Laboratoire de Neurobiologie Cellulaire et Moléculaire

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide that was first isolated from ovine hypothalamic extracts on the basis of its ability to stimulate cAMP formation in anterior pituitary cells. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-glucagon-growth hormone releasing factor-secretin superfamily. The sequence of PACAP has been remarkably well conserved during the evolution from protochordate to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, and respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide whose activity remains unknown. Two types of PACAP binding sites have been characterized. Type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes, the PACAP-specific PAC1 receptor, which is coupled to several transduction systems, and the two PACAP/VIP-indifferent VPAC1 and VPAC2 receptors, which are primarily coupled to adenylyl cyclase. PAC1 receptors are particularly abundant in the brain and pituitary and adrenal glands whereas VPAC receptors are expressed mainly in the lung, liver, and testis. The wide distribution of PACAP and PACAP receptors has led to an explosion of studies aimed at determining the pharmacological effects and biological functions of the peptide. This report reviews the current knowledge concerning the multiple actions of PACAP in the central nervous system and in various peripheral organs including the endocrine glands, the airways, and the cardiovascular and immune systems, as well as the different effects of PACAP on a number of tumor cell types.

Zebrafish (Danio rerio) are rapidly gaining popularity in translational neuroscience and behavioral research. Physiological similarity to mammals, ease of genetic manipulations, sensitivity to pharmacological and genetic factors, robust behavior, low cost, and potential for high-throughput screening contribute to the growing utility of zebrafish models in this field. Understanding zebrafish behavioral phenotypes provides important insights into neural pathways, physiological biomarkers, and genetic underpinnings of normal and pathological brain function. Novel zebrafish paradigms continue to appear with an encouraging pace, thus necessitating a consistent terminology and improved understanding of the behavioral repertoire. What can zebrafish 'do', and how does their altered brain function translate into behavioral actions? To help address these questions, we have developed a detailed catalog of zebrafish behaviors (Zebrafish Behavior Catalog, ZBC) that covers both larval and adult models. Representing a beginning of creating a more comprehensive ethogram of zebrafish behavior, this effort will improve interpretation of published findings, foster cross-species behavioral modeling, and encourage new groups to apply zebrafish neurobehavioral paradigms in their research. In addition, this glossary creates a framework for developing a zebrafish neurobehavioral ontology, ultimately to become part of a unified animal neurobehavioral ontology, which collectively will contribute to better integration of biological data within and across species.

The hippocampus plays a key role in the acquisition of new memories for places and events. Evidence suggests that the consolidation of these memories is enhanced during sleep. At the neuronal level, reactivation of awake experience in the hippocampus during sharp-wave ripple events, characteristic of slow-wave sleep, has been proposed as a neural mechanism for sleep-dependent memory consolidation. However, a causal relation between sleep reactivation and memory consolidation has not been established. Here we show that disrupting neuronal activity during ripple events impairs spatial learning. We trained rats daily in two identical spatial navigation tasks followed each by a 1-hour rest period. After one of the tasks, stimulation of hippocampal afferents selectively disrupted neuronal activity associated with ripple events without changing the sleep-wake structure. Rats learned the control task significantly faster than the task followed by rest stimulation, indicating that interfering with hippocampal processing during sleep led to decreased learning.

The efficient introduction of genetic material into quiescent nerve cells is important in the study of brain function and for gene therapy of neurological disorders. A replication-deficient adenoviral vector that contained a reporter gene encoding beta-galactosidase infected rat nerve cells in vitro and in vivo. beta-Galactosidase was expressed in almost all sympathetic neurons and astrocytes in culture. After stereotactic inoculations into the rat hippocampus and the substantia nigra, beta-galactosidase activity was detected for 2 months. Infected cells were identified as microglial cells, astrocytes, or neurons with anatomical, morphological, and immunohistochemical criteria. No obvious cytopathic effect was observed.

Blockade of acetylcholine release by botulinum neurotoxin type A at the neuromuscular junction induces the formation of an extensive network of nerve-terminal sprouts. By repeated in vivo imaging of N-(3-triethyl ammonium propyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide uptake into identified nerve endings of the mouse sternomastoid muscle after a single intramuscular injection of the toxin, inhibition of stimulated uptake of the dye at the terminals was detected within a few days, together with an increase in staining of the newly formed sprouts. After 28 days, when nerve stimulation again elicited muscle contraction, regulated vesicle recycling occurred only in the sprouts [shown to contain certain soluble N-ethylmaleimide-sensitive factor attachment proteins (SNAREs) and to abut acetylcholine receptors] and not at the parent terminals. Therefore, only these sprouts could be responsible for nerve-muscle transmission at this time. However, a second, distinct phase of the rehabilitation process followed with a return of vesicle turnover to the original terminals, accompanied by an elimination of the by then superfluous sprouts. This extension and later removal of "functional" sprouts indicate their fundamental importance in the repair of paralyzed endplates, a finding with ramifications for the vital process of nerve regeneration.

Computational neuroscience has produced a diversity of software for simulations of networks of spiking neurons, with both negative and positive consequences. On the one hand, each simulator uses its own programming or configuration language, leading to considerable difficulty in porting models from one simulator to another. This impedes communication between investigators and makes it harder to reproduce and build on the work of others. On the other hand, simulation results can be cross-checked between different simulators, giving greater confidence in their correctness, and each simulator has different optimizations, so the most appropriate simulator can be chosen for a given modelling task. A common programming interface to multiple simulators would reduce or eliminate the problems of simulator diversity while retaining the benefits. PyNN is such an interface, making it possible to write a simulation script once, using the Python programming language, and run it without modification on any supported simulator (currently NEURON, NEST, PCSIM, Brian and the Heidelberg VLSI neuromorphic hardware). PyNN increases the productivity of neuronal network modelling by providing high-level abstraction, by promoting code sharing and reuse, and by providing a foundation for simulator-agnostic analysis, visualization and data-management tools. PyNN increases the reliability of modelling studies by making it much easier to check results on multiple simulators. PyNN is open-source software and is available from http://neuralensemble.org/PyNN.

BACKGROUND: We previously described two members of a family affected by an apparently genetically determined fatal disease characterized clinically by progressive insomnia, dysautonomia, and motor signs and characterized pathologically by severe atrophy of the anterior ventral and mediodorsal thalamic nuclei. Five other family members who died of this disease, which we termed "fatal familial insomnia," had broader neuropathologic changes suggesting that fatal familial insomnia could be a prion disease. METHODS: We used antibodies to prion protein (PrP) to perform dot and Western blot analyses, with and without proteinase K, on brain tissue obtained at autopsy from two patients with fatal familial insomnia, three patients with sporadic Creutzfeldt-Jakob disease, and six control subjects. The coding region of the PrP gene was amplified and sequenced in the samples from the two patients with fatal familial insomnia. Restriction-enzyme analysis was carried out with amplified PrP DNA from 33 members of the kindred. RESULTS: Protease-resistant PrP was found in both patients with fatal familial insomnia, but the size and number of protease-resistant fragments differed from those in Creutzfeldt-Jakob disease. In the family with fatal familial insomnia, all 4 affected members and 11 of the 29 unaffected members had a point mutation in PrP codon 178 that results in the substitution of asparagine for aspartic acid and elimination of the Tth111 I restriction site. Linkage analysis showed a close relation between the point mutation and the disease (maximal lod score, 3.4 when theta was zero). CONCLUSIONS: Fatal familial insomnia is a prion disease with a mutation in codon 178 of the PrP gene, but the disease phenotype seems to differ from that of previously described kindreds with the same point mutation.

The role of interneurons in neurovascular coupling was investigated by patch-clamp recordings in acute rat cortical slices, followed by single-cell reverse transcriptase-multiplex PCR (RT-mPCR) and confocal observation of biocytin-filled neurons, laminin-stained microvessels, and immunodetection of their afferents by vasoactive subcortical cholinergic (ACh) and serotonergic (5-HT) pathways. The evoked firing of single interneurons in whole-cell recordings was sufficient to either dilate or constrict neighboring microvessels. Identification of vasomotor interneurons by single-cell RT-mPCR revealed expression of vasoactive intestinal peptide (VIP) or nitric oxide synthase (NOS) in interneurons inducing dilatation and somatostatin (SOM) in those eliciting contraction. Constrictions appeared spatially restricted, maximal at the level of neurite apposition, and were associated with contraction of surrounding smooth muscle cells, providing the first evidence for neural regulation of vascular sphincters. Direct perfusion of VIP and NO donor onto the slices dilated microvessels, whereas neuropeptide Y (NPY) and SOM induced vasoconstriction. RT-PCR analyses revealed expression of specific subtypes of neuropeptide receptors in smooth muscle cells from intracortical microvessels, compatible with the vasomotor responses they elicited. By triple and quadruple immunofluorescence, the identified vasomotor interneurons established contacts with local microvessels and received, albeit to a different extent depending on interneuron subtypes, somatic and dendritic afferents from ACh and 5-HT pathways. Our results demonstrate the ability of specific subsets of cortical GABA interneurons to transmute neuronal signals into vascular responses and further suggest that they could act as local integrators of neurovascular coupling for subcortical vasoactive pathways.

The receptive field of a visual neuron is classically defined as the region of space (or retina) where a visual stimulus evokes a change in its firing activity. At the cortical level, a challenging issue concerns the roles of feedforward, local recurrent, intracortical, and cortico-cortical feedback connectivity in receptive field properties. Intracellular recordings in cat area 17 showed that the visually evoked synaptic integration field extends over a much larger area than that established on the basis of spike activity. Synaptic depolarizing responses to stimuli flashed at increasing distances from the center of the receptive field decreased in strength, whereas their onset latency increased. These findings suggest that subthreshold responses in the unresponsive region surrounding the classical discharge field result from the integration of visual activation waves spread by slowly conducting horizontal axons within primary visual cortex.

The antiepileptic effects of the organic calcium channel blocker verapamil were tested in non-drug-induced epileptiform activities. Low Mg2+ epileptic field potentials (EFP) were elicited in hippocampal slices of guinea pigs. Verapamil reduced frequency of occurrence and amplitude of EFP until EFP failed. The EFP reappeared if verapamil was withdrawn from low Mg2+ solution. Elevating the KCl concentration from 4 to 8 mM resulted in shortening of the latency of EFP abolition by verapamil and prolongation of the depressive effects of verapamil following its withdrawal. The findings indicate that transmembraneous calcium fluxes play also an essential role in low Mg(2+)-induced epileptiform activities.

1. Neurotransmitter-receptors in the membrane of Xenopus oocytes have been studied using electrophysiological techniques. Neurotransmitters and related agents were applied while recording either membrane potential or membrane current. The majority of ovarian oocytes used were at stages IV and V.2. Three types of oocytes were examined: inner ovarian epithelium covered (e.c.) oocytes; epithelium manually removed (e.r.) oocytes; and collagenase treated (c.t.) ooctyes.3. Ovarian oocytes are sensitive to some cholinergic and catecholaminergic agents. Responses to serotonin were seldom observed and when present were much weaker than responses to other agents. No responses were observed to the amino acids: aspartate, glutamate, gamma-aminobutyric acid, and glycine; or to octopamine and histamine.4. Acetylcholine (ACh) usually depolarized the membrane, in a dose-dependent manner, with threshold concentrations as low as 10(-9)m. The ACh-potential was due to an increase in Cl permeability and had a reversal potential around - 19 mV. The intracellular Cl ion activity, measured with a Cl-ion sensitive micro-electrode, was about 65 mm and the estimated Cl-ion equilibrium potential, E(Cl), agreed with the reversal potential of the ACh-potential.5. Curare (10(-4)m), tetrodotoxin (10(-6)m), or alpha-bungarotoxin (10(-6) g/ml.) did not block the response to 10(-6)m-ACh; whereas atropine (10(-7)m) blocked it. No response to nicotinic agents (e.g. nicotine, 1,1-dimethyl-4-phenylpiperazinium) was observed. These results suggest that the ACh receptors in the oocyte membrane are muscarinic in nature.6. The apparent latency of the ACh potential, examined by ionophoretic application of ACh to e.r. oocytes and c.t. oocytes, ranged from 0.5 sec to over 20 sec. Intracellular injection of ACh was without effect.7. Responses to catecholamines were observed mostly in e.c. oocytes; while in e.r. and c.t. oocytes they were rare and of very small amplitudes.8. The usual response to both dopamine and (-)-epinephrine was a transient hyperpolarization manifested by an initial increase in K-permeability followed by a decrease. The latency of these responses ranged from 10 sec to over 30 sec and their reversal potential was nearly - 100 mV, which coincided with E(K).9. Oocytes responded to the beta-adrenergic receptor agonist, isoproterenol, as well as (-)-epinephrine. Pre-treatment with the beta-adrenergic receptor blocker, propranolol, abolished the response to both (-)-epinephrine and (-)-isoproterenol. The dopamine potential was also reduced considerably. Both the alpha-adrenergic receptor agonist, phenylephrine, and the alpha-adrenergic receptor blocker, phentolamine, were without effect.10. Maturation of the oocytes, induced in vivo by gonadotropin or in vitro by progesterone, led to loss of responsiveness to both cholinergic and catecholaminergic agents.

The gliotransmitter D-serine is released upon (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate and metabotropic glutamate receptor stimulation, but the mechanisms involved are unknown. Here, by using a highly sensitive bioassay to continuously monitor extracellular D-serine levels, we have investigated the pathways used in its release. We reveal that D-serine release is inhibited by removal of extracellular calcium and augmented by increasing extracellular calcium or after treatment with the Ca(2+) ionophore A23187. Furthermore, release of the amino acid is considerably reduced after depletion of thapsigargin-sensitive intracellular Ca(2+) stores or chelation of intracellular Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate-acetoxymethyl ester. Interestingly, D-serine release also was markedly reduced by concanamycin A, a vacuolar-type H(+)-ATPase inhibitor, indicating a role for the vesicular proton gradient in the transmitter storage/release. In addition, agonist-evoked D-serine release was sensitive to tetanus neurotoxin. Finally, immunocytochemical and sucrose density gradient analysis revealed that a large fraction of D-serine colocalized with synaptobrevin/VAMP2, suggesting that it is stored in VAMP2-bearing vesicles. In summary, our study reveals the cellular mechanisms subserving D-serine release and highlights the importance of the glial cell exocytotic pathway in influencing CNS levels of extracellular D-serine.

The mushroom bodies, substructures of the Drosophila brain, are involved in olfactory learning and short-term memory, but their role in long-term memory is unknown. Here we show that the alpha-lobes-absent (ala) mutant lacks either the two vertical lobes of the mushroom body or two of the three median lobes which contain branches of vertical lobe neurons. This unique phenotype allows analysis of mushroom body function. Long-term memory required the presence of the vertical lobes but not the median lobes. Short-term memory was normal in flies without either vertical lobes or the two median lobes studied.

Recent research has demonstrated the suitability of adult zebrafish to model some aspects of complex behaviour. Studies of reward behaviour, learning and memory, aggression, anxiety and sleep strongly suggest that conserved regulatory processes underlie behaviour in zebrafish and mammals. The isolation and molecular analysis of zebrafish behavioural mutants is now starting, allowing the identification of novel behavioural control genes. As a result of this, studies of adult zebrafish are now helping to uncover the genetic pathways and neural circuits that control vertebrate behaviour.

Quantifying cell behaviors in animal early embryogenesis remains a challenging issue requiring in toto imaging and automated image analysis. We designed a framework for imaging and reconstructing unstained whole zebrafish embryos for their first 10 cell division cycles and report measurements along the cell lineage with micrometer spatial resolution and minute temporal accuracy. Point-scanning multiphoton excitation optimized to preferentially probe the innermost regions of the embryo provided intrinsic signals highlighting all mitotic spindles and cell boundaries. Automated image analysis revealed the phenomenology of cell proliferation. Blastomeres continuously drift out of synchrony. After the 32-cell stage, the cell cycle lengthens according to cell radial position, leading to apparent division waves. Progressive amplification of this process is the rule, contrasting with classical descriptions of abrupt changes in the system dynamics.

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

Cloning full length cDNAs is a difficult task especially if mRNAs are not abundant or if tissue is only available in limited amounts. Current strategies are based on in vitro amplification of cDNAs after adding a homopolymeric tail at the 3' end of the ss-cDNA. Since subsequent amplification steps yield unspecific amplified DNA mostly due to non-specific annealing of the reverse primer containing a homopolymeric tail, we have devised a new strategy based on the ligation of single-stranded oligodeoxyribonucleotide to the 3' end of single-stranded cDNAs. The efficiency of the strategy was assessed by analyzing the 5' ends of the rat pineal gland tryptophan hydroxylase messenger. The 5' end of the least abundant messenger (0.005% of total mRNAs) could be cloned without selection. Sixty percent of the analyzed clones correspond to TPH. This technique revealed a 5-nt stretch not apparent using dG tailing strategy. The potentiality of the method for generating cDNAs libraries was tested with 10(4) PC12 cells. In this library, the abundance of tyrosine hydroxylase clones (0.03%) correlated well with the abundance of the corresponding messenger, showing that no major distortion was introduced into the construction of the library.

Genome editing has now been reported in many systems using TALEN and CRISPR-Cas9 nucleases. Precise mutations can be introduced during homology-directed repair with donor DNA carrying the wanted sequence edit, but efficiency is usually lower than for gene knockout and optimal strategies have not been extensively investigated. Here, we show that using phosphorothioate-modified oligonucleotides strongly enhances genome editing efficiency of single-stranded oligonucleotide donors in cultured cells. In addition, it provides better design flexibility, allowing insertions more than 100 bp long. Despite previous reports of phosphorothioate-modified oligonucleotide toxicity, clones of edited cells are readily isolated and targeted sequence insertions are achieved in rats and mice with very high frequency, allowing for homozygous loxP site insertion at the mouse ROSA locus in particular. Finally, when detected, imprecise knockin events exhibit indels that are asymmetrically positioned, consistent with genome editing taking place by two steps of single-strand annealing.

Soon after its discovery, microRNA-9 (miR-9) attracted the attention of neurobiologists, since it is one of the most highly expressed microRNAs in the developing and adult vertebrate brain. Functional analyses in different vertebrate species have revealed a prominent role of this microRNA in balancing proliferation in embryonic neural progenitor populations. Key transcriptional regulators such as FoxG1, Hes1 or Tlx, were identified as direct targets of miR-9, placing it at the core of the gene network controlling the progenitor state. Recent data also suggest that this function could extend to adult neural stem cells. Other studies point to a role of miR-9 in differentiated neurons. Moreover miR-9 has been implicated in human brain pathologies, either displaying a protective role, such as in Progeria, or participating in disease progression in brain cancers. Altogether functional studies highlight a prominent feature of this highly conserved microRNA, its functional versatility, both along its evolutionary history and across cellular contexts.

Salicylate, the active component of aspirin, is known to induce tinnitus. However, the site and the mechanism of generation of tinnitus induced by salicylate remains unclear. Here, we developed a behavioral procedure to measure tinnitus in rats. The behavioral model was based on an active avoidance paradigm in which rats had to display a motor task (i.e., to jump on a climbing pole when hearing a sound). Giving salicylate led to a decrease in the percentage of correct responses (score) and a drastic increase in the number of false positive responses (i.e., animals execute the motor task during a silent period). Presentation of the sound at a constant perceptive level prevents decrease of the score, leading to the proposal that score is related to hearing performance. In contrast, the increase of false positive responses remained unchanged. In fact, animals behaved as if they hear a sound, indicating that they are experiencing tinnitus. Mefenamate in place of salicylate also increased the number of false positive responses, suggesting that salicylate-induced tinnitus is related to an inhibition of cyclooxygenase. One physiological basis of salicylate ototoxicity is likely to originate from altered arachidonic acid metabolism. Because arachidonic acid potentiates NMDA receptor currents, we tested the involvement of cochlear NMDA receptors in the occurrence of tinnitus. Application of NMDA antagonists into the perilymphatic fluids of the cochlea blocked the increase in pole-jumping behavior induced by salicylate, suggesting that salicylate induces tinnitus through activation of cochlear NMDA receptors.