Cellular Aspects of the Control of Physiological Color Changes in Crustaceans

SYNOPSIS. Red chromatophores(erythrophores) of the prawn, Palaemonetesvulgaris, are controlled by pigment—dispersing and -concentratinghormones. Recent experiments on the modes of action of thesehormones are described, followed by a theory which satisfactorilyexplains the data. Red pigment-concentrating hormone is dependentupon sodium ions for a strong response to occur. There is asimilar dependency of red pigment—dispersing hormone uponcalcium ions. Ouabain inhibits the response to red pigment—concentratinghormone; tetrodotoxin enhances it. Erythrophores with maximallydispersed pigment had a transmembrane potential of 55±15mv inside negative in one series of experiments and 56±4mv in another. No appreciable changes in permeability occurwhen depolarizing and hyperpolarizing currents are passed througha microelectrode within the chromatophore. Red pigmentconcentratinghormone causes hyperpolarization of the transmembrane potential.The magnitude of hyperpolarization is directly related to thedegree of pigment concentration. Adenosine 3`;, 5`-monophosphate(cyclic AMP) causes dispersion of the red pigment but has nopigment-concentrating effect. The primary action of red pigmentconcentratinghormone is most likely stimulation of a pump which exchangessodium ions from inside the chromatophore with potassium ionsfrom the outside, whereas red pigment-dispersing hormone quitelikely stimulates entry of calcium ions into the chromatophore.     

Cellular Aspects of the Control of Physiological Color Changes in Fishes

SYNOPSIS. Recent advances in the cellular aspects of chromatophoricactivities in fishes are reviewed, special emphasis being laidon the black pigment-containing cells, the melanophores. A fewrecent electron-microscopic studies have disclosed the finestructure of melanophores. They are enclosed with a single cellmembrane, within which melanosomes and other cell organellesare found. All observations favor the view that melanosomesare selectively moved through the cellular processes, leavingthe cell contour rather fixed. In regard to these findings,current ideas about the mechanisms of pigment movements arediscussed. Particular attention is directed to the possibleintervention of microtubules and the theory of migration ofpigment by intracellular electrophoresis. The regulatory mechanismsof pigment cells are then dealt with. The adrenergic natureof transmission is affirmed in the peripheral melanin-aggregatingnervous system. The mode of nervous supply to a melanophoreis also analyzed. Investigations of the antagonistic, melanin—dispersing,nervous system are also considered, with special reference torecent physiological studies and to the finding of synapticvesicles by electron microscopy. On the basis of these results,a new interpretation of the so-called Parker effect is proposed.     

Physiological Color Changes in Reptiles

SYNOPSIS. The physiological regulation of color changes in reptilesas studied in the lizard, Anolis carolinensis, is discussed.In Anolis, the ability to adapt to a background is dependentupon the level of circulating MSH, therelease of which is dependenton information received through the eyes. Blinded (or intact)lizards are brown under conditions of strong illumination andgreen under conditions of lower light intensities, and, again,these color changes are regulated by MSH. According to Kleinholz,color changes in the blinded lizard are regulated by dermalphotoreceptors. High or low temperatures directly affect thecolor of Anolis skins and alter the rate at which skins respondto hormones. Aggregationof melanin granules within Anolis melanophoresin response to sympathomimetic stimulation is regulated throughalpha adrenergic receptors whereas dispersion of melanin granulesin response to such stimulation is controlled through beta adrenergicreceptorspossessed by the melanophores. Most Anolis melanophores possessboth alpha and beta adrenergic receptors, but some melanophorespossess only beta adrenergic receptors. In the normal physiologyof the lizard, under conditions of stress, stimulation of alphaadrenergic receptors by catecholamines leads to an "excitement—pallor"followedby an "excitement—darkening" resulting from stimulationof beta adrenergic receptors which causes dispersion of melaningranules within localized populations of melanophores. Thus,in Anolis, dispersion of melanin granules within melanophoresis regulated by both MSH and by catecholamines. Evidence ispresented that the intracellular level of cyclic 3', 5'-AMPwithin melanophores may be responsible for the regulation ofmovement of melanin granules.     

Fundamental Aspects of Morphological Melanin Color Changes in Vertebrate Skin

SYNOPSIS. Consideration of some biochemical mechanisms in synthesisof melanin from the biological viewpoint has yielded some insightinto various aspects of the problem. A fundamental considerationis the procedure which must unequivocally demonstrate tyrosinaseand determine its level of activity with sensitivity and precision.Only the radiometric assay utilizing ¹⁴C—abelled L—tyrosinefulfills these criteria. Although integumental tyrosinase activityis usually correlated with the degree of melanoderma, exceptionalcases are sufficiently documented to provide a basis for thepresence of normal melanogenic control mechanisms in the skin.In addition, the enzyme may not always be bound to a subcellularorganelle, thus suggesting its origin is at a distance fromits site of action (premelanosome). A number of biological factorsaffect the enzymatic activity and its subcellular distributionindicating that the biological state of the organism cannotbe disregarded in biochemical studies. Further, the use of variouslylabelled substrates has revealed the poikilopolymeric natureof melanin and the possibility of the direct effect of the intracellularenvironment upon the nature of the polymer. Several types ofprimary control mechanisms directly affecting the activity oftyrosinase are present in the vertebrate integument. It is probablethat additional mechanisms will be uncovered eventually.     

The Evolution of the Motor Control of Feeding in Amphibians

Based on studies of a few model taxa, amphibians have been consideredstereotyped in their feeding movements relative to other vertebrates.However, recent studies on a wide variety of amphibian specieshave revealed great diversity in feeding mechanics and kinematics,and illustrate that stereotypy is the exception rather thanthe rule in amphibian feeding. Apparent stereotypy in some taxamay be an artifact of unnatural laboratory conditions. The commonancestor of lissamphibians was probably capable of some modulationof feeding movements, and descendants have evolved along twotrajectories with regard to motor control: (1) an increase inmodulation via feedback or feed-forward mechanisms, as exemplifiedby ballistic-tongued plethodontid salamanders and hydrostatic-tonguedfrogs, and (2) a decrease in variation dictated by biomechanicsthat require tight coordination between different body parts,such as the tongue and jaws in toads and other frogs with ballistictongue projection. Multi-joint coordination of rapid movementsmay hamper accurate tongue placement in ballistic-tongued frogsas compared to both short-tongued frogs and ballistic tongued-salamandersthat face simpler motor control tasks. Decoupling of tongueand jaw movements is associated with increased accuracy in bothhydrostatic-tongued frogs and ballistic-tongued salamanders.     

Cellular and Dynamic Aspects of Oocyte Growth in Teleosts

SYNOPSIS. Four principal stages of oocyte growth are recognizedamong teleosts. During gonadotropin-independent primary growth,multiple nucleoli form as well as a Balbiani body which eventuallydisperses throughout the ooplasm. The first gonadotropin-dependentstage involves the formation of yolk vesicles, the precursorsto the cortical alveoli. True vitellogenesis follows duringwhich vitellogenin is sequestered from the maternal blood andpackaged into yolk granules or spheres. The latter generallyfuse centripetally at some time during oocyte growth to givea continuous fluid phase surrounded by a peripheral layer ofcytoplasm containing the cortical alveoli. Maturation representsthe final stage and is accompanied in many teleosts by wateruptake; among marine teleosts with pelagic eggs, most of thefinal egg volume may be achieved by this process. Ovaries maybe synchronous, asynchronous, or group-synchronous. Among thelatter, a clutch of oocytes may be recruited from an asynchronouspopulation of earlier stages into any of the subsequent stages.In teleosts which spawn repeatedly, recruitment of new clutchescan usually be associated with the transition of a previouslyrecruited clutch from one stage to the next. Teleosts thus offerexamples of virtually every conceivable type of ovarian physiologyand provide a wealth of experimental material for exploringthe cellular and hormonal mechanisms which regulate oocyte recruitmentand growth throughout ovarian recrudescence.     

Physiological and Biochemical Aspects of Halophyte Ecology

Physiological and biochemical features of euhalophytes, сrinohalophytes, and glycohalophytes growing in natural conditions in El’ton Lake area were studied. The water content in tissues, intensity of lipid peroxidation, and membrane permeability were found to determine the differentiation of plants by their salt accumulation strategy. The concentration of pigments and their ratio are related to the mesostructure of leaves and are dependent on the salt accumulation strategy and life form. The membrane complex is connected with the cell structure and photosynthetic apparatus. The specificity of ion transportation depends on the specific features of plants.     

Morphological and Physiological Aspects of Evolution in Common Buckwheat

Comparative morphological and physiological studies of the ancestral forms (Fagopyrum homotropicumO. and F. esculentumssp. ancestraleO.) and the various morphogenotypes of common buckwheat (F. esculentumMoench.) were carried out in glasshouse experiments in a soil culture. A considerable reduction of plant morphogenesis, a restriction of the growth of the vegetative organs, and the ecological and agricultural specialization (accompanied by the change in the primary adaptive life strategy from competitive (c) to ruderal (r) or to combined c/rtype) occurred in the evolution of common buckwheat. The reduction of morphogenesis was accompanied by changes in some of the morphological and anatomical structures and their functions, primarily, the source–sink relationships among plant organs. Compensatory mechanisms were developed, and the nutritional compounds became reutilized as an additional source for fruit formation and ripening.