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ABSTRACT: We describe Ciona intestinalis gamma-aminobutyric acid (GABA)-ergic neurons during development, studying the expression pattern of Ci-GAD (glutamic acid decarboxylase: GABA synthesizing enzyme) by in situ hybridization. Moreover, we cloned two GABA(B) receptor subunits (Ci-GABA(B)Rs), and a phylogenetic analysis (neighbor-joining method) suggested that they clustered with their vertebrate counterparts. We compared Ci-GAD and Ci-GABA(B)Rs expression patterns in C. intestinalis embryos and larvae. At the tailbud stage, Ci-GAD expression was widely detected in central and peripheral nervous system (CNS/PNS) precursors, whereas Ci-GABA(B)Rs expression was evident at the level of the precursors of the visceral ganglion. GABA was localized by immunohistochemistry at the same developmental stage. In the larva, Ci-GAD transcripts and GABA immunofluorescence were also detected throughout the CNS and in some neurons of the PNS, whereas transcripts of both GABA(B) receptor subunits were found mainly in the CNS. The expression pattern of Ci-GABA(B)Rs appeared restricted to Ci-GAD-positive territories in the sensory vesicle, whereas, in the visceral ganglion, Ci-GABA(B)Rs transcripts were found in ventral motoneurons that did not express Ci-GAD. Insofar as GABAergic neurons are widely distributed also in the CNS and PNS of vertebrates and other invertebrate chordates, it seems likely that GABA signaling was extensively present in the protochordate nervous system. Results from this work show that GABA is the most widespread inhibitory neurotransmitter in C. intestinalis nervous system and that it can signal through GABA(B) receptors both pre- and postsynaptically to modulate different sensory inputs and subsequent swimming activity.
The Journal of Comparative Neurology 02/2008; 506(3):489-505. · 3.81 Impact Factor
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ABSTRACT: To describe the serotonergic system in a tunicate larva, we cloned a gene encoding for tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, in the ascidian Ciona intestinalis and studied its expression pattern during development. Ci-TPH expression was found from tailbud stage in the precursor cells of the visceral ganglion and in the tail. In the larva, TPH-expressing neurons formed two clusters in the anterior central nervous system at the level of the visceral ganglion. Moreover, we found Ci-TPH expression at the level of the muscle cells of the tail and suggested that this localisation might be at the level of neuro-muscular junctions. Moreover, we discussed the involvement of serotonin in the control of larval locomotory activity.
Archiv für Entwickelungsmechanik der Organismen 05/2007; 217(4):307-13. · 1.77 Impact Factor
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ABSTRACT: Fluconazole (FLUCO) is an azole derivative used to treat fungal and yeast infections. Embryotoxicity tests on the ascidian Phallusia mammillata were performed to evaluate the effects of this drug. FLUCO proved to have strong consequences on P. mammillata development. Incidence of malformations and of lethality increased in a dose dependent way. Probit analysis showed that FLUCO had a high TI value (Teratogenic Index, LC(50)/TC(50)), thus this substance could be classified as a teratogenic compound for ascidians. Larvae exposed to FLUCO showed a typical phenotype characterized by malformations restricted to the trunk region: the trunk appeared round in shape with flat palps, the sensory vesicle cavity was absent or reduced and the anterior central nervous system failed to correctly differentiate. These anomalies resulted similar to those induced by retinoic acid (RA) treatment. Thus, it could be hypothesized that FLUCO and RA may act with a similar pathogenic mechanism in ascidian larvae, as it has been proposed for mammals.
Environmental Toxicology and Pharmacology 05/2007; 23(3):265-71. · 1.47 Impact Factor
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ABSTRACT: Azole compounds are fungicides used in agriculture and in clinical area and are suspected to produce craniofacial malformations in vertebrates. Toxicity tests on sperm viability, fertilization and embryogenesis of the solitary ascidian Phallusia mammillata were performed to evaluate the effects of two azole derivatives, Imazalil and Triadimefon. Ascidian (Chordata, Ascidiacea) embryos and larvae could provide biological criteria for seawater quality standards because the larvae are lecitotrophic and have a short pelagic period, allowing to run the larval toxicity tests over a short period of time. Imazalil and Triadimefon proved to have strong consequences on P. mammillata. They could influence the reproductive rate of the animal exerting their effects at different levels: acting as spermiotoxic agents, inhibiting fertilization and impairing embryological development. Fertilization rate significantly decreased after 30min exposure of sperm to 25microM Imazalil (P<0.0001) and after exposure of both gametes to 50microM Imazalil (P<0.05) and 1mM Triadimefon (P<0.0001) as compared to controls. Malformations caused by exposure of embryos to both substances were dose dependent. Imazalil median teratogenic concentration (TC50 concentration, the concentration that resulted in 50% malformed larvae) value was 0.67microM and median lethal concentration (LC50, the concentration that resulted in 50% embryos dead before completing the development) value was 10.23microM while for Triadimefon TC50 value was 29.56 and LC50 value was 173.7microM. Larvae developed from embryos treated with Imazalil and Triadimefon showed alterations of the anterior structures of the trunk: papillary nerves and the anterior central nervous system failed to correctly differentiate, as showed by immunostaining with anti-beta-tubulin antibody. Comparing the anomalies caused by retinoic acid, reported in a previous study, it was possible to hypothesize that malformations induced by Imazalil and Triadimefon could be due to a perturbation of the endogenous retinoid content, as it has been proposed for mammals. Ascidians proved to be good models to study the toxic effects of pesticides since they offered both the convenience of working with an invertebrate species and the tissue sensitivity to chemical compound comparable to vertebrates.
Aquatic Toxicology 10/2006; 79(3):205-12. · 3.76 Impact Factor
