The antipsychotic amisulpride: ultrastructural evidence of its secretory activity in salivary glands

OBJECTIVE

Amisulpride is reported to inhibit clozapine-induced sialorrhea. Preclinically, clozapine evokes muscarinic-M1-type-mediated secretion that, however, amisulpride does not reduce. Instead, amisulpride, without causing any overt secretion per se, enhances both nerve- and autonomimetic-evoked salivation by unknown mechanism(s). Hypothesizing that amisulpride prepares the gland for secretion, we looked for ultrastructural events indicating secretory activity in intercellular canaliculi of serous/seromucous cells, that is, density increase in protrusions (reflecting anchored granules) and in microbuds (reflecting recycling membranes and/or vesicle secretion) and decrease in microvilli (reflecting the cytoskeletal re-arrangement related to exocytosis).

MATERIAL AND METHODS

Rat parotid and submandibular glands were exposed to amisulpride in vivo or in vitro. Glands were processed for transmission electron and scanning electron microscopy and then morphometrically assessed.

RESULTS

Cells were packed with secretory granules. The density of protrusions increased in both glands, whereas significant and parallel changes in microvilli and microbuds occurred only in parotid glands, and in vitro.

CONCLUSIONS

Amisulpride induced ultrastructural signs of secretory activity but to varying extent; in submandibular glands, in contrast to parotid glands, changes were not brought beyond the granular anchoring stage. Amisulpride may provide an overall readiness for secretion that will result in augmented responses to agonists, a phenomenon of potential interest in dry-mouth treatment.

Subcellular distribution of melatonin receptors in human parotid glands

The hormone melatonin influences oral health through a variety of actions, such as anti-inflammatory, anti-oxidant, immunomodulatory and antitumour. Many of these melatonin functions are mediated by a family of membrane receptors expressed in the oral epithelium and salivary glands. Using immunoblotting and immunohistochemistry, recent studies have shown that the melatonin membrane receptors, MT1 and MT2, are present in rat and human salivary glands. To date, no investigation has dealt with the ultrastructural distribution of the melatonin receptors. This was the aim of the present study, using the immunogold method applied to the human parotid gland. Reactivity to MT1 and, with less intensity, to MT2 appeared in the secretory granules of acinar cells and in the cytoplasmic vesicles of both acinar and ductal cells. Plasma membranes were also stained, albeit slightly. The peculiar intracytoplasmic distribution of these receptors may indicate that there is an uptake/transport system for melatonin from the circulation into the saliva.

Cortical adrenal mitochondrial morphology changes in functional state: new insights

We compared changes in the morphology of mitochondrial cristae with those in the blood and adrenal content of steroid hormones after the stimulation or inhibition of steroidogenesis. Rats were treated with adrenocorticotrophic hormone or angiotensin II to elicit steroidogenesis and with dexamethasone to inhibit it. Blood and adrenal glands were collected after several time intervals for measurements of steroids and their main intermediates. In the zona fasciculata, mitochondrial ultrastructure was investigated by high resolution scanning electron microscopy. We found that the morphometric data correlated well with the measurements of hyper- or hypo-activity of steroidogenesis over short periods of time (4 h) but not over longer observation times. A peculiar finding was that, contrary to previous reports, 11-deoxycortisol was present in adult rat adrenal tissue.

Morphological evidence that pentagastrin regulates secretion in the human parotid gland

Salivary secretion is principally regulated by autonomic nerves. However, recent evidence from in vivo animal experiments suggests that gastrointestinal peptide hormones can also influence saliva production. The aim of the present study was to define the secretagogue activity of the gastrin-analogue pentagastrin in human salivary glands. For this purpose, parotid tissues were exposed to pentagastrin in vitro. Morphological techniques were used to evaluate modifications to serous acinar cells associated with secretion. Using a variant of the osmium maceration method, high resolution scanning electron microscopy allowed assessment of the morphology of the cytoplasmic aspect of the plasmalemma to demonstrate secretory activity. To quantify responses to pentagastrin, we recorded morphometric data on microvilli, microbuds, and protrusions. Dose-dependent morphological changes were observed, whereas protein concentration increased in the incubate. The use of selective receptor antagonists showed pentagastrin to act principally via cholecystokinin-A receptors. The morphological responses observed following exposure to pentagastrin differed from those elicited following exposure to the pan-muscarinic agonist carbachol. This study provides the first demonstration of a direct secretory action of gastrointestinal peptides on salivary glands in humans.

Suggestive evidence of a vesicle-mediated mode of cell degranulation in chromaffin cells. A high-resolution scanning electron microscopy investigation

In this study we used a modified osmium maceration method for high-resolution scanning electron microscopy to study some ultrastructural details fitting the schema of piecemeal degranulation in chromaffin cells. Piecemeal degranulation refers to a particulate pattern of cell secretion that is accomplished by vesicle-mediated extracellular transport of granule-stored material. We investigated adrenal samples from control and angiotensin II-treated rats, and identified a variable proportion of smooth, 30-60-nm-diameter vesicles in the cytoplasm of chromaffin cells. A percentage of these vesicles were interspersed in the cytosol among chromaffin granules but the majority appeared to be attached to granules. Remarkably, the number of unattached cytoplasmic vesicles was greatly increased in chromaffin cells from angiotensin II-treated animals. Vesicles of the same structure and dimension were detected close to or attached to the cytoplasmic face of the plasma membrane; these, too, were increased in number in chromaffin cells from rats stimulated with angiotensin II. In specimens shaken with a rotating agitator during maceration, the cytoplasmic organelles could be partially removed and the fine structure of the vesicular interaction with the inner side of the plasma membrane emerged most clearly. A proportion of chromaffin granules showed protrusions that we interpreted as vesicular structures budding from the granular envelope. In some instances, the transection plane intersected granules with putative vesicles emerging from the surfaces. In these cases, the protrusions of budding vesicles could be observed from the internal side. This study provides high-resolution scanning electron microscopy images compatible with a vesicle-mediated degranulation mode of cell secretion in adrenal chromaffin cells. The data indicating an increase in the number of vesicles observed in chromaffin cells after stimulation with the chromaffin cell secretagogue angiotensin II suggests that this secretory process may be susceptible to fine regulation.

Mitochondria of human Leydig cells as seen by high resolution scanning electron microscopy

The three-dimensional ultrastructure of over 1000 mitochondria in human Leydig cells (from twelve sexually mature patients) was examined by high resolution scanning electron microscopy (HRSEM) of osmium-macerated specimens, as well as by transmission electron microscopy of conventional ultrathin sections. The stereo-pair imaging of the osmium-macerated specimens by HRSEM is also very useful for investigating the three-dimensional structure of cytoplasmic membranous organelles with great clarity. The mitochondria, which mainly are elongated (although some are ovate), possess cristae that are almost exclusively tubular and that occasionally display constrictions and terminal bulbules. Lamelliform cristae are quite rare. Occasionally, the tubular cristae are joined together to form a simple network. Classic crista junctions could not be identified with certainty, although the base of the tubular cristae might correspond functionally to such junctions. As a whole, in line with the identical and common embryological origin of adrenal cortex and gonads, mitochondria of human Leydig cell closely resemble those of steroidogenic cells of human suprarenal cortex treated by the same maceration method.

Oxytocin immunoreactivity in the human urethral (Littrè's) glands

Oxytocin is a cyclic nonapeptide whose best known effects are stimulation of uterine smooth muscle cells during labor and of milk ejection during lactation. Circulating oxytocin originates from the hypothalamus, but its production has also been documented in peripheral tissues. Furthermore, seminal plasma also contains oxytocin, but its functional role is still unknown, although its secretion is generally ascribed to the prostate. In this study, we investigated the possibility that seminal oxytocin is also secreted by other exocrine glands of the human male genital tract. Intramural (Littrè's) glands isolated from bioptic specimens of normal urethrae were processed for immunogold localization of oxytocin. Immunostaining was detected in principal cells, with gold particles specifically found on secretory granules. Basal and endocrine cells were unstained. The present findings suggest that urethral glands not only produce the mucinous layer that protects and lubricates the urethral wall, but also are potential sources of other seminal components, such as oxytocin, which probably play still unclear roles in reproductive physiology.

The three-dimensional morphology of Candida albicans as seen by high-resolution scanning electron microscopy

The fine structure of Candida albicans has been repeatedly described by transmission electron microscopy, whereas studies by high-resolution scanning electron microscopy (HRSEM) are rare and devoted solely to the study of its external morphology. This report describes the results of an HRSEM study on C. albicans carried out by an osmium maceration protocol modified to better retain the structural characteristics of this yeast. Thus, we visualized various intracellular structures including invaginations of cell membrane (plasmalemmasomes), nuclear envelope, mitochondria, the vacuolar system, and two additional structures that might represent a form of endoplasmic reticulum and the Golgi apparatus. The present investigation, which for the first time shows the organelles of C. albicans at the 3D level, may lead to a better understanding of its cell physiology.

Acute nicotine changes dynorphin and prodynorphin mRNA in the striatum

RATIONALE

Nicotine displays rewarding and aversive effects, and while dopamine has been linked with nicotine's reward, the neurotransmitter(s) involved with aversion remains speculative. The kappa-dynorphinergic system has been associated with negative motivational and affective states, and whether dynorphin (Dyn) contributes to the behavioral pharmacology of nicotine is a pertinent question.

OBJECTIVE

We determined whether administration of a single dose of nicotine alters the biosynthesis of Dyn in the striatum of mice.

RESULTS

Nicotine free base, 1 mg/kg, sc, induced a biphasic, protracted increase of striatal Dyn, an initial rise by 1 h, which declined to control levels by 2 h, and a subsequent increase, between 6 and 12 h, lasting over 24 h. At 1 h, the nicotine effect was dose dependent, with doses>or=0.5 mg/kg inducing a response. Prodynorphin mRNA increased by 30 min for over 24 h, and in situ hybridization demonstrated elevated signal in caudate/putamen and nucleus accumbens. The nicotinic antagonist mecamylamine prevented the Dyn response, and a similar effect was observed with D1- and D2-like dopamine receptor antagonists, SCH 23390, sulpiride, and haloperidol. The glutamate NMDA receptor antagonist MK-801 reversed the nicotine-induced increase of Dyn, while the AMPA antagonist NBQX had a marginal effect.

CONCLUSIONS

We interpret our findings to indicate that acute nicotine enhances the synthesis and release of striatal Dyn. We propose that nicotine influences Dyn primarily through dopamine release and that glutamate plays a modulatory role. A heightened dynorphinergic tone may contribute to the aversive effects of nicotine in naive animals and first-time tobacco smokers.

Dynorphin and prodynorphin mRNA changes in the striatum during nicotine withdrawal

Nicotine withdrawal causes somatic and negative affective symptoms that contribute to relapse and continued tobacco smoking. So far, the neuronal substrates involved are not fully understood, and an opioid role has been suggested. In this regard, the opioid dynorphin (Dyn) is of interest as it produces aversive states and has been speculated to play a role in the nicotine behavioral syndrome. These studies explore whether Dyn metabolism is altered during withdrawal following chronic administration of nicotine. Mice were administered nicotine, 2 mg/kg, s.c., four times daily for 14 days, and Dyn and prodynorphin (PD) mRNA estimated in selective brain regions at various times (30 min to 96 h) following drug discontinuation. The content of Dyn, estimated by RIA, was decreased in the striatum for a protracted time, from 30 min to over 72 h. In contrast, the mRNA for PD, evaluated by Northern blot, was elevated, appearing by 8 h and lasting over 96 h. Dyn was decreased in both ventral and dorsal striatum, and PD mRNA was differentially increased in the two striatal compartments as demonstrated by in situ hybridization. PD message was predominantly augmented in the nucleus accumbens, rostral pole, core, and shell, and the medial aspects of caudate/putamen. We interpret these data to indicate increased activity of striatal, particularly accumbal, dynorphinergic neurons during nicotine withdrawal resulting in enhanced peptide release and compensatory synthesis. Heightened dynorphinergic tone might be responsible, in part, for the emergence of the negative affective states observed during nicotine withdrawal.

Histatin-induced alterations in Candida albicans: a microscopic and submicroscopic comparison

Despite the numerous studies performed in an attempt to clarify the issue, the mechanism of action of salivary histatins remains unclear. The aim of the present study was to correlate histatin-induced morphological changes in Candida albicans by fluorescence microscopy (FM), transmission electron microscopy (TEM), and high resolution scanning electron microscopy (HRSEM). Each of the fluorescent dyes used by FM (i.e., tetramethylrhodamine methyl ester perchlorate for mitochondrial potential, Lysotracker for lysosome acidic compartment, and 4',6-diamino-2-phenylindole dihydrochloride for DNA) exhibited a specific staining in control cells. Following histatin treatment, we observed a recurring staining pattern, corresponding to fluorescence concentration along the cell periphery, suggesting a loss of dye specificity. To assess histatin-induced cytoplasmic modifications, ultrastructural analysis was then carried out. After treatments with histatins, TEM revealed characteristic intracellular modifications including: vacuole overgrowth, nuclear disappearance, loss of organelle identity, as well as the appearance of electron-dense membranes, likely of mitochondrial origin. Additionally, structures resembling autophagosomes were occasionally observed. By HRSEM, mitochondrial swelling was invariably the first sign of a histatin-induced effect. Other modifications included intracellular membrane disarrangement, organelles in disarray, and a large central cavity with deformed bodies displaced to the cell periphery, similar to what was detected by TEM. In summary, our study illustrates the occurrence of ultrastructural modifications following administration of histatins. Observations made with FM, TEM, and HRSEM provided different views of the same signs, demonstrating a definite action of histatins on C. albicans morphology. The possible functional meanings of these morphological results is discussed in light of the most recent biochemical data on histatin fungicidal activity.

Intracellular distribution of fluorescent probes delivered by vesicles of different lipidic composition

In order to study mechanisms involved in liposome-cell interaction, this work attempted to assess the influence of vesicle composition on the delivery of liposomal content to Hela cells. In particular, to evaluate pH-sensitive properties and cell interaction of the prepared liposomes, the lipid formulations contained cholesterol (Chol) and they were varied by using phosphatidylcholines with different purity degree: soy lecithin (SL; 80% phosphatidylcholine), a commercial mixture of soy phosphatidylcholine (P90; 90% phosphatidylcholine) or dipalmitoylphosphatidylcholine (DPPC; 99% of purity). A second series of liposomes also contained stearylamine (SA). Dehydration-rehydration vesicles (DRV) were prepared and then sonicated to decrease vesicle size. Vesicle-cell interactions and liposomal uptake were examined by fluorescence microscopy using carboxyfluorescein (CF) and phosphatidylethanolamine-dioleoyl-sulforhodamine B (Rho-PE) as fluorescent markers. Fluorescence dequenching assay was used to study the influence of pH on CF release from the liposomal formulations. Liposome adhesion on the cell surface and internalization were strongly dependent on vesicle bilayer composition. SA vesicles were not endocytosed. DPPC/Chol liposomes were endocytosed but did not release their fluorescent content into the cytosol. SL/Chol and P90/Chol formulations displayed a diffuse cytoplasmic fluorescence of liposomal marker.

New findings on 3-D microanatomy of cellular structures in human tissues and organs. An HRSEM study

We present here findings obtained on a large number of human tissues over a period of more than ten years, by our modification of the Osmium maceration method for high resolution scanning electron microscopy (HRSEM). Data are documented by original pictures which illustrate both some 3-D intracellular features not previously shown in human tissues, and results obtained in our current studies on mitochondrial morphology and on the secretory process of salivary glands. We have demonstrated that mitochondria of cells of practically all human tissues and organs have usually tubular cristae, and that even the cristae that look lamellar are joined to the inner mitochondrial membrane by tubular connexions similar to the crista junctions later seen by electron tomography. Concerning salivary glands an important result is the development of a morphometric method that allows the quantitative evaluation of the secretory events.

High resolution scanning electron microscopy of the intracellular surface of intercalated disks in human heart

The three-dimensional architecture of human cardiac intercalated disks was examined by high resolution scanning electron microscopy of osmium-macerated specimens. This methodology permits viewing of in situ intercalated disks from a vantage point inside individual cardiomyocytes. The erose nature of these structures was rendered in stark relief. Areas covered with clusters of particles were present on some membranous projections--these may represent a combination of desmosomes and fasciae adherentes. On the other hand, areas devoid of particles may correspond to gap junctions.

Characterization of depolarization and repolarization phases of mitochondrial membrane potential fluctuations induced by tetramethylrhodamine methyl ester photoactivation

Depolarization and repolarization phases (D and R phases, respectively) of mitochondrial potential fluctuations induced by photoactivation of the fluorescent probe tetramethylrhodamine methyl ester (TMRM) were analyzed separately and investigated using specific inhibitors and substrates. The frequency of R phases was significantly inhibited by oligomycin and aurovertin (mitochondrial ATP synthase inhibitors), rotenone (mitochondrial complex I inhibitor) and iodoacetic acid (inhibitor of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase). Succinic acid (mitochondrial complex II substrate, given in the permeable form of dimethyl ester) abolished the rotenone-induced inhibition of R phases. Taken together, these findings indicate that the activity of both respiratory chain and ATP synthase were required for the recovery of the mitochondrial potential. The frequency of D phases prevailed over that of R phases in all experimental conditions, resulting in a progressive depolarization of mitochondria accompanied by NAD(P)H oxidation and Ca2+ influx. D phases were not blocked by cyclosporin A (inhibitor of the permeability transition pore) or o-phenyl-EGTA (a Ca2+ chelator), suggesting that the permeability transition pore was not involved in mitochondrial potential fluctuations.

Mitochondrial alterations and autofluorescent conversion ofCandida albicans induced by histatins

The mechanism of the candidacidal activity of histatins 3 and 5 (Hst) is still a matter of debate. Previous studies have indicated that Hst induce cell permeabilization, generation of reactive oxygen species (ROS) by mitochondria, inhibition of the respiratory chain, and energy-dependent cytotoxic release of ATP. On the other hand, the multiplicity of effects and the apparent contrast between experimental data continue to render the mechanism of Hst-induced killing of C. albicans unclear. In this investigation, using fluorescent probes (the potential-sensitive mitochondrial probe tetramethylrhodamine methyl ester perchlorate, TMRM; the ROS-sensitive probe dihydrofluorescein diacetate, DHF; the membrane-impermeant probe, calcein) and autofluorescence data we observed that Hst induce ROS generation by mitochondria undergoing a high energy swelling condition, accompanied by oxidation of cytosolic NAD(P)H and mitochondrial flavoproteins. ROS generation and swelling, attributable to an inhibition of the respiratory chain and to impairment of the K/H-exchanger, were followed by mitochondrial depolarization. Mitochondrial changes were accompanied by massive calcein influx, indicative of cell permeabilization, and prominent alterations of the cell size, shape, and optical density. The loss of proliferative activity was correlated, on a single cell basis, to the acquisition of a lipofuscin-like autofluorescence.

Mitochondrial localization of reactive oxygen species by dihydrofluorescein probes

Mitochondria are the main source of reactive oxygen species (ROS). The aim of this work was to verify the ROS generation in situ in HeLa cells exposed to prooxidants and antioxidants (menadione, tert-butyl hydroperoxide, antimycin A, vitamin E, N-acetyl-L-cysteine, and butylated hydroxytoluene) using the ROS-sensitive probes 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate di-acetomethyl ester (DCDHF) and dihydrofluorescein diacetate (DHF). Mitochondria were counterstained with the potential-sensitive probe tetramethylrhodamine methyl ester perchlorate (TMRM). Both DCDHF and DHF were able to detect the presence of ROS in mitochondria, though with distinct morphological features. DCDHF fluorescence was invariably blurred, smudged, and spread over the cytoplasm surrounding the major mitochondrial clusters. On the contrary, DHF fluorescence was sharp and delineated thin filaments which corresponded in all details to TMRM-stained mitochondria. These data suggest that DCDHF does not reach the mitochondrial matrix but is oxidized by ROS released by mitochondria in the cytosol. On the other hand, DHF enters mitochondria and reacts with ROS released in the matrix. Cytosolic (DCDHF+) ROS but not matrix (DHF+) ROS, were significantly decreased by vitamin E. N-acetyl-L-cysteine was effective in reducing DCDHF and DHF photooxidation in the medium, but was unable to reduce intracellular ROS. ROS generation was accompanied by partial mitochondrial depolarization.

Met-enkephalin and preproenkephalin mRNA changes in the striatum of the nicotine abstinence mouse

We studied the changes of met-enkephalin (Met-Enk) content and preproenkephalin (PPE) mRNA in the striatum in a mouse model of nicotine abstinence. Nicotine, 2 mg/kg, s.c., was administered four times daily for 14 days and Met-Enk and PPE mRNA evaluated at various times (4-96 h) following drug discontinuation. Met-Enk, assayed by radioimmunoassay, was increased in the ventral (nucleus accumbens) but not dorsal (putamen/caudate) striatum, while PPE mRNA, assayed in whole striatum by Northern blotting was elevated. Both changes were seen early during withdrawal and lasted over 72 h. In situ hybridization revealed enhanced signal in the dorsal striatum, mostly laterally, and smaller increases in the rostral pole, core and shell of the nucleus accumbens. These observations indicate that during nicotine withdrawal, striatal enkephalinergic neurons undergo adaptative responses, which might contribute to the abstinence behavioral syndrome.

Intra- and intercellular distribution of mitochondrial probes and changes after treatment with MDR modulators

Fluorescent probes are currently used to evaluate the mitochondrial transmembrane potential in situ. However, in parallel experiments using the probes JC-1 and TMRM in different cell types (human astrocytes, HEp-2, Vero, KB, and HeLa cells), we found that the distribution of JC-1 and TMRM is highly variable not only in different cell types but also in different cells of the same cell type, a condition that has never been documented until our work. This phenomenon depends on a hidden, widespread multidrug resistance (MDR) phenotype that can be recognized only by comparative assays with MDR inhibitors (progesterone, verapamil, and cyclosporin A) and represents a serious risk of error in the evaluation of the mitochondrial potential.

Glutamate receptors participate in the nicotine-induced changes of met-enkephalin in striatum

A single dose of nicotine given to mice induces first a rapid decrease (presumed release/enhanced degradation) and then a rise (presumed synthesis/enhanced accumulation) of met-enkephalin (Met-Enk) in dorsal and ventral striatum observed at 30 and 60 min post-treatment, respectively. These studies investigated whether the nicotine effect on Met-Enk was mediated indirectly, in part, via other neurotransmitters known to be released by nicotine. Based on the ability of selective antagonists of dopamine (Sch 23390, D1; Sulpiride, D2), glutamate (CPP, competitive NMDA; dizocilpine, non-competitive NMDA; NBQX, AMPA) and GABA (bicuculline, GABA(A); Sch 50911, GABA(B)) receptors, to inhibit or enhance the response to nicotine, we conclude that nicotine alters striatal Met-Enk, in part, via glutamate NMDA and AMPA receptors. These findings further support the notion that glutamate might play a role in the pharmacology of nicotine.