Showing papers in "Anatomy and Embryology in 1986"

The primitive streak

Abstract: The emphasis of this review is on the primitive streak of the chick embryo, collated with such information as is available on the mouse embryo. Little modern work has been published on any reptile primitive streak.

Projection from the inferior colliculus to the superior olivary complex in the albino rat.

Abstract: The origin and termination of the fibers projecting from the inferior colliculus to the superior olivary complex have been studied in rat by means of the Fink and Heimer and horseradish peroxidase techniques (anterograde and retrograde transport of free horseradish peroxidase and peroxidase conjugated to wheat germ agglutinin). The colliculoolivary fibers originate in layer 3 of the external cortex and the adjacent part of the central nucleus, particularly in the former. Via the lateral lemniscus the fibers reach the ipsilateral periolivary region where they terminate in the rostral and medioventral zones. The terminal field contains at least two types of cells which could constitute the next link in the descending projection to the cochlea and/or the cochlear nuclei. One of these is the large olivocochlear neuron, and the other a smaller neuron projecting to the cochlear nuclei. Judged by their topographic relationship in the inferior colliculus and in the superior olive, the colliculoolivary neurons may form a link in a oligosynaptic projection from the auditory cortex to the cochlea and/or the cochlear nuclei. The observations are based on light microscopy, however, and do not allow conclusions concerning synaptic contacts.

On the development of the pyramidal tract in the rat. II. An anterograde tracer study of the outgrowth of the corticospinal fibers.

Abstract: An anterograde tracer study has been made of the developing corticospinal tract (CST) in the rat using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). Analysis of normal Rager stained material revealed that corticospinal axons reach upper cervical spinal cord levels at the day of birth (PO). Postnatal rats ranging in age from one (P1) to fourteen (P14) days received multiple WGA-HRP injections into the cortex of their left hemisphere and were allowed to survive for 24 h. The first labeled CST fibers caudally extend into the third thoracic spinal cord segment at P1; into the eighth thoracic segment at P3; into the first or second lumbar segment at P7 and into the second to third sacral segment at Pg. Thus the outgrowth of the leading 'pioneer' fibers of the CST is completed at P9 but later developing axons are continuously added even beyond P9. Quantitative analysis of the amount of label along the length of the outgrowing CST revealed a characteristic pattern of labeling varying with age. The most striking features of that pattern are: the formation of two standing peaks at the level of the cervical and lumbar enlargements respectively and the transient presence of a smaller running peak which moves caudally with the front of the outgrowing bundle. The standing peaks are ascribed to the branching of the axon terminals at both intumescences, whereas the running peak probably arises by the accumulation of tracer within the growth cones at the tips of the outgrowing CST axons. Factors such as the number of axons, the varying axon diameters, the branching collaterals, the presence of varicosities, the transport rate of the tracer, the uptake of the tracer at the injection site, which possibly may affect the amount of label present in both the entire bundle and in the individual axons are discussed. Current research is focused upon an analysis of the relation between the site of injection within the cortex and the pattern of labeling of the CST. A delay of two days was found between the arrival of the CST axons at a particular spinal cord level and their outgrowth into the adjacent spinal gray. However, combined HRP and electronmicroscopic experiments are necessary to determine the factors behind the maturation of the CST as well as the maturation of the spinal gray.

The central projections of primary afferent neurons of greater splanchnic and intercostal nerves in the rat. A horseradish peroxidase study.

Abstract: The central projections of primary afferent fibers of the greater splanchnic nerve of the rat were investigated using the transganglionic horseradish peroxidase transport technique. In addition, the corresponding spinal ganglion cells and the preganglionic sympathetic neurons were demonstrated. For comparing visceral and somatic afferents, intercostal nerve afferents were labelled by the same technique. Splanchnic afferent dorsal root ganglion cells were found at segments T3 to T13 ipsilaterally, with the greatest density at T8 to T12. Labelled cells represented about 10%-15% of all neurons in the ganglia at maximal projection levels. They were randomly distributed within individual ganglia. The great majority were medium to small sized and round to slightly oval in shape. In the spinal cord, labelled visceral afferent axons were found maximally at T8 to T11, but could be detected in decreasing density up to T1 and down to L1. They were distributed over Lissauer's tract and the dorsal funiculus to a medial and lateral collateral pathway (MCP and LCP, respectively). The MCP, somewhat more prominent than the LCP, was destined primarily to clustered presumptive terminal fields in medial lamina I and outermost lamina IIa. Only a few axons continued further to laminae V and X. Splanchnic afferent axons, most likely derived from the MCP, formed a longitudinal bundle ventral to the central canal. The LCP consisted of more or less well-defined axon bundles emanating from the lateral Lissauer's tract and curving round the lateral edge of the dorsal horn and through the dorsolateral funiculus. Presumptive terminal sites of LCP axons are the lateral laminae I and IIa, the nucleus of the dorsolateral funiculus and the dorsal part of lamina V. A few LCP axons were seen in the vicinity of lateral dendrites of preganglionic sympathetic axons. Visceroafferent terminals were absent from laminae IIb-IV and VII. The possible consequences of the MCP/LCP duality for the central connections of splanchnic afferents are discussed. Some splanchnic afferents ascended to the gracile and cuneate nuclei, and rarely to the spinal trigeminal nucleus. These results fit into the general concept of visceroafferent terminal organization that has emerged during the last few years. Differences to other reports in the detailed arrangement of fibers and terminals are discussed. Somatoafferent cell bodies represented the vast majority of neurons in the respective spinal ganglia. Cell sizes encompassed the whole range from very small to very large without a clear predominance of one particular size class.(ABSTRACT TRUNCATED AT 400 WORDS)

The endocrine cells of the digestive system: amines, peptides, and modes of action

Abstract: The endocrine cells of the digestive system (entero-endocrine cells of gastro-intestinal epithelia and Langerhans' islets of the pancreas) and the chemical messengers produced by them constitute a complicated and complex system. The physiological function of this system is the regulation of all processes related to digestion and resorption, and to homeostasis of carbohydrate metabolism. Using morphological and histochemical features of this cellular community, the present review deals with amines and amine metabolism, polypeptides and their immunohistochemical identification, and with the modes of action of enteric and pancreatic hormones. Special attention is paid to the significance of amine precursor uptake and decarboxylation (APUD), to immunohistochemical methodology and the interpretation of immunohistochemical findings, and to local regulatory mechanisms, especially paracrinia. Finally, unifying concepts for the integration of these cells and similar endocrine cells of other organs into a common system are considered.

Neocortical layers I and II of the hedgehog (Erinaceus europaeus). I. Intrinsic organization.

Abstract: The intrinsic organization and interlaminar connections in neocortical layers I and II have been studied in adult hedgehogs (Erinaceus europaeus) using the Golgi method. Layer I contains a dense plexus of horizontal fibers, the terminal dendritic bouquets of pyramidal cells of layer II and of underlying layers, and varieties of intrinsic neurons. Four main types of cells were found in layer I. Small horizontal cells represent most probably persisting foetal horizontal cells described for other mammals. Large horizontal cells, tufted cells, and spinous horizontal cells were also found in this layer. Layer II contains primitive pyramidal cells representing the most outstanding feature of the neocortex of the hedgehog. Most pyramidal cells in layer II have two, three or more apical dendrites, richly covered by spines predominating over the basal dendrites. These cells resemble pyramidal cells found in the piriform cortex, hippocampus and other olfactory areas. It is suggested that the presence of these neurons reflects the retention of a primitive character in neocortical evolution. Cells with intrinsic axons were found among pyramidal cells in layer II. These have smooth dendrites penetrating layer I and local axons forming extremely complex terminal arborizations around the bodies and proximal dendritic portions of pyramidal cells. They most probably effect numerous axo-somatic contacts resembling basket cells. The similarity of some axonal terminals with the chandelier type of axonal arborization is discussed. Other varieties of cells located in deep cortical layers and having ascending axons for layers I and II were also studied. It is concluded that the two first neocortical layers represent a level of important integration in this primitive mammal.

Polyovular follicles in the ovary of immature mice exposed prenatally to diethylstilbestrol.

Abstract: Polyovular follicles (PF) occur in the ovary of 30-day-old offspring of ICR/JCL mice given 4 daily subcutaneous injections of 20–2,000 μg diethylstilbestrol (DES)/day from days 15 to 18 of gestation. PF containing 2–9 oocytes per follicle in the prenatally DES-exposed mice are increased 33- to 112-fold as compared to controls. In 5- to 25-day-old offspring of mothers given injections of 2,000 μg DES/day, PF are observed 17–65 times more frequent than in controls.

A study of lamellar organisation in juvenile and adult human bone.

Abstract: The scanning electron microscope (SEM) has been used to study the three-dimensional organisation of collagen in slices of human rib and femur which were “etched” by chick osteoclasts, mechanically isolated and grown on their surfaces in vitro. Collagen organisation in the two bones showed a spectrum of appearances, ranging from lamellae of approximately equal thickness, but alternating fibre orientations, to an almost exclusive orientation of collagen apparently in a longitudinal direction. The rib contained a smaller component of transversely oriented collagen which may be related to a different functional loading. The thickness of circumferential lamellae was less than that of osteonal lamellae in the two adult ribs examined. Also, in the rib there was a trend towards increased average lamellar thickness with age in the range studied. This may be related to the fact that more of the lamellae in the rib cortex in children have been formed circumferentially. Correlation of results obtained with the SEM and the polarised light microscope (PLM) from the same substratum demonstrated that the latter grossly exaggerated the apparent component of collagen with a transverse orientation. This will always be true unless sections comparable with the lamellar thickness are used with the PLM.

An electron microscope study of vagus nerve composition in the ferret.

Abstract: The total number of axons in the cervical and abdominal vagus nerves of the ferret was counted. The ratio of myelinated to non-myelinated, and afferent to efferent axons was determined. The fibre diameter spectrum of myelinated axons was measured. The total number of axons in the ferret cervical vagus is similar to other mammals (approximately 28,000); the majority of axons are afferent (approx. 24,000) and also the majority of axons are nonmyelinated (approx, 27,000). The dorsal abdominal trunk is about twice the size of the ventral trunk although both trunks have the same number of efferent axons. The abdominal vagal trunks are over 90% afferent.

Development of the auditory hair cell surface in human fetuses. A scanning electron microscopy study.

Abstract: Thirteen human fetal cochleas were investigated by scanning electron microscopy. Our observations concentrated on the hair cell surface. Ciliogenesis appeared to start during the 11th week of gestation on the inner hair cells (IHCs) and one week later on the outer hair cells (OHCs). The earliest stages of stereociliary development were similar on both types of cell and were characterized by the presence of round bundles of cilia arising from the surrounding microvilli. A three-dimensional V-shaped arrangement suddenly appeared, accompanied by the disappearance of short cilia on the internal side. Between the 20th and the 22nd weeks of gestation, both types of hair cell had an adult stereociliary pattern, i.e. a rectilinear arrangement on IHCs and W-shaped on OHCs. However, there were signs of immaturity, such as a disarray of OHCs and the presence of the kinocilium, suggesting that the surface of the auditory hair cells achieves its maturation during the last trimester of pregnancy.

Atriopeptin distribution in the developing rat heart.

Abstract: The embryonic distribution of atriopeptin (atrial natriuretic factor) in the Sprague-Dawley rat heart was mapped by immunoperoxidase staining of embryonic and neonatal hearts using rabbit antiserum to atriopeptigen purified from adult rat atrium. During the period of cardiac septation (days 14 and 16), immune serum reacted strongly with myocardial cytoplasmic granules in two sites: the inner cell layer along the cephalic curvature of the atria and the trabeculae of the incompletely divided ventricles. The youngest hearts studied (gestational day 11) displayed only nonspecific diffuse peroxidase reactivity within blood cells, indistinguishable from control sections incubated with normal rabbit serum. One week following birth, intense antiatriopeptin reactivity was widely distributed through both atria. In addition, immunoreactive cytoplasmic granules were found at several sites in the ventricular myocardium. Along the fiber tracts of the concentric layers of the ventricahar walls and interventricular septum, scattered granular foci were seen between nuclei of contiguous elongated myocytes. Positive staining was also seen within the papillary muscles and trabeculae carnae, regions shown by Alcian blue/periodic acid-Schiff base staining of sister sections to be relatively rich in glycogen. These patterns of antibody reactivity suggest the coupling of early atriopeptin secretory activity with developing cardiac function.

Neocortical layers I and II of the hedgehog (Erinaceus europaeus). II. Thalamo-cortical connections.

Abstract: This study examines the thalamo-cortical projections to the most superficial neocortical layers in the hedgehog (Erinaceus europaeus) after small injections of horseradish peroxidase and horseradish peroxidase conjugated to wheat germ agglutinin in the somato-sensory cortex. The injections were limited to layers I, II and upper parts of layer III/IV. Retrogradely labeled cells were plotted in serial sections through the thalamus. Injections in the somato-sensory cortex gave a pattern of elongated columns of labeled cells, extending rostro-caudally in the nucleus ventralis thalami. In the neocortex, labeled fibers extended for considerable distances running horizontally in layer I. Complementary observations demonstrate the thalamic origin of certain, coarse ascending bundles observed previously in Golgi preparations of the hedgehog. It is concluded that a major cortical input to layer I originates in the hedgehog in the principal thalamic (relay) nuclei. After injections in the somato-sensory cortex, retrogradely labeled cells were also found in the nucleus ventro-medialis thalami and very few in a zone medial to the nucleus ventralis thalami corresponding to the intralaminar thalamic nuclei. The contributions of this latter system seem to be limited in comparison with other mammals.

Non-pyramidal neurons in the guinea pig hippocampus. A combined Golgi-electron microscope study.

Abstract: Morphological characteristics of non-pyramidal neurons in the guinea pig hippocampus (regions CA1 and CA3) were analyzed by a correlated light and electron microscopic approach. Following Golgi impregnation, the cells were first studied under the light microscope and classified according to the location of their cell bodies and the distribution of their dendrites in the different hippocampal layers. Next, the Golgi impregnated non-pyramidal neurons were gold-toned and deimpregnated, allowing an electron microscopic analysis of the identified structures.

The development of the human brain and the closure of the rostral neuropore at stage 11

Abstract: Twenty embryos of stage 11 (24 days) were studied in detail and graphic reconstructions of twelve of them were prepared. The characteristic feature of this stage is 13-20 pairs of somites. The notochord sensu stricto appears first during this stage, and its rostral and caudal parts differ in origin. Rostrally, the notochordal plate is being transformed into the notochord in a caudorostral direction. The caudal part, however, arises from the axial condensation in the caudal eminence in a rostrocaudal direction. The caudal eminence (or end bud) represents the former primitive streak. The somites are increasing in number at a mean rate of 6.6 h per pair. The rostral neuropore closes towards the end of stage 11. The closure is basically bidirectional, being more rapid in the roof region and producing the embryonic lamina terminalis and future commissural plate in the basal region. The caudal neuropore is constantly open. The brain comprises telencephalon medium (represented by the embryonic lamina terminalis) and a series of neuromeres: 2 for the forebrain (D1 and D2), 1 for the midbrain, and 6-7 for the hindbrain (RhA-C; RhD is not clearly delineated). The forebrain still occupies a small proportion of the total brain, whereas the spinal part of the neural tube is lengthening rapidly. Some occlusion of the lumen of the neural tube was noted in 4 embryos, all of which had an open rostral neuropore. Hence there is at present no evidence that occlusion plays a role in expansion of the human brain. The marginal (primordial plexiform) layer is appearing, particularly in rhombomere D and in the spinal portion of the neural tube. The neural crest is still forming from both the (open) neural groove and the (closed) neural tube, and exclusively from both neural (including optic) and (mainly) otic ectoderm. The optic sulcus is now prominent, and its wall becomes transformed into the optic vesicle towards the end of stage 11. At this time also, an optic sheath derived from mesencephalic crest and optic crest is present. The mitotic figures of the optic neural crest are exceptional in being situated in the external part of the neural epithelium. The otic pit is becoming deeper, and its wall is giving rise to neural crest that is partly added to the faciovestibulocochlear ganglion and partly forms an otic sheath. The nasal plate does not yet give off neural crest.

Meningeal cells influence cerebellar development over a critical period.

Abstract: We have investigated the influence of meningeal cells on the development of the cerebellum by destroying these cells with 6-hydroxydopamine in hamsters of different ages. The ensuing foliation and lamination disruption in the cerebellar vermis is attributed to a disintegration of the cerebellar surface and a disorganization of the glial scaf-fold of the cerebellar cortex due to a loss of meningeal-glial interaction in stabilizing the extracellular matrix at the glia limitans superficialis (v. Knebel Doeberitz et al. 1986, Neuroscience 17:409–426). The severity of these cerebellar defects is correlated with the ontogenetic stage at which meningeal cells are destroyed, being greatest after treatment at postnatal day 1 and decreasing thereafter until day 5 and beyond, when no abnormalities occur, although all meningeal cells are destroyed throughout. The absence of cerebellar defects after destruction of meningeal cells at day 5 or later is associated firstly with the end of the period of branching morphogenesis of the cerebellum when all folial primordia are established, and, secondly, with the maturation of the glia limitans superficialis. These findings indicate that meningeal cells stabilize the cerebellar surface and glial scaffold over a critical period that ends, when the pattern of cerebellar foliation is established, and when the glia limitans superficialis has reached a mature state. Beyond this stage glial end-feet alone are sufficient to maintain the epithelial integrity of the cerebellum.

Immunocytochemical evidence for CDD/ANP-like peptides in strands of myoendocrine cells associated with the ventricular conduction system of the rat heart

Abstract: Immunohistochemical investigations with different antisera against cardiodilatin 99–126 or alpha atrial natriuretic polypeptide revealed the presence of cardiac hormones not only in the atria of rats but also in strands of myoendocrine cells located in subendocardial regions of the ventricular septum. The localization of CDD-IR (cardiodilatin immunoreactivity) in the ventricle is associated with the location of the conduction system in the rat. The significance of the morphological relationship between cardiodilatin and the conduction system of the rat heart is discussed.

Development of the lateral amygdaloid nucleus in the human fetus: transient presence of discrete cytoarchitectonic units

Abstract: The cytoarchitectonic development of the lateral amygdaloid nucleus has been studied on Nissl-stained sections through brains of human fetuses ranging between 11 to 24 weeks of gestation. The first sign of cytoarchitectonic inhomogeneity of the lateral amygdaloid nucleus is the appearance of 2-3 ovoid cell clusters around 12 weeks of gestation. Between 12.5-16 weeks of gestation, the ventral part of the lateral amygdaloid nucleus contains 7-11 columnar cell clusters separated by "septa" of lower cell-packing density. These columnar clusters, stretching in the rostrocaudal direction, appear on cross-section as ovoid structures elongated in the ventrodorsal direction. In subsequent development (16-24 weeks of gestation) this distinct columnar appearance becomes less obvious, owing to the disappearance of "septa" along the dorsal edges of cellular clusters. This process begins first in the medial part of the columnar field. As a result, the cytoarchitectonic units gradually fuse into a homogeneous grey mass. However, the ventral part of the columnar field retains an undulated appearance throughout late gestation, showing multiple indentations as a sign of former cytoarchitectonic inhomogeneities. In conclusion, the fetal lateral amygdaloid nucleus contains a number of cytoarchitectonic "moduli" which could serve as a new parameter for an estimation of histogenetic maturity of the human amygdala. This transient cytoarchitectonic inhomogeneity could be a sign of the temporary predominance of one characteristic afferent-efferent system during a given developmental stage. Alternatively, it could reflect a clustered type of neurogenesis.

Ontogenetic development of the nervus terminalis in toothed whales. Evidence for its non-olfactory nature.

Abstract: For the first time in cetaceans, the development of the terminalis system and its continuity between the olfactory placode and the telencephalon has been demonstrated by light microscopy. In the early development of toothed whales (Odontoceti) this system is partially incorporated within the fila olfactoria which grow out from the olfactory placode. As the peripheral olfactory system is reduced in later stages, a strongly developed ganglionlike structure (terminalis ganglion) remains within the primitive meninx. Peripherally it is connected via the cribriform plate with ganglionic cell clusters near the septal mucosa. Centrally it is attached to the telencephalon (olfactory tubercle, septal region) by several nerve fibre bundles. In contrast to all other mammalian groups, toothed whales and dolphins are anosmatic while being totally adapted to aquatic life. Therefore the remaining ganglion and plexus must have non-olfactory properties. They may be responsible for the autonomic innervation of intracranial arteries and of the large mucous epithelia in the accessory nasal air sacs. The morphology, evolution and functional implications of the terminalis system in odontocetes and other mammals are discussed.

Ontogenesis of the laminar structure in areas 17 and 18 of the human visual cortex. A quantitative study.

Abstract: A quantitative morphological study of the pre-and postnatal development in the primary (area 17) and secondary (area 18) visual cortical regions was performed on 108 human brains. The neuropil proportion and thickness were measured with an image analyzer for the different cortical layers and the resulting data were approximated with logistic growth functions. The different layers show a marked heterochrony both within and between the areas. The neuropil proportion of layer 1 is the compartment to develop first in both areas. It has the lowest growth velocity, followed by layer VI and layers V, IV, III and II. This maturational sequence reflects the sequence of appearance of immature neurons during the migration period of neocortical ontogenesis. The development of the neuropil proportion is highly synchronized between areas 17 and 18 during the prenatal period, but in the first postnatal weeks, area 17 grows more quickly than area 18. Later on, this relation is reversed and area 18 reaches adult values of neuropil proportions about three months earlier than area 17. The growth in thickness of all layers is complated later than the growth in neuropil proportion. The growth in layer thickness is completed in Area 18 about two months earlier than in area 17, although area 18 has a greater cortical thickness. The results are compared with data on growth in volume, dendritic arborization and the development of visual function.

Sequential cell and tissue interactions governing organogenesis of the kidney.

Abstract: The complex development of the metanephric kidney illustrates the decisive role of sequential morphogenetic interactions of varying type in organogenesis. In this review the following steps were singled out from this continuous, strictly controlled organogenesis: determination of the mesoderm during the blastula stage, induction of pronephric nephrons during gastrulation, guided migration of the pronephric duct, mesenchyme-controlled branching of the ureter, induced aggregation of the mesenchymal cells of the metanephric blastema, homotypically controlled polarization of the cells in the renal vesicle and remodelling of the vesicle into the S-shaped body, guided migration of endothelial cells into the nephric blastema and the glomerular crevice, and the matrix interaction(s) completing the formation of the glomerular basement membrane with dual origin.

Undulating course of nerve fibres and bands of Fontana in peripheral nerves of the rat

Abstract: The undulating course of nerve fibres and the optical effect of that course, i.e. the bands of Fontana, were studied in the peripheral nerves of the adult rat using light microscopy. The arrangement of collagen fibres in the endoneurium of these nerves was evaluated using transmission and scanning electron microscopy. No nerve fibres undulation was noted on the intracranial sections of the cranial nerves or on the spinal roots. In their endoneurium a few, irregularly arranged collagen fibrils were found. In contrast, the nerve fibres undulation and Fontana's bands were a constant feature in the peripheral course of the nerve trunks. They were discernible in vivo and on excised unfixed as well as fixed nerves. The nerve fibres follow a sine-curve course of variable frequence and amplitude. Exposed in vivo, the nerve fibres retained their wave-like course even after removal of the epineurium and perineurium. The endoneurium of these nerves contained numerous undulating longitudinally oriented bundles of collagen fibrils. These findings suggest that the undulating course of the nerve fibres in peripheral nerves is conditional upon the quantity and arrangement of their endoneurial collagen fibrils. When the nerve was stretched in the course of movement, the undulation became straightened out until it disappeared. Conversely, nerve shortening enhanced the undulation. Thus the wave-like alignment of the nerve fibres represents a physiological reserve length for nerve stretching.

Ultrastructural observations on nucleoli and related structures during human spermatogenesis.

Abstract: The ultrastructural study of nucleoli and ribonucleoprotein-containing structures in human seminiferous tubules revealed that the nucleoli of spermatogonia, spermatocytes and Sertoli cells exhibited a tripartite structure consisting of: (1) a fibrillar center, (2) a compact granular portion, and (3) a reticular portion containing both pars fibrosa and pars granulosa. The nucleoli of primary spermatocytes showed a developed reticular portion. At pachytene, the compact granular portion enlarged and lost its connection with the fibrillar center and the reticular portion which decreased in size. This suggests a nucleolar segregation similar to that of ovocytes in many species. Two similar developmental stages of nucleoli were observed in spermatogonia. In addition to nucleoli, there were other ribonucleoprotein-containing structures such as intranuclear closely-packed granules in Ap spermatogonia, coarse granules in the chromatin rarefaction zone of Ad spermatogonia, the nuage and Lubarsch crystals of spermatogonia, the chromatoid body of spermatids, the annulate lamellae of both spermatids and Sertoli cells, and many structures of the spermatid neck region.

Naturally occurring and induced ganglion cell death. A retinal whole-mount autoradiographic study in Xenopus.

Abstract: The retina in frogs grows continuously throughout the whole life of the animal by the addition of rings of cells at the ciliary margin. Naturally occurring neuron death cannot, consequently, be established by counting surviving neurons. A new approach, retinal whole-mount auto-radiography was introduced in this study to estimate cell loss occurring in the ganglion cell layer over a long period of time. 3H-thymidine injection at stage 53 (midlarval stage) labels a ring of cells, thereby marking the extent of retina formed up to the time of isotope administration. In the present study the number of neurons in the ganglion cell layer within the autoradiographically identified central retinal sector was estimated from midlarval stage to 6 months after metamorphosis in Xenopus laevis. The mean neuron number in the central retinal sector formed up to stage 53 was 17,420 and this was reduced by 20% to 13,515 by 6 months after metamorphosis. Optic nerve section at the time of isotope injection and subsequent regeneration brought about a reduction of the number of surviving neurons in the part of the retina formed up to stage 53 to 7,720, or to about 57% of the normal neuron number in an equivalent retinal area of an intact eye of the same age. A further reduction to 20% of normal neuron population was observed in retinae where the optic nerve failed to regenerate. The surviving neurons are assumed to be amacrine cells. The bulk of natural neuron loss in the retinal centre occurs during premetamorphic stages while little further loss takes place in the next 6 months suggesting that the underlying mechanism is a fine tuning of the developing retinal projections.

Diencephalic and mesencephalic afferents of the rat claustrum.

Abstract: The retrograde fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) have been used to study subcortical afferents of the claustrum. DY or FB was injected into the claustrum. The greatest amount of labeled cell bodies were observed in the posterior thalamic nuclear complex. They were especially abundant in its caudal part, lying between the medial geniculate body and the pretectal area. In comparison to the numerous labeled cells near the diencephalic-mesencephalic junction, the number of fluorescing neurons in the brain stem was considerably lower. These neurons were mostly concentrated in the monoaminergic cell groups. The results indicate the presence of a substantial projection from the posterior thalamic and anterior pretectal region to the calustrum.

An experimental and morphological analysis of the tail bud mesenchyme of the chick embryo

Abstract: In the chick embryo, the tail bud reaches its maximum length at about stage 22 of Hamburger and Hamilton, after which it starts to regress By this stage the neural tube and notochord extend right to the tip of the tail, but the somites do not do so, the terminal tail bud mesoderm never becoming segmented The investigation is concerned with analysing why this mesoderm fails to segment When tail buds were explanted to the chorio-allantoic membrane, they continued to form somites only until the "correct" number had segmented, ie, the tail bud formed no more somites when isolated from the embryo than it would have formed if undisturbed Morphological studies suggest that in the normal embryo massive cell death overtakes the tail bud mesoderm before it can segment It is suggested therefore that cell death may be a contributory factor in preventing segmentation

The local expression of adult chicken heart myosins during development. II. Ventricular conducting tissue.

Abstract: The development of the ventricular conducting tissue of the embryonic chicken heart has been studied using a previous finding that morphologically recognizable atrial conducting tissue coexpresses the atrial and the ventricular myosin isoforms. It is found that, by these criteria, at 9 days part of the ventricular conduction system consists of a myocardial ring located around the infundibula of the aorta and truncus pulmonalis. Part of this ring is formed by the retro-aortic root branch. The ring continues via the septal branch into the atrioventricular bundle and its branches, that all express both myosin isoforms. The retro-aortic root branch could be traced back as a part of the myocardial wall of the truncus arteriosus at the 4 days embryonic stage. At the 16th day of development, the septal branch, atrioventricular bundle and left and right bundle branches no longer express the atrial isomyosin, but two bundles originating from the septal branch still express both isomyosins, one being the retro-aortic root branch, the other being only immunologically recognizable and directed to the ventral side of the truncus pulmonalis; this latter we call the pulmonary root branch. Both bundles are remnants of the myocardial ring.

Cardiodilatin-immunoreactivity in specific atrial granules of human heart revealed by the immunogold stain.

Abstract: The immunogold technique was applied to detect cardiodilatin-immunoreactivity (CDD-IR) in human heart. Using antibodies directed against C-terminal regions of CDD, we could identify colloidal gold label in specific atrial granules of human heart. The granules in all areas of the myoendocrine cells were homogeneously labelled and all right atrial biopsy specimen of patients with different heart diseases reacted positively and had the same distribution of label. The Golgi-apparatus and ergastoplasma exhibited and extremely weak CDD-IR. The results indicate a predominant storage of CDD in specific granules.

Distribution of calcitonin gene-related peptide-like immunoreactivity in the guinea pig heart.

Abstract: The distribution of calcitonin gene-related peptide like-immunoreactivity (CGRP-IR) within the heart and adjacent blood vessels of the guinea pig was investigated anmunohistochemically by use of the peroxidase-antiperoxidase (PAP) technique. Numerous paravascular and perivascular immunoreactive nerve fibers were localized around the aorta, coronary arteries and their branches down to the teminal vasculature. Arterioles in the atria showed greatest density of immunoreactive varicosities of all blood vessels. The epicardium, endocardium and the conductive system also contained numerous CGRP-IR nerve fibers. In the muocardium the number of immunoreactive varicosities was variable. Many were present in both atria, moderate amounts were seen in the right ventricle and parts of the intraventricular septum, and only a few occurred in the left ventricle. CGRP-IR was infrequently found within intracardial ganglionic cells but was abundantly distributed in the surrounding nerve fibers.

Tracheal submucosal gland development in the rhesus monkey, Macaca mulatta: ultrastructure and histochemistry.

Abstract: The submucosal glands are thought to be the primary source of the mucus overlying the primate trachea and conducting airways. This study characterizes the development of submucosal glands in the trachea of the rhesus monkey. Tracheas from 46 age-dated fetal, 8 postnatal and 3 adult rhesus were fixed in glutaraldehyde/paraformaldehyde and slices processed for electron microscopy. The earliest (70 days gestational age (DGA)) indication of gland development was the projection of a group of closely packed electron lucent cells with few organelles and small pockets of glycogen into the submucosa. This configuration was observed up to 110 DGA. In fetuses younger than 87 DGA it was present almost exclusively over cartilaginous areas. Between 80 and 140 DGA, a cylinder of electron lucent cells projected into the submucosal connective tissue perpendicular to the surface. In fetuses younger than 100 DGA, it was restricted to cartilaginous areas. By 90 DGA, some glycogen containing cells in proximal regions contained apical cored granules. By 106 DGA, cells in proximal areas contained apical electron lucent granules. More distal cells had abundant GER and electron dense granules. The most distal cells resembled the undifferentiated cells at younger ages. Ciliated cells were present in the most proximal portions of glands at 120 DGA. This glandular organization was found in older animals, including adults, with the following changes: (1) abundance of proximal cells with electron lucent granules increased; (2) abundance of distal cells with electron dense granules increased; and (3) abundance of distal cells with abundant glycogen and few organelles decreased. We conclude that submucosal gland development in the rhesus monkey: (1) is primarily a prenatal process; (2) occurs first over cartilage; (3) continues into the postnatal period; and (4) involves secretory cell maturation in a proximal to distal sequence with mucous cells differentiating before serous cells.

Survival and resorptive activity of chick osteoclasts in culture.

Abstract: Previous studies have shown that osteoclasts obtained from chopped bones resorb surrogate calcified tissue substrata in vitro. These cultures contained all bone and marrow cell type pooled together. We have now parted the marrow from the bone and cultured the cells from the two fractions separately: on both resorbable substrates and on plastic in order to test their longevity in culture and ability to resorb following trypsinisation. Marrow-fraction, bone-fraction or whole bone derived cells were harvested from prehatch chick long bone shafts after removing the periosteum; seeded on sperm whale dentine (SWD) slices or plastic dishes and cultured continously, or trypsinised and reseeded on to fresh substrata at weekly or half-weekly intervals. Observations were made by light microscopy and SEM. Many multinucleate cells were observed in the marrow fraction immediately after settling, deriving presumably from poorly adherent osteoclasts, next to bone, which had not been resorbing at the time of harvesting. By three days in culture on plastic, multinucleate cells were very large both in terms of plant extent and nuclear number: cell fusion occurred between osteoclasts and between osteoclasts and small, round uninuclear cells. SWD was extensively resorbed. The adherence of the osteoclasts was greater (a) to plasuc upon trypsinisation than that of the other cells; and (b) to SWD than to plastic, particularly if the cells were resorbing. Trypsinised cells regained their resorptive capacity after seeding on to new SWD, but only for 1 or 2 treatments. Bone derived cells were similar to the marrow cultures, except for the much higher proportion of other bone cell types. Trypsinisation caused a higher proportional loss of multinucleate cells from both SWD and plastic. Resorption was still occurring at 6 weeks in all cultures. A wide diversity existed in the shapes, depths, plan areas and volumes of the resorption pits.