<p>A number of cellular products present during fetal development, but absent from normal adult tissues, have been shown to be re-expressed in cancer cells. One example of these oncofetal substances is carcinoembryonic antigen (CEA). Studies were undertaken to examine the expression of CEA at the surface of human colon carcinoma cells grown in vitro and to develop a radioimmunoassay for quantitation of CEA and antibodies to CEA in the serum of cancer patients.</p> <p>Antibodies specific for CEA were prepared in goats and these antibodies were found to induce polar redistribution or capping of the antigen. As with other systems in which polar redistribution of surface molecules have been studied, the capping was temperature-dependent and required an intact microfilament system. Fluorescent-labeled antibodies were utilized to demonstrate that while CEA would undergo capping, blood group antigen A did not, hence these antigens exist as separate molecules at the cell surface. The capping process was further characterized using ¹²⁵I-labeled antibodies and it was demonstrated that upon capping the majority of cell surface CEA underwent endocytosis. The ability to specifically remove CEA from the cell surface with antibody was used to demonstrate a rapid reappearance of CEA on the tumor cell surface, and this reappearance appeared to require protein synthesis.</p> <p>A precise quantitative radioimmunoassay for CEA was developed and used to determine the amount of CEA expressed on cell surfaces. Various strains of cells were established in vitro which differed in the amount of CEA they produced. Two strains which differed in the amount of CEA expressed at their cell surfaces were shown to be equally tumorigenic in nude mice, which suggested a lack of correlation between CEA production and tumorigenicity.</p> <p>The radioimmunoassay was also used to study the control of genetic expression of CEA. There was a direct correlation between the amount of cell surface CEA and the amount of CEA secreted into the culture medium. Control over the level of CEA expressed by various strains appeared genetically stable. Yet, a number of lines of evidence suggested that the parental population from which the strains were derived was heterogeneous with respect to CEA synthesis.</p> <p>The effects of various inducing agents on CEA expression by various cell strains was examined. One strain (HCT-8 Nu2), a very low CEA producing strain, could be induced to express high levels of CEA by inclusion of theophylline in the culture medium. This effect appeared after three days of incubation and reached a maximum after five days. Enhanced expression was dosedependent and time-dependent, requiring continual presence of the drug. The effect also appeared to require continual protein synthesis and did not cause marked alteration of cell morphology or growth. It was demonstrated that the effect was not density-dependent and did not appear to be due to selective proliferation of a high expressor population. Further, the effect could not be mimicked with dibutyryl cyclic adenosine monophosphate. Similarly, another strain (HCT-8R) could be induced to produce higher levels of CEA with bromodeoxyuridine (BrdU). This effect was not as dramatic as the theophylline effect and only appeared transiently. The response to BrdU was dose-dependent.</p> <p>The specific inhibition of binding of ¹²⁵I-Iabeled anti-CEA antibodies by unlabeled anti-CEA antibodies, was used to demonstrate that no antibodies to CEA could be detected in control or cancer patient sera. The radioimmunoassay was also examined to determine its ability to quantitate the amount of CEA in serum from cancer patients and controls. It was determined that this test could measure comparable ranges of standard reference CEA, obtained from international or marketed sources. The results obtained from tests of patient sera closely correlated with results obtained using a marketed assay kit. A limited number of sera from patients was examined for CEA using the assay. Comparable percentages of patients with CEA-related cancers were found positive by my assay as reported in studies using standard assays. However, my assay appeared to have greater specificity than standard assays in that a lesser percent of patients without CEA-related cancers were positive.</p> / Doctor of Philosophy (PhD)

<p>The first step in hemostasis and thrombosis is the adherence of platelets to the damaged vessel wall. The factors involved in platelet adherence are not well understood, mainly because of the lack of a suitable method to measure quantitatively platelet adherence to surfaces. The aim of the present studies was to develop a quantitative method to measure platelet adherence to collagen containing surfaces. The following results were obtained with this method: (1) In this quantitative method for measuring platelet adherence to collagen-coated glass surfaces and to subendothelium the platelelets are labeled with ⁵¹Cr and adherence can be measured over a large area without sampling bias. Platelets are suspended at pH 7.35, at 37°C in an artificial medium which can be modified as required. The medium contains physiological concentrations of calcium and magnesium and platelet aggregation is prevented by the inclusion of apyrase to degrade any ADP released. There is no plasma present and thus no thrombin generation or fibrin formation occurs. Adherence is measured using a rotating probe device under controlled flow conditions and various surfaces can be tested (collagen-coated glass, everted aorta damaged to expose the subendothelium). (2) Platelet adherence to collagen-coated glass or to subendothelium is greatly reduced in the absence of divalent cations. Thus, methods which measure platelet adherence in the presence of chelating agents are difficult to interpret. (3) Increasing the albumin concentration of the medium decreases platelet adherence, but there is less variation among replicates. (4) Increasing the hematocrit increases the number of platelets adhering to the surface. (5) Platelets adhere tightly to collagen or to subendothelium and are not dislodged by agents which readily deaggregate platelets such as EDTA, EGTA, or PGE₁. (6) Exposure of undamaged endothelium to thrombin increases the number of platelets adherent to the surface and this is blocked by heparin. (7) This method of measuring platelet adherence to collagen can be used to screen drugs which may be useful as antithrombotic agents. The best system is to test the effect of a drug in the presence of 4% albumin and 40% hematocrit, however, for initial screening a simpler system can be used (0.35% albumin, zero hematocrit). (9) Several treatments which modify the platelet surface have been tested for their effect on adherence to collagen. Removal of sialic acid with neuraminidase do not affect platelet adherence whereas treatment with sodium periodate and the proteolytic enzymes thrombin, plasmin and chymotrypsin decrease adherence. (10) UDP and UDPG do not have an effect on platelet adherence to collagen and this observation does not support the collagen: glucosyltransferase theory of platelet adhesion to collagen. (11) Clq, a subcomponent of the first component of complement specifically inhibits platelet adhesion to collagen and may compete with the collagen receptor on the platelet membrane. (12) A wide variety of agents inhibits platelet adherence to collagen-coated surfaces and to subendothelium. Among the inhibitors which decrease platelet adherence in a system containing 4% albumin and 40% hematocrit are agents which chelate divalent cations (EGTA, EDTA, citrate), indomethacin, agents which increase cAMP levels (prostaglandin E₁, dipyridamole, RA 433), methylprednisolone, penicillin G and cephalothin. (13) Aspirin inhibits platelet adherence to collagen-coated surface or to subendothelium, but its inhibitory effect is not evident in the presence of 40% hematocrit or citrated plasma indicating that the conditions of the experiments are important in determining the effect of drugs. (14) Modifications of platelelets by treatment with thrombin, penicillin G or cephalothin which inhibit platelet adherence to collagen or subendothelium do not affect platelet survival. Modification of the platelet surface sialic acid by neuraminidase or periodate is followed by rapid clearance of platelets from the circulation. Thus there is no correlation between platelet adherence and platelet survival. (15) Treatments which decrease platelet to collagen and to the subendothelium also reduce the platelets in hemostasis.</p> / Doctor of Philosophy (PhD)

<p>The mechanism by which physiological stimuli increase cyclic GMP formation in platelets or in other cells is unknown. Agents that promote the formation of cyclic GMP in intact cells have in general not been found to stimulate the activity of guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2.] in broken cell preparations. Therefore, possible mechanisms for the activation and control of guanylate cyclase activity in platelets were investigated in this thesis.</p> <p>It was found that over 90% of the total guanylate cyclase activity is present in supernatant fractions of hypotonically lysed platelets. Platetet particulate fractions contained no guanylate cyclase activity that could not be accounted for by contaminating soluble enzyme, suggesting that physiological aggregating agents may increase cyclic GMP levels in intact platelets through the effects of intermediary factors. Because of the possibility that soluble as well as particulate factors may be involved in the control of enzyme activity, whole platelet lysate was used in studies of the properties and activation of guanylate cyclase.</p> <p>Under optimal ionic conditions (4.0 mM-MnCl₂), the specific activity of guanylate cyclase in fresh platelet lysates was about 10 nmol of cyclic GMP formed/20 min per mg of protein at 30°C, which is higher than that of any other mammalian cells or tissues studied. Activity was 15% of optimum with 10.0 mM-MgCl₂ and negligible with 4.0 mM-CaCl₂. Synergism between MnCl₂ and MgCl₂ or CaCl₂ was observed when [MnCI₂] ≤ [GTP]; under more physiological ionic conditions (Mg²⁺ present), micromolar concentrations of Ca²⁺ stimulated enzyme activity by about 50%.</p> <p>Lower than optimal specific activities were obtained in assays containing large volumes of platelet lysate, owing to the presence of inhibitory factors that could be removed by ultrafiltration. Adenine nucleotides and glutathione accounted for less than 50% of the inhibitory activity. The combined effects of inhibitory factors and of suboptimal ionic conditions are likely to lower the guanylate cyclase activity in intact platelets to almost negligible values in the absence of activating factors.</p> <p>Dithiothreitol (5.0 mM) and N-ethylmaleimide (0.1 mM) inhibited the activity of platelet lysate by about 70 and 50%, respectively. Preincubation of lysate for 60 min at 37°C increased guanylate cyclase activity on average by 225%. This effect could be blocked with dithiothreitol or N-ethylmaleimide, but dithiothreitol could not fully reverse activation once it had occurred. Oxidants such as 4,4'-dithiodipyridine (0.04 mM), diamide (0.4 mM) and tert-butylhydroperoxide (1.0 mM) increased enzyme activity on average, by 40, 87 and 165% respectively. Neither diamide nor tert-butylhydroperoxide had an effect on enzyme that had been preincubated or treated with N-ethylmaleimide.</p> <p>Sodium azide (10.0 mM) increased guanylate cyclase activity by an average of 335%; this effect was both time- and temperature-dependent. Activation by sodium azide was not prevented by dithiothreitol. Sodium nitroprusside (1.0 mM) increased enzyme activity by about 1000%; this effect could be blocked by preincubation or by tert-butylhydroperoxide, but not by either dithiothreitol or N-ethylmaleimide.</p> / Doctor of Philosophy (PhD)

<p>The role of RNA and protein synthesis in follicular testeterone production has been investigated in the rabbit ovarian follicle in vitro.</p> <p>lsolated follicles were incubated (usually 2 hours) with labeled amino acids or uridine plus LH, cyclic AMP or cyclic GMP alone, or together with various metabolic inhibitors.</p> <p>In dose response studies, testosterone production was stimulated at all concentrations of LH (0.1 to 10 μg/ml) tested (p < .05), with optimal stimulation occurring at 5 μg LH/ml (p < .01). However, a significant uptake of ³H-leucine into follicular protein occurred only at > 2.5 μg LH/ml (p < .01), with optimal stimulation occurring at 5 and 10 μg LH/ml. Cyclic AMP (5 and 10 mM) enhanced both testosterone production and the uptake of ³H-leucine into follicular protein (p < .01). Lower cyclic AMP concentrations were ineffective. Neither LH nor cyclic AMP had any effect on the incorporation of labeled uridine into follicular RNA.</p> <p>In time course studies, testosterone was stimulated within 15 minutes (p < .01), in the presence of LH (5 μg/ml) or cyclic AMP (5 mM). The incorporation of ³H-leucine also increased with time in both LH and cyclic AMP treated follicles, compared to controls, but a significant difference was observed only after 90 and 60 minutes, respectively (p < .01). However, electrophoretic fractionation and radio autographic examination of total follicular proteins after exposure, of LH and ³⁵S-methionine for 15, 60 and 120 minutes showed no apparent difference in the distribution of protein bands when compared to controls.</p> <p>Actinomycin D (20, 80 and 160 μg/ml) together with LH (5 μg/ml) inhibited the incorporation of ³H-uridine into follicular RNA by 79, 85 and 86%, respectively (p < .01). At these concentrations, no inhibitory effect on LH-induced testosterone production was observed. Paradoxically, Actinomycin D (1 μg/ml) enhanced LH-induced testosterone production above that elicited by LH alone.</p> <p>Cycloheximide (20 and 10 μg/ml) inhibited LH-induced testosterone production by 64 and 57% (p < .01), as well as the uptake of ³H-leucine into follicular protein by 94 and 93%, respectively. However, cycloheximide (1 μg/ml) did rot inhibit LH-induced testosterone production, yet inhibited ³H-leucine incorporation by 81.7%. Similarly, puromycin (40 μg/ml) inhibited LH-induced testosterone production by 66%, and the uptake of ³H-leucine into protein by 74% (p < .01). However, puromycin (10, 1 or 0.1 μg/ml) did not inhibit LH-induced testosterone production, yet ³H-leucine incorporation was inhibited by 58, 37 and 31%, respectively (p < .01).</p> <p>The methylxanthines, theophylline (25, 10 and 1 mM) and MIX (5 and 0.5 mM) had no synergistic effects with cyclic AMP on follicular testosterone production. However, these methylxanthines inhibited the incorporation of ³H-uridine (35 to 68%) and ³H-amino acids (45 to 69%) into follicular RNA and protein.</p> <p>Cyclic GMP (25, 10 and 1 mM) had no stimulatory effect on follicular testosterone production or the uptake of protein. However, cyclic GMP (25 and 10 mM) significantly enhanced the uptake of ³H-uridine into follicular RNA (p < .01).</p> <p>These data collectively suggest that de novo RNA and protein synthesis are not required for acute LH-induced testosterone production in the rabbit follicle.</p> / Doctor of Philosophy (PhD)

<p>The origins of the immunoglobulin-containing cells in the intestinal, respiratory, mammary, and genital tissues were studied in mice, rats, and guinea pigs by using an adoptive lymphocyte transfer method. Proliferating lymphocytes (lymphoblasts) were obtained from various donor lymphoid sources and radiolabelled in vitro with either ³H-thymidine or ¹²⁵-deoxyuridine. Radiolabelled lymphoblasts were then injected into the circulation of recipient animals. Twenty-two - 24 h later, various tissues taken from recipient animals were examined for the presence of radiolabelled donor cells by either radiocounting or autoradiographic techniques. Furthermore, radiolabolled B-cells containing different immunoglobulin isotypes were identified in mouse tissues by a combination of immunofluorescent staining with autoradiographic procedures. It was found possible to greatly accelerate this procedure by the use of liquid scintillation fluid so that ³H-thymidine-labelled cells could be identified in less than 24 h as opposed to 4-6 wks in the absence of scintillation fluid.</p> <p>In mice and rats, mesenteric lymph node (MLN) lymphoblasts showed a propensity to selectively localize in the cut mucosa. Careful examination of other mouse tissues revealed that MLN lymphoblasts were present, not only in the intestinal lamina propria, but also beneath the mucosal epithelia of the respiratory and genital tracts, the mammary glands and in the MLN. In these mucosal tissues approximately 60% of these cells contained IgA and 25% contained IgG. In peripheral lymph noded (PLN), a few labelled MLN cells were observed and 40% of these contained IgG, whereas only 8% were of tho IgA isotype. The preference of MLN to populate mucosal sites was clear from the results.</p> <p>In marked contrast, when labelled PLN cells were adoptively transferred, the majority returned to their sites of origin and contained IgG. Of the small number of labelled PLN cells found in mucosal tissues, approximately equal percontages (30%) of IgA- and IgG-containing cells were soon.</p> <p>Dividing cells prepared from bronchial (mediastinal) lymph nodes (BLN) showed a propensity to localize in the lungs rather than in the intestine or lymph nodes. However, tho predominant immunoglobulin content of these donor cells in tho gut, lungs, and MLN was IgA. Thus, the BLN made a quantitatively minor, but presumably significant, contribution to the IgA plasmacytes found in the gut lamina propria; in the lungs, BLN made a quantitatively major contribution to population of IgA-containing cells residing in the lung mucosa.</p> <p>It was concluded that, in rodents, the MLN was a major contributor of the immunoglobulin-containing celIs beneath the mucosal epithelia of the gut, lungs, cervix, and vagina and gestational mammary glands. Thus, lymph nodes draining two mucosal surfaces, though differing in IgA plasmacyte precursor content, both possessed cells destained to localize in mucosal tissues. Furthermore, there was organ specificity for the distribution of these cells; those immediately derived from the lymph nodes draining the bowel tended to return to the bowel, whereas those from the lungs tended to return to the lungs.</p> <p>To further explore the properties of MLN lymphoblasta, the influence of the mouse estrous cycle on MLN lymphoblast localization in the cervix and vagina was investigated. Compared to proestrus and estrus, a 2-fold reduction in the number of MLN lymphoblasts localizing in the diestral cervix and vagina was observed. Detection of the immunoglobulin isotype of these cells suggested that this reduction was restricted to the IgA plasmacyte progenitor population, i.e., the major B-lymphocyte subpopulation entering these sites. No significant changes in B-lymphoblast subpopulation lodging in the small intestine were observed over the course of the estrous cycle. Moreover, although the small intestine more than doubled in wet weight by late gestation, this increased quantity of gut tissue did not appear to compete for a finite number of donor MLN lymphoblasts. It was concluded that changes in the sex hormone status of mice may influence selective localization of MLN lymphoblasts in sex hormone target tissues.</p> <p>Since subpopulations of cells can often be separated from each other on the basis of cell size, some preliminary studies were done to purify, on the basis of size, subpopulations of mouse MLN lyphoblasts. These results indicated that the labelled cells being transferred were all large in size, likely lymphoblasts, and that it was possible to use this technique to obtain donor cell populations highly enriched in the proportion of labelled cells. Some evidence was obtained to suggest that the MLN contained a minor population of lymphoblasta with a propensity to localize in the spleen.</p> <p>To examine the possibility that some lymphocytes in the gut mucosa may themselves have a predisposition to localize in other mucosal tissues (assuming that they were able to migrate), lymphocytes were mechanically prepared from the lamina propria of the guinea pig small intestine. A subpopulation of these cells incorporated ¹²⁵I-deoxyuridine and localized (within 24 h after adoptive transfer) in the gut mucosa in a manner similar to transferred MLN lymphoblasts and different from either PLN or Peyer's patch lymphoblasts. It was concluded that a portion of the lymphocytes seen in the gut mucosa were similar in migration characteristics to cells found in the MLN.</p> <p>The results of these studies support the concept of a common mucosal immunologic system in which different mucosal surfaces are linked by migrating IgA plasmacyte precursors originating primarily in the lymphoid tissue associated with the intestinal and respiratory tracts. s of these studies support the concept of a which different mucosal surfaces migrating IgA plasmacyte precursors originating primarily in the lymphoid tissue associated with the intestinal and respiratory tracts.</p> / Doctor of Philosophy (PhD)

<p>For a wide variety of visual tasks, subjects perform more poorly when stimuli are oriented obliquely than when they are oriented vertically or horizontally. It is generally believed that this 'oblique effect' has two manifestations. One is meridional anisotrophy, i.e., lower acuity for obliquely oriented stimuli than for vertical or horizontal stimuli. The second is poor oblique discrimination; i.e., greater difficulty discriminating between mirror-image oblique stimuli than between vertical and horizontal ones, even when the stimuli are above the threshold of acuity. This thesis explores whether these two phenomena are in fact both manifestations of the same effect.</p> <p>Chapter One provides a detailed survey of studies showing meridional anisotrophy and considers the nature of its etiology and development. Chapter Two provides a review of the existing literature on the discrimination problem as evidenced in young children. The author argues that while meridional anisotrophy and poor oblique discrimination by young children appear to be related phenomena, it is possible that both are not manifestations of the same effect. The author tested this possibility by comparing the developmental course of poor oblique discrimination with the know developmental course of meridional anisotrophy.</p> <p>Chapters Three through Six present four experiments in which the author tested young infants' ability to discriminate between mirror-image oblique stripes with their ability to discriminate between "vertical-and horizontal ones, with the stripes above the threshold of acuity. In one experiment six week olds were tested; in the other three, 17-18 week old infants were tested using different variants of the habituation procedure.</p> <p>The major finding of the research is that neither 6 week nor 17-18 week old infants, both of whom are known to show meridional ranisotrophy, show evidence that a mirror-image oblique discrimination is more difficult than a discrimination between a vertical and horizontal. Furthermore, modification of the testing procedure, so that it more closely mimics a task in which children show difficulty discriminating mirror-image oblique lines, does not appear to affect 17-18 week olds discrimination performance.</p> <p>In the final chapter, the author discusses the implications of the research findings. The author concludes that since infants known to show meridional anisotrophy do not show poor oblique discrimination, then it is probable that these two phenomena are not both manifestations of the same effect nor do they appear to be generated by the same underlying mechanism. The author also discusses the implications of the research findings for two cognitive theories which have been advanced to explain how children process obliquely oriented stimuli.</p> / Doctor of Philosophy (PhD)

<p>The effects of strength training and immobilization upon neuromuscular function in man were investigated. The selected measures of neuromuscular function were voluntary strength and a number of electrophysiological measurements, including motor unit counts, motor nerve conduction velocity, reflex potentiation, and the contractile properties of isometric twitch contractions.</p> <p>Three kinds of experiments were conducted. First, subjects participated in training and immobilization experiments. Training, which consisted of maximal isometric and concentric muscle contractions and weight lifting, was performed three times per week over a period of 10-20 weeks. Relative disuse of selected muscle groups was achieved by immobilizing the elbow, wrist and thumb joints in a cast for 3-6 weeks. Second, measurements were made in selected groups of athletes (weight lifters, gymnasts, cyclists, sprinters, cross country skiers) to provide cases of long term training. Third, measurements were made on control subjects, whose results were compared to those of the athletes.</p> <p>Training resulted in an increase in voluntary strength. As cases of long term training, voluntary strength was enhanced in weight lifters and cyclists. Immobilization resulted in a decrease in voluntary strength.</p> <p>Training had no effect upon motor unit counts and the motor unit counts in the weight lifters were normal; however, the gymnasts exhibited reduced motor unit counts in distal but not proximal muscles. It was hypothesized that injury to the nerves at the wrist and ankles was responsible for the reduced motor unit counts in the gymnasts. Immobilization had no effect upon motor unit counts.</p> <p>Neither training nor immobilization caused a change in motor nerve conduction velocity in relation to the control condition; however, in one group of subjects, there was a small though significant difference between the greater post training and the lesser post immobilization values. Nerve conduction velocity was greater in weight lifters and gymnasts than in controls.</p> <p>Reflex potentiation increased following training, providing new evidence in support of the hypothesis that adaptation occurs within the nervous system in response to training. In agreement with the above finding was the enhanced reflex potentiation in the weight lifters. Immobilization caused a decrease in reflex potentiation, indicating that the nervous system is involved in the adaptation to relative disuse as well as to training.</p> <p>Muscle (triceps surac) twitch tension and contraction time were greater in weight lifters than in controls. In this same muscle, short term training resulted in an increase in twitch half relaxation-time. These findings represent the first report of a slowing of muscle contraction in response to training.</p> <p>In conclusion, the present investigation provided new evidence indicating adaptation within both the muscle and the nervous system in response to strength training and within the nervous system in response to immobilization.</p> / Doctor of Philosophy (PhD)

<p>The purpose of the studies reported in this thesis was to obtain data concerning the embryonic origin and formation of the pectoralis major muscle of the chicken. This muscle is used extensively in studies on muscle development because it is large; readily available, and is composed almost entirely of one muscle fiber type. Moreover, it is the largest muscle to be affected by hereditary muscular dystrophy in the line of chickens afflicted with this disease. Information concerning its embryonic origin could be used for in vivo studies on the early development of both normal and dystrophic muscles.</p> <p>Previous investigations into the embryonic origin od skeletal muscle in several classes of vertebrates have resulted in controversy. Some investigators have concluded that all skeletal muscles arise from the myotomal layer of the somites. Others have cited evidence to show that some muscles, including the pectoralis major muscle of the chick, are derived from the somatopleuric mesoderm adjacent to the somites.</p> <p>In the present investigation, interspecific chimaeras have been used to study the problem. Whole somites, somite halves, or limb-buds were grafted from quail to chick embryos between 2 and 3 days in ovo. After further development, the chimaeras were fixed, embedded in paraffin, sectioned, and stained using the Feulgen reaction for chromatin. This procedure permitted the identification of those structures that were derived from the grafted quail tissue.</p> <p>The observations in this study have led to the following conclusions:</p> <p>The pectoralis major muscle arises from the dorsal halves of somites 16-21 of the 2-day in ovo chick embryo. These somites also give rise to all other wing and wing-associated muscles of the shoulder and thorax. Each somite plays a specific role in the development of these muscles. The cells that ultimately form the pectoralis and other brachial muscles migrate from the somites into the lateral mesoderm between 2 and 2.5 days in ovo. The myotomal layers of the somites do not appear until 2.5 days in ovo and do not contribute to the formation of the brachial muscles.</p> / Doctor of Philosophy (PhD)

<p>The studies presented in this thesis are the first attempts to compare in a comprehensive manner the basic electrical and mechanical properties of the two muscle layers of the small intestine of the rabbit, a species that showed electrical control activity (ECA). The activities of the two muscle layers were distinctly different. Cells in the longitudinal muscle layer (LM) were spontaneously active with action potentials occurring on every control potential (CP). Similarly, muscle strips dissected along the long axis of LM (LS) contracted spontaneously at the same frequencies as the ECA. Cells of the circular muscle layer (CM) usually did not exhibit spontaneous spiking activity although ECA was also present.</p> <p>The characteristics of the ECA of the two muscle layers from the same muscle strips were similar in terms of amplitude, frequency, and their response to temperature change and external electrical stimuli. How the ECAs of the two muscle layers interact was investigated in light of the hypothesis that LM is the site of origin of ECA and that the ECA in CM is the result of electrotonic spread from LM (Bortoff, 1961, 1976; Connor, Kreulen, Prosser & Weigel, 1977). This hypothesis was tested directly in this study by measuring electrotonic coupling between the two muscle layers. It was found the there was little electrotonic interaction between muscle layers. Therefore, the result of this study is not consistent with the existing model in regard to the origin of the ECA.</p> <p>Study of the control of muscle function by the intrinsic nerves also showed drastic differences between the two muscle layers. LM was innervate by cholinergic excitatory nerves and possibly by an inhibitory neural system. In CM, three types of neural excitatory events were identified in addition to the powerful non-adrenergic inhibitory nerves. Besides the familiar cholinergic excitatory nerves, a tetrodotoxin-resistant component and an excitatory response that emerged only after prolonged repetitive stimulation was also observed. The neurotransmitters for these two excitatory neural systems remain to be identified.</p> <p>The results of this study indicate that the properties of the two muscle layers of the small intestine are very different. Nonetheless, normal physiological function of the intestine requires good coordination of the two muscle layers. The exact role of the individual layers in motility is not well defined. How these two muscle layers each with its separate neural, hormonal and local control mechanisms interact to produce the final intestinal motility pattern will be a challenging problem in the future.</p> / Doctor of Philosophy (PhD)

<p>Human muscles are composed of different percentages of two major fibre types which have specific metabolic and physiological properties. Previous studies the metabolic differentiation of these fibres during foetal development did not agree as to when differentiation occurred. They did however agree that differentiation was completed at full term based on criteria which had not been validated.</p> <p>Developmental studies in a number of different mammalian species have shown that both metabolic and physiological properties change postnatally. Preliminary studies by this author suggested that postnatal differentiation may also occur in human muscles.</p> <p>A detailed study of how and when fibre type differentiation occurs during development should contribute to an understanding of the mechanisms controlling differentiation. In addition, the results of normal development are essential for determining the involvement of neuromuscular disorders in foetal and postnatal muscle.</p> <p>The objective of this thesis was to study the metabolic differentiation of fibres during foetal and postnatal development.</p> <p>Five limb muscles, the soleus, triceps, biceps, vastus lateralis, gastrocnemius, and in some cases the diaphragm were excised at autopsy from 21 foetuses ranging in age from 25-43 weeks gestation. The same limb muscles were examined in five infants between one and 20 months, three children between 6-8 years and four adults aged 18-28 years. Multiple sites were taken from each muscle, mounted cross-sectionally and frozen rapidly in isopentane at -160°C. Serial sections were cut at 10 μm and the following reactions run, m-ATPase pH 10.3, 10.0, 4.58, 4.28, NADH-TR, SDH, α-GPD, Rna-Dna, gomori trichrome and H&E. One longitudinal sample was taken from the motor end plate zone of each foetal muscle for examination of motor nerves and end plates by an acetylcholinesterase reaction. Fibre type distributions were determined in three areas per site, from 35 mm. colour slides of the m-ATPase pH 10.3 reaction.</p> <p>In order to determine the number of sites it was necessary to sample per muscle, the between site variability of fibre type distributions was studied in four different muscles from four adults. Fifteen sites were sampled and a mean of 15,000 fibres counted per muscle. Distributions between and within sites showed greater variation (p<0.01) than could be expected from a homogeneously distributed muscle. Between site standard deviations ranged from 6.63% to 8.12% type II fibres in the different muscles. At least two and up to five sites need to be sampled to reliably estimate the fibre type distribution of adult muscle.</p> <p>The results of the developmental study suggest that the process of metabolic differentiation can be described in four stages. During stage 1, i.e. 6-20 weeks, all muscle fibres were shown by previous studies to have the same histochemical properties. During stage 2, i.e. 20-30 weeks, the m-ATPase pH 10.3, 4.3 and NADH-TR reactions could classify all fibres as either type I or type II. Most muscles had approximately 7% type I distributions and weak α-GPD and SDH reactions between 25-30 weeks. During stage 3, i.e. 30-43 weeks, a type IIC fibre could also be distinguished. At full term, type I fibres had increased to approximately 35%, type II fibres decreased to 51% from 93%, and 15% were type IIC. The activities of the metabolic enzymes had also greatly increased. On this evidence the increase in type I fibres is thought to be due to a conversion of type II to type I fibres, with type IIC fibres being in a transitional stage of conversion.</p> <p>Based on postnatal increases in the percentage of type I fibres in different muscles and decreases in type IIC fibres; differentiation was not completed at full term. The soleus had the greatest postnatal increase in type I fibres from 30% at term up to 70-80% in the children and adults. The results suggested that differentiation may be completed by the end of the first year of life.</p> <p>This study has led to a better understanding of the normal process of differentiation, the results of which are helpful in the clinical investigation of neonates and infants thought to have neuromuscular disorders.</p> / Doctor of Philosophy (PhD)