MRI Techniques and New Animal Models for Imaging the Brain

Chapitre 10absen

Neuroanatomical organization of gonadotropin-releasing hormone neurons during the oestrus cycle in the ewe

BACKGROUND: During the preovulatory surge of gonadotropin-releasing hormone (GnRH), a very large amount of the peptide is released in the hypothalamo-hypophyseal portal blood for 24-36H00. To study whether this release is linked to a modification of the morphological organization of the GnRH-containing neurons, i.e. morphological plasticity, we conducted experiments in intact ewes at 4 different times of the oestrous cycle (before the expected LH surge, during the LH surge, and on day 8 and day 15 of the subsequent luteal phase). The cycle stage was verified by determination of progesterone and LH concentrations in the peripheral blood samples collected prior to euthanasia. RESULTS: The distribution of GnRH-containing neurons throughout the preoptic area around the vascular organ of the lamina terminalis was studied following visualisation using immunohistochemistry. No difference was observed in the staining intensity for GnRH between the different groups. Clusters of GnRH-containing neurons (defined as 2 or more neurons being observed in close contact) were more numerous during the late follicular phase (43 ± 7) than during the luteal phase (25 ± 6), and the percentage of clusters was higher during the beginning of the follicular phase than during the luteal phase. There was no difference in the number of labelled neurons in each group. CONCLUSIONS: These results indicate that the morphological organization of the GnRH-containing neurons in ewes is modified during the follicular phase. This transitory re-organization may contribute to the putative synchronization of these neurons during the surge. The molecular signal inducing this plasticity has not yet been identified, but oestradiol might play an important role, since in sheep it is the only signal which initiates the GnRH preovulatory surge

La restauration du Christ en croix de la cathédrale Saint-Pierre de Nantes : redécouverte d’une technique de sculpture inédite grâce à la tomodensitométrie et aux micro-analyses

La cathédrale Saint-Pierre de Nantes conserve un Christ en croix de facture espagnole, daté de la fin du XVIe ou du début du XVIIe siècle. C’est à l’occasion de sa restauration que cette œuvre atypique appartenant au corpus des « sculptures légères » et aux œuvres de procession, proche des techniques de fabrication des Christ de maïs mexicains, a été redécouverte. Afin de recueillir des informations sur la technologie et les matériaux employés, plusieurs méthodes d’investigation assorties de micro-analyses approfondies ont été nécessaires. La réalisation d’une couverture tomodensitométrique détaillée a notamment été un élément décisif dans la compréhension des modes de construction originels et de l’état d’altération interne, et a démontré l’intérêt de cette technique d’imagerie performante pour les pratiques de restauration.Nantes Cathedral houses a Spanish Crucifixion dating from the late 16th or early 17th century. This atypical work,belonging to the group of “lightweight sculptures” and processional artefacts, closely related to the Mexican art of making sculptures of Christ from maize-stalk paste, was rediscovered during its restoration. In order to garner information about the technique and materials used, several methods of investigation and in-depth microanalyses were necessary. Producing a detailed CT scan image played a decisive role in understanding the original construction methods and internal alterations, and demonstrated the advantage of using this efficient imaging procedure in restoration practices

Neuro-glial plasticity of neuroendocrine networks

Neuro-glial plasticity of neuroendocrine networks is a major mechanism involved in key events of physiological functions such as parturition and lactation (oxytocinergic system) and preovulatory surge (GnRH system). This type of plasticity is classically described as rearrangements between glial cells and neuroendocrine neurones. Neuro-glial plasticity can occur within several hours. Cellular and molecular mechanisms involved are complex and imply an active regulation of neuroendocrine networks activity. In the present study we show that GnRH pulsatile secretion studied in vitro is regulated by gap junction communication between glial cells. Glial cells forming the microenvironment of GnRH neuronal network could represent a new system for integrating environmental cues and for regulating GnRH secretionLa plasticité neuro-gliale des réseaux neuroendocrines est un élément majeur de la régulation d’évènements clés de grandes fonctions, comme la plasticité du système ocytocinergique lors de la parturition et de la lactation et celle du système GnRH dans le déclenchement du pic pré-ovulatoire de LH. Cette plasticité est décrite par des réarrangements neuroanatomiques des cellules gliales associées aux neurones neuroendocrines. Elle peut se mettre en place en quelques heures. Les mécanismes cellulaires et moléculaires sont complexes et mettent en jeu une régulation active de l’activité des neurones par les cellules gliales. Dans l’étude présentée ici, nous montrons que la pulsatilité de sécrétion des neurones à GnRH étudiés in vitro est régulée par la communication des cellules gliales via des jonctions gap. Les cellules gliales du microenvironnement des neurones à GnRH pourraient ainsi représenter un nouveau système d’intégration des signaux environnementaux et de régulation de la sécrétion de GnR

The Fibrillar Collagen Family

Collagens, or more precisely collagen-based extracellular matrices, are often considered as a metazoan hallmark. Among the collagens, fibrillar collagens are present from sponges to humans, and are involved in the formation of the well-known striated fibrils. In this review we discuss the different steps in the evolution of this protein family, from the formation of an ancestral fibrillar collagen gene to the formation of different clades. Genomic data from the choanoflagellate (sister group of Metazoa) Monosiga brevicollis, and from diploblast animals, have suggested that the formation of an ancestral α chain occurred before the metazoan radiation. Phylogenetic studies have suggested an early emergence of the three clades that were first described in mammals. Hence the duplication events leading to the formation of the A, B and C clades occurred before the eumetazoan radiation. Another important event has been the two rounds of “whole genome duplication” leading to the amplification of fibrillar collagen gene numbers, and the importance of this diversification in developmental processes. We will also discuss some other aspects of fibrillar collagen evolution such as the development of the molecular mechanisms involved in the formation of procollagen molecules and of striated fibrils

Distribution of central catecholaminergic neurons: a comparison between ungulates, humans and other species

In ungulates and primates, the distribution of central catecholaminergic neurons identified using antibodies raised against catecholamine synthesizing enzymes and catecholamines themselves, shows many differences if compared to rats. Catecholaminergic neurons are more loosely clustered in ungulates and primates than in rat. In the medulla oblongata, the density of noradrenergicladrenergic neurons is lower in ungulates than in other species and, particularly in sheep, the adrenergic group C1 is not observed. The noradrenergic neurons of the locus coeruleus are present in a larger area in ungulates than in rodents. In the hypothalamus, the density of dopamine neurons is lower in ungulates and primates than in rodents. In the rostra1 hypothalamus of ungulates, the dorsal part of the group A14 is missing, and these species present only the ventral part of the group A15. In primates the group A15 extends into the supraoptic and paraventricular nuclei which have large tyrosine hydroxylase-immunoreactive (TH-IR) neurons not observed in other species. In addition, in all studied species, not all cells expressing catecholamine synthesizing enzymes also express catecholamines, as found in some TH-IR neurons in the arcuate nucleus, thereby demonstrating the necessity of using different markers to ascertain the true catecholaminergic nature of labeled neurons. These anatomical differences between species show the difficulty in extrapolating the distribution of catecholamine neurons from one species to another and may be related to adaptative physiological differences between mammals

Catecholaminergic neuronal systems in the diencephalon of mammals

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Distribution of neurotransmitters in the sheep brain

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Adrenergic neurons in sheep brain demonstrated by immunohistochemistry with antibodies to phenylethanolamine N.methyl transferase (PnMt) and dopamine-beta-hydroxylase (DBH) : absence of the C1 cell group in the sheep brain

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Immunocytochemical localization of serotonin-containing neurons in the myelencephalon, brainstem and diencephalon of the sheep.

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