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Repeated culture of rat conceptuses of between 101/2 and 111/2 days' gestation in the same sample of rat serum showed that the serum has a finite ability to support embryonic growth and development. After four consecutive cultures of rat conceptuses the serum became exhausted and analysis of it showed that rat conceptuses utilized glucose and certain proteins present within the serum. It was also concluded that rat conceptuses secreted toxic dialysable and non-dialysable components into the medium during culture and these materials affected embryonic growth during subsequent culture of conceptuses in exhausted serum. The nutritional value of free amino acids as a substitute for serum proteins was studied by the addition of leupeptin - a specific lysosomal enzyme inhibitor - to the culture serum. The effect of this was partially reversed if free amino acids were included in the leupeptin-containing serum. The inclusion of both essential and non-essential amino acids in the culture medium was found to be necessary for embryonic growth. A model system for further studies of histiotrophic nutrition (the giant yolk sac) was devised by simple modification of New's culture technique to beyond the usual 48 hours thus allowing for maximum growth of the extra-embryonic membranes in vitro. After 7 extra days' culture in rat serum the giant yolk sac was 2 cm. in diameter and contained approximately 600 micro1 yolk sac fluid. The morphology, junctional permeability, histochemistry and endocytic activity of the giant yolk sac showed this system was, in general, similar to the in vivo yolk sac of a comparable gestational age. The giant yolk sac transported radio-labelled free amino acids which accumulated in the yolk sac fluid and analysis of this fluid showed it to contain 14 major proteins; some of these contained radio-labelled amino acids and were, therefore, synthesised by the giant yolk sac. Finally, giant yolk sac fluid was able to improve the nutritional status of exhausted serum and, therefore, contained components which are vital to normal embryonic growth and development. The major feature of the giant yolk sac system is its capacity to produce the products of histiotrophic nutrition in large quantities for biochemical analysis.

An investigation has been made into the mechanisms involved in the photocontrol of stem elongation in the ruderal species, Sinapis alba L; particularly those mechanisms concerned with the changes in stem elongation mediated by variations in the degree of vegetational shade. Throughout the investigation an attempt was made to grow plants in conditions which were as natural as possible; i.e., in white light at a suitable fluence rate and with a 16h photoperiod. The effects of white light fluence rate and redrfar-.;d ratio (R:FR), on hypocotyland internode elongation are compared and contrasted; but the main thrust of the thesis is an examination of the rapid increase in internode elongation rate which occurs in response to reductions in R:FR perceived by the internode itself. The R:FR was reduced by giving supplementary far-red light directly to the internodes of plants in background white light, and linear displacement transducers were used for the high-resolution, continuous monitoring of elongation. The elongation rate was inversely and linearly related to the phytochrome photoequilibrium, set up by the light treatment, over a wide range of values. Moreover, phytochrome cycling rate is not involved in modulating internode elongation, and elongation rates can only be related to Pfr concentration if the total amount of phytochrome is constant. A similar rapid response to supplementary far-red has been demonstrated in isolated internode segments, and this has allowed a study of the effect of R:FR on cell enlargement. From this study an hypothesis is proposed that suggests phytochrome modulates cell enlargement by regulating the secretion of protons into the cell wall. Supplementary far-red could cause a lowering of cell wall pH, which may bring about the displacement of Ca.

The work submitted in this thesis describes three investigations of the relationship between stimuli, the pike and the pike's inclination to feed. Consideration is given to the importance of relating internal and external factors to the causation of behaviour. The effects of individual pike and the time lapsed after feeding on predatory behaviour are firstly assessed. Use of multivariate analysis determined key behaviours in the repertoire of pike that could be successfully employed in analysing prey-capture sequences. The modifying influence of hunger, as categorised by stomach content, on prey capture sequences is presented and discriminant function analysis is used as a method of describing differences in predatory behaviour. A simple treatment of bout criteria is also given. The interaction of the components of visual stimuli and its influence on predatory response revealed that particular movements and shape of a stimulus altered the attack behaviour of pike. The relative strength of a visual cue, for example, how "fish-like" a stimulus is, has dependence on how inclined an individual is to feed. A view of how these factors influence the behaviour of pike in a wider context is expressed.

The distribution and characteristics of a- and ?-adrenoceptors, histamine H1 - and muscarinic cholinergic receptors has been studied in guinea-pig airways by radio-ligand binding studies, functional measurements of a mech-anical response and light microscope autoradiography. Radioligand binding studies were performed on homogenates of three different regions of the airways; the trachea, bronchi and parenchyma. The results have shown that whilst histamine H1 - and muscarinic cholinergic receptors were relatively evenly distributed throughout the airways, the density of a1 - and ?- adrenoceptors increased towards peripheral regions of the lung with the highest density in the parenchyma and lowest in the trachea. There was no evidence for the presence of a2 - adrenoceptors, but studies with selective ?- adrenocptor agents indicated that both ?1- and ?2- subtypes were present throughout the lung with the relative proportion being in the order of 15 : 85%. Isolated preparations of tracheal spirals and paren-chymal lung strips were then used to determine the response mediated by these receptor systems, in central and peripheral airways respectively. a1-, histamine H1- and muscarinic receptor agonists all produced concentration-dependant contractions of both preparations and antagonist pA2 values were almost identical to -log KI values obtained from binding studies. ?- adrenoceptor agonists however caused concentration-dependant relaxations of these preparations and the response appeared to be mediated by both ?1- and ?2- subtypes in tracheal spirals as the pA2 value for atenolol (?1-selective), varied depending on which agonist was used. In addition, the agonists noradrenaline and isoprenaline produced biphasic concentration-effect curves in the presence of the ?2- selective antagonist ICI 118,551. In contrast, only one subtype was involved in parenchymal lung strips as antagonist pA2 values were not dependant on the agonist used and the properties were consistent with those expected for a ?2- adrenoceptor. A more precise localisation of the receptors identified by binding and functional studies was then obtained by light microscope autoradiography, using frozen sections of whole lung tissue. The results support previous findings which suggested that ?- adrenoceptors, histamine H1- and muscarinic receptors were all located on airway smooth muscle, but it was not possible to study the localisation of a1- adrenoceptors by this method. ?- adrenoceptors were also found to be located on the smooth muscle of pulmonary blood vessels and there was a particularly dense labelling of alveolar tissue. Neither histamine H1- nor muscarinic receptors were identified on alveolar tissue or the smooth muscle of blood vessels. Further experiments were also per-formed whereby the labelling of ?2- adrenoceptors in the sections was prevented by incubating in the presence of the ?2- selective antagonist ICI 118,551, at a concentration that should not have affected labelling of ?1- adrenoceptors. These studies showed that whilst ?- adrenoceptors on the alveoli consisted of both the and ?1 and ?2- subtypes, those on the smooth muscle of airways and blood vessels were of the ?2- subtype only. The present findings indicate that by combining the three-types of approach it should be possible to obtain detailed information on the regulation of a particular organ or tissue by various receptor systems. In particular, it has been shown that autoradiography is a useful technique that can be used to complement binding studies performed on homogenates giving no indication of the cellular location of receptors and classical pharmacological techniques, where prior knowledge of their function is required.

Light and electron microsope techniques have been used to investigate the normal stage 4-5 epiblast periphery and wound closure at the epithelial margin. The stage 4-5 epiblast is attached to the vitelline membrane by an association of flattened 'edge cells'. Basal 'edge cells' possess lamellipodia oriented in the direction of epiblast expansion. Adjacent cells are connected by junctions and appear to retain their respective positions during the 'gliding' movement of the attached periphery. Fixation at low temperatures produces an alteration in 'edge cell' morphology consistent with a retraction of the epiblast margin. After the excision of approximately 200?m of epiblast periphery, the wound gapes due to tensions within the proximal epithelium. The epiblast cells respond to the trauma of wounding by rounding. Wound closure commences within 1 hour of 'edge cell' excision as epiblast cells at the margins attach to the membrane in distal-proximal sequence. The attached wound margins migrate toward each other across the membrane and close the wound at around 10 hours reincubation. Junctions are not observed at the wound margins and the cells appear to employ a 'rolling and sliding' form of locomotion. These results suggest that 'edge cells' are intrinsically different from those of the proximal epiblast. The normal stage 4-5 epiblast is overlain by a basement membrane. This structure is not observed at the early wound margin. The migrating wound margins deposit extracellular materials on the vitelline membrane and these resemble substances associated with the normal stage 4-5 epiblast basement membrane. Similar materials are also produced by explants and isolated cells of the epiblast periphery when cultured on the vitelline membrane. It is suggested that these materials may represent an attempt to reconstitute a basement membrane during wound closure.

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