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PubMed1981

Dopaminergic mechanisms in the teleost retina. I. Dopamine-sensitive adenylate cyclase in homogenates of carp retina; effects of agonists, antagonists, and ergots.

A specific dopamine-sensitive adenylate cyclase has been identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 microM-dopamine resulted in a 5--10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 microM. l-Noradrenaline and l-adrenaline were some 10 times less potent than dopamine whilst the alpha- and beta-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity whilst various ergot alkaloids produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, alpha-flupenthixol and alpha-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with the alpha- and beta-adrenoreceptor blocking agents, phentolamine and propranolol respectively were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. These data suggest the presence of a highly specific dopamine-sensitive adenylate cyclase in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the mammalian central nervous system.

Adenylyl Cyclases↗
PubMed1998

Varied redox forms of teleost IgM: an alternative to isotypic diversity?

Teleosts (bony fish) are thought to primarily or exclusively possess a single structural form of immunoglobulin (Ig), a tetrameric IgM. However, in species wherein intact Ig has been electrophoretically analyzed under denaturing, non-reducing conditions, a significant degree of structural diversity has been revealed. This IgM molecule appears to be assembled with great latitude in the degree of disulfide crosslinking between monomeric or halfmer subunits composing the complete IgM molecule. This heterogeneity in the basic structure (herein referred to as redox forms) is not due to isotypic differences as each B cell produces this heterogeneity within its immunoglobulin product. Additionally, in the case of the catfish, a single fish/mouse chimeric Ig H gene is capable of producing IgM with a comparable amount of structural heterogeneity within the mouse cell. Thus, the piscine B lymphocyte routinely assembles a variety of redox forms from one IgM chain. This has both profound biosynthetic implications for macromolecular assembly processes as well as intriguing possibilities for the generation of teleost Ig functional diversity.

Animals↗
PubMed1998

The salmonid class I MHC: limited diversity in a primitive teleost.

Three MHC class I genes have been characterized in salmonids: A, B, and UA. Levels of polymorphism vary among the genes, but they all share one common feature: a lack of sequence diversity. Although individual species can carry over 30 alleles at a given locus (A), intraspecific diversity is generally less than 5% in Pacific salmon (genus Oncorhynchus), and less than 10% in Atlantic salmon (genus Salmo). These levels of diversity suggest that few ancient allelic lineages have persisted within species, and that most of the allelic radiation has occurred during or since speciation. Also apparent is the greater retention of allelic lineages in Atlantic salmon than Pacific salmon, which reflects historic differences of the two genera. Comparison of the salmonid class I sequences with those of other teleosts reveals two well supported groups: one containing the Cypriniformes and the salmonid UA, and the other containing the neoteleosts and the salmonid A and B. There is no homology between known Cypriniformes and neoteleostean sequences. If this relationship is borne out, it offers strong support for the hypothesis that the higher teleosts diverged more recently from the Salmoniformes than the Cypriniformes. The salmonid MHC may provide a snapshot of the neoteleostean MHC prior to the extensive class I duplication that has taken place in at least some of the more advanced species.

Animals↗
PubMed1998

Activity of alkaline and acid phosphatases in dental epithelial cells and enameloid during odontogenesis in two teleost fish, Oreochromis niloticus and Tilapia buttikoferi.

The dental epithelial cells and enameloid at the stages of enameloid matrix formation, mineralization and maturation in the teleosts Oreochromis niloticus and Tilapia buttikoferi were investigated by means of enzyme histochemistry in order to identify their functions associated with the structural modification. No marked enzyme activities were found in the inner dental epithelial cells in the stage of enameloid matrix formation, although the outer dental epithelial cells often exhibited moderate alkaline phosphatase (ALPase) activity. In the stages of enameloid mineralization and maturation, the inner dental epithelial cells, which possessed a ruffled border at the distal ends, showed intense ALPase activity at their lateral and proximal cell membranes. At the same time, many acid phosphatase (ACPase)-positive vesicles and granules were localized at the distal cytoplasm of the inner dental epithelial cells. The outer dental epithelial cells, which contained well-developed labyrinthine canalicular spaces, showed neither marked ALPase nor ACPase activity. It is postulated that the dental epithelial cells in these two teleosts are mainly involved in the removal of the organic matrix from the enameloid, and in material transport to the enameloid during the later half of odontogenesis.

Acid Phosphatase↗
PubMedDate not supplied

Dermal and epidermal chromatophores of the Antarctic teleost Trematomus bernacchii.

The physiological response and ultrastructure of the pigment cells of Trematomus bernacchii, an Antarctic teleost that lives under the sea ice north of the Ross Ice Shelf, were studied. In the integument, two types of epidermal chromatophores, melanophores and xanthophores, were found; in the dermis, typically three types of chromatophores--melanophores, xanthophores, and iridophores--were observed. The occurrence of epidermal xanthophore is reported for the first time in fish. Dermal melanophores and xanthophores have well-developed arrays of cytoplasmic microtubules. They responded rapidly to epinephrine and teleost melanin-concentrating hormone (MCH) with pigment aggregation and to theophylline with pigment dispersion. Total darkness elicited pigment aggregation in the majority of dermal xanthophores of isolated scales, whereas melanophores remained dispersed under both light and dark conditions. Pigment organelles of epidermal and dermal xanthophores that translocate during the pigmentary responses are carotenoid droplets of relatively large size. Dermal iridophores containing large reflecting platelets appeared to be immobile.

Animals↗
PubMed1991

Protein-kinase C mediates MCH signal transduction in teleost, synbranchus marmoratus, melanocytes.

MCH (melanin concentrating hormone) is a heptadecapeptide, Asp-Thr-Met-Arg-Cys-Met-Val-Gly-Arg-Val-Tyr-Arg-Pro-Cys-Trp-Glu-Val, which stimulates melanosome (melanin granule) aggregation to a perinuclear position within teleost fish integumental melanocytes, resulting in lightening of the skin. The mechanisms of action of MCH are unknown. Drugs that affect the diacylglycerol/inositol triphosphate pathway were used to investigate the possible roles of this pathway in the mechanisms of action of MCH on Synbranchus marmoratus (teleost) melanocytes. The shift of the dose-response curve to MCH in the presence of various concentrations of 4-bromophenacyl bromide and neomycin sulphate, phospholipase C inhibitors, suggests that phospholipase C is stimulated after MCH receptor activation. Low concentrations (10(-9) to 10(-8) M) of the phorbol ester TPA exhibited MCH-like activity, eliciting a dose-dependent melanosome aggregation. Higher doses, however, displaced to the right the dose-response curve to MCH, as did the protein kinase C inhibitors, dibucaine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). These results support the assumption that protein kinase C mediates the pigment aggregating activity of MCH. Both MCH and norepinephrine lightening actions were abolished by beta-glycerophosphate, a phosphatase inhibitor, suggesting that a protein dephosphorylation occurs during melanosome aggregation, and is, therefore, a common event triggered by MCH and norepinephrine, although both agonists act through separate receptors and exhibit different transduction mechanisms.

Amino Acid Sequence↗
PubMed2006

Melanogenesis and evidence for melanosome transport to the plasma membrane in a CD83 teleost leukocyte cell line.

Visceral organs of ectothermic vertebrates harbour melanin-containing leukocytes termed melanomacrophages. These cells are thought to participate in immune reactions and free-radical trapping. In teleosts, the melanin-producing ability of melanomacrophages has hitherto not been confirmed by molecular techniques. Here, a leukocyte marker and the apparatus for melanosome production and transport were investigated in an Atlantic salmon (Salmo salar) pronephros-derived mononuclear leukocyte (SHK-1) cell line. The SHK-1 cells expressed transcripts specific for a mammalian CD83 homologue, a standard surface marker for activated or differentiated dendritic cells, and dopachrome tautomerase/tyrosinase-related protein-2, a melanocyte specific enzyme essential for melanin production. Reduction potential of melanin or its precursors was demonstrated histochemically after prolonged cultivation. Ultrastructural investigations revealed tyrosinase and acid phosphate activity in identical organelles and BSA-gold co-localized with multilamellar melanosomes after 2 h internalization. Apparently, melanosomes were transported and released through periodically occurring tubules fusing with the plasma membrane. Video monitoring revealed filopodia and macropinocytosis. These results showed that the SHK-1 cell line is capable of melanogenesis and melanosome secretion. Melanin-producing cells in teleost pronephros may represent a distinct CD83(+) leukocyte population consisting of phylogenetically relict multifunctional cells. This is the first report of a melanin-producing leukocyte cell-line.

Animals↗
PubMed1994

Role of the endothelium in regulation of vascular functions in two teleosts.

Functional and structural aspects of the vascular endothelium were studied in major blood vessels from two distantly related species, the Atlantic salmon (S. salar) and the cod (G. morhua). The ventral aorta (VA) of both teleosts and the dorsal aorta (DA) and the coeliaco mesenteric artery (CMA) of the cod and the salmon respectively were examined for endothelium dependent and independent responses to acetylcholine (ACh), adrenaline (A) and endothelin-1 (ET-1). In the salmon, endothelial probing resulted in reduced contractile responses to high K+ in both VA and CMA while the responses to ACh and A were reduced only in CMA. Indomethacin, but not L-NMMA, enhanced vasoconstrictions to high K+, ACh and A in the unprobed CMA. In the cod vessels the endothelial probing caused reduced contractile responses to the two effective vasoconstrictors in both vessels, to high K+ and A in VA and to high K+ and ET-1 in DA. Both indomethacin and L-NMMA enhanced contractile tension to A in VA, while indomethacin, but not L-NMMA, enhanced the constrictions by high K+ in VA and by ET-1 in DA. These experiments have revealed heterogeneous patterns of endothelial function in blood vessels of two teleosts, reflecting differences in endothelial morphology and in production of potent endothelial derived contracting factors as well as prostanoic and non-prostanoic endothelium-derived dilating factors.

Acetylcholine↗
PubMed2001

Immune responses of teleost fish.

In fish all the pre-requisites to mount a specific immune response are present, but the main differences from the mammalian system are that the secondary response is relatively minor and IgG is not present. In teleosts mainly IgM is present, and IgD has been recently described but its function is, as yet, unknown. However, different forms of fish IgM and its observed flexibility of structure may compensate for a lack of Ig class diversity. The innate immune response of teleosts is highly developed. Multiple forms of key constitutive and inducible components, such as lysozyme, C3, alpha2-macroglobulin and C-reactive protein, are present, and may enhance immune recognition. Low ambient temperature appears to have an impact on all aspects of the immune response, particularly the T-dependent specific immune response due to the non-adaptive lipid composition of T-cell membranes. Temperature effects on the nonspecific immune system are less well characterised, but there is evidence that low temperatures are also suppressive. Knowledge of immune system function becomes essential for disease prevention strategies such as the development of vaccines, selection for increased disease resistance and identification of genes suitable for trangenesis.

Animals↗
PubMed1961

New arrangement of interrenal and chromaffin tissues of teleost fishes.

An unusual morphologic arrangement of interrenal and chromaffin tissues has been observed in two families of teleost fishes. In most teleosts in which these cell types occur together in association with the postcardinal veins and their branches, the chromaffin cells are located between the lumen of the vein and the interrenal cells. This typical relationship is reversed in some of the Labridae and Scaridae.

Chromaffin Cells↗
PubMed1969

Seawater teleosts: evidence for a sodium-potassium exchange in the branchial sodium-excreting pump.

The net sodium extrusion rate by the gill of the seawater-adapted euryhaline flounder is identical to the potassium influx. The excretion of sodium is blocked in K(+)-free seawater solutions. The instantaneous sodium outflux readjustment pattern of flounders transferred from seawater to solutions of various sodium chloride or potassium chloride concentrations is consistent with the hypothesis of a linkage between Na(+) outflux and K(+) influx through a common exchange carrier. External Na(+) and K(+) compete for this comnmonz carrier. It is suggested that the exchange diffusion mechanism (linkage of sodium influx and outflux) and the high internal sodium turnover rate which characterizes all seawater teleosts are the results of this competitive process. The sodium-potassium dependent adenosine triphosphatase system occurring in the gill of the seawater teleosts may play a central role in this sodium-potassium exchange pump.

Adaptation, Physiological↗
PubMed1998

A divergent CFTR homologue: highly regulated salt transport in the euryhaline teleost F. heteroclitus.

The killifish, Fundulus heteroclitus, is a euryhaline teleost fish capable of adapting rapidly to transfer from freshwater (FW) to four times seawater (SW). To investigate osmoregulation at a molecular level, a 5.7-kilobase cDNA homologous to human cystic fibrosis transmembrane conductance regulator (hCFTR) was isolated from a gill cDNA library from SW-adapted killifish. This cDNA encodes a protein product (kfCFTR) that is 59% identical to hCFTR, the most divergent form of CFTR characterized to date. Expression of kfCFTR in Xenopus oocytes generated adenosine 3',5'-cyclic monophosphate-activated, Cl(-)-selective currents similar to those generated by hCFTR. In SW-adapted killifish, kfCFTR was expressed at high levels in the gill, opercular epithelium, and intestine. After abrupt exposure of FW-adapted killifish to SW, kfCFTR expression in the gill increased severalfold, suggesting a role for kfCFTR in salinity adaptation. Under similar conditions, plasma Na+ levels rose significantly after 8 h and then fell, although it is not known whether these changes are directly responsible for the changes in kfCFTR expression. The killifish provides a unique opportunity to understand teleost osmoregulation and the role of CFTR.

Adaptation, Physiological↗
PubMed1988

Effect of teleost GnRH on reinitiation of oocyte meiosis in goldfish, in vitro.

The effects of native and an agonist analogue of teleost gonadotropin-releasing hormone (GnRH) [(D-Arg6, Trp7, Leu8, Pro9-NHEt)-GnRH; tGnRH-A] on the hormone-induced meiotic maturation of goldfish oocytes were investigated. Incubation of follicle-enclosed goldfish oocytes with either carp gonadotropin (GtH) or meiogenic progestogens, including 17 alpha-hydroxyprogesterone (HP) and 17 alpha,20 beta-dihydroxyprogesterone (DHP), reinitiated oocyte meiosis in vitro, as indicated by germinal vesicle dissolution (GVD). Addition of tGnRH-A (10(-7) M) significantly attenuated the GVD response to GtH, HP, and DHP in a dose-related fashion; tGnRH-A reduced the magnitude of progestogen-induced GVD response without significantly affecting the sensitivity of the oocytes to the meiogenic steroids. Similarly, administration of native teleost GnRH (tGnRH) significantly attenuated GtH-induced GVD response, although the 50% maximal response of the native peptide was significantly higher than that of tGnRH-A (380.9 +/- 125 and 2.72 +/- 0.94 nM, respectively). The present results provide the first demonstration of an inhibitory action of a GnRH agonist on the process of progestogen-induced oocyte meiosis and support the hypothesis that GnRH or a GnRH-like peptide might play a modulating role in the control of oocyte meiosis at the ovarian level in goldfish.

Animals↗
PubMed1991

Glutamine metabolism in a holostean (Amia calva) and teleost fish (Salvelinus namaycush).

Amino acid metabolism was examined in mitochondria from the lateral red muscle of a teleost (lake char, Salvelinus namaycush) and a nonteleost fish (bowfin, Amia calva). Isolated mitochondria oxidize a wide variety of substrates and have high respiratory control ratios. In both species, glutamine is oxidized more rapidly than any other amino acid. The rate of glutamine oxidation by bowfin mitochondria exceeds that of lake char mitochondria, and the bowfin displays correspondingly higher levels of mitochondrial phosphate-dependent glutaminase. It is suggested that amino acids in general, and glutamine in particular, are important oxidative substrates for nonteleost red muscle. The teleost red muscle, however, may rely on both glutamine and fatty acids as oxidative substrates. It appears that glutamate derived from glutamine is oxidized primarily via glutamate dehydrogenase, whereas exogenous glutamate is oxidized primarily via aspartate aminotransferase. Complete oxidation of glutamine may be accomplished in the absence of other substrates by conversion of glutamine-derived malate to pyruvate via malic enzyme. To assess the relative abilities of various tissues to synthesize and oxidize glutamine, the activities of glutamine synthetase and glutaminase were measured. The results of these studies indicate that the organization of glutamine metabolism of fish differs markedly from that in mammals.

Amino Acids↗
PubMed1994

Nocodazole inhibition of organic anion secretion in teleost renal proximal tubules.

The impact of the microtubule-disrupting drug nocodazole on renal tubular secretion of organic anions was examined in vitro using proximal tubular masses from teleost fish. Nocodazole reversibly inhibited 20-30% of the tubular accumulation of two model organic anions, p-aminohippurate and fluorescein (FL), by winter flounder tubular masses. However, the drug had no effect on the initial rate of organic anion uptake. Thus it did not reduce transport into the cells at the basolateral membrane, either directly by affecting basolateral organic anion transport proteins or indirectly by altering metabolism or ion gradients. Instead, epifluorescence video microscopy and digital image analysis of killifish tubules showed that nocodazole greatly reduced luminal accumulation of FL and had a smaller effect on cellular dye accumulation. Luminal FL accumulation returned to control levels when tubules were incubated in drug-free medium. Confocal fluorescence microscopy confirmed the marked reduction in luminal FL concentration and demonstrated that intracellular punctate FL accumulation was also markedly reduced. Finally, immunohistochemistry with an anti-tubulin antibody showed that the concentrations of nocodazole used in the above experiments reversibly disrupted microtubules within renal epithelial cells. These data indicate that a component of organic anion secretion in teleost proximal tubule is dependent on an intact microtubular network.

Animals↗
PubMed1992

Renal acid-base physiology in marine teleost, the long-horned sculpin (Myoxocephalus octodecimspinosus).

We have sought to define urinary acid-base excretion in the marine teleost using the long-horned sculpin, Myoxocephalus octodecimspinosus. Urine flow (1.7 ml.h-1.kg-1) is relatively high, and glomerular filtration rate is very low (2.9 ml.h-1.kg-1). The urine-to-plasma ratio of inulin is 2. Renal clearance of p-aminohippurate is very high (108 ml.h-1.kg-1); phosphate and divalent cations are also secreted. In this framework we found urinary pH to average 6.6, but infusion of acid or alkali elicited a pH range of 6.1-7.8. Untreated fish may also have alkaline urine; so it is not surprising that precipitates of calcium or magnesium phosphate are sometimes found in bladder. These are of fine sandy quality and never cause blockage. Infusion of buffer (imidazole) increased the concentration of titratable acid 11-fold and output 2.5-fold. Carbonic anhydrase inhibitors had no effect on any urinary component, and histochemical studies revealed that cytoplasm and membranes did not yield the specific cobalt stain for the enzyme. An alkaline load (NaHCO3) is rapidly dissipated by gill excretion, mediated in part by carbonic anhydrase. An acid load (HCl) is rapidly dissipated by gill excretion, not dependent on carbonic anhydrase, and some renal excretion. Comparison and contrast of the low rates of HCO3- reabsorption in the marine teleost (and elasmobranch) with those of mammals suggest strongly that renal carbonic anhydrase evolved in connection with these high reabsorptive rates beginning in freshwater fish and continuing through amphibia and birds.

Acid-Base Equilibrium↗
PubMed2001

Encoding of different aspects of afferent activities by two types of cells in the corpus glomerulosum of a teleost brain.

The corpus glomerulosum (CG) is an expansive nucleus in acanthopterigian teleosts that has been suggested to be involved in vision-related information processing and the control of the hypothalamic function. The CG has only two types of constituent cells, the large cell and the small cell, and well-defined afferent/efferent fiber connections. One of the three types of teleostean CG, type III has additional outstanding morphological characters: clearly laminated organization and giant (>50 microm in diameter) tips of postsynaptic dendrites. Although such histological architecture is potentially advantageous for the study of information processing in a brain nucleus based on the physiological properties of identified cells and synapses, previous studies on the CG have been limited to anatomy. In this study, we developed a slice preparation of the type III CG in a teleost, Stephanoplepis cirrhifer, and studied the morphology and physiology of individual cells and synaptic transmission by means of dendritic intracellular and somatic whole cell recordings. The characteristic morphology of the two types of cells was revealed by intracellular staining. While both of them received similar glutamatergic and GABAergic projections from the nucleus corticalis mediated by AMPA, N-methyl-D-aspartate, and GABA(A) receptors, they showed quite distinctive firing properties and postsynaptic responses with current injection and synaptic inputs: the large cell fired a single spike, and the small cell fired a spike train whose frequency was dependent on the stimulus intensity. Furthermore, the large cell showed low-pass temporal filtering properties with paired stimuli. These results suggest that the large cell and the small cell may encode different aspects of the corticalis activities.

Action Potentials↗
PubMed1998

Sonic/vocal motor pathways in catfishes: comparisons with other teleosts.

Among teleost fishes, representatives of several distantly related groups have sound-producing (sonic/vocal) muscles associated with the swimbladder or pectoral girdle/fin. Here, the diversity of vocal organs and central motor pathways in four families of catfish, order Siluriformes, is compared to that in families from two distantly related orders, the Scorpaeniformes and Batrachoidiformes. Several catfish families have two sonic mechanisms--a swimbladder vibration established by 'drumming muscles' that differ in origin and insertion between families, and a pectoral spine stridulatory apparatus. In ariids, mochokids and doradids, sonic swimbladder muscles originate at various cranial or postcranial elements and insert onto an 'elastic spring' that vibrates the swimbladder, while in pimelodids the muscles insert ventrally at the swimbladder. Sonic motoneurons are located along the midline, ventral to the fourth ventricle/central canal in doradids and mochokids but lateral to the medial longitudinal fasciculus in ariids; pimelodids have motoneurons in both locations. The axonal trajectory for the lateral motoneurons in pimelodids and ariids implies that they are a migrated, midline population of sonic motoneurons. Pectoral spine-associated motoneurons are located in the ventral motor column. Unlike catfishes, a diversity of sonic mechanisms in Scorpaeniformes is not associated with different positions for sonic motoneurons. Cottids (sculpin) lack a swimbladder but have sonic muscles that originate at the occipital cranium and insert at the pectoral girdle; sonic motoneurons are located within the ventral motor column. Some triglids have intrinsic swimbladder muscles, although ontogenetic data indicate a transient association with the pectoral girdle; sonic motoneurons are in the same location as in cottids. Among Batrachoidiformes, all known representatives have intrinsic swimbladder muscles that are never associated with the pectoral girdle and are innervated by midline sonic motoneurons. The results suggest two patterns of organization for sound-producing systems in teleost fishes: pectoral fin/girdle-associated muscles are innervated by sonic motoneurons positioned within the ventral motor column, adjacent to the ventral fasciculus; non-pectoral associated muscles are innervated by sonic motoneurons located on or close to the midline, adjacent to the medial longitudinal fasciculus.

Air Sacs↗