The newly resurgent field of evolutionary developmental biology integrates the study of evolutionarily important anatomical changes and developmental biology to describe the genetic and developmental changes that have led to anatomical changes. In this dissertation I describe candidate developmental mechanisms in the context of axial elongation and pectoral fin musculature evolution in fishes. Both axial elongation and increase in pectoral fin muscle subdivisions have important ecological correlates. Elongate fishes tend to be found in highly structured environments and fishes with an increased number of fin muscles tend to use fin-based locomotion to swim. Both of these morphologies have evolved multiple times within the ray-finned fish radiation. In Chapter 1 I focus on a specific predator avoidance behavior that is only seen in elongate fishes. Deeper-bodied fish tend to perform a unilateral bend of the body and swim away whereas elongate fish, when startled, bend bilaterally and hide. Although all elongate fishes perform head retraction, their specific anatomy indicates multiple explanations for how elongation occurs. In Chapter 2, I describe changes in the vertebral column in lineages of actinopterygian fishes that have elongate members. Elongation occurs through three different mechanisms: addition of abdominal vertebrae, addition of caudal vertebrae, and lengthening of all the vertebral cents. This study suggests that the number of abdominal vertebrae, number of caudal vertebrae, and length of the vertebral cents are controlled by separate developmental modules. Fin-based locomotion has evolved multiple times independently within actinopterygian fishes and is correlated with a modification of the pectoral fin musculature. In order to increase the understanding of fin muscle development, in Chapter 3 I describe the wildtype anatomy and embryology of the pectoral fin musculature in the zebrafish, Danio rerio. Zebrafish have six muscles in the pectoral fin. Early in development, the fin musculature consists of two muscle masses, one on each side of the fin. The arrector ventralis is the first muscle to individuate from the initial abductor muscle mass, and the adult musculature is present by 3 weeks postfertilization. This study provides a basic understanding of the embryology of the fin muscles and will provide a baseline for examining mutant fin muscle morphologies in zebrafish and diverse fin muscle morphologies in other species.

The studies included in this dissertation address the role of blood flow and cellular oxygenation in skeletal muscle fatigue, with an underlying interest in age-related differences in muscle fatigue. In the first study, I found that blood flow immediately post-contraction was tightly coupled to contraction intensity throughout an incremental isometric dorsiflexor contraction protocol in healthy young men. This relationship was independent of fatigue, and the onset of fatigue occurred before any reduction or plateau in blood flow. These data suggest that fatigue during intermittent incremental contractions does not result from a blood flow limitation. The second study used magnetic resonance spectroscopy of deoxymyoglobin to examine the role of intracellular oxygenation in muscle fatigue during slow and rapid incremental contractions in healthy young men and women. Data from this study showed that the rate of deoxygenation relative to force during contractions was predictive of fatigue, and this was true for slow and rapid contractions. Further, intracellular oxygenation was lower, and fatigue greater, during more metabolically demanding rapid contractions. These data support a role for intracellular oxygenation in the development of fatigue. The final study investigated whether differences in intracellular oxygenation could explain age-related differences in muscle fatigue. During slow contractions, intracellular oxygenation was higher, but fatigue lower, in older compared to young subjects. After matching a subset of subjects by muscle strength, age-group differences in oxygenation were eliminated, but fatigue was still less in older subjects, suggesting that while differences in oxygenation exist between young and older subjects, they cannot explain the age-group differences in fatigue. This conclusion was supported by a similar oxygenation, but greater fatigue, in young compared to older subjects during rapid contractions. Based on these findings, intracellular oxygenation does not appear to play a role in the age-related differences in fatigue observed in this and other studies. Together, data from this dissertation suggest that intracellular oxygenation plays a role in the development of muscle fatigue, despite the ability of blood flow to match contraction intensity. Differences in oxygenation, however, cannot explain age-related differences in muscle fatigue.

The peripubertal period is a period during which significant brain re-organization occurs, and during which changes in the neuroendocrine milieu normally lead to the onset of fertility. Shipping female mice during the peripubertal period causes a long-lasting behavioral defeminization of feminine sexual behavior. Because shipping is a stressor, it was suggested that peripubertal stress exposure might interfere with the regulation of feminine sexual behaviors in adult female mice. As a result, the goal of this research was to examine the effects of peripubertal stress exposure on neuroendocrine regulation of the hypothalamo-pituitary-gonadal (HPG) and the hypothalamo-pituitary-adrenal (HPA) axis. However, although peripubertally exposing female mice to shipment stress caused a significant decrease in sexual receptivity, peripubertal exposure to restraint stress, food deprivation, social stress and instability, or multiple stressors (heat, light, and restraint) did not decrease sexual receptivity during adulthood. Only exposure to a high dose of bacterial endotoxin during the peripubertal period duplicated the defeminizing effect of shipping during the peripubertal period on adult mouse feminine sexual behavior. Interestingly, significant long-term effects of peripubertal stress exposure were also observed in the regulation of the HPA axis, where exposure to peripubertal shipping and LPS led to blunted stress-induced corticosterone responses in adult female mice. Peripubertal exposure to shipping and LPS had long-lasting effects on steroid receptor expression in brain areas relevant to female reproduction. Nevertheless, peripubertal exposure to LPS did not interfere with the ability of estradiol to induce the release of LH. Moreover, although peripubertal exposure to shipping decreased masculine sexual behavior in male, but not female, mice, peripubertal exposure to LPS was without effect on masculine sexual behavior. These results suggest that exposure to some, but not all, peripubertal stressors can induce long-lasting changes in reproductive behaviors, as well as changes in the expression of sex steroid receptors known to regulate these behaviors.

No description available.

No description available.

The control of balance and orientation comprises various forms of sensory input, reflexive action and anticipatory mechanisms. An important sensory input is the vestibular system. When a destabilising or disorientating perturbation is sensed by the vestibular apparatus a corrective response is generated. This thesis investigated how the processing of vestibular signals is affected by postural and sensory context. Orientation reflexes evoked by a vestibular signal of head roll were shown to be continuously modulated and even reversed direction during self-generated head pitch movements (Chapter 2). Results also raised the possibility that the direction of a vestibular-evoked balance reflex is automatically rotated following adaptation of motor output (Chapter 3). In addition to modulating the response direction, the context was also found to affect the response amplitude. Passive cutaneous sensory input was shown to attenuate a vestibular-evoked balance reflex (Chapter 4). If, however, such changes in sensory context were anticipated, then response amplitude was unchanged (Chapter 5). Furthermore, the initial balance reflex was not affected by a fear of falling (Chapter 6). The present findings demonstrate that the processing of vestibular signals is indeed context-dependent. However, the modulation of vestibular-evoked reflexes is seemingly automatic, and is not affected by cognition or emotion.

This study demonstrates the use of submerged limb culture in teratologic testing. Pregnant mice were treated on day 11 of gestation (E11, plug date = E0) with 10, 20 or 40 mg of 5-fluorouracil (FU) per kg body weight. On E17, treated and untreated fetuses were examined for gross malformations and were fixed in 95% ethanol. Reduction of limb size and digital defects, including ectrodactyly (ED), syndactyly (SD), microdactyly and polydactyly were dose-dependent. In parallel studies, pregnant mice were treated on the morning of E11 and embryos were removed either 7h (E11) or 24h (E12) later for submerged limb culture. Changes in limb area showed a dose-response relationship while treatment had little effect on the shape of individual bones. This indicates the relatively unspecific nature of FU-induced embryotoxicity. E11 studies revealed a dose dependent response of ED, SD and fusion of the metacarpals/metatarsals (MC/MT) to the proximal phalanges. Unlike E11 cultures, middle phalanges were present but decreased in number as dosage increased. Limbs from embryos of untreated females were cultured (E11) in the presence of 0.002, 0.02, 0.2 or 2.0 mg FU/ml culture medium. The percentage of limbs void of paw cartilage or with decreased numbers of MC/MT was dose-dependent. A dose-dependent decrease in the deleterious effects of 0.02 mg FU/ml was observed when 0.2 or 0.02 mg thymine/ml was added to the cultures. In both culture and non-culture studies, hindlimbs (HL) were more affected than forelimbs (FL) and distal regions were more affected than proximal ones. In addition to the morphometric analyses, biochemical parameters of growth and differentiation were examined at 0, 36 and 72h of culture in untreated and treated limbs. Both DNA and protein of FU treated limbs were decreased compared to untreated controls. FL demonstrated greater capacity for regulation of losses in protein content, HL for DNA content. Submerged limb culture provides a useful model for the examination of xenobiotic effects on limb development and allows some comparative evaluation among in vivo, in vivo/in vitro and in vitro studies. (Abstract shortened with permission of author.)

Thesis (Ph. D. (Botany))--Rhodes University, 2006.

The role of vibration in exercise is controversial, with much debate about its potential benefits. The aim of the research reported in this PhD thesis was to inform evidence based practice by investigating the underlying responses of the human body during exercise with vibration. Human neuromuscular and cardiovascular systems were investigated using 3D motion analysis, near infra-red spectroscopy (NIRS), laser Doppler blood flow analysis and electromyography (EMG). Analysis of a prototype vibrating stationary cycle identified significant increases in muscle activation. However, the validity of the results was limited by a confounding issue of increasing resistance with increasing cadence due to the cycle’s vibration mechanism. Consistency of exercise performance on vibration platforms was measured by 3D analysis; vibration did not affect the kinematic parameters of exercises such as heel raises or press ups, even though significant physiological changes occurred. NIRS indicated a significant reduction in the depletion of oxygenated haemoglobin, total haemoglobin and the normalised tissue haemoglobin index of the lateral gastrocnemius in heel raise exercises. During quiet standing laser Doppler measurements of the dorsalis pedis artery indicated that the NIRS results were not a consequence of vasospastic responses or increased resistance to blood flow in response to vibration. Whilst heart rate and blood pressure remained constant, blood flow velocity significantly increased, suggesting the peripheral changes occurred independently of central cardiovascular function. Heel raise exercises with whole body vibration showed significant increases in muscle activation of the soleus, but not the gastrocnemius, indicating varied muscular responses to vibration. The influence of blood flow and tissue oxygenation on EMG parameters was demonstrated via the protection of muscle conduction velocity during static squats, despite a downward shift in median frequency of the EMG power spectra. Analysis of upper body muscles during press ups yielded significant increases in muscle activation, equivalent to increasing the load of the bench press by 10% of the one repetition maximum. The results indicate that vibration influenced the dynamic muscles more than stabiliser muscles; reinforcing the lower body studies showing that vibration has a varied influence on muscle function. The aforementioned results demonstrate the ability of vibration to augment the effects of exercise on the muscular and vascular physiological systems of the human body.

Monitoring blood perfusion and oxygenation changes is of vital importance and for this reason many different techniques have been developed over the decades. Photoplethysmography (PPG) is an optical technique that measures blood volume variations in vascular tissue and it is well known for its utilisation in pulse oximetry for the estimation of arterial blood oxygen saturation (SpO2). In pulse oximetry, mainly the pulsatile component of the signal (AC PPG) is used while the continuous DC component is mostly excluded. Near Infrared Spectroscopy (NIRS) is another optical technique that measures changes in the concentration of oxygenated (ΔHbO2), deoxygenated (ΔHHb), and total haemoglobin (ΔtHb) from the variations in light attenuations at different wavelengths. The main motivation of this research is to explore the capability of Photoplethysmography in assessing tissue perfusion and oxygenation similarly as NIRS. The hypothesis underlining this research is that the DC component of the PPG signal contains information on the overall absorbed light and this part of the PPG signal, acquired at least two wavelengths, may be used to obtain ΔHbO2, ΔHHb, and ΔtHb as performed in NIRS. Therefore, DC PPG attenuations may be related to haemoglobin concentrations by the modified Beer-Lambert law (MBLL). In order to investigate this, novel reflectance, custom-made PPG sensors and measurement systems, including advanced signal processing algorithms, have been developed for the acquisition and analysis of raw PPG signals (AC + DC) from different anatomical locations. Three in vivo studies on healthy volunteers were carried out in order to investigate if ΔHbO2, ΔHHb, and ΔtHb estimated from PPG could indicate changes in blood perfusion and oxygenation. The studies consisted of vascular occlusions on the forearm, negative bed tilting, and whole body cold exposure. Raw PPG signals were acquired from different locations such as the forearm, fingers, and forehead, whereas simultaneous NIRS signals were used as a reference. The results showed that ΔHbO2, ΔHHb, and ΔtHb could be effectively estimated from PPG signals. These parameters indicated the changes in blood volumes and/or oxygenation, whereas comparison with NIRS signals showed good levels of correlation and trending. These promising results showed that DC PPG signals could be used to monitor changes in blood perfusion and oxygenation, extending the range of applications of Photoplethysmography.