Developmental stages in the rabbit embryo: guidelines to choose an appropriate experimental model

Trophoblast emboli in the lung of a snowshoe hare (Lepus americanus)

Spontaneous migration of placental trophoblasts into maternal blood vessels and embolization to other organs (ie, lung, adrenal gland, spleen, and liver) occurs in women and certain animals with hemochorial placentation. Although considered incidental in most species, increased incidence and numbers of trophoblast emboli are reported in women with gestational diseases with arterial hypertension (pre-eclampsia and eclampsia). To the best of our knowledge, trophoblast emboli have not been reported in lagomorphs. This case report describes the identification of trophoblast emboli in the lung of a wild snowshoe hare (Lepus americanus). Death of this hare was attributed to pulmonary hemorrhages and hemothorax, but a definitive cause for the hemorrhages was not determined. It is unclear whether trophoblast embolism normally occurs in this species and represents an incidental finding, or whether it possibly contributed to rupture of pulmonary or thoracic blood vessels leading to hemorrhage.

Central nervous system development in rabbits (Oryctolagus cuniculus L. 1758)

The present study describes the embryonic and fetal development of the central nervous system in rabbits from the seventh day after conception until the end of the full-term fetal period. A total of 19 embryonic and fetal samples were carefully dissected and microscopically analyzed. Neural tube closure was observed between 7.5 and 8 days of gestation. Primordial encephalic vesicle differentiation and spinal canal delimitation were observed on the 12th day of gestation. Histologically, on the 15th day of gestation, the brain, cerebellum, and brain stem were delimited. On the 18th day of gestation, the cervical and lumbar intumescences of the spinal cord were visible. On the 28th day of gestation, four-cell layers could be distinguished in the cerebral cortex, while the cerebellar cortex was still differentiating. Overall, the morphological aspects of the embryonic and fetal developmental phases in rabbits were highly similar to those in humans. Thus, the present study provides relevant information highlighting rabbits as an excellent candidate animal model for preclinical research on human neurological diseases given the high adaptability of rabbits to bioterium conditions and the similarity of morphological events between rabbits and humans.

Role of the Pubic Symphysis in Osseous Pelvic Development: A Novel Model of Bladder Exstrophy in Rabbits

BACKGROUND

It has been posited that the osseous pelvic anomalies seen in patients with classic bladder exstrophy (CBE) result from disruption of the pubic symphysis. This hypothesis, however, has not been tested. In the present animal study, our objective was to determine whether the tension of the pubic symphysis helps maintain the shape of the pelvic ring, or whether the growing bones maintain a ring shape even without the tension of the symphysis.

METHODS

In total, 12 neonatal New Zealand White rabbits underwent pubic symphysiotomy (experimental group, n=9) or sham surgery (control group, n=3) on days 3 or 4 of life. Rabbits were scanned with cone-beam computed tomography at 1, 4, 12, and 20 weeks postoperatively to monitor changes in the following pelvic parameters, which are known to be altered in CBE: anterior segment angle, anterior segment length, intertriradiate distance, interpubic distance, and posterior segment angle. Changes within the experimental and control groups were evaluated using repeated-measures analysis of variance and post hoc Tukey honest significant difference testing. Two-tailed t tests were used to compare treatment groups at each time point.

RESULTS

Both groups showed increases in anterior segment length and intertriradiate distance during the study period; rabbits in the experimental group also showed a steady increase in interpubic distance (F=43.9; P<0.001). Experimental rabbits had significantly larger mean values for anterior segment angle, intertriradiate distance, interpubic distance, and posterior segment angle than did control rabbits at all time points. We found no difference in mean anterior segment length between control and experimental groups at any time point. The difference in interpubic distance was particularly pronounced by 20 weeks (experimental group, 13±2.7 mm; control group, 1.1±0.1 mm; P<0.001).

CONCLUSIONS

The pubic symphysis is essential for normal pelvic development. Its absence led to early pelvic angulation and progressive pubic separation in a rabbit model. However, we found no significant difference in the mean anterior segment length, and it is likely that other factors are also implicated in the growth disturbance seen in CBE.

LEVEL OF EVIDENCE

Level V.

Subsynovial connective tissue development in the rabbit carpal tunnel

The carpal tunnel contains the digital flexor tendons and the median nerve, which are embedded in a unique network of fibrovascular interconnected subsynovial connective tissue (SSCT). Fibrous hypertrophy of the SSCT and subsequent adaptations in mechanical response are found in patients with carpal tunnel syndrome (CTS), but not much is known about the development of the SSCT. This observational study describes the morphological development of SSCT using histology and ultramicroscopy in an animal model at four time points between late-term fetuses through adulthood. A transition is seen between 3 days and 6 weeks post-partum from a dense solid SSCT matrix to a complex multilayered structure connected with collagenous fibrils. These preliminary data show a developmental pattern that matches an adaptive response of the SSCT to loading and motion. Understanding the anatomical development aids in recognizing the pathophysiology of CTS and supports research on new therapeutic approaches.

Models of Intrauterine growth restriction and fetal programming in rabbits

Intrauterine growth restriction (IUGR) affects approximately 10% of human pregnancies globally and has immediate and life-long consequences for offspring health. However, the mechanisms underlying the pathogenesis of IUGR and its association with later health and disease outcomes are poorly understood. To address these knowledge gaps, the use of experimental animals is critically important. Since the 50's different environmental, pharmacological, and surgical manipulations have been performed in the rabbit to improve our knowledge of the control of fetal growth, fetal responses to IUGR, and mechanisms by which offspring may be programmed by an adverse gestational environment. The purpose of this review is therefore to summarize the utility of the rabbit as a model for IUGR research. It first summarizes the knowledge of prenatal and postnatal development in the rabbit and how these events relate to developmental milestones in humans. It then describes the methods used to induce IUGR in rabbits and the knowledge gained about the mechanisms determining prenatal and postnatal outcomes of the offspring. Finally, it discusses the application of state of the art approaches in the rabbit, including high-resolution ultrasound, magnetic resonance imaging, and gene targeting, to gain a deeper integrative understanding of the physiological and molecular events governing the development of IUGR. Overall, we hope to engage and inspire investigators to employ the rabbit as a model organism when studying pregnancy physiology so that we may advance our understanding of mechanisms underlying IUGR and its consequences in humans and other mammalian species.

Effect of PPARGC1A on the development and metabolism of early rabbit embryos in vitro

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A) is a central regulator of mitochondrial biogenesis and metabolism, and its expression is closely related to embryo development. To gain insights into the possible mechanisms of PPARGC1A during early embryogenesis, the development potential, mitochondrial biogenesis, and the culture medium metabolomics of embryos were evaluated when PPARGC1A overexpressed or suppressed in rabbit zygotes. Results showed that different PPARGC1A levels in rabbit zygotes could affect blastocyst percentage, and the expressions of mitochondrial biogenesis and metabolic-related genes, as well as the glutathione and adenosine triphosphate levels during early embryo development. In addition, compared with the controls, 12 and 10 different metabolites involved in carbohydrate, amino acid, and fatty acid metabolism were screened in the 5 day's spent culture medium of PPARGC1A overexpressed and suppressed embryos by gas chromatography-mass spectrometer, respectively. Consistent with these metabolite changes, the transcriptions of genes encoding glucose transporters and fatty acid biosynthetic proteins in the embryos from different groups were regulated by PPARGC1A during rabbit embryo development. Taken together, these data provide evidence that PPARGC1A may regulate early rabbit embryo development through mitochondrial biogenesis and metabolism.

Ultrasonographic evaluation of feto-placental tissues at different intrauterine locations in rabbit

The main purpose of examining multiparous species with real-time ultrasonography is to determine the gestational age and make various fetal measurements for early diagnosis of growth anomalies and sibling mismatches. This study investigated changes in fetometric measurements, obstetric Doppler indices and placental image analysis results based on gestational age and fetal location in fetuses located cranially and caudally between 16 and 24 days gestation in 22 healthy pregnant New Zealand rabbits. The first study group consisted of fetuses positioned at the cranial end (n = 22) while the second group consisted of fetuses positioned at the caudal end (n = 22) in each pregnancy. Fetal biparietal head diameter (BPD) and trunk diameter (TD) were measured, and mean grayness values (MGV) were determined from placental image analysis of each fetus. Using Doppler USG, the pulsatile (PI) and resistance (RI) indices of the uterine artery (UtA) and umbilical artery (UmA) were recorded. By the end of the study, BPD and TD values for cranial and caudal fetuses had significantly increased with gestational age (P < 0.001). The MGV values of caudal fetuses were significantly higher (except for the 16th day) (P < 0.05). The UtA PI value of the caudal fetuses was significantly higher (except for the 18th day) (P < 0.01). The UtA RI values of caudal fetuses were significantly higher than cranial ones on the 16 and 24th days (P < 0.05). The PI of the UmA increased until the 20th day before decreasing significantly in both study groups (P < 0.001). The UmA RI value decreased according to the gestational age in both groups (P < 0.001). It was significantly higher in the caudal fetuses on the 20th day (P < 0.05). The somatic rate of all fetuses peaked at the end of the second trimester, although caudal fetuses had higher fetometric values, and this location difference also affected placental echotexture. In both vessels of caudal fetuses, pulsatility and resistance values were higher. The 20th day of pregnancy was a threshold for the Doppler exam results. In conclusion, growth and metabolic status of fetuses located in different uterine locations in healthy pregnant New Zealand rabbits vary. Based on the these growth curves and hemodynamic data, more comprehensive studies of intrauterine life may be possible.

The effects of sildenafil citrate on feto-placental development and haemodynamics in a rabbit model of intrauterine growth restriction

The present study evaluated the effectiveness of sildenafil citrate (SC) to improve placental and fetal growth in a diet-induced rabbit model of intrauterine growth restriction (IUGR). Pregnant rabbits were fed either ad libitum (Group C) or restricted to 50% of dietary requirements (Group R) or restricted and treated with SC (Group SC). The treatment with SC improved placental development by increasing vascularity and vessel hypertrophy in the decidua. The assessment of feto-placental haemodynamics showed higher resistance and pulsatility indices at the middle cerebral artery (MCA) in fetuses treated with SC when compared with Group R, which had increased systolic peak and time-averaged mean velocities at the MCA. Furthermore, fetuses in the SC group had significantly higher biparietal and thoracic diameters and longer crown-rump lengths than fetuses in Group R. Hence, the SC group had a reduced IUGR rate and a higher kit size at birth compared with Group R. In conclusion, SC may provide potential benefits in pregnancies with placental insufficiency and IUGR, partially counteracting the negative effects of food restriction on placental development and fetal growth. However, the present study also found evidence of a possible blood overflow in the brain that warrants further investigation.

Development of the cardiorespiratory system in dogs from days 16 to 46 of pregnancy

Dogs have been studied for several reasons, such as the genetic improvement, their use as experimental models, in zoonotic research, cell therapy and as a model for human diseases. However, many features relating to the embryonic development of dogs remain unknown because of the absence of embryological studies. Considering the importance of the cardiorespiratory system in the development of embryos, the aim of this study was to investigate the development of the main cardiorespiratory organs of dog embryos and foetuses with estimated gestational ages from 16 to 46 days using macro- and microscopic descriptions. On day 16 of development, the neural tube and crest were formed, the anterior and posterior neuropore closure had begun and the somites had developed. Between days 22 and 27 of gestation, the lung buds and the initial formation of the primary bronchi and heart chambers were observed. The heart chambers exhibited the endo-, myo- and epicardial layers but did not have obvious differences in thickness among each other. Between days 41 and 46 of gestation, the nasal conchae and septa and trachea were formed, which exhibited characteristic epithelia. The lung formation and lobation were complete. The heart and major vessels exhibited mature histological architecture when their anatomical development was complete. The results of this study contribute to a more accurate definition of the embryonic and foetal developmental stages in dogs.

Characterization of early changes in fetoplacental hemodynamics in a diet-induced rabbit model of IUGR

Intrauterine growth restriction (IUGR) is associated with adverse perinatal outcomes and late-onset diseases in offspring. Eating disorders, voluntary caloric restriction and maternal undernutrition can all induce IUGR but a relevant model is required to measure all its possible consequences. In this work, pregnant rabbits were used as an IUGR model. Control females (n=4) received ad libitum diet throughout pregnancy, whereas underfed females (n=5) were restricted to 50% of their daily requirements. Offspring size was measured by ultrasonography and in vivo at birth. Hemodynamic features of the umbilical cords and middle cerebral arteries (systolic peak velocity, end diastolic velocity, pulsatility index and resistance index) were characterized by Doppler ultrasonography. At day 21, maternal underfeeding resulted in a significant reduction of fetal size (occipito-nasal length). At birth, the size of kits from the underfed group was significantly lower (lower crown-rump length, biparietal and transversal thoracic diameters) and a reduced weight with respect to the control group. Feed restriction altered blood flow perfusion compared with does fed ad libitum (significant higher systolic peak, time-averaged mean velocities and lower end diastolic velocity). Fetuses affected by IUGR presented with compensative brain-sparing effects when compared with the control group. In conclusion, the present study supports using rabbits and the underfeeding approach as a valuable model for IUGR studies. These results may help to characterize IUGR alterations due to nutrient restriction of mothers in future research.

Comparative Development of Embryonic Age by Organogenesis in Domestic Dogs and Cats

The precise determination of the embryonic chronology is very important in reproductive biotechnologies, especially in estimating embryonic age. Thus, there is a need for greater knowledge and standardization for determining the chronology of embryonic development and functional morphology. We describe aspects of embryonic development in two domestic carnivores to add knowledge about organ peculiarities and for application in veterinary practice, in prenatal development and in the biotechnology fields. We found that the development of differential characteristics of embryonic organs occurs in the first trimester of pregnancy for both species. Thus, using the combination of the crown-rump length, macroscopic analysis and optical microscopy, it is possible to predict gestational age more precisely in animals that lack a defined breed and establish an embryonic pattern.

Repairing Fetal Membranes with a Self-adhesive Ultrathin Polymeric Film: Evaluation in Mid-gestational Rabbit Model

Preterm premature rupture of membranes causes 40% of all preterm births, affecting 150000 women each year in the United States. Prenatal diagnostic procedures and surgical interventions increase incidence of adverse events, leading to iatrogenic membrane rupture after a fetoscopic procedure in 45% of cases. We propose an ultrathin, self-adherent, poly-L-lactic acid patch ("nanofilm") as a reparative wound closure after endoscopic/fetoscopic procedures. These nanofilms are compatible with application in wet conditions and with minimally invasive instrumentation. Ex vivo studies to evaluate the nanofilm were conducted using human chorion-amnion (CA) membranes. A custom-built inflation device was used for mechanical characterization of CA membranes and for assessment of nanofilm adhesion and sealing of membrane defects up to 3 mm in size. These ex vivo tests demonstrated the ability of the nanofilm to seal human CA defects ranging in size from 1 to 3 mm in diameter. In vivo survival studies were conducted in 25 mid-gestational rabbits, defects were created by perforating the uterus and the CA membranes and subsequently using the nanofilm to seal these wounds. These in vivo studies confirmed the successful sealing of defects smaller than 3 mm observed ex vivo. Histological analysis of whole harvested uteri 7 days after surgery showed intact uterine walls in 59% of the nanofilm repaired fetuses, along with increased uterine size and intrauterine development in 63% of the cases. In summary, we have developed an ultrathin, self-adhesive nanofilm for repair of uterine membrane defects.

Intrauterine growth restriction is associated with cardiac ultrastructural and gene expression changes related to the energetic metabolism in a rabbit model

Intrauterine growth restriction (IUGR) affects 7–10% of pregnancies and is associated with cardiovascular remodeling and dysfunction, which persists into adulthood. The underlying subcellular remodeling and cardiovascular programming events are still poorly documented. Cardiac muscle is central in the fetal adaptive mechanism to IUGR given its high energetic demands. The energetic homeostasis depends on the correct interaction of several molecular pathways and the adequate arrangement of intracellular energetic units (ICEUs), where mitochondria interact with the contractile machinery and the main cardiac ATPases to enable a quick and efficient energy transfer. We studied subcellular cardiac adaptations to IUGR in an experimental rabbit model. We evaluated the ultrastructure of ICEUs with transmission electron microscopy and observed an altered spatial arrangement in IUGR, with significant increases in cytosolic space between mitochondria and myofilaments. A global decrease of mitochondrial density was also observed. In addition, we conducted a global gene expression profile by advanced bioinformatics tools to assess the expression of genes involved in the cardiomyocyte energetic metabolism and identified four gene modules with a coordinated over-representation in IUGR: oxygen homeostasis (GO: 0032364), mitochondrial respiratory chain complex I (GO:0005747), oxidative phosphorylation (GO: 0006119), and NADH dehydrogenase activity (GO:0003954). These findings might contribute to changes in energetic homeostasis in IUGR. The potential persistence and role of these changes in long-term cardiovascular programming deserves further investigation.

Mice embryology: a microscopic overview

In this work, we studied the embryology of mice of 12, 14, and 18 days of gestation by gross observation, light microscopy, and scanning electron microscopy. Grossly, the embryos of 12 days were observed in C-shaped region of the brain, eye pigmentation of the retina, first, second, and third pharyngeal arches gill pit nasal region on the fourth ventricle brain, cervical curvature, heart, liver, limb bud thoracic, spinal cord, tail, umbilical cord, and place of the mesonephric ridge. Microscopically, the liver, cardiovascular system and spinal cord were observed. In the embryo of 14 days, we observed structures that make up the liver and heart. At 18 days of gestation fetuses, it was noted the presence of eyes, mouth, and nose in the cephalic region, chest and pelvic region with the presence of well-developed limbs, umbilical cord, and placenta. Scanning electron microscopy in 18 days of gestation fetuses evidenced head, eyes closed eyelids, nose, vibrissae, forelimb, heart, lung, kidney, liver, small bowel, diaphragm, and part of the spine. The results obtained in this work describe the internal and external morphology of mice, provided by an integration of techniques and review of the morphological knowledge of the embryonic development of this species, as this animal is of great importance to scientific studies.

Estudo microscópico e macroscópico, com enfoque radiográfico e de alizarina, no desenvolvimento embrionário e fetal de gatos domésticos (Felis catus) em diferentes idades gestacionais

O gato doméstico (Felis catus) foi nomeado por Carolus Linnaeus em seu livro Systema Naturae, em 1798. A família Felidea apresenta muita semelhança morfológica com os felinos selvagens. O estudo da embriologia do gato doméstico é de grande valia, uma vez que, é considerado um importante modelo animal quando comparado aos gatos selvagem em extinção, especialmente relacionado às pesquisas sobre biologia reprodutiva. Este trabalho objetivou análisar e comparar as fases embrionárias de quatro embriões e um feto de felinos domésticos. Nos embriões com idade gestacional estimada em 17 dias (0,5cm CR) podemos observar pela análise macroscópica a presença de dilatação rostral correspondente ao prosencéfalo, o local placóide do cristalino, a flexura cervical, os quatro arcos faríngeos com os sulcos que o dividem, a proeminência cardíaca, o indício do brotamento do membro pélvico, além da presença de somitos. Na região caudal do embrião, visualizamos a curvatura cranio-caudal, permitindo ao mesmo uma posição em formato de "C". Nos embriões com idade gestacional estimada em 22 dias (1,2cm CR), na análise macroscópica foi visualizado o prosencéfalo, vesícula óptica com pigmentação da retina, vesícula ótica, quarto ventrículo, fígado, membros torácicos e pélvicos com discreta distinção dos dígitos e vascularização superficial. Nos embriões com idade gestacional estimada em 25 dias (1,5cm CR) notamos a presença do prosencéfalo e mesencéfalo, a curvatura cervical pronunciada, vesícula óptica com forte pigmentação da retina, vesícula ótica, membros pélvicos e torácicos bem desenvolvidos, com distinção dos dígitos e fígado bem pronunciado. Os fetos com idade gestacional estimada em 52 dias (10cm CR) possuem estruturas internas e externas facilmente identificadas em animais adultos. Com relação às estruturas ósseas notamos que as mesmas não apresentam nenhuma epífise óssea formada, sendo visíveis somente as diáfises ósseas. Na análise microscópica, o embrião de idade gestacional de 19 dias (0,9cm CR) revelou a presença do rostro, cavidade oral com lábio superior e inferior, cavidade nasal, olho e a abertura do 4º ventrículo encefálico, esôfago, coração com átrio e ventrículo, pulmão, fígado, crista mesonéfrica, gônada primitiva, estômago, broto do membro torácico, coluna vertebral e a medula espinhal em formação. Esse trabalho é de grande importância para o estudo da morfologia externa e interna de gatos domésticos, principalmente no que diz respeito ao desenvolvimento ósseo e articular, considerando as alterações que podem ou não ser promovidas pelo uso de terapias medicamentosas ou celulares durante o desenvolvimento embrionário e fetal.

Characteristics of the equine embryo and fetus from days 15 to 107 of pregnancy

In spite of numerous, substantial advances in equine reproduction, many stages of embryonic and fetal morphological development are poorly understood, with no apparent single source of comprehensive information. Hence, the objective of the present study was to provide a complete macroscopic and microscopic description of the equine embryo/fetus at various gestational ages. Thirty-four embryos/fetuses were aged based on their crown rump length (CRL), and submitted to macroscopic description, biometry, light and scanning microscopy, as well as the alizarin technique. All observed developmental changes were chronologically ordered and described. As examples of the main observed features, an accentuated cervical curvature was observed upon macroscopic examination in all specimens. In the nervous system, the encephalic fourth ventricle and the encephalic vesicles forebrain, midbrain, and hindbrain, were visualized from Day 19 (ovulation = Day 0). The thoracic and pelvic limbs were also visualized; their extremities gave rise to the hoof during development from Day 27. Development of other structures such as pigmented optical vesicle, liver, tail, cardiac area, lungs, and dermal vascularization started on Days 25, 25, 19, 19, 34, and 35, respectively. Light and scanning microscopy facilitated detailed examinations of several organs, e.g., heart, kidneys, lungs, and intestine, whereas the alizarin technique enabled visualization of ossification. Observations in this study contributed to the knowledge regarding equine embryogenesis, and included much detailed data from many specimens collected over a long developmental interval.

Fetal liver-derived mesenchymal stem cell engraftment after allogeneic in utero transplantation into rabbits

Prenatal transplantation of genetically engineered mesenchymal stem cells (MSCs) might benefit prevention or treatment of early-onset genetic disorders due to the cells' intrinsic regenerative potential plus the acquired advantage from therapeutic transgene expression. However, a thorough assessment of the safety, accessibility, and behavior of these MSCs in the fetal environment using appropriate animal models is required before we can advance toward a clinical application. We have recently shown that fetal rabbit liver MSCs (fl-MSCs) have superior growth rate, clonogenic capability, and in vitro adherence and differentiation abilities compared with adult rabbit bone marrow MSCs. In this follow-up study, we report safe and widespread distribution of recombinant pSF-EGFP retrovirus-transduced fl-MSCs (EGFP(+)-fl-MSCs) in neonatal rabbit tissues at 10 days after fetal allogeneic transplantation through both intrahepatic and intra-amniotic administration. Conversely, a more restricted biodistribution pattern according to the route of administration was apparent in the young rabbits intervened at 16 weeks after fetal EGFP(+)-fl-MSC transplantation. Furthermore, the presence of these cells in the recipients' tissues, tracked with the reporter provirus, was inversely related to the developmental stage of the fetuses at the time of intervention. Long-term engraftment was confirmed both by fluorescence in situ hybridization analysis on touch tissue imprints using a chromosome Y-specific BAC probe, and by immunohistochemical localization of EGFP expression. Finally, there was no evidence of immune responses against the transplanted EGFP(+)-fl-MSCs or the EGFP transgenic product in the treated young rabbits. Thus, cell transplantation approaches using genetically engineered fetal MSCs may prove particularly valuable to frontier medical treatments for congenital birth defects in perinatology.

Os histricomorfos sul-americanos: uma análise comparativa do desenvolvimento embriológico

O objetivo do estudo foi realizar uma análise embriológica dos roedores histricomorfos (paca, cutia, preá e capivara), a fim de comparar com a de outros roedores e com a morfogênese humana um padrão embriológico. Utilizaram-se 8 espécimes de roedores sendo, 2 embriões para cada espécie coletada, ambas em inicio de gestação. Estes foram retirados dos úteros gestantes através de ovariosalpingohisterectomia parcial, seguido de fixação em solução de paraformaldeído 4%. Para as mensurações de Crow-Rump, adotou-se como referência a crista nucal numa extremidade e da última vértebra sacral na extremidade oposta. De forma geral, os embriões analisados mostraram as seguintes características morfológicas: divisão dos arcos branquiais, o não fechamento do neuróporo cranial em alguns embriões estudados, a curvatura cranial acentuada e os somitos delimitados e individualizados. O broto dos membros apresentava-se em desenvolvimento em formato de remo, além da impressão cardíaca e fígado. Na região caudal, visualizou-se a curvatura crânio-caudal, a vesícula óptica com e sem pigmentação da retina, a abertura do tubo neural na região do quarto ventrículo encefálico, a fosseta nasal e a formação das vesículas encefálicas. Concluímos que desenvolvimento embriológico dos roedores histricomorfos pode ser comparado à morfogênese de ratos, cobaios, coelhos e humanos nos diferentes estágios de desenvolvimento, tomando apenas o cuidado com as particularidades de cada espécie, além da implementação de tecnologias reprodutivas, especialmente a de embriões, a qual requer o conhecimento do desenvolvimento pré-implantação referente às fases de desenvolvimento.

Embryopathic effects of thalidomide and its hydrolysis products in rabbit embryo culture: evidence for a prostaglandin H synthase (PHS)-dependent, reactive oxygen species (ROS)-mediated mechanism

Thalidomide (TD) causes birth defects in humans and rabbits via several potential mechanisms, including bioactivation by embryonic prostaglandin H synthase (PHS) enzymes to a reactive intermediate that enhances reactive oxygen species (ROS) formation. We show herein that TD in rabbit embryo culture produces relevant embryopathies, including decreases in head/brain development by 28% and limb bud growth by 71% (P<0.05). Two TD hydrolysis products, 2-phthalimidoglutaramic acid (PGMA) and 2-phthalimidoglutaric acid (PGA), were similarly embryopathic, attenuating otic vesicle (ear) and limb bud formation by up to 36 and 77%, respectively (P<0.05). TD, PGMA, and PGA all increased embryonic DNA oxidation measured as 8-oxoguanine (8-oxoG) by up to 2-fold (P<0.05). Co- or pretreatment with the PHS inhibitors eicosatetraynoic acid (ETYA) or acetylsalicylic acid (ASA), or the free-radical spin trap phenylbutylnitrone (PBN), completely blocked embryonic 8-oxoG formation and/or embryopathies initiated by TD, PGMA, and PGA. This is the first demonstration of limb bud embryopathies initiated by TD, as well as its hydrolysis products, in a mammalian embryo culture model of a species susceptible to TD in vivo, indicating that all likely contribute to TD teratogenicity in vivo, in part through PHS-dependent, ROS-mediated mechanisms.

Doppler evaluation of maternal and fetal vessels during normal gestation in rabbits

The aim of this work was to evaluate the hemodynamic changes in the utero-placental arterial vessels in rabbits (Orictolagus cuniculus) throughout pregnancy as well as those in the umbilical cord, aorta, and caudal vena cava of fetuses to establish their normal reference ranges for systolic peak velocity (SPV), end diastolic velocity (EDV), pulsatility index (PI), and resistance index (RI). The blood flow waveforms were monitored every 4 d in 10 rabbits from Day 10 of pregnancy onward by means of color and pulsed wave Doppler ultrasonography using a 5.5-7.5 MHz microconvex transabdominal probe. The utero-placental blood flow was characterized by steep increases and decrease in the SPV with a slow diastolic wave and relatively high EDV, whereas that of the umbilical artery was discontinuous until Day 22 of pregnancy, when a diastolic waveform was also detectable. From Day 10 to 22 of pregnancy, the fetal aorta blood flow was discontinuous, but thereafter a diastolic peak was measurable. The blood flow of the fetal caudal vena cava was characterized by a systolic peak followed by a small diastolic peak. Throughout the gestation, the SPV and the EDV of maternal and fetal vessels increased (alpha<0.05), whereas the PI and the RI decreased (alpha<0.05), except for the utero-placental vessels. This work confirms that the rabbit could also be a valid experimental animal model to study, by Doppler ultrasonography, functional hemodynamic changes of the fetuses and placenta vessels in both normal and pathophysiologic conditions.

Feasibility of retroviral vector-mediated in utero gene transfer to the fetal rabbit

OBJECTIVES

Successful treatment or prevention of severe hereditary diseases could conceivably be achieved by genetic intervention early in development. Viral vector-mediated fetal gene transfer is proving a valuable tool to test the above concept in relevant animal models. Although the pregnant rabbit is a well-recognized model for fetal therapy, few preclinical assays have used it to validate fetal gene transfer approaches. In this preliminary study we assessed for the first time the feasibility of retroviral vector-mediated in utero gene transfer in the fetal rabbit.

METHODS

Different amounts of the vesicular stomatitis virus G pseudotyped MFG(nls)LacZ retroviral vector, expressing a nuclear-localized beta-galactosidase reporter protein were injected intraperitoneally and -hepatically into 20- to 22-day-old fetuses. At 8-9 days post-treatment, the pups were sacrificed and the tissues harvested for analysis. Evidence of gene transfer was obtained by PCR amplification of proviral sequences within genomic DNA isolated from the treated samples. Transgenic beta-galactosidase expression was assessed by X-gal histochemical staining.

RESULTS

By intraperitoneal injection 43% of the viable fetuses treated (3/7) showed evidence of successful LacZ gene transfer and low-level beta-galactosidase expression into liver and heart, whereas by intrahepatic injection roughly 38% (3/8) of the livers were positive for LacZ gene transfer and expression. The success rate for the viable fetuses rose to 67% positive livers (4/6) when a near double amount of recombinant virus was injected using a 10-fold concentrated virus stock. In terms of short-term safety, fetal and maternal survival rates approached 80% of treated fetuses, and 100% of treated does.

CONCLUSIONS

The pregnant rabbit is a useful and reliable model allowing the design of further studies to optimize the conditions for effective, safer, and persistent retroviral vector-mediated fetal gene transfer.

Teratogenic effects in rabbits of simultaneous exposure to ochratoxin A and aflatoxin B1 with special reference to microscopic effects

To elucidate the teratogenic effects, ochratoxin A (OTA) and aflatoxin B1 (AFB1) were dissolved in corn oil and administered in combination to New Zealand White rabbits during 6-18 days of gestation orally with the dose levels of OTA+AFB1, 0.05+0.05 and 0.1+0.1mg/kg body weight. To assess pathomorphological features of the anomalies, the fetal serial sections were histologically examined. There was no mortality in any of the treated groups. Body weights and body weight gains of dams in the combined treatment groups were comparable with those of controls and individual treatments. The mean crown to rump lengths in both the combination dose groups and mean fetal weights in high dose combination group were significantly decreased. In the high dose combination, there was increase in the percent of implants resorbed and significant increase in the incidence of visceral anomalies. The combination treatment resulted in various gross, skeletal and visceral anomalies such as wrist drop, scoliosis, bent metacarpals, rudimentary ribs, cardiac defects and microphthalmia. There was a dose-related increase in the percent of litters showing the histopathological changes in the fetal tissues. The incidence of histopathological changes in the tissue sections prepared from fetal liver, kidneys, brain, heart and eyes was found increased in the high dose combination group. The comparative evaluation of the results of combination versus individual treatments revealed that certain anomalies observed in the individual treatment of OTA such as knuckling of fetlock, rudimentary tail or agenesis of tail, wavy ribs, hydrocephalus and agenesis of kidney and AFB1 as enlarged eye sockets and enlarged liver were absent in the combination treatment. However, some new manifestations such as cardiac defects and scoliosis were seen. The results of the present study indicated that in combination, OTA and AFB1 have antagonistic interaction. The presence of subtle lesions histologically due to an interference with normal development suggested that microscopic examination of the fetal tissues could provide additional, useful information to a developmental toxicity study.

Effects of aflatoxin B1 on embryo fetal development in rabbits

Aflatoxin B1 (AFB1), is a food borne mycotoxin produced by fungal species of the genera Aspergillus. To elucidate the teratogenic effects, AFB1 was dissolved in corn oil and given orally to New Zealand White rabbits during 6-18 days of gestation with the dose levels of 0.025, 0.05 and 0.1 mg/kg body weight. To assess pathomorphological features of the anomalies induced by AFB1, the fetal serial sections were histologically examined. There was no maternal mortality in any group. There was non-significant decrease in percent of live fetuses and increase in the percent resorptions and post-implantation losses at 0.1 mg/kg dose group as compared with those of controls. The mean crown to rump lengths of 0.05 and 0.1 mg/kg dose groups were significantly reduced than that of the control. The mean fetal weights were significantly reduced in 0.1 mg/kg dose group than that of other treated groups. The gross anomalies observed included wrist drop and enlarged eye socket whereas, skeletal anomalies were agenesis of caudal vertebrae, incomplete ossification of skull bones and bent metacarpals. The visceral anomalies of microphthalmia and cardiac defects were seen at 0.1 mg/kg dose group. The characteristic histological findings of fetal tissues were distortion of normal hepatic cord pattern and reduced megakaryocytes in liver, fusion of auriculo-ventricular valves, mild degenerative changes in myocardial fibers, microphthalmic eyes and lenticular degeneration. The results of this study indicated that AFB1 was found to be teratogenic in rabbits when given by oral route during gestation days 6-18 and the dose of 0.1 mg/kg could be considered as the minimum oral teratogenic dose. The histological examination of the fetal tissues indicated its importance in identifying the visceral anomalies which were otherwise not visible.