Crocodilians and birds comprise sister taxa of archosaurs, the development of these vertebrates occurs within an egg case that leaves developing embryos susceptible to fluctuations in the nesting environment. Studies suggest that sub-optimal conditions alter morphological growth and cardiovascular physiology. Regulation of the cardiovascular system is immature in the subjects studied, and embryos may rely on humoral rather than neural control of the cardiovascular system. The primary focus of this dissertation was to assess regulatory mechanisms responsible for maintenance of arterial pressure and heart rate. Dehydration stress had marked effects on embryo growth, and altered baseline cardiovascular parameters, while leaving the response to humoral regulator, angiotensin II (Ang II), unaffected. However, dehydrated alligator embryos developed cholinergic tone on heart rate. Hypoxic incubated chicken embryos were reduced in embryo mass, and altered response to humoral regulatory components Ang I and adenosine in addition identifying a novel regulatory component of the cardiovascular response to acute hypoxia. Collectively, these studies add to the existing knowledge of cardiovascular physiology in embryonic archosaurs and suggest that some components of cardiovascular regulation are plastic following developmental stress.

This study concerned the effect of ethanol on cardiac activity and brain respiration in chick embryos. Ethanol dosages tested ranged from 1.0 mg to 4.0 mg/g weight. Each experiment lasted at least 150 minutes. Cardiac activity in terms of total waveform energies was integrated and printed out for plotting and analysis. The embryonic heart rates were simultaneously determined from physical graph tracings. The embryonic brain respiration was measured using a differential microrespirometer. The effect of ethanol on cardiac activity was one of slight (10 to 13), but statistically significant (p<.05) rate depression. The brain slices exhibited a marked, immediate, and irreversible decrease (39 to 89%) in oxygen consumption at both ethanol dosages. The data indicated that chick embryonic brain tissues were more susceptible to alcohol effects than cardiac tissue. Therefore, the mental abnormalities seen in the offspring of alcoholic mothers may be more cerebral in nature than cardiovascular.

Graduation date: 1993

Includes bibliography / vii, 161, [208] leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Biochemistry, 1985

Bibliography: leaves 148-166. / xi, 166 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The chicken embryo's ability to match the perfusion of its chorioallantoic membrane to regional differences in shell conductance was investigated. / Thesis (Ph.D.)--Adelaide University, Dept. of Environmental Biology, 2001

Glucocorticoids known to be such powerful agents that cell growth, differentiation and cell death are influenced in the brain of mammals throughout life. Despite this, relatively little toxicological information regarding prenatal exposure is available. The aim of this study was to determine the effect of prenatal hydrocortisone exposure on cell viability and cell morphology in chick embryonic neurons. Four different histological staining techniques namely, Hematoxylin and Eosin (H&E), Cresyl Fast Violet, Silver impregnation and a combination of Gold Chloride and Toluidine Blue were used to evaluate chick embryo neural tissue exposed to 0.137ƒÝM or 0.685ƒÝM hydrocortisone on day 3.75 (Carnegie stage 16) and day 5.5 (Carnegie stage 18) of development. Histological processing was optimized and neural tissue evaluated for any changes in neuron morphology and cell number. Specific ultrastructural changes to membraneous structures were evaluated by transmission electron microscopy (TEM). Fixation procedures that resulted in little to no disruption of these structures were optimized and used in studies evaluating the effect of hydrocortisone on neuron morphology. Primary chick embryonic neuronal cultures were prepared and increasing concentrations of hydrocortisone (26.3nM, 0.16ƒÝM, 0.63ƒÝM, 3.8ƒÝM, and 22.8ƒÝM) added. Fluorescence microscopy was applied to the in vitro hydrocortisone exposed primary neuronal cultures. A combination of fluorescein diacetate (FDA) and propidium iodide (PI) was used to evaluate the effect of hydrocortisone on cell viability, whereas dichlorodihydrofluorescein diacetate (DCH2FDA) was used to visualize reactive oxygen species (ROS) generation in neurons. Histological evaluation of the neural tissue of chick embryos exposed to 0.137ƒÝM and 0.685ƒÝM hydrocortisone showed reduced neuron density and morphological changes associated with cell death. Glutaraldehyde with added magnesium chloride (MgCl2) as stabilizing chemical and potassium permangenate were two fixatives that caused minimal disruption to neural tissue. These two fixating methods were applied to control neural tissue as well as tissues exposed to 0.137ƒÝM and 0.685ƒÝM hydrocortisone. When evaluated by TEM, the control tissue appeared to be intact with no displacement. Exposure of neurons to 0.137ƒÝM hydrocortisone appeared to have severe effects on the morphology of the mitochondria, endoplasmic reticulum (ER), nuclear and plasma membranes. More extensive damage was noted with 0.685ƒÝM hydrocortisone, leaving almost no cellular structure. Both concentrations of hydrocortisone indicated cell death associated with apoptosis and necrosis. In vitro studies using primary cultures of chick neurons indicated that hydrocortisone is non-toxic at low concentrations (26.3nM ¡V 3.8ƒÝM) with the percentage viability ranging between 73% and 88%. A more toxic effect was seen at high concentrations (22.8ƒÝM). Cell death at the higher concentrations (22.8ƒÝM and 3.8ƒÝM) of hydrocortisone occurred due to ROS generation, as indicated by DCH2FDA fluorescence In conclusion, hydrocortisone indicated neurotoxicity at high concentrations of exposure. Although cell death could be detected, the exact mechanism (apoptosis or necrosis) still needs to be investigated. Since the developing brain is so susceptible to chemical insults care should be taken when administering this drug to pregnant mothers or young children. / Dissertation (MSc (Cell Biology)))--University of Pretoria, 2007. / Anatomy / unrestricted

Developing chicken embryos have two ductus arteriosus (DA) that shunt blood away from the lungs and to the chorioallantoic membrane, the embryonic gas exchanger. In mammals, DA closure is stimulated by an increase in blood gas O2 that occurs as the animal begins to breathe with its lungs. The goal of this study was to determine the influence of O2 levels during incubation on the vascular reactivity and morphology of the O2-sensitive DA and to examine the effects of changing O2 levels during late incubation on the morphology of the DA from chicken embryos. In comparison to normoxia, hypoxia (15%) reduced venous O2 levels in day 16 and day 18 embryos and reduced aircell O2 values in day 16, day 18, and internally pipped (IP) embryos, whereas hyperoxia (30%) increased venous O2 levels and aircell O2 level in day 16, day 18, and IP embryos. In comparison to normoxia, hypoxia delayed closure of the DA, whereas hyperoxia accelerated DA closure. In comparison to the left DA from externally pipped (EP) normoxic embryos, the left DA from EP hypoxic embryos exhibited a significantly weaker contractile response to O2. The DA from day 18 hypoxic embryos exhibited a significantly weaker contractile response to norepinephrine and phenylephrine when compared with the DA from day 18 normoxic and hyperoxic embryos. The effect of incubation in hypoxia / hyperoxia during different developmental windows on the DA O2-induced contractile response was observed only in IP embryos that were incubated in normoxia for 16 days and were then moved to hyperoxia. Incubation in hypoxia / hyperoxia resulted in differences in embryo mass, yolk mass, and heart mass. There is an association between the decreased contractile response to O2 and delayed closure in the proximal portion of the DA from hypoxic embryos; as well as an increased contractile response to O2 and accelerated closure in the proximal portion of the DA from hyperoxic embryos.

Cardiac, metabolic and growth response of early-stage chicken embryos to perturbations in yolk environment was investigated. Also, effects of parental hypoxia exposure on hypoxia resistance, thermal tolerance and body length of zebrafish larvae were investigated. In the first study, thyroxine, triiodothyronine and testosterone produced differential effects on heart rate and development rate of chicken embryos during the first 4 days of development. Triiodothyronine caused a dose-dependent increase in heart rate when applied at 40 or 70 hours of age, while thyroxine caused a dose-dependent increase in heart rate when applied at 40 hours only. Testosterone and propyl-thiouracil (deiodinase antagonist) did not have an effect on heart rate. Development rate was not changed by thyroxine, triiodothyronine, testosterone or propyl-thiouracil, which suggested that heart rate changes did not result from changes in embryo maturity. In the second study, chicken embryos exposed to yolks of different bird species during early-stage embryonic development showed changes in heart rate, mass-specific oxygen consumption and body mass that scaled with the egg mass, incubation period length, and yolk triiodothyronine and testosterone levels of the species from which yolk was derived. In the third study, this phenomenon was investigated between layer and broiler chickens. Heart rate, oxygen consumption and body mass of broiler and layer embryos were significantly changed by a breed-specific change in yolk environment. Yolk triiodothyronine and testosterone concentrations of broiler and layer eggs did not suggest that these hormones were responsible for physiological and morphological changes observed. The final study demonstrated that hypoxia resistance and body lengths, but not thermal tolerance of zebrafish larvae was increased by parental hypoxia exposure.

Thesis (MSc. Agriculture (Animal Production)) -- University of Limpopo, 2015 / Three experiments were conducted to determine the effect of in ovo glucose injection on egg hatchability, chick hatch-weight, productivity and carcass characteristics of indigenous Potchefstroom koekoek chickens. A complete randomized design was used in all the three parts of the study (from incubation, 1-49 days old unsexed chickens and 50-91 days old female chickens). On day 18 of incubation the developing eggs were subjected to the following treatments: 0- (no glucose or water injected), 0+ (only water injected), 5, 10, 15 or 20 mg of glucose per egg. Each treatment had three replications and there were 20 eggs per replicate. A quadratic model was used to determine in ovo glucose injection levels for optimal egg hatchability, chick hatch-weight and chick to egg weight ratio of Potchefstroom koekoek chickens. In ovo glucose injection improved (P<0.05) egg hatchability, chick hatch-weight and chick to egg weight ratio of the chickens. Egg hatchability, chick hatch-weight and chick to egg weight ratio Potchefstroom koekoek chickens were optimized at different injection levels of 4.50, 10.43 and 12.00 mg of glucose per egg, respectively. Unsexed day-old chicks from the first experiment (according to their initial treatments and replicates) were used in a complete randomized design having six treatments, replicated three times, and having ten birds per replicate. Glucose injection levels increased (P<0.05) feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy and nitrogen retention of female Potchefstroom koekoek chickens aged 1 to 49 days. However, growth rate, live weight, metabolisable energy intake and nitrogen retention of the chickens were optimized at glucose injection levels of 3.92, 4.36, 10.67 and 13.50 mg per egg, respectively. Female chickens from the second part of the study (according to their initial treatments and replicates) were used in a complete randomized design having six treatments, replicated three times, and having five birds per replicate. In ovo glucose injection levels improved (P<0.05) on feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy and nitrogen retention of female Potchefstroom koekoek chickens aged 50 to 91 days. However, only feed conversion ratio and metabolisable energy intake of the chickens were optimized at glucose injection levels of 12.15 and 5.57 mg per egg, respectively. Injection level also improved (P<0.05) carcass, breast, v drumstick, thigh, wing, gizzard and liver weights of female Potchefstroom koekoek chickens aged 13 weeks. In ovo glucose injection increased (P<0.05) breast meat tenderness, juiciness and flavour of female Potchefstroom koekoek chickens aged 91 days. However, breast tenderness, juiciness and flavour of female Potchefstroom koekoek chickens were optimized injection levels of 13.50, 19.25 and 10.83 mg of glucose per egg, respectively. No chicken deaths were observe

In adult vertebrates, cardiovascular regulation is accomplished by numerous systems with neural, hormonal and local components responsible for the majority of regulation. These regulatory components work in concert to maintain the essential function of blood perfusion to adult tissues. Given the essential nature of this function it is therefore surprising that the development of cardiovascular regulation during gestation is poorly understood. The majority of what is known is based on a single vertebrate model, the fetal lamb. The fetal lamb has been used in multiple studies due to the clear clinical applications and has been pivotal in understanding the onset of regulation in developing vertebrates. However, study on the fetal lamb is limited to the latter 40% of gestation and has the added complication of an in-utero developmental strategy. Therefore the primary focus of this dissertation was to characterize basic cardiovascular regulation in the chicken embryo to provided the needed information for it's use an alternative to the fetal lamb. Developing chicken embryos rely on both alpha and beta adrenergic tones to maintain normal heart rate and arterial blood pressure during incubation. However, on day 21, just prior to hatch, these animals lose both tones on arterial pressure suggesting the onset of adult regulation. Cholinergic tone, however, was absent throughout chicken development indicating that it must mature during the neonatal life. Adult cardiovascular reflexes become apparent late in chicken development with a clear baroreflex specifically operating initially on day. However, an adult response to changes in ambient gas tension was absent during incubation suggesting embryos possess unique regulatory systems that are absent in adult chickens. This mechanism is comprised entirely of adrenergic systems with no cholinergic action during change in ambient gas tension. Similar developmental patterns were determined in embryos of the desert tortoise suggesting fundamental differences between in-utero and ex-utero developing vertebrates.