Anatomical basis of syringomyelia occurring with hindbrain lesions

Hindbrain lesions that distort or compress the cervicomedullary junction are commonly associated with syringomyelia. As a basis for discussing pathogenetic mechanisms, the upper end of the central canal of the spinal cord was examined histologically in six aborted fetuses and 14 adults dying of natural causes; the results were correlated with magnetic resonance images in 40 normal subjects. The central canal of the medulla, which extends from the cervicomedullary junction to the fourth ventricle, was found to migrate dorsally, elongate in dorsoventral diameter, and dilate beneath the tip of the obex to form a large, everted aperture. This opening communicates directly with the subarachnoid space through the foramen of Magendie and is indirectly continuous with the main body of the fourth ventricle. In adults, the aperture of the central canal is located approximately 1.0 cm below the tela choroidea inferior and 3.5 cm below the midpoint of the fourth ventricle. Analysis of magnetic resonance imaging scans in 45 patients with syringomyelia and simple hindbrain lesions revealed two patterns of cavity formation: 1) lesions that obstructed the upper end of the central canal or its continuity with the subarachnoid space produced a noncommunicating type of syringomyelia; and 2) lesions that obstructed the basilar cisterns or the foraminal outlets of the fourth ventricle produced a communicating type of syringomyelia (hydromyelia) in association with hydrocephalus. Evidence is presented that syrinxes occurring with hindbrain lesions are not caused by a caudal flow of cerebrospinal fluid from the fourth ventricle into the central canal of the spinal cord.

Prenatal ontogeny of substance P-like immunoreactivity in the nucleus tractus solitarii and dorsal motor nucleus of the vagus nerve of the human fetus: an immunocytochemical study

By using immunocytochemical method, the prenatal ontogeny of substance P-like immunoreactivity (SP-LI) was demonstrated in the dorsal motor nucleus of the vagus nerve (nX) and the nucleus tractus solitarii (nTS) of the human fetus at fetal age (menstruation age) of 11.5 weeks to 40 weeks. The time of initial appearance of SP-LI in the human brainstem nTS was between the fetal age 11.5 weeks and 16 weeks. At fetal age 16 weeks, the nTS showed moderate density of SP-LI fibers and terminals in subnucleus dorsalis of the nTS and nX. While the fetus grew, the density of SP-LI in the human fetus brainstem nTS and nX increased gradually from fetal age 16 weeks to 40 weeks. According to the Nissl staining, at fetal age 23 weeks, the nTS of human fetus can be subdivided into dorsal, medial, dorsolateral, ventrolateral, ventral and gelatinosus subnuclei. The cytoarchitectonic subdivisions of human fetus nTS is in good agreement with the results obtained by immunocytochemical staining. These findings indicated that substance P (SP) might play an important role in the development of human brainstem nX, nTS, their related cranial nerves, and in their functional establishment during the prenatal period.

Ontogenetic study of early brain stem projections to the spinal cord in the rat

In an attempts to describe the early development of the brain stem-spinal projections, we implanted DiI crystals at the C3 level of the spinal cord of 13- and 14-day fixed embryos. After a diffusion period of 2 to 4 months, neurons of the rhombencephalic reticular formation were retrogradely labeled by the tracer. This group of neurons was situated ventromedially in the tegmentum. Their axons coursed into the ventral marginal layer at bulbar levels and entered the ventral funiculus when reaching the spinal cord. Neurons of the lateral vestibular nucleus were also labeled and gave rise to descending fibers that gradually moved medially and entered the spinal cord in the ventral funiculus. In the mesencephalon, labeled cell bodies of the interstitial nucleus of Cajal (InC) were found lying ventrally in the tegmentum, at the rostral end of the medial longitudinal fasciculus (mlf), in which their axons coursed. Also, in the midbrain, several cells lying dorsal to the InC, with axons descending in the lateral tegmentum, were tentatively identified as part of the mesencephalic reticular formation.

Optical monitoring of early appearance of spontaneous membrane potential changes in the embryonic chick medulla oblongata using a voltage-sensitive dye

Using a voltage-sensitive merocyanine-rhodamine dye (NK2761) and a 12 x 12-element photodiode matrix array, we recorded optically spontaneous membrane potential changes in a slice preparation from the embryonic chick brain stem during early development. The spontaneous optical signals, related to membrane potential changes, showed a simple monophasic shape with a relatively long duration, and they were synchronized among the different regions in the medulla oblongata. The spontaneous signals were first detected from seven-day-old embryos, and were not present in six-day-old embryos. The spontaneous signals appeared sporadically, and their frequency was very low. Three modes of optical signals termed "singlet-mode", "doublet-mode", and "triplet-mode" were observed. In the doublet- and triplet-modes, the spatial pattern of the first signal was primarily similar to that of the singlet-mode signal, whereas the signal size and spatial extent of the second and third signals appeared to decay.

Immunohistochemical localization of enkephalin and substance P in the nucleus caudalis of the spinal trigeminal V in the medulla oblongata of the human fetus

The distribution of enkephalin-positive neurons, substance P-positive and enkephalin-positive fibers was studied in the nucleus caudalis of the trigeminal spinal V in the medulla oblongata regions of developing humans (12 weeks gestation to 40 weeks gestation). Enkephalin-positive neurons were identified in all the subnuclei of the nucleus caudalis as early as 12 weeks of gestation and increased in number as the fetus aged. Substance P-positive neurons were absent in this area throughout development. On the other hand, substance P-positive and enkephalin-positive fibers were present in all the subnuclei, again commencing as early as 12 weeks of gestation. These fibers tended to be linked to each other in the different subnuclei and to the reticular formation in this area and to increase significantly in quantity by the latter quarter of pregnancy. These results show the early presence of these neurons and fibers in the first trimester of development.

Differentiation of the brain stem structures in the salamander, Hynobius nebulosus

Differentiation of the internal structure of the brain stem was analyzed in the salamander with special reference to neurons distributed in the marginal layer. It was found that the salamander brain stem was at first composed exclusively of the mantle layer. The marginal layer later differentiated peripherally. In these developmental stages, the mantle and marginal layers were clearly differentiated: the former was made up exclusively of the somata, while the latter was composed mainly of nerve fibers. As the development proceeded, these organization patterns were modified: a few cells migrated into the marginal layer. Cells migrating into the marginal layer formed various nuclei and layers such as the raphe nuclei, reticular formation and superficial cellular layers of the optic tectum. In later development stages, fibers in the marginal layer were myelinated, and neurons in the marginal layer were observed to become embedded among numerous myelinated fibers. Cytologically, the majority of neurons in early developmental stages were unipolar, extending a process peripherally into the marginal layer. In later developmental stages, neurons in a deep zone of the mantle layer remained unipolar, whereas those in the marginal layer and in the superficial zone of the mantle layer differentiated into multipolar cells. Thus, (1) the marginal layer differentiated peripherally as a cell free region; (2) cells in the mantle layer later migrated into the marginal layer, changing into multipolar neurons; (3) cells in the marginal layer formed reticular formation as well as various nuclei and layers in the peripheral white matter; and (4) as development proceeded, fibers in the marginal layer became myelinated.

Effect of ethanol on the release of prostaglandins from ovine fetal brain stem during gestation

Prostaglandins (PGs) have been implicated as mediators of the ethanol-induced suppression of ovine fetal breathing movements (FBM). The objectives of the present study were to determine the ontogeny of the in vitro efflux of PGE2 and 6-keto PGF1 alpha in ovine fetal brain stem during the second half of gestation and to determine the effect of in vitro ethanol exposure on the efflux of these PGs. Ovine fetal brain stem tissue was obtained at mean gestational ages of 80 days (n = 6), 105 days (n = 10), and 135 days (n = 16) by rapid excision following maternal euthanization. Tissue slices (400 microM thickness) were prepared from the lower pons-medulla region of the brain stem. After a 1-hr equilibration period in artificial cerebrospinal fluid, efflux of PGE2 and 6-keto PGF1 alpha in the brain stem was determined using the brain slice-superfusion method, and the PGE2 and 6-keto PGF1 alpha concentrations in the superfusate were determined by specific radioimmunoassay. The mean spontaneous efflux of PGE2 and 6-keto PGF1 alpha expressed as pmol PG/gram wet weight of tissue/5-min collection period was, respectively, 31.9 +/- 4.2 and 26.6 +/- 2.4 at 80 days, 38.3 +/- 5.2 and 29.6 +/- 2.2 at 105 days, and 57.4 +/- 3.1 and 27.1 +/- 1.1 at 135 days of gestation. In vitro exposure to 20, 40, and 80 mM ethanol did not affect PG efflux in the brain stem at 80 and 105 days of gestation. In vitro ethanol exposure decreased PGE2 and 6-keto PGF1 alpha efflux at 135 days of gestation to 36.8 +/- 5.3% and 41.6 +/- 4.3% of spontaneous efflux within 15 min, respectively; this effect of ethanol was not dose-dependent. The data do not support the hypothesis that ethanol increases PG efflux in the ovine fetal brain stem. In view of these findings and the data implicating PGs in the mechanism of ethanol-induced suppression of FBM, it is possible that ethanol acts at either central sites rostral to the brain stem (i.e., upstream CSF) or peripheral sites to increase the synthesis of PGs and their efflux into the systemic circulation, with subsequent transfer to the respiratory control region(s) of the brain stem.

Further data on the development of SRIF-like immunoreactive nerve cell populations in the chick embryo brain stem. I. Medulla and pons

Further immunocytochemical analysis of the neuroblasts with SRIF-like immunoreactivity (ir) was carried out on the chick embryo medulla and pons. 5 or 100 microns rombencephalon sections were obtained from 60 White Leghorn chick embryos at stages (E = Embryonic days) ranging from E4 1/2 to E18 and incubated with rabbit polyclonal antibodies against synthetic cyclic Somatostatin-14, according to PAP-DAB technique. In the medulla and pons the ir appeared as from E12. From E12 to E13 1/2-E14 the ir distribution gradually changed. From E14 to E18 numbers and spatial arrangement of the positive neuroblast groups did not show substantial changes; in these respects the ir distributional pattern proved to be markedly different from the one observed by the Authors in adult animals. Moreover, from E13 to E15 the positive neuroblast density appeared to be higher than that of positive neurons in adults. These results are consistent with a possible SRIF local regulative role.

Respiratory and locomotor patterns generated in the fetal rat brain stem-spinal cord in vitro

An in vitro brain stem-spinal cord preparation from last trimester (E13-E21) fetal rats, which generates rhythmic respiratory and locomotor patterns, is described. These coordinated motor patterns emerge at stages E17-E18. Synchronous rhythmic motor activity, not clearly characterized as respiratory or locomotor, can occur as early as E13. With this preparation, it is now possible to study the ontogenesis of circuits and cellular mechanisms underlying these critical movements.

Developmental pattern of muscarinic receptors in normal and Down's syndrome fetal brain--an autoradiographic study

The ontogeny of muscarinic cholinergic receptors in developing human brain was analyzed by in vitro receptor autoradiography with [3H]Quinuclidinyl Benzilate. It was found that muscarinic receptors develop relatively early; the levels at 24 weeks of gestation were comparable or even higher then the values in the adult brain, and that the levels of both M1 and M2 receptors increase with age. M1 receptors were concentrated mainly in forebrain regions while M2 receptors dominated in the thalamus. Scatchard analysis revealed Kd and Bmax values which are comparable to the adult values. Three brains of aborted Down's syndrome fetuses were examined in parallel and exhibited comparable levels and similar distribution to normal non-Down fetuses except for a modest increase of receptor levels which was observed in the striatum.

Development of projections of primary afferent fibers from the hindlimb to the gracile nucleus: a WGA-HRP study in the rat

The projection of primary afferent fibers to the gracile nucleus was studied during development. Injections of wheat germ agglutinin-horseradish peroxidase were made into the hindlimb of fetal, postnatal and adult rats. In most cases the sections were alternately stained for wheat germ agglutinin-horseradish peroxidase including counter stain with Neutral red and for acetylcholinesterase. At embryonic day 17 labelled fibers could be traced to the mid-cervical spinal cord but not further rostrally. At embryonic days E18 and E19 labelled fibers penetrate the rostral pole of the nucleus, which does not happen more caudally. At embryonic day E21 the caudal-most pole of the gracile nucleus still is not penetrated by labelled fibers. From postnatal day 1 onwards labelled fibers are found throughout the entire rostrocaudal extent of the gracile nucleus. These results suggest that primary afferent fibers from the hindlimb first grow to the rostral pole of the gracile nucleus and penetrate the rostral pole immediately upon their arrival. During further development more caudal parts of the gracile nucleus are gradually penetrated in a rostrocaudal fashion by primary afferent fibers of the hindlimb.

Characterization of beta-endorphin-related peptides in the caudal medulla oblongata and hypothalamus of the prenatal, postnatal and adult rat

A comparison was made of beta-endorphin (B-END) concentrations versus post-translation products during the perinatal period in the hypothalamus and the caudal medulla oblongata. The concentration of B-END-like immunoreactivity did not differ statistically between embryonic day 21 (E21) and postnatal day 1 (P1) in either area. There were significant differences in forms, with a shift from larger precursors at E21 to smaller peptides at P1, with the predominant form of B-END being the 31 residue form at E21 in both regions. B-END varied between the two regions at P1, the 27-26 residue predominant in the hypothalamus, and the 31 residue in the caudal medulla.

The earliest ultrastructural development of the tangential vestibular nucleus in the chick embryo

The tangential nucleus is a primary vestibular nucleus located where the vestibular fibers enter the medulla. It is composed of neurons that migrate between 5 and 8 days in the chick embryo. Although primary vestibular fibers enter the medulla at 3 days, the first synapses are formed at 5 days on the processes of neuron precursors by longitudinally coursing fibers. Since the major components, or their precursors, are present at 3 days within the presumptive nucleus, we are interested in determining what cellular interactions occur among these structures following their entry and during the time leading up to synapse formation. At 2 days, prior to the appearance of VIIth and VIIIth nerve fibers in the medulla, the tangential nucleus anlage contained processes and endfeet of primitive epithelial cells, separated from each other by enlarged extracellular spaces. Longitudinal fibers first appeared within these spaces coincident with the appearance of root fibers, including some identified VIIth motor axons, associated with the primordial VII/VIIIth ganglia. By 3 days, some vestibular and VIIth nerve fibers could be identified by their ultrastructure and relative positions within the marginal zone and nerve roots. However, it was not until 4 days that the presumptive tangential nucleus acquired its orderly, characteristic organization. Although synapses were rare from 2 to 4 days, attachment plaques and coated pits were observed commonly between structures, especially between future synaptic structures. Thus, we confirm that synapse formation begins at 5 days. This represents the first detailed ultrastructural study of cranial sensory nerve ingrowth into the medulla.

Formation of the cochlea in the chicken embryo: sequence of innervation and localization of basal lamina-associated molecules

The purpose of this study was to determine the temporal and spatial gradients in the innervation of the chicken cochlea, the basilar papilla, as it develops in the early embryo. A series of white Leghorn chick embryos (Hamburger-Hamilton Stage 20-43) were prepared for serial sectioning and stained by Toluidine blue or by antibodies to fibronectin or laminin. Light microscopic observations were made on the first fiber bundles to reach each region of the basilar papilla. There is a distinct temporo-spatial pattern of the ingrowth of fiber bundles to the developing basilar papilla. The primary pattern is not described as any simple linear gradient. Fiber ingrowth begins proximally, shifts to a distal and then to a mid-proximal region. The fiber ingrowth correlates temporally and spatially with disruption of fibronectin and laminin staining of the basal lamina where fiber bundles are penetrating. This pattern may reflect not only the sequence of fiber ingrowth but also the displacement of cells and fibers in the elongating basilar papilla, which grows as a result of a contemporaneous mitotic activity throughout the structure rather than progressing from one end to the other.

Development of the nuclei and cell migration in the medulla oblongata. Application of the quail-chick chimera system

We have tried to obtain new insight into the development of the medulla oblongata by using the quail-to-chick chimera system. Five types of isotopic and isochronic grafts were carried out, between quail and chick embryos, at the 10- to 12-somite stage: exchanges of (I) the entire myelencephalon, (II) the dorsal half of the myelencephalon, (III) the ventral half of the myelencephalon, (IV) the right half of the myelencephalon and (V) the dorsal quarter of the myelencephalon. Before analyzing the chimeric embryos, we studied the ontogeny of the various nuclei in the medulla oblongata of normal birds. The first appearance of nuclei in quail embryos preceded in many cases that of their chick counterpart by 12 to 24 h. The adult pattern of the nuclei was established by E8 in quail and E9 in chick. Similarly, during early development of chimeras, the migration of quail cells began earlier than that of chick cells. This shows that the species specific temporal sequence of proliferation and migration is not significantly altered by transplantation into the host. The possibility of grafting selectively the ventral or dorsal half of the neural tube allowed us to distinguish the fate of the cells belonging respectively to the alar and the basal plate. The nuclei with a total or partial motor function, such as the nucleus nervi abducentis, the nucleus nervi facialis, the nucleus nervi glossopharyngei and the nucleus motorius dorsalis nervi vagi, have either an exclusive or predominant origin from the basal plate. In contrast, the nuclei with essentially or exclusively sensory components (i.e., nucleus angularis, nucleus laminaris, nucleus magnocellularis) arise from the alar plate. The reticular formation such as the nucleus reticularis gigantocellularis and the nucleus reticularis subtrigeminalis was strikingly mixed, with both alar and basal plate origin of neurons. Active dorsoventral migrations of cells originating migrations from the dorsal neural tube, the "rhombic lip", contribute the ventral nuclei (i.e., nuclei pontis medialis, lateralis and olivaris inferior), whose functions are essentially associative. This study shows different types of cell migration. Dorsoventral and ventrodorsal movements are essentially active from E5 to E8. In the medulla oblongata, the dorsoventral stream is highly predominant. From E8 to E9, cells belonging to the marginal stream cross the midline laterally in both directions. Beyond E12, longitudinal migrations occur ventrally in both rostrocaudal and caudorostral directions. The immunohistochemical analyses carried out on chimeras generated in experiment V revealed the existence of fibers in marginal zones prior to the onset of the migration of cell bodies.(ABSTRACT TRUNCATED AT 400 WORDS)

Formation of synapses in cerebellar explants by axons from co-cultured medulla

Explants of cerebellum from E12-E14 chick embryos were co-cultured with pieces of medulla from the same embryos for periods of up to 4 weeks and examined by EM with or without prior transection of the fibre bundles that formed rapidly between the co-cultured explants. The cerebellar explants developed a rich and complex neuropil within which a variety of presynaptic endings could be recognised, including some resembling climbing fibre endings and some mossy fibre endings. Four to six hours after transection of linking fibre bundles about 5% of preterminal and terminal profiles were undergoing intense degeneration indicating their origin from cell bodies in the adjacent explant of medulla and showing that most of the synaptic contacts are of intrinsic origin. The degenerating terminals contained spherical synaptic vesicles and made Gray Type I synaptic contacts. They appeared to be predominantly small-medium sized en passant terminals from long, thin, branched preterminal axons, and most closely resembled climbing fibre terminals.

Differentiation of the brain stem reticular formation in the triturus, Triturus pyrrhogaster

The brain stem of the triturus was observed to be initially composed exclusively of the mantle layer. A few days before hatching, a narrow marginal layer differentiated peripherally. At the time of hatching, the marginal layer was clearly visible throughout the brain stem, except for in a medial region of the optic tectum. Approximately one week after hatching, a few cells migrated into the marginal layer, and almost simultaneously, a few fibers in that layer were myelinated. Cells migrating into the marginal layer formed reticular neurons as well as the raphe nuclei and superficial cellular layers of the optic tectum. As the development proceeded, the number of myelinated fibers in the marginal layer increased, and cells in that layer, especially reticular neurons, were seen to be embedded among numerous myelinated fibers, assuming the characteristic features of the reticular formation.

Migration of neuroblasts by perikaryal translocation: role of cellular elongation and axonal outgrowth in the acoustic nuclei of the chick embryo medulla

The neuroblasts forming nucleus magnocellularis, the avian homologue of the mammalian ventral cochlear nucleus, migrate by growth and elongation of their leading processes and by perikaryal translocation through these processes from the matrix zone of the rhombic lip to the acoustico-vestibular anlage. Golgi methods were used on staged chick embryos to reconstruct the morphogenetic phases of migration and early differentiation in situ. Fluorescence labeling of the living cells in vitro elucidated the role of axonal growth in the migratory process. In situ, branching cochlear nerve fibers, tipped with growth cones, enter the acoustico-vestibular anlage at E4.5-5.5 before migration of the magnocellularis neuroblasts at E.5.5-6.5. The premigratory neuroblasts in the matrix zone of the rhombic lip resemble primitive epithelial cells, which extend branched, curving processes into a characteristic formation, the rhombic whorl. The leading process of the migrating magnocellularis neuroblasts gives rise to a bifurcating axon at the interface between the matrix and mantle zones. The lateral branch becomes the recurrent ipsilateral collateral; the medial branch crosses the midline, heading toward the contralateral target site in the region of the presumptive nucleus laminaris. The cell bodies of the migratory neuroblasts appear in intermediate locations along the migration route as they translocate radially through their leading processes past the axonal bifurcation and then tangentially and obliquely into the mantle zone. Neuroblasts destined for nucleus laminaris migrate coincidentally with magnocellularis neuroblasts. Nucleus angularis neuroblasts migrate later in development, after E6.5. In vitro, injections of a nontoxic fluorescent dye (diI) were made into explants of the medulla in the region of the contralateral target area at the time of neuroblast migration. DiI retrogradely labeled the cell bodies of premigratory magnocellularis neuroblasts in the matrix zone and of migratory neuroblasts in the mantle zone through their medial, crossing axonal branches. The morphology of the living neuroblasts in the explants resembled that in the Golgi impregnations at the corresponding stages of migration. Anterograde axonal transport also occurred. These results demonstrate migration by perikaryal translocation and early axon extension of a specific group of neuroblasts in the central nervous system. The morphology of the migrating neuroblasts is such that a simple radial arrangement of cellular guides, glial or otherwise, would not account for their configurations. The available evidence supports the proposition that cellular elongation and perikaryal translocation constitute the general mode of neuronal migration in the central nervous system. The early extension of axons into their target sites may play a critical role in migration and early development of specific types of neurons.

Migratory pathways and selective aggregation of the lateral reticular neurons in the rat embryo: a horseradish peroxidase in vitro study, with special reference to migration patterns of the precerebellar nuclei

The migration and ultimate domain invasion of postmitotic lateral reticular nucleus (LRN) neurons were followed in embryonic day 15-20 (E15-E20) rat embryos, by using a horseradish peroxidase (HRP) in vitro axonal tracing method. All of the LRN axons elongate and neuronal somata migrate via the subpial or marginal migratory stream (mms), circumnavigating the ventrolateral aspect of the medulla at the glial endfeet level. They reach the ventral midline at E16, bypass it, and begin to settle in their final territory at E17. At E18 the LRN anlage is fully formed, and at E19-E20 its cells have finished their migration and are rapidly differentiating. Comparison of these sequential steps with their counterparts in the development of the inferior olive (ION) and external cuneatus (ECN) brings to light the essential role of the neuroepithelial cells of the interolivary commissure (the "floor plate"). This zone is likely to act as 1) a chemoattractant for the growth cones of the LRN, ION, and ECN, and 2) a decision-making center, which instructs the somata of these neurons to cross the midline or not, ultimately governing the crossed or uncrossed pattern of their projection to their common target, the cerebellum. Finally, the ontogeny of the LRN and ECN provides a most surprising example, even unique in the central nervous system, of long-distance, neurophilic migration that conveys neuronal cell bodies contralaterally to the side on which they proliferate.

Eliminating afferent impulse activity does not alter the dendritic branching of the amphibian Mauthner cell

In the developing amphibian, the formation of extra vestibular contacts on the Mauthner cell (M-cell) enhances dendritic branching, while deprivation reduces it (Goodman and Model, 1988a). The mechanism underlying the interaction between afferent fibers and developing dendritic branches is not known; neural activity may be an essential component of the stimulating effect. We examined the role of afferent impulse activity in the regulation of M-cell dendritic branching in the axolotl (Ambystoma mexicanum) embryo. M-cells occur as a pair of large, uniquely identifiable neurons in the axolotl medulla. Synapses from the ipsilateral vestibular nerve (nVIII) are restricted to a highly branched region of the M-cell lateral dendrite. We varied the amount of nVIII innervation and eliminated neural activity. First, unilateral transplantation of a vestibular primordium deprived some M-cells of nVIII innervation and superinnervated others. Second, surgical fusion of axolotls to TTX-harboring California newt (Taricha torosa) embryos paralyzed the Ambystoma twin: voltage-sensitive Na+ channel blockade by TTX eliminated action potential propagation. Reconstruction of M-cells in 18 mm larvae revealed that dendritic growth was influenced by in-growing axons even in the absence of incoming impulses: impulse blockade had no effect on the stimulation of dendritic growth by the afferent fibers.

Development and localization of enkephalin and substance P in the nucleus of tractus solitarius in the medulla oblongata of human fetuses

The presence of enkephalin and substance P-positive neurons and fibers were studied by immunohistochemistry (peroxidase-antiperoxidase or avidin-biotin-peroxidase complex methods) in 26 human fetuses ranging from 11 weeks of gestation to 40 weeks of gestation. Enkephalin-positive neurons were localized in the commissural, medial and intermediate subnuclei as early as 11-12 weeks' gestation. Positive enkephalin fibers were localized around 12 weeks' gestation and in many subnuclei, notably the medial, commissural, intermediate, ventrolateral, ventral and dorsolateral subnuclei. Substance P-positive neurons were localized in the commissural and medial subnuclei around gestation age 13 weeks. Positive substance P fibers appeared even earlier, around 11 weeks of gestation in many subnuclei, notably the medial, intermediate, ventral, ventrolateral and dorsolateral subnuclei. Increase in both enkephalin- and substance P-positive fibers was evident in the later stages of development (e.g. around 26 weeks of gestation). The importance of the early appearance of enkephalin and substance P neurons and fibers of the pain pathways in the major subnuclei connecting with the cardiovascular, gastrointestinal and respiratory functions in the human has to be stressed.

Pre- and postnatal aminopeptidase activities in the rat brain

Research concerning the functional role of brain peptides is performed, in part, by studying peptidase enzymes which might be involved in brain peptide processing or inactivation. Aminopeptidase (AP) activity has been proposed as a candidate regulator of the degradation of these peptides. In this paper, changes in Lys- and Leu-aminopeptidase activities in rat brain hemispheres, cerebellum and medulla were examined in 20 day fetuses and one day postnatal subjects. Aminopeptidase activities were studied by measuring the rate of hydrolysis of the artificial substrates Lys- and Leu-2-naphthylamides (fluorimetrically detected in triplicate). Both enzyme activities increase from the last fetal stage up to the first day of birth in all the brain areas examined except for the case of Leu-AP activity in the medulla. It is suggested that these activities play a part in the neurochemical changes that take place during rat brain maturation, possibly by regulating the activity of several neuroactive peptides.

Migration of immature neurons along tangentially oriented fibers in the subpial part of the fetal mouse medulla oblongata

Migration of neuronal cells in the subpial part of the medulla oblongata was examined in the fetal mouse by light and electron microscopy. Cells were observed forming a migratory stream in the period between the thirteenth and sixteenth days of gestation, and were associated with tangentially oriented fibers. Many of these tangential fibers were present prior to the onset of the migration, and the fibers were filled with longitudinally arrayed microtubules. The cell-bodies were elongated and arranged along, and often apposed to the fibers. Some relocating neurons extended fibers, i.e. leading processes, in the direction of the migration. Generally, these cells exhibited features of immature neurons; they displayed a high concentration of ribosomal rosettes and contained mitochondria, Golgi apparatus, a few rough endoplasmic reticula, and occasionally, centrioles. Junctional complexes, coated pits and coated vesicles were frequently observed in the region of the migratory stream, and these structures are considered to be related to cell locomotion. The present findings strongly suggest that such tangential fibers, including leading processes of moving neurons, serve as guidance substrates for the relocation of immature neurons in the mouse subpial medullary region.

Differential expression of human HOX-2 genes along the anterior-posterior axis in embryonic central nervous system

We have investigated the structure of the human HOX-2 locus, which encompasses a 90-kb region on chromosome 17q21. Five new human HOX-2 homeoboxes, termed HOX-2.5, 2.4, 2.6, 2.7 and 2.8, have been identified, and their nucleotide sequences are reported. They have the same 5'-3' transcriptional orientation and are clustered with three previously described HOX-2 homeoboxes (5'-2.5-2.4-2.3-2.2-2.1-2.6-2.7-2.8-3'). We have also investigated the region-specific expression of HOX-2 genes in human embryonic-fetal life by Northern-blot analysis. All genes are expressed in whole embryos and fetuses at 5-9 weeks from conception. Their major site of expression lies within the central nervous system (CNS), although they are transcribed at a lower level in body structures other than the CNS. Their relatively abundant expression in CNS has been analyzed along the anterior-posterior axis by dissecting the brain, the medulla oblongata and the spinal cord proper. HOX-2.5, 2.4 and 2.3 transcripts are markedly more abundant in spinal cord than in medulla, whereas 2.2, 2.1, 2.6 and 2.7 mRNAs are progressively more abundant in the medulla. Additionally, expression in brain was detected, although at lower level, for HOX-2.1, 2.6, 2.7, 2.8. Thus, the relative position of HOX-2 homeobox genes along the chromosome in the 5'-3' direction appears to correlate with the relative position of their expression domains along the CNS longitudinal axis in the caudal-cephalic direction.

Development of the human hypoglossal nucleus: a morphometric study

Development of the human hypoglossal nucleus was studied using complete serial sections of the brains of 9 fetuses at 16, 18, 21, 23, 27, 32, 33, 35 and 40 weeks of gestation, a 2-month-old infant, a 16-year-old adolescent and a 63-year-old adult. Morphometric analysis produced the following three findings pertaining to the development of the human hypoglossal nucleus: (1) development may accelerate after 32 weeks of gestation; (2) postnatal maturation is observable, and (3) natural cell death, as indicated by a decrease in the number of neurons and the appearance of degenerating neurons, may occur during fetal development.