The development of spontaneous body movement in prenatal and perinatal mice

A systematic investigation of the effects of TGF-β3 and mechanical stimulation on tenogenic differentiation of mesenchymal stromal cells in a poly(ethylene glycol)/gelatin-based hydrogel

Background

High post-surgical failure rates following tendon injury generate high medical costs and poor patient recovery. Cell-based tendon tissue engineering has the potential to produce fully functional replacement tissue and provide new strategies to restore tendon function and healing. In this endeavour, the application of mesenchymal stromal cells (MSCs) encapsulated in biomaterial scaffolds has shown great promise. However, a consensus on optimal promotion of tenogenic differentiation of MSCs has yet to be reached, although growth factors and mechanical cues are generally acknowledged as important factors.

Methods

In this study, we prepared a hydrogel cell culture system consisting of methacrylated poly(d,l-lactic acid-ethylene glycol-d,l-lactic acid) (P(LA-EG-LA)) and gelatin methacrylate (GelMA) to encapsulate human bone marrow-derived MSCs (hBMSCs). We further systematically investigated the influence of static and intermittent cyclic uniaxial strain mechanical stimulation, in combination with transforming growth factor-β3 (TGF-β3) supplementation, on tenogenic differentiation of hBMSCs.

Results

Increased TGF-β3 concentration upregulated the tenogenic genes Scleraxis (SCX) and collagen type I (COL1A1) but showed no effects on tenascin-c (TNC) and collagen type III (COL3A1) expression. Mechanical stimulation had no observable effect on gene expression, but intermittent cyclic uniaxial strain stimulation improved matrix deposition. Together, these data provide new insights into how TGF-β3 and mechanical stimulation regulate MSC tenogenesis, with TGF-β3 promoting the expression of key tenogenic genes whilst mechanical stimulation aided matrix deposition in the engineered tissue. Furthermore, intermittent cyclic uniaxial strain at 3% elongation and 0.33 ​Hz for 1 ​h/day showed improved matrix effects compared to static strain.

Conclusion

Together, the most promising result for tenogenic differentiation of hBMSCs was identified as treatment with 5 ​ng/ml TGF-β3 under intermittent cyclic uniaxial strain (3% strain; 0.33 ​Hz; 1 ​h/day). This knowledge is of importance for the development of an improved protocol for tenogenic differentiation of MSCs and thereby for tendon tissue engineering.

The translational potential of this article

Tissue-engineered strategies for tendon repair require a consensus on the differentiation of mesenchymal stromal cells to tenocytes, which is currently lacking. This article provides a systematic investigation of two main tenogenic differentiation conditions to further development of a tenogenic differentiation protocol.

Lack of skeletal muscle contraction disrupts fibrous tissue morphogenesis in the developing murine knee

Externally applied forces, such as those generated through skeletal muscle contraction, are important to embryonic joint formation, and their loss can result in gross morphologic defects including joint fusion. While the absence of muscle contraction in the developing chick embryo leads to dissociation of dense connective tissue structures of the knee and ultimately joint fusion, the central knee joint cavitates whereas the patellofemoral joint does not in murine models lacking skeletal muscle contraction, suggesting a milder phenotype. These differential results suggest that muscle contraction may not have as prominent of a role in the growth and development of dense connective tissues of the knee. To explore this question, we investigated the formation of the menisci, tendon, and ligaments of the developing knee in two murine models that lack muscle contraction. We found that while the knee joint does cavitate, there were multiple abnormalities in the menisci, patellar tendon, and cruciate ligaments. The initial cellular condensation of the menisci was disrupted and dissociation was observed at later embryonic stages. The initial cell condensation of the tendon and ligaments were less affected than the meniscus, but these tissues contained cells with hyper-elongated nuclei and displayed diminished growth. Interestingly, lack of muscle contraction led to the formation of an ectopic ligamentous structure in the anterior region of the joint as well. These results indicate that muscle forces are essential for the continued growth and maturation of these structures during this embryonic period.

Mechanical loading is required for initiation of extracellular matrix deposition at the developing murine myotendinous junction

The myotendinous junction (MTJ) contributes to the generation of motion by connecting muscle to tendon. At the adult MTJ, a specialized extracellular matrix (ECM) is thought to contribute to the mechanical integrity of the muscle-tendon interface, but the factors that influence MTJ formation during mammalian development are unclear. Here, we combined 3D imaging and proteomics with murine models in which muscle contractility and patterning are disrupted to resolve morphological and compositional changes in the ECM during MTJ development. We found that MTJ-specific ECM deposition can be initiated via static loading due to growth; however, it required cyclic loading to develop a mature morphology. Furthermore, the MTJ can mature without the tendon terminating into cartilage. Based on these results, we describe a model wherein MTJ development depends on mechanical loading but not insertion into an enthesis.

Robust alternative to the righting reflex to assess arousal in rodents

The righting reflex (RR) is frequently used to assess level of arousal and applied to animal models of a range of neurological disorders. RR produces a binary result that, when positive, is used to infer restoration of consciousness, often without further behavioral corroboration. We find that RR is an unreliable metric for arousal/recovery of consciousness. Instead, cortical activity and motor behavior that accompany RR are a non-binary, superior criterion that accurately calibrates and establishes level of arousal in rodents.

The Development of Integration in Marsupial and Placental Limbs

The morphological interdependence of traits, or their integration, is commonly thought to influence their evolution. As such, study of morphological integration and the factors responsible for its generation form an important branch of the field of morphological evolution. However, most research to date on post-cranial morphological integration has focused on adult patterns of integration. This study investigates patterns of correlation (i.e., morphological integration) among skeletal elements of the fore- and hind limbs of developing marsupial and placental mammals. The goals of this study are to establish how patterns of limb integration vary over development in marsupials and placentals, and identify factors that are likely responsible for their generation. Our results indicate that although the overall pattern of correlation among limb elements is consistent with adult integration throughout mammalian development, correlations vary at the level of the individual element and stage. As a result, the relative integration among fore- and hind limb elements varies dynamically between stages during development in both marsupial and placental mammals. Therefore, adult integration studies of the limbs may not be indicative of developmental integration. Results are also consistent with integration during early limb development being more heavily influenced by genetic and developmental factors, and later by function. Additionally, results are generally consistent with a constraint on marsupial forelimb evolution caused by the functional requirements of the crawl to the teat that operates by limiting morphological variation before and at the time of birth, and not after.

Distinct transcriptomic changes in E14.5 mouse skeletal muscle lacking RYR1 or Cav1.1 converge at E18.5

In skeletal muscle the coordinated actions of two mechanically coupled Ca2+ channels-the 1,4-dihydropyridine receptor (Cav1.1) and the type 1 ryanodine receptor (RYR1)-underlie the molecular mechanism of rapid cytosolic [Ca2+] increase leading to contraction. While both [Ca2+]i and contractile activity have been implicated in the regulation of myogenesis, less is known about potential specific roles of Cav1.1 and RYR1 in skeletal muscle development. In this study, we analyzed the histology and the transcriptomic changes occurring at E14.5 -the end of primary myogenesis and around the onset of intrauterine limb movement, and at E18.5 -the end of secondary myogenesis, in WT, RYR1-/-, and Cav1.1-/- murine limb skeletal muscle. At E14.5 the muscle histology of both mutants exhibited initial alterations, which became much more severe at E18.5. Immunohistological analysis also revealed higher levels of activated caspase-3 in the Cav1.1-/- muscles at E14.5, indicating an increase in apoptosis. With WT littermates as controls, microarray analyses identified 61 and 97 differentially regulated genes (DEGs) at E14.5, and 493 and 1047 DEGs at E18.5, in RYR1-/- and Cav1.1-/- samples, respectively. Gene enrichment analysis detected no overlap in the affected biological processes and pathways in the two mutants at E14.5, whereas at E18.5 there was a significant overlap of DEGs in both mutants, affecting predominantly processes linked to muscle contraction. Moreover, the E18.5 vs. E14.5 comparison revealed multiple genotype-specific DEGs involved in contraction, cell cycle and miRNA-mediated signaling in WT, neuronal and bone development in RYR1-/-, and lipid metabolism in Cav1.1-/- samples. Taken together, our study reveals discrete changes in the global transcriptome occurring in limb skeletal muscle from E14.5 to E18.5 in WT, RYR1-/- and Cav1.1-/- mice. Our results suggest distinct functional roles for RYR1 and Cav1.1 in skeletal primary and secondary myogenesis.

Comparative analysis of mesenchymal stem cell and embryonic tendon progenitor cell response to embryonic tendon biochemical and mechanical factors

Introduction

Advances in tendon engineering with mesenchymal stem cells (MSCs) are hindered by a need for cues to direct tenogenesis, and markers to assess tenogenic state. We examined the effects of factors involved in embryonic tendon development on adult MSCs, and compared MSC responses to that of embryonic tendon progenitor cells (TPCs), a model system of tenogenically differentiating cells.

Methods

Murine MSCs and TPCs subjected to cyclic tensile loading, transforming growth factor-β2 (TGFβ2), and fibroblast growth factor-4 (FGF4) in vitro were assessed for proliferation and mRNA levels of scleraxis, TGFβ2, tenomodulin, collagen type I and elastin.

Results

Before treatment, scleraxis and elastin levels in MSCs were lower than in TPCs, while other tendon markers expressed at similar levels in MSCs as TPCs. TGFβ2 alone and combined with loading were tenogenic based on increased scleraxis levels in both MSCs and TPCs. Loading alone had minimal effect. FGF4 downregulated tendon marker levels in MSCs but not in TPCs. Select tendon markers were not consistently upregulated with scleraxis, demonstrating the importance of characterizing a profile of markers.

Conclusions

Similar responses as TPCs to specific treatments suggest MSCs have tenogenic potential. Potentially shared mechanisms of cell function between MSCs and TPCs should be investigated in longer term studies.

Embryonic mechanical and soluble cues regulate tendon progenitor cell gene expression as a function of developmental stage and anatomical origin

Stem cell-based engineering strategies for tendons have yet to yield a normal functional tissue, due in part to a need for tenogenic factors. Additionally, the ability to evaluate differentiation has been challenged by a lack of markers for differentiation. We propose to inform tendon regeneration with developmental cues involved in normal tissue formation and with phenotypic markers that are characteristic of differentiating tendon progenitor cells (TPCs). Mechanical forces, fibroblast growth factor (FGF)-4 and transforming growth factor (TGF)-β2 are implicated in embryonic tendon development, yet the isolated effects of these factors on differentiating TPCs are unknown. Additionally, developmental mechanisms vary between limb and axial tendons, suggesting the respective cell types are programmed to respond uniquely to exogenous factors. To characterize developmental cues and benchmarks for differentiation toward limb vs. axial phenotypes, we dynamically loaded and treated TPCs with growth factors and assessed gene expression profiles as a function of developmental stage and anatomical origin. Based on scleraxis expression, TGFβ2 was tenogenic for TPCs at all stages, while loading was for late-stage cells only, and FGF4 had no effect despite regulation of other genes. When factors were combined, TGFβ2 continued to be tenogenic, while FGF4 appeared anti-tenogenic. Various treatments elicited distinct responses by axial vs. limb TPCs of specific stages. These results identified tenogenic factors, suggest tendon engineering strategies should be customized for tissues by anatomical origin, and provide stage-specific gene expression profiles of limb and axial TPCs as benchmarks with which to monitor tenogenic differentiation of stem cells.

Mechanical factors in embryonic tendon development: potential cues for stem cell tenogenesis

Tendons are connective tissues required for motion and are frequently injured. Poor healing and inadequate return to normal tissue structure and mechanical function make tendon a prime candidate for tissue engineering; however functional tendons have yet to be engineered. The physical environment, from substrate stiffness to dynamic mechanical loading, may regulate tenogenic stem cell differentiation. Tissue stiffness and loading parameters derived from embryonic development may enhance tenogenic stem cell differentiation and tendon tissue formation. We highlight the current understanding of the mechanical environment experienced by embryonic tendons and how progenitor cells may sense and respond to physical inputs. We further discuss how mechanical factors have only recently been used to induce tenogenic fate in stem cells.

beta-Catenin protects the epidermis from mechanical stresses

β-Catenin provides stability to epithelia exposed to mechanical stress in part by strengthening adherens junctions in response to tension.

Many tissues in our body experience mechanical stresses caused by both internal and external forces. The skin, for example, must tolerate diverse mechanical insults. In this paper, we report a role for β-catenin in providing stability to epithelia under stress. Loss of β-catenin during epidermal development caused perinatal lethality. Mutant embryos up-regulated stress responses at sites of active morphogenesis, which became more widespread after the stresses associated with birth. In addition, selective loss of tight junctions occurred in focal regions. This was recapitulated in cultured β-catenin–null cells exposed to externally applied forces. In addition, mutant cells were defective in tension-induced engagement of adherens junctions. We found that β-catenin was required to recruit vinculin to the cell cortex and to strengthen the junction’s association with the underlying cytoskeleton in response to tension. These data demonstrate that a complete understanding of the functions of cell adhesion proteins must take into account their roles in response to mechanical stresses.

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.

The dysraphic levels of skin and vertebrae are different in mouse fetuses and neonates with myelomeningocele

BACKGROUND

Mouse fetuses with spontaneous myelomeningocele (MMC) were investigated, determining the various levels of dysraphism in soft tissue, spinal cord, and vertebrae. Morphology was correlated with hind limb function.

METHODS

Viable curly tail/loop tail mouse fetuses underwent qualitative standardized ex utero examination of tail and hind limb sensitivity and motor response. Afterward, they were processed either for histology or skeletal preparation.

RESULTS

All animals displayed identical cranial levels of soft tissue and neural defects. The cranial opening of the vertebral defects were invariably located more cranially (range, 0.5-5 vertebrae; mean = 2.25). The caudal opening of soft/neural tissue and bony defects was invariably at the coccygeal base. The comparison of functional with morphological levels demonstrated that, in 52.5%, the level of the soft/neural tissue dysraphism and, in 47.5%, the level of the bony opening correlated with the neurologic deficit.

CONCLUSION

The naturally occurring soft tissue coverage over the MMC could exert a protective effect toward the underlying spinal cord. This interpretation supports the concept that in utero acquired destruction of exposed neural tissue is a main factor for the neonatal functional deficit. Thus, these data are consistent with the rationale for prenatal MMC repair in humans.

The development of descending projections from the brainstem to the spinal cord in the fetal sheep

Background

Although the fetal sheep is a favoured model for studying the ontogeny of physiological control systems, there are no descriptions of the timing of arrival of the projections of supraspinal origin that regulate somatic and visceral function. In the early development of birds and mammals, spontaneous motor activity is generated within spinal circuits, but as development proceeds, a distinct change occurs in spontaneous motor patterns that is dependent on the presence of intact, descending inputs to the spinal cord. In the fetal sheep, this change occurs at approximately 65 days gestation (G65), so we therefore hypothesised that spinally-projecting axons from the neurons responsible for transforming fetal behaviour must arrive at the spinal cord level shortly before G65. Accordingly we aimed to identify the brainstem neurons that send projections to the spinal cord in the mature sheep fetus at G140 (term = G147) with retrograde tracing, and thus to establish whether any projections from the brainstem were absent from the spinal cord at G55, an age prior to the marked change in fetal motor activity has occurred.

Results

At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract. This pattern of labelling is similar to that previously reported in other species. The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus.

Conclusion

The brainstem nuclei that contain neurons which project axons to the spinal cord in the fetal sheep are the same as in other mammalian species. All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation. The demonstration that the neurons responsible for transforming fetal behaviour in early ontogeny have already reached the spinal cord by G55, an age well before the change in motor behaviour occurs, suggests that the projections do not become fully functional until well after their arrival at the spinal cord.

Fetal spina bifida in a mouse model: loss of neural function in utero

OBJECT

The devastating neurological deficit associated with myelomeningocele has previously been assumed to be a direct and inevitable consequence of the primary malformation-failure of neural tube closure. An alternative view is that secondary damage to the pathologically exposed spinal cord tissue in utero is responsible for the neurological deficiency. If the latter mechanism were shown to be correct, it would provide an objective rationale for the performance of in utero surgery for myelomeningocele, because coverage of the exposed spinal cord could be expected to alleviate or perhaps prevent neurodegeneration. To examine this question, the authors studied the development of neuronal connections and neurological function of mice during fetal and neonatal stages in a genetic model of exposed lumbosacral spina bifida.

METHODS

The persistently exposed spinal cord of mouse fetuses carrying both curly tail and loop-tail mutations exhibited essentially normal anatomical and functional hallmarks of development during early gestation (embryonic Days 13.5-16.5), including sensory and motor projections to and from the cord. A significant proportion of fetuses with spina bifida at early gestation exhibited sensorimotor function identical to that seen in age-matched healthy controls. However, at later gestational stages, increasing neurodegeneration within the spina bifida lesion was detected, which was paralleled by a progressive loss of neurological function.

CONCLUSIONS

These findings provide support for the hypothesis that neurological deficit in human myelomeningocele arises following secondary neural tissue destruction and loss of function during pregnancy.

Development of spontaneous mouth/tongue movement and related neural activity, and their repression in fetal mice lacking glutamate decarboxylase 67

Spontaneous body movement starts at early fetal stage, at embryonic day (E) 12-15 in mice. In the present study, the movement of the head region was studied in E13-14 mice by in utero ultrasound imaging, together with the in vitro recording of underlying neural activities in the hypoglossal nerve and the ventral root of the upper cervical cord of an isolated brainstem-spinal cord preparation. The role of gamma-aminobutyric acid (GABA) in the generation of fetal movement was assessed using mice lacking GABA-synthesizing glutamate decarboxylase 67 (GAD67). At E14, mouth opening and tongue withdrawal were observed independently at frequency of 14/h each. This movement was rarely observed in the GAD67-deficient mouse. The intraventricular administration of picrotoxin or 3-mercaptopropionic acid abolished mouth opening in the wild-type mice. In a brainstem-spinal cord preparation, three types of neural discharge were recorded: mouth/tongue-moving burst, respiratory burst and irregular activity on the basis of their waveform, regularity in occurrence and concomitant muscle activity. In the GAD67-deficient mice, the occurrence of mouth/tongue-moving burst and irregular activity was inhibited to about 15 and 40% of those in the wild-type mice, respectively. Respiratory burst was slightly inhibited but the difference was not significant. Picrotoxin greatly reduced the frequency of mouth/tongue-moving burst. These results indicate that GABA is involved in rhythm generation in movement of the head region and support the hypothesis that cleft palate in the GAD67-deficient mouse is due to the impairment of mouth or tongue movement that assists palate formation.

Development of interlimb movement synchrony in the rat fetus

In the fetal rat, interlimb synchrony is a prominent form of temporally organized spontaneous motor activity in which movement of different limbs occurs at nearly the same instant. In the present study, synchrony profiles were created for different pairwise combinations of limbs over the last 5 days of gestation. Observed rates of synchrony differentiated from randomized time series from Gestational Day 19 to Day 21 (E19-E21), with forelimb synchrony emerging earlier than that of other limb pairs. Synchrony profiles were elevated at the shortest intervals between successive limb movements, indicating that movements became more tightly coupled toward the end of gestation. Interlimb synchrony appears to be a robust method of quantifying fetal movement and may prove useful as a tool for assessing prenatal nervous system functioning.

Distribution of cartilage molecules in the developing mouse joint

This study describes the precise spatial and temporal patterns of protein distribution for aggrecan, fibromodulin, cartilage oligomeric matrix protein (COMP) and cartilage matrix protein (CMP) in the developing mouse limb with particular attention to those cells destined to form articular chondrocytes in comparison to those cells destined to form a mineralized tissue and become replaced by bone. Mouse glenohumeral joints from fetal mice (12-18 days post coitus (dpc) to the young adult (37 days after birth) were immunostained with antibodies specific for these molecules. Aggrecan staining defined the general chondrocytic phenotype, whether articular or transient. Fibromodulin was associated with prechondrocytic mesenchymal cells in the interzone prior to joint cavitation and with the mesenchymal cells of the perichondrium or the periosteum encapsulating the joint elements of the maturing and young adult limb. Staining was most intense around developing articular chondrocytes and much less abundant or absent in those differentiating cells along the anlage. CMP showed an almost reciprocal staining pattern to fibromodulin and was not detected in the matrix surrounding articular chondrocytes. COMP was not detected in the cells at the articular surface prior to cavitation but by 18 dpc, as coordinated movement of the mouse forelimb intensifies, staining for COMP was most intense around the maturing articular chondrocytes. These results show that the cells that differentiate into articular chondrocytes elaborate an extracellular matrix distinct from those cells that are destined to form bone. Fibromodulin may function in the early genesis of articular cartilage and COMP may be associated with elaboration of a weight-bearing chondrocyte matrix.

Highly reproducible spatiotemporal patterns of mammalian embryonic movements at the developmental stage of the earliest spontaneous motility

The principles underlying the variations in patterns of mammalian embryonic movements have not been established. In an attempt to clarify the mechanism that is responsible for the variations in motor patterns, we carried out a precise quantitative spatiotemporal analysis of movements in mouse embryos, using a transplacental perfusion method for the in vitro maintenance of live mammalian embryos. Episodes of spontaneous movements at the inception of motility, at embryonic day 12.5, occurred once every few minutes, lasted for several seconds and consisted of successive movements of body regions, the spatiotemporal patterns of which varied from episode to episode. By analysing and categorizing the patterns of these movements, we found that embryonic movements follow relatively few restricted patterns with respect to the order of the movements of body regions. A further analysis of episodes at high spatiotemporal resolution revealed that most of the episodes in a major category could be classified into two distinct subtypes. Each of these subtypes had its own highly reproducible spatiotemporal patterns of movement. Overall, these results show that early embryonic movements follow relatively few rather stereotyped patterns, and random local fluctuations have little effect on such movement patterns. The appearance of one pattern out of several rather stereotyped patterns may be the main cause of apparent variations in patterns of early embryonic movements. The stereotyped patterns may represent important orderly characteristics of spontaneous embryonic activities that may be involved in the development of orderly structures and functions in higher animals.

Implications of a neural network model of early sensori-motor development for the field of developmental neurology

This paper reports on a neural network model for early sensori-motor development and on the possible implications of this research for our understanding and, eventually, treatment of motor disorders like cerebral palsy. We recapitulate the results we published in detail in a series of papers [1-4]. The neural circuits in the model self-organize on the basis of rhythmic activity spontaneously generated in the model. This indicates the importance of endogenously generated activity in the developing brain. We also show that afferent feed-back from the mechanical part of the model is easily incorporated in the neural part of the model. In this way the model acquires reflex-related properties which have long been demonstrated in man. In the discussion we relate these experimental findings to the variability concept from developmental neurology and show how variable motor performance is important for motor learning. We also discuss possible implications of our modelling effort for movement disorders, specifically spastic cerebral palsy.

Movements of mouse fetuses in early stages of neural development studied in vitro

The transplacental perfusion method enables the in vitro maintenance and close observation of live mouse fetuses under conditions free of maternal influences. In the present study, this method was used to detect spontaneous movements of mouse fetuses in early developmental stages. When mouse fetuses at embryonic day (E) 12.5 were isolated together with the uterus and were maintained in vitro, they displayed periodic body movements that occurred every few minutes. Fetal movements were abolished after the application of drugs that depress neural activities. The present results obtained in in vitro mouse fetuses suggest that fetal movements and neural activities may be present during the early stages of motor system development and may play a role in the normal maturation of the motor systems.

Mouse fetuses in late gestation maintained in vitro by a transplacental perfusion method and their physiological activities

The present study demonstrated that live mouse fetuses in late gestation can be kept in vitro and their physiological activities maintained for over 24 h. Fetuses together with uterus were isolated from pregnant mice at 11.5-17.5 days gestation and transplacentally perfused with a physiological solution through a cannula inserted into the uterine artery. Under these conditions, various physiological activities including heartbeats and spontaneous and stimulation-induced fetal movements were observed.

The GABA-A agonist muscimol facilitates muscular twitches and locomotor movements in the neonatal mouse

The effects of nonsedative doses of muscimol, a postsynaptic GABA-A agonist, on neurobehavioral activities in 5- and 11-day-old newborn mice were assessed using an observational point sampling procedure. Muscimol activated the emission of muscular twitches after injections of 0.025 or 0.050 mg/kg in 5-day-old pups, and 0.075 mg/kg in 11-day-old pups. At 0.075 mg/kg, the GABA agonist also produced an increase of locomotor movement levels in the younger age group. Given that muscimol at low dosages typically produces an increase of locomotion in mature mice, it is suggested that the GABAergic activity involved in locomotor behaviors is functional very early in life. Furthermore, since twitching behavior exhibited while lying presumably indicates paradoxical sleep early in life, it is speculated that muscimol may have activated this form of sleep in our newborn mice.

Development of the surgically produced singleton mouse fetus

All but one mouse embryo were removed from uteri on Day 8 of gestation and delivered via cesarean section on Day 18. Singletons were compared on various developmental indices to similarly delivered controls permitted to reside in uteri containing the normal complement of fetuses. The former were heavier at birth and weaning, had smaller ano-genital distance ratios (ano-genital distance/delivery weight), and displayed walking, gripping, eye-opening, and vaginal-opening earlier than controls. Singletons also exhibited greater durations and frequencies of various prenatal activities relative to controls when observed on Day 17 of gestation. Singleton status did not advance the onset of prenatal activity.

The importance of fetal/neonatal REM sleep

The emergence of behavioral states is one of the most significant aspects of development. The rat is very immature at birth and in some structural and functional aspects of CNS (central nervous system) development it is comparable to a 7-month-old human fetus. At this stage of development synchronization of different state criteria is poorly organized. Infant rats spend very little time in wakefulness and, once asleep, they still display a very high level of motor activation, with frequent rapid eye movements and uncoordinated myoclonic jerks. Although it is questioned whether the activated state of sleep in the newborn rat is comparable to rapid-eye movement sleep (REM) in adults, it has been shown that the CNS displays an increased level of endogenous neuronal activation even in very immature animals during this state. To study the functional significance of REM in early life, rat pups were deprived of this state from 1 to 3 wk of age and tested as adults. In the rat, chronic suppression of REM by interfering with monoamines during early development induced hyperactivity, hyperanxiety, attentional distractability, sleep disturbances, reduced sexual performance and reduced cerebral cortical size. In studies using instrumental, surgical or other pharmacological treatments to suppress REM similar effects on the development of brain and behavior were found. Taken together, these findings point to a role for REM during early development, so that more attention should be given to the potential hazards of medicines (and/or pathologic conditions) which induce reduced levels of REM and or disturbed monoamine activities in the brain during late prenatal and early postnatal life.

Pathologic myoclonus of the newborn: electrographic and clinical correlations

Previous reports have described neonatal myoclonus as a benign movement in healthy premature newborns or as a clinical seizure in neonates with severe encephalopathies. The present report describes electroencephalographic-myoclonic correlations which occur independently from sustained electrical discharges in ten neonates. Cortical, reticular, and segmental types of neonatal myoclonus, similar to adult forms, are described.