The olfactory hypothesis of the salmonids' homing assumes that the juvenile is conditioned to recognize a specific scent of its native river during the smolt stage and that it uses this characteristic to locate its river for upstream migration. We tested this hypothesis and exposed, in artificial conditions, some farmed coho salmon, rainbow trout and fario trout, aged 18 months, to a chemical (morpholine or alcoolphenetyl) introduced in the natural production environment (mixed with the scents of the native river), in order to determine if they will be responsive to this product to locate their initial production environment during upstream migration.

Olfactory imprinting and homing in salmon

The thyroid hormones are very hydrophobic and those that exhibit biological activity are 3',5',3,5-L-tetraiodothyronine (T4), 3',5,3-L-triiodothyronine (T3), 3',5',3-L-triiodothyronine (rT3) and 3,5',-L-diiothyronine (3,5-T2). At physiological pH, dissociation of the phenolic -OH group of these iodothyronines is an important determinant of their physical chemistry that impacts on their biological effects. When non-ionized these iodothyronines are strongly amphipathic. It is proposed that iodothyronines are normal constituents of biological membranes in vertebrates. In plasma of adult vertebrates, unbound T4 and T3 are regulated in the picomolar range whilst protein-bound T4 and T3 are maintained in the nanomolar range. The function of thyroid-hormone-binding plasma proteins is to ensure an even distrubtion throughout the body. Various iodothyronines are produced by three types of membrane-bound cellular deiodinase enzyme systems in vertebrates. The distribution of deiodinases varies between tissues and each has a distinct developmental profile. Thyroid hormones. (1) the nuclear receptor mode is especially important in the thyroid hormone axis that controls plasma and cellular levels of these hormones. (2) These hormones are strongly associated with membranes in tissues and normally rigidify these membranes. (3) They also affect the acyl composition of membrane bilayers and it is suggested that this is due to the cells responding to thyroid-hormone-induced membrane rigidificataion. Both their immediate effects on the physical state of membranes and the consequent changes in membrane composition result in several other thyroid hormone effects. Effects on metabolism may be due primarily to membrane acyl changes. There are other actions of thyroid hormones involving membrane receptors and influences on cellular interactions with the extracellulara matrix. The effects of thyroid hormones are reviewed and appear to b combinations of these various modes of action. During development, vertebrates show a surge in T4 and other thyroid hormones, as well as distinctive profiles in the appearance of the deiodinase enzymes and nuclear receptors. Evidence from the use of analogues supports multiple modes of action. Re-examination of data from th early 1960s supports a membrane action. Findings from receptor 'knockout' mice supports an important role for receptors in the development of the thyroid axis. These iodothyronines may be better thought of as 'vitamone'-like molecules than traditional hormonal messengers.

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Thyroid hormones and their effects: a new perspective

With the continued integration of mechanical engineering, electronics and computer technology, the author considers the key elements of a true mechatronics solution.

http://ieeexplore.ieee.org/iel1/2189/9205/00412754.pdf

An integrative approach

The phenomena of development and metamorphosis have fascinated biologists and naturalists alike for centuries, and comparative physiologists, biochemists, and endocrinologists have systematically studed these processes for almost a century now. Accordingly, a large body of information has accumulated on various aspects of vertebrate biology relating to growth and transformation. Space limitations require that we restrict our coverage in this chapter primarily to recent work on the endocrine control of development and metamorphosis in amphibians. Hence, we will not be able to consider environmental factors that affect these processes, or the recent findings on the control of transformations in other vertebrates, such as smoltification in salmonids. In addition, we will not be able to cite many pertinent references on the control of growth and metamorphosis even in the amphibians. Readers are referred to the excellent and comprehensive reviews of Frieden and Just (1970) and Dodd and Dodd (1976), and to other chapters in this volume for references on some of the earlier literature not cited by us.

Hormonal Control of Amphibian Metamorphosis

Publisher Summary This chapter reviews recent studies on metamorphosis from the perspective of hormonal control. It also focuses on biochemical and cell-biological aspects of amphibian metamorphosis. The developmental stages of larvae of representative species are presented. Amphibian metamorphosis appears to be under multihormonal control and the secretion and function of these hormones are regulated in various ways. Thyroid hormone levels need to be low for premetamorphic tadpoles to grow without showing metamorphic changes. For the final phase of metamorphosis, known as climax, higher levels of thyroid hormones are required because no tail shortening occurs in thyroidectomized tadpoles with relatively low concentrations of thyroid hormone. Thyroid hormone mRNA concentrations decrease in most of the tissues that undergo substantial remodeling. However, in the developing ovary of the juvenile toad, high levels of thyroid hormone α-receptor mRNA are detected. The accumulation of thyroid hormone receptor transcripts in oocytes is sustained and continues to increase throughout further development. The presence of thyroid-stimulating hormone in the amphibian pituitary has been confirmed indirectly by evidence of a difference in thyroid function between normal and hypophysectomized tadpoles at TK stage III and by the stimulating effect of crude extracts prepared from the pituitaries of prometamorphic and climax Xenopus larvae on uptake of 131I by the thyroid.

Philip M. Mondou

Papers

Thyroxine concentrations in blood serum and pericardial fluid of metamorphosing tadpoles and of adult frogs.