RESUMO
UNLABELLED: Sensory perception emerges from the confluence of sensory inputs that encode the composition of external environment and top-down feedback that conveys information from higher brain centers. In olfaction, sensory input activity is initially processed in the olfactory bulb (OB), serving as the first central relay before being transferred to the olfactory cortex. In addition, the OB receives dense connectivity from feedback projections, so the OB has the capacity to implement a wide array of sensory neuronal computation. However, little is known about the impact and the regulation of this cortical feedback. Here, we describe a novel mechanism to gate glutamatergic feedback selectively from the anterior olfactory cortex (AOC) to the OB. Combining in vitro and in vivo electrophysiological recordings, optogenetics, and fiber-photometry-based calcium imaging applied to wild-type and conditional transgenic mice, we explore the functional consequences of circuit-specific GABA type-B receptor (GABABR) manipulation. We found that activation of presynaptic GABABRs specifically depresses synaptic transmission from the AOC to OB inhibitory interneurons, but spares direct excitation to principal neurons. As a consequence, feedforward inhibition of spontaneous and odor-evoked activity of principal neurons is diminished. We also show that tunable cortico-bulbar feedback is critical for generating beta, but not gamma, OB oscillations. Together, these results show that GABABRs on cortico-bulbar afferents gate excitatory transmission in a target-specific manner and thus shape how the OB integrates sensory inputs and top-down information. SIGNIFICANCE STATEMENT: The olfactory bulb (OB) receives top-down inputs from the olfactory cortex that produce direct excitation and feedforward inhibition onto mitral and tufted cells, the principal neurons. The functional role of this feedback and the mechanisms regulating the balance of feedback excitation and inhibition remain unknown. We found that GABAB receptors are expressed in cortico-bulbar axons that synapse on granule cells and receptor activation reduces the feedforward inhibition of spontaneous and odor-driven mitral and tufted cells' firing activity. In contrast, direct excitatory inputs to these principal neurons remain unchanged. This study demonstrates that activation of GABAB receptors biases the excitation/inhibition balance provided by cortical inputs to the OB, leading to profound effects on early stages of sensory information processing.
Assuntos
Potenciais Pós-Sinápticos Excitadores/fisiologia , Retroalimentação , Bulbo Olfatório/citologia , Córtex Olfatório/citologia , Receptores de GABA-B/metabolismo , Olfato/fisiologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Anestésicos Locais/farmacologia , Animais , Quinase da Proteína Quinase Dependente de Cálcio-Calmodulina/genética , Quinase da Proteína Quinase Dependente de Cálcio-Calmodulina/metabolismo , Channelrhodopsins , Agonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Técnicas In Vitro , Lidocaína/farmacologia , Luz , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Odorantes , Condutos Olfatórios/fisiologia , Quinoxalinas/farmacologia , Receptores de GABA-B/genéticaRESUMO
The production of new neurons in the olfactory bulb (OB) through adulthood is a major mechanism of structural and functional plasticity underlying learning-induced circuit remodeling. The recruitment of adult-born OB neurons depends not only on sensory input but also on the context in which the olfactory stimulus is received. Among the multiple steps of adult neurogenesis, the integration and survival of adult-born neurons are both strongly influenced by olfactory learning. Conversely, optogenetic stimulation of adult-born neurons has been shown to specifically improve olfactory learning and long-term memory. However, the nature of the circuit and the synaptic mechanisms underlying this reciprocal influence are not yet known. Here, we showed that olfactory learning increases the spine density in a region-restricted manner along the dendritic tree of adult-born granule cells (GCs). Anatomical and electrophysiological analysis of adult-born GCs showed that olfactory learning promotes a remodeling of both excitatory and inhibitory inputs selectively in the deep dendritic domain. Circuit mapping revealed that the malleable dendritic portion of adult-born neurons receives excitatory inputs mostly from the regions of the olfactory cortex that project back to the OB. Finally, selective optogenetic stimulation of olfactory cortical projections to the OB showed that learning strengthens these inputs onto adult-born GCs. We conclude that learning promotes input-specific synaptic plasticity in adult-born neurons, which reinforces the top-down influence from the olfactory cortex to early stages of olfactory information processing.
Assuntos
Dendritos/metabolismo , Memória de Longo Prazo/fisiologia , Neurogênese/fisiologia , Plasticidade Neuronal/fisiologia , Bulbo Olfatório/metabolismo , Condutos Olfatórios/metabolismo , Animais , Masculino , Camundongos , Camundongos Transgênicos , Bulbo Olfatório/citologia , Condutos Olfatórios/citologiaRESUMO
Sensory perception depends on interactions between external inputs transduced by peripheral sensory organs and internal network dynamics generated by central neuronal circuits. In the sensory cortex, desynchronized network states associate with high signal-to-noise ratio stimulus-evoked responses and heightened perception. Cannabinoid-type-1-receptors (CB1Rs) - which influence network coordination in the hippocampus - are present in anterior piriform cortex (aPC), a sensory paleocortex supporting olfactory perception. Yet, how CB1Rs shape aPC network activity and affect odor perception is unknown. Using pharmacological manipulations coupled with multi-electrode recordings or fiber photometry in the aPC of freely moving male mice, we show that systemic CB1R blockade as well as local drug infusion increases the amplitude of gamma oscillations in aPC, while simultaneously reducing the occurrence of synchronized population events involving aPC excitatory neurons. In animals exposed to odor sources, blockade of CB1Rs reduces correlation among aPC excitatory units and lowers behavioral olfactory detection thresholds. These results suggest that endogenous endocannabinoid signaling promotes synchronized population events and dampen gamma oscillations in the aPC which results in a reduced sensitivity to external sensory inputs.
Assuntos
Canabinoides , Percepção Olfatória , Córtex Piriforme , Camundongos , Masculino , Animais , Percepção Olfatória/fisiologia , Endocanabinoides , Olfato/fisiologia , Odorantes , Canabinoides/farmacologia , Condutos Olfatórios/fisiologia , Bulbo Olfatório/fisiologiaRESUMO
In mammals, olfactory bulb granule cells (GCs) are generated throughout life in the subventricular zone. GABAergic inputs onto newborn neurons likely regulate their maturation, but the details of this process remain still elusive. Here, we investigated the differentiation, synaptic integration, and survival of adult-born GCs when their afferent GABAergic inputs are challenged by conditional gene targeting. Migrating GC precursors were targeted with Cre-eGFP-expressing lentiviral vectors in mice with a floxed gene encoding the GABA(A) receptor α2-subunit (i.e., Gabra2). Ablation of the α2-subunit did not affect GC survival but dramatically delayed their maturation. We found a reduction in postsynaptic α2-subunit and gephyrin clusters accompanied by a decrease in the frequency and amplitude of GABAergic postsynaptic currents beginning â¼14 d post-injection (dpi). In addition, mutant cells exhibited altered dendritic branching and spine density. Spine loss appeared with mislocation of glutamatergic synapses on dendritic shafts and a reduction of spontaneous glutamatergic postsynaptic currents, underscoring the relevance of afferent GABAergic transmission for a proper synaptic integration of newborn GCs. To test the role of GABAergic signaling during much early stages of GC maturation, we used a genetic strategy to selectively inactivate Gabra2 in precursor cells of the subventricular zone. In these mice, labeling of newborn GCs with eGFP lentiviruses revealed similar morphological alterations as seen on delayed Gabra2 inactivation in migrating neuroblasts, with reduced dendritic branching and spine density at 7 dpi. Collectively, these results emphasize the critical role of GABAergic synaptic signaling for structural maturation of adult-born GCs and formation of glutamatergic synapses.
Assuntos
Células-Tronco Adultas/fisiologia , Neurônios GABAérgicos/fisiologia , Neurônios/fisiologia , Bulbo Olfatório/citologia , Sinapses/fisiologia , Análise de Variância , Animais , Animais Recém-Nascidos , Área Sob a Curva , Proteínas de Transporte/metabolismo , Dendritos/fisiologia , Estimulação Elétrica , Transportador 1 de Aminoácido Excitatório/genética , Lobo Frontal/citologia , Lobo Frontal/fisiologia , Regulação da Expressão Gênica/genética , Proteínas de Fluorescência Verde/genética , Herbicidas/toxicidade , Técnicas In Vitro , Potenciais Pós-Sinápticos Inibidores/genética , Integrases/genética , Integrases/metabolismo , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Microscopia Confocal , Microscopia Imunoeletrônica , Proteínas do Tecido Nervoso , Neurônios/citologia , Neurônios/ultraestrutura , Nitrilas/toxicidade , Odorantes , Bulbo Olfatório/efeitos dos fármacos , Bulbo Olfatório/lesões , Técnicas de Patch-Clamp , Receptores de GABA/metabolismo , Receptores de GABA-A/genética , Privação Sensorial/fisiologia , Sinapses/genética , Sinapses/ultraestrutura , Tamoxifeno/farmacologiaRESUMO
Neuronal precursors are continuously integrated into the adult olfactory bulb (OB). The vast majority of these precursor cells originates from the subventricular zone and migrates along the rostral migratory stream (RMS) en route to the OB. This process, called postnatal neurogenesis, results from intricate pathways depending both on cell-autonomous factors and extrinsic regulation provided by the local environment. Using electroporation in postnatal mice to label neuronal precursors with green fluorescent protein (GFP) and to reduce the expression levels of doublecortin (DCX) with short-hairpin (Sh) RNA, we investigated the consequences of impairing migration on the fate of postnatal-formed neurons. First, we showed that electroporation of Dcx ShRNA plasmid efficiently knocks down the expression of DCX and disrupts cells migration along the RMS. Second, we found misplaced anomalous migrating cells that displayed defects in polarity and directionality. Third, patch-clamp recordings performed at 5-7 days post-electroporation (dpe) revealed increased density of voltage-dependent Na(+) channels and enhanced responsiveness to GABA(A) receptor agonist. At later time points (i.e., 12 and 30 dpe), most of the Dcx ShRNA(+) cells developed in the core of the OB and displayed aberrant dendritic length and branching. Additional analysis revealed the formation of GABAergic and glutamatergic synaptic inputs on the mispositioned neurons. Finally, quantifying fate determination by numbering the proportion of GFP(+)/calretinin(+) newborn neurons revealed that Dcx ShRNA(+) cells acquire mature phenotype despite their immature location. We conclude that altering the pace of migration at early stages of postnatal neurogenesis profoundly modifies the tightly orchestrated steps of neuronal maturation, and unveils the influence of microenvironment on controlling neuronal development in the postnatal forebrain.
Assuntos
Movimento Celular/fisiologia , Neurogênese/fisiologia , Neurônios/fisiologia , Bulbo Olfatório/crescimento & desenvolvimento , Animais , Animais Recém-Nascidos , Proteínas do Domínio Duplacortina , Proteína Duplacortina , Camundongos , Camundongos Endogâmicos C57BL , Proteínas Associadas aos Microtúbulos/deficiência , Proteínas Associadas aos Microtúbulos/genética , Neurônios/citologia , Neuropeptídeos/deficiência , Neuropeptídeos/genética , Bulbo Olfatório/citologiaRESUMO
The fragile X mental retardation protein (FMRP) is an RNA-binding protein essential for multiple aspects of neuronal mRNA metabolism. Its absence leads to the fragile X syndrome, the most prevalent genetic form of mental retardation. The anatomical landmark of the disease, also present in the Fmr1 knock-out (KO) mice, is the hyperabundance of immature-looking lengthened dendritic spines. We used the well known continuous production of adult-born granule cells (GCs) in the mouse olfactory bulb (OB) to analyze the consequences of Fmrp loss on the differentiation of GCs. Morphological analysis of GCs in the Fmr1 KO mice showed an increase in spine density without a change in spine length. We developed an RNA interference strategy to cell-autonomously mutate Fmr1 in a wild-type OB network. Mutated GCs displayed an increase in spine density and spine length. Detailed analysis of the spines through immunohistochemistry, electron microscopy, and electrophysiology surprisingly showed that, despite these abnormalities, spines receive normal glutamatergic synapses, and thus that mutated adult-born neurons are synaptically integrated into the OB circuitry. Time-course analysis of the spine defects showed that Fmrp cell-autonomously downregulates the level and rate of spine production and limits their overgrowth. Finally, we report that Fmrp does not regulate dendritogenesis in standard conditions but is necessary for activity-dependent dendritic remodeling. Overall, our study of Fmrp in the context of adult neurogenesis has enabled us to carry out a precise dissection of the role of Fmrp in neuronal differentiation and underscores its pleiotropic involvement in both spinogenesis and dendritogenesis.
Assuntos
Diferenciação Celular/genética , Proteína do X Frágil da Deficiência Intelectual/metabolismo , Neurogênese/fisiologia , Neurônios/fisiologia , Bulbo Olfatório/citologia , Análise de Variância , Animais , Diferenciação Celular/efeitos dos fármacos , Dendritos/efeitos dos fármacos , Dendritos/fisiologia , Dendritos/ultraestrutura , Espinhas Dendríticas/efeitos dos fármacos , Espinhas Dendríticas/fisiologia , Espinhas Dendríticas/ultraestrutura , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/genética , Proteína do X Frágil da Deficiência Intelectual/genética , Proteínas de Fluorescência Verde/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia Eletrônica de Transmissão , Mutação/genética , Neurogênese/genética , Neurônios/efeitos dos fármacos , Técnicas de Patch-Clamp/métodos , RNA Interferente Pequeno/farmacologia , Sinapses/metabolismo , Sinapses/ultraestrutura , Fatores de TempoRESUMO
In the olfactory system, the olfactory cortex sends glutamatergic projections back to the first stage of olfactory processing, the olfactory bulb (OB). Such corticofugal excitatory circuits - a canonical circuit motif described in all sensory systems- dynamically adjust early sensory processing. Here, we uncover a corticofugal inhibitory feedback to OB, originating from a subpopulation of GABAergic neurons in the anterior olfactory cortex and innervating both local and output OB neurons. In vivo imaging and network modeling showed that optogenetic activation of cortical GABAergic projections drives a net subtractive inhibition of both spontaneous and odor-evoked activity in local as well as output neurons. In output neurons, stimulation of cortical GABAergic feedback enhances separation of population odor responses in tufted cells, but not mitral cells. Targeted pharmacogenetic silencing of cortical GABAergic axon terminals impaired discrimination of similar odor mixtures. Thus, corticofugal GABAergic projections represent an additional circuit motif in cortical feedback control of sensory processing.
Assuntos
Bulbo Olfatório , Olfato , Retroalimentação , Bulbo Olfatório/fisiologia , Olfato/fisiologia , Odorantes , Neurônios GABAérgicos/fisiologia , Percepção , Condutos Olfatórios/fisiologiaRESUMO
Gut bacteria influence brain functions and metabolism. We investigated whether this influence can be mediated by direct sensing of bacterial cell wall components by brain neurons. In mice, we found that bacterial peptidoglycan plays a major role in mediating gut-brain communication via the Nod2 receptor. Peptidoglycan-derived muropeptides reach the brain and alter the activity of a subset of brain neurons that express Nod2. Activation of Nod2 in hypothalamic inhibitory neurons is essential for proper appetite and body temperature control, primarily in females. This study identifies a microbe-sensing mechanism that regulates feeding behavior and host metabolism.
Assuntos
Proteína Adaptadora de Sinalização NOD2 , Peptidoglicano , Animais , Apetite , Bactérias/genética , Bactérias/metabolismo , Temperatura Corporal , Camundongos , Neurônios/metabolismo , Proteína Adaptadora de Sinalização NOD2/genética , Proteína Adaptadora de Sinalização NOD2/metabolismo , Peptidoglicano/metabolismoRESUMO
In adult mammals, thousands of new neurons integrate in the olfactory bulb (OB) each day. This process of adult neurogenesis has received a great deal of scientific attention aimed at understanding how mature neural networks withstand neuronal replacement, and medical interest to explore the promise that these cells may be manipulated for brain repair therapies. In the present review, we focus on the mechanisms and consequences of the functional integration of newborn interneurons in the OB network. We first describe the steps of synaptic integration and functional maturation of adult-born interneurons in the OB. We then examine the physiological control of cell maturation and survival. Finally, we explore the potential impact of adult neurogenesis on the function of the OB.
Assuntos
Células-Tronco Adultas/fisiologia , Neurônios/fisiologia , Bulbo Olfatório/citologia , Sinapses/fisiologia , Células-Tronco Adultas/citologia , Animais , Diferenciação Celular , Rede Nervosa/anatomia & histologia , Rede Nervosa/fisiologia , Neurogênese/fisiologia , Neurônios/citologia , Bulbo Olfatório/fisiologiaRESUMO
New olfactory bulb granule cells (GCs) are GABAergic interneurons continuously arising from neuronal progenitors and integrating into preexisting bulbar circuits. They receive both GABAergic and glutamatergic synaptic inputs from olfactory bulb intrinsic neurons and centrifugal afferents. Here, we investigated the spatiotemporal dynamic of newborn GC synaptogenesis in adult mouse olfactory bulb. First, we established that GABAergic synapses onto mature GC dendrites contain the GABA(A) receptor alpha2 subunit along with the postsynaptic scaffolding protein gephyrin. Next, we characterized morphologically and electrophysiologically the development of GABAergic and glutamatergic inputs onto newborn GCs labeled with eGFP (enhanced green fluorescent protein) using lentiviral vectors. Already when reaching the GC layer (GCL), at 3 d post-vector injection (dpi), newborn GCs exhibited tiny voltage-dependent sodium currents and received functional GABAergic and glutamatergic synapses, recognized immunohistochemically by apposition of specific presynaptic and postsynaptic markers. Thereafter, GABAergic and glutamatergic synaptic contacts increased differentially in the GCL, and at 7 dpi, PSD-95 clusters outnumbered gephyrin clusters. Thus, the weight of GABAergic input was predominant at early stages of GC maturation, but not later. Newborn GC dendrites first reached the external plexiform layer at 4 dpi, where they received functional GABAergic contacts at 5 dpi. Reciprocal synapses initially were formed on GC dendritic shafts, where they might contribute to spine formation. Their presence was confirmed ultrastructurally at 7 dpi. Together, our findings unravel rapid synaptic integration of newborn GCs in adult mouse olfactory bulb, with GABAergic and glutamatergic influences being established proximally before formation of output synapses by apical GC dendrites onto mitral/tufted cells.
Assuntos
Interneurônios/fisiologia , Neurogênese/fisiologia , Bulbo Olfatório/citologia , Sinapses/fisiologia , Análise de Variância , Animais , Biofísica , Proteínas de Transporte/metabolismo , Diferenciação Celular , Dendritos/metabolismo , Dendritos/ultraestrutura , Estimulação Elétrica , Antagonistas de Aminoácidos Excitatórios/farmacologia , Glutamato Descarboxilase/genética , Proteínas de Fluorescência Verde/genética , Técnicas In Vitro , Interneurônios/metabolismo , Interneurônios/ultraestrutura , Masculino , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Microscopia Imunoeletrônica/métodos , N-Metilaspartato/farmacologia , Neurogênese/efeitos dos fármacos , Bulbo Olfatório/ultraestrutura , Técnicas de Patch-Clamp/métodos , Terminações Pré-Sinápticas/metabolismo , Terminações Pré-Sinápticas/ultraestrutura , Receptores de GABA-A/metabolismo , Sinapses/ultraestrutura , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiônico/farmacologia , Ácido gama-Aminobutírico/metabolismo , Ácido gama-Aminobutírico/farmacologiaRESUMO
The first synapse in olfaction undergoes considerable anatomical plasticity in both early postnatal development and adult neurogenesis, yet we know very little concerning its functional maturation at these times. Here, we used whole-cell recordings in olfactory bulb slices to describe olfactory nerve inputs to developing postnatal neurons and to maturing adult-born cells labeled with a GFP-encoding lentivirus. In both postnatal development and adult neurogenesis, the maturation of olfactory nerve synapses involved an increase in the relative contribution of AMPA over NMDA receptors, and a decrease in the contribution of NMDA receptors containing the NR2B subunit. These postsynaptic transformations, however, were not mirrored by presynaptic changes: in all cell groups, paired-pulse depression remained constant as olfactory nerve synapses matured. Although maturing cells may therefore offer, transiently, a functionally distinct connection for inputs from the nose, presynaptic function at the first olfactory connection remains remarkably constant in the face of considerable anatomical plasticity.
Assuntos
Plasticidade Neuronal/fisiologia , Neurônios/citologia , Neurônios/fisiologia , Olfato/fisiologia , Sinapses/fisiologia , Animais , Animais Recém-Nascidos , Diferenciação Celular/fisiologia , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BLRESUMO
ClC-K2, a member of the ClC family of Cl(-) channels and transporters, forms the major basolateral Cl(-) conductance in distal nephron epithelial cells and therefore plays a central role in renal Cl(-) absorption. However, its regulation remains largely unknown because of the fact that recombinant ClC-K2 has not yet been studied at the single-channel level. In the present study, we investigate the effects of voltage, pH, Cl(-), and Ca(2+) on native ClC-K2 in the basolateral membrane of intercalated cells from the mouse connecting tubule. The â¼10-pS channel shows a steep voltage dependence such that channel activity increases with membrane depolarization. Intracellular pH (pHi) and extracellular pH (pHo) differentially modulate the voltage dependence curve: alkaline pHi flattens the curve by causing an increase in activity at negative voltages, whereas alkaline pHo shifts the curve toward negative voltages. In addition, pHi, pHo, and extracellular Ca(2+) strongly increase activity, mainly because of an increase in the number of active channels with a comparatively minor effect on channel open probability. Furthermore, voltage alters both the number of active channels and their open probability, whereas intracellular Cl(-) has little influence. We propose that changes in the number of active channels correspond to them entering or leaving an inactivated state, whereas modulation of open probability corresponds to common gating by these channels. We suggest that pH, through the combined effects of pHi and pHo on ClC-K2, might be a key regulator of NaCl absorption and Cl(-)/HCO3 (-) exchange in type B intercalated cells.
Assuntos
Proteínas de Transporte de Ânions/metabolismo , Canais de Cloreto/metabolismo , Néfrons/metabolismo , Animais , Cálcio/metabolismo , Membrana Celular/metabolismo , Cloretos/metabolismo , Concentração de Íons de Hidrogênio , Ativação do Canal Iônico/fisiologia , Masculino , Camundongos , Cloreto de Sódio/metabolismoRESUMO
The distal-convoluted tubule (DCT) of the kidney absorbs NaCl mainly via an Na+-Cl- cotransporter located at the apical membrane, and Na+, K+ ATPase at the basolateral side. Cl- transport across the basolateral membrane is thought to be conductive, but the corresponding channels have not yet been characterized. In the present study, we investigated Cl- channels on microdissected mouse DCTs using the patch-clamp technique. A channel of approximately 9 pS was found in 50% of cell-attached patches showing anionic selectivity. The NPo in cell-attached patches was not modified when tubules were preincubated in the presence of 10-5 M forskolin, but the channel was inhibited by phorbol ester (10-6 M). In addition, NPo was significantly elevated when the calcium in the pipette was increased from 0 to 5 mM (NPo increased threefold), or pH increased from 6.4 to 8.0 (NPo increased 15-fold). Selectivity experiments conducted on inside-out patches showed that the Na+ to Cl- relative permeability was 0.09, and the anion selectivity sequence Cl(-)--I(-) > Br(-)--NO3(-) > F(-). Intracellular NPPB (10-4 M) and DPC (10-3 M) blocked the channel by 65% and 80%, respectively. The channel was inhibited at acid intracellular pH, but intracellular ATP and PKA had no effect. ClC-K Cl- channels are characterized by their sensitivity to the external calcium and to pH. Since immunohistochemical data indicates that ClC-K2, and perhaps ClC-K1, are present on the DCT basolateral membrane, we suggest that the channel detected in this study may belong to this subfamily of the ClC channel family.
Assuntos
Membrana Celular/fisiologia , Canais de Cloreto/classificação , Canais de Cloreto/fisiologia , Potenciais da Membrana/fisiologia , Animais , Cálcio/metabolismo , Membrana Celular/química , Membrana Celular/efeitos dos fármacos , Células Cultivadas , Canais de Cloreto/química , Colforsina/farmacologia , Condutividade Elétrica , Concentração de Íons de Hidrogênio , Ativação do Canal Iônico/efeitos dos fármacos , Ativação do Canal Iônico/fisiologia , Túbulos Renais Distais , Masculino , Potenciais da Membrana/efeitos dos fármacos , Camundongos , Proteína Quinase C/metabolismo , Acetato de Tetradecanoilforbol/farmacologiaRESUMO
Chloride channels located on the basolateral membrane are known to be involved in chloride absorption in several parts of the renal tubule, and particularly in the thick ascending limb and distal convoluted tubule. The data available suggest that the ClC-K channels play the major role in this process. We provide here a description of the electrophysiological properties of these channels, still very incomplete at this stage, and we attempt to compare ClC-Ks to three chloride channels that we have identified in the basolateral membrane of microdissected fragments of the mouse renal tubule using the patch-clamp technique. Based on anion selectivity and dependence on external pH and calcium shown by the ClC-Ks, we propose candidate ClC-K1 and ClC-K2 in native tissue. We also discuss the possibility that chloride channels that do not belong to the ClC family may also be involved in the absorption of chloride across the cortical thick ascending limb.
Assuntos
Cloro/metabolismo , Ativação do Canal Iônico/fisiologia , Túbulos Renais Distais/fisiologia , Animais , Canais de Cloreto , Humanos , CamundongosRESUMO
For a long time, the mammalian brain has been perceived to be a static organ. However, the discovery of adult neurogenesis in most mammalian species, including humans, monkeys, and rodents, has disrupted this view. As this continuous regeneration has an effect on established behavioral patterns, it holds promising therapeutic potential. However, before harnessing this potential regenerative power, we must understand what effects new neurons have on existing brain circuits. Ongoing research contributes to several important steps toward bridging the gap between adult-born neurons, circuits, and behavior. The study of adult neurogenesis in different neurogenic regions from a systems neuroscience perspective will pave the way to understanding how it supports adaptive behavior and why its dysfunction correlates with some human brain disorders.
Assuntos
Encefalopatias/fisiopatologia , Pareamento Cromossômico/fisiologia , Rede Nervosa/fisiologia , Neurogênese/fisiologia , Neurônios/fisiologia , Medicina Regenerativa/tendências , Rejuvenescimento/fisiologia , Adulto , Pesquisa Biomédica/tendências , Previsões , Hipocampo/fisiologia , Humanos , Rememoração Mental/fisiologia , Plasticidade Neuronal/fisiologiaRESUMO
Hunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior.
Assuntos
Agonistas de Receptores de Canabinoides/farmacologia , Ingestão de Alimentos/fisiologia , Endocanabinoides/fisiologia , Comportamento Alimentar/fisiologia , Condutos Olfatórios/fisiologia , Percepção Olfatória/fisiologia , Receptor CB1 de Canabinoide/metabolismo , Transmissão Sináptica/fisiologia , Animais , Ingestão de Alimentos/efeitos dos fármacos , Endocanabinoides/metabolismo , Retroalimentação Fisiológica/fisiologia , Comportamento Alimentar/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Bulbo Olfatório/efeitos dos fármacos , Bulbo Olfatório/metabolismo , Bulbo Olfatório/fisiologia , Condutos Olfatórios/efeitos dos fármacos , Condutos Olfatórios/metabolismo , Percepção Olfatória/efeitos dos fármacos , Receptor CB1 de Canabinoide/genética , Transmissão Sináptica/efeitos dos fármacosRESUMO
The olfactory bulb (OB) receives and integrates newborn interneurons throughout life. This process is important for the proper functioning of the OB circuit and consequently, for the sense of smell. Although we know how these new interneurons are produced, the way in which they integrate into the pre-existing ongoing circuits remains poorly documented. Bearing in mind that glutamatergic inputs onto local OB interneurons are crucial for adjusting the level of bulbar inhibition, it is important to characterize when and how these inputs from excitatory synapses develop on newborn OB interneurons. We studied early synaptic events that lead to the formation and maturation of the first glutamatergic synapses on adult-born granule cells (GCs), the most abundant subtype of OB interneuron. Patch-clamp recordings and electron microscopy (EM) analysis were performed on adult-born interneurons shortly after their arrival in the adult OB circuits. We found that both the ratio of N-methyl-D-aspartate receptor (NMDAR) to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), and the number of functional release sites at proximal inputs reached a maximum during the critical period for the sensory-dependent survival of newborn cells, well before the completion of dendritic arborization. EM analysis showed an accompanying change in postsynaptic density shape during the same period of time. Interestingly, the latter morphological changes disappeared in more mature newly-formed neurons, when the NMDAR to AMPAR ratio had decreased and functional presynaptic terminals expressed only single release sites. Together, these findings show that the first glutamatergic inputs to adult-generated OB interneurons undergo a unique sequence of maturation stages.
RESUMO
To explore the functional consequences of adult neurogenesis in the mouse olfactory bulb, we investigated plasticity at glutamatergic synapses onto GABAergic interneurons. We found that one subset of excitatory synapses onto adult-born granule cells showed long-term potentiation shortly after their arrival in the bulb. This property faded as the newborn neurons matured. These results indicate that recently generated adult-born olfactory interneurons undergo different experience-dependent synaptic modifications compared with their pre-existing mature neighbors and provide a possible substrate for adult neurogenesis-dependent olfactory learning.
Assuntos
Interneurônios/metabolismo , Neurogênese/fisiologia , Plasticidade Neuronal/fisiologia , Bulbo Olfatório/metabolismo , Condutos Olfatórios/metabolismo , Sinapses/metabolismo , Animais , Interneurônios/citologia , Aprendizagem/fisiologia , Potenciação de Longa Duração/fisiologia , Camundongos , Bulbo Olfatório/citologia , Condutos Olfatórios/citologia , Olfato/fisiologia , Sinapses/ultraestruturaRESUMO
In the olfactory bulb (OB), odorants induce oscillations in the gamma range (20-80 Hz) that play an important role in the processing of sensory information. Synaptic transmission between dendrites is a major contributor to this processing. Glutamate released from mitral cell dendrites excites the dendrites of granule cells, which in turn mediate GABAergic inhibition back onto mitral cells. Although this reciprocal synapse is thought to be a key element supporting oscillatory activity, the mechanisms by which dendrodendritic inhibition induces and maintains gamma oscillations remain unknown. Here, we assessed the role of the dendrodendritic inhibition, using mice lacking the GABA(A) receptor alpha1-subunit, which is specifically expressed in mitral cells but not in granule cells. The spontaneous inhibitory postsynaptic current frequency in these mutants was low and was consistent with the reduction of GABA(A) receptor clusters detected by immunohistochemistry. The remaining GABA(A) receptors in mitral cells contained the alpha3-subunit and supported slower decaying currents of unchanged amplitude. Overall, inhibitory-mediated interactions between mitral cells were smaller and slower in mutant than in WT mice, although the strength of sensory afferent inputs remained unchanged. Consequently, both experimental and theoretical approaches revealed slower gamma oscillations in the OB network of mutant mice. We conclude, therefore, that fast oscillations in the OB circuit are strongly constrained by the precise location, subunit composition and kinetics of GABA(A) receptors expressed in mitral cells.
Assuntos
Dendritos/metabolismo , Bulbo Olfatório/metabolismo , Sinapses/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Potenciais Pós-Sinápticos Inibidores , Camundongos , Modelos Neurológicos , Bulbo Olfatório/ultraestrutura , Fenótipo , Receptores de GABA-A/metabolismo , Sinapses/ultraestruturaRESUMO
Using the patch-clamp technique, we investigated Cl- channels on the basolateral membrane of the connecting tubule (CNT) and cortical collecting duct (CCD). We found a approximately 10-pS channel in CNT cell-attached patches. Substitution of sodium gluconate for NaCl in the pipette shifted the reversal potential by +25 mV, whereas N-methyl-D-gluconate chloride had no effect, indicating anion selectivity. On inside-out patches, we determined a selectivity sequence of Cl- > Br- approximately NO3(-) > F-, which is compatible with that of ClC-K2, a Cl- channel in the distal nephron. In addition, the number of open channels (NP(o)) measured in cell-attached patches was significantly increased when Ca2+ concentration or pH in the pipette was increased, which is another characteristic of ClC-K. These findings suggest that the basis for this channel is ClC-K2. A similar Cl- channel was found in CCD patches. Because CNT and CCD are heterogeneous tissues, we studied the cellular distribution of the Cl- channel using recording conditions (KCl-rich solution in the pipette) that allowed us to detect simultaneously Cl- channels and inwardly rectifying K+ channels. We detected Cl- channels alone in 45% and 42% and K+ channels alone in 51% and 58% of CNT and CCD patches, respectively. Cl- and K+ channels were recorded simultaneously from two patches (4% of patches) in the CNT and from none of the patches in the CCD. This indicates that Cl- and K+ channels are located in different cell types, which we suggest may be the intercalated cells and principal cells, respectively.