RESUMO
Fetal alcohol spectrum disorder (FASD) encompasses a range of cognitive and behavioral deficits, with aberrances in the function of cerebral cortical pyramidal neurons implicated in its pathology. However, the mechanisms underlying these aberrances, including whether they persist well beyond ethanol exposure in utero, remain to be explored. We addressed these issues by employing a mouse model of FASD in which pregnant mice were exposed to binge-type ethanol from embryonic day 13.5 through 16.5. In both male and female offspring (postnatal day 28-32), whole-cell patch clamp recording of layer V/VI somatosensory cortex pyramidal neurons revealed increases in the frequency of excitatory and inhibitory postsynaptic currents. Furthermore, expressing channelrhodopsin in either GABAergic interneurons (Nkx2.1Cre-Ai32) or glutamatergic pyramidal neurons (Emx1IRES Cre-Ai32) revealed a shift in optically evoked paired-pulse ratio. These findings are consistent with an excitatory-inhibitory imbalance with prenatal ethanol exposure due to diminished inhibitory but enhanced excitatory synaptic strength. Prenatal ethanol exposure also altered the density and morphology of spines along the apical dendrites of pyramidal neurons. Thus, while both presynaptic and postsynaptic mechanisms are affected following prenatal exposure to ethanol, there is a prominent presynaptic component that contributes to altered inhibitory and excitatory synaptic transmission in the somatosensory cortex.
Assuntos
Etanol/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Somatossensorial/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Animais , Dendritos/efeitos dos fármacos , Dendritos/fisiologia , Modelos Animais de Doenças , Feminino , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Camundongos , Córtex Pré-Frontal/fisiologia , Gravidez , Efeitos Tardios da Exposição Pré-Natal/fisiopatologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/fisiologia , Córtex Somatossensorial/fisiopatologia , Transmissão Sináptica/fisiologiaRESUMO
Deficits in sensory processing in Fetal Alcohol Spectrum Disorders (FASD) implicate dysfunction in the somatosensory cortex. However, the effects of prenatal ethanol exposure on the development of this region await elucidation. Here, we used an established mouse model of FASD with binge-type ethanol exposure from embryonic day 13.5-16.5 to investigate the effects of prenatal ethanol exposure on pyramidal neurons in the somatosensory cortex. Specifically, we focused on the radial migration of primordial pyramidal neurons during embryonic corticogenesis and their morphology and function during active synaptogenesis in early postnatal development. We found that prenatal ethanol exposure resulted in aberrant radial migration, particularly affecting the populations of postmitotic pyramidal neurons. In addition, there was an enduring effect of prenatal ethanol exposure on glutamate-mediated synaptic transmission in layer V/VI pyramidal neurons. This persisted beyond a transient decrease in pyramidal neuron dendritic complexity that was evident only during early postnatal development. Adolescent mice exposed prenatally to ethanol also displayed decreased tactile sensitivity, as revealed by a modified adhesive tape removal assay. Our findings demonstrate the persistent effects of binge-type in utero ethanol exposure on pyramidal neuron form and function and ultimately sensory processing, the latter being reminiscent of that seen in individuals with FASD.
Assuntos
Movimento Celular/efeitos dos fármacos , Etanol/administração & dosagem , Transtornos do Espectro Alcoólico Fetal/fisiopatologia , Células Piramidais/efeitos dos fármacos , Córtex Somatossensorial/efeitos dos fármacos , Córtex Somatossensorial/embriologia , Animais , Modelos Animais de Doenças , Feminino , Masculino , Potenciais da Membrana/efeitos dos fármacos , Camundongos Endogâmicos C57BL , Células Piramidais/patologia , Células Piramidais/fisiologia , Córtex Somatossensorial/patologiaRESUMO
Gestational exposure to ethanol has been reported to alter the disposition of tangentially migrating GABAergic cortical interneurons, but much remains to be elucidated. Here we first established the migration of interneurons as a proximal target of ethanol by limiting ethanol exposure in utero to the gestational window when tangential migration is at its height. We then asked whether the aberrant tangential migration of GABAergic interneurons persisted as an enduring interneuronopathy in the medial prefrontal cortex (mPFC) later in the life of offspring prenatally exposed to ethanol. Time pregnant mice with Nkx2.1Cre/Ai14 embryos harboring tdTomato-fluorescent medial ganglionic eminence (MGE)-derived cortical GABAergic interneurons were subjected to a 3 day binge-type 5% w/w ethanol consumption regimen from embryonic day (E) 13.5-16.5, spanning the peak of corticopetal interneuron migration in the fetal brain. Our binge-type regimen increased the density of MGE-derived interneurons in the E16.5 mPFC. In young adult offspring exposed to ethanol in utero, this effect persisted as an increase in the number of mPFC layer V parvalbumin-immunopositive interneurons. Commensurately, patch-clamp recording in mPFC layer V pyramidal neurons uncovered enhanced GABA-mediated spontaneous and evoked synaptic transmission, shifting the inhibitory/excitatory balance toward favoring inhibition. Furthermore, young adult offspring exposed to the 3 day binge-type ethanol regimen exhibited impaired reversal learning in a modified Barnes maze, indicative of decreased PFC-dependent behavioral flexibility, and heightened locomotor activity in an open field arena. Our findings underscore that aberrant neuronal migration, inhibitory/excitatory imbalance, and thus interneuronopathy contribute to indelible abnormal cortical circuit form and function in fetal alcohol spectrum disorders. SIGNIFICANCE STATEMENT: The significance of this study is twofold. First, we demonstrate that a time-delimited binge-type ethanol exposure in utero during early gestation alters corticopetal tangential migration of GABAergic interneurons in the fetal brain. Second, our study is the first to integrate neuroanatomical, electrophysiological, and behavioral evidence that this "interneuronopathy" persists in the young adult offspring and contributes to enduring changes in (1) the distribution of parvalbumin-expressing GABAergic cortical interneurons in the medial prefrontal cortex, (2) GABA-mediated synaptic transmission that resulted in an inhibitory/excitatory synaptic imbalance, and (3) behavioral flexibility. These findings alert women of child-bearing age that fetal alcohol spectrum disorders can be rooted very early in fetal brain development, and reinforce evidence-based counseling against binge drinking even at the earliest stages of pregnancy.
Assuntos
Etanol/administração & dosagem , Neurônios GABAérgicos/efeitos dos fármacos , Interneurônios/efeitos dos fármacos , Córtex Pré-Frontal/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/patologia , Animais , Feminino , Neurônios GABAérgicos/metabolismo , Neurônios GABAérgicos/patologia , Interneurônios/metabolismo , Interneurônios/patologia , Camundongos , Parvalbuminas/metabolismo , Córtex Pré-Frontal/metabolismo , Córtex Pré-Frontal/patologia , GravidezRESUMO
BACKGROUND: Exposure to ethanol (EtOH) in utero alters the disposition of tangentially migrating GABAergic interneurons in the fetal brain. The medial ganglionic eminence (MGE) gives rise to a large portion of cortical GABAergic interneurons, including the parvalbumin-expressing interneurons that shape and contribute to inhibitory/excitatory (I/E) balance of the intracortical circuit. Here, we investigated in the mouse medial prefrontal cortex (mPFC) the hypothesis that low levels of maternal EtOH consumption from closure of the neural tube embryonic day (E) 9.5 until birth result in an enduring interneuronopathy. METHODS: Pregnant mice were subjected to a 2% w/w EtOH consumption regimen starting at neural tube closure and ending at parturition. Neurogenesis in the MGE was assessed by 5-bromo-2-deoxyuridine (BrdU) immunofluorescence at E12.5. The count and distribution of parvalbumin-expressing interneurons were determined in adult animals, and patch clamp electrophysiology was performed to determine GABAergic function and I/E balance. Open-field behavior in adult mice was assessed to determine whether the EtOH-exposed cohort displayed a lasting alteration in exploratory behavior. RESULTS: In embryos exposed to EtOH in utero, we found increased BrdU labeling in the MGE, pointing to increased neurogenesis. Adult mice prenatally exposed to EtOH were hyperactive, and this was associated with an increase in parvalbumin-expressing GABAergic interneurons in the mPFC. In addition, prenatal EtOH exposure altered the balance between spontaneous inhibitory and excitatory synaptic input and attenuated GABAergic tone in layer V mPFC pyramidal neurons in juvenile mice. CONCLUSIONS: These findings underscore that altered migration of GABAergic interneurons contributes to the EtOH-induced aberration of cortical development and that these effects persist into adulthood as altered cortical form and function.
Assuntos
Consumo de Bebidas Alcoólicas/efeitos adversos , Etanol/toxicidade , Neurônios GABAérgicos/fisiologia , Neurogênese/efeitos dos fármacos , Córtex Pré-Frontal/fisiologia , Efeitos Tardios da Exposição Pré-Natal/fisiopatologia , Animais , Movimento Celular/efeitos dos fármacos , Comportamento Exploratório/efeitos dos fármacos , Feminino , Interneurônios/fisiologia , Masculino , Camundongos , Camundongos Transgênicos , Córtex Pré-Frontal/efeitos dos fármacos , GravidezRESUMO
BACKGROUND: Prenatal exposure to ethanol exerts teratogenic effects on the developing brain. Here, we tested the hypothesis that exposure to ethanol in utero alters the disposition of Cajal-Retzius cells that play a key role in orchestrating proliferation, migration, and laminar integration of cortical neurons in the embryonic cortex. METHODS: Pregnant Ebf2-EGFP mice, harboring EGFP-fluorescent Cajal-Retzius cells, were subjected to a 2% w/w ethanol consumption regimen starting at neural tube closure and lasting throughout gestation. Genesis of Cajal-Retzius cells was assessed by means of 5-bromo-2-deoxyuridine (BrdU) immunofluorescence at embryonic day 12.5, their counts and distribution were determined between postnatal day (P)0 and P4, patch clamp electrophysiology was performed between P2 and P3 to analyze GABA-mediated synaptic activity, and open-field behavioral testing was conducted in P45-P50 adolescents. RESULTS: In Ebf2-EGFP embryos exposed to ethanol in utero, we found increased BrdU labeling and expanded distribution of Cajal-Retzius cells in the cortical hem, pointing to increased genesis and proliferation. Postnatally, we found an increase in Cajal-Retzius cell number in cortical layer I. In addition, they displayed altered patterning of spontaneous GABA-mediated synaptic barrages and enhanced GABA-mediated synaptic activity, suggesting enhanced GABAergic tone. CONCLUSIONS: These findings, together, underscore that Cajal-Retzius cells contribute to the ethanol-induced aberration of cortical development and abnormal GABAergic neurotransmission at the impactful time when intracortical circuits form.
Assuntos
Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/patologia , Etanol/toxicidade , Neurônios/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/induzido quimicamente , Animais , Proliferação de Células/efeitos dos fármacos , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/fisiopatologia , Feminino , Neurônios GABAérgicos/efeitos dos fármacos , Camundongos , Camundongos Transgênicos , Potenciais Pós-Sinápticos em Miniatura/efeitos dos fármacos , Atividade Motora/efeitos dos fármacos , Neurogênese/efeitos dos fármacos , Gravidez , Efeitos Tardios da Exposição Pré-Natal/patologia , Efeitos Tardios da Exposição Pré-Natal/fisiopatologia , Proteína ReelinaRESUMO
Neurotrophins have been implicated in regulating neuronal differentiation, promoting neuronal survival, and modulating synaptic efficacy and plasticity. The prevailing view is that, depending on the target and mode of action, most neurotrophins can be trafficked and released either anterogradely or retrogradely in an activity-dependent manner. However, the prototypic neurotrophin, nerve growth factor (NGF), is not thought to be anterogradely delivered. Here we provide the neuroanatomical substrate for an anterograde hippocamposeptal transport of NGF by demonstrating its presence in mouse hippocampal GABAergic neurons and in their hippocamposeptal axons that ramify densely and abut neurons in the medial septum/diagonal band of Broca (MS/DB). We also demonstrate an activity-dependent increase in septal NGF levels that is dependent on the pattern of intrahippocampal stimulation. In addition, we show that acute exposure to NGF, via activation of TrkA, attenuates GABA(A) receptor-mediated inhibitory synaptic currents and reduces sensitivity to exogenously applied GABA. These acute actions of NGF display cell type and functional selectivity insofar as (1) they were found in cholinergic, but not GABAergic, MS/DB neurons, and (2) glutamate-mediated excitatory synaptic activity as well as AMPA-activated current responses were unaffected. Our results advocate a novel anterograde, TrkA-mediated NGF signaling in the CNS.
Assuntos
Neurônios GABAérgicos/fisiologia , Hipocampo/citologia , Hipocampo/metabolismo , Fator de Crescimento Neural/metabolismo , Sinapses/fisiologia , Análise de Variância , Animais , Animais Recém-Nascidos , Biofísica , Colina O-Acetiltransferase/genética , Estimulação Elétrica , Ensaio de Imunoadsorção Enzimática , Fármacos Atuantes sobre Aminoácidos Excitatórios/farmacologia , Lateralidade Funcional , GABAérgicos/farmacologia , Neurônios GABAérgicos/citologia , Neurônios GABAérgicos/efeitos dos fármacos , Glutamato Descarboxilase/genética , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/genética , Camundongos , Camundongos Transgênicos , Fator de Crescimento Neural/farmacologia , Inibição Neural/efeitos dos fármacos , Vias Neurais/fisiologia , Técnicas de Patch-Clamp , Núcleos Septais/citologia , Septo do Cérebro/citologiaRESUMO
Alzheimer's disease (AD) is the most common cause of dementia, affecting approximately 50 million people worldwide. Early life risk factors for AD, including prenatal exposures, remain underexplored. Exposure of the fetus to alcohol (ethanol) is not uncommon during pregnancy, and may result in physical, behavioral, and cognitive changes that are first detected during childhood but result in lifelong challenges. Whether or not prenatal ethanol exposure may contribute to Alzheimer's disease risk is not yet known. Here we exposed a mouse model of Alzheimer's disease (3xTg-AD), bearing three dementia-associated transgenes, presenilin1 (PS1M146V), human amyloid precursor protein (APPSwe), and human tau (TauP301S), to ethanol on gestational days 13.5-16.5 using an established binge-type maternal ethanol exposure paradigm. We sought to investigate whether prenatal ethanol exposure resulted in a precocious onset or increased severity of AD progression, or both. We found that a brief binge-type gestational exposure to ethanol during a period of peak neuronal migration to the developing cortex resulted in an earlier onset of spatial memory deficits and behavioral inflexibility in the progeny, as assessed by performance on the modified Barnes maze task. The observed cognitive changes coincided with alterations to both GABAergic and glutamatergic synaptic transmission in layer V/VI neurons, diminished GABAergic interneurons, and increased ß-amyloid accumulation in the medial prefrontal cortex. These findings provide the first preclinical evidence for prenatal ethanol exposure as a potential factor for modifying the onset of AD-like behavioral dysfunction and set the groundwork for more comprehensive investigations into the underpinnings of AD-like cognitive changes in individuals with fetal alcohol spectrum disorders.
Assuntos
Doença de Alzheimer , Cognição , Etanol , Neurônios , Efeitos Tardios da Exposição Pré-Natal , Animais , Feminino , Humanos , Camundongos , Gravidez , Doença de Alzheimer/induzido quimicamente , Doença de Alzheimer/genética , Precursor de Proteína beta-Amiloide/genética , Cognição/efeitos dos fármacos , Modelos Animais de Doenças , Etanol/toxicidade , Camundongos Transgênicos , Neurônios/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/induzido quimicamente , Efeitos Tardios da Exposição Pré-Natal/genéticaRESUMO
During rodent corticogenesis, a sizeable subpopulation of γ-aminobutyric acid (GABA)ergic interneurons arises extracortically from the medial ganglionic eminence (MGE). These neurons progressively acquire responsiveness to GABA in the course of corticopetal tangential migration, a process regulated by ambient GABA and mediated by GABA(A) receptors. Here, we combined patch clamp electrophysiology and single-cell reverse transcription-polymerase chain reaction to examine GABA(A) receptor expression in green fluorescent MGE-derived (eGFP+) cells in telencephalic slices from gestational day 14.5 BAC-Lhx6 embryos. GABA concentration-response curves revealed lower apparent affinity and efficacy in eGFP+ cells in and around the MGE than their counterparts in the cortex. Pharmacological tests revealed subunit-selective response profiles in the MGE and cortex consistent with differential expression of GABA(A) receptor isoforms. Profiling of GABA(A) receptor subunit transcripts (α1-5, ß1-3, and γ1-3, δ) uncovered increased expression of the α1-, α2-, α5-, γ2-, and γ3-subunit messenger RNAs in the cortex. We propose that the dynamic expression of certain GABA(A) receptor subunits contributes to assembling receptor isoforms that confer functional attributes important in regulating the migration and maturation of primordial GABAergic cortical interneurons.
Assuntos
Diferenciação Celular/fisiologia , Movimento Celular/fisiologia , Córtex Cerebral/embriologia , Gânglios/metabolismo , Interneurônios/citologia , Neurogênese/fisiologia , Receptores de GABA-A/fisiologia , Telencéfalo/citologia , Animais , Córtex Cerebral/citologia , Feminino , Gânglios/citologia , Gânglios/embriologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Interneurônios/metabolismo , Interneurônios/fisiologia , Camundongos , Camundongos Transgênicos , Técnicas de Cultura de Órgãos , Gravidez , Subunidades Proteicas/fisiologia , Telencéfalo/embriologiaRESUMO
Exposure of the fetus to alcohol (ethanol) via maternal consumption during pregnancy can result in fetal alcohol spectrum disorders (FASD), hallmarked by long-term physical, behavioral, and intellectual abnormalities. In our preclinical mouse model of FASD, prenatal ethanol exposure disrupts tangential migration of corticopetal GABAergic interneurons (GINs) in the embryonic medial prefrontal cortex (mPFC). We postulated that ethanol perturbed the normal pattern of tangential migration via enhancing GABAA receptor-mediated membrane depolarization that prevails during embryonic development in GABAergic cortical interneurons. However, beyond this, our understanding of the underlying mechanisms is incomplete. Here, we tested the hypothesis that the ethanol-enhanced depolarization triggers downstream an increase in high-voltage-activated nifedipine-sensitive L-type calcium channel (LTCC) activity and provide evidence implicating calcium dynamics in the signaling scheme underlying the migration of embryonic GINs and its aberrance. Tangentially migrating Nkx2.1+ GINs expressed immunoreactivity to Cav1.2, the canonical neuronal isoform of the L-type calcium channel. Prenatal ethanol exposure did not alter its protein expression profile in the embryonic mPFC. However, exposing ethanol concomitantly with the LTCC blocker nifedipine prevented the ethanol-induced aberrant migration both in vitro and in vivo In addition, whole-cell patch clamp recording of LTCCs in GINs migrating in embryonic mPFC slices revealed that acutely applied ethanol potentiated LTCC activity in migrating GINs. Based on evidence reported in the present study, we conclude that calcium is an important intracellular intermediary downstream of GABAA receptor-mediated depolarization in the mechanistic scheme of an ethanol-induced aberrant tangential migration of embryonic GABAergic cortical interneurons.
Assuntos
Canais de Cálcio Tipo L , Etanol , Animais , Córtex Cerebral , Desenvolvimento Embrionário , Etanol/toxicidade , Feminino , Interneurônios , Camundongos , Córtex Pré-Frontal , GravidezRESUMO
ACh release into the rodent prefrontal cortex is predictive of successful performance of cue detection tasks, yet the cellular mechanisms underlying cholinergic modulation of cortical function are not fully understood. Prolonged ("tonic") muscarinic ACh receptor (mAChR) activation increases the excitability of cortical pyramidal neurons, whereas transient ("phasic") mAChR activation generates inhibitory and/or excitatory responses, depending on neuron subtype. These cholinergic effects result from activation of "M1-like" mAChRs (M1, M3, and M5 receptors), but the specific receptor subtypes involved are not known. We recorded from cortical pyramidal neurons from wild-type mice and mice lacking M1, M3, and/or M5 receptors to determine the relative contribution of M1-like mAChRs to cholinergic signaling in the mouse prefrontal cortex. Wild-type neurons in layer 5 were excited by tonic mAChR stimulation, and had biphasic inhibitory followed by excitatory, responses to phasic ACh application. Pyramidal neurons in layer 2/3 were substantially less responsive to tonic and phasic cholinergic input. Cholinergic effects were largely absent in neurons from mice lacking M1 receptors, but most were robust in neurons lacking M3, M5, or both M3 and M5 receptors. The exception was tonic cholinergic suppression of the afterhyperpolarization in layer 5 neurons, which was absent in cells lacking either M1 or M3 receptors. Finally, we confirm a role for M1 receptors in behavior by demonstrating cue detection deficits in M1-lacking mice. Together, our results demonstrate that M1 receptors facilitate cue detection behaviors and are both necessary and sufficient for most direct effects of ACh on pyramidal neuron excitability.
Assuntos
Córtex Pré-Frontal/fisiologia , Células Piramidais/fisiologia , Receptor Muscarínico M1/metabolismo , Potenciais de Ação/efeitos dos fármacos , Análise de Variância , Animais , Carbacol/farmacologia , Agonistas Colinérgicos/farmacologia , Condicionamento Clássico/fisiologia , Sinais (Psicologia) , Técnicas In Vitro , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Atividade Motora/fisiologia , Técnicas de Patch-Clamp , Córtex Pré-Frontal/efeitos dos fármacos , Células Piramidais/efeitos dos fármacos , Receptor Muscarínico M1/agonistas , Receptor Muscarínico M1/genética , Receptor Muscarínico M3/agonistas , Receptor Muscarínico M3/genética , Receptor Muscarínico M3/metabolismo , Receptor Muscarínico M5/agonistas , Receptor Muscarínico M5/genética , Receptor Muscarínico M5/metabolismoRESUMO
The septohippocampal system has been implicated in the cognitive deficits associated with ethanol consumption, but the cellular basis of ethanol action awaits full elucidation. In the medial septum/diagonal band of Broca (MS/DB), a muscarinic tone, reflective of firing activity of resident cholinergic neurons, regulates that of their noncholinergic, putatively GABAergic, counterparts. Here we tested the hypothesis that ethanol alters this muscarinic tone. The spontaneous firing activity of cholinergic and noncholinergic MS/DB neurons were monitored in acute MS/DB slices from C57Bl/6 mice. Exposing the entire slice to ethanol increased firing in both cholinergic and noncholinergic neurons. However, applying ethanol focally to individual MS/DB neurons increased firing only in cholinergic neurons. The differential outcome suggested different mechanisms of ethanol action on cholinergic and noncholinergic neurons. Indeed, with bath-perfused ethanol, the muscarinic antagonist methyl scopolamine prevented the increase in firing in noncholinergic, but not cholinergic, MS/DB neurons. Thus, the effect on noncholinergic neuronal firing was secondary to ethanol's direct action of acutely increasing muscarinic tone. We propose that the acute ethanol-induced elevation of muscarinic tone in the MS/DB contributes to the altered net flow of neuronal activity in the septohippocampal system that underlies compromised cognitive function.
Assuntos
Depressores do Sistema Nervoso Central/farmacologia , Colina O-Acetiltransferase/metabolismo , Etanol/farmacologia , Neurônios/efeitos dos fármacos , Receptores Muscarínicos/metabolismo , Septo do Cérebro/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Imuno-Histoquímica , Técnicas In Vitro , Camundongos , Camundongos Endogâmicos C57BL , Antagonistas Muscarínicos/farmacologia , N-Metilescopolamina/farmacologia , Neurônios/fisiologia , Técnicas de Patch-Clamp , Septo do Cérebro/fisiologiaRESUMO
Consumption of alcohol (ethanol) during pregnancy can lead to developmental defects in the offspring, the most devastating being the constellation of symptoms collectively referred to as fetal alcohol syndrome (FAS). In the brain, a hallmark of FAS is abnormal cerebral cortical morphology consistent with insult during corticogenesis. Here, we report that exposure to a relatively low level of ethanol in utero (average maternal and fetal blood alcohol level of 25 mg/dl) promotes premature tangential migration into the cortical anlage of primordial GABAergic interneurons, including those originating in the medial ganglionic eminence (MGE). This ethanol-induced effect was evident in vivo at embryonic day 14.5 (E14.5) in GAD67 knock-in and BAC-Lhx6 embryos, as well as in vitro in isotypic telencephalic slice cocultures obtained from E14.5 embryos exposed to ethanol in utero. Analysis of heterotypic cocultures indicated that both cell-intrinsic and -extrinsic factors contribute to the aberrant migratory profile of MGE-derived cells. In this light, we provide evidence for an interaction between ethanol exposure in utero and the embryonic GABAergic system. Exposure to ethanol in utero elevated the ambient level of GABA and increased the sensitivity to GABA of MGE-derived cells. Our results uncovered for the first time an effect of ethanol consumption during pregnancy on the embryonic development of GABAergic cortical interneurons. We propose that ethanol exerts its effect on the tangential migration of GABAergic interneurons extrinsically by modulating extracellular levels of GABA and intrinsically by altering GABA(A) receptor function.
Assuntos
Movimento Celular/efeitos dos fármacos , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/embriologia , Etanol/administração & dosagem , Interneurônios/efeitos dos fármacos , Ácido gama-Aminobutírico/fisiologia , Consumo de Bebidas Alcoólicas/efeitos adversos , Animais , Movimento Celular/fisiologia , Córtex Cerebral/citologia , Técnicas de Cocultura , Etanol/toxicidade , Feminino , Feto , Interneurônios/citologia , Interneurônios/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Gravidez , Fatores de TempoRESUMO
In the mature nervous system, changes in synaptic strength correlate with changes in neuronal structure. Members of the Nogo-66 receptor family have been implicated in regulating neuronal morphology. Nogo-66 receptor 1 (NgR1) supports binding of the myelin inhibitors Nogo-A, MAG (myelin-associated glycoprotein), and OMgp (oligodendrocyte myelin glycoprotein), and is important for growth cone collapse in response to acutely presented inhibitors in vitro. After injury to the corticospinal tract, NgR1 limits axon collateral sprouting but is not important for blocking long-distance regenerative growth in vivo. Here, we report on a novel interaction between NgR1 and select members of the fibroblast growth factor (FGF) family. FGF1 and FGF2 bind directly and with high affinity to NgR1 but not to NgR2 or NgR3. In primary cortical neurons, ectopic NgR1 inhibits FGF2-elicited axonal branching. Loss of NgR1 results in altered spine morphologies along apical dendrites of hippocampal CA1 neurons in vivo. Analysis of synaptosomal fractions revealed that NgR1 is enriched synaptically in the hippocampus. Physiological studies at Schaffer collateral-CA1 synapses uncovered a synaptic function for NgR1. Loss of NgR1 leads to FGF2-dependent enhancement of long-term potentiation (LTP) without altering basal synaptic transmission or short-term plasticity. NgR1 and FGF receptor 1 (FGFR1) are colocalized to synapses, and mechanistic studies revealed that FGFR kinase activity is necessary for FGF2-elicited enhancement of hippocampal LTP in NgR1 mutants. In addition, loss of NgR1 attenuates long-term depression of synaptic transmission at Schaffer collateral-CA1 synapses. Together, our findings establish that physiological NgR1 signaling regulates activity-dependent synaptic strength and uncover neuronal NgR1 as a regulator of synaptic plasticity.
Assuntos
Espinhas Dendríticas/fisiologia , Receptores de Superfície Celular/fisiologia , Sinapses/fisiologia , Animais , Células COS , Células Cultivadas , Chlorocebus aethiops , Espinhas Dendríticas/ultraestrutura , Potenciais Pós-Sinápticos Excitadores/fisiologia , Proteínas Ligadas por GPI , Humanos , Camundongos , Camundongos Mutantes , Receptor Nogo 2 , Ligação Proteica/fisiologia , Ratos , Sinapses/ultraestruturaRESUMO
Understanding the biology of adult neural stem cells has important implications for nervous system development and may contribute to our understanding of neurodegenerative disorders and their treatment. We have characterized the process of olfactory neurogenesis in adult mice lacking inhibitor of DNA binding 2(-/-) (Id2(-/-)). We found a diminished olfactory bulb containing reduced numbers of granular and periglomerular neurons with a distinct paucity of dopaminergic periglomerular neurons. While no deficiency of the stem cell compartment was detectable, migrating neuroblasts in Id2(-/-) mutant mice prematurely undergo astroglial differentiation within a disorganized rostral migratory stream. Further, when evaluated in vitro loss of Id2 results in decreased proliferation of neural progenitors and decreased expression of the Hes1 and Ascl1 (Mash1) transcription factors, known mediators of neuronal differentiation. These data support a novel role for sustained Id2 expression in migrating neural progenitors mediating olfactory dopaminergic neuronal differentiation in adult animals.
Assuntos
Dopamina/metabolismo , Proteína 2 Inibidora de Diferenciação/fisiologia , Neurogênese/genética , Neurônios/fisiologia , Bulbo Olfatório/citologia , Células-Tronco Adultas/fisiologia , Animais , Animais Recém-Nascidos , Astrócitos/fisiologia , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Bromodesoxiuridina/metabolismo , Contagem de Células/métodos , Diferenciação Celular/genética , Células Cultivadas , Discriminação Psicológica/fisiologia , Regulação da Expressão Gênica no Desenvolvimento/genética , Proteína Glial Fibrilar Ácida/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Proteína 2 Inibidora de Diferenciação/deficiência , Camundongos , Camundongos Knockout , Neurogênese/fisiologia , Bulbo Olfatório/crescimento & desenvolvimento , Condutos Olfatórios/citologia , Condutos Olfatórios/fisiologia , Olfato/genética , Estatísticas não Paramétricas , Fatores de Transcrição HES-1 , Tirosina 3-Mono-Oxigenase/metabolismoRESUMO
Prenatal exposure to ethanol induces aberrant tangential migration of corticopetal GABAergic interneurons, and long-term alterations in the form and function of the prefrontal cortex. We have hypothesized that interneuronopathy contributes significantly to the pathoetiology of fetal alcohol spectrum disorders (FASD). Activity-dependent tangential migration of GABAergic cortical neurons is driven by depolarizing responses to ambient GABA present in the cortical enclave. We found that ethanol exposure potentiates the depolarizing action of GABA in GABAergic cortical interneurons of the embryonic mouse brain. Pharmacological antagonism of the cotransporter NKCC1 mitigated ethanol-induced potentiation of GABA depolarization and prevented aberrant patterns of tangential migration induced by ethanol in vitro. In a model of FASD, maternal bumetanide treatment prevented interneuronopathy in the prefrontal cortex of ethanol exposed offspring, including deficits in behavioral flexibility. These findings position interneuronopathy as a mechanism of FASD symptomatology, and posit NKCC1 as a pharmacological target for the management of FASD.
Assuntos
Consumo de Bebidas Alcoólicas/efeitos adversos , Bumetanida/administração & dosagem , Transtornos do Espectro Alcoólico Fetal/prevenção & controle , Complicações na Gravidez/prevenção & controle , Inibidores de Simportadores de Cloreto de Sódio e Potássio/administração & dosagem , Membro 2 da Família 12 de Carreador de Soluto/metabolismo , Animais , Córtex Cerebral/efeitos dos fármacos , Modelos Animais de Doenças , Feminino , Transtornos do Espectro Alcoólico Fetal/fisiopatologia , Neurônios GABAérgicos/efeitos dos fármacos , Camundongos , Córtex Pré-Frontal/efeitos dos fármacos , Gravidez , Complicações na Gravidez/fisiopatologia , Resultado do Tratamento , Ácido gama-Aminobutírico/metabolismoRESUMO
Nerve growth factor (NGF) has been implicated in maintaining and regulating normal functioning of the septohippocampal pathway. However, many aspects of its physiological actions and the underlying mechanisms await elucidation. In this study, we investigated the effect of acute NGF exposure on neurons in the mouse medial septum/diagonal band of Broca (MS/DB), focusing on the cholinergic neurons and the subpopulation of noncholinergic neurons that were identified to be putatively GABAergic. We report that MS/DB neurons in a thin slice preparation, when exposed to NGF via bath perfusion, rapidly and indiscriminately increased the rate of spontaneous firing in all MS/DB neurons. However, focal application of NGF to individual MS/DB neurons increased spontaneous firing in cholinergic, but not in the noncholinergic, subpopulation. The NGF-induced effect on cholinergic neurons was direct, requiring activation and signaling via TrkA receptors, which were immunohistochemically localized to the cholinergic neurons in the MS/DB. TrkA receptors were absent in putative GABAergic MS/DB neurons, and blockade of TrkA signaling in these and other noncholinergic neurons had no effect on their firing activity after exposure to NGF. Conversely, methyl scopolamine, blocked the increased firing activity of noncholinergic neurons during bath perfusion of NGF. We propose a cell type-specific mode of action for NGF in the MS/DB. The neurotrophin directly enhances cholinergic neuronal activity in the MS/DB through TrkA-mediated signaling, increasing acetylcholine release and, thus, muscarinic tone. This increase in muscarinic tone, in turn, results in heightened firing activity in noncholinergic MS/DB neurons.
Assuntos
Feixe Diagonal de Broca/citologia , Muscarina/metabolismo , Fatores de Crescimento Neural/farmacologia , Neurônios/efeitos dos fármacos , Septo do Cérebro/citologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Potenciais de Ação/efeitos da radiação , Animais , Animais Recém-Nascidos , Western Blotting/métodos , Calbindina 2 , Calbindinas , Carbazóis/farmacologia , Colina O-Acetiltransferase/metabolismo , Inibidores da Colinesterase/farmacologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Estimulação Elétrica/métodos , Inibidores Enzimáticos/farmacologia , Imunofluorescência/métodos , Técnicas In Vitro , Alcaloides Indólicos , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Potenciais da Membrana/efeitos da radiação , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Antagonistas Muscarínicos/farmacologia , Neostigmina/farmacologia , Parvalbuminas/metabolismo , Técnicas de Patch-Clamp/métodos , Receptor de Fator de Crescimento Neural/deficiência , Receptor trkA/metabolismo , Receptor trkB/metabolismo , Proteína G de Ligação ao Cálcio S100/metabolismo , Escopolamina/farmacologia , Fatores de TempoRESUMO
Epidemiological studies have reported a reduction in the prevalence of Alzheimer's disease in individuals that ingest low amounts of alcohol. Also, it has been found that moderate consumption of ethanol might protect against ß-amyloid (Aß) toxicity. However, the mechanism underlying its potential neuroprotection is largely unknown. In the present study, we found that ethanol improved the cognitive processes of learning and memory in 3xTgAD mice. In addition, we found that a low concentration of ethanol (equivalent to moderate ethanol consumption) decreased the binding of Aß (1 and 5 µM) to neuronal membranes and, consequently, its synaptotoxic effect in rat hippocampal and cortical neurons under acute (30 minutes) and chronic (24 hours) incubation conditions. This effect appears to be exerted by a direct action of ethanol on Aß because electron microscopy studies showed that ethanol altered the degree of Aß aggregation. The action of ethanol on Aß also prevented the peptide from perforating the neuronal membrane, as assayed with patch clamp experiments. Taken together, these results contribute to elucidating the mechanism by which low concentrations of ethanol protect against toxicity induced by Aß oligomers in primary neuronal cultures. These results may also provide an explanation for the decrease in the risk of Alzheimer's disease in people who consume moderate doses of alcohol.
Assuntos
Doença de Alzheimer/etiologia , Doença de Alzheimer/prevenção & controle , Peptídeos beta-Amiloides/metabolismo , Peptídeos beta-Amiloides/toxicidade , Etanol/administração & dosagem , Etanol/farmacologia , Hipocampo/metabolismo , Hipocampo/patologia , Animais , Células Cultivadas , Relação Dose-Resposta a Droga , Camundongos Transgênicos , Fármacos Neuroprotetores , Ratos Sprague-DawleyRESUMO
Despite the fact that ethanol is one of the most widely used psychoactive agents, the mechanisms and sites of action by which it modifies brain functions are only now being elucidated. Studies over the last decade have shown that ethanol can specifically alter the function of several ligand-activated ion channels including N-methyl-D-aspartate (NMDA), serotonin (5-HT(3)), glycine and GABA(A) receptors. After several years of extensive research in this field, the resolution of what, where and how ethanol modifies GABA(A) receptors continues to be controversial. For example, after demonstrating that ethanol was able to alter Cl(-) flux in synaptoneurosomes and cultured neurons, several electrophysiological studies were unable to show enhancement of the GABA(A) receptor current in single neurons. The lack of positive results with low ethanol concentrations was interpreted as being due to receptor heterogeneity and differences in intracellular modulation by protein kinases and calcium. The existence of high receptor heterogeneity with respect to ethanol sensitivity has been supported by studies done in a variety of cell types which showed that ethanol potentiated some, but not other neurons. Adding to this complexity, it was shown that while some hippocampal GABA(A) receptors can be affected by ethanol concentrations between 1 and 100 mM, others are only sensitive to concentrations above 200 mM. The curve of the relationship between low ethanol concentrations and current enhancement suggests a high degree of complexity in the molecular interaction because of its steepness and "inverted" U shape. Similarly, the effects of ethanol on GABA(A) receptors seems much more complex than those of benzodiazepines, barbiturates and neurosteroids. The major problem encountered in advancing understanding of the mechanism of ethanol action in native neuronal receptors has been the large variability detected in ethanol sensitivity. For example, several studies have shown that only some groups of neurons are sensitive to pharmacologically relevant concentrations of ethanol (1-100 mM). This receptor sensitivity variability has not been resolved using recombinant expression systems. For example, studies performed in recombinant receptors, although important for elucidating molecular requirements, have shown that they are less sensitive to ethanol suggesting that neuronal substrates are important for ethanol actions. In this review, we discuss the possibility that ethanol's action on the GABA(A) receptor may not be due solely to a direct interaction with the receptor protein, but that its effects could also be modulated by intracellular regulation, and that this latter effect is the more physiologically relevant one. Data in cortical and hippocampal neurons suggest that ethanol action on the receptor is labile, and that it also depends on repetitive stimulation and neuron integrity. In addition, the action of ethanol can be modified by activation of protein kinases and neuronal development. Finally, we discuss that the best approach for studying the interaction between the receptor and ethanol is through the combined use of recombinant receptors and overexpression in neurons.
Assuntos
Encéfalo/efeitos dos fármacos , Depressores do Sistema Nervoso Central/farmacologia , Etanol/farmacologia , Receptores de GABA-A/efeitos dos fármacos , Animais , Sítios de Ligação , Encéfalo/citologia , Encéfalo/metabolismo , Cálcio/fisiologia , Depressores do Sistema Nervoso Central/metabolismo , Eletrofisiologia , Etanol/metabolismo , Hipocampo/citologia , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Humanos , Neurônios/metabolismo , Subunidades Proteicas , Receptores de GABA-A/metabolismo , Transdução de Sinais/fisiologiaRESUMO
Changes in brain reward systems are thought to contribute significantly to the cognitive and behavioral impairments of schizophrenia, as well as the propensity to develop co-occurring substance abuse disorders. Presently, there are few treatments for persons with a dual diagnosis and little is known about the neural substrates that underlie co-occurring schizophrenia and substance abuse. One goal of the present study was to determine if a change in the concentration of kynurenic acid (KYNA), a tryptophan metabolite that is increased in the brains of people with schizophrenia, affects reward-related behavior. KYNA is an endogenous antagonist of NMDA glutamate receptors and α7 nicotinic acetylcholine receptors, both of which are critically involved in neurodevelopment, plasticity, and behavior. In Experiment 1, rats were treated throughout adolescence with L-kynurenine (L-KYN), the precursor of KYNA. As adults, the rats were tested drug-free in an autoshaping procedure in which a lever was paired with food. Rats treated with L-KYN during adolescence exhibited increased sign-tracking behavior (lever pressing) when they were tested as adults. Sign-tracking is thought to reflect the lever acquiring incentive salience (motivational value) as a result of its pairing with reward. Thus, KYNA exposure may increase the incentive salience of cues associated with reward, perhaps contributing to an increase in sensitivity to drug-related cues in persons with schizophrenia. In Experiment 2, we tested the effects of exposure to KYNA during adolescence on hippocampal long-term potentiation (LTP). Rats treated with L-KYN exhibited no LTP after a burst of high-frequency stimulation that was sufficient to produce robust LTP in vehicle-treated rats. This finding represents the first demonstrated consequence of elevated KYNA concentration during development and provides insight into the basis for cognitive and behavioral deficits that result from exposure to KYNA during adolescence.