The design of the neuroendocrine system: a unifying concept and its consequences

Single-cell transcriptome analysis identifies a unique tumor cell type producing multiple hormones in ectopic ACTH and CRH secreting pheochromocytoma

Ectopic Cushing’s syndrome due to ectopic ACTH&CRH-secreting by pheochromocytoma is extremely rare and can be fatal if not properly diagnosed. It remains unclear whether a unique cell type is responsible for multiple hormones secreting. In this work, we performed single-cell RNA sequencing to three different anatomic tumor tissues and one peritumoral tissue based on a rare case with ectopic ACTH&CRH-secreting pheochromocytoma. And in addition to that, three adrenal tumor specimens from common pheochromocytoma and adrenocortical adenomas were also involved in the comparison of tumor cellular heterogeneity. A total of 16 cell types in the tumor microenvironment were identified by unbiased cell clustering of single-cell transcriptomic profiles from all specimens. Notably, we identified a novel multi-functionally chromaffin-like cell type with high expression of both POMC (the precursor of ACTH) and CRH, called ACTH+&CRH + pheochromocyte. We hypothesized that the molecular mechanism of the rare case harbor Cushing’s syndrome is due to the identified novel tumor cell type, that is, the secretion of ACTH had a direct effect on the adrenal gland to produce cortisol, while the secretion of CRH can indirectly stimulate the secretion of ACTH from the anterior pituitary. Besides, a new potential marker (GAL) co-expressed with ACTH and CRH might be involved in the regulation of ACTH secretion. The immunohistochemistry results confirmed its multi-functionally chromaffin-like properties with positive staining for CRH, POMC, ACTH, GAL, TH, and CgA. Our findings also proved to some extent the heterogeneity of endothelial and immune microenvironment in different adrenal tumor subtypes.

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.

On the non-adrenergic, non-cholinergic contribution to the parasympathetic nerve-evoked secretion of parotid saliva in the rat

A secretion of parotid saliva in the anaesthetized rat in response to stimulation of the parasympathetic nerve occurs in the presence of atropine and adrenoceptor antagonists, albeit reduced and transient in the face of continuous high-frequency stimulation (40 Hz). In non-atropinized rats prolonged stimulation of the parasympathetic nerve at a high frequency (40 Hz, 40 min), aiming at depletion of the neuronal stores of transmitters thought to be responsible for the non-adrenergic, non-cholinergic (NANC) secretion of parotid saliva, was performed. The magnitude of the secretory response to various stimulation frequencies (0.2-60 Hz) applied to the parasympathetic nerve was assessed before and after the period of high-frequency stimulation. The second time, the frequency-response curve was shifted to the right and, moreover, the initial maximal secretory response was not reached. Control experiments suggested that this reduction in secretory responses could be attributed neither to impaired cholinergic neurotransmission nor to decreased responsiveness of the secretory cells. The secretory responses to parasympathetic nerve stimulation after high-frequency stimulation are thought to be evoked by acetylcholine predominantly. When these responses were compared with (1) those obtained before high-frequency stimulation and thought to be evoked by acetylcholine and non-adrenergic, non-cholinergic transmitters in conjunction and (2) those depending on non-adrenergic, non-cholinergic transmitters only it appears that the non-adrenergic, non-cholinergic transmission contributes to the parasympathetic secretory response at a frequency (0.2 Hz) far below threshold frequency (5 Hz) for the non adrenergic, non-cholinergic evoked secretory response. At frequencies below 20 Hz it appears that acetylcholine and non-adrenergic, non-cholinergic transmitters interact positively thereby enhancing the secretory responses.

Intestinal endocrine cells in Hirschsprung's disease. No reduction in density in aganglionic compared with ganglionic segment

The aganglionic intestine in Hirschsprung's disease displays a severe neuronal derangement. The changes are particularly evident in the muscular innervation. In the gut the endocrine cells are among the cells known to be influenced by neurons. We have, therefore, examined the endocrine cells in ganglionic and aganglionic intestine using immunocytochemistry and immunochemistry. The endocrine cells were studied using antibodies against the neuroendocrine marker chromogranin A, the amine serotonin and the hormonal peptides somatostatin, glucagon/glicentin and peptide YY (PYY), thus covering virtually all endocrine cell types known to occur in this region. The PYY concentration in the mucosal layer was measured by radioimmunoassay. In ganglionic as well as in aganglionic intestine large populations of cells storing chromogranin A, serotonin, glucagon and PYY and a smaller population of somatostatin cells were seen. There was an increase in the density of these cells in the aganglionic intestine compared with ganglionic. The data indicate that the endocrine cell populations in the intestinal wall can be maintained despite severe derangements of the nerve supply.

Attenuation of long-lasting effects of sympathetic stimulation after repeated stimulation

Neuropeptide Y (NPY) is stored with norepinephrine in sympathetic nerves throughout the cardiovascular system and is released during activation of the sympathetic nervous system in humans and other animals. After stimulation of the cardiac sympathetic nerves in anesthetized dogs, the action of the vagus nerve on heart rate is attenuated for a prolonged period. This attenuation of cardiac vagal action is also seen after injection of NPY. Both sympathetic stimulation and exogenous NPY inhibit cardiac vagal effects by acting on postganglionic vagal nerves. Because the supply of neuropeptides to nerve terminals is by axonal transport, it might be expected that repeated stimulation of cardiac sympathetic nerves would deplete the sympathetic neural factor, proposed to be NPY. In all 11 dogs of this study, repeated episodes of stimulating the cardiac sympathetic nerve (16 Hz for 1 minute each) had a diminishing effect in attenuating cardiac vagal action. However, the episodes of sympathetic stimulation did not show diminishing effectiveness in increasing heart rate. Exogenous NPY had similar inhibitory effects on vagal action whether given at the beginning or the end of the episodes of sympathetic stimulation. Transmural stimulation of sympathetic nerves around rabbit ear arteries produced effects that are also mimicked by NPY. These are prolonged potentiation of contractions evoked by injection of norepinephrine or by brief bursts of transmural stimulation. Repeated stimulations in this case also had diminishing abilities to evoke such potentiations. Both sets of observations are consistent with repeated stimulation of sympathetic nerves causing depletion of a nonadrenergic transmitter, possibly NPY.

Calcitonin gene-related peptide (CGRP) immunoreactivity in the neuroendocrine Merkel cells and nerve fibres of pig and human skin

The presence of calcitonin gene-related peptide (CGRP) in the skin of pig snout and human fingertip was investigated using immunohistochemical techniques. CGRP immunoreactivity was found in Merkel cells and nerve fibres of both species. In pig snout skin, Merkel cells containing CGRP were seen forming clusters at the tips of rete ridge epidermis and in the external root sheath of sinus hair follicles (vibrissae). Human Merkel cells immunostained for CGRP were found isolated or forming small groups in the basal layer of glandular epidermal ridges. In all cases, immunoreactivity was more intense on the side of the Merkel cell facing the associated nerve terminal (which was never positive for CGRP). This part of the Merkel cell has the greatest density of dense-cored granules, suggesting that CGRP must be stored in these granules. Nerve bundles containing CGRP-immunoreactive fibres were found at dermal and hypodermal level, and blood vessels were often surrounded by CGRP nerve fibres. In pig snout skin some nerve fibres containing CGRP penetrated the epidermis and terminated as free endings, and in the human fingertip a small number of CGRP-immunoreactive nerve fibres were seen in Meissner's corpuscles.

The dispersed neuroendocrine cells: the structure, function, regulation and effects of xenobiotics on this system

Cells which express morphological and functional markers originally described in neurons and neural crest-derived endocrine cells are now known to originate from both ectodermal and endodermal progenitors. These cells are organized to secrete peptides, amines, and other regulatory products in response to neurogenic or chemical stimulation. Individual products may function in endocrine, paracrine, neurotransmitter, or neuromodulatory roles. Multiple products are often produced by individual cells and stored in the same secretory granules. The hormonal profiles of particular types of neuroendocrine cells can, to varying degrees, be changed by environmental signals during development or in adult life. These changes are caused both by transcriptional and post-transcriptional mechanisms. Hormonal profiles are also altered during the development and progression of neoplasia. Signals which stimulate hormone secretion produce a number of ancillary effects, including activation and induction of enzymes which replenish hormone stores, activation of cellular oncogenes, and stimulation of cell proliferation. The effects of environmental signals on neuroendocrine cells are mediated by intracellular transduction pathways which involve cyclic AMP, phosphatidylinositol, calcium, and receptor protein kinase activity. These effects can be potentiated, inhibited, or qualitatively altered by exogenous agents.

Endocrine cells in the human colorectal mucosa: immunocytochemical observations on patients with prolapse or internal procidentia of the rectum

We have examined the occurrence and distribution of endocrine cells storing serotonin and the regulatory peptides somatostatin, glicentin, peptide YY in rectal mucosa on 16 patients with prolapse or intussusception of the rectum. There were no significant differences compared with normal rectal mucosa. Our results do not support the assumption that these endocrine cells of the rectum are involved in the pathophysiology of rectal prolapse.

Neuropeptides and secretion

In the rat parotid gland, an atropine-resistant parasympathetic-nerve-evoked secretion was demonstrated in vivo. In the absence of atropine, the non-adrenergic, non-cholinergic transmitter release seemed to contribute to the fluid secretion and to be largely responsible for the secretion of amylase and acinar secretory granules. The gland was reached by nerve fibers containing substance P (SP), vasoactive intestinal peptide (VIP), and, to some extent, calcitonin-gene-related peptide (CGRP) via the parasympathetic auriculo-temporal nerve. Upon electrical stimulation of the nerve, these peptides were released. SP and substance K (SK), a novel tachykinin, induced a profuse watery secretion when injected i.v., while VIP caused a sparse but amylase-rich secretion. CGRP caused no secretion on its own. The tachykinin-evoked secretory response was enhanced by VIP and CGRP. A SP-analogue almost abolished the SP-evoked response, while the atropine-resistant parasympathetic response was only halved. None of the peptides under study can on its own account for the atropine-resistant parasympathetic secretion. The neuropeptides may play complementary roles in the regulation of the exocrine functions of the gland.

Depletion of neuropeptides in rat parotid glands and declining atropine-resistant salivary secretion upon continuous parasympathetic nerve stimulation

In rats the parasympathetic auriculo-temporal nerve on one side was continuously stimulated at 40 Hz for 20-80 min in the presence of adrenergic blockers (dihydroergotamine and propranolol) +/- atropine. During the first 10 min this gave rise to a flow of saliva from the parotid gland that in the atropinized rats amounted to 35% of that found in rats not treated with atropine, while the protein and amylase outputs were 75% of those in non-atropinized rats. The atropine-resistant secretion of fluid and proteins declined to 5-10% of the initial value within 40 min but did not cease completely even after 80 min. The marked reduction in secretory responses was not due to desensitization or exhaustion of the gland cells. The nerve stimulation reduced the parotid gland content of vasoactive intestinal peptide (VIP) and substance P (SP) to approximately 60 and 25% of that of contralateral glands after 20 and 60 min, respectively. The probable explanation for the decline in secretory response seems to be depletion of non-adrenergic, non-cholinergic transmitter(s). The present results suggest that neuropeptides are involved in the regulation of salivary secretion but provide no direct evidence that either VIP or SP is responsible for the atropine-resistant salivary secretion.

Endocrine-paracrine cells of the prostate and prostatic urethra: an ultrastructural study

A remarkable morphologic diversity among the endocrine-paracrine (EP) cells of the prostate and prostatic urethra was found in this study. Based on granule morphology, a wide variety of EP cell "types" was discerned, although many intermediate and mixed cells, forming a continuum, were also observed. The EP cells were of both the open (containing luminal borders) and closed types. The latter often had long dendritic processes. Prominent lamellar bodies, possibly representing a form of crinophagy, were present in some EP cells. The variety and morphologic complexity of these prostatic and urethral EP cells suggest that they play an important role in both normal and pathologic conditions.