Fine structure and innervation of the avian adrenal gland. I. Fine structure of adrenal chromaffin cells and ganglion cells

The role of the Notch signalling pathway in regulating the balance between neuronal and nonneuronal cells in sympathetic ganglia and the adrenal gland

Sympathetic neurons and endocrine chromaffin cells of the adrenal medulla are catecholaminergic cells that derive from the neural crest. According to the classic model, they develop from a common sympathoadrenal (SA) progenitor that has the ability to differentiate into both sympathetic neurons and chromaffin cells depending on signals provided by their final environment. Our previous data revealed that a single premigratory neural crest cell can give rise to both sympathetic neurons and chromaffin cells, indicating that the fate decision between these cell types occurs after delamination. A more recent study demonstrated that at least half of chromaffin cells arise from a later contribution by Schwann cell precursors. Since Notch signalling is known to be implicated in the regulation of cell fate decisions, we investigated the early role of Notch signalling in regulating the development of neuronal and non-neuronal SA cells within sympathetic ganglia and the adrenal gland. To this end, we implemented both gain and loss of function approaches. Electroporation of premigratory neural crest cells with plasmids encoding Notch inhibitors revealed an elevation in the number of SA cells expressing the catecholaminergic enzyme tyrosine-hydroxylase, with a concomitant reduction in the number of cells expressing the glial marker P0 in both sympathetic ganglia and adrenal gland. As expected, gain of Notch function had the opposite effect. Numbers of neuronal and non-neuronal SA cells were affected differently by Notch inhibition depending on the time of its onset. Together our data show that Notch signalling can regulate the ratio of glial cells, neuronal SA cells and nonneuronal SA cells in both sympathetic ganglia and the adrenal gland.

Single-cell transcriptomics of human embryos identifies multiple sympathoblast lineages with potential implications for neuroblastoma origin

Characterization of the progression of cellular states during human embryogenesis can provide insights into the origin of pediatric diseases. We examined the transcriptional states of neural crest- and mesoderm-derived lineages differentiating into adrenal glands, kidneys, endothelium and hematopoietic tissue between post-conception weeks 6 and 14 of human development. Our results reveal transitions connecting the intermediate mesoderm and progenitors of organ primordia, the hematopoietic system and endothelial subtypes. Unexpectedly, by using a combination of single-cell transcriptomics and lineage tracing, we found that intra-adrenal sympathoblasts at that stage are directly derived from nerve-associated Schwann cell precursors, similarly to local chromaffin cells, whereas the majority of extra-adrenal sympathoblasts arise from the migratory neural crest. In humans, this process persists during several weeks of development within the large intra-adrenal ganglia-like structures, which may also serve as reservoirs of originating cells in neuroblastoma.

Synaptic protein and pan-neuronal gene expression and their regulation by Dicer-dependent mechanisms differ between neurons and neuroendocrine cells

BACKGROUND

Neurons in sympathetic ganglia and neuroendocrine cells in the adrenal medulla share not only their embryonic origin from sympathoadrenal precursors in the neural crest but also a range of functional features. These include the capacity for noradrenaline biosynthesis, vesicular storage and regulated release. Yet the regulation of neuronal properties in early neuroendocrine differentiation is a matter of debate and the developmental expression of the vesicle fusion machinery, which includes components found in both neurons and neuroendocrine cells, is not resolved.

RESULTS

Analysis of synaptic protein and pan-neuronal marker mRNA expression during mouse development uncovers profound differences between sympathetic neurons and adrenal chromaffin cells, which result in qualitatively similar but quantitatively divergent transcript profiles. In sympathetic neurons embryonic upregulation of synaptic protein mRNA follows early and persistent induction of pan-neuronal marker transcripts. In adrenal chromaffin cells pan-neuronal marker expression occurs only transiently and synaptic protein messages remain at distinctly low levels throughout embryogenesis. Embryonic induction of synaptotagmin I (Syt1) in sympathetic ganglia and postnatal upregulation of synaptotagmin VII (Syt7) in adrenal medulla results in a cell type-specific difference in isoform prevalence. Dicer 1 inactivation in catecholaminergic cells reduces high neuronal synaptic protein mRNA levels but not their neuroendocrine low level expression. Pan-neuronal marker mRNAs are induced in chromaffin cells to yield a more neuron-like transcript pattern, while ultrastructure is not altered.

CONCLUSIONS

Our study demonstrates that remarkably different gene regulatory programs govern the expression of synaptic proteins in the neuronal and neuroendocrine branch of the sympathoadrenal system. They result in overlapping but quantitatively divergent transcript profiles. Dicer 1-dependent regulation is required to establish high neuronal mRNA levels for synaptic proteins and to maintain repression of neurofilament messages in neuroendocrine cells.

Sympathetic neurons and chromaffin cells share a common progenitor in the neural crest in vivo

BACKGROUND

The neural crest (NC) is a transient embryonic structure unique to vertebrates, which generates peripheral sensory and autonomic neurons, glia, neuroendocrine chromaffin and thyroid C-cells, melanocytes, and mesenchymal derivatives such as parts of the skull, heart, and meninges. The sympathoadrenal (SA) cell lineage is one major sub-lineage of the NC that gives rise to sympathetic neurons, chromaffin cells, and the intermediate small intensely fluorescent (SIF) cells. A key question is when during NC ontogeny do multipotent progenitors segregate into the different NC-derived lineages. Recent evidence suggested that sympathetic, sensory, and melanocyte progenitors delaminate from the thoracic neural tube (NT) in successive, largely non-overlapping waves and that at least certain NC progenitors are already fate-restricted within the NT. Whether sympathetic neurons and chromaffin cells, suggested by cell culture studies to share a common progenitor, are also fate segregated in ovo prior to emigration, is not known.

RESULTS

We have conducted single cell electroporations of a GFP-encoding plasmid into the dorsal midline of E2 chick NTs at the adrenomedullary level of the NC. Analysis of their derivatives, performed at E6, revealed that in most cases, labelled progeny was detected in both sympathetic ganglia and adrenal glands, where cells co-expressed characteristic marker combinations.

CONCLUSIONS

Our results show that sympathetic neurons and adrenal chromaffin cells share a common progenitor in the NT. Together with previous findings we suggest that phenotypic diversification of these sublineages is likely to occur after delamination from the NT and prior to target encounter.

Signals and switches in Mammalian neural crest cell differentiation

Neural crest cells (NCCs) comprise a multipotent, migratory cell population that generates a diverse array of cell and tissue types during vertebrate development. These include cartilage and bone, tendons, and connective tissue, as well as neurons, glia, melanocytes, and endocrine and adipose cells; this remarkable lineage potential persists into adult life. Taken together with a limited capacity for self-renewal, neural crest cells bear the hallmarks of stem and progenitor cells and are considered to be synonymous with vertebrate evolution. The neural crest has provided a system for exploring the mechanisms that govern developmental processes such as morphogenetic induction, cell migration, and fate determination. Today, much of the focus on neural crest cells revolves around their stem cell-like characteristics and potential for use in regenerative medicine. A thorough understanding of the signals and switches that govern mammalian neural crest patterning is central to potential therapeutic application of these cells and better appreciation of the role that neural crest cells play in vertebrate evolution, development, and disease.

Ultrastructural evidence of a vesicle-mediated mode of cell degranulation in chicken chromaffin cells during the late phase of embryonic development

In the present investigation, we attempted to determine whether ultrastructural features indicative of a vesicle-mediated mode of cell secretion were detectable in chick chromaffin cells during embryo development. The adrenal anlagen of domestic fowls were examined at embryonic days (E) 12, 15, 19 and 21 by electron microscopy quantitative analysis. Morphometric evaluation revealed a series of granule and cytoplasmic changes highly specific for piecemeal degranulation (PMD), a secretory process based on vesicular transport of cargoes from within granules for extracellular release. At E19 and E21 we found a significant peak in the percentage of granules exhibiting changes indicative of progressive release of secretory materials, i.e. granules with lucent areas in their cores, reduced electron density, disassembled matrices, residual cores and membrane empty containers. A dramatic raise in the density of 30-80-nm-diameter, membrane-bound, electron-dense and electron-lucent vesicles--which were located either next to granules or close to the plasma membrane--was recognizable at E19, that is, during the prehatching phase. The cytoplasmic burst of dense and clear vesicles was paralleled by the appearance of chromaffin granules showing outpouches or protrusions of their profiles ('budding features'). These ultrastructural data are indicative of an augmented vesicle-mediated transport of chromaffin granule products for extracellular release in chick embryo chromaffin cells during the prehatching stage. In conclusion, this study provides new data on the fine structure of chromaffin cell organelles during organ development and suggests that PMD may be part of an adrenomedullary secretory response that occurs towards the end of chicken embryogenesis. From an evolutionary point of view, this study lends support to the concept that PMD is a secretory mechanism highly conserved throughout vertebrate classes.

Lineage specification in neural crest cell pathfinding

There are two principal models to explain neural crest patterning. One assumes that neural crest cells are multipotent precursors that migrate throughout the embryo and differentiate according to cues present in the local environment. A second proposes that the neural crest is a population of cells that becomes restricted to particular fates early in its existence and migrates along particular pathways dependent on unique cell-autonomous properties. Although it is now evident that the neural crest cell population, as a whole, is actually heterogenous (composed of both multipotent and restricted progenitors), evidence supporting the model of prespecification has increased over the past few years. This review will begin by telling the story of melanoblasts: a neural crest subpopulation that is biased toward a single fate and subsequently acquires intrinsic properties that guide cells of this lineage to their final destination. The remainder of this review will explore whether this model is exclusive to melanoblasts or if it can also be used to explain the patterning of other neural crest cells like those of the sensory, sympathoadrenal, and enteric lineages.

The Chromaffin Cell and its Development

This article summarizes some of the recent progress in understanding the development of chromaffin cells. These cells are derivatives of the neural crest and are intimately associated with the sympathetic nervous system. Although a common sympathoadrenal (SA) progenitor cell for chromaffin cells and sympathetic neurons has been postulated, there is evidence to suggest that chromaffin progenitors are already distinct, at least in part, from neuronal SA progenitors prior to invading the adrenal gland. The concept of an essential role of glucocorticoid signalling for chromaffin cell development has been shaken by the observation that chromaffin cells in mice lacking the glucocorticoid receptor develop largely normal. Distinct developmental requirements of chromaffin cells and sympathetic neurons must also be assumed based on the analyses of mice carrying targeted mutations of the genes for two transcription factors, MASH1 and Phox2B. Both genes are expressed by SA progenitors, but are distinctly required for the development of chromaffin cells and sympathetic neurons. There is an ongoing search for molecules selectively operating at the sites, where chromaffin cells develop. Such molecules may be candidates for triggering the distinct developmental pathway of chromaffin cells, as opposed to sympathetic neurons.

Expression of neuronal markers suggests heterogeneity of chick sympathoadrenal cells prior to invasion of the adrenal anlagen

We have analyzed the distribution of neural crest-derived precursors and the expression of catecholaminergic and neuronal markers in developing adrenal tissue of chick embryos. Undifferentiated neural crest cells are found in presumptive adrenal regions from embryonic day 3 (E3) onward. An increasing proportion of cells expressing tyrosine hydroxylase (TH) mRNA indicates catecholaminergic differentiation of precursors not only in primary sympathetic ganglia, but also in presumptive adrenal regions. Whereas precursors and differentiating cells show mesenchymal distribution until E5, discrete adrenal anlagen form during E6. Even during E5, catecholaminergic cells with low or undetectable neurofilament M (NF-M) mRNA expression prevail in positions at which adrenal anlagen become distinct during E6. The predominance of TH-positive and NF-M-negative cells is maintained throughout embryogenesis in adrenal tissue. RNA encoding SCG10, a pan-neuronal marker like NF-M, is strongly expressed throughout adrenal anlagen during E6 but is found at reduced levels in chromaffin cells compared with neuronal cells at E15. Two additional neuronal markers, synaptotagmin 1 and neurexin 1, are expressed at low to undetectable levels in developing chromaffin cells throughout embryogenesis. The developmental regulation of neuronal markers shows at least three different patterns among the four mRNAs analyzed. Importantly, there is no generalized downregulation of neuronal markers in developing adrenal anlagen. Thus, our observations question the classical concept of chromaffin differentiation from a common sympathoadrenal progenitor expressing neuronal properties and suggest alternative models with changing instructive signals or separate progenitor populations for sympathetic neuronal and chromaffin endocrine cells.

Reduction of endogenous TGF-beta does not affect phenotypic development of sympathoadrenal progenitors into adrenal chromaffin cells

Adrenal chromaffin cells and sympathetic neurons are related, but phenotypically distinct derivatives of the neural crest. Molecular cues that determine the chromaffin cell phenotype have not yet been identified; in contrast to a widely held belief, glucocorticoid signaling is apparently not relevant (Development 126 (1999) 2935). Transforming growth factor-betas (TGF-betas) regulate various aspects of embryonic development and are expressed in the environment of sympathoadrenal (SA) progenitor cells. We have previously shown that neutralization of endogenous TGF-beta from E4 to E8 in the quail embryo significantly increases numbers of adrenal tyrosine hydroxylase-positive cells. Whether endogenous TGF-beta may also be involved in influencing phenotypic development of adrenal chromaffin cells and their SA progenitors has not been analyzed. We now demonstrate that neutralization of endogenous TGF-beta1, -beta2 and -beta3 with a pan-anti-TGF-beta antibody in quail embryos during distinct time windows does not alter phenotypic development of chromaffin cells. In situ hybridizations revealed unaltered expression of neurofilament (NF-160), synaptotagmin I and neurexin I in adrenal glands. Likewise, the NF-associated antigen 3A10, and polyphosphorylated NF epitopes (RT 97) were unaltered. Most importantly, the typical ultrastructure of adrenal chromaffin cells including their large chromaffin secretory granules, a hallmark of the neuroendocrine phenotype, which distinguishes them from sympathetic neurons, was not affected. We therefore conclude that neutralization of endogenous TGF-beta influences chromaffin cell proliferation, but does not interfere with the development of the typical chromaffin cell phenotype.

Phenotype of intraadrenal ganglion neurons during postnatal development in rat

The postnatal development of intraadrenal ganglion neurons was studied in rat by using indirect immunohistochemistry and in situ hybridization. The large neuropeptide tyrosine (NPY)-expressing ganglion neurons (type I ganglion neurons) matured postnatally, with marked increases in acetylcholinesterase (AChE)-, neurofilament 10 (NF10)-, and tyrosine hydroxylase (TH)-like immunoreactivities (LIs) paralleled by increasing levels of mRNAs encoding NPY, low-affinity neurotrophin receptor (LANR), and tropomyosin kinase receptor (trk). The smaller vasoactive intestinal polypeptide (VIP)-immunoreactive (IR) ganglion neurons (type II ganglion neurons) expressed increasing levels of VIP mRNA postnatally and also contained immunoreactive nitric oxide synthase (NOS) and its mRNA. These type II ganglion neurons appeared to be relatively mature already at postnatal day (P2) and did not express detectable levels of LANR or trk mRNAs. The cell size of both the type I and type II ganglion neurons increased about 2.5-fold postnatally. The type I ganglion neurons formed more densely packed clusters with increasing age, whereas the type II ganglion neurons were spread out in small groups or individually, mainly in the peripheral parts of the medulla, and appeared to fulfill their migration into the medulla and/or to the inner regions of the cortex early postnatally, possibly after establishing contact with their cortical targets. We suggest that the type I ganglion neurons represent sympathetic ganglion neurons of the same origin as the chromaffin cells and that they mature mainly postnatally. The development of the type II (VIP/NOS) ganglion neurons takes place earlier; however, their phenotype remains more uncertain.

Disordered differentiation as a target for novel approaches to the treatment of neuroblastoma

Some childhood malignant neoplasms are thought to arise in embryonic tissues. These tumors present unique opportunities for studying the maturation of specific cellular lineages and examining the possible role of alterations in the regulation of differentiation in tumor development. Several features of neuroblastoma, a tumor thought to arise in cells originating in the embryonic neural crest, suggest that it may be particularly useful in this regard. The identification of a series of markers that characterize the various cell types of the peripheral nervous system that are detectable in neuroblastoma tumor tissues has made it possible to recognize that the cells of neuroblastoma tumor cell lines and tissues correspond to specific stages of adrenal gland development. Experiments directed at understanding the cellular signals by which neural crest cell maturation is mediated may provide insights of therapeutic import because neuroblastoma tumors corresponding to some stages of differentiation respond very differently to nonspecific cytotoxic therapies than tumors corresponding to other stages.

Developmental expression of serotonin-like immunoreactivity in the sympathoadrenal system of the chicken

The avian sympathoadrenal system has been used as a model to examine the differentiation of cells expressing neuroactive substances derived from the neural crest. Previous studies have dealt with the expression of the "classical" neurotransmitters acetylcholine and catecholamines and of the neuropeptides somatostatin and vasoactive intestinal polypeptide. We have used immunocytochemistry to examine the developmental expression of the monoamine serotonin (5HT) in the chicken sympathoadrenal system. 5HT-like immunoreactivity (5HT-LI) was found to be transiently expressed by cells of the sympathetic ganglia very early in development (E-5 to E-8), disappearing almost entirely at more advanced embryonic stages (E-10 to E-19) and post-hatched chickens where only a population of cells similar to mammalian small intensely fluorescent cells express immunoreactivity to the amine. In contrast, in the adrenal gland of embryos and post-hatched chickens, most chromaffin cells also express 5HT-LI. Double labeling experiments show that in both the adrenal gland and the sympathetic ganglia catecholaminergic properties and somatostatin immunoreactivity are co-expressed with 5-HT-LI. Moreover, the cells that transiently express 5HT-LI in sympathetic ganglia also transiently express somatostatin. The catecholaminergic cells expressing serotonin and somatostatin appear to define a biochemical phenotype common to some chromaffin cells, small intensely fluorescent cells and early sympathoblasts.

Differentiation of embryonic chick sympathetic neurons in vivo: ultrastructure, and quantitative determinations of catecholamines and somatostatin

The ultrastructural and transmitter development of lumbar sympathetic ganglia was studied in embryonic day-6 through -18 chick embryos. At embryonic day 6, ganglia are populated by two morphologically distinct types of neuronal cells and Schwann cell precursors. The neuronal populations basically comprise a granule-containing cell and a developing principal neuron. Granule-containing cells have an irregularly shaped or oval nucleus with small clumps of chromatin attached to the inner nuclear membrane and numerous large (up to 300 nm) membrane-limited granules. Developing principal neurons display a more rounded vesicular nucleus with evenly distributed chromatin, prominent nucleoli, more developed areas of Golgi complexes, and rough endoplasmic reticulum and large dense-core vesicles up to 120 nm in diameter. There are granule-containing cells with fewer and smaller granules which still display the nucleus typical for granule-containing cells. These granule-containing cells may develop toward developing principal neurons or the resting state of granule-containing cells found in older ganglia. Both granule-containing cells and developing principal neurons proliferate and can undergo degeneration. At embryonic day 9 there are far more developing principal neurons than granule-containing cells. Most granule-containing cells have very few granules. Mitotic figures and signs of cell degeneration are still apparent. Synapse-like terminals are found on both developing principal neurons and granule-containing cells. Ganglionic development from embryonic day 11 through 18 comprises extensive maturation of developing principal neurons and a numerical decline of granule-containing cells. Some granule-containing cells with very few and small granules still persist at embryonic day 18. The mean catecholamine content per neuron increases from 0.044 femtomol at embryonic day 7 to 0.22 femtomol at embryonic day 15. Concomitantly, there is a more than 6-fold increase in tyrosine hydroxylase activity. Adrenaline has a 14% share in total catecholamines at embryonic day 15. Somatostatin levels are relatively high at embryonic day 7 (1.82 attomol per neuron) and are 10-fold reduced by embryonic day 15. Our results suggest the presence of two morphologically distinct sympathetic neuronal precursors at embryonic day 6: one with a binary choice to become a principal neuron or to die, the other one, a granule-containing cell, which alternatively may develop into a principal neuron, acquire a resting state or die.

The neuro-endocrine ambiguity of sympathoadrenal cells

This introductory article presents a survey of the principle cellular constituents of the sympathoadrenal section in the peripheral autonomic nervous system, their development and plasticity and factors that govern the expression of particular morphologic and transmitter phenotypes. The article focuses on results obtained in cell culture studies with isolated chromaffin cells that have permitted the analysis of molecular signals possibly serving as environmental cues during the development of sympathoadrenal cells.

Chromaffin cell heterogeneity of process formation and neuropeptide content under control and nerve growth factor-altered conditions in cultures of chick embryonic adrenal gland

Adrenal glands from embryonic day 11 (E-11) chicks were cryostat-sectioned, and it was determined that tyrosine hydroxylase-like immunoreactive (TLI) cells, somatostatin-like immunoreactive (SLI) cells, and methionine-enkephalin-like immunoreactive (ELI) cells occupied chromaffin regions of the gland. Similar age adrenals were dissociated, and the cells were cultured under serum-free conditions. Cultured TLI cells, ELI cells, and SLI cells were characterized according to cell size, cell number, and neurite formation. ELI and SLI cells composed two largely separate populations, with SLI cells tending to have larger cell areas, to be more numerous, and to be less likely to form neurites than ELI cells. The population of TLI cells, although unique in itself, was diverse and numerous enough to include all or portions of the neuropeptide-immunoreactive populations. Neurites of some cells from each of the above populations were strongly immunoreactive for alpha neurofilament protein, and for NAPA73 neurofilament-associated protein. However, neurites could also be observed in all populations that showed poor immunoreactivity for these cytoskeletal proteins. Exogenously added NGF significantly increased neurite-like process formation among TLI and ELI cells, but not among SLI cells. Reductions in the number of neurite-like processes following treatment with anti-nerve growth factor (NGF) were not significant for any of the populations. However, if shorter and broader process were included, anti-NGF caused a significant reduction in total cell processes among TLI and ELI cells. Anti-NGF inhibition of process formation among ELI cells could be reversed with exogenous NGF. Neither NGF or anti-NGF treatments showed a significant effect on cell numbers among TLI and ELI populations. The implications are that a compound of antigenic and physiological similarity to mouse salivary NGF is made by embryonic chick adrenal cells in culture, but the effects of NGF do not appear to be the same for all neural-crest-derived cells from the adrenal, and greater heterogeneity of phenotypes may exist among chromaffin cells than has previously been accepted. Some questions are also raised concerning the neurite-like nature of processes formed by some chromaffin cells in vitro.

Phenotypical changes of embryonic chick adrenal medullary cells in vitro induced by nerve growth factor and ciliary neuronotrophic factor

This study investigates the survival properties and changes in the morphological phenotype of adrenal medullary (chromaffin and neuronal) cells cultured from embryonic chicks at different developmental ages (embryonic days E8 to E16) in response to nerve growth factor (NGF) and ciliary neuronotrophic factor (CNTF). The 4-day survival of medullary cells from all embryonic ages except E8 was about 80% of the seeded cells and was only slightly enhanced by the addition of saturating doses of CNTF (10 ng/ml). With no factors, after 4 days 10-30% of the surviving medullary cells extended neurites. NGF (100 ng/ml) and, even more, CNTF (10 ng/ml) and their combination substantially increased the proportions of neurite-bearing cells (up to 70%). The effect of the factors were maximal at E10 and E12 and declined at older developmental ages. Neurite growth was virtually unaffected by NGF and CNTF at E8. These results show that in vitro survival and neurite growth of chick adrenal medullary cells in response to trophic factors is developmentally regulated.

Ultrastructural changes in adrenaline- and SGC-cells after morphine coincide with alterations of adrenaline and dopamine levels

The effects of morphine on chromaffin cell ultrastructure and catecholamine contents were studied using the adrenal glands from male mice (ICR strain). After 2 h adrenaline was increased 25% from 8.1 to 11.6 mumol/g tissue, followed by a 50% decrease to 5.2 mumol/g between 8-24 h and low values persisting at 72 h. Dopamine increased initially, reaching peak values of 0.5 mumol/g between 8-24 h, but had returned towards control values of 0.29 mumol/g by 72 h. Noradrenaline remained unchanged at 2.5 mumol/gram. Naloxone prevented alterations in adrenaline and dopamine levels. Ultrastructural examination revealed several types of catecholamine-storing cells. Of these the adrenaline and small-granule chromaffin (SGC) cells were more affected by morphine than noradrenaline cells. While the initial elevation of adrenaline 2 h after morphine was not accompanied by significant ultrastructural changes, the decrease after 8 and 24 h was paralleled by a significant (p less than 0.001) loss of adrenaline granules. Signs of active membrane turnover included an increase in the number of vacuoles, and the appearance of numerous coated omega profiles and coated (77.7 +/- 0.6 nm) vesicles. Clusters of synaptic-like vesicles (59.8 +/- 8.2 nm), slightly larger than neuronal vesicles (45.4 +/- 6.4), increased in the SGC-cells. After 72 h, the chromaffin granules in adrenaline cells remained low in numbers and were heterogeneous in electron density. Many synaptic-like vesicles were aligned along the SGC-cell membranes where only few chromaffin granules (109.3 +/- 20 nm) remained. Thus, continuous morphine exposure for 8-72 h increases the turnover of storage granules in adrenaline and SGC-cells with less effect on the noradrenaline cells which maintain catecholamine levels as indicated by biochemical analysis.

Effects of 3-acetylpyridine on the adrenal medulla of the mouse

In the present work, the effects of 3-acetylpyridine (3-AP) on the adrenal medulla were investigated for biochemical and morphological changes. Adrenaline- and noradrenaline-storing cells treated with 3-AP one day previously had lost almost all their granules. A large number of lipoid droplets appeared in the cytoplasm. At the same time, the concentrations of adrenaline and noradrenaline cells were significantly decreased below control values (P less than 0.01). However, these significant changes were ameliorated 19 days after 3-AP treatment. Morphologically and biochemically, the adrenaline- and noradrenaline-storing cells had recovered completely at 35 days.

Development of chick paravertebral sympathetic ganglia. I. Fine structure and correlative histofluorescence of catecholaminergic cells

Paravertebral sympathetic ganglia from the lumbosacral region of a series of chick embryos have been studied with electron microscopic methods, including aldehyde-osmium and permanganate fixatives, and correlative histofluorescence (Grillo et al, '74). Our purpose was to assess the differentiation of catecholaminergic (CA) cells during histogenesis in ovo. Examination of comparable adult ganglia as a baseline for differentiating stages confirmed that the principal sympathetic neuron (PN) is similar to those of other species in that it contains predominately small dense-cored vesicles (SDCV) preserved only by permanganate, and does not histofluoresce following the method of Grillo et al. ('74). At embryonic day (E) 7--8, when ganglia have just formed, areas fluorescing bright yellow-green are correlated with two types of cells: 1) Neuroblasts with vesicular nuclei and large dense-cored vesicles (LDCV) are common. As the neuroblasts grow and differentiate, LDCV move away from perikaryal cytoplasm into developing processes. Around E13-15, LDCV appear in the neuroblasts which continue to develop until they resemble miniature adult PN in late embryos and hatchlings. 2) Granule (GR) cells with clumped chromatin and sparse cytoplasm are clustered in te ganglionic periphery at E7-8, but are rare. The GR cells increase somewhat in size and numbers by E11, but retail essentially the same characteristics as at earlier stages. Neither bright fluorescence nor GR cells appear later than stages E13-15. These results are interpreted to mean that when chick sympathetic stem cells have migrated from the primary ganglia into the paravertebral ganglia, they give rise to two separate lines of CA cells, one of which is not maintained and subsequently disappears. The results are significant as a basis for understanding how a mixed population of CA cells might arise within sympathetic ganglia in situ.

Morphology and histochemistry of the adrenal medulla. I. Various types of primary catecholamine-storing cells in the mouse adrenal medulla

Semithin sections (Araldite) of mouse adreno-medullary tissue were examined in the light microscope after perfusion fixation with glutaraldehyde, glutaraldehyde/formaldehyde or after freeze-drying followed by a treatment with hot formaldehyde gas. The following methods were employed: (i) aldehyde-induced fluorescence of catecholamines, (ii) Schmorl's ferric ferricyanide reaction, (iii) argentaffin reaction, and (iiii) staining with alkaline lead citrate followed by Timm's silver sulphide reaction. The correspondence of results obtained by the various methods was proven in consecutive sections or by successively applying different methods to identical sections. Four types of primary catecholamine-storing cells were identified. NA1 cells contain cytoplasmic granules up to 0.3 mum in diameter which stain black with ammoniacal silver and display a bright white to yellow fluorescence. NA2 cells show smaller cytoplasmic granules which stain brown with the argentaffin method and give white catecholamine fluorescence. NA3 cells appear yellow-earth after applying the argentaffin reaction and show greenish fluorescence. NA4 cells are hardly identified in the light microscope. These cells are significantly smaller than the above mentioned cells and characterized by a high nucleo-cytoplasmic ratio. They become straw coloured with ammoniacal silver and show greenish fluorescence. The argentaffin reaction was also used to identify these cells in semithin sections of glutaraldehyde/osmium tetroxide fixed material. The fine structure of the various noradrenalin-storing cells was studied in consecutive thin sections. NA1 cells were found to contain two populations of granules, the larger ones measuring between 300 and 350 nm, the smaller ones about 175 nm. The granules in NA2 cells correspond to this latter population (175 nm). NA3 cells contain an uniform granule population with a main diameter of 120 nm. The smallest granules are seen in NA4 cells being in the dimension of 80 nm. Granules in NA1 and NA2 cells show uniformly high density, whereas those in NA3 and NA4 cells display cores of varying density. Granules with moderately dense cores in NA3 and NA4 cells may represent partially emptied sites of noradrenalin storage or dopamin containing particles.