Joint development recovery on resumption of embryonic movement following paralysis.

Fetal activity in utero is a normal part of pregnancy and reduced or absent movement can lead to long-term skeletal defects, such as Fetal Akinesia Deformation Sequence, joint dysplasia and arthrogryposis. A variety of animal models with decreased or absent embryonic movements show a consistent set of developmental defects, providing insight into the aetiology of congenital skeletal abnormalities. At developing joints, defects include reduced joint interzones with frequent fusion of cartilaginous skeletal rudiments across the joint. At the spine, defects include shortening and a spectrum of curvature deformations. An important question, with relevance to possible therapeutic interventions for human conditions, is the capacity for recovery with resumption of movement following short-term immobilisation. Here, we use the well-established chick model to compare the effects of sustained immobilisation from embryonic day (E)4-10 to two different recovery scenarios: (1) natural recovery from E6 until E10 and (2) the addition of hyperactive movement stimulation during the recovery period. We demonstrate partial recovery of movement and partial recovery of joint development under both recovery conditions, but no improvement in spine defects. The joints examined (elbow, hip and knee) showed better recovery in hindlimb than forelimb, with hyperactive mobility leading to greater recovery in the knee and hip. The hip joint showed the best recovery with improved rudiment separation, tissue organisation and commencement of cavitation. This work demonstrates that movement post paralysis can partially recover specific aspects of joint development, which could inform therapeutic approaches to ameliorate the effects of human fetal immobility. This article has an associated First Person interview with the first author of the paper.

Loss of REEP4 causes paralysis of the Xenopus embryo.

Members of the REEP (Receptor expression enhancing protein) family contain a TB2/DP1, HVA22 domain that is involved in intracellular trafficking and secretion. Consistent with the presence of this domain, REEP1 and REEP3 enhance the expression of odorant and taste receptors in mammals, while mutation of these genes causes defects in neural development. REEP4 was identified in the course of a functional antisense morpholino oligonucleotide screen searching for genes involved in the early development of Xenopus tropicalis: although over-expression of the gene causes no phenotype, embryos lacking REEP4 develop a slightly kinked body axis and are paralysed. At tailbud stages of development, REEP4 is expressed in the somites and neural tube. The paralysis observed in embryos lacking REEP4 might therefore be caused by defects in the nervous system or in muscle. To address this point, we examined the expression of various neural and muscle markers and found that although all are expressed normally at early stages of development, many are down regulated by the tailbud stage. This suggests that REEP4 plays a role in the maintenance of both the nervous system and the musculature.

Fetal ultrasonography to prevent irreversible neurological sequelae of neonatal neuroblastoma.

An intra-abdominal mass was observed by fetal ultrasonography at 32 weeks of gestation. The baby was diagnosed as having neuroblastoma at the time of delivery at 39 weeks and its lower extremities were completely paralyzed. The chemotherapy after birth was quite effective to reduce the mass volume but neurological sequelae failed to improve. By carefully monitoring the movement of extremities, it may have been possible to prevent irreversible by inducing delivery before that state was reached.

Intrauterine onset of a mononeuropathy: peroneal neuropathy in a newborn with electromyographic findings at age one day compatible with prenatal onset.

Mononeuropathies are unusual at birth, and electromyographic (EMG) definition the first day of life has not been reported previously. Although neonatal mononeuropathies may be related to obstetric complications, prenatal mechanisms also merit consideration. We report an infant, born with a peroneal neuropathy, whose EMG was performed 18 h after birth. An isolated peroneal nerve lesion with lack of compound muscle action potential and the presence of fibrillation potentials, confined to the tibialis anterior muscle, suggested a primary intrauterine mechanism for this mononeuropathy. Because of an infant's small size, the temporal profile used in adults for appearance of EMG signs of wallerian degeneration may not apply. Inaccurate conclusions may result if the EMG standards for timing adult nerve injury are applied to newborns. To our knowledge, previous published cases of neonatal mononeuropathies have not included babies whose first EMG was performed before age 4 days. Therefore, an EMG study shortly after birth needed to be accomplished if strong support for the hypothesis of a prenatal onset were to be generated. Our findings are compatible with an intrauterine onset of this baby's peroneal neuropathy.

The paralysis associated with myelomeningocele: clinical and experimental data implicating a preventable spinal cord injury.

Paralysis seen in children with myelomeningocele has been attributed to congenital myelodysplasia. We suspected that paralysis may be due in part to a spinal cord injury caused by exposure of the neural tube to the amniotic fluid. This hypothesis was tested using a fetal rat model of surgically created dysraphism. Each pup from the experimental group of rats in which the spinal cord was intentionally exposed to the amniotic fluid was born with severe deformity and weakness of the hind limbs and tail. Control fetal rats, subjected to the same procedure without directly exposing the spinal cord to the intrauterine environment, were normal at birth. Histological studies of the exposed spinal cord revealed extensive erosion and necrosis, findings similar to those described in children with myelomeningocele. We therefore propose a "two-hit" hypothesis to explain the paralysis seen in children with myelomeningocele: congenital myelodysplasia complicated by an intrauterine spinal cord injury. Intrauterine protection of the exposed spinal cord might prevent some or all of the paralysis. The possible implications of these findings for the future treatment of myelomeningocele are discussed.

Upper airway resistances in fetal sheep: the influence of breathing activity.

Fetal breathing movements (FBM) and lung liquid volume are known to affect lung development, but little is known about mechanisms controlling movement of liquid through the upper respiratory tract (URT). Therefore we measured resistances of the URT in 8 unanesthetized fetal sheep during late gestation while FBM were monitored from pressures in the lower trachea or from electromyogram of respiratory muscles. URT resistance to liquid flow toward the amniotic sac increased from 3.5 +/- 1.9 Torr X ml-1 X min during episodes of FBM to 21.1 +/- 5.7 Torr X ml-1 X min during apnea. Laryngeal resistance during apnea was greater (P less than 0.001) than supralaryngeal resistance in each of six fetuses in which URT resistance was partitioned. Fetal paralysis abolished the increase in laryngeal resistance to efflux that was previously related to the high-voltage electrocortical state and apnea. We were unable to quantify URT resistance to fluid movement toward the lungs because the larynx acted as a valve, permitting flow toward the lungs only in the presence of FBM. The supralaryngeal portion of the URT also apparently acts as a valve, normally preventing the entry of amniotic fluid into the pharynx. These findings help to explain our earlier observations that efflux of liquid from the fetal lungs is greater during episodes of FBM than during apnea.

Abnormal development of vertebrae in paralyzed chick embryos.

Ventral bars, cartilaginous projections from the ventral aspect of the synsacrum that contact and form a joint with the ilium, were found in all normal chick embryos of age E9 and older. Bars were absent in a number of embryos which had been paralyzed from age E4 by the use of the acetylcholine receptor blocker alpha-bungarotoxin. They were also absent in some embryos that had been paralyzed between ages E4 and E10 but allowed to move thereafter. The bars, already formed, remained present in a third group of embryos in which paralysis was initiated age E10. Apparently, normal embryonic movements induce the formation of bars. In support of this conclusion is the observation that two of three embryos which had had their hindlimb buds amputated at age E3 lacked bars. In these embryos with amputations, the ilium was present at least in part, but the forces exerted on the region where the bars develop would have been greatly reduced because of the lack of hind limb musculature. It is concluded that the bars, which form part of the iliosynsacral joint, are induced epigenetically by normal embryonic movements.

Development of the articular cavity in paralyzed chick embryos and in chick embryo limb buds cultured on chorioallantoic membranes.

The development of digital joints of chick embryo paralyzed with dacamethonium bromide and of joints in chick embryo limb buds cultured on chorioallantoic membranes was studied. The digital joints of 45 paralyzed and 40 control embryos and the joints of 37 grafts and 30 control legs were examined histologically. Six preselected grafts were studied by electron microscope. Our results demonstrate that paralysis does not completely inhibit the early stages of joint clefting. In many paralysis does not completely inhibit the early stages of joint clefting. In many paralyzed embryos, small clefts appeared in the periphery and occasionally in the central part of the interzone. Unlike in normal embryos, they rapidly disappeared, inducing fusions across the joints. Early, 2-day paralysis during a period of normal clefting inhibited irreversibly the development of the articular cavity that failed to appear after a cessation of the drug. Paralysis initiated in older embryos caused rapid regression and partial fibrous ankylosis of previously fully differentiated joints. Grafts from 4- to 6-day-old embryos usually failed to develop a full range of skeletal segments. Normal development of skeletal segments occurred in grafts from older donors. The articular cavity failed to develop in almost all grafts. Early cavitation accompanied by characteristic cell changes was found in a few joints. These cellular changes are suggestive of an intrinsic mechanism of early cavitation, but joint motion is required for the full differentiation and maintenance of the joint cavity.

The role of movement in the development of a digital flexor tendon.

D-tubocurarine was injected into the air sac of 8-day chick embryos to prevent movement of the digits of the hind limb. The embryos were paralyzed from the tenth to the eighteenth day, when the experiment was terminated. The immobilization of the flexor digitorum profundus tendons in the tarsus resulted in a loss of specialized structures around and on this tendon, as determined by light and electron microscopy. Specialized areas observed in the normal chick (synovial cavity, fibrocartilaginous area, and elastic vinculum) failed to form, as a result of the paralysis of the digit. Several authors have shown previously that movement is a requirement for the molding and maintenance of joint cavities in vivo, in ovo and in vitro (see text for references). We have shown that movement of the tendon is required to produce a functional tendon apparatus in the embryo and predict that movement is also required for regeneration after injury.