes appear to possess a mammalian-typeheavy chain gene organization. Additionally, immunoglobulingenes are being characterized in two relict fish species whoseexact systematic relationships are unknown. Isolation of putativeimmunoglobulin genes from the phylogenetically- ancient hagfishis being attempted using a PCR-based approach. Other ongoingor future research efforts involve characterization of lowervertebrate light chain genes, heavy chain isotype evolution,and the divergence of the immunoglobulins and T-cell antigenreceptors     

Are mushroom bodies cerebellum-like structures?

The mushroom bodies are distinctive neuropils in the protocerebral brain segments of many protostomes. A defining feature of mushroom bodies is their intrinsic neurons, masses of cytoplasm-poor globuli cells that form a system of lobes with their densely-packed, parallel-projecting axon-like processes. In insects, the role of the mushroom bodies in olfactory processing and associative learning and memory has been studied in depth, but several lines of evidence suggest that the function of these higher brain centers cannot be restricted to these roles. The present account considers whether insight into an underlying function of mushroom bodies may be provided by cerebellum-like structures in vertebrates, which are similarly defined by the presence of masses of tiny granule cells that emit thin parallel fibers forming a dense molecular layer. In vertebrates, the shared neuroarchitecture of cerebellum-like structures has been suggested to underlie a common functional role as adaptive filters for the removal of predictable sensory elements, such as those arising from reafference, from the total sensory input. Cerebellum-like structures include the vertebrate cerebellum, the electrosensory lateral line lobe, dorsal and medial octavolateral nuclei of fish, and the dorsal cochlear nucleus of mammals. The many architectural and physiological features that the insect mushroom bodies share with cerebellum-like structures suggest that it might be fruitful to consider mushroom body function in light of a possible role as adaptive sensory filters. The present account thus presents a detailed comparison of the insect mushroom bodies with vertebrate cerebellum-like structures.     

Development of the cerebellum and cerebellar neural circuits

The cerebellum, a structure derived from the dorsal part of the most anterior hindbrain, is important for integrating sensory perception and motor control. While the structure and development of the cerebellum have been analyzed most extensively in mammals,recent studies have shown that the anatomy and development of the cerebellum is conserved between mammals and bony fish (teleost) species, including zebrafish. In the mammalian and teleost cerebellum,Purkinje and granule cells serve, respectively, as the major GABAergic and glutamatergic neurons. Purkinje cells originate in the ventricular zone (VZ), and receive inputs from climbing fibers. Granule cells originate in the upper rhombic lip (URL) and receive inputs from mossy fibers. Thus, the teleost cerebellum shares many features with the cerebellum of other vertebrates, and isa good model system for studying cerebellar function and development. The teleost cerebellum also has features that are specific to teleosts or have not been elucidated in mammals, including eurydendroid cells and adult neurogenesis. Furthermore, the neural circuitry in part of the optic tectum and the dorsal hindbrain closely resembles the circuitry of the teleost cerebellum; hence,these are called cerebellum-like structures. Here we describe the anatomy and development of cerebellar neurons and their circuitry, and discuss the possible roles of the cerebellum and cerebellum-like structures in behavior and higher cognitive functions. We also consider the potential use of genetics and novel techniques for studying the cerebellum in zebrafish.     

爬行动物MHC基因研究进展

主要组织相容性复合体(MHC)是有颌脊椎动物中发现的编码免疫球蛋白受体的高度多态的基因群,因其在免疫系统中的重要作用而备受关注。脊椎动物不同支系间MHC的结构和演化差异较大。尽管MHC基因特征在哺乳类、鸟类、两栖类和鱼类中已被较好地描述,但对爬行动物MHC的了解仍较少。鉴于爬行动物对于理解MHC基因的演化占据很重要的系统发育位置,研究其MHC具有重要意义。本文就近年来爬行动物MHC的分子结构、多态性维持机制、功能和主要应用的研究现状进行了系统地回顾和总结,并展望了其研究前景。     

Development and organization of polarity-specific segregation of primary vestibular afferent fibers in mice

A striking feature of vestibular hair cells is the polarized arrangement of their stereocilia as the basis for their directional sensitivity. In mammals, each of the vestibular end organs is characterized by a distinct distribution of these polarized cells. We utilized the technique of post-fixation transganglionic neuronal tracing with fluorescent lipid soluble dyes in embryonic and postnatal mice to investigate whether these polarity characteristics correlate with the pattern of connections between the endorgans and their central targets; the vestibular nuclei and cerebellum. We found that the cerebellar and brainstem projections develop independently from each other and have a non-overlapping distribution of neurons and afferents from E11.5 on. In addition, we show that the vestibular fibers projecting to the cerebellum originate preferentially from the lateral half of the utricular macula and the medial half of the saccular macula. In contrast, the brainstem vestibular afferents originate primarily from the medial half of the utricular macula and the lateral half of the saccular macula. This indicates that the line of hair cell polarity reversal within the striola region segregates almost mutually exclusive central projections. A possible interpretation of this feature is that this macular organization provides an inhibitory side-loop through the cerebellum to produce synergistic tuning effects in the vestibular nuclei. The canal cristae project to the brainstem vestibular nuclei and cerebellum, but the projection to the vestibulocerebellum originates preferentially from the superior half of each of the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells or may be an evolutionary atavism reflecting a different polarity organization in ancestral vertebrate ears.     

A NEW SPECIES OF ALLIGATOR FROM SHANWANG, SHANDONG

<正> A crocodilian specimen is described and identified, as a new species of Alligalor in present paper. The material was collected from the Middle Member of the Shanwang Formation, Linqu County, Shandong Province by the members of the Linqu Paleontological Museum in 1984. Nearly 40 taxa of fossil vertebrates, including fishes, amphibians, reptiles, birds and mammals, have been reproted from this Miocene locality since 1930's (Yian et al. 1983, Qiu et al. 1986). Within the vertebrate fauna the fossil mammals and fishes are very rich, but the other are relatively rare. This is the first record of a crocodilan from the diatomaceous quarry of Shanwang.     

Evolution of muscle activity patterns driving motions of the jaw and hyoid during chewing in Gnathostomes

Although chewing has been suggested to be a basal gnathostome trait retained in most major vertebrate lineages, it has not been studied broadly and comparatively across vertebrates. To redress this imbalance, we recorded EMG from muscles powering anteroposterior movement of the hyoid, and dorsoventral movement of the mandibular jaw during chewing. We compared muscle activity patterns (MAP) during chewing in jawed vertebrate taxa belonging to unrelated groups of basal bony fishes and artiodactyl mammals. Our aim was to outline the evolution of coordination in MAP. Comparisons of activity in muscles of the jaw and hyoid that power chewing in closely related artiodactyls using cross-correlation analyses identified reorganizations of jaw and hyoid MAP between herbivores and omnivores. EMG data from basal bony fishes revealed a tighter coordination of jaw and hyoid MAP during chewing than seen in artiodactyls. Across this broad phylogenetic range, there have been major structural reorganizations, including a reduction of the bony hyoid suspension, which is robust in fishes, to the acquisition in a mammalian ancestor of a muscle sling suspending the hyoid. These changes appear to be reflected in a shift in chewing MAP that occurred in an unidentified anamniote stem-lineage. This shift matches observations that, when compared with fishes, the pattern of hyoid motion in tetrapods is reversed and also time-shifted relative to the pattern of jaw movement.     

Genomic organization of the Hoxa4-Hoxa10 region from Morone saxatilis: implications for Hox gene evolution among vertebrates.

The physical mapping of Hox gene clusters from a limited number of vertebrates has shown an overall conservation in gene organization in which major evolutionary changes appear to be primarily restricted to the deletion of one or more genes, with the exception of the amplification of additional clusters as postulated from zebrafish. We have sequenced a 31 kb region of the HoxA cluster from the teleost Morone saxatilis (striped bass), both to provide a detailed physical map of this region and to better understand the nature of Hox cluster evolution among vertebrate taxa. We identified five linked Hox genes: Hoxa4, Hoxa5, Hoxa7, Hoxa9, and Hoxa10, which are organized similarly to those of other vertebrates. Furthermore, we have documented the absence of the Hoxa6 and Hoxa8 genes within the 31 kb contig. Comparison of our results to those published for other vertebrates suggests that the absence of Hoxa6 is a common characteristic of teleosts, whereas the absence of Hoxa8 is common to vertebrates in general, with the possible exception of zebrafish. Further comparisons between the HoxA genes from Morone with those from the pufferfish, Fugu rubripes, revealed the likely presence of a previously unreported Hoxa7 gene, or gene fragment, in the Fugu genome, which suggests that the Hoxa7 gene, unlike Hoxa6 or Hoxa8, is present in teleosts. In addition to these differences in vertebrate Hox cluster structure, we also observed a marked reduction in the length of the Hoxa4--a10 region between vertebrate lineages representative of teleosts and mammals. Comparative analysis of HoxA cluster organization among teleosts and mammals suggests that cluster length reduction and lineage-specific gene loss events are hallmarks of Hox cluster evolution.     

Comparative aspects of adult neural stem cell activity in vertebrates

At birth or after hatching from the egg, vertebrate brains still contain neural stem cells which reside in specialized niches. In some cases, these stem cells are deployed for further postnatal development of parts of the brain until the final structure is reached. In other cases, postnatal neurogenesis continues as constitutive neurogenesis into adulthood leading to a net increase of the number of neurons with age. Yet, in other cases, stem cells fuel neuronal turnover. An example is protracted development of the cerebellar granular layer in mammals and birds, where neurogenesis continues for a few weeks postnatally until the granular layer has reached its definitive size and stem cells are used up. Cerebellar growth also provides an example of continued neurogenesis during adulthood in teleosts. Again, it is the granular layer that grows as neurogenesis continues and no definite adult cerebellar size is reached. Neuronal turnover is most clearly seen in the telencephalon of male canaries, where projection neurons are replaced in nucleus high vocal centre each year before the start of a new mating season—circuitry reconstruction to achieve changes of the song repertoire in these birds? In this review, we describe these and other examples of adult neurogenesis in different vertebrate taxa. We also compare the structure of the stem cell niches to find common themes in their organization despite different functions adult neurogenesis serves in different species. Finally, we report on regeneration of the zebrafish telencephalon after injury to highlight similarities and differences of constitutive neurogenesis and neuronal regeneration.     

Speciation durations and Pleistocene effects on vertebrate phylogeography.

An approach applied previously to avian biotas is extended in this paper to other vertebrate classes to evaluate Pleistocene phylogeographic effects and to estimate temporal spans of the speciation process (speciation durations) from mitochondrial (mt) DNA data on extant taxa. Provisional molecular clocks are used to date population separations and to bracket estimates of speciation durations between minimum and maximum values inferred from genetic distances between, respectively, extant pairs of intraspecific phylogroups and sister species. Comparisons of genetic-distance trends across the vertebrate classes reveal the following: (i) speciation durations normally entail at least two million years on average; (ii) for mammals and birds, Pleistocene conditions played an important role in initiating phylogeographic differentiation among now-extant conspecific populations as well as in further sculpting pre-existing phylogeographic variety into many of today''s sister species; and (iii) for herpetofauna and fishes, inferred Pleistocene biogeographic influences on present-day taxa differ depending on alternative but currently plausible mtDNA rate calibrations.     

The Renin-Angiotensin System in Fishes

It has been suggested that the renin-angiotensin system (RAS)in mammals may participate in the control of blood pressure,regulation of aldosterone secretion, or in renal functions byinfluencing intrarenal hemodynamics, or possibly by directlyaltering renal tubular sodium reabsorption. Comparative studieshave shown that this system is present among most vertebrates.Renal renin activity and juxtaglomerular cells (JGC), the possiblesite of formation and accumulation of renin, have not been foundin the cyclostomes and elasmobranchs. They seem to have evolvedin primitive bony fishes, being present in all living groupsof actinopterygians and sarcopterygians. Both renin and JGCmay also exist in a holocephalian, the ratfish, Hydrolagus colliei.The functions of the RAS are not yet denned in fishes. Thereis no clear evidence for sodium retaining function of the RASin fishes. Fish angiotensins (angiotensin-like substances) havechemical properties that differ from those of mammals and othertetrapods. It is possible that they also serve quite differentfunctions in fishes than in mammals.     

Zebrin II / Aldolase C Expression in the Cerebellum of the Western Diamondback Rattlesnake (Crotalus atrox)

Aldolase C, also known as Zebrin II (ZII), is a glycolytic enzyme that is expressed in cerebellar Purkinje cells of the vertebrate cerebellum. In both mammals and birds, ZII is expressed heterogeneously, such that there are sagittal stripes of Purkinje cells with high ZII expression (ZII+), alternating with stripes of Purkinje cells with little or no expression (ZII-). The patterns of ZII+ and ZII- stripes in the cerebellum of birds and mammals are strikingly similar, suggesting that it may have first evolved in the stem reptiles. In this study, we examined the expression of ZII in the cerebellum of the western diamondback rattlesnake (Crotalus atrox). In contrast to birds and mammals, the cerebellum of the rattlesnake is much smaller and simpler, consisting of a small, unfoliated dome of cells. A pattern of alternating ZII+ and ZII- sagittal stripes cells was not observed: rather all Purkinje cells were ZII+. This suggests that ZII stripes have either been lost in snakes or that they evolved convergently in birds and mammals.     

Phylogenetic analysis of vertebrate kininogen genes

Kininogens, the precursors of bradykinins, vary extremely in both structure and function among different taxa of animals, in particular between mammals and amphibians. This includes even the most conserved bradykinin domain in terms of biosynthesis mode and structure. To elucidate the evolutionary dynamics of kininogen genes, we have identified 19 novel amino acid sequences from EST and genomic databases (for mammals, birds, and fishes) and explored their phylogenetic relationships using combined amino acid sequence and gene structure as markers. Our results show that there were initially two paralogous kininogen genes in vertebrates. During their evolution, the original gene was saved with frequent multiplication in amphibians, but lost in fishes, birds, and mammals, while the novel gene was saved with multiple functions in fishes, birds, and mammals, but became a pseudogene in amphibians. We also propose that the defense mechanism against specific predators in amphibian skin secretions has been bradykinin receptor dependent. Our findings may provide a foundation for identification and structural, functional, and evolutionary analyses of more kininogen genes and other gene families.     

Recurrent cerebellar architecture solves the motor-error problem

Current views of cerebellar function have been heavily influenced by the models of Marr and Albus, who suggested that the climbing fibre input to the cerebellum acts as a teaching signal for motor learning. It is commonly assumed that this teaching signal must be motor error (the difference between actual and correct motor command), but this approach requires complex neural structures to estimate unobservable motor error from its observed sensory consequences. We have proposed elsewhere a recurrent decorrelation control architecture in which Marr-Albus models learn without requiring motor error. Here, we prove convergence for this architecture and demonstrate important advantages for the modular control of systems with multiple degrees of freedom. These results are illustrated by modelling adaptive plant compensation for the three-dimensional vestibular ocular reflex. This provides a functional role for recurrent cerebellar connectivity, which may be a generic anatomical feature of projections between regions of cerebral and cerebellar cortex.