Behavioral response of altricial and precocial rodent fetuses to acute umbilical cord compression

Three-Dimensional Imaging Analysis of the Developmental Process of Posterior Meniscofemoral Ligaments in Rat Embryos

INTRODUCTION

The posterior meniscofemoral ligament (pMFL) of knee joint is a ligament that runs posterior to the posterior cruciate ligament and it is known that the height of the pMFL attachment site causes meniscus avulsion. Therefore, understanding the three-dimensional (3D) structure of the pMFL attachment site is essential to better understand the pathogenesis of meniscus disorders. However, the developmental process of pMFL has not been well investigated. The purpose of this study was to analyze pMFL development in rat knee joints using 3D reconstructed images produced from episcopic fluorescence image capture (EFIC) images and examine its relationship with other knee joint components.

METHODS

Knee joints of Wistar rat embryos between embryonic day (E) 16 and E21 were observed with HE-stained tissues. Serial EFIC images of the hind limbs of E17-E21 were, respectively, captured from which 3D images were reconstructed and the features of pMFL structure: length and angle were measured. Besides, the chronological volume changes and the volume ratio of the knee joint components compared to E17 were calculated to identify the differences in growth by components.

RESULTS

pMFL was observed from E17 and was attached to the medial femoral condyle and lateral meniscus at all developmental stages, as in mature rats. The lack of marked variation in the attachment site and angle of the pMFL with the developmental stage indicates that the pMFL and surrounding knee joint components developed while maintaining their positional relationship from the onset of development.

CONCLUSION

Current results may support to congenital etiology of meniscus disorder.

A remarkable rodent: Regeneration and reproduction in spiny mice (Acomys)

Although certain organisms are chosen and employed to better understand a specific problem in biology (so-called model organisms), sometimes an animal model reveals its' biomedical importance by happenstance. In many ways, the advent of spiny mice (Acomys) as an emerging model to study regeneration and menstruation stands as a case study in scientific pseudoserendipity (Diaz de Chumaceiro, 1995). As we recount in this chapter, the discovery of these phenotypes, while not entirely accidental, was nonetheless unexpected. In addition to recounting how we uncovered these unusual mammalian traits, we outline recent work by our groups and others that has begun to outline the cellular and genetic mechanisms underlying bonafide mammalian tissue regeneration and a human-like mode of reproduction in spiny mice.

Model systems for regeneration: the spiny mouse, Acomys cahirinus

The spiny mouse, Acomys spp., is a recently described model organism for regeneration studies. For a mammal, it displays surprising powers of regeneration because it does not fibrose (i.e. scar) in response to tissue injury as most other mammals, including humans, do. In this Primer article, we review these regenerative abilities, highlighting the phylogenetic position of the spiny mouse relative to other rodents. We also briefly describe the Acomys tissues that have been used for regeneration studies and the common features of their regeneration compared with the typical mammalian response. Finally, we discuss the contribution that Acomys has made in understanding the general principles of regeneration and elaborate hypotheses as to why this mammal is successful at regenerating.

Neuroimaging perspectives on fetal motor behavior

We are entering a new era of understanding human development with the ability to perform studies at the earliest time points possible. There is a substantial body of evidence to support the concept that early motor behaviour originates from supraspinal motor centres, reflects neurological integrity, and that altered patterns of behaviour precede clinical manifestation of disease. Cine Magnetic Resonance Imaging (cineMRI) has established its value as a novel method to visualise motor behaviour in the human fetus, building on the wealth of knowledge gleaned from ultrasound based studies. This paper presents a state of the art review incorporating findings from human and preclinical models, the insights from which, we propose, can proceed a reconceptualisation of fetal motor behaviour using advanced imaging techniques. Foremost is the need to better understand the role of the intrauterine environment, and its inherent unique set of stimuli that activate sensorimotor pathways and shape early brain development. Finally, an improved model of early motor development, combined with multimodal imaging, will provide a novel source of in utero biomarkers predictive of neurodevelopmental disorders.

Responsiveness of rat fetuses to sibling motor activity: Communication in utero?

Previous research has revealed that fetuses detect and respond to extrauterine stimuli such as maternal movement and speech, but little attention has been cast on how fetuses may directly influence and respond to each other in the womb. This study investigated whether motor activity of E20 rat fetuses influenced the behavior of siblings in utero. Three experiments showed that; (a) contiguous siblings expressed a higher frequency of synchronized movement than noncontiguous siblings; (b) fetuses that lay between two siblings immobilized with curare showed less movement relative to fetuses between saline or uninjected controls; and (c) fetuses between two siblings behaviorally activated by the opioid agonist U50,488 also showed less activity and specific behavioral changes compared to controls. Our findings suggest that rat fetuses are directly impacted by sibling motor activity, and thus that a rudimentary form of communication between siblings may influence the development of fetuses in utero.

Prenatal behavior of the C57BL/6J mouse: a promising model for human fetal movement during early to mid-gestation

The study of fetal neurobehavioral development in genetically altered mice promises a significant advance in our understanding of the prenatal origins of developmental disabilities in humans. Despite their importance, little is known about fetal neurobehavioral development in mice. In this study, we observed prenatal behavioral patterns of the C57BL/6J mouse, a common background strain for genetically altered mice, and report their similarity to those observed in the early to mid-gestation human fetus. Fetal offspring from pregnant C57BL/6J dams were observed on the day before birth (E18 of a 19-day gestation). Scoring and analysis of fetal movement included Prechtl's Method for Qualitative Assessment, Interlimb Movement Synchrony, a measure of the temporal relationship between movements of limb pairs, and Behavioral State, quantified through detailed analysis of high and low amplitude limb movements. With the exception of fetal breathing movements, all categories and patterns of behavior typically reported in the early to mid-gestation human fetus were observed in the C57BL/6J mouse fetus. Our results suggest that behavioral analysis of fetal C57BL/6J mice may yield important new insights into early to mid-gestation human behavioral development.

Prenatal Development of Interlimb Motor Learning in the Rat Fetus

The role of sensory feedback in the early ontogeny of motor coordination remains a topic of speculation and debate. On E20 of gestation (the 20th day after conception, 2 days before birth), rat fetuses can alter interlimb coordination after a period of training with an interlimb yoke, which constrains limb movement and promotes synchronized, conjugate movement of the yoked limbs. The aim of this study was to determine how the ability to express this form of motor learning may change during prenatal development. Fetal rats were prepared for in vivo study at 4 ages (E18-21) and tested in a 65-min training-and-testing session examining hind limb motor learning. A significant increase in conjugate hind limb activity was expressed by E19, but not E18 fetuses, with further increases in conjugate hind limb activity on E20 and E21. These findings suggest substantial development of the ability of fetal rats to modify patterns of interlimb coordination in response to kinesthetic feedback during motor training before birth.

Fetal behavior and the endogenous opioid system: D1 dopamine receptor interactions with the kappa opioid system

Opioid or dopaminergic drugs can alter the motor behavior of rat fetuses on day 21 of gestation (E21). This study was conducted to a) characterize the behavioral effects of specific opioid agonists in the fetus, b) determine the effects of selective blockade of opioid receptors, and c) characterize the interaction between the dopamine and kappa opioid systems. Neither morphine nor the mu agonist DAMGO produced effects on fetal motor activity, whereas the kappa agonist U50,488 resulted in a pronounced increase in motor behavior. The selective antagonists beta-funaltrexamine (mu) and nor-binaltorphimine (kappa) produced no behavioral effects when administered alone. The D1 antagonist SCH-23390 did not reverse the activational effects produced by U50,488, but the kappa antagonist nor-binaltorphimine successfully blocked the increases in fetal behavior produced by the D1 agonist SKF-38393. These results are consistent with the hypothesis that activation of the dopamine system promotes activity at kappa opioid receptors to bring about changes in fetal motor activity.

Fundamental motor patterns of the mammalian fetus

Techniques that permit direct observation of fetuses in vivo recently have expanded our understanding of prenatal behavioral development in mammals. Although fetal motor activity seems to lack the dynamic, goal-directed character of postnatal behavior, the dimensions that define behavioral organization after birth are applicable to the movements expressed by fetuses. Fetal activity exhibits temporal, sequential, and spatial organization that emerges between the inception of movement and term. Fetal rodents, for example, exhibit coordinated motor patterns antecedent to postnatal righting, locomotion, suckling, maternal-infant communication and grooming behavior, while other action patterns appear to be functional adaptations to the intrauterine niche. Fetuses also are behaviorally responsive to sensory stimulation and changes in environmental conditions in utero. Expression of these behavioral properties emphasizes continuity between prenatal and postnatal life while implying an adaptive role for behavior before birth.