Osmoregulation in the eel requires that NaCl is pumped across the gill epithelium, inwards in the freshwater eel and outwards in the seawater eel. It has been proposed that the transfer of NaCl takes place in mitochondria-rich "chloride cells" and is effected by (Na++ K+)-dependent ATPase. The work of this thesis confirmed that the chloride cells of gills were rich in (Na++ K+)-dependent ATPase and a mitochondrial marker enzyme, succinic dehydrogenase. Both enzymes were shown to have higher activities in the gills of seawater eels, a consequence of the increased salt load to be pumped across the gill epithelium in sea water. (Na++ K+)-dependent ATPases prepared from freshwater and seawater gills were examined on the basis of subcellular distribution, kinetic properties and subunit structure and found to be indistinguishable. Thus, it is likely that the same enzyme pumps NaCl across the gill epithelium in both directions. Adaptation of immature yellow freshwater eels to sea water resulted in an increase in the percentage of chloride cells in the gill followed by an increase in the activities of (Nat+ }.)-dependent ATPase and succinic dehydrogenase. However, adaptation of cature freshwater eels to sea water revealed that the cature silver eel in fresh water is ready for life in sea water. There were no differences in either the percentage of chloride cells or the activity of (Na ++ K+)-dependent ATPase in the gills of the latter fish. Differences were found in the structures of freshwater and seawater chloride cells which could account for the inward pumping of NaCl in fresh water and the outward pumping of NaCl in sea water. Models of mechanisms for pumping NaCl across cellular epithelia were extended to include the stoicheiometry of the transfer of ions and the direction of NaCl pumping effected by (Na ++ K+)-dependentATPase.

The total gestation period in the roe deer is approximately 290 days (10 months). When the blastocyst reaches the 20-30 stage it enters a 5-month period of diapause. During the last six weeks of diapause the blastocyst undergoes mitosis and reactivates in late December or early January at the 100-cell stage. The conceptus undergoes a period of rapid growth, which lasts between 7 and 25 days, before attachment to the endometrium and normal fetal growth. By studying the period between late diapause and early fetal development, it was possible to monitor changes in the reproductively important hormones, progesterone, oestradiol-17<I>β</I>, prolactin and pregnancy-associated glycoproteins as well as the secretion of important signalling proteins by the conceptus and uterus. In addition, investigations were undertaken to determine whether a regimen of long day photoperiod manipulation would effect the duration of diapause. Both peripheral concentrations and luteal release of progesterone remained consistent throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 ± 1.97 ng ml^-1; luteal progesterone: 6.72 ± 0.81 ng mg^-1 protein). Oestradiol concentrations remained low during diapause (1.07 ± 0.4 pg ml^-1) and expansion (1.2 ± 0.4 pg ml^-1) but increased 30 times at trophoblast elongation (49.17 ± 0.37 pg ml^-1) but increased 30 times at trophoblast elongation (49.17 ± 0.37 pg ml^-1). Both prolactin and pregnancy-associated glycoproteins remained at basal concentrations (4.69 ± 0.86 pg ml^-1 and <4.5 ng-ml^-1 respectively) and increased after implantation (12.34 ± 2.71 ng ml^-1 and 7.74 ± 0.47 ng ml^-1 respectively). Incorporation of a radiolabel into conceptus secretory proteins increased four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Endometrial secretions remained at these levels until implantation when they decreased linearly as fetal development progressed. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident.

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No description available.

1) A thymus-independent alioimmune system emerges early in the life of the clawed toad, independent of changes in the lymphoid system occurring at metamorphosis. Studies in Chapter 2 on first and second-set allograft rejection, both in larvae blocked from metamorphosing and in normally developing toads, show that there is no qualitative difference between the larval and adult allo-immune response. 2) In the intact adult, the spleen is shown to be a major site of cellular reactivity following allografting. Spleen transfer experiments between mutually tolerant partners demonstrate that this reactivity has an immunological basis. Preliminary studies in Chapter 3 implicate the spleen as a site of alioimmune memory.3) Work in Chapter 4 employs the sensitive ICA technique for investigating the role of thymus and spleen in humoral immunity. RFC kinetics in the spleen following administration of different doses of sheep erythrocytes reveal a dose response curve more similar to that described in mammals than in other amphibian species. Higher immunegen doses result in more rapid and more elevated RFC production. Morphological characterisation of rosettes failed to distinguish separate functional populations (i.e. "helper" and antibody producing) of lymphocytes in Xenopus. Early thymectomy abrogates responsiveness to injected SRBC as measured by cellular proliferation and RFC levels.4) Chapter 5 identifies a critical role of the thymus throughout much of larval life in the maturation of humoral immunity. Thymectomy up to stage 53 abrogates RFC production to SRBC, and antibody production is impaired by thymectomy as late as stage 57. Thymectomy later at stage 52 has no effect on allograft responses. The larval thymus controls development of both alioimmunity and humoral immunity but commands the maturation of the latter for a more prolonged period of development. Adult thymectomy has no effect on SRBC responsiveness up to 250 days post-surgery. 5) Chapter 6 provides new insight into the ultrastructure of developing thymus and emphasises the rudimentary nature of this organ at the time when thymectomy is routinely performed.

The body composition of juvenile Willow Warblers, Phylloscopus trochilus, was examined during the autumn moult and premigratory period. Premigratory birds exhibited hyperphagia and lipid deposition. Weight decreases of the pectoralis muscles and their glycogen reserves during moult are interpreted as responses to increased thermoregulatory demands, and not to utilization of muscle amino-acids for feather growth. Apparent premigratory muscle 'hypertrophy' represents merely a recovery to pre-moult values. Mean liver weights do not vary between the post-juvenile moult and the premigratory period, but the times of day at which weight maxima of water and protein occur are earlier in premigratory birds. These birds also show an earlier increase in liver lipid levels during the day than moulting birds. Premigratory birds also have greater evening lipid concentrations than moulting birds. As the dawn lipid levels of moulting and premigratory birds do not differ, all lipid synthesized (or processed) by the latter group must be stored solely in adipose tissue. The marked diurnal cycle of liver glycogen of moulting birds is absent in the premigratory period. Samples of Willow and Grasshopper Warblers (locustella naevia ) killed during migratory flight had different potential ranges but similar potential flight times, due to a lipid-correlated increase in body water in the latter species Injections of prolactin in photosensitive Bramblings, Fringilla montifringilla, showed that the stimulation of appetite by thishormone was independent of the time of its injection, whereas lipid, deposition was strongly dependent. In Bramblings given restricted food body and liver weights still increased when birds were injected with prolactin confirming that prolactin acts directly on liver lipid synthesis, independently of its effects on appetite. Changes in liver size produced by prolactin injections were similar to size changes found in photostimulated birds. It is concluded that prolactin is the probable cause of changes in liver composition of autumnal premigratory Willow Warblers.

A number of aspects of the humoral and cellular immune responses of the common dogfish Scyliorhinus canicula L. were examined in order to define the immunological status of the animal in relation to its phylogenetic origins. The dogfish was shown to have the ability to produce specific antibody in response to a variety of soluble and particulate protein antigens. The existence of several non-specific defence mechanisms was demonstrated including a well established reticulo-endothelial system capable of rapidly clearing injected foreign material from the blood and also the bacteriolytic enzyme, lysozyme. Specific antibody from the fish had marked agglutinating properties which could be destroyed with reducing agents but which could not be demonstrated to form precipitin lines in agar gels. It could also fix complement. Isolation and characterisation of the antibody molecule showed it to have virtually neutral electrophoretic mobility, a molecular weight of approximately 800,000 daltons and a sedimentation coefficient of 18.6S. On reduction the molecule was shown to comprise heavy and light polypeptide chains with molecular weights of 76,000 and 18,000 daltons, respectively. On the basis of these findings the antibody was considered to be of the IgM class of immunoglobulin found in higher vertebrates. This was the only immunoglobulin found in the dogfish although an antigenically identical protein with a molecular weight of 160,000 daltons was also demonstrated and this was considered to be a monomeric form of an IgM pentamer. A survey of lymphoid tissues revealed that the fish had a well developed spleen. This organ was also shown to be directly involved in immunological reactions. Conversely, the thymus was poorly developed and involuted during an early stage in the life of the fish. Its immunological contribution was not determined. Two other tissues, the organ of Leydig and the epigonal tissue were found to comprise a high proportion of poorly differentiated lymphoid cells and these were considered to be similar to the stem cells of the bone marrow found in mammals. Ultrastructural examination of peripheral blood leucocytes showed that they comprised populations of cells analagous, to mammalian lymphocytes, plasma cells, granulocytes, and monocytes. Using a specific antiserum and an immunofluorescence technique, a high proportion of leucocytes were revealed to have immunoglobulin determinants on their surface. In a number of experiments to investigate cellular functions in vitro it was found that dogfish leucocytes could be stimulated by a variety of mitogenic substances but these results were insufficient to provide evidence for lymphocyte heterogeneity. Evidence that the dogfish was capable of weak recognition of histocompatibility antigens was provided in vitro by mixed lymphocyte cultures and in vivo by reaction to injected allogeneic leucocytes. Although several different techniques were used no evidence of immediate hypersensitivity reactions could be demonstrated. Delayed hypersensitivity was shown, however, by the leucocyte migration inhibition test and possibly by local skin reactions. The immunological relationship of the dogfish to an intestinal helminth parasite, Proleptus obtusus, was also investigated. The fish was found to be capable of producing antibody specific for the cuticle of the nematode. The parasite could also invoke several cellular reactions including the stimulation of leucocytes in vitro and delayed but not immediate hypersensitivity.

The epidermis of the eel A. Anguilla L. secretes a mucous layer mainly from its mucous cells although there may also be a contribution from surface epidermal cells . Under certain conditions, the epidermal cells may transform to a secretory cell type that resembles, but is structurally distinct from a mucous cell . This observation has not previously been reported in fish epidermis. Specialised club cells, characteristic of the Anguillidae contain filamentous material that may be secreted beneath the epidermal surface. This previously unobserved phenomenon together with an increase in cell numbers around the lateral region may suggest an additional protective mechanism which may be of use, for example, during 'burrowing'. The quantitative distribution of mucous cells over the body was also determined and the cellular contents of the main cell types characterised histochemically. Lymphocytes and previously unseen granular neutrophil-like cells may function in more specific protective mechanisms against pathogenic organisms . The mucus has been examined biochemically and separated by chromatography and electrophoresis to reveal several components. Rheological study has established shear thinning properties of the mucus and functional groups essential to maintain the integrity of the mucous structure. The dynamics of mucous secretion have been observed autoradiographically and a model for the mechanism of secretion proposed . Attempts have been made to measure the rate of mucous secretion under a number of experimental conditions which are discussed in relation to the viscous nature of mucus and the proposed model for secretion. The epidermis and its mucous secretion thus provide an effective lubricative barrier to the environment extremely important for locomotion and protection from dessication, osmotic stress and disease organisms.

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The structure and innervation of the extrafusal muscle fibres and the muscle spindles in sheep superior rectus, levator palpebrae superioris, and peroneus brevis muscles are compared. Superior rectus is organized into three layers: A central core of mainly large-diameter fibres contains three plate-innervated types of 'twitch' fibre, with 7% large-diameter grape-innervated fibres; an orbital rim of small-diameter fibres contains mainly plate-innervated ‘twitch’ fibres, together with a third of small diameter grape-innervated fibres; and a thin peripheral patch at either end of the muscle is composed mainly of intermediate- diameter grape-innervated fibres. Levator palpebrae and peroneus brevis are not layered and they are composed of three plate-innervated types of 'twitch' fibre, the 'slowest' of which are not represented in superior rectus. The functional significance of the histochemical and ultrastructural characteristics of the fibre types is discussed. In superior rectus, about 180 spindles are peripherally distributed in the orbital rim and peripheral patch layers, throughout the length of the muscle. The ultrastructure, histochemical profile, and innervation of the nuclear-bag and nuclear-chain fibres are the same as the extrafusal peripheral grape-innervated (G) and plate- innervated (G) fibre types, respectively. Motor innervation is collateral and segregated with grape innervation distributed to the bag fibres, and plate innervation to the chains. Levator palpebrae has about 60 evenly-distributed spindles. The bag fibres correspond histochemically and ultrastructurally to the bag fibres of superior rectus, and receive a purely fusimotor grape innervation. The chain fibres correspond to those of superior rectus, and receive a similar plate innervation. Sheep extraocular spindles receive both a primary and secondary sensory innervation. In peroneus brevis the spindles are composed of typical bag, intermediate bag and nuclear-chain fibres, and these receive an innervation typical of mammalian hindlimb muscle spindles.