Accessory right spermatic ganglion: possible embryological basis and clinical significance.

The spermatic ganglia are collections of sympathetic neuron cell bodies located within the cords of the infrarenal aortic plexus, positioned at the origin of the testicular arteries in males. During routine dissection of the aortic plexus at our institution, one specimen exhibited a second (accessory) testicular artery on the right side that coursed retrocaval. Histology was used to confirm the presence of an accessory right spermatic ganglion at the base of the accessory retrocaval testicular artery. Interestingly, the accessory spermatic ganglion was also supplied by its own right lumbar splanchnic nerve. This is the first case to describe the anatomy of an accessory spermatic ganglion in a specimen that exhibits an accessory testicular artery on the right side. This neurovascular variation is of interest to surgeons who aim to perform nerve-sparing retroperitoneal lymph node dissections for malignancy.

Morphological structure and variations of lumbar plexus in human fetuses.

The objective of this study is to study the anatomy of lumbar plexus on human fetuses and to establish its morphometric characteristics and differences compared with adults. Twenty lumbar plexus of 10 human fetal cadavers in different gestational ages and genders were dissected. Lumbar spinal nerves, ganglions, and peripheral nerves were exposed. Normal anatomical structure and variations of lumbar plexus were investigated and morphometric analyses were performed. The diameters of lumbar spinal nerves increased from L1 to L4. The thickest nerve forming the plexus was femoral nerve, the thinnest was ilioinguinal nerve, the longest nerve through posterior abdominal wall was iliohypogastric nerve, and the shortest nerve was femoral nerve. Each plexus had a single furcal nerve and this arose from L4 nerve in all fetuses. No prefix or postfix plexus variation was observed. In two plexuses, L1 nerve was in the form of a single branch. Also, in two plexuses, genitofemoral nerve arose only from L2 nerve. Accessory obturator nerve was observed in four plexuses. According to these findings, the morphological pattern of the lumbar plexus in the fetus was found to be very similar to the lumbar plexus in adults.

Distinct roles for secreted semaphorin signaling in spinal motor axon guidance.

Neuropilins, secreted semaphorin coreceptors, are expressed in discrete populations of spinal motor neurons, suggesting they provide critical guidance information for the establishment of functional motor circuitry. We show here that motor axon growth and guidance are impaired in the absence of Sema3A-Npn-1 signaling. Motor axons enter the limb precociously, showing that Sema3A controls the timing of motor axon in-growth to the limb. Lateral motor column (LMC) motor axons within spinal nerves are defasciculated as they grow toward the limb and converge in the plexus region. Medial and lateral LMC motor axons show dorso-ventral guidance defects in the forelimb. In contrast, Sema3F-Npn-2 signaling guides the axons of a medial subset of LMC neurons to the ventral limb, but plays no major role in regulating their fasciculation. Thus, Sema3A-Npn-1 and Sema3F-Npn-2 signaling control distinct steps of motor axon growth and guidance during the formation of spinal motor connections.

The course and branching pattern of pudendal nerve in fetus.

The pudendal nerve is a considerably large branch of the sacral plexus. There are many articles in the literature concerning the pudendal nerve in adults, but as far as we know, there is none on the branching pattern and variations in pudendal nerve anatomy in fetus. This study investigates the pudendal nerve trunking with respect to the piriformis muscle in 25 formalin-fixed fetuses (50 sides of pelves, 15 females, 10 males), ranging from 20 to 37 weeks of gestation. We investigate pudendal nerve trunking in four types: Type I-a is defined as single-trunk with the inferior rectal nerve branching proximal to the dorsal nerve of penis/clitoris (38%), Type I-b is also single-trunk with the dorsal nerve of penis/clitoris branching proximal to the inferior rectal nerve (24%), Type II is double-trunk with medial trunk as an inferior rectal nerve (34%), and Type III is triple-trunk (4%). We measured the average diameter of the main trunk of pudendal nerve in Type I-a and I-b groups to be 0.98 +/- 0.33 mm. We also measured the average length of the pudendal nerve trunks before the dorsal nerve of penis/clitoris branch to be 7.35 +/- 3.50 mm. There was no significant statistical difference in the average length, diameter, number of trunks, and pudendal nerve variations between male and female and also right and left sides of the pelves. This first and detailed fetal study of pudendal nerve trunking with respect to the piriformis muscle would be useful for educational anatomy dissections and anatomical landmark definitions for relevant clinical procedures.

Reduction of the naturally occurring motor neuron loss by enlargement of the periphery.

Motor hyperplasia following the enlargement of the periphery by implantation of a supernumerary leg is not due to "remote control" of proliferation, as shown by motor neuron counts in 6-day chick embryos. We have tested the alternative hypothesis that we are dealing with reduction of the naturally occurring cell death. In normal development, the lumbar lateral motor column (l.m.c.) undergoes motor neuron degeneration resulting in a cell loss of at least 40%, which occurs between six and one-half and nine and one-half days. Following transplantation of supernumerary legs, cases selected for vigorous motility showed a numerical difference between experimental and contralateral (control) sides amounting to +11.0% to +27.5%. The transplants were innervated by varying combinations of thoracic and rostral lumbar nerves. We interpret our data in terms of survival of motor neurons which normally would have failed in a competition at the periphery but which were sustained by the enlarged peripheral fields. Our data do not permit a decision between the two alternatives: competition for synaptic sites or for a trophic agent. The surviving motor neurons are not limited to the rostral segments of the motor column but in most instances distributed along its entire rostro-caudal extent, implying a redistribution of all l.m.c. axons. The term "hyperplasia" is no longer appropriate for the phenomenon under consideration and should be replaced by the term "hypothanasia.""

The morphogenesis of the thigh of the mouse with special reference to tetrapod muscle homologies.

In order to provide an ontogenetic basis for the establishment of tetrapod muscle homologies and for the analysis of complex mammalian muscle states, a descriptive analysis of the morphogenesis of the thigh of Mus musculus has been made. The pattern and sequence of muscle cleavage and the migrations of individual muscle primordia are characterized from the eleventh day of gestation, when cleavage begins, through early neonatal stages. Observations on skeletal differentiation and lumbosacral plexus formation are also included. Thigh muscle morphogenesis is compared to that in the lizard, Lacerta, (Romer, '42) and the chick (Romer, '27) and homologies identified. An onogenetic basis for the definition of ancestral and derived muscle states is provided in muscles that are morphologically variable in mammals. These include the gluteus minimus, gracilis, adductor brevis and several hamstring muscles. Certain muscles that show variable innervation patterns in adult mammals, i.e., pectineus, quadratus and adductor magnus, typically develop from premuscle regions that separate muscle anlagen innervated by different nerves. Two muscle anlagen appear in the embryonic mouse thigh and then disappear late in prenatal or early postnatal development. Comparisons with other mammals, especially the marsupial, Marmosa, reveal that these muscles are phylogenetic vestiges that degenerate before maturity. A sartorius vestige is identifiable through the thirteenth day of gestation. A tenuissimus anlage is present until shortly after birth and is clearly innervated by a branch of the peroneal nerve.

The rostrocaudal organization in the dorsal root ganglia of the rat: a consequence of plexus formation?

The dorsal root ganglia (DRGs) of the rat have a rostrocaudal organization. This organization can most easily be demonstrated in fetal and neonatal rats because the spatial relationships of their DRGs are maintained better in tissue sections than those of mature rats. This review is concerned with the way in which the rostrocaudal organization of the DRGs is generated. Wheat germ agglutinin--horseradish peroxidase/horseradish peroxidase labeling of peripheral nerves of the brachial and lumbar plexuses shows that the position of the somata of the sensory neurons of the labeled nerves can be restricted to rostral or caudal halves of DRGs. Labeling of the thoracic nerve or its branches always results in labeling throughout the entire thoracic DRG. After application of the marker to forelimb nerves, it was observed that whenever a DRG is labeled only partially, its spinal nerve is correspondingly labeled partially as well. These data suggest that the rostrocaudal organization in the DRG is related to the formation of the plexuses. During development nerve fibers can be segmentally labeled, using the subdivision of the DRGs into a rostral and a caudal half to keep together as they find their way through the plexus. Application of label to forelimb skin, hindlimb skin and even thoracic skin can result in labeling of rostral or caudal halves of a DRG. A possible explanation might be that each dermatome can be divided into a skin area innervated by the rostral half of a DRG and a skin area innervated by the caudal half of the same dorsal root ganglion. In the rat, the segmental sensory innervation of muscles during development has not yet been investigated. The question of whether the segmental unit of innervation of a muscle is a whole DRG or half a DRG therefore still remains unanswered.

The uterosacral complex: ligament or neurovascular pathway? Anatomical and histological study of fetuses and adults.

The aim of this study was to define the anatomical relationships of the uterosacral ligament complex (USLC) and to analyze histologically its content. Three fetal and four adult cadavers were used. Anatomical dissections were carried out. Eight fresh biopsies (four fetal and four adult) of the USLC were analyzed histologically and immunohistochemically. Specimens were stained with hematoxylin eosin safran coloration, with anti-nervous cell antibodies (PS 100) and with anti-smooth muscle antibodies (to visualize vessel walls). By removing the visceral pelvic fascia, nervous fibers were found within the USLC forming the hypogastric plexus. Histologically, the USLC contained connective tissue, nervous fibers, sympathetic nodes, vessels, and fatty tissue. No structured ligamentous organization was identified. The uterosacral "ligament" is a "complex" integrating connective tissue as well as nervous and vascular elements. Radical excisions and USLC suspension during pelvic floor reconstructive surgery should be performed with caution in order to preserve pelvic innervation.

[Reconstruction of the lumbosacral plexus of an embryo at stage 23 (25mm) and an embryo at stage 16 (7,5mm)]. / Réconstruction du plexus lombo-sacral d'un embryon du stade 23 (25 mm) et d'un embryon du stade 16 (7,5 mm).

Two embryos, one at stage 23 and another at stage 16, are reconstructed in view of studying the evolution of the lumbosacral plexus. At stage 16, the sacral plexus begins its development with anastomosis of L5, S1 and S2 roots, while the pelvic member is scarcely sketched. At stage 23, the evolution is complete, the pelvis is entirely constitued and the femoral, sciatic and obturator nerves of adult type. The coccygian plexus is in process of construction.

Specificity of early motoneuron growth cone outgrowth in the chick embryo.

During development, chick lumbosacral motoneurons have been reported to form precise topographic projections within the limb from the time of initial outgrowth. This observation implies, first, that motoneurons select the appropriate muscle nerve pathway and, second, that they restrict their ramification within the primary uncleaved muscle masses to appropriate regions. Several reports based on electrophysiology and orthograde horseradish peroxidase (HRP) labeling have shown muscle nerve pathway selection to be fairly precise. However, studies based on retrograde labeling with HRP have produced conflicting reports on the extent to which vertebrate motoneurons make projection errors. Since it is difficult to distinguish between true projection errors and HRP leakage when using retrograde labeling, we decided to assess the distribution of labeled growth cones in 25-micron serial plastic sections, following orthograde labeling of identifiable subpopulations of motoneurons during the period of initial axon outgrowth. Examination of a large number of muscle nerves revealed no segmentally inappropriate axons, confirming earlier reports that muscle nerve pathway selection is very accurate. In addition, we observed that growth cones take widely divergent trajectories into the same muscle nerve, suggesting that growth cones are responding independently to some specific environmental cue rather than being passively channeled at this point. The distribution of labeled growth cones within the muscle masses provided direct evidence that motoneurons did not at any time project to obviously inappropriate muscle regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth cone morphology and trajectory in the lumbosacral region of the chick embryo.

We quantitatively analyzed several features of orthogradely labeled peripheral growth cones in the lumbosacral region of the chick embryo. We compared motoneuron growth cones in regions where they appear to express specific directional preferences (the plexus region and regions where muscle nerves diverge from main nerve trunks), which we operationally defined as "decision regions," to motoneuron growth cones in other pathway regions (the spinal nerve, nerve trunk, and muscle nerve pathways) which we termed, for contrast, "non-decision region." We found that motoneuron growth cones are larger, more lamellepodial, and have more complex trajectories in decision regions. Sensory growth cone populations, which are thought to be dependent upon motoneurons for outgrowth (Landmesser, L., and M. Honig (1982) Soc. Neurosci. Abstr. 8: 929), do not enlarge or become more lamellepodial in motoneuron decision regions, suggesting that this local environment does not affect all species of growth cones equally and that the alterations in motoneuron growth cones in these regions may be relevant to their specific guidance. In addition, the resemblance between the sensory population and other closely fasciculating growth cones lends support to the suggestion that sensory neurons utilize motoneuron neurites as a substratum. We suggest that the convoluted trajectories, enlarged size, and more lamellepodial morphology of motoneuron growth cones in decision regions is either related directly to the presence of specific cues that guide motoneurons or to some aspect of this environment that allows them to respond to specific cues.

Bidirectional inhibitory interactions between the embryonic chicken metanephros and lumbosacral nerves in vitro.

During chicken embryonic development the metanephros forms from the uretic duct at embryonic day (E) 7. As the metanephric tissue develops between E7 and E10, it comes into close apposition with lumbosacral nerves. Coculturing of metanephric and nerve explants demonstrated that the Schwann cells of the sciatic nerve inhibit the migration of metanephric cells in a contact-dependent manner. Conversely, metanephric cells inhibit dorsal root ganglion axon extension in a contact-dependent manner. However, metanephric cells are not inhibited by contact with growth cones or axons. Dorsal root ganglion growth cones become sensitive to the inhibitory signals on the surfaces of metanephric cells around E8, a time when the metanephros is expanding into the territory occupied by nerves in vivo. These observations demonstrate inhibitory bidirectional tissue-tissue interactions in vitro and provide a novel model system for the study of contact-based guidance of both neuronal and non-neuronal cell migration.

The human vertebral column at the end of the embryonic period proper. 4. The sacrococcygeal region.

The sacral and coccygeal vertebrae at 8 postovulatory weeks (the end of the embryonic period proper) have been studied by means of graphic reconstructions. The cartilaginous sacrum is now a definitive unit composed of five separable vertebrae, each of which consists of a future centrum and bilateral neural processes. The base of each neural process consists of an anterolateral or alar element, not present in the lumbar region, and a posterolateral part, which includes costal and transverse elements. The usual illustrations, in which the costal component is placed in the alar element, are incorrect. The future dorsal foramina (containing dorsal rami) face laterally in the embryo and are in line with the thoracicolumbar intervertebral foramina. Considerable differential growth is required to change the dorsal openings from a lateral to a dorsal positions. The intervertebral foramina transmit ventral rami, but pelvic foramina are not yet present. The lumbosacral plexus is completed by S.N.1-3; S.N.4, 5 and Co.N.1 form the pelvic plexus. The inferior hypogastric plexus and the hypogastric nerves are present. The sacrum takes part in the spina bifida occulta that characterises the entire length of the embryonic vertebral column. The coccygeal vertebrae, which are variable, were 4-6 in number in the present series. The first is the best developed. The ventriculus terminalis ends usually at the level of Co.V.1 and the spinal cord generally at Co.V.5. The coccygeal notochord ends commonly in bifurcation or trifurcation. 'Haemal arches' were not observed.

The early development of the lymphatic system in mouse embryos.

The early development of the lymphatic system was studied in embryos of an inbred strain of the laboratory mouse. During the first stage of its development the system is represented by a more or less regular series of small and blind-ending outgrowths of the major embryonic veins which develop in a cranio-caudalward direction from the jugular to the pelvic region. As a result of differences in growth rates of adjacent anatomical structures this series of early lymphatic primordia becomes subdivided into 4 singular primordia and 12 groups of primordia. After the constituents of each group of early primordia have fused, 16 isolated lymphatic plexuses (sacs) are formed of which 14 are in bilaterally symmetric and 2 are in a median line position: i.e. bilaterally: (1) the jugulo-axillary lymph sac situated lateral to the anterior cardinal vein and dorsal to the primitive ulnar vein and its major branch, the external mammary vein, (2) the paratracheal lymph plexus situated medial to the anterior cardinal vein, (3) the internal thoracic lymph plexus situated lateral to the thoracic part of the posterior cardinal vein, (4) the thoracic ducts situated medial to the thoracic part of the posterior cardinal vein, (5) the lumbar lymph plexus situated dorso-lateral to the abdominal part of the posterior cardinal vein, (6) the subcardinal lymph plexus and (7) the iliac lymph plexus situated ventro-lateral to the abdominal part of the posterior cardinal vein; and in the median line: (8) the subtracheal lymph plexus situated at the confluence of the pulmonary veins and (9) the mesenteric lymph plexus situated near the confluence of the splenic and the superior mesenteric veins. Except for some openings at the jugulo-subclavian confluence all connections with the veins disappear. From the primordia extensions grow out centrifugally. They invade the surrounding tissues and, in part, fuse with similar sprouts of adjacent primordia. In this way a continuous system of lymph truncs is formed that opens into the venous system at the jugulo-subclavian confluence.

Sacral neural crest cells colonise aganglionic hindgut in vivo but fail to compensate for lack of enteric ganglia.

The vagal neural crest is the origin of majority of neurons and glia that constitute the enteric nervous system, the intrinsic innervation of the gut. We have recently confirmed that a second region of the neuraxis, the sacral neural crest, also contributes to the enteric neuronal and glial populations of both the myenteric and the submucosal plexuses in the chick, caudal to the level of the umbilicus. Results from this previous study showed that sacral neural crest-derived precursors colonised the gut in significant numbers only 4 days after vagal-derived cells had completed their migration along the entire length of the gut. This observation suggested that in order to migrate into the hindgut and differentiate into enteric neurons and glia, sacral neural crest cells may require an interaction with vagal-derived cells or with factors or signalling molecules released by them or their progeny. This interdependence may also explain the inability of sacral neural crest cells to compensate for the lack of ganglia in the terminal hindgut of Hirschsprung's disease in humans or aganglionic megacolon in animals. To investigate the possible interrelationship between sacral and vagal-derived neural crest cells within the hindgut, we mapped the contribution of various vagal neural crest regions to the gut and then ablated appropriate sections of chick vagal neural crest to interrupt the migration of enteric nervous system precursor cells and thus create an aganglionic hindgut model in vivo. In these same ablated animals, the sacral level neural axis was removed and replaced with the equivalent tissue from quail embryos, thus enabling us to document, using cell-specific antibodies, the migration and differentiation of sacral crest-derived cells. Results showed that the vagal neural crest contributed precursors to the enteric nervous system in a regionalised manner. When quail-chick grafts of the neural tube adjacent to somites 1-2 were performed, neural crest cells were found in enteric ganglia throughout the preumbilical gut. These cells were most numerous in the esophagus, sparse in the preumbilical intestine, and absent in the postumbilical gut. When similar grafts adjacent to somites 3-5 or 3-6 were carried out, crest cells were found within enteric ganglia along the entire gut, from the proximal esophagus to the distal colon. Vagal neural crest grafts adjacent to somites 6-7 showed that crest cells from this region were distributed along a caudal-rostral gradient, being most numerous in the hindgut, less so in the intestine, and absent in the proximal foregut. In order to generate aneural hindgut in vivo, it was necessary to ablate the vagal neural crest adjacent to somites 3-6, prior to the 13-somite stage of development. When such ablations were performed, the hindgut, and in some cases also the cecal region, lacked enteric ganglionated plexuses. Sacral neural crest grafting in these vagal neural crest ablated chicks showed that sacral cells migrated along normal, previously described hindgut pathways and formed isolated ganglia containing neurons and glia at the levels of the presumptive myenteric and submucosal plexuses. Comparison between vagal neural crest-ablated and nonablated control animals demonstrated that sacral-derived cells migrated into the gut and differentiated into neurons in higher numbers in the ablated animals than in controls. However, the increase in numbers of sacral neural crest-derived neurons within the hindgut did not appear to be sufficiently high to compensate for the lack of vagal-derived enteric plexuses, as ganglia containing sacral neural crest-derived neurons and glia were small and infrequent. Our findings suggest that the neuronal fate of a relatively fixed subpopulation of sacral neural crest cells may be predetermined as these cells neither require the presence of vagal-derived enteric precursors in order to colonise the hindgut, nor are capable of dramatically altering their proliferation or d

Sacral neural crest cell migration to the gut is dependent upon the migratory environment and not cell-autonomous migratory properties.

Avian neural crest cells from the vagal (somite level 1-7) and the sacral (somite level 28 and posterior) axial levels migrate into the gut and differentiate into the neurons and glial cells of the enteric nervous system. Neural crest cells that emigrate from the cervical and thoracic levels stop short of the dorsal mesentery and do not enter the gut. In this study we tested the hypothesis that neural crest cells derived from the sacral level have cell-autonomous migratory properties that allow them to reach and invade the gut mesenchyme. We heterotopically grafted neural crest cells from the sacral axial level to the thoracic level and vice versa and observed that the neural crest cells behaved according to their new position, rather than their site of origin. Our results show that the environment at the sacral level is sufficient to allow neural crest cells from other axial levels to enter the mesentery and gut mesenchyme. Our study further suggests that at least two environmental conditions at the sacral level enhance ventral migration. First, sacral neural crest cells take a ventral rather than a medial-to-lateral path through the somites and consequently arrive near the gut mesenchyme many hours earlier than their counterparts at the thoracic level. Our experimental evidence reveals only a narrow window of opportunity to invade the mesenchyme of the mesentery and the gut, so that earlier arrival assures the sacral neural crest of gaining access to the gut. Second, the gut endoderm is more dorsally situated at the sacral level than at the thoracic level. Thus, sacral neural crest cells take a more direct path to the gut than the thoracic neural crest, and also their target is closer to the site from which they initiate migration. In addition, there appears to be a barrier to migration at the thoracic level that prevents neural crest cells at that axial level from migrating ventral to the dorsal aorta and into the mesentery, which is the portal to the gut.