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

Developmental heterogeneity of embryonic neuroendocrine chromaffin cells and their maturation dynamics

During embryonic development, nerve-associated Schwann cell precursors (SCPs) give rise to chromaffin cells of the adrenal gland via the "bridge" transient stage, according to recent functional experiments and single cell data from humans and mice. However, currently existing data do not resolve the finest heterogeneity of developing chromaffin populations. Here we took advantage of deep SmartSeq2 transcriptomic sequencing to expand our collection of individual cells from the developing murine sympatho-adrenal anlage and uncover the microheterogeneity of embryonic chromaffin cells and their corresponding developmental paths. We discovered that SCPs on the splachnic nerve show a high degree of microheterogeneity corresponding to early biases towards either Schwann or chromaffin terminal fates. Furthermore, we found that a post-"bridge" population of developing chromaffin cells gives rise to persisting oxygen-sensing chromaffin cells and the two terminal populations (adrenergic and noradrenergic) via diverging differentiation paths. Taken together, we provide a thorough identification of novel markers of adrenergic and noradrenergic populations in developing adrenal glands and report novel differentiation paths leading to them.

Studies of the neuronal transdifferentiation process in cultured human pheochromocytoma cells: effects of steroids with differing functional groups on catecholamine content and cell morphology

The neuronal differentiation of adrenal pheochromocytoma cells from human subjects was studied in vitro for periods of up to 65 days. Changes with time in culture were observed in both intracellular catecholamine content (progressive decreases in epinephrine, norepinephrine, and dopamine, except for a possible transient early increase in the latter) and in morphology (increases in neurite outgrowth) of cells cultured in control medium; supplementation of cultures with nerve growth factor resulted in a substantial increase in neurite formation. The effects on these changes of the presence in the culture medium of various steroids were examined. The addition of 11-oxygenated steroids (aldosterone, corticosterone, cortisol, or dexamethasone) at 10(-5) M concentrations caused at least 2.5-fold increases in mean intracellular dopamine and norepinephrine levels; with dexamethasone, 9-10-fold increases were observed. Intracellular epinephrine content was also enhanced by 11,17-oxygenated steroids (dexamethasone and cortisol), but not by the other 11-oxygenated compounds studied. These two 11,17-oxygenated glucocorticoids also inhibited the morphologic changes seen with extended periods in culture, decreasing the outgrowth of neurite projections and causing cells to attain a vacuolated and granular appearance; the presence of dexamethasone strongly inhibited the morphologic changes induced by nerve growth factor. 11-Deoxy steroid intermediates (pregnenolone, 11-deoxycorticosterone, and 11-deoxycortisol) had little or no effect on catecholamine content or on morphology. Preliminary observations suggest that C-18 and C-19 sex steroid hormones (17 beta-estradiol and testosterone) may have morphologic effects opposite to those of the 11-oxygenated compounds, showing a slight stimulatory influence on the formation of neurite projections, but no significant effect on catecholamine content.

Peripherin-like immunoreactivity in type II spiral ganglion cell body and projections

Peripherin, an intermediate filament protein, is present in neuronal subpopulations of both peripheral and central nervous systems. The distribution of peripherin was studied in the adult rat cochlea using immunohistochemistry on whole mount material, in cryostat sections and sections of plastic embedded tissue. In the spiral ganglion, peripherin labeling was restricted to the perikarya of a subpopulation of neurons and their peripheral and central processes. Peripherin positive neurons had the following features: (i) they have a large eccentric nucleus, they were often found in a cluster of 2 or 3 cells, (ii) they were often located near the intraganglionic spiral bundle fibers, (iii) they represented roughly 8% of the whole ganglion population and (iv) on the average they had smaller perikarya than non-immunoreactive cells. Immunostaining on semithin plastic sections revealed positive reactivity on Type II ganglion cells, while Type I neurons were negative. Double labeling using peripherin and three neurofilament (NF) subunit antibodies confirmed the presence of both markers within the same spiral ganglion cell type. Type II neurons have been previously documented as the only subpopulation of the spiral ganglion that presents a strong positive NF immunoreactivity within their perikarya. In the organ of Corti, peripherin-positive fibers formed bundles that course beneath the outer hair cells and send branches that end as boutons contacting the outer hair cells. All these characteristics suggest that peripherin-positive cells are Type II neurons, and that peripherin constitutes a reliable marker for this spiral ganglion subpopulation, as well as their peripheral and central processes.

Frog chromaffin and adrenocortical cell co-cultures: a model for the study of medullary control of corticosteroidogenesis

Phylogenetic, physiological and morphological evidence indicates that interactions between chromaffin and adrenocortical cells are involved in the differentiation and maintenance of function of both cell types. Chromaffin-adrenocortical interaction has become recognized as an important component of adrenocortical regulation; however, the mechanisms by which chromaffin cells modulate adrenocortical function are not well understood. To study directly chromaffin-adrenocortical cellular interactions, we developed primary frog (Rana pipiens) adrenal co-cultures. In these co-cultures, chromaffin cells extend processes that project towards or onto adrenocortical cells, mimicking their organization in vivo and indicating a potential for interaction between the two cell types. Cell survival and differentiation were optimized using a combination of NGF, FGF and histamine to enhance neurite outgrowth and fetal calf serum plus 10(-10) M ACTH to maintain steroidogenesis. Characterization of the cells by immunocytochemistry and histochemistry showed that chromaffin cells maintain expression of catecholamine biosynthetic enzymes and that adrenocortical cells maintain expression of steroidogenic enzymes. Furthermore, chromaffin cells release catecholamines upon stimulation with carbamylcholine or potassium while adrenocortical cells sustain a basal secretion rate of aldosterone and corticosterone that is augmented 10-40-fold by 0.1 nM to 10 nM ACTH. We therefore propose that these co-cultures serve as a useful model system to study the cellular and molecular mechanisms by which chromaffin cells modulate adrenocortical cell function.

Peptidergic, catecholaminergic and morphological properties of avian chromaffin cells are modulated distinctively by growth factors

Most neurons and endocrine cells are known to co-express a 'classical neurotransmitter' with one or more neuropeptides. Although their expression has been shown to be modulated by differentiation factors, it is not known if particular combinations of neurotransmitter/neuropeptide(s) are co-regulated. We have analyzed the effect of nerve growth factor (NGF), neurotrophin-3 (NT-3), brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and transforming growth factor beta 1 (TGF-beta 1) on the modulation of neuroactive substances co-expressed by avian chromaffin cells. The content of the neuropeptides neuropeptide Y (NPY), enkephalin (ENK) and somatostatin (SS) was measured by radioimmunoanalysis, and the content of the catecholamines norepinephrine (NE) and epinephrine (E) by high pressure liquid chromatography-electrochemistry (HPLC-EC). In addition, the morphological differentiation of chromaffin cells in response to the growth factors was assessed. All of the studied factors had distinct effects on the chromaffin content of neuropeptides and catecholamines. Our results show that the modulation of CAs and neuropeptides, and among the neuropeptides themselves is completely dissociated. Moreover, the cellular responses to the different growth factors show that neurochemical properties are modulated independently of morphological ones.

Depolarization effects on the peptidergic phenotypes of chick sympathetic and adrenal cells

Depolarizing stimuli are among the factors known to influence the phenotypic plasticity of nerve cells. In order to determine the prevalence of the depolarization effects in terms of cell and neuropeptide phenotypes, we have analyzed the effect of potassium (K+)-induced depolarization on the avian sympathoadrenal system. The expression of three peptidergic phenotypes, somatostatin (SS), neuropeptide Y (NPY) and enkephalin (Enk) by two cell types, adrenal and sympathetic, was studied under different depolarizing regimens. Cells from the sympathetic paravertebral ganglion and adrenal gland of 10-11-day chick embryos were cultured and the peptide levels were measured by radioimmunoassays. Chronic depolarization causes differential effects on the peptidergic phenotypes increasing NPY and Enk but decreasing SS in both adrenal and sympathetic cultures. However, shorter exposures to depolarizing stimuli revealed diverse effects on NPY and Enk phenotypes and even between adrenal and sympathetic cells. Moreover, the maintenance of the effects after removal of the depolarizing stimuli showed additional differences among the phenotypes. Our results are not compatible with a previously established hypothesis stating that depolarization increases the synthesis of whichever neurotransmitters a neuron is already producing. They provide evidence indicating that the depolarization effect is much more complex than originally thought, and serve to initiate an in depth probe into the effect of depolarization of cellular plasticity.

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.

Immunocytochemical localization of the intermediate filament protein peripherin in adult mouse adrenal chromaffin cells in culture

Peripherin is the main intermediate filament protein in sympathetic neurons. Immunoreactivity to peripherin was studied in mouse adrenal chromaffin cells after 6 days in culture, and compared to immunoreactivity to tyrosine hydroxylase used as a general marker of chromaffin cells in culture. Most of the cells immunoreactive to tyrosine hydroxylase were rounded, with a glandular phenotype and a few of them had processes. The cells reactive to peripherin only constituted a small proportion of the chromaffin cells (2%), and most of them sent out processes. However, not all the cells with processes were reactive for peripherin. These results did not change in the presence of nerve growth factor. The discussion focuses on the significance of the sub-population of cells reactive to peripherin. We suggest that these cells resemble the small granule chromaffin cells, regarded as an intermediate cell type between glandular cells and neurons. The cells that expressed peripherin here are compared to those selected to form the PC12 clone. The presence of peripherin in only a few of the cells sending out neurite-like processes is discussed in relation to the expression of other neurofilament proteins in developing cells and to the influence of non-chromaffin cells.