Plasticity of dopaminergic phenotype and locomotion in larval zebrafish induced by brain excitability changes during the embryonic period

During the embryonic period, neuronal communication starts before the establishment of the synapses with alternative forms of neuronal excitability, called here Embryonic Neural Excitability (ENE). ENE has been shown to modulate the unfolding of development transcriptional programs, but the global consequences for developing organisms are not all understood. Here we monitored calcium transients in the telencephalon of zebrafish embryos as a proxy for ENE to assess the efficacy of transient pharmacological treatments to either increase or decrease ENE. Increasing or decreasing ENE at the end of the embryonic period promoted an increase or a decrease in the numbers of dopamine (DA) neurons, respectively. This plasticity of dopaminergic specification occurs in the subpallium of zebrafish larvæ at 6 dpf, within a relatively stable population of vMAT2-positive cells. Non-dopaminergic vMAT2-positive cells hence constitute an unanticipated biological marker for a reserve pool of DA neurons that can be recruited by ENE.Modulating ENE also affected larval locomotion several days after the end of the treatments. In particular, the increase of ENE from 2 to 3 dpf promoted hyperlocomotion of larvæ at 6 dpf, reminiscent of zebrafish endophenotypes reported for Attention Deficit with Hyperactivity Disorders. These results provide a convenient framework for identifying environmental factors that could disturb ENE as well as to study the molecular mechanisms linking ENE to neurotransmitter specification.Significance Statement- Spontaneous calcium transients, used as a proxy for Embryonic Neural Excitability (ENE), are detected in the forebrain of embryonic zebrafish.- Short-term pharmacological treatments by bath application could increase or decrease ENE.- The post-mitotic differentiation of the dopaminergic phenotype is modulated by ENE in the zebrafish forebrain.- The plasticity of the dopaminergic specification occurs within a reserve pool of vMAT2-positive cells.- Transient increase of ENE at the end of the embryonic period induces hyperlocomotion, a phenotype associated with ADHD in this model.- Our results provide a convenient framework to study the molecular mechanisms linking ENE to neurotransmitter specification.

Time-Gated FRET Nanoprobes for Autofluorescence-Free Long-Term In Vivo Imaging of Developing Zebrafish

The zebrafish is an important vertebrate model for disease, drug discovery, toxicity, embryogenesis, and neuroscience. In vivo fluorescence microscopy can reveal cellular and subcellular details down to the molecular level with fluorescent proteins (FPs) currently the main tool for zebrafish imaging. However, long maturation times, low brightness, photobleaching, broad emission spectra, and sample autofluorescence are disadvantages that cannot be easily overcome by FPs. Here, a bright and photostable terbium-to-quantum dot (QD) Förster resonance energy transfer (FRET) nanoprobe with narrow and tunable emission bands for intracellular in vivo imaging is presented. The long photoluminescence (PL) lifetime enables time-gated (TG) detection without autofluorescence background. Intracellular four-color multiplexing with a single excitation wavelength and in situ assembly and FRET to mCherry demonstrate the versatility of the TG-FRET nanoprobes and the possibility of in vivo bioconjugation to FPs and combined nanoprobe-FP FRET sensing. Upon injection at the one-cell stage, FRET nanoprobes can be imaged in developing zebrafish embryos over seven days with toxicity similar to injected RNA and strongly improved signal-to-background ratios compared to non-TG imaging. This work provides a strategy for advancing in vivo fluorescence imaging applications beyond the capabilities of FPs.

Non-thalamic origin of zebrafish sensory nuclei implies convergent evolution of visual pathways in amniotes and teleosts

Ascending visual projections similar to the mammalian thalamocortical pathway are found in a wide range of vertebrate species, but their homology is debated. To get better insights into their evolutionary origin, we examined the developmental origin of a thalamic-like sensory structure of teleosts, the preglomerular complex (PG), focusing on the visual projection neurons. Similarly to the tectofugal thalamic nuclei in amniotes, the lateral nucleus of PG receives tectal information and projects to the pallium. However, our cell lineage study in zebrafish reveals that the majority of PG cells are derived from the midbrain, unlike the amniote thalamus. We also demonstrate that the PG projection neurons develop gradually until late juvenile stages. Our data suggest that teleost PG, as a whole, is not homologous to the amniote thalamus. Thus, the thalamocortical-like projections evolved from a non-forebrain cell population, which indicates a surprising degree of variation in the vertebrate sensory systems.

Mesencephalic origin of the inferior lobe in zebrafish

BACKGROUND

Although the overall brain organization is shared in vertebrates, there are significant differences within subregions among different groups, notably between Sarcopterygii (lobe-finned fish) and Actinopterygii (ray-finned fish). Recent comparative studies focusing on the ventricular morphology have revealed a large diversity of the hypothalamus. Here, we study the development of the inferior lobe (IL), a prominent structure forming a bump on the ventral surface of the teleost brain. Based on its position, IL has been thought to be part of the hypothalamus (therefore forebrain).

RESULTS

Taking advantage of genetic lineage-tracing techniques in zebrafish, we reveal that cells originating from her5-expressing progenitors in the midbrain-hindbrain boundary (MHB) participate in the formation of a large part of the IL. 3D visualization demonstrated how IL develops in relation to the ventricular system. We found that IL is constituted by two developmental components: the periventricular zone of hypothalamic origin and the external zone of mesencephalic origin. The mesencephalic external zone grows progressively until adulthood by adding new cells throughout development.

CONCLUSION

Our results disprove a homology between the IL and the mammalian lateral hypothalamus. We suggest that the IL is likely to be involved in multimodal sensory integration rather than feeding motivation. The teleost brain is not a simpler version of the mammalian brain, and our study highlights the evolutionary plasticity of the brain which gives rise to novel structures.

A workflow to process 3D+time microscopy images of developing organisms and reconstruct their cell lineage

The quantitative and systematic analysis of embryonic cell dynamics from in vivo 3D+time image data sets is a major challenge at the forefront of developmental biology. Despite recent breakthroughs in the microscopy imaging of living systems, producing an accurate cell lineage tree for any developing organism remains a difficult task. We present here the BioEmergences workflow integrating all reconstruction steps from image acquisition and processing to the interactive visualization of reconstructed data. Original mathematical methods and algorithms underlie image filtering, nucleus centre detection, nucleus and membrane segmentation, and cell tracking. They are demonstrated on zebrafish, ascidian and sea urchin embryos with stained nuclei and membranes. Subsequent validation and annotations are carried out using Mov-IT, a custom-made graphical interface. Compared with eight other software tools, our workflow achieved the best lineage score. Delivered in standalone or web service mode, BioEmergences and Mov-IT offer a unique set of tools for in silico experimental embryology.

Dopaminergic Neurons Controlling Anterior Pituitary Functions: Anatomy and Ontogenesis in Zebrafish

Dopaminergic (DA) neurons located in the preoptico-hypothalamic region of the brain exert a major neuroendocrine control on reproduction, growth, and homeostasis by regulating the secretion of anterior pituitary (or adenohypophysis) hormones. Here, using a retrograde tract tracing experiment, we identified the neurons playing this role in the zebrafish. The DA cells projecting directly to the anterior pituitary are localized in the most anteroventral part of the preoptic area, and we named them preoptico-hypophyseal DA (POHDA) neurons. During development, these neurons do not appear before 72 hours postfertilization (hpf) and are the last dopaminergic cell group to differentiate. We found that the number of neurons in this cell population continues to increase throughout life proportionally to the growth of the fish. 5-Bromo-2'-deoxyuridine incorporation analysis suggested that this increase is due to continuous neurogenesis and not due to a phenotypic change in already-existing neurons. Finally, expression profiles of several genes (foxg1a, dlx2a, and nr4a2a/b) were different in the POHDA compared with the adjacent suprachiasmatic DA neurons, suggesting that POHDA neurons develop as a distinct DA cell population in the preoptic area. This study offers some insights into the regional identity of the preoptic area and provides the first bases for future functional genetic studies on the development of DA neurons controlling anterior pituitary functions.

The thyroid angiofollicular units, a biological model of functional and morphological integration

The fundamental role of the thyroid gland is to ensure the biosynthesis of thyroid hormones whose primary role during embryonic development and the maintenance of homeostasis after birth is well known. The challenge here is double, as the hormone synthesis depends on both potentially toxic biochemical processes, as long as they are not fully contained, and the availability of a trace element, iodine, whose uptake may be extremely variable depending on the geographical location and the physiological status of individuals. The squaring of the circle has been resolved by the thyroid gland during its phylogenetic maturation by setting up angiofollicular units, morphological entities whose the perfect functional coherence between the different compartments within them (epithelial, endothelial and interstitial) results from a high level three-dimensional assemblage. This morphological and functional integration warrants adequate supplies of thyroid hormones whose mobilization must be triggered at any time when necessary. This functional requirement finds its expression in the morphological heterogeneity that ultimately culminates in the formation of nodules. Each angiofollicular unit is an individualized entity with its own genotypic and phenotypic asset that runs on the extrinsic control of TSH and a host of autocrine and paracrine factors. But subtle intrinsic mechanisms of self-regulation, operating out of any outside influences, constantly adjust the availability of players involved in the hormonal synthesis (iodine, thyroglobulin) within a biochemical entity (the thyroxisome) that is perfectly suited for this synthesis taking place without prejudice to the thyrocyte. The hormonal synthesis generates oxygen-derived substances as oxidative load or stress, though perfectly controlled in healthy thyrocytes. Any injury related to the nature, the amount, or where in the cell oxygen-derived substances are produced, may lead to morphological and functional breakdowns responsible for various disease processes, including those of autoimmune or even neoplastic nature.

Identification of the Zebrafish IFN Receptor: Implications for the Origin of the Vertebrate IFN System

The recent description of virus-induced fish IFNs has raised questions about the evolution of this complex antiviral system. Identification of the receptor of the zebrafish virus-induced IFN (zIFN) was sought to help resolve these questions. We set up an experimental system to study the zIFN system in the course of a viral infection of zebrafish embryos. In this setting, zIFN was induced by viral infection, and we identified zIFN-dependent induced transcripts. Embryos quickly died from the infection, but zIFN overexpression increased their survival. We took advantage of this experimental system to perform in vivo loss and gain of function analysis of candidate receptors of the class II helical receptor family and identified zCRFB1 and zCRFB5 as the two subunits of the zebrafish IFN receptor. Based on the organization of the zIFN gene and the protein structure of the identified receptor components, the virus-induced fish IFNs appear as orthologs of mammalian IFN-lambda, specifying type III IFN as the ancestral antiviral system of vertebrates.

Neurokinin release in the rat nucleus of the solitary tract via NMDA and AMPA receptors

Neurokinins (substance P, neurokinin A and neurokinin B) and the neurokinin receptors, the NK1 and NK3 receptors, are largely expressed in the nucleus of the solitary tract (NST) where they are involved in the central regulation of visceral function. Studying the mechanisms that control neurokinin release can provide valuable information concerning the control of autonomic functions subserved by the NST. Glutamate is the principal excitatory neurotransmitter in the NST and the main neurotransmitter of afferent vagal fibers. Neurokinins and glutamate may interact within the NST. In the present study, we have examined the contribution of the N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtypes of glutamate receptors on the release of the endogenous neurokinins in the NST. We used internalization of the NK1 or NK3 receptor as an index of endogenous neurokinin release assessed by immunocytochemical visualization of the NK1 or NK3 receptor endocytosis. Experiments were performed in vitro using rat brainstem slices. A first series of experiments were done in order to validate our in vitro preparation. Application of substance P, neurokinin A or neurokinin B induced dose-dependent internalization of NK1 and NK3 receptor. This was blocked by the endocytosis inhibitor, phenylarzine oxide. The NK1 receptor antagonist SR140333 blocked internalization of NK1 receptor induced by the three neurokinins. In addition, the internalization NK1 or NK3 receptor was reversible. These results demonstrate that internalization and recycling mechanisms of NK1 or NK3 receptor were preserved in in vitro brainstem slices. Application of NMDA or AMPA induced internalization of NK1 receptor. This was blocked by the application of SR140333 suggesting that NK1 receptor internalization is due to the binding of endogenous neurokinin released under the effects of NMDA and AMPA. Application of NMDA or AMPA had no effect on NK3 receptor. Application of tetrodotoxin blocked NK1 receptor internalization induced by NMDA, demonstrating that the release of neurokinins is dependent of axon potential propagation. This result excludes the hypothesis of a release on neurokinins via pre-synaptic NMDA receptors located on neurokinin-containing axon terminals. NMDA or AMPA may directly induce neurokinin release in the NST by acting on receptors located on the cell bodies and dendrites of neurokinin-containing neurons. Release of neurokinins may also be the result of a general activation of neuron networks of the NST by NMDA or AMPA. To conclude, our results suggest that glutamate, through activation of post-synaptic NMDA and AMPA receptors, contributes to neurokinin signaling in the NST.

Ontogenesis of CYP2C-dependent arachidonic acid metabolism in the human liver: relationship with sudden infant death syndrome

A modification of the human monooxygenase system have been previously associated with the sudden infant death syndrome (SIDS): the hepatic CYP2C content was markedly enhanced and resulted from an activation of CYP2C gene transcription. To determine the possible consequence of the up-regulation of CYP2C in SIDS, we examined the metabolism of arachidonic acid (AA) an endogenous substrate of CYP2C involved in the physiologic regulation of vascular tone. The overall AA metabolism was extremely low during the fetal period and rose after birth to generate 14,15 epoxyeicosatrienoic acid (EET), 11,12 EET and the sum of 5,6 dihydroxyeicosatrienoic acid (diHETE)+omega/omega-1 hydroxy AA. In SIDS, the accumulation of CYP2C proteins was associated with a significant increase in the formation of 14,15 and 11,12 diHETE, which were shown to be supported by individually expressed CYP2C8 and 2C9 and HETE1 (presumably 15 HETE). This increase was markedly inhibited by addition of sulfaphenazole, a selective inhibitor of CYP2C9. So, we propose that the higher CYP2C content in SIDS stimulates the production of EETs and diHETEs and might have severe pathologic consequences in children.

Localization of components of glycinergic synapses during rat spinal cord development

The sequence of events leading to the chemical matching of presynaptic neurotransmitters and postsynaptic transmitter receptors is investigated here in vivo for the spinal glycine receptor (GlyR) by using immunocytochemical methods. In the ventral horn of adult rat spinal cord, GlyRs are only present at glycinergic postsynaptic differentiations where they are stabilized by the associated protein gephyrin. With quantitative confocal microscopy, we found that gephyrin is detected before GlyRs at embryonic day (E)13-E14 and at E15, respectively, inside the cytoplasm and at plasmalemmal loci. Around the time of birth, the number of cell surface gephyrin-immunoreactive (-IR) spots exceeds that of GlyR. They first match 10 days after birth. The densities of postsynaptic gephyrin- and GlyR-IR were quantified between birth and the adult stage with post-embedding immunogold staining. Immunostaining for gephyrin and GlyR was not detected in the extrasynaptic membrane. The density of staining in postsynaptic membrane increased progressively with development. The inhibitory amino-acid content of the presynaptic terminal boutons opposed to gephyrin-IR sites was also analyzed. In the newborn, postnatal day 10, and adult, more than 90% of these boutons were immunostained for glycine. As seen with serial sections, 38% and 51.2% of the terminals also contained gamma-aminobutyric acid (GABA) in neonate and adult, respectively. These data indicate that around the time of birth, most glycine-containing boutons, some also containing GABA, are opposed to gephyrin-IR postsynaptic densities, whereas GlyRs are not present. Our results suggest that gephyrin determines subsynaptic loci on the plasma membrane where GlyR will subsequently accumulate.

Antigoitrogenic effect of combined supplementation with dl-alpha-tocopherol, ascorbic acid and beta-carotene and of dl-alpha-tocopherol alone in the rat

The effects of the vitamins dl-alpha-tocopherol, ascorbic acid and beta-carotene, free radical scavengers and lipid peroxidation inhibitors, were analyzed in male Wistar rats made goitrous by feeding a low iodine diet (< 20 micrograms iodine/kg) and perchlorate (1% in drinking water) for 4, 8, 16, and 32 days. Groups of control or goitrous rats received for at least 16 days before killing a diet containing 0.6% vitamin E (as dl-alpha-tocopherol acetate), 1.2% vitamin C (ascorbic acid) and 0.48% beta-carotene, either simultaneously (vitamin cocktail) or separately. This treatment led to a 5-fold increase of vitamin E in the thyroid gland, a 24-fold increase in the liver and a 3-fold increase in the plasma. In control rats, vitamin cocktail administration increased slightly the thyroid weight with little changes in thyroid function parameters. During iodine deficiency, administration of the vitamin cocktail or vitamin E alone reduced significantly the rate of increase in thyroid weight, and DNA and protein contents, as well as the proportion of [3H]thymidine labeled thyroid follicular cells, but not that of labeled endothelial cells. Plasma tri-iodothyronine, thyroxine, TSH levels, thyroid iodine content and concentration as well as relative volumes of glandular compartments were not modified. The proportion of necrotic cells rose from 0.5% in normal animals to about 2% after 16 days of goiter development. No significant protective effect of the vitamins was observed. These results suggest that these vitamins, particularly vitamin E, modulate one of the regulatory cascades involved in the control of thyroid follicular cell growth, without interfering with the proliferation of endothelial cells.

Gephyrin accumulates at specific plasmalemma loci during neuronal maturation in vitro

The distribution of glycine receptor (GlyR)-associated gephyrin has been investigated in rat spinal cord neurons maintained in vitro by means of immunocytochemical techniques. Gephyrin, which is crucial for the stabilization of postsynaptic GlyR microdomains, is present in mature neurons at postsynaptic differentiations. With immunofluorescence, discontinuous patches of gephyrin were detected within the neuronal soma of spinal cord neurons on the 1st day after plating. Subsequently, gephyrin was present at membrane areas that correspond to points of contact between cells or with the culture dish. By the 5th day, gephrin was mostly associated with the MAP2-positive somatodendritic compartment. With immunoelectron microscopy, gephyrin blobs detected at the earliest stages (1-3 days after plating) were found within the cytoplasm or associated with the plasma membrane. Asymmetrically immunostained intercellular contacts were only detected after 5 days, and gephyrin was found in association with clearly differentiated postsynaptic membranes at 7 days. At later stages, we observed gephyrin immunoreactivity only at some synapses. Our results suggest that gephyrin accumulates initially at the locus of cell-to-cell contacts involved in adhesion processes. These localizations may define hot spots for later accumulation of the GlyR and possibly other receptors.

Expression of glycine receptor alpha subunits and gephyrin in cultured spinal neurons

The inhibitory glycine receptor is a pentameric membrane protein composed of alpha and beta subunits. In the postsynaptic membrane, the glycine receptor and the copurifying peripheral membrane protein gephyrin are clustered underneath glycine-releasing nerve terminals. Here, we describe the expression of gephyrin and the neonatal and adult glycine receptor alpha subunit isoforms alpha1 and alpha2 during in vitro differentiation of rat spinal neurons. Analysis by immunoassays and the reverse transcriptase-polymerase chain reaction showed that gephyrin and alpha subunit mRNA and protein levels exhibited a marked increase from 1 to 5 days in vitro, i.e. prior to the formation of functional synaptic contacts. Using confocal and standard immunofluorescence, we determined the number of immunoreactive cells and the cellular localization of the alpha subunits and gephyrin. At 3 days in vitro, glycine receptor immunoreactivity revealed by the monoclonal antibody mAb4a was found in < 10% of cells and was mainly localized intracellularly; in contrast, gephyrin was detected in in vitro, gephyrin was essentially localized at the neuronal surface. At this stage, the number of glycine receptor-positive cells approached that of gephyrin-containing neurons (50%), and glycine receptor antigen was found both intracellularly and at the periphery of the cells. The antibody mAb2b, which binds exclusively to the alpha1 subunit, revealed aggregates at the surface of a few neurons. At 10 days in vitro, glycine receptor and gephyrin staining was localized in clusters at the periphery of the soma and the neurites. This quantitative analysis corroborates temporal differences in the cellular distribution of gephyrin and glycine receptor alpha subunits, the former being accumulated first at the neuronal surface.

Long-term reduction of microalbuminuria after 3 years of angiotensin-converting enzyme inhibition by perindopril in hypertensive insulin-treated diabetic patients

We studied the long-term effects of the angiotensin-converting enzyme (ACE) inhibitor perindopril, administered for 36 months on glycemic control, creatinine clearance, and albuminuria in hypertensive insulin-treated diabetics. After 1 month treatment with placebo, 39 patients entered the study and received 4-8 mg perindopril/day. Within the first 3 months, diastolic blood pressure was normalized in 80% of the patients. From these, 23 were followed during a total of 3 years on perindopril therapy, and divided in three groups according to their initial urinary albumin excretion rate (AER): 11 had normal AER (less than 15 mg/24 hours), eight had microalbuminuria (AER 15-150 mg/24 hour), and four had AER greater than 150 mg/24 hours and had overt proteinuria. Long-term (3 years) diastolic blood pressure normalization (less than or equal to 90 mm Hg) was achieved throughout the study. Concomitant with blood pressure reduction, a long-term decrease in AER was observed in normo- and microalbuminuric patients. Macroproteinuria was unaffected by perindopril. Glycemic control and creatinine clearance remained stable during the whole study period. No major side effects were observed. We conclude that perindopril safely produces a long-term normalization of elevated blood pressure in hypertensive insulin-treated diabetics without affecting glycemic control. Blood pressure normalization is associated with long-term AER reduction in normo- and microalbuminuric patients.

Detection and identification of endothelin-1 immunoreactivity in rat and porcine thyroid follicular cells

Endothelin-1 immunoreactivity (irET-1) was observed in rat and porcine thyroid glands. Using a radioimmunoassay for endothelin-1, the mean concentration in extracts of rat and porcine thyroid glands were 0.75 pg/mg +/- 0.03 (n = 4) and 1.5 pg/mg +/- 0.2 (n = 8) (mean +/- SE) respectively. Gel-filtration and reverse-phase HPLC showed that ir ET-1 eluted in a position identical to synthetic endothelin-1. In addition, immunohistochemical study showed that irET-1 is located within epithelial follicular cells. No immunostaining was seen in parafollicular C-cells nor in parathyroid.

Urinary proteins and red blood cell membrane negative charges in diabetes mellitus

The nature and origin of proteinuria in diabetes mellitus have been investigated by measuring the urinary excretion of seven specific proteins of low (beta 2-microglobin, retinol-binding protein) or high molecular weight (albumin, transferrin, hemopexin and IgG). Using the Alcian Blue binding test, we also measured negative charges on red blood cell (RBC) membrane which according to recent studies might mirror the glomerular polyanion charge. A group of 190 diabetics was examined, including 90 patients with type I diabetes, 23 type II diabetics treated with diet and/or hypoglycaemic agents and 77 longstanding type II diabetics requiring insulin therapy. With the exception of beta 2-microglobulin all proteins measured were excreted in the urine of diabetics in significantly higher amounts than in controls. The assay of transferrin proved the most sensitive (58% positive) followed by albumin (49%), IgG (34%), hemopexin (28%) and retinol-binding protein (26%). Practically the same ranking was obtained when only type I diabetics were considered. RBC membrane negative charges were diminished in diabetics and negatively correlated with the urinary excretion of albumin (r = -0.61, n = 190). RBC charges were also negatively correlated with other urinary proteins of high molecular mass (r between - 0.5 and - 0.2) but presented no relation with urinary beta 2-microglobulin or retinol-binding protein. The loss of RBC charges in diabetics most likely reflects the concomitant depletion of the glomerular polyanion responsible for the increased glomerular leakage of high molecular mass plasma proteins. The preferential increase in transferrin excretion together with the progressive rise in the urinary excretion of IgG lead us to postulate that the loss of glomerular polyanion in diabetes is accompanied, from the early stage, by a progressive decrease in the size-selectivity of the glomerular filter. The urinary excretion of retinol-binding protein was weakly correlated with albuminuria (r = 0.26, n = 186). Eight % of diabetics showed an elevation of urinary retinol-binding protein without evidence of microalbuminuria, which clearly demonstrates that a proximal tubular impairment can occur independently of the glomerular alterations in the course of diabetic nephropathy.

Correlated morphological and functional study of isolated rat thyroid follicles in suspension culture

Rat thyroid follicles were isolated by collagenase digestion and cultured in suspension on agarose for 1-12 days with 0-0.1-1 mU/ml thyrotropin (TSH). After a 4 h exposure to Na125I they were processed for light and electron microscopy, autoradiography and biochemical analysis. Follicular 125I accumulation (A) and organification (PBI) were measured. Thyroglobulin (Tg) content of follicles and 125I-labelled amino acids in Tg were analyzed by high-performance liquid chromatography (HPLC). Without TSH, follicular lumina and cell polarity persisted. From day 3, the rough endoplasmic reticulum (RER) and ribosomes disappeared while autophagic vacuoles appeared: 125I accumulation and PBI were significantly reduced. From day 6, ultrastructural cell dedifferentiation occurred. At day 12, autoradiographic labelling was found over very few lumina; half of the 125I accumulated was still organified. With 1 mU TSH, follicles formed aggregates with narrow densely labelled lumina lined by tall cells. The RER was well developed up to day 12. 125I accumulation, PBI and iodothyronine (T3, T4) formation in Tg remained significantly higher than in follicles cultured without TSH, showing a transient decrease at days 6 and 9. Monoiodotyrosine/diiodotyrosine (MIT/DIT) and T3/T4 ratios in Tg were not modified, suggesting the persistence in the follicles of a significant iodine pool available for iodination. With 0.1 mU TSH, alterations of cell morphology and reduction of functional properties occurred later than without TSH. In the presence of TSH, morphological signs of new follicle formation were seen. These data demonstrate that closed follicles keep their follicular structure up to 12 days of culture, even without TSH. However, TSH is necessary to maintain iodine accumulation and organification.

Are adrenergic neurons subject to a serotoninergic influence in the nucleus tractus solitarii? A morphological and biochemical study in the rat

The possible relationships between adrenaline-synthesizing neurons and serotoninergic afferent fibers in the nucleus tractus solitarii of the rat were investigated both morphologically and biochemically. Adrenergic elements (cell bodies, dendrites and nerve endings) were detected simultaneously with serotoninergic axonal varicosities in the same electron-microscopic sections by means of combined phenylethanolamine-N-methyltransferase immunocytochemistry and [3H]serotonin-uptake radioautography. Among some 500 serotoninergic varicosities scanned in the areas of significant overlap between the 2 types of labeling, only 3 were directly apposed to an adrenergic process, identified as a dendrite in each case. No synaptic membrane differentiations were seen at these occasional sites of contact. Destruction of the serotonin input by 5,7-dihydroxytryptamine had no significant effect on the tyrosine hydroxylase dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase enzymatic activities in the C2 adrenergic region, but induced 22% and 38% increases of tyrosine hydroxylase and dopamine-beta-hydroxylase activities, respectively, in the neighboring A2 noradrenergic area. Taken together, these results suggest that serotoninergic and adrenergic neurons do not significantly interact in the nucleus tractus solitarii; this implies that the possible catecholaminergic relays for the action of serotonin in autonomic regulation at this level could consist of noradrenergic neurons rather than of their adrenergic counterparts.

Direct toxic effect of iodide in excess on iodine-deficient thyroid glands: epithelial necrosis and inflammation associated with lipofuscin accumulation

Involution of thyroid hyperplasia (induced by a low iodine diet and a goitrogen, propylthiouracil, PTU) was obtained in mice by administering a high or a moderate dose of iodide (HID or MID, respectively). In HID involuting glands, vasoconstriction was observed after 12 hr whereas necrosis and inflammation were very abundant as early as after 6 hr and maximal after 48 hr. They were not prevented by papaverine by which vasoconstriction was inhibited, but were inhibited by the continuation of PTU by which iodide oxidation and organification were inhibited. Lipofuscin inclusions in thyroid and inflammatory cells were always associated with necrosis. On the contrary, when involution was induced by MID or by HID + triiodothyronine (T3), or by T3 alone, neither necrosis nor inflammation occurred and apoptosis was the only mode of cell deletion. No lipofuscin inclusion occurred. Our results demonstrate that iodide in excess, after being oxidized or organified, is directly toxic for iodine-deficient thyroid cells. The presence of lipofuscin suggests that its toxicity is mediated by lipid peroxidation, a consequence of production of free radicals in excess.