Classes Of Non-mammalian Vertebrates Research Articles

Locus Coeruleus in Non-Mammalian Vertebrates.

The locus coeruleus (LC) is a vertebrate-specific nucleus and the primary source of norepinephrine (NE) in the brain. This nucleus has conserved properties across species: highly homogeneous cell types, a small number of cells but extensive axonal projections, and potent influence on brain states. Comparative studies on LC benefit greatly from its homogeneity in cell types and modularity in projection patterns, and thoroughly understanding the LC-NE system could shed new light on the organization principles of other more complex modulatory systems. Although studies on LC are mainly focused on mammals, many of the fundamental properties and functions of LC are readily observable in other vertebrate models and could inform mammalian studies. Here, we summarize anatomical and functional studies of LC in non-mammalian vertebrate classes, fish, amphibians, reptiles, and birds, on topics including axonal projections, gene expressions, homeostatic control, and modulation of sensorimotor transformation. Thus, this review complements mammalian studies on the role of LC in the brain.

Disruption by stealth - Interference of endocrine disrupting chemicals on hormonal crosstalk with thyroid axis function in humans and other animals

Thyroid hormones (THs) are important regulators of growth, development, and homeostasis of all vertebrates. There are many environmental contaminants that are known to disrupt TH action, yet their mechanisms are only partially understood. While the effects of Endocrine Disrupting Chemicals (EDCs) are mostly studied as “hormone system silos”, the present critical review highlights the complexity of EDCs interfering with TH function through their interactions with other hormonal axes involved in reproduction, stress, and energy metabolism. The impact of EDCs on components that are shared between hormone signaling pathways or intersect between pathways can thus extend beyond the molecular ramifications to cellular, physiological, behavioral, and whole-body consequences for exposed organisms. The comparatively more extensive studies conducted in mammalian models provides encouraging support for expanded investigation and highlight the paucity of data generated in other non-mammalian vertebrate classes. As greater genomics-based resources become available across vertebrate classes, better identification and delineation of EDC effects, modes of action, and identification of effective biomarkers suitable for HPT disruption is possible. EDC-derived effects are likely to cascade into a plurality of physiological effects far more complex than the few variables tested within any research studies. The field should move towards understanding a system of hormonal systems’ interactions rather than maintaining hormone system silos.

Alternative Splice Variants of the Rainbow Trout Leptin Receptor Encode Multiple Circulating Leptin-Binding Proteins

In mammals, leptin (Lep) binding proteins (LepBPs) derived from Lep receptor (LepR) gene or protein bind most of the circulating Lep, but to date, information on LepBPs in nonmammalian vertebrate classes is lacking. This study details the characterization of multiple LepBPs in rainbow trout (Oncorhynchus mykiss), an early poikilothermic vertebrate, and presents the complete coding sequences for 3 of them. Size-exclusion chromatography and cross-linking assay identified plasma proteins bound to Lep ranging from 70 to 100 kDa. LepBPs were isolated from plasma by affinity chromatography, and their binding specificity was assessed by a competitive binding assay. A RIA for LepBPs indicates that plasma LepBP levels decline after fasting for 3 weeks. Immunoblotting of LepBPs using antibodies against different LepR epitopes shows that the LepBPs are indeed LepR isoforms. The alternatively spliced LepR transcripts (LepR(S1-3)) that include only the extracellular segment transcribe the 90-kDa LepBP1, the 80-kDa LepBP2, and the 70-kDa LepBP3, respectively. LepR(S1) generally has lower expression than the long-form LepR in most tissues. LepR(S2) is primarily expressed in adipose tissue, whereas LepR(S3) is expressed abundantly in brain and spleen, and moderately in liver and gills. The mRNA levels of hepatic LepR(S3) increase after 2 weeks of fasting. This study demonstrates a mechanism in fish for the generation of LepBPs that differs from that seen in mammals and indicates that the physiologic action of Lep in these poikilothermic vertebrates can be modulated, both centrally and peripherally, by the differentiated, tissue-specific expression of multiple LepBPs.

The unique paired retinal vascular pattern in marsupials: structural, functional and evolutionary perspectives based on observations in a range of species

Background:In the few marsupial species studied to date that possess a retinal vasculature, the arterial and venous segments, down to the smallest calibre capillaries, have been shown to occur in...

Role of corticotropin-releasing hormone as a thyrotropin-releasing factor in non-mammalian vertebrates

The finding that thyrotropin-releasing hormone does not always act as a thyrotropin (TSH)-releasing factor in non-mammalian vertebrates has led researchers to believe that another hypothalamic factor may exhibit this function. In representatives of all non-mammalian vertebrate classes, corticotropin-releasing hormone (CRH) appears to be a potent stimulator of hypophyseal TSH secretion, and might therefore function as a common regulator of both the thyroidal and adrenal/interrenal axes. CRH exerts its dual hypophysiotropic action through two different types of CRH receptors. Thyrotropes express type 2 CRH receptors, while CRH-induced corticotropin (ACTH) secretion is mediated by type 1 CRH receptors on the corticotropic pituitary cells. The stimulating effect of CRH on both TSH and ACTH release has profound consequences for the peripheral action of both hormonal axes. The simultaneous stimulation of the thyroidal and adrenal/interrenal axes by CRH, possibly fine-tuned by differential regulation of the expression of the different CRH receptor isoforms, provides a potential mechanism for developmental plasticity.

Primary cilia in vertebrate corneal endothelial cells.

The presence of primary cilia in corneal endothelial cells of a range of species from six non-mammalian vertebrate classes (Agnatha, Elasmobranchii, Amphibia, Teleostei, Reptilia and Aves) is examined by scanning and transmission electron microscopy. Our aim is to assess whether these non-motile cilia protruding into the anterior chamber of the eye are a consistent phylogenetic feature of the corneal endothelium and if a quantitative comparison of their morphology is able to shed any new light on their function. The length (0.42-3.80 microm) and width (0.12-0.44 microm) of the primary cilia varied but were closely allied with previous studies in mammals. However, interspecific differences such as the presence of a terminal swelling in the Teleostei and Amphibia suggest there are functional differences. Approximately one-third of the endothelial cells possess cilia but the extent of protrusion above the cell surface varies greatly, supporting a dynamic process of retraction and elongation. The absence of primary cilia in primitive vertebrates (Agnatha and Elasmobranchii) that possess other mechanisms to control corneal hydration suggests an osmoregulatory and/or chemosensory function.

A comparative study of sertoli cell ectoplasmic specializations in selected non-mammalian vertebrates

Ectoplasmic specializations (ES) facing spermatids were studied in species representative of four classes of non-mammalian vertebrates (Pisces—bluegill; Amphibia—bullfrog; Reptilia—red eared turtle; Aves—domestic chicken). ES was not seen in the bluegill but was present in all other species studied. In the frog, turtle, and chicken, ES did not resemble its mammalian counterpart and could only be characterized by the presence of 6 nm filaments (presumedly actin) within the somatic cell facing the head region of elongating spermatids. ES filaments were sparse in the frog and were sometimes associated with more deeply situated endoplasmic reticulum. Turtle ES filaments were abundant and encircled the acrosomal region of the spermatid head and were delimited by fenestrated saccules of endoplasmic reticulum. In the chicken, ES filaments were prominent but less abundant than in the turtle. Six nanometer filaments of the chicken ES appeared in a tangled mass and were not associated with clearly defined endoplasmic reticulum. In the three species where ES was found, it first developed as spermatids became entrenched within the surrounding somatic cell. Neither cell elongation, nuclear elongation, or movement of the nucleus to the cell surface was synchronized with the onset of ES development. That ES development was seen concomitant with spermatid entrenchment and spermatid orientation suggested a role for ES in these processes. This hypothesis was further strengthened by observations in the fish where ES was lacking and where spermatid entrenchment within the somatic cell, did not occur. The study also supported the hypothesis that ES acts as a cytoskeletal mantle to which other cytoskeletal elements within the cell interact to affect the position of elongate spermatids within the epithelium. The dissolution of ES prior to spermiation and concomitant loss of a close relationship between cells suggests that ES is also related to somatic cell-germ cell adhesion and therefore plays an important role in the spermiation process.

Dihydropyridine calcium channel antagonist binding in non-mammalian vertebrates: characterization and relationship to ‘peripheral-type’ binding sites for benzodiazepines

The densities of dihydropyridine calcium antagonist binding sites were examined in brains and cardiac issues of representative species from 4 classes of non-mammalian vertebrates (aves, pigeon; amphibia, frog; reptilia, chameleon; and osteichthyes, trout) previously shown to have low or undetectable levels of 'peripheral-type' binding sites for benzodiazepines. Dihydropyridine binding sites were present in brain and cardiac tissue of these 4 classes of non-mammalian vertebrates. The apparent dissociation constants for [3H]nitrendipine in non-mammalian vertebrates were comparable to those found in mammalian (rat) tissues. The densities of [3H]nitrendipine binding sites in brain and cardiac tissues were highest in the pigeon, with lower densities in tissues from chameleon, frog and trout. The densities of dihydropyridine binding sites in the latter tissues were comparable to those observed in the rat. Thus, dihydropyridine binding sites are phylogenetically diverse yet have similar kinetic characteristics in mammals and non-mammalian vertebrates. Despite the pharmacologic evidence that links dihydropyridine binding sites and peripheral binding sites for benzodiazepines in mammals, the earlier evolutionary appearance of the former sites suggest that even though they may share one or more common effector mechanisms, they are discrete entities.

Late evolutionary appearance of ‘peripheral-type’ binding sites for benzodiazepines

Four classes of non-mammalian vertebrates were examined for the presence of both ‘brain-specific’ and ‘peripheral-type’ binding sites for benzodiazepines in the central nervous system. ‘Brain-specific’ binding sites for benzodiazepines were found in the central nervous systems of all non-mammalian vertebrates studied. However, in contrast to mammals, either very low or undetectable levels of ‘peripheral-type’ binding sites for benzodiazepines were observed in the central nervous systems of these non-mammalian vertebrates. Furthermore, the density of ‘peripheral-type’ binding sites for benzodiazepines in non-mammalian vertebrate heart was ≦ 2% of that found in mammalian cardiac tissue. These findings suggest a very late evolutionary appearance of ‘peripheral-type’ binding sites for benzodiazepines, implying that these sites may have (a) highly specialized function(s) in both peripheral tissues and the central nervous system.

Effects of Competition on Rates of Evolution, With Special Reference to Bivalve Mollusks and Mammals

The high degree of interspecific competition typical of mammals is associated with specialized feeding habits, frequent limitation of population densities by food supply, highly developed mobility and behavior, aggressive interactions, and territoriality. Features associated with weak interspecific competition among most coexisting bivalve species are primitive behavior patterns, sedentary modes of life, generalized feeding habits, ability to endure long periods of near-starvation, and widespread limitation of population densities by physical disturbances and intense predation. By providing what Mayr has termed a centrifugal force in evolution, competition has produced rapid divergence in the Mammalia. Higher taxa of mammals have tended to maintain distinct adaptive zones, and ecologic displacement of one group by another has been common. Rate of appearance of new families has declined since early in the group's Cenozoic radiation because established groups have tended to preempt portions of the overall adaptive zone. In contrast, competition has played a minor role in bivalve evolution and divergence has been gradual. Adaptive zones of subtaxa have tended to overlap, and displacement has been rare. Despite the success of advanced bivalve taxa, many primitive groups have persisted for hundreds of millions of years, and various seemingly primitive groups have arisen quite recently. Competition has also contributed to higher rates of taxonomic turnover among mammals than among bivalves by accelerating rates of extinction. The anomalously high evolutionary rates of reef-building rudist bivalves resulted from competition for space. Similarly, reef-building scleractinian corals have radiated much more rapidly than have nonreef-building forms. The nonmammalian vertebrate classes, the trilobites, and the ammonites have all been characterized by competitive traits like those of the mammals and have also undergone notably rapid adaptive radiations.

Antibody response to bacteriophage phi-X-174 in non-mammalian vertebrates.

Discussion and SummaryAfter a single injection of 108–10 bacteriophage ΦX 174, the chicken, frog and goldfish were shown to produce approximately the same levels of neutralizing, rapidly sedimenting, γ-globulin antibodies as those previously obtained in analogously immunized mammals(5,6). Repeated injections of bacteriophage in the frog and goldfish, at intervals of 2–4 weeks, did not elicit an anamnestic antibody response. However, higher levels of antibody, mainly in the slowly sedimenting γ-globulin fraction were produced after immunization with bacteriophage in complete Freund's adjuvant, and, in the case of the goldfish, after further elevation of the environmental temperature to 32°C. Thus, in 3 classes of non-mammalian vertebrates a change was observed in the sedimentation properties of antibody γ-globulins produced during immunization. This change appeared similar to the replacement of 19S by 7S antibodies in the circulation of immunized mammals. These findings suggest that the mechanisms responsi...