Lead exerts a depression of neurotransmitter release through a blockade of voltage dependent calcium channels in chromaffin cells

The present work, using chromaffin cells of bovine adrenal medullae (BCCs), aims to describe what type of ionic current alterations induced by lead (Pb2+) underlies its effects reported on synaptic transmission. We observed that the acute application of Pb2+ lead to a drastic depression of neurotransmitters release in a concentration-dependent manner when the cells were stimulated with both K+ or acetylcholine, with an IC50 of 119,57 μM and of 5,19 μM, respectively. This effect was fully recovered after washout. Pb2+ also blocked calcium channels of BCCs in a time- and concentration-dependent manner with an IC50 of 6,87 μM. This blockade was partially reversed upon washout. This compound inhibited the calcium current at all test potentials and shows a shift of the I-V curve to more negative values of about 8 mV. The sodium current was not blocked by acute application of high Pb2+ concentrations. Voltage-dependent potassium current was also shortly affected by high Pb2+. Nevertheless, the calcium- and voltage-dependent potassium current was drastically depressed in a dose-dependent manner, with an IC50 of 24,49 μM. This blockade was related to the prevention of Ca2+ influx through voltage-dependent calcium channels coupled to Ca2+-activated K+-channels (BK) instead a direct linking to these channels. Under current-clamp conditions, BCCs exhibit a resting potential of -52.7 mV, firing spontaneous APs (1-2 spikes/s) generated by the opening of Na+ and Ca2+-channels, and terminated by the activation of K+ channels. In spite of the effect on ionic channels exerted by Pb2+, we found that Pb2+ didn't alter cellular excitability, no modification of the membrane potential, and no effect on action potential firing. Taken together, these results point to a neurotoxic action evoked by Pb2+ that is associated with changes in neurotransmitter release by blocking the ionic currents responsible for the calcium influx.

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.

Phaeochromocytoma and paraganglioma

Phaeochromocytomas and paragangliomas are rare catecholamine-producing neuroendocrine tumours which can potentially cause catastrophic crises with high morbidity and mortality. This best practice article considers the causes and presentation of such tumours, screening and diagnostic tests, management of these patients and consideration of family members at risk.

The Role of Nicotinic Receptors on Ca2+ Signaling in Bovine Chromaffin Cells

Chromaffin cells have been used as a physiological model to understand neurosecretion in mammals for many years. Nicotinic receptors located in the cells' membrane are stimulated by acetylcholine, and they participate in the exocytosis of chromaffin granules, releasing catecholamines in response to stress. In this work, we discuss how the participation of nicotinic receptors and the localization of active zones in the borders of the cytoskeleton can generate local calcium signals leading to secretion. We use a computational model of a cytoskeleton cage to simulate Ca2+ levels in response to voltage and acetylcholine pulses. We find that nicotinic receptors are able to enhance the differences between local and average calcium values, as well as the heterogeneous distributions around the active zones, producing a non-linear, highly localized Ca2+ entry that, although consisting of a few ions, is able to improve secretion responses in chromaffin cells. Our findings emphasize the intricate interplay among nicotinic receptors, the cytoskeleton, and active zones within chromaffin cells as an example of Ca2+-dependent neurosecretion in mammals.

Phospholipase C-ε defines a PACAP-stimulated pathway for secretion in the chromaffin cell

Adrenomedullary chromaffin cells respond to splanchnic (sympathetic) nerve stimulation by releasing stress hormones into the circulation. The signal for hormone secretion is encoded in the neurotransmitters - especially acetylcholine (ACh) and pituitary adenylate cyclase activating polypeptide (PACAP) - that are released into the splanchnic-chromaffin cell synapse. However, functional differences in the effects of ACh and PACAP on the chromaffin cell secretory response are not well defined. Here, selective agonists of PACAP receptors or nicotinic and muscarinic acetylcholine receptors were applied to chromaffin cells. The major differences in the effects of these agents were not on exocytosis, per se, but rather on the steps upstream of exocytosis. In almost every respect, the properties of individual fusion events triggered by PACAP and cholinergic agonists were similar. On the other hand, the properties of the Ca2+ transients evoked by PACAP differed in several ways from those evoked by muscarinic and nicotinic receptor stimulation. A defining feature of the PACAP-stimulated secretory pathway was its dependence on signaling through exchange protein directly activated by cAMP (Epac) and PLCε. However, the absence of PLCε did not disrupt Ca2+ transients evoked by cholinergic agonists. Accordingly, inhibition of Epac activity did not disrupt secretion triggered by acetylcholine or specific agonists of muscarinic and nicotinic receptors. Thus, PACAP and acetylcholine stimulate chromaffin cell secretion via separate and independent pathways. This feature of stimulus-secretion coupling may be important for sustaining hormone release from the adrenal medulla under conditions associated with the sympathetic stress response.

Post-hatching developmental changes in the adrenal gland of the Japanese quail (Coturnix coturnix japonica): Histological, immunohistochemical, and electron microscopic studies

The adrenal glands are paired abdominal endocrine organs vital to the bird's health. The present research aimed to provide a comprehensive examination of the histological, ultrastructural, and immunohistochemical investigations of the adrenal gland in Japanese quail during the post hatching period. The current study was performed on 21 healthy Japanese quail chicks at different post hatching periods. Our results showed the adrenal gland is surrounded by a connective tissue capsule, which consists of dense collagen fibers containing large blood vessels, chromaffin cells, autonomic ganglia, fibroblasts, and migrating Schwann cells. The zonation of the adrenal gland is composed of a subcapsular layer, a peripheral zone, and a central zone, which gets more pronounced with age. At the ultrastructural level, the interrenal cells take the steroid-secreting cells characters; they have varying amounts of lipid droplets and abundant mitochondria. Adrenal medullary chromaffin cells showed positive immunoreactivity to the NSE. With increasing age, the chromaffin tissue's Sox10 immunoreactivity increased. β-catenin is expressed within the plasmalemma and the cytoplasm of the interrenal and chromaffin cells and its reactivity increased with age, especially in the chromaffin cells. Our results indicate the adrenal gland undergoes significant morphological changes during the postnatal life. Overall, the postnatal period is an important time for the development and maturation of the adrenal glands.

The human channel gating-modifying A749G CACNA1D (Cav1.3) variant induces a neurodevelopmental syndrome-like phenotype in mice

Germline de novo missense variants of the CACNA1D gene, encoding the pore-forming α1 subunit of Cav1.3 L-type Ca2+ channels (LTCCs), have been found in patients with neurodevelopmental and endocrine dysfunction, but their disease-causing potential is unproven. These variants alter channel gating, enabling enhanced Cav1.3 activity, suggesting Cav1.3 inhibition as a potential therapeutic option. Here we provide proof of the disease-causing nature of such gating-modifying CACNA1D variants using mice (Cav1.3AG) containing the A749G variant reported de novo in a patient with autism spectrum disorder (ASD) and intellectual impairment. In heterozygous mutants, native LTCC currents in adrenal chromaffin cells exhibited gating changes as predicted from heterologous expression. The A749G mutation induced aberrant excitability of dorsomedial striatum-projecting substantia nigra dopamine neurons and medium spiny neurons in the dorsal striatum. The phenotype observed in heterozygous mutants reproduced many of the abnormalities described within the human disease spectrum, including developmental delay, social deficit, and pronounced hyperactivity without major changes in gross neuroanatomy. Despite an approximately 7-fold higher sensitivity of A749G-containing channels to the LTCC inhibitor isradipine, oral pretreatment over 2 days did not rescue the hyperlocomotion. Cav1.3AG mice confirm the pathogenicity of the A749G variant and point toward a pathogenetic role of altered signaling in the dopamine midbrain system.

Serotonin and the serotonin transporter in the adrenal gland

The adrenal glands are key components of the mammalian endocrine system, helping maintain physiological homeostasis and the coordinated response to stress. Each adrenal gland has two morphologically and functionally distinct regions, the outer cortex and inner medulla. The cortex is organized into three concentric zones which secrete steroid hormones, including aldosterone and cortisol. Neural crest-derived chromaffin cells in the medulla are innervated by preganglionic sympathetic neurons and secrete catecholamines (epinephrine, norepinephrine) and neuropeptides into the bloodstream, thereby functioning as the neuroendocrine arm of the sympathetic nervous system. In this article we review serotonin (5-HT) and the serotonin transporter (SERT; SLC6A4) in the adrenal gland. In the adrenal cortex, 5-HT, primarily sourced from resident mast cells, acts as a paracrine signal to stimulate aldosterone and cortisol secretion through 5-HT4/5-HT7 receptors. Medullary chromaffin cells contain a small amount of 5-HT due to SERT-mediated uptake and express 5-HT1A receptors which inhibit secretion. The atypical mechanism of the 5-HT1A receptors and interaction with SERT fine tune this autocrine pathway to control stress-evoked catecholamine secretion. Receptor-independent signaling by SERT/intracellular 5-HT modulates the amount and kinetics of transmitter release from single vesicle fusion events. SERT might also influence stress-evoked upregulation of tyrosine hydroxylase transcription. Transient signaling via 5-HT3 receptors during embryonic development can limit the number of chromaffin cells found in the mature adrenal gland. Together, this emerging evidence suggests that the adrenal medulla is a peripheral hub for serotonergic control of the sympathoadrenal stress response.

Adrenal Abscesses: A Systematic Review of the Literature

Objective: To summarize the existing knowledge about adrenal gland abscesses, including etiology, clinical presentation, common laboratory and imaging findings, management and overall morbidity and mortality. Design: Systematic literature review. Methods: We performed a search in the PubMed database using search terms: 'abscess and adrenal glands', 'adrenalitis', 'infection and adrenal gland', 'adrenal abscess', 'adrenal infection' and 'infectious adrenalitis'. Articles from 2017 to 2022 were included. We found total of 116 articles, and after applying exclusion criteria, data from 73 articles was included in the final statistical analysis. Results: Of 84 patients included in this review, 68 were male (81%), with a mean age of 55 years (range: 29 to 85 years). Weight loss was the most frequent symptom reported in 58.3% patients, followed by fever in 49%. Mean duration of symptoms was 4.5 months. The most common laboratory findings were low cortisol (51.9%), elevated ACTH (43.2%), hyponatremia (88.2%) and anemia (83.3%). Adrenal cultures were positive in 86.4% cases, with Histoplasma capsulatum (37.3%) being the leading causative agent. Blood cultures were positive in 30% of patients. The majority of the adrenal infections occurred through secondary dissemination from other infectious foci and abscesses were more commonly bilateral (70%). A total of 46.4% of patients developed long-term adrenal insufficiency requiring treatment. Abscess drainage was performed in 7 patients (8.3%) and adrenalectomy was performed in 18 (21.4%) patients. The survival rate was 92.9%. Multivariate analysis showed that the only independent risk factor for mortality was thrombocytopenia (p = 0.048). Conclusion: Our review shows that adrenal abscesses are usually caused by fungal pathogens, and among these, Histoplasma capsulatum is the most common. The adrenal glands are usually involved in a bilateral fashion and become infected through dissemination from other primary sources of infection. Long-term adrenal insufficiency develops in 46% of patients, which is more common than what is observed in non-infectious etiology of adrenal gland disorders. Mortality is about 7%, and the presence of thrombocytopenia is associated with worse prognosis. Further prospective studies are needed to better characterize optimal testing and treatment duration in patients with this relatively rare but challenging disorder.

Serotonergic Modulation of Neurovascular Transmission: A Focus on Prejunctional 5-HT Receptors/Mechanisms

5-Hydroxytryptamine (5-HT), or serotonin, plays a crucial role as a neuromodulator and/or neurotransmitter of several nervous system functions. Its actions are complex, and depend on multiple factors, including the type of effector or receptor activated. Briefly, 5-HT can activate: (i) metabotropic (G-protein-coupled) receptors to promote inhibition (5-HT₁, 5-HT₅) or activation (5-HT₄, 5-HT₆, 5-HT₇) of adenylate cyclase, as well as activation (5-HT₂) of phospholipase C; and (ii) ionotropic receptor (5-HT₃), a ligand-gated Na⁺/K⁺ channel. Regarding blood pressure regulation (and beyond the intricacy of central 5-HT effects), this monoamine also exerts direct postjunctional (on vascular smooth muscle and endothelium) or indirect prejunctional (on autonomic and sensory perivascular nerves) effects. At the prejunctional level, 5-HT can facilitate or preclude the release of autonomic (e.g., noradrenaline and acetylcholine) or sensory (e.g., calcitonin gene-related peptide) neurotransmitters facilitating hypertensive or hypotensive effects. Hence, we cannot formulate a specific impact of 5-HT on blood pressure level, since an increase or decrease in neurotransmitter release would be favoured, depending on the type of prejunctional receptor involved. This review summarizes and discusses the current knowledge on the prejunctional mechanisms involved in blood pressure regulation by 5-HT and its impact on some vascular-related diseases.

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.

Mitochondrial dysfunction in chromaffin cells from the R6/1 mouse model of Huntington's disease: Impact on exocytosis and calcium current regulation

From a pathogenic perspective, Huntington's disease (HD) is being considered as a synaptopathy. As such, alterations in brain neurotransmitter release occur. As the activity of the sympathoadrenal axis is centrally controlled, deficits in the exocytotic release of catecholamine release may also occur. In fact, in chromaffin cells (CCs) of the adrenal medulla of the R6/1 model of HD, decrease of secretion and altered kinetics of the exocytotic fusion pore have been reported. Those alterations could be linked to mitochondrial deficits occurring in peripheral CCs, similar to those described in brain mitochondria. Here we have inquired about alterations in mitochondrial structure and function and their impact on exocytosis and calcium channel currents (I_Ca). We have monitored various parameters linked to those events, in wild type (WT) and the R6/1 mouse model of HD at a pre-disease stage (2 months age, 2 m), and when motor deficits are present (7 months age, 7 m). In isolated CCs from 7 m and in the adrenal medulla of R6/1 mice, we found the following alterations (with respect 7 m WT mice): (i) augmented fragmented mitochondria and oxidative stress with increased oxidized glutathione; (ii) decreased basal and maximal respiration; (iii) diminution of ATP cell levels; (iv) mitochondrial depolarization; (v) drastic decrease of catecholamine release with poorer potentiation by protonophore FCCP; (vi) decreased I_Ca inhibition by FCCP; and (vii) lesser potentiation by BayK8644 of I_Ca and smaller prolongation of current deactivation. Of note was the fact several of these alterations were already manifested in CCs from 2 m R6/1 mice at pre-disease stages. Based on those results, a plausible hypothesis can be raised in the sense that altered mitochondrial function seems to be an early primary event in HD pathogenesis. This is in line with an increasing number of mitochondrial, metabolic, and inflammatory alterations being recently reported in various HD peripheral tissues.

Forty years of the adrenal chromaffin cell through ISCCB meetings around the world

This historical review focuses on the evolution of the knowledge accumulated during the last two centuries on the biology of the adrenal medulla gland and its chromaffin cells (CCs). The review emerged in the context of a series of meetings that started on the Spanish island of Ibiza in 1982 with the name of the International Symposium on Chromaffin Cell Biology (ISCCB). Hence, the review is divided into two periods namely, before 1982 and from this year to 2022, when the 21st ISCCB meeting was just held in Hamburg, Germany. The first historical period extends back to 1852 when Albert Kölliker first described the fine structure and function of the adrenal medulla. Subsequently, the adrenal staining with chromate salts identified the CCs; this was followed by the establishment of the embryological origin of the adrenal medulla, and the identification of adrenaline-storing vesicles. By the end of the nineteenth century, the basic morphology, histochemistry, and embryology of the adrenal gland were known. The twentieth century began with breakthrough findings namely, the experiment of Elliott suggesting that adrenaline was the sympathetic neurotransmitter, the isolation of pure adrenaline, and the deciphering of its molecular structure and chemical synthesis in the laboratory. In the 1950s, Blaschko isolated the catecholamine-storing vesicles from adrenal medullary extracts. This switched the interest in CCs as models of sympathetic neurons with an explosion of studies concerning their functions, i.e., uptake of catecholamines by chromaffin vesicles through a specific coupled transport system; the identification of several vesicle components in addition to catecholamines including chromogranins, ATP, opioids, and other neuropeptides; the calcium-dependence of the release of catecholamines; the underlying mechanism of exocytosis of this release, as indicated by the co-release of proteins; the cross-talk between the adrenal cortex and the medulla; and the emission of neurite-like processes by CCs in culture, among other numerous findings. The 1980s began with the introduction of new high-resolution techniques such as patch-clamp, calcium probes, marine toxins-targeting ion channels and receptors, confocal microscopy, or amperometry. In this frame of technological advances at the Ibiza ISCCB meeting in 1982, 11 senior researchers in the field predicted a notable increase in our knowledge in the field of CCs and the adrenal medulla; this cumulative knowledge that occurred in the last 40 years of history of the CC is succinctly described in the second part of this historical review. It deals with cell excitability, ion channel currents, the exocytotic fusion pore, the handling of calcium ions by CCs, the kinetics of exocytosis and endocytosis, the exocytotic machinery, and the life cycle of secretory vesicles. These concepts together with studies on the dynamics of membrane fusion with super-resolution imaging techniques at the single-protein level were extensively reviewed by top scientists in the field at the 21st ISCCB meeting in Hamburg in the summer of 2022; this frontier topic is also briefly reviewed here. Many of the concepts arising from those studies contributed to our present understanding of synaptic transmission. This has been studied in physiological or pathophysiological conditions, in CCs from animal disease models. In conclusion, the lessons we have learned from CC biology as a peripheral model for brain and brain disease pertain more than ever to cutting-edge research in neurobiology. In the 22nd ISCCB meeting in Israel in 2024 that Uri Asheri is organizing, we will have the opportunity of seeing the progress of the questions posed in Ibiza, and on other questions that undoubtedly will arise.

Aluminum alters excitability by inhibiting calcium, sodium, and potassium currents in bovine chromaffin cells

Aluminum (Al³⁺ ) has long been related to neurotoxicity and neurological diseases. This study aims to describe the specific actions of this metal on cellular excitability and neurotransmitter release in primary culture of bovine chromaffin cells. Using voltage-clamp and current-clamp recordings with the whole-cell configuration of the patch clamp technique, online measurement of catecholamine release, and measurements of [Ca²⁺ ]_c with Fluo-4-AM, we have observed that Al³⁺ reduced intracellular calcium concentrations around 25% and decreased catecholamine secretion in a dose-dependent manner, with an IC₅₀ of 89.1 μM. Al³⁺ blocked calcium currents in a time- and concentration-dependent manner with an IC₅₀ of 560 μM. This blockade was irreversible since it did not recover after washout. Moreover, Al³⁺ produced a bigger blockade on N-, P-, and Q-type calcium channels subtypes (69.5%) than on L-type channels subtypes (50.5%). Sodium currents were also inhibited by Al³⁺ in a time- and concentration-dependent manner, 24.3% blockade at the closest concentration to the IC₅₀ (399 μM). This inhibition was reversible. Voltage-dependent potassium currents were low affected by Al³⁺ . Nonetheless, calcium/voltage-dependent potassium currents were inhibited in a concentration-dependent manner, with an IC₅₀ of 447 μM. This inhibition was related to the depression of calcium influx through voltage-dependent calcium channels subtypes coupled to BK channels. In summary, the blockade of these ionic conductance altered cellular excitability that reduced the action potentials firing and so, the neurotransmitter release and the synaptic transmission. These findings prove that aluminum has neurotoxic properties because it alters neuronal excitability by inhibiting the sodium currents responsible for the generation and propagation of impulse nerve, the potassium current responsible for the termination of action potentials, and the calcium current responsible for the neurotransmitters release.

PACAP and acetylcholine cause distinct Ca2+ signals and secretory responses in chromaffin cells

The adrenomedullary chromaffin cell transduces chemical messages into outputs that regulate end organ function throughout the periphery. At least two important neurotransmitters are released by innervating preganglionic neurons to stimulate exocytosis in the chromaffin cell-acetylcholine (ACh) and pituitary adenylate cyclase activating polypeptide (PACAP). Although PACAP is widely acknowledged as an important secretagogue in this system, the pathway coupling PACAP stimulation to chromaffin cell secretion is poorly understood. The goal of this study is to address this knowledge gap. Here, it is shown that PACAP activates a Gαs-coupled pathway that must signal through phospholipase C ε (PLCε) to drive Ca2+ entry and exocytosis. PACAP stimulation causes a complex pattern of Ca2+ signals in chromaffin cells, leading to a sustained secretory response that is kinetically distinct from the form stimulated by ACh. Exocytosis caused by PACAP is associated with slower release of peptide cargo than exocytosis stimulated by ACh. Importantly, only the secretory response to PACAP, not ACh, is eliminated in cells lacking PLCε expression. The data show that ACh and PACAP, acting through distinct signaling pathways, enable nuanced and variable secretory outputs from chromaffin cells.

CACNA1D-Related Channelopathies: From Hypertension to Autism

Tightly controlled Ca²⁺ influx through voltage-gated Ca²⁺ channels (Cavs) is indispensable for proper physiological function. Thus, it is not surprising that Cav loss and/or gain of function have been implicated in human pathology. Deficiency of Cav1.3 L-type Ca²⁺ channels (LTCCs) causes deafness and bradycardia, whereas several genetic variants of CACNA1D, the gene encoding the pore-forming α1 subunit of Cav1.3, have been linked to various disease phenotypes, such as hypertension, congenital hypoglycemia, or autism. These variants include not only common polymorphisms associated with an increased disease risk, but also rare de novo missense variants conferring high risk. This review provides a concise summary of disease-associated CACNA1D variants, whereas the main focus lies on de novo germline variants found in individuals with a neurodevelopmental disorder of variable severity. Electrophysiological recordings revealed activity-enhancing gating changes induced by these de novo variants, and tools to predict their pathogenicity and to study the resulting pathophysiological consequences will be discussed. Despite the low number of affected patients, potential phenotype-genotype correlations and factors that could impact the severity of symptoms will be covered. Since increased channel activity is assumed as the disease-underlying mechanism, pharmacological inhibition could be a treatment option. In the absence of Cav1.3-selective blockers, dihydropyridine LTCC inhibitors clinically approved for the treatment of hypertension may be used for personalized off-label trials. Findings from in vitro studies and treatment attempts in some of the patients seem promising as outlined. Taken together, due to advances in diagnostic sequencing techniques the number of reported CACNA1D variants in human diseases is constantly rising. Evidence from in silico, in vitro, and in vivo disease models can help to predict the pathogenic potential of such variants and to guide diagnosis and treatment in the clinical practice when confronted with patients harboring CACNA1D variants.

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Two firing modes and well-resolved Na+, K+, and Ca2+ currents at the cell-microelectrode junction of spontaneously active rat chromaffin cell on MEAs

We recorded spontaneous extracellular action potentials (eAPs) from rat chromaffin cells (CCs) at 37 °C using microelectrode arrays (MEAs) and compared them with intracellularly recorded APs (iAPs) through conventional patch clamp recordings at 22 °C. We show the existence of two distinct firing modes on MEAs: a ~ 4 Hz irregular continuous firing and a frequent intermittent firing mode where periods of high-intraburst frequency (~ 8 Hz) of ~ 7 s duration are interrupted by silent periods of ~ 12 s. eAPs occurred either as negative- or positive-going signals depending on the contact between cell and microelectrode: either predominantly controlled by junction-membrane ion channels (negative-going) or capacitive/ohmic coupling (positive-going). Negative-going eAPs were found to represent the trajectory of the Na⁺, Ca²⁺, and K⁺ currents passing through the cell area in tight contact with the microelectrode during an AP (point-contact junction). The inward Nav component of eAPs was blocked by TTX in a dose-dependent manner (IC₅₀ ~ 10 nM) while the outward component was strongly attenuated by the BK channel blocker paxilline (200 nM) or TEA (5 mM). The SK channel blocker apamin (200 nM) had no effect on eAPs. Inward Nav and Cav currents were well-resolved after block of Kv and BK channels or in cells showing no evident outward K⁺ currents. Unexpectedly, on the same type of cells, we could also resolve inward L-type currents after adding nifedipine (3 μM). In conclusion, MEAs provide a direct way to record different firing modes of rat CCs and to estimate the Na⁺, Ca²⁺, and K⁺ currents that sustain cell firing and spontaneous catecholamines secretion.

Methodologies for Detecting Quantal Exocytosis in Adrenal Chromaffin Cells Through Diamond-Based MEAs

Diamond-based multiarray sensors are suitable to detect in real-time exocytosis and action potentials from cultured, spontaneously firing chromaffin cells, primary hippocampal neurons, and midbrain dopaminergic neurons. Here, we focus on how amperometric measurements of catecholamine release are performed on micrographitic diamond multiarrays (μG-D-MEAs) with high temporal and spatial resolution by 16 electrodes simultaneously.

Real Time Recording of Perifused Chromaffin Cells

Amperometry is an electrochemical method based on the oxidation or reduction of molecules. Many secretion products, including catecholamines, contain in their molecule chemical groups with the ability to yield (oxidize) or capture (reduce) electrons upon its exposure to an electrical field. In order to measure the secretion of catecholamines, they are oxidized at +650 mV with a carbon electrode, releasing every molecule of catecholamine that is oxidized two electrons (e^-) that are recorded as an electrical current. Amperometry is an easy-to-use and noninvasive technique for cells (unlike patch-clamp techniques for measuring membrane capacitance) and has been widely used to monitor online catecholamine release from perifused bovine chromaffin cell populations.

Cell Networks in Endocrine/Neuroendocrine Gland Function

Reproduction, growth, stress, and metabolism are determined by endocrine/neuroendocrine systems that regulate circulating hormone concentrations. All these systems generate rhythms and changes in hormone pulsatility observed in a variety of pathophysiological states. Thus, the output of endocrine/neuroendocrine systems must be regulated within a narrow window of effective hormone concentrations but must also maintain a capacity for plasticity to respond to changing physiological demands. Remarkably most endocrinologists still have a "textbook" view of endocrine gland organization which has emanated from 20^th century histological studies on thin 2D tissue sections. However, 21^st -century technological advances, including in-depth 3D imaging of specific cell types have vastly changed our knowledge. We now know that various levels of multicellular organization can be found across different glands, that organizational motifs can vary between species and can be modified to enhance or decrease hormonal release. This article focuses on how the organization of cells regulates hormone output using three endocrine/neuroendocrine glands that present different levels of organization and complexity: the adrenal medulla, with a single neuroendocrine cell type; the anterior pituitary, with multiple intermingled cell types; and the pancreas with multiple intermingled cell types organized into distinct functional units. We give an overview of recent methodologies that allow the study of the different components within endocrine systems, particularly their temporal and spatial relationships. We believe the emerging findings about network organization, and its impact on hormone secretion, are crucial to understanding how homeostatic regulation of endocrine axes is carried out within endocrine organs themselves. © 2022 American Physiological Society. Compr Physiol 12:3371-3415, 2022.

Alterations of the Sympathoadrenal Axis Related to the Development of Alzheimer’s Disease in the 3xTg Mouse Model

Simple Summary

Alzheimer’s disease (AD), the most common form of dementia, is becoming a global health problem and public health priority. In the advanced stages of AD, besides the initial cognitive symptoms, behavioral problems, particularly agitation and aggressiveness, become prevalent in AD patients. These non-cognitive symptoms could be related to alterations in the regulatory mechanism of the sympathetic nervous system. In this study, we used chromaffin cells (CCs) isolated from the adrenal gland of 3xTg (an AD mouse model) mice to characterize potential alterations in the regulation of the responses to stress mediated by the secretion of catecholamines. We compared these regulatory mechanisms in mice at two different ages: in 2-month-old mice, where no AD symptoms were observed, and in mice over 12 months of age, when AD-related cognitive impairment related was fully established. We found that the modulation of neurotransmitter release was stronger in CCs isolated from the adrenal medulla of 3xTg mice older than 12 months of age, an effect likely related to disease progression as it was not observed in CCs from age-matched wild-type (WT) mice. This enhanced modulation leads to an increased catecholamine release in response to stressful situations, which may explain the non-cognitive behavioral problems found in AD patients.

Abstract

Alzheimer’s disease (AD), the most common form of dementia, is becoming a global health problem and public health priority. In the advanced stages of AD, besides the initial cognitive symptoms, behavioral problems, particularly agitation and aggressiveness, become prevalent in AD patients. These non-cognitive symptoms could be related to a noradrenergic overactivation. In this study, we used chromaffin cells (CCs) isolated from the adrenal gland of 3xTg AD model mice to characterize potential alterations in the autocrine-paracrine modulation of voltage-dependent calcium channels (VDCCs), which in turn serve to regulate the release of catecholamines. We used mice at the presymptomatic stage (2 months) and mice over 12 months of age, when AD-related cognitive impairment was fully established. We found that the modulation of inward currents through VDCCs induced by extracellular ATP was stronger in CCs isolated from the adrenal medulla of 3xTg mice older than 12 months of age, an effect likely related to disease progression as it was not observed in CCs from age-matched WT mice. This enhanced modulation leads to increased catecholamine release in response to stressful situations, which may explain the non-cognitive behavioral problems found in AD patients.

Basal and Stress-Induced Network Activity in the Adrenal Medulla In Vivo

The adrenal medulla plays a critical role in mammalian homeostasis and the stress response. It is populated by clustered chromaffin cells that secrete epinephrine or norepinephrine along with peptides into the bloodstream affecting distant target organs. Despite been heavily studied, the central control of adrenal medulla and in-situ spatiotemporal responsiveness remains poorly understood. For this work, we continuously monitored the electrical activity of individual adrenomedullary chromaffin cells in the living anesthetized rat using multielectrode arrays. We measured the chromaffin cell activity under basal and physiological stress conditions and characterized the functional micro-architecture of the adrenal medulla. Under basal conditions, chromaffin cells fired action potentials with frequencies between ~0.2 and 4 Hz. Activity was almost completely driven by sympathetic inputs coming through the splanchnic nerve. Chromaffin cells were organized into independent local networks in which cells fired in a specific order, with latencies from hundreds of microseconds to a few milliseconds. Electrical stimulation of the splanchnic nerve evoked almost exactly the same spatiotemporal firing patterns that occurred spontaneously. Hypoglycemic stress, induced by insulin administration resulted in increased activity of a subset of the chromaffin cells. In contrast, respiratory arrest induced by lethal anesthesia resulted in an increase in the activity of virtually all chromaffin cells before cessation of all activity. These results suggest a stressor-specific activation of adrenomedullary chromaffin cell networks and revealed a surprisingly complex electrical organization that likely reflects the dynamic nature of the adrenal medulla's neuroendocrine output during basal conditions and during different types of physiological stress.

Novel Purine Derivative ITH15004 Facilitates Exocytosis through a Mitochondrial Calcium-Mediated Mechanism

Upon depolarization of chromaffin cells (CCs), a prompt release of catecholamines occurs. This event is triggered by a subplasmalemmal high-Ca2+ microdomain (HCMD) generated by Ca2+ entry through nearby voltage-activated calcium channels. HCMD is efficiently cleared by local mitochondria that avidly take up Ca2+ through their uniporter (MICU), then released back to the cytosol through mitochondrial Na+/Ca2+ exchanger (MNCX). We found that newly synthesized derivative ITH15004 facilitated the release of catecholamines triggered from high K+-depolarized bovine CCs. Such effect seemed to be due to regulation of mitochondrial Ca2+ circulation because: (i) FCCP-potentiated secretory responses decay was prevented by ITH15004; (ii) combination of FCCP and ITH15004 exerted additive secretion potentiation; (iii) such additive potentiation was dissipated by the MICU blocker ruthenium red (RR) or the MNCX blocker CGP37157 (CGP); (iv) combination of FCCP and ITH15004 produced both additive augmentation of cytosolic Ca2+ concentrations ([Ca2+]c) K+-challenged BCCs, and (v) non-inactivated [Ca2+]c transient when exposed to RR or CGP. On pharmacological grounds, data suggest that ITH15004 facilitates exocytosis by acting on mitochondria-controlled Ca2+ handling during K+ depolarization. These observations clearly show that ITH15004 is a novel pharmacological tool to study the role of mitochondria in the regulation of the bioenergetics and exocytosis in excitable cells.

Pro-arrhythmogenic effects of Trypanosoma cruzi conditioned medium proteins in a model of bovine chromaffin cells

Asymptomatic sudden death is the principal cause of mortality in Chagas disease. There is little information about molecular mechanisms involved in the pathophysiology of malignant arrhythmias in Chagasic patients. Previous studies have involved Trypanosoma cruzi secretion proteins in the genesis of arrhythmias ex vivo, but the molecular mechanisms involved are still unresolved. Thus, the aim was to determine the effect of these secreted proteins on the cellular excitability throughout to test its effects on catecholamine secretion, sodium-, calcium-, and potassium-conductance and action potential (AP) firing. Conditioned medium was obtained from the co-culture of T. cruzi and Vero cells (African green monkey kidney cells) and ultra-filtered for concentrating immunogenic high molecular weight parasite proteins. Chromaffin cells were assessed with the parasite and Vero cells control medium. Parasite-secreted proteins induce catecholamine secretion in a dose-dependent manner. Additionally, T. cruzi conditioned medium induced depression of both calcium conductance and calcium and voltage-dependent potassium current. Interestingly, this fact was related to the abolishment of the hyperpolarization phase of the AP produced by the parasite medium. Taken together, these results suggest that T. cruzi proteins may be involved in the genesis of pro-arrhythmic conditions that could influence the appearance of malignant arrhythmias in Chagasic patients.

Development of the hypersecretory phenotype in the population of adrenal chromaffin cells from prehypertensive SHRs

The hypersecretory phenotype of adrenal chromaffin cells (CCs) from early spontaneously hypertensive rats (SHRs) mainly results from enhanced Ca²⁺-induced Ca²⁺-release (CICR). A key question is if these abnormalities can be traced to the prehypertensive stage. Spontaneous and stimulus-induced catecholamine exocytosis, intracellular Ca²⁺ signals, and dense-core granule size and density were examined in CCs from prehypertensive and hypertensive SHRs and compared with age-matched Wistar-Kyoto rats (WKY). During the prehypertensive stage, the depolarization-elicited catecholamine exocytosis was ~ 2.9-fold greater in SHR than in WKY CCs. Interestingly, in half of CCs the exocytosis was indistinguishable from WKY CCs, while it was between 3- and sixfold larger in the other half. Likewise, caffeine-induced exocytosis was ~ twofold larger in prehypertensive SHR. Accordingly, depolarization and caffeine application elicited [Ca²⁺]i rises ~ 1.5-fold larger in prehypertensive SHR than in WKY CCs. Ryanodine reduced the depolarization-induced secretion in prehypertensive SHR by 57%, compared to 14% in WKY CCs, suggesting a greater contribution of intracellular Ca²⁺ release to exocytosis. In SHR CCs, the mean spike amplitude and charge per spike were significantly larger than in WKY CCs, regardless of age and stimulus type. This difference in granule content could explain in part the enhanced exocytosis in SHR CCs. However, electron microscopy did not reveal significant differences in granule size between SHRs and WKY rats' adrenal medulla. Nonetheless, preSHR and hypSHR display 63% and 82% more granules than WKY, which could explain in part the enhanced catecholamine secretion. The mechanism responsible for the heterogeneous population of prehypertensive SHR CCs and the bias towards secreting more medium and large granules remains unexplained.

Glucagon-like peptide-1 receptor controls exocytosis in chromaffin cells by increasing full-fusion events

Agonists for glucagon-like-peptide-1 receptor (GLP-1R) are currently used for the treatment of type 2 diabetes and obesity. Their benefits have been centered on pancreas and hypothalamus, but their roles in other organ systems are not well understood. We studied the action of GLP-1R on secretions of adrenal medulla. Exendin-4, a synthetic analog of GLP-1, increases the synthesis and the release of catecholamines (CAs) by increasing cyclic AMP (cAMP) production, without apparent participation of cAMP-regulated guanine nucleotide exchange factor (Epac). Exendin-4, when incubated for 24 h, increases CA synthesis by promoting the activation of tyrosine hydroxylase. Short incubation (20 min) increases the quantum size of exocytotic events by switching exocytosis from partial to full fusion. Our results give a strong support to the role of GLP-1 in the fine control of exocytosis.

Adrenal medulla development and medullary-cortical interactions

The mammalian adrenal gland is composed of two distinct tissue types in a bidirectional connection, the catecholamine-producing medulla derived from the neural crest and the mesoderm-derived cortex producing steroids. The medulla mainly consists of chromaffin cells derived from multipotent nerve-associated descendants of Schwann cell precursors. Already during adrenal organogenesis, close interactions between cortex and medulla are necessary for proper differentiation and morphogenesis of the gland. Moreover, communication between the cortex and the medulla ensures a regular function of the adult adrenal. In tumor development, interfaces between the two parts are also common. Here, we summarize the development of the mammalian adrenal medulla and the current understanding of the cortical-medullary interactions under development and in health and disease.

Fast inactivation of Nav1.3 channels by FGF14 proteins: An unconventional way to regulate the slow firing of adrenal chromaffin cells

Using Nav1.3 and FGF14 KO mice, Martinez-Espinosa et al. provide new findings on how intracellular FGF14 proteins interfere with the endogenous fast inactivation gating and regulate the “long-term inactivation” of Nav1.3 channels that sets Nav channel availability and spike adaptation during sustained stimulation in adrenal chromaffin cells.

Fast inactivation of Nav current in rat adrenal chromaffin cells involves two independent inactivation pathways

Voltage-dependent sodium (Nav) current in adrenal chromaffin cells (CCs) is rapidly inactivating and tetrodotoxin (TTX)–sensitive. The fractional availability of CC Nav current has been implicated in regulation of action potential (AP) frequency and the occurrence of slow-wave burst firing. Here, through recordings of Nav current in rat CCs, primarily in adrenal medullary slices, we describe unique inactivation properties of CC Nav inactivation that help define AP firing rates in CCs. The key feature of CC Nav current is that recovery from inactivation, even following brief (5 ms) inactivation steps, exhibits two exponential components of similar amplitude. Various paired pulse protocols show that entry into the fast and slower recovery processes result from largely independent competing inactivation pathways, each of which occurs with similar onset times at depolarizing potentials. Over voltages from −120 to −80 mV, faster recovery varies from ∼3 to 30 ms, while slower recovery varies from ∼50 to 400 ms. With strong depolarization (above −10 mV), the relative entry into slow or fast recovery pathways is similar and independent of voltage. Trains of short depolarizations favor recovery from fast recovery pathways and result in cumulative increases in the slow recovery fraction. Dual-pathway fast inactivation, by promoting use-dependent accumulation in slow recovery pathways, dynamically regulates Nav availability. Consistent with this finding, repetitive AP clamp waveforms at 1–10 Hz frequencies reduce Nav availability 80–90%, depending on holding potential. These results indicate that there are two distinct pathways of fast inactivation, one leading to conventional fast recovery and the other to slower recovery, which together are well-suited to mediate use-dependent changes in Nav availability.

Acute reversible SERCA blockade facilitates or blocks exocytosis, respectively in mouse or bovine chromaffin cells

Pre-blockade of the sarco-endoplasmic reticulum (ER) calcium ATPase (SERCA) with irreversible thapsigargin depresses exocytosis in adrenal bovine chromaffin cells (BCCs). Distinct expression of voltage-dependent Ca2+-channel subtypes and of the Ca2+-induced Ca2+ release (CICR) mechanism in BCCs versus mouse chromaffin cells (MCCs) has been described. We present a parallel study on the effects of the acute SERCA blockade with reversible cyclopizonic acid (CPA), to repeated pulsing with acetylcholine (ACh) at short (15 s) and long intervals (60 s) at 37 °C, allowing the monitoring of the initial size of a ready-release vesicle pool (RRP) and its depletion and recovery in subsequent stimuli. We found (i) strong depression of exocytosis upon ACh pulsing at 15-s intervals and slower depression at 60-s intervals in both cell types; (ii) facilitation of exocytosis upon acute SERCA inhibition, with back to depression upon CPA washout in MCCs; (iii) blockade of exocytosis upon acute SERCA inhibition and pronounced rebound of exocytosis upon CPA washout in BCCs; (iv) basal [Ca2+]c elevation upon stimulation with ACh at short intervals (but not at long intervals) in both cell types; and (v) augmentation of basal [Ca2+]c and inhibition of peak [Ca2+]c amplitude upon CPA treatment in both cell types, with milder effects upon stimulation at 60-s intervals. These results are compatible with the view that while in MCCs the uptake of Ca2+ via SERCA contributes to the mitigation of physiological ACh triggered secretion, in BCCs the uptake of Ca2+ into the ER facilitates such responses likely potentiating a Ca2+-induced Ca2+ release mechanism. These drastic differences in the regulation of ACh-triggered secretion at 37 °C may help to understand different patterns of the regulation of exocytosis by the circulation of Ca2+ at a functional ER Ca2+ store.

A sodium background conductance controls the spiking pattern of mouse adrenal chromaffin cells in situ

KEY POINTS

Mouse chromaffin cells in acute adrenal slices exhibit two distinct spiking patterns, a repetitive mode and a bursting mode. A sodium background conductance operates at rest as demonstrated by the membrane hyperpolarization evoked by a low Na⁺ -containing extracellular saline. This sodium background current is insensitive to TTX, is not blocked by Cs⁺ ions and displays a linear I-V relationship at potentials close to chromaffin cell resting potential. Its properties are reminiscent of those of the sodium leak channel NALCN. In the adrenal gland, Nalcn mRNA is selectively expressed in chromaffin cells. The study fosters our understanding of how the spiking pattern of chromaffin cells is regulated and adds a sodium background conductance to the list of players involved in the stimulus-secretion coupling of the adrenomedullary tissue.

ABSTRACT

Chromaffin cells (CCs) are the master neuroendocrine units for the secretory function of the adrenal medulla and a finely-tuned regulation of their electrical activity is required for appropriate catecholamine secretion in response to the organismal demand. Here, we aim at deciphering how the spiking pattern of mouse CCs is regulated by the ion conductances operating near the resting membrane potential (RMP). At RMP, mouse CCs display a composite firing pattern, alternating between active periods composed of action potentials spiking with a regular or a bursting mode, and silent periods. RMP is sensitive to changes in extracellular sodium concentration, and a low Na⁺ -containing saline hyperpolarizes the membrane, regardless of the discharge pattern. This RMP drive reflects the contribution of a depolarizing conductance, which is (i) not blocked by tetrodotoxin or caesium, (ii) displays a linear I-V relationship between -110 and -40 mV, and (iii) is carried by cations with a conductance sequence g_Na  > g_K  > g_Cs . These biophysical attributes, together with the expression of the sodium-leak channel Nalcn transcript in CCs, state credible the contribution of NALCN. This inaugural report opens new research routes in the field of CC stimulus-secretion coupling, and extends the inventory of tissues in which NALCN is expressed to neuroendocrine glands.

Effect of fluoride on endocrine tissues and their secretory functions -- review

The effects of fluoride on endocrine tissues has not been sufficiently explored to date. The current body of knowledge suggest significant effects of that mineral on reducing sex hormone levels, which may consequently impair fertility and disrupt puberty. The majority of studies confirm that sodium fluoride increases TSH levels and decreases the concentrations of T3 and T4 produced by the thyroid. Moreover, a correlation was observed between NaF and increased secretion of PTH by the parathyroid glands, without a significant impact on body calcium levels. Probably, fluoride may exert adverse effects on insulin levels, impairing pancreatic function and resulting in abnormal glucose tolerance. Observations also include decreased levels of cortisol secreted by the adrenal glands. In light of the few existing studies, the mechanism of fluoride toxicity on the endocrine system has been described.

The Adrenal Medulla Modulates Mechanical Allodynia in a Rat Model of Neuropathic Pain

We have investigated whether the stress response mediated by the adrenal medulla in rats subjected to chronic constriction injury of the sciatic nerve (CCI) modulates their nocifensive behavior. Treatment with SK29661 (300 mg/kg; intraperitoneal (I.P.)), a selective inhibitor of phenylethanolamine N-methyltransferase (PNMT) that converts noradrenaline (NA) into adrenaline (A), fully reverted mechanical allodynia in the injured hind paw without affecting mechanical sensitivity in the contralateral paw. The effect was fast and reversible and was associated with a decrease in the A to NA ratio (A/NA) in the adrenal gland and circulating blood, an A/NA that was elevated by CCI. 1,2,3,4-tetrahydroisoquinoline-7-sulfonamide (SKF29661) did not affect exocytosis evoked by Ca²⁺ entry as well as major ionic conductances (voltage-gated Na⁺, Ca²⁺, and K⁺ channels, nicotinic acetylcholine receptors) involved in stimulus-secretion coupling in chromaffin cells, suggesting that it acted by changing the relative content of the two adrenal catecholamines. Denervation of the adrenal medulla by surgical splanchnectomy attenuated mechanical allodynia in neuropathic animals, hence confirming the involvement of the adrenal medulla in the pathophysiology of the CCI model. Inhibition of PNMT appears to be an effective and probably safe way to modulate adrenal medulla activity and, in turn, to alleviate pain secondary to the injury of a peripheral nerve.

Chronic resveratrol consumption prevents hypertension development altering electrophysiological currents and Ca2+ signaling in chromaffin cells from SHR rats

Resveratrol (RESV) is one of the most abundant polyphenol-stilbene compounds found in red wine with well-established cardioprotective and antihypertensive effects. Hyperactivity of the sympathoadrenal axis seems to be one of the major contributing factors in the pathogenesis of human essential hypertension. Alterations in outward voltage-dependent potassium currents (I_K) and inward voltage-dependent sodium (I_Na), calcium (I_Ca) and nicotinic (I_ACh) currents, CCs excitability, Ca²⁺ homeostasis, and catecholamine exocytosis were previously related to the hypertensive state. This raised the issue of whether in vivo long-term RESV treatment can directly act as a modulator of Ca²⁺ influx or a regulator of ion channel permeability in CCs. We monitored outward and inward currents, and cytosolic Ca²⁺ concentrations ([Ca²⁺]_c) using different pharmacological approaches in CCs from normotensive (WKY) and hypertensive (SHR) animals chronically exposed to trans-RESV (50 mg/L/v.o, 28 days). The long-term RESV treatment prevented the increase of the systolic blood pressure (SBP) in SHR, without reversion of cardiac hypertrophy. We also found an increase of the outward I_K, reduction in inward I_Na,I_Ca, and I_ACh, and the mitigation of [Ca²⁺]_c overload in CCs from SHR at the end of RESV treatment. Our data revealed that electrophysiological alterations of the CCs and in its Ca²⁺ homeostasis are potential new targets related to the antihypertensive effects of long-term RESV treatment.

Cav1.2 channelopathies causing autism: new hallmarks on Timothy syndrome

Cav1.2 L-type calcium channels play key roles in long-term synaptic plasticity, sensory transduction, muscle contraction, and hormone release. De novo mutations in the gene encoding Cav1.2 (CACNA1C) causes two forms of Timothy syndrome (TS1, TS2), characterized by a multisystem disorder inclusive of cardiac arrhythmias, long QT, autism, and adrenal gland dysfunction. In both TS1 and TS2, the missense mutation G406R is on the alternatively spliced exon 8 and 8A coding for the IS6-helix of Cav1.2 and is responsible for the penetrant form of autism in most TS individuals. The mutation causes specific gain-of-function changes to Cav1.2 channel gating: a "leftward shift" of voltage-dependent activation, reduced voltage-dependent inactivation, and a "leftward shift" of steady-state inactivation. How this occurs and how Cav1.2 gating changes alter neuronal firing and synaptic plasticity is still largely unexplained. Trying to better understanding the molecular basis of Cav1.2 gating dysfunctions leading to autism, here, we will present and discuss the properties of recently reported typical and atypical TS phenotypes and the effective gating changes exhibited by missense mutations associated with long QTs without extracardiac symptoms, unrelated to TS. We will also discuss new emerging views achieved from using iPSCs-derived neurons and the newly available autistic TS2-neo mouse model, both appearing promising for understanding neuronal mistuning in autistic TS patients. We will also analyze and describe recent proposals of molecular pathways that might explain mistuned Ca²⁺-mediated and Ca²⁺-independent excitation-transcription signals to the nucleus. Briefly, we will also discuss possible pharmacological approaches to treat autism associated with L-type channelopathies.

Norepinephrine-stimulated HSCs secrete sFRP1 to promote HCC progression following chronic stress via augmentation of a Wnt16B/β-catenin positive feedback loop

Background

Sustained adrenergic signaling secondary to chronic stress promotes cancer progression; however, the underlying mechanisms for this phenomenon remain unclear. Hepatocellular carcinoma (HCC) frequently develops within fibrotic livers rich in activated hepatic stellate cells (HSCs). Here, we examined whether the stress hormone norepinephrine (NE) could accelerate HCC progression by modulating HSCs activities.

Methods

HCC cells were exposed to conditioned medium (CM) from NE-stimulated HSCs. The changes in cell migration and invasion, epithelial-mesenchymal transition, parameters of cell proliferation, and levels of cancer stem cell markers were analyzed. Moreover, the in vivo tumor progression of HCC cells inoculated with HSCs was studied in nude mice subjected to chronic restraint stress.

Results

CM from NE-treated HSCs significantly promoted cell migration and invasion, epithelial-mesenchymal transition (EMT), and expression of cell proliferation-related genes and cancer stem cell markers in HCC cells. These pro-tumoral effects were markedly reduced by depleting secreted frizzled related protein 1 (sFRP1) in CM. The pro-tumoral functions of sFRP1 were dependent on β-catenin activation, and sFRP1 augmented the binding of Wnt16B to its receptor FZD7, resulting in enhanced β-catenin activity. Additionally, sFRP1 enhanced Wnt16B expression, reinforcing an autocrine feedback loop of Wnt16B/β-catenin signaling. The expression of sFRP1 in HSCs promoted HCC progression in an in vivo model under chronic restraint stress, which was largely attenuated by sFRP1 knockdown.

Conclusions

We identify a new mechanism by which chronic stress promotes HCC progression. In this model, NE activates HSCs to secrete sFRP1, which cooperates with a Wnt16B/β-catenin positive feedback loop. Our findings have therapeutic implications for the treatment of chronic stress-promoted HCC progression.

Disruption of Exocytosis in Sympathoadrenal Chromaffin Cells from Mouse Models of Neurodegenerative Diseases

Synaptic disruption and altered neurotransmitter release occurs in the brains of patients and in murine models of neurodegenerative diseases (NDDs). During the last few years, evidence has accumulated suggesting that the sympathoadrenal axis is also affected as disease progresses. Here, we review a few studies done in adrenal medullary chromaffin cells (CCs), that are considered as the amplifying arm of the sympathetic nervous system; the sudden fast exocytotic release of their catecholamines—stored in noradrenergic and adrenergic cells—plays a fundamental role in the stress fight-or-flight response. Bulk exocytosis and the fine kinetics of single-vesicle exocytotic events have been studied in mouse models carrying a mutation linked to NDDs. For instance, in R6/1 mouse models of Huntington’s disease (HD), mutated huntingtin is overexpressed in CCs; this causes decreased quantal secretion, smaller quantal size and faster kinetics of the exocytotic fusion pore, pore expansion, and closure. This was accompanied by decreased sodium current, decreased acetylcholine-evoked action potentials, and attenuated [Ca²⁺]c transients with faster Ca²⁺ clearance. In the SOD1^G93A mouse model of amyotrophic lateral sclerosis (ALS), CCs exhibited secretory single-vesicle spikes with a slower release rate but higher exocytosis. Finally, in the APP/PS1 mouse model of Alzheimer’s disease (AD), the stabilization, expansion, and closure of the fusion pore was faster, but the secretion was attenuated. Additionally, α-synuclein that is associated with Parkinson’s disease (PD) decreases exocytosis and promotes fusion pore dilation in adrenal CCs. Furthermore, Huntington-associated protein 1 (HAP1) interacts with the huntingtin that, when mutated, causes Huntington’s disease (HD); HAP1 reduces full fusion exocytosis by affecting vesicle docking and controlling fusion pore stabilization. The alterations described here are consistent with the hypothesis that central alterations undergone in various NDDs are also manifested at the peripheral sympathoadrenal axis to impair the stress fight-or-flight response in patients suffering from those diseases. Such alterations may occur: (i) primarily by the expression of mutated disease proteins in CCs; (ii) secondarily to stress adaptation imposed by disease progression and the limitations of patient autonomy.