A quantitative analysis of rat adrenal chromaffin tissue: morphometric analysis at tissue and cellular level correlated with catecholamine content

Prehatching development of the adrenal gland in Japanese quail (Coturnix japonica): Histological, immunohistochemical, and electron microscopic studies

The adrenal glands play a key role in maintaining the physiological balance of birds and helping them to survive environmental changes. The objective of the present work was to give a detailed investigation of the histological, ultrastructural, and immunohistochemical findings of the adrenal gland in Japanese quail during the prehatching phase. The current study was performed on 45 healthy Japanese quail embryos at different prehatching periods. Our results showed the primordium of the quail's adrenocortical tissue appeared at 3 days of incubation as a thickening of the splanchnic mesoderm. The prospective chromaffin cells appeared at 5 days as clusters of cells migrated from the neural crest cells along the dorsal aorta toward the interrenal tissue. TH immunoreactivity was observed in the neural crest cells during their migration toward the adrenal primordium. Furthermore, these TH immunopositive cells were intermingled with the developing interrenal cell cords that developed from the coelomic epithelium. NSE immunostaining was detected within the cytoplasm of interrenal cells, chromaffin cells, and ganglion cells. Sox10 is expressed in chromaffin and ganglion cells with different staining intensities. On the 13th day of prehatching, both interrenal and chromaffin cells were β-catenin immunonegative, but on the 17th day, both cells were immunopositively. Our findings show that during prenatal life, the adrenal gland undergoes significant morphological changes. Together, the present data suggest that studying the prenatal development of the adrenal gland in birds is important for advancing our understanding of this critical organ and its functions. RESEARCH HIGHLIGHTS: The present study aimed to give a detailed study of the histological, ultrastructural, and immunohistochemical investigations of the adrenal gland in Japanese quail during the prehatching period. The interrenal primordium was observed on the third embryonic day, on the fifth ED the primordium of the chromaffin tissue appeared as row of migrating neural crest cell. At the ultrastructural level, the interrenal cells take steroid-secreting cells characters, they have varying amounts of lipid droplets and abundant mitochondria at 15th ED contained moderate number of lysosomes and mitochondria.

3D organization of the rat adrenal medulla

Without knowledge of the spatial [three-dimensional, (3D)] organization of an organ at the tissue and cellular levels, it is impossible to form a complete picture of its structure and function. At the same time, tissue components hidden in the thickness of the organ are the most difficult to study. The rapid development of computer technologies has contributed both to the development and implementation of new methods for studying 3D microstructures of organs, and the improvement of classical ones but the most complete picture can still be obtained only by recreating 3D models from serial histological sections. This fully applies to the important, but hidden in the thickness of the organ, and difficult to study 3D organization of the adrenal medulla. Only 3D reconstruction from serial sections makes it possible to identify all the main tissue components of the adrenal medulla simultaneously and with good resolution. Of particular importance to this method is the ability to reliably differentiate and study separately the 3D organization of the two main subpopulations of medulla endocrinocytes: adrenaline-storing (A-) cells and noradrenaline-storing (NA-) cells. In this chapter, we discuss the 3D organization of the adrenal medulla based on these original serial section 3D reconstructions and correlating them with data obtained by other methods.

Adaptive remodeling of the stimulus-secretion coupling: Lessons from the 'stressed' adrenal medulla

Stress is part of our daily lives and good health in the modern world is offset by unhealthy lifestyle factors, including the deleterious consequences of stress and associated pathologies. Repeated and/or prolonged stress may disrupt the body homeostasis and thus threatens our lives. Adaptive processes that allow the organism to adapt to new environmental conditions and maintain its homeostasis are therefore crucial. The adrenal glands are major endocrine/neuroendocrine organs involved in the adaptive response of the body facing stressful situations. Upon stress episodes and in response to activation of the sympathetic nervous system, the first adrenal cells to be activated are the neuroendocrine chromaffin cells located in the medullary tissue of the adrenal gland. By releasing catecholamines (mainly epinephrine and to a lesser extent norepinephrine), adrenal chromaffin cells actively contribute to the development of adaptive mechanisms, in particular targeting the cardiovascular system and leading to appropriate adjustments of blood pressure and heart rate, as well as energy metabolism. Specifically, this chapter covers the current knowledge as to how the adrenal medullary tissue remodels in response to stress episodes, with special attention paid to chromaffin cell stimulus-secretion coupling. Adrenal stimulus-secretion coupling encompasses various elements taking place at both the molecular/cellular and tissular levels. Here, I focus on stress-driven changes in catecholamine biosynthesis, chromaffin cell excitability, synaptic neurotransmission and gap junctional communication. These signaling pathways undergo a collective and finely-tuned remodeling, contributing to appropriate catecholamine secretion and maintenance of body homeostasis in response to stress.

Rat adrenal medulla modular organization

Relevance. The concept of the tissue morpho-functional units (modules) of the adrenal medulla is currently not fully developed for adrenaline-storing (A-) cells and completely undeveloped for noradrenaline-storing (NA-) cells. Aim. Separately for A- and NA-cells, establish modules in adrenal medulla based on criteria developed by fundamental histology. Materials and Methods. The study used serial, semithin, and ultrathin sections of the adrenal glands, 7-9 µm thick, from 6 adult male Wistar rats (weight 335 ± 25 g). The sections were stained according to the Honoré method with additional staining with toluidine blue, which allows one to reliably distinguish between A and HA cells in the medulla. A cells are stained blue and HA cells are stained green. Light and electron microscopy was used to visualize serial, semithin, and ultrathin sections of the adrenal glands of adult male rats with A- and HA-cell differentiation. Results and Discussion. A-cells formed round clusters, in which they were located in one layer on the basement membrane. Their lateral sides closely adjoined each other, while the inner sides (the central part of the complexes) formed intercellular expansions, microprotrusions, and primary cilia. Less firmly pressed NA-cells formed polyhedral beams. Both types of cell complexes were associated with auxiliary components (stromal, nervous, circulatory, etc.). The central expansions of A-cell round clusters apparently to serve to retain some of the already produced adrenaline, which increases the readiness of the medulla to rapidly release large amounts of adrenaline in case of hyperacute stress. Accordingly, the adherence of A-cell complexes to a rounded shape is determined by the need to create such central isolated storage expansions. NA-cells are located more freely and do not form isolated intercellular expansions. This allows NA-cells to wedge between stably round A-cell complexes and form polyhedral beams as a result. Conclusion. It was found that the rat adrenal medulla contains two logically and morpho-functionally distinct types of specific modules. A-module are A-cells rounded cluster and NA-module is polyhedral NA-cells beam, both associated with auxiliary components.

Impact of Prenatal and Postnatal Exposure to Endocrine Disrupter DDT on Adrenal Medulla Function

Epinephrine is the most abundant catecholamine hormone, produced by the nervous system and adrenal glands. Endocrine disruption of epinephrine synthesis, secretion and signaling is less studied than steroid and thyroid hormones. Dichlorodiphenyltrichloroethane (DDT) is recognized as one of the most prominent environmental contaminants with a long half-life. It is a potent endocrine disrupter affecting sex steroid, mineralocorticoid, glucocorticoid and thyroid hormone production. Exposure to low doses of DDT is universal and begins in utero. Therefore, we studied adrenal medulla growth and function in male Wistar rats exposed to low doses of DDT during prenatal and postnatal development until puberty and adulthood, as well as rats exposed to DDT since the first day of postnatal development. All the exposed rats demonstrated lowered epinephrine blood levels, gradually reducing with age. DDT was found to inhibit the synthesis of tyrosine hydroxylase and affect the mitochondrial apparatus of epinephrine-producing cells during puberty and even after maturation. Low-dose exposure to DDT from birth resulted in more pronounced changes in adrenomedullary cells and a more profound decrease (up to 50%) in epinephrine secretion in adult rats. Prenatal onset of exposure demonstrated a mild effect on epinephrine-producing function (30% reduction), but was associated with lower rate of adrenal medulla growth during maturation and 25% smaller adrenal medullar size in adult rats. All subjects exposed to low doses of DDT failed to develop adaptive changes and restore proper epinephrine production. These results indicate a dysmorphogenetic effect of prenatal exposure and disruption of secretory function of adrenal chromaffin cells by postnatal exposure to DDT.

Nav1.3 and FGF14 are primary determinants of the TTX-sensitive sodium current in mouse adrenal chromaffin cells

Adrenal chromaffin cells (CCs) in rodents express rapidly inactivating, tetrodotoxin (TTX)-sensitive sodium channels. The resulting current has generally been attributed to Nav1.7, although a possible role for Nav1.3 has also been suggested. Nav channels in rat CCs rapidly inactivate via two independent pathways which differ in their time course of recovery. One subpopulation recovers with time constants similar to traditional fast inactivation and the other ∼10-fold slower, but both pathways can act within a single homogenous population of channels. Here, we use Nav1.3 KO mice to probe the properties and molecular components of Nav current in CCs. We find that the absence of Nav1.3 abolishes all Nav current in about half of CCs examined, while a small, fast inactivating Nav current is still observed in the rest. To probe possible molecular components underlying slow recovery from inactivation, we used mice null for fibroblast growth factor homology factor 14 (FGF14). In these cells, the slow component of recovery from fast inactivation is completely absent in most CCs, with no change in the time constant of fast recovery. The use dependence of Nav current reduction during trains of stimuli in WT cells is completely abolished in FGF14 KO mice, directly demonstrating a role for slow recovery from inactivation in determining Nav current availability. Our results indicate that FGF14-mediated inactivation is the major determinant defining use-dependent changes in Nav availability in CCs. These results establish that Nav1.3, like other Nav isoforms, can also partner with FGF subunits, strongly regulating Nav channel function.

The receptor tyrosine kinase EPHB6 regulates catecholamine exocytosis in adrenal gland chromaffin cells

The erythropoietin-producing human hepatocellular receptor EPH receptor B6 (EPHB6) is a receptor tyrosine kinase that has been shown previously to control catecholamine synthesis in the adrenal gland chromaffin cells (AGCCs) in a testosterone-dependent fashion. EPHB6 also has a role in regulating blood pressure, but several facets of this regulation remain unclear. Using amperometry recordings, we now found that catecholamine secretion by AGCCs is compromised in the absence of EPHB6. AGCCs from male knockout (KO) mice displayed reduced cortical F-actin disassembly, accompanied by decreased catecholamine secretion through exocytosis. This phenotype was not observed in AGCCs from female KO mice, suggesting that testosterone, but not estrogen, contributes to this phenotype. Of note, reverse signaling from EPHB6 to ephrin B1 (EFNB1) and a 7-amino acid-long segment in the EFNB1 intracellular tail were essential for the regulation of catecholamine secretion. Further downstream, the Ras homolog family member A (RHOA) and FYN proto-oncogene Src family tyrosine kinase (FYN)-proto-oncogene c-ABL-microtubule-associated monooxygenase calponin and LIM domain containing 1 (MICAL-1) pathways mediated the signaling from EFNB1 to the defective F-actin disassembly. We discuss the implications of EPHB6's effect on catecholamine exocytosis and secretion for blood pressure regulation.

Monitoring the Secretory Behavior of the Rat Adrenal Medulla by High-Performance Liquid Chromatography-Based Catecholamine Assay from Slice Supernatants

Catecholamine (CA) secretion from the adrenal medullary tissue is a key step of the adaptive response triggered by an organism to cope with stress. Whereas molecular and cellular secretory processes have been extensively studied at the single chromaffin cell level, data available for the whole gland level are much scarcer. We tackled this issue in rat by developing an easy to implement experimental strategy combining the adrenal acute slice supernatant collection with a high-performance liquid chromatography-based epinephrine and norepinephrine (NE) assay. This technique affords a convenient method for measuring basal and stimulated CA release from single acute slices, allowing thus to individually address the secretory function of the left and right glands. Our data point that the two glands are equally competent to secrete epinephrine and NE, exhibiting an equivalent epinephrine:NE ratio, both at rest and in response to a cholinergic stimulation. Nicotine is, however, more efficient than acetylcholine to evoke NE release. A pharmacological challenge with hexamethonium, an α3-containing nicotinic acetylcholine receptor antagonist, disclosed that epinephrine- and NE-secreting chromaffin cells distinctly expressed α3 nicotinic receptors, with a dominant contribution in NE cells. As such, beyond the novelty of CA assays from acute slice supernatants, our study contributes at refining the secretory behavior of the rat adrenal medullary tissue, and opens new perspectives for monitoring the release of other hormones and transmitters, especially those involved in the stress response.

The Rat Adrenal Medulla. II. Proliferative Lesions

Many strains of rats develop spontaneous or drug-induced adrenal medullary proliferative lesions. However, there is often ambiguity about whether the changes observed are hyperplastic or neoplastic and if the term “pheochromocytoma” is appropriate for the lesion in rodents. Various considerations are presented, and the evolution and morphology of the changes are discussed. The lesions are of practical interest because they have at times impeded drug licensing applications.

The Rat Adrenal Medulla. I. The Normal Adrenal

The morphology and physiology of the adrenal medulla are described, emphasizing the rat medulla as an experimental model. Current concepts are reviewed relating to the development of medullary cell lineages and to factors that affect synthesis, storage, and secretion of hormones in the adrenal medulla. The pathophysiological implications of adrenal medullary cells as a multimessenger system are discussed.

Heterogeneous levels of oxidative phosphorylation enzymes in rat adrenal glands

Mitochondria are organelles that produce ATP and reactive oxygen species, which are thought to be responsible for a decline in physiological function with aging. In this study, we morphologically and biochemically examined mitochondria in the rat adrenal gland. Immunohistochemistry showed that the rank order for intensity of immunolabelling for complex IV was zona reticularis > zona fasciculata >> adrenal medulla, whereas for complex V α and β subunits, it was zona fasciculata > zona reticularis and adrenal medulla. The immunolabelling for complex I was homogeneous in the adrenal gland. The difference in immunolabelling between complexes I and IV indicates that the ratio of levels of complex I to that of complex IV in the zona reticularis was smaller than that in the zona fasciculata and the adrenal medulla. Electron microscopy revealed that aging rats had zona reticularis cells with many lysosomes and irregular nuclei. The result suggests that the level of proteins involved in oxidative phosphorylation is coordinated within the complex, but differs between the complexes. This might be responsible for degeneration of zona reticularis cells with aging.

Fine ultrastructure and biochemistry of PC12 cells: a comparative approach to understand neurotoxicity

The PC12 cell line is commonly used as a tool to understand the biochemical mechanisms underlying the physiology and degeneration of central dopamine neurons. Despite the broad use of this cell line, there are a number of points differing between PC12 cells and dopamine neurons in vivo which are missed out when translating in vitro data into in vivo systems. This led us to compare the PC12 cells with central dopamine neurons, aiming at those features which are predictors of in vivo physiology and degeneration of central dopamine neurons. We carried out this comparison, either in baseline conditions, following releasing or neurotoxic stimuli (i.e. acute or chronic methamphetamine), to end up with therapeutic agents which are suspected to produce neurotoxicity (l-DOPA). Although the neurotransmitter pattern of PC12 cells is close to dopamine neurons, ultrastructural morphometry demonstrates that, in baseline conditions, PC12 cells possess very low vesicles density, which parallels low catecholamine levels. Again, compartmentalization of secretory elements in PC12 cells is already pronounced in baseline conditions, while it is only slightly affected following catecholamine-releasing stimuli. This low flexibility is caused by the low ability of PC12 cells to compensate for sustained catecholamine release, due both to non-sufficient dopamine synthesis and poor dopamine storage mechanisms. This contrasts markedly with dopamine-containing neurons in vivo lending substance to opposite findings between these compartments concerning the sensitivity to a number of neurotoxins.

Vesicular roundness and compound release in PC-12 cells

The principal goals of this study were to establish a quantitative morphological analysis of spatial and regional properties of dense core vesicles, and to use this analysis to assess whether homotypic fusion is prominent in chronically treated PC-12 cells at elevated release levels. Simple computerized image processing of electron-micrographs provided the binary images of vesicular dense cores, whilst the artificial intelligence methods were needed to determine the vesicular membranes. As in the past, the presence of large, highly irregular vesicles, provided the morphological evidence of fused vesicles, but the irregularity of vesicular shape was assessed quantitatively-from its roundness. Free space of each vesicle was determined from the distance to its nearest-neighbor, or from the size of its Voronoi polygon. Within a Voronoi polygon, each point is closer to that vesicle than to any other vesicle. Large vesicles were not less round and did not have larger free space, as expected if they result from fusion of several smaller vesicles. In conclusion, we present a novel and rigorous morphological analysis of spatial and regional properties of dense core vesicles. The results demonstrate that the homotypic fusion is not prominent in PC-12 cells, before or following a chronic treatment that enhances release.

Mode of mitochondrial Ca2+ clearance and its influence on secretory responses in stimulated chromaffin cells

To study the role of mitochondrial Ca(2+) clearance in stimulated cells, changes in free Ca(2+) concentration in the cytosol, [Ca(2+)](c) and that in mitochondria, [Ca(2+)](m) along with secretory responses were observed using chromaffin cells co-loaded with Fura-2 and Rhod-2 in the perfused rat adrenal medulla. When the cells were stimulated with 40 mM K(+) in the perfusate, the duration of [Ca(2+)](m) response markedly increased with prolongation of the stimulation period, exhibiting a mean half-decay time of 21 min with 30s stimulation, whereas its amplitude was not altered with stimulations of 10-30s. A computer simulation analysis showed that such a mode of [Ca(2+)](m) response can be produced if excess Ca(2+) taken up by mitochondria precipitates as calcium phosphate (Pi) salt. In the presence of 5 microM rotenone plus 10 microM oligomycin, a decrease in the duration of [Ca(2+)](m) response and a slight but significant increase (24%) in the secretory response to 30s stimulation with 40 mM K(+) were observed. Simulation analyses suggested that this effect of rotenone may be due to reduction in mitochondrial Ca(2+) uptake induced by rotenone-elicited partial depolarization of the mitochondrial membrane potential. In chromaffin cells transsynaptically stimulated through the splanchnic nerve, the intensity of NAD(P)H autofluorescence changed with time courses similar to those of [Ca(2+)](m) responses. The temporal profiles of those two responses were prolonged in a similar manner by application of an inhibitor of mitochondrial Na(+)/Ca(2+) exchanger, CGP37157. Thus, due to the unique Ca(2+) buffering mechanism, [Ca(2+)](m) responses associated with massive mitochondrial Ca(2+) uptake may occur within a limited concentration range in which Ca(2+)-sensitive dehydrogenases are activated to control the mitochondrial redox state in stimulated chromaffin cells.

InsP3 receptor type 2 and oscillatory and monophasic Ca2+ transients in rat adrenal chromaffin cells

Muscarinic receptor stimulation induced oscillatory and monophasic Ca(2+) transients in rat adrenal chromaffin cells in the absence of external Ca(2+). As this Ca(2+) mobilization may be mediated by InsP(3), we first explored types of InsP(3) receptors and their intracellular distribution in chromaffin cells. The InsP(3) receptor type 1 was not immunodetected in precipitates of adrenal medulla homogenates and in dissociated adrenal chromaffin cells, whereas an anti-type 3 mAb recognized a faint band with about 250 kDa, but no significant immunoreaction was visible in chromaffin cells. The anti-type 2 mAb strongly detected a band with about 220 kDa and the immunoreaction was observed perinuclearly and at the cell periphery. These results indicate that InsP(3) receptor type 2 is predominant in chromaffin cells. The oscillatory and monophasic Ca(2+) transients were reproduced in simulation based on a three-state kinetic model (shut, open, and inactivated states). Ca(2+) ions were found experimentally and theoretically to turn over rapidly between stores and the cytosol during stimulation. The results suggest that InsP(3) receptor type 2 is responsible for both oscillatory and monophasic Ca(2+) transients and that change in mode of Ca(2+) responses may be accounted for by the kinetic property of the type 2 receptor.

Involvement of mitochondrial Na+-Ca2+ exchange in intracellular Ca2+ increase induced by ATP in PC12 cells

The involvement of mitochondrial Na+-Ca2+ exchange in Ca2+ responses to ATP was examined in rat pheochromocytoma (PC) 12 cells. Intracellular Ca2+ ([Ca2+]i) and Na+ concentrations ([Na+]i) were measured using fura-2 and SBFI, respectively. ATP caused concentration-dependent increases in [Ca2+]i and [Na+]i. High concentrations of ATP elicited a Ca2+ transient followed by a slow recovery of [Ca2+]i (a sustained phase) in 77% of PC12 cells. The sustained phase of Ca2+ response appeared only when the peak Ca2+ transient exceeded 500 nM. FCCP, a protonophore, greatly enhanced Ca2+ responses to ATP only in cells with the sustained phase but not without this phase. The sustained phase was decreased by clonazepam and CGP37157, mitochondrial Na+-Ca2+ exchange inhibitors, and extracellular Na+ removal but not by cyclosporin A, an inhibitor of permeability transition pores. The reintroduction of Na+ 3.5 min after ATP stimulation in the absence of Na+ caused Na+ concentration-dependent increases in [Ca2+]i and [Na+]i. The increase in [Na+]i was correlated with that in [Ca2+]i. FCCP caused a great increase in [Ca2+]i 4.5 min after ATP stimulation in the absence of extracellular Na+ but not in its presence, indicating that mitochondria retain Ca2+ in the absence of Na+. These results suggest that ATP causes a large increase in [Ca2+]i which was sequestered in mitochondria and that the sustained phase of Ca2+ response to ATP are mainly due to the release of mitochondrial Ca2+ through Na+-Ca2+ exchangers in PC12 cells.

Role of ATP decrease in secretion induced by mitochondrial dysfunction in guinea-pig adrenal chromaffin cells

The mechanism related to mitochondrial dysfunction-induced catecholamine (CA) secretion in dispersed guinea-pig adrenal chromaffin cells was investigated using amperometry and confocal laser microscopy. Application of CCCP, which does not stimulate generation of reactive oxygen species (ROS), reversibly induced CA secretion, whereas application of either cyanide or oligomycin (OL), a stimulator for ROS, enhanced CA secretion to a smaller extent. The CCCP-induced secretion was abolished by removal of external Ca2+ ions and was markedly diminished by D600. The mitochondrial membrane potential, measured using rhodamine 123, was rapidly lost in response to CCCP, but did not change noticeably during a 3 min exposure to OL. Prior exposure to OL markedly facilitated depolarization of the mitochondrial membrane potential in response to cyanide. The mitochondrial inhibitors rapidly produced an increase in Magnesium Green (MgG) fluorescence in the absence of external Ca2+ and Mg2+ ions, an increase that was larger in the cytoplasm than in the nucleus. The rank order of potency in increasing MgG fluorescence among the inhibitors was similar to that in increasing secretion. Thus, mitochondrial inhibition rapidly decreases [ATP] and the mitochondrial dysfunction-induced secretion is not due to ROS generation or to mitochondrial depolarization, but is possibly mediated by a decrease in ATP.

Brief and repeated noise exposure produces different morphological and biochemical effects in noradrenaline and adrenaline cells of adrenal medulla

Exposure to stressful stimuli is known to activate the peripheral sympathetic nervous system and the adrenal gland. In this study, we evaluated the effects of single or repeated bouts of exposure to a readily measurable stressful stimulus (loud noise) on the catecholamine content and ultrastructure of the rat adrenal medulla. In particular, we measured tissue levels of dopamine, noradrenaline, adrenaline and metabolites. In parallel studies, we evaluated the fine ultrastructure of catecholamine cells, including a detailed study of catecholamine granules and a morphometric analysis of adrenaline and noradrenaline medullary cells. Animals were exposed either to a single (6 h) session of loud (100 dBA) noise, or to this noise stimulus repeated every day for 21 consecutive days. There was a marked correlation between biochemical indexes of catecholamine activity and the ultrastructural morphometry of specific catecholamine granules. Exposure to loud noise for 6 h induced a parallel increase in dopamine, noradrenaline, adrenaline and their metabolites, a polarization and an increased numerical density of noradrenaline and adrenaline granules in the cells. After repeated noise exposure, noradrenaline levels were significantly higher than in controls, and adrenaline decreased significantly. In addition, adrenaline cells also exhibited ultrastructural alterations consisting of wide homogeneous cytoplasmic areas and large, pale vesicles.

Differential chemoreceptor reflex responses of adrenal preganglionic neurons

Adrenal sympathetic preganglionic neurons (ADR SPNs) regulating the chromaffin cell release of epinephrine (Epi ADR SPNs) and those controlling norepinephrine (NE ADR SPNs) secretion have been distinguished on the basis of their responses to stimulation in the rostral ventrolateral medulla, to glucopenia produced by 2-deoxyglucose, and to activation of the baroreceptor reflex. In this study, we examined the effects of arterial chemoreceptor reflex activation, produced by inhalation of 100% N(2) or intravenous injection of sodium cyanide, on these two groups of ADR SPNs, identified antidromically in urethane-anesthetized, artificially ventilated rats. The mean spontaneous discharge rates of 38 NE ADR SPNs and 51 Epi ADR SPNs were 4.4 +/- 0.4 and 5.6 +/- 0.4 spikes/s at mean arterial pressures of 98 +/- 3 and 97 +/- 3 mmHg, respectively. Ventilation with 100% N(2) for 10 s markedly excited all NE ADR SPNs (+222 +/- 23% control, n = 36). In contrast, the majority (40/48; 83%) of Epi ADR SPNs were unaffected or slightly inhibited by ventilation with 100% N(2) (population response: +6 +/- 10% control, n = 48). Similar results were obtained after injection of sodium cyanide. These observations suggest that the network controlling the spontaneous discharge of NE ADR SPNs is more sensitive to brief arterial chemoreceptor reflex activation than is that regulating the activity of Epi ADR SPNs. The differential responsiveness to activation of the arterial chemoreceptor reflex of the populations of ADR SPNs regulating epinephrine and norepinephrine secretion suggests that their primary excitatory inputs arise from separate populations of sympathetic premotor neurons and that a fall in arterial oxygen tension is not a major stimulus for reflex-mediated adrenal epinephrine secretion.

Modes of secretagogue-induced [Ca(2+)](i) responses in individual chromaffin cells of the perfused rat adrenal medulla

Chromaffin cells in the perfused rat adrenal medulla were loaded with indo-1 for confocal image analyses. Resting levels of [Ca(2+)](i) in chromaffin cells were similar and were stable with time. This is in contrast to the situation in isolated rat chromaffin cells, in which spontaneous oscillations of [Ca(2+)](i) are known to occur. When chromaffin cells were stimulated for 3-4 min by high K(+) or nicotine, [Ca(2+)](i) increased to a peak in 20-30 s and then declined rather smoothly. In contrast, chromaffin cells stimulated by muscarine or low pH (6.5) commonly exhibited irregular oscillations in [Ca(2+)](i). This provides additional evidence supporting the previous claim that muscarine and low pH evoke catecholamine secretion using partly shared mechanisms. Although muscarine and low pH were speculated to produce weaker responses in noradrenaline-secreting cells due to their selective stimulation of adrenaline secretion, no clear indications for segregation of cell types from [Ca(2+)](i) responses to these stimulants were found. The perfused adrenal medulla loaded with Indo-1 was also employed for simultaneously monitoring integrated changes in [Ca(2+)](i)(Ca responses) by conventional microfluorometry and in catecholamine secretion from a whole medulla (secretory responses). When the profiles of secretory responses were approximated by the kth power of the profiles of Ca responses, the k-values were estimated to be 2.2 and 2.3 for high-K(+)- and nicotine-elicited responses, respectively, whereas a k-value of 1.4 was obtained for both muscarine- and low-pH-elicited responses. An analysis showed that the significant difference in the k-value with these two classes of stimulants is accounted for by the stimulant-dependent patterns of [Ca(2+)](i) responses found in confocal image analysis.

Growth and neurotrophic factors regulating development and maintenance of sympathetic preganglionic neurons

The functional anatomy of sympathetic preganglionic neurons is described at molecular, cellular, and system levels. Preganglionic sympathetic neurons located in the intermediolateral column of the spinal cord connect the central nervous system with peripheral sympathetic ganglia and chromaffin cells inside and outside the adrenal gland. Current knowledge is reviewed of the development of these neurons, which share their origin with progenitor cells, giving rise to somatic motoneurons in the ventral horn. Their connectivities, transmitters involved, and growth factor receptors are described. Finally, we review the distribution and functions of trophic molecules that may have relevance for development and maintenance of preganglionic sympathetic neurons.

Embryonic epinephrine synthesis in the rat heart before innervation: association with pacemaking and conduction tissue development

Epinephrine is a potent neurotransmitter and hormone that can influence cardiac performance beginning shortly after the first myocardial contractions occur in developing vertebrate embryos. In the present study, we provide evidence that the heart itself may produce epinephrine during embryonic development. Using antibodies that selectively recognize the catecholamine biosynthetic enzymes, tyrosine hydroxylase, dopamine ss-hydroxylase, and phenylethanolamine N-methyltransferase, we used coimmunofluorescent staining techniques to identify cardiac cells that have the capability of producing catecholamines. Initially, cells expressing catecholamine biosynthetic enzymes were found interspersed throughout the myocardium, but by embryonic day 11.5 (E11.5), they became preferentially localized to the dorsal venous valve and atrioventricular canal regions. As development proceeded, catecholamine biosynthetic enzyme expression decreased in these regions but became quite strong along the crest of the interventricular septum by E16.5. This expression pattern was also transient, decreasing in the ventricular septum by E19.5. These data are consistent with a transient and progressive association of catecholamine-producing cells within regions of the heart that become the sinoatrial node, atrioventricular node, and bundle of His. This is the first evidence demonstrating that intrinsic cardiac adrenergic cells may be preferentially associated with early pacemaking and conduction tissue development.

Enhancement of the dense-core vesicle secretory cycle by glucocorticoid differentiation of PC12 cells: characteristics of rapid exocytosis and endocytosis

The secretory cycle of dense-core vesicles (DCVs) in physiologically stimulated patch-clamped PC12 cells was analyzed using both amperometry and capacitance measurements. Untreated cells had low or undetectable Ca currents and sparse secretory responses to short depolarizations. Dexamethasone (5 microM) treatment for 5-7 d tripled Ca current magnitude and dramatically increased quantal secretion in response to depolarization with action potentials. Such cells expressed L-, N-, and P-type Ca channels, and depolarization evoked rapid catecholamine secretion recorded as amperometric spikes; the average latency was approximately 50 msec. These spikes were much smaller and shorter than those of primary adrenal chromaffin cells, reflecting the smaller size of DCVs in PC12 cells. Depolarizing pulse trains also elicited a rapid increase in membrane capacitance corresponding to exocytosis in differentiated but not in naïve cells. On termination of stimulation, membrane capacitance declined within 20 sec to baseline indicative of rapid endocytosis (RE). RE did not take place when secretion was stimulated in the presence of Ba or Sr, indicating that RE is Ca-specific. RE was blocked when either anti-dynamin antibodies or the pleckstrin homology domain of dynamin-1 was loaded into the cell via the patch pipette. These studies indicate that neuroendocrine differentiation of PC12 cells with glucocorticoids enhances the development of the excitable membrane and increases the coupling between Ca channels and vesicle release sites, leading to rapid exocytosis and endocytosis. Slow catecholamine secretion in undifferentiated cells may be caused in part by a lack of localized secretory machinery rather than being an intrinsic property of dense-core vesicles.

Electro-acupuncture stimulation to a hindpaw and a hind leg produces different reflex responses in sympathoadrenal medullary function in anesthetized rats

The effects of electro-acupuncture stimulation (EAS) of two different areas of a hindlimb with different stimulus intensities on sympathoadrenal medullary functions were examined in anesthetized artificially ventilated rats. Two needles of 160 microm diameter and about 5 mm apart were inserted about 5 mm deep into a hindpaw (Chungyang, S42) or a hind leg (Tsusanli, S36) and current of various intensities passed to excite various afferent nerve fiber groups at a repetition rate of 20 Hz and pulse duration of 0.5 ms for 30-60 s. Fiber groups of afferent nerves stimulated in a hindlimb were monitored by recording evoked action potentials from the afferents innervating the areas stimulated. The sympathoadrenal medullary functions were monitored by recording adrenal sympathetic efferent nerve activity and secretion rates of catecholamines from the adrenal medulla. EAS of a hindpaw at a stimulus strength sufficient to excite the group III and IV somatic afferent fibers produced reflex increases in both adrenal sympathetic efferent nerve activity and the secretion rate of catecholamines. EAS of a hind leg at a stimulus strength sufficient to excite the group III and IV afferent fibers produced reflex responses of either increases or decreases in sympathoadrenal medullary functions. All responses of adrenal sympathetic efferent nerve activity were lost after cutting the afferent nerves ipsilateral to the stimulated areas, indicating that the responses are the reflexes whose afferents nerve pathway is composed of hindlimb somatic nerves. It is concluded that electro-acupuncture stimulation of a hindpaw causes an excitatory reflex, while that of a hind leg causes either excitatory or inhibitory reflex of sympathoadrenal medullary functions, even if both group III and IV somatic afferent fibers are stimulated.

Acetylcholinesterase activity, and neurofilament protein, and catecholamine synthesizing enzymes immunoreactivities in the mouse adrenal gland during postnatal development

The present study showed the acetylcholinesterase (AChE) activity, and neurofilament protein (NFP), catecholamine-synthesizing enzymes, dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) immunoreactivities in the mouse adrenal gland during postnatal development. From birth to postnatal-1-day, AChE activity was weakly and diffusely found in some medullary cells and in very few nerve fibers whereas strong NFP immunoreactivity was seen in a few ganglion cells and in remarkably numerous nerve fibers in the medulla. Almost all meduallary cells were reactive for both DBH and PNMT during this period. From postnatal-2- or -3-day to postnatal-1-week, strong AChE activity was observed in a few large ganglion cells, but the reaction was weak in clusters of chromaffin cells, and the number of strong AChE-active nerve fibers in the medulla was rapidly increased. From postnatal-2-day onwards, the number of NFP-immunoreactive nerve fibers in the medulla were remarkably numerous. Numerous chromaffin cells were reactive for both DBH and PNMT whereas some chromaffin cells were reactive for only DBH from postnatal-2-day onwards. These results suggest that drastic changes such as an increase of acetylcholine in the nerve fibers, differentiation of noradrenaline and adrenaline cells of the medulla may occur during this period. From postnatal-2-week to postnatal-3-week, weak AChE activity was seen in the clusters of several chromaffin cells and a few ganglion cells, and the number of AChE-active nerve fibers in the medulla was gradually increased. From postnatal-4-week to postnatal-8-week (adult), the distribution and frequency of AChE activity in the adrenal gland were similar to those at postnatal-3-week. In the adult, AChE activity was weakly seen in the clusters of several chromaffin cells showing noradrenaline fluorescence in the adrenal medulla. The noradrenaline cells were contacted by denser AChE-reactive nerve fibers than adrenaline cells. These results suggest that the development of cholinergic nervous system in the mouse adrenal medulla may be completed by postnatal-3-week.

Exocytosis in chromaffin cells of the adrenal medulla

The chromaffin cell has been used as a model to characterize releasable components present in secretory granules and to understand the cellular mechanisms involved in catecholamine release. Recent physiological and biochemical developments have revealed that molecular mechanisms implicated in granule trafficking are conserved in all eukaryotic species: a rise in intracellular calcium triggers regulated exocytosis, and highly conserved proteins are essential elements which interact with each other to form a molecular scaffolding, ensuring the docking of granules at the plasma membrane, and perhaps membrane fusion. However, the mechanisms regulating secretion are multiple and cell specific. They operate at different steps along the life of a granule, from the time of granule biosynthesis up to the last step of exocytosis. With regard to cell specificity, noradrenaline and adrenaline chromaffin cells display different receptor and signaling characteristics that may be important to exocytosis. Characterization of regulated exocytosis in chromaffin cells provides not only fundamental knowledge of neurosecretion but is of additional importance as these cells are used for therapeutic purposes.

Changes in intracellular Na+ concentration evoked by nicotinic receptor activation in the guinea-pig adrenal chromaffin cells

Using the whole-cell voltage clamp technique and microfluorometry with sodium-binding benzofuran isophthalate (SBFI), a nicotine-induced inward current and increase in the intracellular Na+ concentration ([Na+]in) were examined simultaneously in guinea-pig adrenal chromaffin cells. The increase in [Na+]in expected from the time-integrated inward current was well correlated with that of [Na+]in measured with SBFI. The ratio of the expected [Na+]in to the measured [Na+]in was 0.64 at -85mV and decreased with increasing holding potentials. The decay time constant of the increased [Na+]in was not affected by ouabain. It is concluded that the Na+ entering the cell is diffusable in about 60% cell volume without fast buffering mechanisms and is eliminated by the exchange of Na+ between the pipette solution and cell interior under the patch clamp condition.

Mitochondrial participation in the intracellular Ca2+ network

Calcium can activate mitochondrial metabolism, and the possibility that mitochondrial Ca2+ uptake and extrusion modulate free cytosolic [Ca2+] (Cac) now has renewed interest. We use whole-cell and perforated patch clamp methods together with rapid local perfusion to introduce probes and inhibitors to rat chromaffin cells, to evoke Ca2+ entry, and to monitor Ca2+-activated currents that report near-surface [Ca2+]. We show that rapid recovery from elevations of Cac requires both the mitochondrial Ca2+ uniporter and the mitochondrial energization that drives Ca2+ uptake through it. Applying imaging and single-cell photometric methods, we find that the probe rhod-2 selectively localizes to mitochondria and uses its responses to quantify mitochondrial free [Ca2+] (Cam). The indicated resting Cam of 100-200 nM is similar to the resting Cac reported by the probes indo-1 and Calcium Green, or its dextran conjugate in the cytoplasm. Simultaneous monitoring of Cam and Cac at high temporal resolution shows that, although Cam increases less than Cac, mitochondrial sequestration of Ca2+ is fast and has high capacity. We find that mitochondrial Ca2+ uptake limits the rise and underlies the rapid decay of Cac excursions produced by Ca2+ entry or by mobilization of reticular stores. We also find that subsequent export of Ca2+ from mitochondria, seen as declining Cam, prolongs complete Cac recovery and that suppressing export of Ca2+, by inhibition of the mitochondrial Na+/ Ca2+ exchanger, reversibly hastens final recovery of Cac. We conclude that mitochondria are active participants in cellular Ca2+ signaling, whose unique role is determined by their ability to rapidly accumulate and then release large quantities of Ca2+.

Selective neural regulation of epinephrine and norepinephrine cells in the adrenal medulla -- cardiovascular implications

The innervation of the adrenal medulla regulates the release of catecholamines from the two, epinephrine (EPI) and norepinephrine (NE), populations of chromaffin cells. Adjustments in the neural output to the adrenal medulla are made by centers in the brain that integrate the sensory input arising from a variety of challenges and the resulting changes in secretion assist in the restoration of homeostasis. Interestingly, the adrenal medullary secretory responses do not simply reflect increments a fixed ratio of EPI to NE as might be expected if release was proportional to the number EPI and NE cells. Instead, the ratio of EPI to NE changes depending on the magnitude and type of stimulus that initiates neural activation of the medulla. The variability in the EPI:NE release ratio implies that the EPI and NE cells can be differentially stimulated. Although the underlying mechanisms are not fully characterized, this review presents an emerging view that the selective control of EPI and NE cells is accounted for, first, by the existence of separate neural circuits between brain centers and the chromaffin cells, and second, through neuromodulation that selectively influences EPI and NE cells. The presence of mechanisms that allow for separate control of the EPI and NE cells may significantly augment the range of cardiovascular and metabolic responses mediated through activation of the adrenal medulla.

Ca2+ clearance mechanisms in isolated rat adrenal chromaffin cells

1. Intracellular Ca2+ clearance mechanisms were studied in rat adrenal chromaffin cells, by measuring slow tail currents through small-conductance Ca(2+)-activated K+ channels and using indo-1 photometry following depolarization-induced Ca2+ loading. 2. Following several-hundred millisecond depolarizations, [Ca2+]i decayed in three phases. An initial fast decay was followed by a long-lasting, low plateau, then [Ca2+]i returned to the resting level slowly. 3. Replacement of external Na+ moderately slowed [Ca2+]i decay, indicating a contribution of plasma membrane Na(+)-Ca2+ exchange. 4. Raising external pH or application of extracellular Eosin of La3+ prolonged slow tail currents, indicating a contribution of plasma membrane Ca(2+)-ATPase to Ca2+ clearance. 5. Ca(2+)-induced Ca2+ release from caffeine-sensitive stores occurred during depolarization. 6. Inhibition of endoplasmic reticulum Ca(2+)-ATPase had little effect on Ca2+ clearance. 7. Slow tail currents and [Ca2+]i decay following 0.2 - 2 s depolarizations were much prolonged by mitochondrial inhibition with carbonyl cyanide m-chlorophenylhydrazone (CCCP) or Ruthenium Red, which abolished the initial rapid decay and plateau of [Ca2+]i. 8. In conclusion, mitochondrial Ca2+ uptake plays a major role in Ca2+ clearance by rapidly and reversibly sequestering Ca2+ during depolarization-evoked Ca2+ loads.

Dominant role of mitochondria in clearance of large Ca2+ loads from rat adrenal chromaffin cells

Cytosolic Ca2+ (Ca2+c) clearance from adrenal chromaffin cells was studied by whole-cell patch clamp and indo-1 Ca2+ photometry after influx of Ca2+ through voltage-dependent Ca2+ channels. We isolated the rates of Ca2+c clearance by several mechanisms using combinations of the following agents (with their expected targets): Li+ or TEA substituted for Na+ (Na(+)-Ca2+ exchange), 1 mM La3+ applied after the depolarization (Na(+)-Ca2+ exchange and plasma membrane Ca(2+)-ATPase), 1 microM thapsigargin (pumping into reticular stores), and 2 microM carbonyl cyanide m-chlorophenylhydrazone (uptake into mitochondria). Remarkably, whenever [Ca2+]c rose above approximately 500 nM, Ca2+c clearance by mitochondria exceeded clearance by either Na(+)-Ca2+ exchange or the Ca2+ pumps of the plasma and reticular membranes. As [Ca2+]c fell again, Ca2+ reemerged from mitochondria, prolonging the final return to basal levels.

DNA regulatory sequences of the rat tyrosine hydroxylase gene direct correct catecholaminergic cell-type specificity of a human growth hormone reporter in the CNS of transgenic mice causing a dwarf phenotype

Transgenic mice bearing 4.8 kilobases (kb) of upstream rat tyrosine hydroxylase (TH) sequences linked to a human growth hormone gene (hGH) exhibited cell-specific expression of hGH in all the appropriate catecholaminergic neurons in the central nervous system (CNS), although with different penetrance in two different mouse lineages. No ectopic expression was observed in any brain or peripheral region in one founder and its progeny. In another founder there was some ectopic expression in addition to appropriate and high levels of tissue-specific expression in all catecholaminergic areas. These results identify regulatory sequences that are sufficient for targeting expression to all catecholaminergic CNS neurons. Also, expression of exogenous hGH in the hypothalamus caused a dwarf phenotype, generating a novel genetic model for GH deficiency of hypothalamic origin.

Characterization of low pH-induced catecholamine secretion in the rat adrenal medulla

Catecholamine (CA) secretion was evoked when the isolated rat adrenal gland was perfused with HEPES-buffered Krebs solution acidified by the addition of HCl or by gassing with 95% O2/5% CO2. The secretion was detectable at pH 7.0 and increased with decreasing pH until at approximately 6.4. The low pH-induced CA secretion consisted of two phases, an initial transient response followed by a sustained phase. An intracellular Ca2+ antagonist, 3,4,5-trimethoxybenzoic acid 8-(N,N-diethylamino)octyl ester, selectively inhibited the initial phase of secretion. Both of the responses were resistant to nifedipine, a blocker of voltage-gated Ca2+ channel, but were completely inhibited in Ca(2+)-free (1 mM EGTA containing) solution. Adrenaline was an exclusive component in CAs released by low pH. The time course and extent of intracellular acidification caused either by low pH in the external medium or by the offset of a transitory NH4Cl application had no correlation with those of the secretory responses in the corresponding period. These results suggest that extracellular acidification preferentially activates adrenaline secretive cells to evoke CA secretion and that this low pH-induced CA secretion may be mediated by dihydropyridine-insensitive Ca2+ influx. Furthermore, the initial transient phase of the low pH-induced CA secretion might be caused by a Ca2+ release from intracellular stores, which is also induced by the Ca2+ influx.

Differential secretion of catecholamines in response to peptidergic and cholinergic transmitters in rat adrenals

1. Rat adrenal medulla is stimulated by cholinergic and peptidergic transmitters released from splanchnic nerves. The peptidergic transmitter has been identified as vasoactive intestinal polypeptide (VIP) and its contribution in comparison to that of acetylcholine (ACh) is more prominent at low neuronal activity. The purpose of this study is to determine if ACh and VIP cause differential secretion of adrenaline and noradrenaline and whether the differential secretion also occurs when splanchnic nerves are stimulated at different frequencies. 2. Perfusion of the left adrenal gland with Krebs solution for several hours did not change adrenaline and noradrenaline contents (15.2 micrograms and 3.5 micrograms, respectively) and their ratio (4.4) from those of the unperfused right adrenal medulla (15.2 micrograms, 3.3 micrograms and 4.8, respectively). 3. Perfusion with ACh (10 microM for 4 min) resulted in the secretion of 109 ng of catecholamines and the ratio of adrenaline to noradrenaline was 3.8. Although the secretion increased with increased concentrations of ACh (30 and 100 microM), the ratios remained between 3 and 4. 4. Perfusion with VIP (10 microM for 4 min) resulted in the secretion of 27 ng of catecholamines and the ratio of adrenaline to noradrenaline was 9.7. A higher concentration of VIP (20 microM for 4 min) resulted in the secretion of greater amounts of catecholamines (102 ng) without significantly altering the ratio of adrenaline to noradrenaline (10.9). 5. Perfusion with as low as 0.01 microM pituitary adenylate cyclase-activating polypeptide (PACAP) increased the secretion of catecholamines to 31 ng and the secretion increased in a dose-dependent manner up to 0.3 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in competence determine the timing of two sequential glucocorticoid effects on sympathoadrenal progenitors

We have studied the control of adrenal chromaffin cell development by glucocorticoids (GCs), in a reconstituted in vitro system. The development of the chromaffin phenotype involves two sequential, GC-dependent events: the decision not to become a sympathetic neuron, and the decision to express the epinephrine-synthesizing enzyme, phenylethanolamine-N-methyltransferase (PNMT). Both decisions appear to be mediated by the type II GC receptor. Competence to express PNMT develops on a schedule in vitro which parallels that seen in vivo, but only in progenitors that have first failed to undergo neuronal differentiation. The schedule of PNMT induction is thus controlled by the time of appearance of neither the inducing signal nor its receptor, as previously suggested, but rather by a cell-intrinsic timed process in chromaffin precursors. The two effects of GCs are pharmacologically distinct, suggesting that the GC receptor may interact differently with different genes in the same cell, in a manner that changes with development.

Immortalized retinal neurons used as immunogen for the generation of cell-specific antisera

We have recently described a class of immortalized neurons which were derived from retinal tumors induced in PNMT-SV40 transgenic mice (TgBri59)9. These neurons possess a differentiated neuronal phenotype which includes the elaboration of extensive neurite processes and the expression of markers specific for amacrine and horizontal neurons, as well as the expression of the neurofilament triplet proteins. As these 'RT-1' neurons are derived from a restricted set of retinal neurons, they represent an enriched source of immunogen for the production of cell-specific antisera. Therefore, we have used RT-1 cell cultures to generate polyclonal antisera in rabbits. Two of these antisera have been characterized in immunocytochemical and Western blotting experiments using normal mouse and rat tissues. The antisera recognize neurons in the inner nuclear layer and particularly in the ganglion cell layer in the normal retina and cells of the adrenal medulla. These data indicate that specific cell lines derived from transgenic animals provide a rich source of antigen for the production of cell-specific antibodies. These antibodies should prove valuable for studies of retinal development and function.

A v-myc-immortalized sympathoadrenal progenitor cell line in which neuronal differentiation is initiated by FGF but not NGF

Sympathetic neurons differentiate from a developmentally restricted progenitor cell in the neural crest-derived sympathoadrenal lineage. We have isolated these progenitors by fluorescence-activated cell sorting and immortalized them using a v-myc-containing retrovirus. The complement of antigenic markers expressed by these lines suggests that they have retained many of the properties of their normal counterparts. These lines initiate neuronal differentiation in response to basic FGF, but not to NGF, and do not contain NGF receptor mRNA. In NGF plus FGF, however, a small percentage of the cells differentiate to NGF-dependent postmitotic neurons. Furthermore, an induction of NGF receptor mRNA can be observed in response to FGF. Thus, the development of sympathetic neurons may involve a relay, in which FGF both initiates differentiation and induces the NGF receptor, which in turn controls further maturation and survival.

Chromatin structure as a molecular marker of cell lineage and developmental potential in neural crest-derived chromaffin cells

Adrenal medullary chromaffin cells have the capacity to transdifferentiate into sympathetic neurons. We show here that SCG10, a neural-specific gene that is induced during this transdifferentiation, is maintained in mature chromaffin cells in a potentially active chromatin conformation marked by two DNAase I hypersensitive sites (HSS). A low level of transcription is associated with this conformation. The HSS are also present in neurons expressing high levels of SCG10, but not in nonneuronal cells. Experiments using transgenic mice suggest that these HSS can in principle form in any cell type expressing the gene, but that a cis-repression mechanism normally prevents their assembly in nonneuronal cells. We suggest that the SCG10 HSS may represent a molecular marker of the lineage and phenotypic plasticity of chromaffin cells.

The rat adrenal medulla

Adult adrenal medullary cells, in many strains of rats, develop diffuse and nodular hyperplasia and neoplasia under a variety of conditions. Both endogenous and exogenous factors affect the development of these proliferative changes. The former include the animals' strain, age, and sex. The latter include drugs and other environmental agents, diet, and perhaps stress. Adrenal medullary neoplasms which arise under diverse circumstances often closely resemble each other both morphologically and functionally, and exhibit characteristics of immature chromaffin cells. Recent data indicate that normal, mature-appearing epinephrine- and norepinephrine-type chromaffin cells are able to divide, and suggest that signals which regulate chromaffin cell function also regulate cell proliferation. Prolongation of these signals or superimposed abnormalities might initiate pathological proliferative states. It remains to be determined whether the mechanisms which promote or prevent cell proliferation in the adult adrenal are related to those involved in normal development.

Time required for transmitter accumulation inside monoaminergic storage vesicles differs in peripheral and in central systems

Monoamine storage vesicles accumulate transmitters via an active transport process which presents similar pharmacological and bioenergetic properties in all monoaminergic systems. Using [3H]reserpine, a specific ligand of the vesicular monoamine transporter on isolated storage vesicles, we have determined the molecular turnover number of the monoamine transporter and found in various monoaminergic systems an identical value of 135 molecules of substrate transported per min. Using high performance liquid chromatography-electrochemical monoamine determination and the binding of [3H]dihydrotetrabenazine, a specific ligand of the vesicular monoamine transporter in tissue homogenates, we have measured the ratio of transmitter molecules per transporter in various rat tissues containing high amounts of monoamines. This ratio is about 500 in brain regions (striatum, hypothalamus, midbrain) and in the maxillary gland, it varies from 2000 to 7000 in sympathetic nerve terminals in the heart, brown adipose tissue and vas deferens, and it is 6000 in platelets and 280,000 in the adrenal medulla. The minimal time required in vivo for biogenic amine accumulation inside storage vesicles could be derived from these data. Values of 2-4 min were found for brain or maxillary gland synaptic vesicles, 15-50 min for heart, brown adipose tissue or vas deferens sympathetic vesicles and for platelet granules, and 35 h for adrenal medulla chromaffin granules. Thus the maturation time of monoaminergic vesicles, in terms of monoamine accumulation, is highly variable, being short in the brain and maxillary glands, 5-20-fold longer in the sympathetic nervous system and in platelets, and much increased in adrenals.(ABSTRACT TRUNCATED AT 250 WORDS)