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Sensory neurogenesis in the dorsal root ganglion (DRG) occurs in two waves of differentiation with larger, myelinated proprioceptive and low-threshold mechanoreceptor (LTMR) neurons differentiating before smaller, unmyelinated (C) nociceptive neurons. This temporal difference was established from early birthdating studies based on DRG soma cell size. However, distinctions in birthdates between molecular subtypes of sensory neurons, particularly nociceptors, is unknown. Here, we assess the birthdate of lumbar DRG neurons in mice using a thymidine analog, EdU, to label developing neurons exiting mitosis combined with co-labeling of known sensory neuron markers. We find that different nociceptor subtypes are born on similar timescales, with continuous births between E9.5 to E13.5, and peak births from E10.5 to E11.5. Notably, we find that thinly myelinated Aδ-fiber nociceptors and peptidergic C-fibers are born more broadly between E10.5 and E11.5 than previously thought and that non-peptidergic C-fibers and C-LTMRs are born with a peak birth date of E11.5. Moreover, we find that the percentages of nociceptor subtypes born at a particular timepoint are the same for any given nociceptor cell type marker, indicating that intrinsic or extrinsic influences on cell type diversity are occurring similarly across developmental time. Overall, the patterns of birth still fit within the classical "two wave" description, as touch and proprioceptive fibers are born primarily at E10.5, but suggest that nociceptors have a slightly broader wave of birthdates with different nociceptor subtypes continually differentiating throughout sensory neurogenesis irrespective of myelination., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Objective: Spina bifida (SB) is a congenital birth defect defined as a failure of the neural tube formation during the embryonic development phase. Fetoscopic repair of SB is a novel treatment technique that allows to close spinal defect early and prevent potential neurological and psychomotor complications., Case Report: We present a case report of a 32-year-old-multigravida whose fetus was diagnosed with lumbosacral myelomeningocele at 23rd week. Fetoscopic closure of MMC was performed at 26 weeks. At 32 weeks, due to premature amniorrhexis and placental abruption, an emergency C-section was performed. Newborn's psychomotor development was within normal limits., Conclusion: Although intrauterine treatment has an increased risk of premature labor, placental abruption, prenatal closure is associated with improved postnatal psychomotor development. Prenatal surgery decreases the risk of Arnold-Chiari II malformation development and walking disability. Fetoscopic closure of SB is becoming a choice for treatment with beneficial outcomes for mother and fetus., Competing Interests: Conflicts of interest The authors state no conflict of interest., (Copyright © 2021. Published by Elsevier B.V.)

Although there are improvements in treatment of anorectal malformations (ARMs), patients can still develop fecal incontinence, constipation, and soiling with loss in quality of life. Recent evidence suggests that malformations in the lumbosacral spinal cord are one of the factors that affect postoperative anorectal function. However, the underlying mechanism that produces these malformations has yet to be elucidated. The bone morphogenetic proteins (BMPs) comprise a large group of highly conserved molecules that are involved in multiple processes and play important roles in the formation, development, and differentiation of the spinal cord. This study was designed to investigate the levels of BMP4 expression in the lumbosacral spinal cord in ARMs rat embryos induced by ethylenethiourea (ETU). Specifically, we assessed the association of BMP4 levels with the maldevelopment of the lumbosacral spinal cord and whether BMP4 acted through the canonical intracellular pathway in embryonic rats with ARMs. BMP4 expression was confirmed with immunohistochemical staining, RT-qPCR and western blot analyses of embryonic day (E) 16, E17, E19 and E21 embryos, moreover Smad1/5 and pSmad1/5 expression were confirmed with western blot analyses at peak time point of BMP4 expression. Our results reveal that BMP4 expression in the lumbosacral spinal cord of ARMs rat embryos is decreased at both the mRNA and protein levels and could decrease the phosphorylation of smad1/5, when compared with their expression levels in normal tissue. These results also suggest that reductions in BMP4 expression were possibly responsible for dysfunction of the lumbosacral spinal cord during late developmental stages in ARMs fetal rats. Taken together, we conclude a role for BMP4 in the pathogenesis of lumbosacral spinal cord maldevelopment in developing ARMs rats., (Copyright © 2018 ISDN. Published by Elsevier Ltd. All rights reserved.)

Fecal incontinence and constipation still remain the major complications after procedures for anorectal malformations (ARMs). Previous studies have demonstrated a decrease of neural cell in lumbosacral spinal cord of ARMs patients and rat models. However, the underlying mechanism remains elusive. In this study, the neural cell apoptosis and Bcl-2/Bax expression were explored during lumbosacral spinal cord development in normal and ARMs fetuses. ARMs rat fetuses were induced by treating pregnant rats with ethylenethiourea on embryonic day 10. TUNEL staining was performed to identify apoptosis, and the expression of Bcl-2/Bax was confirmed with immunohistochemical staining, RT-qPCR and Western blot analysis on E16, E17, E19 and E21. Apoptosis index (AI) in the ARMs group was significantly higher compared to normal group. Our results showed that TUNEL-positive cells were mainly localized in the ventral horn, which is the location of neural cells controlling defecation. And the expression of Bcl-2 decreased, whereas the level of Bax increased in the ARMs fetuses. In addition, there was a significantly negative correlation between protein expression of Bcl-2/Bax ratio and AI in the ARMs group. Abnormal apoptosis might be a fundamental pathogenesis for the number decrease of neural cells in lumbosacral spinal cord, which leads to complications after procedures for ARMs. The negative correlation between the ratio of Bcl-2/Bax and AI manifested that Bcl-2/Bax pathway might be the mechanism for neural cell apoptosis in ARMs.

Objective: To evaluate the need for postnatal neurosurgical intervention after fetoscopic patch coverage of spina bifida aperta (SBA)., Methods: This was a retrospective analysis of a cohort of 71 fetuses which underwent minimally invasive fetoscopic patch coverage of SBA between 21 + 0 and 29 + 1 weeks of gestation. Postnatal neurosurgical procedures were classified into two types: re-coverage of the SBA within the first 3 months following birth, and shunt placement as treatment of associated hydrocephalus within the first year., Results: Location of the SBA was lumbosacral in 59 cases, lumbar in seven, thoracic in three and sacral in two. In total, 20/71 (28%) patients underwent early postnatal neurosurgical intervention by means of re-coverage of the SBA. This was performed because of cerebrospinal fluid leakage in seven (35%), adhesions with functional deterioration in three (15%), incomplete coverage in five (25%) and skin defect in five (25%) cases. Ventriculoperitoneal shunt placement within 1 year was required in 32 (45%) cases and was preceded by ventriculostomy in two. Three (4%) infants needed Chiari decompression surgery in the first 12 months following birth, because of syringomyelia or gait disturbance., Conclusions: Fetoscopic patch coverage of SBA may require postnatal re-coverage in some cases. In most cases, conservative wound treatment shows good results, without requiring neurosurgical intervention. The low 1-year-shunt rate is comparable to data of the Management of Myelomeningocele Study and lower compared with published data of patients with postnatal only coverage of SBA., (Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.)

During embryonic and early postnatal development, retinoic acid (RA) regulates genes that control neuronal differentiation and neurite outgrowth from the neural tube. The effects of high levels of RA on the CNS can be detected via nitric oxide (NO), which plays a crucial role in neural transmission. The aim of the study was to investigate the prenatal influence of high levels of RA on postnatal development of nitrergic structures in lumbar spinal cord and antioxidant status. RA was administered orally at a dose of 10mg/kg body weight to pregnant female Wistar rats during days 8-10 of gestation. Neuronal nitric oxide synthase (nNOS) of lumbar spinal cord sections was processed for visualization via nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry on postnatal day one, day twenty-one and in adults. The results suggest that prenatal administration of high levels of RA is not associated with postnatal morphological changes in nNOS-positive neurons in the rat lumbar spinal cord. An estimation of the activity of enzymes related to the storage of retinoid in the liver showed possible side effects. Suppression and deepening of superoxide dismutase activity persisted into adulthood, and a concurrent downregulation of glutathione reductase was noted. A decrease in reduced glutathione persisted until adulthood when other compensatory mechanisms were probably active to maintain an appropriate level., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

Objective: To examine the impact of introduction of the mid-trimester scan on pregnancy outcome in cases of open spina bifida in two regions of The Netherlands., Methods: This was a retrospective cohort study of 190 cases of open spina bifida diagnosed pre- or postnatally, with an estimated date of delivery between 2003 and 2011., Results: With implementation of the mid-trimester scan the percentage of cases of open spina bifida detected before the 24(th) week of pregnancy increased from 43% to 88%. The rise in prenatal detection rate was associated with a significant increase in the number of terminated pregnancies and a decrease in the rate of perinatal loss; the percentage of children born alive did not change significantly. In the subgroup that underwent a scan between 18 and 24 weeks of pregnancy, cranial signs were present in 94.4% of cases., Conclusion: Introduction of the mid-trimester scan has led to an increase in early identification of pregnancies complicated by open spina bifida. Pregnancies previously destined to end in perinatal loss are now terminated whilst pregnancies with a relatively good prognosis are frequently continued; the number of children with open spina bifida who are born alive has not changed significantly. Our study confirms that prenatal diagnosis is usually triggered by visualization of a lemon-shaped skull or a banana-shaped cerebellum., (Copyright © 2013 ISUOG. Published by John Wiley & Sons Ltd.)

OBJECTIVES; The purpose of this study was to establish reference ranges for vertebral body areas of the fetal lumbosacral spine in the coronal plane on 3-dimensional sonography using volume contrast imaging with OmniView (GE Healthcare, Zipf, Austria). METHODS; An observational cross-sectional study was conducted on 576 healthy pregnant women at gestational ages of 20 weeks to 34 weeks 6 days. Volume contrast imaging with OmniView was used to measure the vertebral body areas (L1-L5, S1, and S2) by positioning a curved line along the fetal lumbosacral spine. To create reference ranges, first- and second-degree linear regression models adjusted using residual analysis and the coefficient of determination (R(2)) were created. To assess reproducibility, two examiners evaluated 40 random volumes using the intraclass correlation coefficient. RESULTS; The mean areas of the vertebral bodies were 102.72 (range, 25-254), 107.29 (range, 30-245), 105.10 (range, 31-231), 99.09 (range, 31-211), 87.74 (range, 11-178), 65.80 (range, 18-161), and 46.54 (range, 12-129) mm(2) for L1, L2, L3, L4, L5, S1, and S2, respectively. In the intraobserver and interobserver reproducibility assessments, intraclass correlation coefficients of greater than 0.80 were found for all fetal vertebral body areas. CONCLUSIONS; Reference values for fetal lumbosacral spine vertebral body areas were determined by 3-dimensional sonography using volume contrast imaging with OmniView, and they were shown to be reproducible.

Purpose: Between 1997 and 2002 a large number of fetal myelomeningocele closures were performed at our institution. Previously early reports showed little improvement in neonatal bladder function after fetal back closure. We evaluated the long-term urological impact of this procedure., Materials and Methods: Using a combination of retrospective review and survey questionnaire we reviewed the records of 28 patients in whom fetal myelomeningocele closure was done at our institution between 1997 and 2002. The areas addressed included medical management for neurogenic bladder and bowel, need for lower urinary tract reconstruction and functional bladder assessment by videourodynamics. Parameters after fetal myelomeningocele closure were compared to those of 33 age and sex matched patients with myelomeningocele who underwent standard postnatal closure., Results: We reviewed the records of 28 patients after fetal myelomeningocele closure. At a mean age of 9.6 years 23 used clean intermittent catheterization to manage the bladder, 24 required a bowel regimen to manage constipation and 6 underwent lower urinary tract reconstruction with enterocystoplasty and a catheterizable bladder channel. Videourodynamics performed in 14 patients at a mean age of 7.4 years revealed decreased bladder capacity in 71%, detrusor overactivity in 35% and increased detrusor pressure in 25%. Compared to age and sex matched children who underwent postnatal closure we noted no significant differences in bladder management, urinary tract surgery or urodynamics., Conclusions: Neurogenic bowel and bladder management continues to be a significant issue for patients after fetal myelomeningocele closure. After fetal surgery patients should be followed closely, similar to patients who undergo postnatal closure., (Copyright © 2011 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Many significant human birth defects originate around the time of neural tube closure or early during post-closure nervous system development. For example, failure of the neural tube to close generates anencephaly and spina bifida, faulty cell cycle progression is implicated in primary microcephaly, while defective migration of neuroblasts can lead to neuronal migration disorders such as lissencephaly. At the stage of neural tube closure, basement membranes are becoming organised around the neuroepithelium, and beneath the adjacent non-neural surface ectoderm. While there is circumstantial evidence to implicate basement membrane dynamics in neural tube and surface ectodermal development, we have an incomplete understanding of the molecular composition of basement membranes at this stage. In the present study, we examined the developing basement membranes of the mouse embryo at mid-gestation (embryonic day 9.5), with particular reference to laminin composition. We performed in situ hybridization to detect the mRNAs of all eleven individual laminin chains, and immunohistochemistry to identify which laminin chains are present in the basement membranes. From this information, we inferred the likely laminin variants and their tissues of origin: that is, whether a given basement membrane laminin is contributed by epithelium, mesenchyme, or both. Our findings reveal major differences in basement composition along the body axis, with the rostral neural tube (at mandibular arch and heart levels) exhibiting many distinct laminin variants, while the lumbar level where the neural tube is just closing shows a much simpler laminin profile. Moreover, there appears to be a marked difference in the extent to which the mesenchyme contributes laminin variants to the basement membrane, with potential contribution of several laminins rostrally, but no contribution caudally. This information paves the way towards a mechanistic analysis of basement membrane laminin function during early neural tube development in mammals., (Copyright © 2011 International Society of Matrix Biology. Published by Elsevier B.V. All rights reserved.)

During embryogenesis, limb-innervating lateral motor column (LMC) spinal motor neurons (MN) are generated in excess and subsequently nearly half of them die. Many motor neuron survival factors (MnSFs) have been shown to suppress this default programmed cell death (PCD) program through their receptors (MnSFRs), raising the possibility that they are involved in matching specific MNs with their target muscles. Published observations suggest a combinatorial model of MnSF/Rs function, which assumes that during the PCD phase, MNs are expressing combinations of MnSFRs, whereas the limb muscles innervated by these MNs express cognate combinations of MnSFs. We tested this model by expression profiling of MnSFs and their receptors in the avian lumbosacral spinal cord and limb muscles during the peak PCD period. Our findings highlight the complexity of MnSF/Rs function in the control of LMC motor neuron survival., (Copyright (c) 2010 Wiley-Liss, Inc.)

Objective: Prenatal diagnosis of open spina bifida is carried out by ultrasound examination in the second trimester of pregnancy. The diagnosis is suspected by the presence of a 'lemon-shaped' head and a 'banana-shaped' cerebellum, thought to be consequences of caudal displacement of the hindbrain. The aim of the study was to determine whether in fetuses with spina bifida this displacement of the brain is evident from the first trimester of pregnancy., Methods: In women undergoing routine ultrasound examination at 11-13 weeks' gestation as part of screening for chromosomal abnormalities, a mid-sagittal view of the fetal face was obtained to measure nuchal translucency thickness and assess the nasal bone. In this view the fourth ventricle, which presents as an intracranial translucency (IT) between the brain stem and choroid plexus, is easily visible. We measured the anteroposterior diameter of the fourth ventricle in 200 normal fetuses and in four fetuses with spina bifida., Results: In the normal fetuses the fourth ventricle was always visible and the median anteroposterior diameter increased from 1.5 mm at a crown-rump length (CRL) of 45 mm to 2.5 mm at a CRL of 84 mm. In the four fetuses with spina bifida the ventricle was compressed by the caudally displaced hindbrain and no IT could be seen., Conclusion: The mid-sagittal view of the face as routinely used in screening for chromosomal defects can also be used for early detection of open spina bifida.

Onuf's nucleus in the lumbosacral spinal cord, comprising somatic motoneurons that innervate the pelvic floor muscles via the pudendal nerve, shares some characteristics with the autonomic preganglionic neurons and functions in coordination with the autonomic nervous system. In mouse, neurons projecting to the urethral sphincter and ischiocavernosus muscles form the dorsolateral (DL) nucleus at the caudal lumbar levels, whereas neurons projecting to the limb and hip joint muscles comprise the retrodorsolateral and ventral nucleus, as well as the DL nucleus at the rostral lumbar levels. The results of the present study in mouse revealed that the expression pattern of a LIM homeodomain protein Islet-1, an embryonic marker for motoneurons in the spinal cord, was different among motoneuronal groups at the prenatal stage (embryonic days 13.5-15.5); the highest expression was observed in the DL at the caudal lumbar cord, whereas there was little expression in the lateral part of the rostral DL. Islet-1 expression was also observed in the parasympathetic preganglionic neurons at the sacral spinal cord. These findings provide evidence that the DL neurons at the caudal lumbar cord, corresponding to Onuf's nucleus, are chemically distinct among the motoneuronal groups at the prenatal stages. This differential Islet-1 expression among the motoneuronal groups suggests that Islet-1 not only leads to a motoneuronal lineage, but also to the differentiation of motoneuronal subsets in the lumbosacral spinal cord.

Lumbar hernia is the protrusion of intraperitoneal or extraperitoneal contents through a defect of the posterolateral abdominal wall. Barbette was the first, in 1672, to suggest the existence of lumbar hernias. The first case was reported by Garangeot in 1731. Petit and Grynfeltt delineated the boundaries of the inferior and superior lumbar triangles in 1783 and 1866, respectively. These two anatomical sites account for about 95 per cent of lumbar hernias. Approximately 20 per cent of lumbar hernias are congenital. The rest are either primarily or secondarily acquired. The most common cause of primarily acquired lumbar hernias is increased intra-abdominal pressure. Secondarily acquired lumbar hernias are associated with prior surgical incisions, trauma, and abscess formation. During embryologic development, weakening of the area of the aponeuroses of the layered abdominal muscles that derive from somitic mesoderm, which invades the somatopleure, may potentially lead to lumbar hernias. Repair of lumbar hernias should be performed as early as possible to avoid incarceration and strangulation. The classic repair technique uses the open approach, where closure of the defect is performed either directly or using prosthetic mesh. The laparoscopic approach, either transabdominal or extraperitoneal, is an alternative.

Here, we present evidence that Lrp6, a coreceptor for Wnt ligands, is required for the normal formation of somites and bones. By positional cloning, we demonstrate that a novel spontaneous mutation ringelschwanz (rs) in the mouse is caused by a point mutation in Lrp6, leading to an amino acid substitution of tryptophan for the evolutionarily conserved residue arginine at codon 886 (R886W). We show that rs is a hypomorphic Lrp6 allele by a genetic complementation test with Lrp6-null mice, and that the mutated protein cannot efficiently transduce signals through the Wnt/beta-catenin pathway. Homozygous rs mice, many of which are remarkably viable, exhibit a combination of multiple Wnt-deficient phenotypes, including dysmorphologies of the axial skeleton, digits and the neural tube. The establishment of the anteroposterior somite compartments, the epithelialization of nascent somites, and the formation of segment borders are disturbed in rs mutants, leading to a characteristic form of vertebral malformations, similar to dysmorphologies in individuals suffering from spondylocostal dysostosis. Marker expression study suggests that Lrp6 is required for the crosstalk between the Wnt and notch-delta signaling pathways during somitogenesis. Furthermore, the Lrp6 dysfunction in rs leads to delayed ossification at birth and to a low bone mass phenotype in adults. Together, we propose that Lrp6 is one of the key genetic components for the pathogenesis of vertebral segmentation defects and of osteoporosis in humans.

The early development of the neural tube has been well studied in animals and humans. After axial determinants have been accomplished the processes of primary and secondary neurulation take place. Successful completion results in a spinal cord that has arisen from primary neurulation and a lower sacro-coccygeal portion from secondary neurulation. The latter region is the site of numerous skin-covered clinical lesions, which include tumors and malformations. A listing of selected features in 764 cases of skin-covered sacrococcygeal lesions is presented. The manner in which these lesions arise and the potential for genetic factors being responsible is discussed., (Copyright 2003 S. Karger AG, Basel)

In a large collection of human embryos (the Kyoto Collection of Human Embryos, Kyoto University), we encountered five cases with abnormal dilatation of the neural tube at the lumbosacral level. In these examples, the central canal was enlarged, and the roof plate of the neural tube was extremely thin and expanded. The mesenchymal tissue was scarce or lacking between the roof plate and the surface ectoderm. This type of anomaly was assumed to be formed after neural tube closure and may be an early form of spina bifida. In two of the cases, some abnormal cells were found ectopically between the thin roof plate and the surface ectoderm. Morphologically, these cells resembled those forming spinal ganglia and could be of the neural crest origin. Since neural crest cells are pluripotent and can differentiate into a variety of tissues, such ectopic cells might undergo abnormal differentiation into teratomatous tumors and/or lipomas, which are frequently associated with spina bifida. We also discuss the definition of spina bifida and the classification of neural tube defects from the embryological and pathogenic viewpoints and propose a new classification of neural tube defects.

We have used Hoxd10 expression as a primary marker of the lumbosacral region to examine the early programming of regional characteristics within the posterior spinal cord of the chick embryo. Hoxd10 is uniquely expressed at a high level in the lumbosacral cord, from the earliest stages of motor column formation through stages of motoneuron axon outgrowth. To define the time period when this gene pattern is determined, we assessed Hoxd10 expression after transposition of lumbosacral and thoracic segments at early neural tube stages. We present evidence that there is an early prepattern for Hoxd10 expression in the lumbosacral neural tube; a prepattern that is established at or before stages of neural tube closure. Cells within more posterior lumbosacral segments have a greater ability to develop high level Hoxd10 expression than the most anterior lumbosacral segments or thoracic segments. During subsequent neural tube stages, this prepattern is amplified and stabilized by environmental signals such that all lumbosacral segments acquire the ability to develop high levels of Hoxd10, independent of their axial environment. Results from experiments in which posterior neural segments and/or paraxial mesoderm segments were placed at different axial levels suggest that signals setting Hoxd10 expression form a decreasing posterior-to-anterior gradient. Our experiments do not, however, implicate adjacent paraxial mesoderm as the only source of graded signals. We suggest, instead, that signals from more posterior embryonic regions influence Hoxd10 expression after the early establishment of a regional prepattern. Concurrent analyses of patterns of LIM proteins and motor column organization after experimental surgeries suggest that the programming of these characteristics follows similar rules.

Neuro-osteology stresses the biological connection during development between nerve and hard tissues. It is a perspective that has developed since associations were first described between pre-natal peripheral nerve tissue and initial osseous bone formation in the craniofacial skeleton (Kjaer, 1990a). In this review, the normal connection between the central nervous system and the axial skeleton and between the peripheral nervous system and jaw formation are first discussed. The early central nervous system (the neural tube) and the axial skeleton from the lumbosacral region to the sella turcica forms a unit, since both types of tissue are developmentally dependent upon the notochord. In different neurological disorders, the axial skeleton, including the pituitary gland, is malformed in different ways along the original course of the notochord. Anterior to the pituitary gland/sella turcica region, the craniofacial skeleton develops from prechordal cartilage, invading mesoderm and neural crest cells. Also, abnormal development in the craniofacial region, such as tooth agenesis, is analyzed neuro-osteologically. Results from pre-natal investigations provide information on the post-natal diagnosis of children with congenital developmental disorders in the central nervous system. Examples of these are myelomeningocele and holoprosencephaly. Three steps are important in clinical neuro-osteology: (1) clinical definition of the region of an osseous or dental malformation, (2) embryological determination of the origin of that region and recollection of which neurological structure has developed from the same region, and (3) clinical diagnosis of this neurological structure. If neurological malformation is the first symptom, step 2 results in the determination of the osseous region involved, which in step 3 is analyzed clinically. The relevance of future neuro-osteological diagnostics is emphasized.

The development of immunoreactivity for the putative inhibitory amino acid neurotransmitter glycine was investigated in the embryonic and posthatched chick lumbosacral spinal cord by using postembedding immunocytochemical methods. Glycine immunoreactive perikarya were first observed at embryonic day 8 (E8) both in the dorsal and ventral gray matters. The number of immunostained neurons sharply increased by E10 and was gradually augmented further at later developmental stages. The general pattern of glycine immunoreactivity characteristic of mature animals had been achieved by E12 and was only slightly altered afterward. Most of the immunostained neurons were located in the presumptive deep dorsal horn (laminae IV-VI) and lamina VII, although glycine-immunoreactive neurons were scattered throughout the entire extent of the spinal gray matter. By using some of our previously obtained and published data concerning the development of gamma-aminobutyric acid (GABA)-ergic neurons in the embryonic chick lumbosacral spinal cord, we have compared the numbers, sizes, and distribution of glycine- and GABA-immunoreactive spinal neurons at various developmental stages and found the following marked differences in the developmental characteristics of these two populations of putative inhibitory interneurons. (i) GABA immunoreactivity was expressed very early (E4), whereas immunoreactivity for glycine appeared relatively late (E8) in embryonic development. (ii) In the ventral horn, GABA immunoreactivity declined, whereas immunoreactivity for glycine gradually increased from E8 onward in such a manner that the sum of glycinergic and GABAergic perikarya remained constant during the second half of embryonic development. (iii) Glycinergic and GABAergic neurons showed different distribution patterns in the spinal gray matter throughout the entire course of embryogenesis as well as in the posthatched animal. When investigating the colocalization of glycine and GABA immunoreactivities, perikarya immunostained for both amino acids were revealed at all developmental stages from E8 onward, and the proportions of glycine- and GABA-immunoreactive neurons that were also immunostained for the other amino acid were remarkably constant during development. The characteristic features of the development of the investigated putative inhibitory spinal interneurons are discussed and correlated with previous neuroanatomical and physiological studies.

The volume and DNA synthesis of the neuroepithelium in induced myeloschisis in Long-Evans rats as shown by hematoxylin-eosin and BrdU/antiBrdU immunohistochemical staining patterns were examined at different stages of embryonal development. On day 14 of gestation, control animals contained BrdU-incorporating cells mainly at the alar plate of the closed neural tube. On the same day, the everted neural plate of rats with myeloschisis showed active, diffuse uptake of BrdU in the cells of the matrix layer, although an increase in the volume of the everted neural plate was not yet identifiable. On day 21 of gestation, rats with myeloschisis showed a marked increase in the volume of the neuroepithelium compared with controls. Our investigations suggest that, in myeloschisis, more neuroepithelial cells than normal retain their capability for DNA synthesis on day 14 of gestation, and the overgrowth of the neuroepithelium found on day 21 is possibly a secondary effect of failure of neural tube closure.

Myelination in the human central nervous system is well documented after 20 weeks of gestation (WOG). However, earlier stages of this process have not been described in detail, although it is assumed that human myelinogenesis is similar to that observed in other animals. We used light and electron microscopy to study myelination in the human lumbosacral spinal cord during the second trimester of gestation. The kinetics of myelin-associated gene expression were analyzed by immunocytochemistry using antibodies to the myelin markers myelin basic protein (MBP) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase). These studies show that in 12-13 WOG specimens, occasional MBP-positive processes are found in developing white matter in areas distinct from the root entry zones. At this time, ultrastructural study revealed early investment of axons by glial processes and rare compacted myelin. CNPase staining was qualitatively and quantitatively less than that of MBP. The numbers of MBP- and CNPase-positive myelin sheaths increased with time, and by 24 WOG many were evident in all areas of the spinal cord except in the corticospinal tracts. Ultrastructural study of corresponding areas revealed many thin lamellae of compact myelin. This study provides initial normative data for early human myelination in the lumbosacral spinal cord and may serve as a baseline for future developmental and pathological studies.

A quantitative electron microscopic study was conducted on the dorsal and ventral nerve roots (L7-S1) supplying the hindlimbs of control and thalidomide-treated rabbit fetuses. The ventral roots at segmental levels L7 and S1 of treated nondeformed fetuses (TND) and deformed fetuses, demonstrated significant reductions (20-30%) of four of the parameters measured; total fascicular area (TFA), myelinated axon number (AN), Schwann cell counts (SCC) and axoplasmic area. In the dorsal roots of treated animals, thalidomide affected primarily segmental level S2, where significant reductions (15-30%) were observed in three parameters (TFA, AN, SCC). The occurrence of significant reductions in these measures in TND fetuses may indicate a neurotoxic action for thalidomide in the embryo. Despite apparent reductions in Schwann cell numbers in dorsal and ventral nerve roots, analyses of axon caliber and myelin sheath thickness indicated no evidence for any effects of thalidomide on the myelination of either sensory or motor axons. The segmental distribution of the axonal lesion, being maximal at segmental levels L7 and S1 in the ventral roots and at segmental level S2 in the dorsal roots, indicates a discrete period during development when nervous tissue is susceptible to the effects of thalidomide. The results of this study suggest thalidomide may have effects on neural development as well as on limb development.

The development of the vascular patterns of the lumbosacral segments of the chick embryo spinal cord has been analyzed in normal as well as in experimental conditions, after complete removal of the hind limb primordium. The results indicate that in both conditions the development of the vascular network follows the time-space sequence of the cytoarchitectural modifications of the cord, supporting the view that the vascularization does not exert a morphogenetic influence.

1. Retrograde transport of horseradish peroxidase was used to map the initial projection patterns of lumbosacral motoneurones to the embryonic chick hind limb. 2. The stage 28 segmental projection pattern to each of the four primary muscle masses was characteristic and indistinguishable from the stage 36 projection pattern to the sum of the muscles derived from that mass. In addition, the adductor motoneurone pool was found to be similar in position (both rostro-caudal and mediolateral) at stages 29, 30, 32, 33 1/2 and 36. 3. Therefore axons from lumbosacral motoneurones project for the most part only to appropriate regions from early times shortly after they grow into the limb bud. Furthermore, the attainment of the segmental projection pattern occurs prior to the normal time of, and therefore without the aid of, cell death. This conclusion was supported by electrophysiological recordings made from muscle nerves. 4. A regionalization of the projection patterns within a single muscle mass could be shown both anatomically and physiologically prior to the cleavage of the mass into individual muscles and the projections were in a general way appropriate for the muscles derived from those regions. 5. Therefore the process of muscle cleavage does not in itself create the specific projection patterns observed, and motoneurone axons appear to grow to and to ramify and make synapses only within regions which correspond to their adult muscles. 6. Finally, the termination site of each motoneurone axon in the early limb was found to be tightly correlated in a somatotopic fashion with the position occupied by its soma in the cord. This suggests that some feature of the motoneurone related to its position may be of importance in achieving the specific projection patterns observed.