Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 8 de 8
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Br J Pharmacol ; 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31652355

RESUMO

BACKGROUND AND PURPOSE: Excessive GABAergic inhibition contributes to cognitive dysfunctions in Down syndrome (DS). Selective negative allosteric modulators (NAMs) of α5-containing GABAA receptors such as the α5 inverse agonist (α5IA) restore learning and memory deficits in Ts65Dn mice, a model of DS. In this study we have assessed the long-lasting effects of α5IA on in vivo LTP and behaviour in Ts65Dn mice. EXPERIMENTAL APPROACH: We made in vivo LTP recordings for six consecutive days in freely moving Ts65Dn mice and their wild-type littermates, treated with vehicle or α5IA. In parallel, Ts65Dn mice were assessed by various learning and memory tests (Y maze, Morris water maze, or the novel object recognition) for up to 7 days, following one single injection of α5IA or vehicle. KEY RESULTS: LTP was not evoked in vivo in Ts65Dn mice at hippocampal CA3-CA1 synapses. However, this deficit was sustainably reversed for at least six consecutive days following a single injection of α5IA. This long-lasting effect of α5IA was also observed when assessing working and long-term memory deficits in Ts65Dn mice. CONCLUSION AND IMPLICATIONS: We show for the first time in vivo LTP deficits in Ts65Dn mice. These deficits were restored for at least 6 days following acute treatment with α5IA and might be the substrate for the long-lasting pharmacological effects of α5IA on spatial working and long-term recognition and spatial memory tasks. Our results demonstrate the relevance of negative allosteric modulators of α5-containing GABAA receptors to the treatment of cognitive deficits associated with DS.

2.
J Neurosci ; 39(18): 3360-3375, 2019 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-30755493

RESUMO

In the mature mammalian cochlea, inner hair cells (IHCs) are mainly innervated by afferent fibers that convey sound information to the CNS. During postnatal development, however, medial olivocochlear (MOC) efferent fibers transiently innervate the IHCs. The MOC-IHC synapse, functional from postnatal day 0 (P0) to hearing onset (P12), undergoes dramatic changes in the sensitivity to acetylcholine (ACh) and in the expression of key postsynaptic proteins. To evaluate whether there are associated changes in the properties of ACh release during this period, we used a cochlear preparation from mice of either sex at P4, P6-P7, and P9-P11 and monitored transmitter release from MOC terminals in voltage-clamped IHCs in the whole-cell configuration. The quantum content increased 5.6× from P4 to P9-P11 due to increases in the size and replenishment rate of the readily releasable pool of synaptic vesicles without changes in their probability of release or quantum size. This strengthening in transmission was accompanied by changes in short-term plasticity properties, which switched from facilitation at P4 to depression at P9-P11. We have previously shown that at P9-P11, ACh release is supported by P/Q- and N-type voltage-gated calcium channels (VGCCs) and negatively regulated by BK potassium channels activated by Ca2+ influx through L-type VGCCs. We now show that at P4 and P6-P7, release is mediated by P/Q-, R- and L-type VGCCs. Interestingly, L-type VGCCs have a dual role: they both support release and fuel BK channels, suggesting that at immature stages presynaptic proteins involved in release are less compartmentalized.SIGNIFICANCE STATEMENT During postnatal development before the onset of hearing, cochlear inner hair cells (IHCs) present spontaneous Ca2+ action potentials that release glutamate at the first auditory synapse in the absence of sound stimulation. The IHC Ca2+ action potential frequency pattern, which is crucial for the correct establishment and function of the auditory system, is regulated by the efferent medial olivocochlear (MOC) system that transiently innervates IHCs during this period. We show here that developmental changes in synaptic strength and synaptic plasticity properties at the MOC-IHC synapse upon MOC fiber activation at different frequencies might be crucial for tightly shaping the pattern of afferent activity during this critical period.

3.
Free Radic Biol Med ; 114: 33-39, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-28993272

RESUMO

Down syndrome (DS), also known as trisomy 21, is the most common genetic cause of intellectual disability. It is also a model human disease for exploring consequences of gene dosage imbalance on complex phenotypes. Learning and memory impairments linked to intellectual disabilities in DS could result from synaptic plasticity deficits and excitatory-inhibitory alterations leading to changes in neuronal circuitry in the brain of affected individuals. Increasing number of studies in mouse and cellular models converge towards the assumption that excitatory-inhibitory imbalance occurs in DS, likely early during development. Thus increased inhibition appears to be a common trend that could explain synaptic and circuit disorganization. Interestingly using several potent pharmacological tools, preclinical studies strongly demonstrated that cognitive deficits could be restored in mouse models of DS. Clinical trials have not yet provided robust data for therapeutic application and additional studies are needed. Here we review the literature and our own published work emphasizing the over-inhibition hypothesis in DS and their links with gene dosage imbalance paving the way for future basic and clinical research.


Assuntos
Transtornos Cognitivos/induzido quimicamente , Síndrome de Down/tratamento farmacológico , Antagonistas GABAérgicos/efeitos adversos , Receptores de GABA-A/química , Transdução de Sinais/efeitos dos fármacos , Animais , Modelos Animais de Doenças , Humanos , Receptores de GABA-A/efeitos dos fármacos
4.
J Physiol ; 595(24): 7477-7493, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29072780

RESUMO

KEY POINTS: GABAA receptors have been described in the axonal compartment of neurons; contrary to dendritic GABAA receptors, axonal GABAA receptors usually induce depolarizing responses. In this study we describe the presence of functional axonal GABAA receptors in cerebellar Purkinje cells by using a combination of direct patch-clamp recordings from the axon terminals and laser GABA photolysis. In Purkinje cells, axonal GABAA receptors are depolarizing and induce an increase in neurotransmitter release that results in a change of short-term synaptic plasticity. These results contribute to our understanding of the cellular mechanisms of action of axonal GABAA receptors and highlight the importance of the presynaptic compartment in neuronal computation. ABSTRACT: In neurons of the adult brain, somatodendritic GABAA receptors (GABAA Rs) mediate fast synaptic inhibition and play a crucial role in synaptic integration. GABAA Rs are not only present in the somatodendritic compartment, but also in the axonal compartment where they modulate action potential (AP) propagation and transmitter release. Although presynaptic GABAA Rs have been reported in various brain regions, their mechanisms of action and physiological roles remain obscure, particularly at GABAergic boutons. Here, using a combination of direct whole-bouton or perforated patch-clamp recordings and local GABA photolysis in single axonal varicosities of cerebellar Purkinje cells, we investigate the subcellular localization and functional role of axonal GABAA Rs both in primary cultures and acute slices. Our results indicate that presynaptic terminals of PCs carry GABAA Rs that behave as auto-receptors; their activation leads to a depolarization of the terminal membrane after an AP due to the relatively high cytoplasmic Cl- concentration in the axon, but they do not modulate the AP itself. Paired recordings from different terminals of the same axon show that the GABAA R-mediated local depolarizations propagate substantially to neighbouring varicosities. Finally, the depolarization mediated by presynaptic GABAA R activation augmented Ca2+ influx and transmitter release, resulting in a marked effect on short-term plasticity. Altogether, our results reveal a mechanism by which presynaptic GABAA Rs influence neuronal computation.


Assuntos
Potenciais de Ação , Exocitose , Terminações Pré-Sinápticas/metabolismo , Células de Purkinje/metabolismo , Receptores de GABA-A/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Células Cultivadas , Feminino , Masculino , Terminações Pré-Sinápticas/fisiologia , Células de Purkinje/fisiologia , Ratos , Ratos Wistar
5.
J Neurosci ; 33(39): 15477-87, 2013 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-24068816

RESUMO

The synapse between olivocochlear (OC) neurons and cochlear mechanosensory hair cells is cholinergic, fast, and inhibitory. The inhibitory sign of this cholinergic synapse is accounted for by the activation of Ca(2+)-permeable postsynaptic α9α10 nicotinic receptors coupled to the opening of hyperpolarizing Ca(2+)-activated small-conductance type 2 (SK2)K(+) channels. Acetylcholine (ACh) release at this synapse is supported by both P/Q- and N-type voltage-gated calcium channels (VGCCs). Although the OC synapse is cholinergic, an abundant OC GABA innervation is present along the mammalian cochlea. The role of this neurotransmitter at the OC efferent innervation, however, is for the most part unknown. We show that GABA fails to evoke fast postsynaptic inhibitory currents in apical developing inner and outer hair cells. However, electrical stimulation of OC efferent fibers activates presynaptic GABA(B(1a,2)) receptors [GABA(B(1a,2))Rs] that downregulate the amount of ACh released at the OC-hair cell synapse, by inhibiting P/Q-type VGCCs. We confirmed the expression of GABA(B)Rs at OC terminals contacting the hair cells by coimmunostaining for GFP and synaptophysin in transgenic mice expressing GABA(B1)-GFP fusion proteins. Moreover, coimmunostaining with antibodies against the GABA synthetic enzyme glutamic acid decarboxylase and synaptophysin support the idea that GABA is directly synthesized at OC terminals contacting the hair cells during development. Thus, we demonstrate for the first time a physiological role for GABA in cochlear synaptic function. In addition, our data suggest that the GABA(B1a) isoform selectively inhibits release at efferent cholinergic synapses.


Assuntos
Células Ciliadas Auditivas/fisiologia , Potenciais Pós-Sinápticos Inibidores , Receptores de GABA-B/metabolismo , Sinapses/fisiologia , Acetilcolina/metabolismo , Animais , Canais de Cálcio Tipo P/metabolismo , Canais de Cálcio Tipo Q/metabolismo , Neurônios Colinérgicos/metabolismo , Neurônios Colinérgicos/fisiologia , Estimulação Elétrica , Células Ciliadas Auditivas/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Neurônios Eferentes/fisiologia , Receptores de GABA-B/genética , Sinapses/metabolismo , Sinaptofisina/genética , Sinaptofisina/metabolismo , Ácido gama-Aminobutírico/metabolismo
6.
J Neurosci ; 31(41): 14763-74, 2011 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-21994392

RESUMO

In the mammalian inner ear, the gain control of auditory inputs is exerted by medial olivocochlear (MOC) neurons that innervate cochlear outer hair cells (OHCs). OHCs mechanically amplify the incoming sound waves by virtue of their electromotile properties while the MOC system reduces the gain of auditory inputs by inhibiting OHC function. How this process is orchestrated at the synaptic level remains unknown. In the present study, MOC firing was evoked by electrical stimulation in an isolated mouse cochlear preparation, while OHCs postsynaptic responses were monitored by whole-cell recordings. These recordings confirmed that electrically evoked IPSCs (eIPSCs) are mediated solely by α9α10 nAChRs functionally coupled to calcium-activated SK2 channels. Synaptic release occurred with low probability when MOC-OHC synapses were stimulated at 1 Hz. However, as the stimulation frequency was raised, the reliability of release increased due to presynaptic facilitation. In addition, the relatively slow decay of eIPSCs gave rise to temporal summation at stimulation frequencies >10 Hz. The combined effect of facilitation and summation resulted in a frequency-dependent increase in the average amplitude of inhibitory currents in OHCs. Thus, we have demonstrated that short-term plasticity is responsible for shaping MOC inhibition and, therefore, encodes the transfer function from efferent firing frequency to the gain of the cochlear amplifier.


Assuntos
Cóclea/citologia , Nervo Coclear/fisiologia , Células Ciliadas Auditivas/fisiologia , Inibição Neural/fisiologia , Sinapses/fisiologia , Estimulação Acústica , Animais , Animais Recém-Nascidos , Biofísica , Quelantes , Ácido Egtázico/análogos & derivados , Ácido Egtázico/farmacologia , Estimulação Elétrica , Feminino , Glicinérgicos/farmacologia , Células Ciliadas Auditivas/efeitos dos fármacos , Técnicas In Vitro , Indóis/farmacologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Inibição Neural/efeitos dos fármacos , Técnicas de Patch-Clamp/métodos , Peptídeos/farmacologia , Antagonistas da Serotonina/farmacologia , Bloqueadores dos Canais de Sódio/farmacologia , Estricnina/farmacologia , Sinapses/efeitos dos fármacos , Temperatura Ambiente , Tetrodotoxina/farmacologia , Fatores de Tempo , Tropizetrona
7.
J Neurosci ; 30(36): 12157-67, 2010 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-20826678

RESUMO

In the mammalian auditory system, the synapse between efferent olivocochlear (OC) neurons and sensory cochlear hair cells is cholinergic, fast, and inhibitory. This efferent synapse is mediated by the nicotinic alpha9alpha10 receptor coupled to the activation of SK2 Ca(2+)-activated K(+) channels that hyperpolarize the cell. So far, the ion channels that support and/or modulate neurotransmitter release from the OC terminals remain unknown. To identify these channels, we used an isolated mouse cochlear preparation and monitored transmitter release from the efferent synaptic terminals in inner hair cells (IHCs) voltage clamped in the whole-cell recording configuration. Acetylcholine (ACh) release was evoked by electrically stimulating the efferent fibers that make axosomatic contacts with IHCs before the onset of hearing. Using the specific antagonists for P/Q- and N-type voltage-gated calcium channels (VGCCs), omega-agatoxin IVA and omega-conotoxin GVIA, respectively, we show that Ca(2+) entering through both types of VGCCs support the release process at this synapse. Interestingly, we found that Ca(2+) entering through the dihydropiridine-sensitive L-type VGCCs exerts a negative control on transmitter release. Moreover, using immunostaining techniques combined with electrophysiology and pharmacology, we show that BK Ca(2+)-activated K(+) channels are transiently expressed at the OC efferent terminals contacting IHCs and that their activity modulates the release process at this synapse. The effects of dihydropiridines combined with iberiotoxin, a specific BK channel antagonist, strongly suggest that L-type VGCCs negatively regulate the release of ACh by fueling BK channels that are known to curtail the duration of the terminal action potential in several types of neurons.


Assuntos
Cálcio/metabolismo , Células Ciliadas Auditivas Internas/citologia , Órgão Espiral/citologia , Canais de Potássio Cálcio-Ativados/fisiologia , Sinapses/fisiologia , Transmissão Sináptica/fisiologia , Acetilcolina/metabolismo , Animais , Animais Recém-Nascidos , Biofísica/métodos , Bloqueadores dos Canais de Cálcio/farmacologia , Relação Dose-Resposta a Droga , Estimulação Elétrica/métodos , Feminino , Técnicas In Vitro , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Núcleo Olivar/citologia , Técnicas de Patch-Clamp/métodos , Peptídeos/farmacologia , Bloqueadores dos Canais de Potássio/farmacologia , Canais de Potássio Cálcio-Ativados/antagonistas & inibidores , Sinapses/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos
8.
J Assoc Res Otolaryngol ; 8(4): 474-83, 2007 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17647061

RESUMO

The efferent synaptic specialization of hair cells includes a near-membrane synaptic cistern, whose presence suggests a role for internal calcium stores in cholinergic inhibition. Calcium release channels from internal stores include 'ryanodine receptors', whose participation is usually demonstrated by sensitivity to the eponymous plant alkaloid, ryanodine. However, use of this and other store-active compounds on hair cells could be confounded by the unusual pharmacology of the alpha9alpha10-containing hair cell nicotinic cholinergic receptor (nAChR), which has been shown to be antagonized by a broad spectrum of compounds. Surprisingly, we found that ryanodine, rather than antagonizing, is a positive modulator of the alpha9alpha10 nAChR expressed in Xenopus oocytes, the first such compound to be found. The effect of ryanodine was to increase the apparent affinity and efficacy for acetylcholine (ACh). Correspondingly, ACh-evoked currents through the isolated cholinergic receptors of inner hair cells in excised mouse cochleas were approximately doubled by 200 microM ryanodine, a concentration that inhibits gating of the ryanodine receptor itself. This unusual positive modulation was not unique to the mammalian receptor. The response to ACh of chicken 'short' hair cells likewise was enhanced in the presence of 100 microM ryanodine. This facilitatory effect on current through the AChR could enhance brief ( approximately 1 s) activation of associated calcium-dependent K(+) (SK) channels in both chicken short hair cells and rat outer hair cells. This novel effect of ryanodine provides new opportunities for the design of compounds that potentiate alpha9alpha10-mediated responses and for potential inner ear therapeutics based on this interaction.


Assuntos
Células Ciliadas Auditivas/efeitos dos fármacos , Ativação do Canal Iônico/efeitos dos fármacos , Receptores Colinérgicos/efeitos dos fármacos , Rianodina/farmacologia , Acetilcolina/farmacologia , Animais , Galinhas , Relação Dose-Resposta a Droga , Células Ciliadas Auditivas/fisiologia , Camundongos , Canais de Potássio Cálcio-Ativados/efeitos dos fármacos , Canais de Potássio Cálcio-Ativados/fisiologia , Subunidades Proteicas/análise , Ratos , Receptores Colinérgicos/fisiologia , Receptores Nicotínicos/análise , Xenopus laevis
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA