RESUMO
Endocannabinoids (eCBs) released from postsynaptic neurons mediate retrograde suppression of neurotransmitter release at central synapses. eCBs are crucial for establishing proper synaptic connectivity in the developing nervous system. Mobilization of eCBs is driven either by a rise in intracellular Ca(2+) (depolarization-induced suppression of inhibition, DSI) or postsynaptic G protein-coupled receptors (GPCRs) that activate phospholipase C beta (PLCß). To determine whether eCB mobilization changes between neonatal and juvenile ages, we used whole cell voltage-clamp recordings of CA1 neurons from rat hippocampal slices at postnatal days 1-18 (neonatal) and 19-43 (juvenile), because many neurophysiological parameters change dramatically between approximately postnatal days 18-20. We found that DSI was slightly greater in juveniles than in neonates, while eCB mobilization stimulated by GPCRs was unchanged. However, when DSI was elicited during GPCR activation, its increase was much greater in juveniles, suggesting that eCB mobilization caused by the synergy between the Ca(2+) and GPCR pathways is developmentally upregulated. Western blotting revealed significant increases in both metabotropic type glutamate receptor 5 (mGluR5) and PLCß1 proteins in juveniles compared with neonates. Responses to pharmacological activation or inhibition of PLC implied that eCB upregulation is associated with a functional increase in PLC activity. We conclude that synergistic eCB mobilization in hippocampal CA1 neurons is greater in juveniles than in neonates, and that this may result from increases in the mGluR5-PLCß1 eCB pathway. The data enhance our understanding of the developmental regulation of the eCB system and may provide insight into diseases caused by improper cortical wiring, or the impact of cannabis exposure during development.
Assuntos
Região CA1 Hipocampal/crescimento & desenvolvimento , Endocanabinoides/metabolismo , Fosfolipase C beta/metabolismo , Células Piramidais/crescimento & desenvolvimento , Receptor de Glutamato Metabotrópico 5/metabolismo , Animais , Animais Recém-Nascidos , Western Blotting , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/fisiologia , Feminino , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Técnicas de Patch-Clamp , Fosfolipase C beta/antagonistas & inibidores , Células Piramidais/efeitos dos fármacos , Células Piramidais/fisiologia , Ratos Sprague-Dawley , Receptor CB1 de Canabinoide/metabolismo , Receptor de Glutamato Metabotrópico 5/agonistas , Receptores de Glutamato Metabotrópico/agonistas , Receptores de Glutamato Metabotrópico/metabolismo , Técnicas de Cultura de TecidosRESUMO
Anorexia nervosa (AN) is a psychiatric illness characterized by restricted eating and irrational fears of gaining weight. There is no accepted pharmacological treatment for AN, and AN has the highest mortality rate among psychiatric illnesses. Anorexia nervosa most commonly affects females during adolescence, suggesting an effect of sex and hormones on vulnerability to the disease. Activity-based anorexia (ABA) is a rodent model of AN that shares symptoms with AN, including over-exercise, elevation of stress hormones, and genetic links to anxiety traits. We previously reported that ABA in adolescent female rats results in increased apical dendritic branching in CA1 pyramidal cells of the ventral hippocampus at postnatal day 44 (P44). To examine the long-term effects of adolescent ABA (P44) in female rats, we compared the apical branching in the ventral hippocampal CA1 after recovery from ABA (P51) and after a relapse of ABA (P55) with age-matched controls. To examine the age-dependence of the hippocampal plasticity, we examined the effect of ABA during adulthood (P67). We found that while ABA at P44 resulted in increased branching of ventral hippocampal pyramidal cells, relapse of ABA at P55 resulted in decreased branching. ABA induced during adulthood did not have an effect on dendritic branching, suggesting an age-dependence of the vulnerability to structural plasticity. Cells from control animals were found to exhibit a dramatic increase in branching, more than doubling from P44 to P51, followed by pruning from P51 to P55. The proportion of mature spines on dendrites from the P44-ABA animals is similar to that on dendrites from P55-CON animals. These results suggest that the experience of ABA may cause precocious anatomical development of the ventral hippocampus. Importantly, we found that adolescence is a period of continued development of the hippocampus, and increased vulnerability to mental disorders during adolescence may be due to insults during this developmentally critical period.
Assuntos
Anorexia/fisiopatologia , Região CA1 Hipocampal/crescimento & desenvolvimento , Região CA1 Hipocampal/fisiopatologia , Atividade Motora/fisiologia , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiopatologia , Animais , Anorexia/patologia , Peso Corporal , Região CA1 Hipocampal/patologia , Dendritos/patologia , Dendritos/fisiologia , Modelos Animais de Doenças , Feminino , Plasticidade Neuronal/fisiologia , Células Piramidais/patologia , Ratos Sprague-Dawley , RecidivaRESUMO
Calsyntenin-1 is a transmembrane cargo-docking protein important for kinesin-1-mediated fast transport of membrane-bound organelles that exhibits peak expression levels at postnatal day 7. However, its neuronal function during postnatal development remains unknown. We generated a knock-out mouse to characterize calsyntenin-1 function in juvenile mice. In the absence of calsyntenin-1, synaptic transmission was depressed. To address the mechanism, evoked EPSPs were analyzed revealing a greater proportion of synaptic GluN2B subunit-containing receptors typical for less mature synapses. This imbalance was due to a disruption in calsyntenin-1-mediated dendritic transport of NMDA receptor subunits. As a consequence of increased expression of GluN2B subunits, NMDA receptor-dependent LTP was enhanced at Schaffer collateral-CA1 pyramidal cell synapses. Interestingly, these defects were accompanied by a decrease in dendritic arborization and increased proportions of immature filopodia-like dendritic protrusions at the expense of thin-type dendritic spines in CA1 pyramidal cells. Thus, these results highlight a key role for calsyntenin-1 in the transport of NMDA receptors to synaptic targets, which is necessary for the maturation of neuronal circuits during early development.
Assuntos
Região CA1 Hipocampal/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Dendritos/metabolismo , Espinhas Dendríticas/metabolismo , Células Piramidais/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Animais , Região CA1 Hipocampal/citologia , Região CA1 Hipocampal/crescimento & desenvolvimento , Proteínas de Ligação ao Cálcio/genética , Potenciais Pós-Sinápticos Excitadores/fisiologia , Camundongos , Camundongos Knockout , Células Piramidais/citologia , Células Piramidais/crescimento & desenvolvimento , Sinapses/fisiologiaRESUMO
Serotonin (5-HT) plays important roles during neural development. Administration of selective serotonin reuptake inhibitor (SSRI)-type medication during gestation may influence the maturation of the fetal brain and subsequent brain functions. To mimic the condition of late-gestation SSRI exposure, we administered fluoxetine (FLX) in neonatal rats during the first postnatal week, which roughly corresponds to the third trimester period of human gestation. FLX-exposed adult male rats exhibited reduced locomotor activity and depression-like behaviors. Furthermore, sensorimotor gating capacity was also impaired. Interestingly, increased social interaction was noticed in FLX-exposed rats. When the levels of 5-HT and tryptophan hydroxylase were examined, no significant changes were found in FLX rats compared to control (CON) rats. The behavioral phenotypes of FLX rats suggested malfunction of the limbic system. Dendritic architectures of neurons in the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) were examined. Layer II/III mPFC pyramidal neurons in FLX rats had exuberant dendritic branches with elongated terminal segments compared to those in CON rats. In BLA pyramidal neurons, the dendritic profiles were comparable between the two groups. However, in FLX rats, the density of dendritic spines was reduced in both mPFC and BLA. Together, our results demonstrated the long-lasting effects of early FLX treatment on emotional and social behaviors in adult rats in which impaired neuronal structure in the limbic system was also noticed. The risk of taking SSRI-type antidepressants during pregnancy should be considered.
Assuntos
Encéfalo/efeitos dos fármacos , Encéfalo/crescimento & desenvolvimento , Fluoxetina/toxicidade , Inibidores Seletivos de Recaptação de Serotonina/toxicidade , Animais , Animais Recém-Nascidos , Encéfalo/patologia , Encéfalo/fisiopatologia , Dendritos/efeitos dos fármacos , Dendritos/patologia , Dendritos/fisiologia , Depressão/induzido quimicamente , Depressão/patologia , Depressão/fisiopatologia , Ácido Hidroxi-Indolacético/metabolismo , Masculino , Atividade Motora/fisiologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/patologia , Células Piramidais/fisiopatologia , Distribuição Aleatória , Ratos Wistar , Filtro Sensorial/fisiologia , Serotonina/metabolismo , Comportamento Social , Triptofano Hidroxilase/metabolismoRESUMO
Synaptic plasticity rules change during development: while hippocampal synapses can be potentiated by a single action potential pairing protocol in young neurons, mature neurons require burst firing to induce synaptic potentiation. An essential component for spike timing-dependent plasticity is the backpropagating action potential (BAP). BAP along the dendrites can be modulated by morphology and ion channel composition, both of which change during late postnatal development. However, it is unclear whether these dendritic changes can explain the developmental changes in synaptic plasticity induction rules. Here, we show that tonic GABAergic inhibition regulates dendritic action potential backpropagation in adolescent, but not preadolescent, CA1 pyramidal neurons. These developmental changes in tonic inhibition also altered the induction threshold for spike timing-dependent plasticity in adolescent neurons. This GABAergic regulatory effect on backpropagation is restricted to distal regions of apical dendrites (>200 µm) and mediated by α5-containing GABA(A) receptors. Direct dendritic recordings demonstrate α5-mediated tonic GABA(A) currents in adolescent neurons which can modulate BAPs. These developmental modulations in dendritic excitability could not be explained by concurrent changes in dendritic morphology. To explain our data, model simulations propose a distally increasing or localized distal expression of dendritic α5 tonic inhibition in mature neurons. Overall, our results demonstrate that dendritic integration and plasticity in more mature dendrites are significantly altered by tonic α5 inhibition in a dendritic region-specific and developmentally regulated manner.
Assuntos
Potenciais de Ação , Região CA1 Hipocampal/fisiologia , Dendritos/fisiologia , Antagonistas GABAérgicos/farmacologia , Plasticidade Neuronal , Células Piramidais/fisiologia , Animais , Região CA1 Hipocampal/citologia , Região CA1 Hipocampal/crescimento & desenvolvimento , Região CA1 Hipocampal/metabolismo , Dendritos/efeitos dos fármacos , Dendritos/metabolismo , Dendritos/ultraestrutura , Potenciais Pós-Sinápticos Excitadores , Agonistas GABAérgicos/farmacologia , Potenciais Pós-Sinápticos Inibidores , Masculino , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/metabolismo , Ratos , Ratos Wistar , Receptores de GABA-A/metabolismoRESUMO
The hippocampal formation (HF) is a unique structure in the mammalian brain and is subdivided into the dentate gyrus, Ammon's horn, and subiculum by their functions and connectivity in the neuronal circuit. Because behaviors of the neural stem cells, neuronal progenitors, and the differentiating neurons are complex during hippocampal morphogenesis, the differentiation of these subdivisions has not been well understood. In this study, we investigated embryonic and postnatal expression of the proteins Prox1, Math2, and Ctip2, which clearly indicate principal cells of the dentate gyrus (Prox1 positive) and Ammon's horn (Math2 and Ctip2 positive). Expression patterns of Prox1 and Math2 were consistent with previously suggested localization of migratory pathways of the dentate granule cells and hippocampal pyramidal cells. Interestingly, we found intermingling of Prox1-expressing cells and Math2-expressing cells in a cell migratory stream, suggesting previously unknown behaviors of differentiating cells of the HF.
Assuntos
Movimento Celular/fisiologia , Hipocampo/anatomia & histologia , Hipocampo/crescimento & desenvolvimento , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Hipocampo/fisiologia , Proteínas de Homeodomínio/metabolismo , Imuno-Histoquímica , Camundongos Endogâmicos C57BL , Proteínas do Tecido Nervoso/metabolismo , Células-Tronco Neurais/citologia , Células-Tronco Neurais/fisiologia , Neurogênese/fisiologia , Células Piramidais/citologia , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Proteínas Repressoras/metabolismo , Proteínas Supressoras de Tumor/metabolismoRESUMO
Ketamine, a dissociative anesthetic most commonly used in many pediatric procedures, has been reported in many animal studies to cause widespread neuroapoptosis in the neonatal brain after exposure in high doses and/or for a prolonged period. This neurodegenerative change occurs most severely in the forebrain including the anterior cingulate cortex (ACC) that is an important brain structure for mediating a variety of cognitive functions. However, it is still unknown whether such apoptotic neurodegeneration early in life would subsequently impair the synaptic plasticity of the ACC later in life. In this study, we performed whole-cell patch-clamp recordings from the ACC brain slices of young adult rats to examine any alterations in long-term synaptic plasticity caused by neonatal ketamine exposure. Ketamine was administered at postnatal day 4-7 (subcutaneous injections, 20mg/kg given six times, once every 2h). At 3-4weeks of age, long-term potentiation (LTP) was induced and recorded by monitoring excitatory postsynaptic currents from ACC slices. We found that the induction of LTP in the ACC was significantly reduced when compared to the control group. The LTP impairment was accompanied by an increase in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated excitatory synaptic transmission and a decrease in GABA inhibitory synaptic transmission in neurons of the ACC. Thus, our present findings show that neonatal ketamine exposure causes a significant LTP impairment in the ACC. We suggest that the imbalanced synaptic transmission is likely to contribute to ketamine-induced LTP impairment in the ACC.
Assuntos
Anestésicos Dissociativos/toxicidade , Giro do Cíngulo/efeitos dos fármacos , Giro do Cíngulo/crescimento & desenvolvimento , Ketamina/toxicidade , Plasticidade Neuronal/efeitos dos fármacos , Animais , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Feminino , Giro do Cíngulo/fisiopatologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Potenciação de Longa Duração/efeitos dos fármacos , Potenciação de Longa Duração/fisiologia , Masculino , Plasticidade Neuronal/fisiologia , Técnicas de Patch-Clamp , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Distribuição Aleatória , Ratos Sprague-Dawley , Receptores de AMPA/metabolismo , Receptores de GABA-A/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Técnicas de Cultura de TecidosRESUMO
Converging epidemiological studies indicate that cannabis abuse during adolescence increases the risk of developing psychosis and prefrontal cortex (PFC)-dependent cognitive impairments later in life. However, the mechanisms underlying the adolescent susceptibility to chronic cannabis exposure are poorly understood. Given that the psychoactive constituent of cannabis binds to the CB1 cannabinoid receptor, the present study was designed to determine the impact of a CB1 receptor agonist (WIN) during specific windows of adolescence on the functional maturation of the rat PFC. By means of local field potential recordings and ventral hippocampal stimulation in vivo, we found that a history of WIN exposure during early (postnatal days - P35-40) or mid-(P40-45) adolescence, but not in late adolescence (P50-55) or adulthood (P75-80), is sufficient to yield a state of frequency-dependent prefrontal disinhibition in adulthood comparable to that seen in the juvenile PFC. Remarkably, this prefrontal disinhibition could be normalized following a single acute local infusion of the GABA-Aα1 positive allosteric modulator Indiplon, suggesting that adolescent exposure to WIN causes a functional downregulation of GABAergic transmission in the PFC. Accordingly, in vitro recordings from adult rats exposed to WIN during adolescence demonstrate that local prefrontal GABAergic transmission onto layer V pyramidal neurons is markedly reduced to the level seen in the P30-35 PFC. Together, these results indicate that early and mid-adolescence constitute a critical period during which repeated CB1 receptor stimulation is sufficient to elicit an enduring state of PFC network disinhibition resulting from a developmental impairment of local prefrontal GABAergic transmission.
Assuntos
Benzoxazinas/farmacologia , Fármacos do Sistema Nervoso Central/farmacologia , Morfolinas/farmacologia , Naftalenos/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/crescimento & desenvolvimento , Receptor CB1 de Canabinoide/agonistas , Ácido gama-Aminobutírico/metabolismo , Animais , Benzodiazepinas/farmacologia , Estimulação Elétrica , Moduladores GABAérgicos/farmacologia , Hipocampo/efeitos dos fármacos , Hipocampo/crescimento & desenvolvimento , Hipocampo/fisiologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Masculino , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Técnicas de Patch-Clamp , Piperidinas/farmacologia , Córtex Pré-Frontal/fisiologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Pirazóis/farmacologia , Distribuição Aleatória , Ratos Sprague-Dawley , Receptor CB1 de Canabinoide/metabolismo , Receptores de GABA-A/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Tiofenos/farmacologiaRESUMO
Sevoflurane is one of inhalation anesthetics and has been commonly used in obstetric and pediatric anesthesia. The widespread use of sevoflurane in newborns and infants has made its safety a health issue of concern. Voltage-gated Ca(2+) channels (VGCCs) play an important role in neuronal excitability and are essential for normal brain development. However, the role of sevoflurane on regulating Ca(2+) channels during the period of rapid brain development is still not well understood. The aim of this study is to explore the effects of sevoflurane on voltage-gated Ca(2+) channels for hippocampal CA1 pyramidal neurons during the period of rapid brain development. 1-week-old Sprague-Dawley rats were randomly divided into 3 groups: control group, 2.1% sevoflurane group (exposed to 2.1% sevoflurane for 6h) and 3% sevoflurane group (exposed to 3% sevoflurane for 6h). Whole-cell patch clamp technique was used. I-V curve, steady-state activation and inactivation curves of Ca(2+) channels were studied in rats of the both 3 treated groups at 5 different ages (1 week, 2 weeks, 3 weeks, 4 and 5 weeks old). After anesthesia with sevoflurane at 1-week-old rats, Ca(2+) channels current density was significantly decreased at week 1 and week 2 (p<0.01). And 3% sevoflurane exposure resulted in a rightward shift in steady-state activation curve at week 1 and week 2, as well as the inactivation curve from week 1 to week 3. However, the 2.1% sevoflurane-induced rightward shift was only found in steady-state inactivation curve of Ca(2+) channels at week 1 and week 2. Both the slope factor (k) of Ca(2+) channels activation and inactivation curves increased by 3% sevoflurane at week 1 (p<0.05). Therefore, early exposure to sevoflurane persistently inhibits Ca(2+) channels activity in hippocampal CA1 pyramidal neurons of developing rats but the development of Ca(2+) channels recovers to normal level at juvenile age. Moreover, the inhibition of 3% sevoflurane on VGCCs is greater than that of 2.1% sevoflurane.
Assuntos
Anestésicos Inalatórios/efeitos adversos , Região CA1 Hipocampal/crescimento & desenvolvimento , Canais de Cálcio/metabolismo , Éteres Metílicos/efeitos adversos , Fatores Etários , Animais , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/fisiologia , Relação Dose-Resposta a Droga , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Técnicas de Patch-Clamp , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Distribuição Aleatória , Ratos , Ratos Sprague-Dawley , SevofluranoRESUMO
Following their birth in the adult hippocampal dentate gyrus, newborn progenitor cells migrate into the granule cell layer where they differentiate, mature, and functionally integrate into existing circuitry. The hypothesis that adult hippocampal neurogenesis is physiologically important has gained traction, but the precise role of newborn neurons in hippocampal function remains unclear. We investigated whether loss of new neurons impacts dendrite morphology and glutamate levels in area CA3 of the hippocampus by utilizing a human GFAP promoter-driven thymidine kinase genetic mouse model to conditionally suppress adult neurogenesis. We found that chronic ablation of new neurons induces remodeling in CA3 pyramidal cells and increases stress-induced release of the neurotransmitter glutamate. The ability of persistent impairment of adult neurogenesis to influence hippocampal dendrite morphology and excitatory amino acid neurotransmission has important implications for elucidating newborn neuron function, and in particular, understanding the role of these cells in stress-related excitoxicity.
Assuntos
Hipocampo/metabolismo , Neurogênese/fisiologia , Neurônios/metabolismo , Células Piramidais/metabolismo , Estresse Fisiológico , Envelhecimento , Animais , Animais Recém-Nascidos , Atrofia/tratamento farmacológico , Giro Denteado/patologia , Feminino , Ácido Glutâmico/metabolismo , Hipocampo/crescimento & desenvolvimento , Hipocampo/patologia , Masculino , Camundongos Endogâmicos C57BL , Células Piramidais/crescimento & desenvolvimentoRESUMO
A compromised γ-aminobutyric acid (GABA)ergic system is hypothesized to be part of the underlying pathophysiology of schizophrenia. N-methyl-D-aspartate (NMDA) receptor hypofunction during neurodevelopment is proposed to disrupt maturation of interneurons causing an impaired GABAergic transmission in adulthood. The present study examines prefrontal GABAergic transmission in adult rats administered with the NMDA receptor channel blocker, phencyclidine (PCP), for 3 days during the second postnatal week. Whole-cell patch-clamp recordings from pyramidal cells in PCP-treated rats showed a 22% reduction in the frequency of miniature inhibitory postsynaptic currents in layer II/III, but not in layer V pyramidal neurons of the prefrontal cortex. Furthermore, early postnatal PCP treatment caused insensitivity toward effects of the GABA transporter 1 (GAT-1) inhibitor, 1,2,5,6-tetrahydro-1-[2-[[(diphenyl-methylene)amino]oxy]ethyl]-3-pyridinecarboxylic acid, and also diminished currents passed by δ-subunit-containing GABAA receptors in layer II/III pyramidal neurons. The observed impairments in GABAergic function are compatible with the alteration of GABAergic markers as well as cognitive dysfunction observed in early postnatal PCP-treated rats and support the hypothesis that PCP administration during neurodevelopment affects the functionality of interneurons in later life.
Assuntos
Antagonistas de Aminoácidos Excitatórios/toxicidade , Fenciclidina/toxicidade , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/crescimento & desenvolvimento , Ácido gama-Aminobutírico/metabolismo , Animais , Animais Recém-Nascidos , Estimulação Elétrica , Antagonistas GABAérgicos/farmacologia , Proteínas da Membrana Plasmática de Transporte de GABA/metabolismo , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Interneurônios/efeitos dos fármacos , Interneurônios/fisiologia , Potenciais Pós-Sinápticos em Miniatura/efeitos dos fármacos , Potenciais Pós-Sinápticos em Miniatura/fisiologia , Ácidos Nipecóticos/farmacologia , Oximas/farmacologia , Técnicas de Patch-Clamp , Córtex Pré-Frontal/fisiologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Piridazinas/farmacologia , Ratos Endogâmicos ACI , Receptores de GABA-A/metabolismo , Técnicas de Cultura de TecidosRESUMO
BACKGROUND: The experience of early stress contributes to the etiology of several psychiatric disorders and can lead to lasting deficits in working memory and attention. These executive functions require activation of the prefrontal cortex (PFC) by muscarinic M1 acetylcholine (ACh) receptors. Such Gαq-protein coupled receptors trigger the release of calcium (Ca(2+)) from internal stores and elicit prolonged neuronal excitation. METHODS: In brain slices of rat PFC, we employed multiphoton imaging simultaneously with whole-cell electrophysiological recordings to examine potential interactions between ACh-induced Ca(2+) release and excitatory currents in adulthood, across postnatal development, and following the early stress of repeated maternal separation, a rodent model for depression. We also investigated developmental changes in related genes in these groups. RESULTS: Acetylcholine-induced Ca(2+) release potentiates ACh-elicited excitatory currents. In the healthy PFC, this potentiation of muscarinic excitation emerges in young adulthood, when executive function typically reaches maturity. However, the developmental consolidation of muscarinic ACh signaling is abolished in adults with a history of early stress, where ACh responses retain an adolescent phenotype. In prefrontal cortex, these rats show a disruption in the expression of multiple developmentally regulated genes associated with Gαq and Ca(2+) signaling. Pharmacologic and ionic manipulations reveal that the enhancement of muscarinic excitation in the healthy adult PFC arises via the electrogenic process of sodium/Ca(2+) exchange. CONCLUSIONS: This work illustrates a long-lasting disruption in ACh-mediated cortical excitation following early stress and raises the possibility that such cellular mechanisms may disrupt the maturation of executive function.
Assuntos
Acetilcolina/metabolismo , Cálcio/metabolismo , Privação Materna , Córtex Pré-Frontal/crescimento & desenvolvimento , Córtex Pré-Frontal/fisiopatologia , Estresse Psicológico/fisiopatologia , Animais , Depressão , Modelos Animais de Doenças , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Masculino , Técnicas de Patch-Clamp , Córtex Pré-Frontal/efeitos dos fármacos , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiopatologia , Distribuição Aleatória , Ratos Sprague-Dawley , Técnicas de Cultura de TecidosRESUMO
Spontaneous network activity is believed to sculpt developing neural circuits. Spontaneous giant depolarizing potentials (GDPs) were first identified with single-cell recordings from rat CA3 pyramidal neurons, but here we identify and characterize a large-scale spontaneous network activity we term global network activation (GNA) in the developing mouse hippocampal slices, which is measured macroscopically by fast voltage-sensitive dye imaging. The initiation and propagation of GNA in the mouse is largely GABA-independent and dominated by glutamatergic transmission via AMPA receptors. Despite the fact that signal propagation in the adult hippocampus is strongly unidirectional through the canonical trisynaptic circuit (dentate gyrus [DG] to CA3 to CA1), spontaneous GNA in the developing hippocampus originates in distal CA3 and propagates both forward to CA1 and backward to DG. Photostimulation-evoked GNA also shows prominent backward propagation in the developing hippocampus from CA3 to DG. Mouse GNA is strongly correlated to electrophysiological recordings of highly localized single-cell and local field potential events. Photostimulation mapping of neural circuitry demonstrates that the enhancement of local circuit connections to excitatory pyramidal neurons occurs over the same time course as GNA and reveals the underlying pathways accounting for GNA backward propagation from CA3 to DG. The disappearance of GNA coincides with a transition to the adult-like unidirectional circuit organization at about 2 weeks of age. Taken together, our findings strongly suggest a critical link between GNA activity and maturation of functional circuit connections in the developing hippocampus.
Assuntos
Hipocampo/crescimento & desenvolvimento , Hipocampo/fisiologia , Animais , Hipocampo/citologia , Hipocampo/efeitos dos fármacos , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Camundongos Endogâmicos C57BL , Microeletrodos , Vias Neurais/efeitos dos fármacos , Vias Neurais/crescimento & desenvolvimento , Vias Neurais/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Estimulação Luminosa , Células Piramidais/citologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/fisiologia , Receptores de GABA-B/metabolismo , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Técnicas de Cultura de Tecidos , Imagens com Corantes Sensíveis à VoltagemRESUMO
Ethanol is known as a potent teratogen having adverse effects on brain and behavior. However, some of the behavioral deficits caused by fetal alcohol exposure and well expressed in juveniles ameliorate with maturation may suggest some kind of functional recovery occurring during postnatal development. The aim of this study was to reexamine age-dependent behavioral impairments in fetal-alcohol rats and to investigate the changes in neurogenesis and gross morphology of the hippocampus during a protracted postnatal period searching for developmental deficits and/or delays that would correlate with behavioral impairments in juveniles and for potential compensatory processes responsible for their amelioration in adults. Ethanol was delivered to the pregnant dams by intragastric intubation throughout 7-21 gestation days at daily dose of 6 g/kg. Isocaloric intubation and intact control groups were included. Locomotor activity, anxiety, and spatial learning tasks were applied to juvenile and young-adult rats from all groups. Unbiased stereological estimates of hippocampal volumes, the total number of pyramidal and granular cells, and double cortin expressing neurons were carried out for postnatal days (PDs) PD1, PD10, PD30, and PD60. Alcohol insult during second trimester equivalent caused significant deficits in the spatial learning in juvenile rats; however, its effect on hippocampal morphology was limited to a marginally lower number of granular cells in dentate gyrus (DG) on PD30. Thus, initial behavioral deficits and the following functional recovery in fetal-alcohol subjects may be due to more subtle plastic changes within the hippocampal formation but also in other structures of the extended hippocampal circuit. Further investigation is required.
Assuntos
Comportamento Animal/fisiologia , Etanol/toxicidade , Transtornos do Espectro Alcoólico Fetal/patologia , Transtornos do Espectro Alcoólico Fetal/fisiopatologia , Hipocampo/patologia , Hipocampo/fisiopatologia , Efeitos Tardios da Exposição Pré-Natal , Animais , Comportamento Animal/efeitos dos fármacos , Contagem de Células , Depressores do Sistema Nervoso Central/efeitos adversos , Proteínas do Domínio Duplacortina , Proteína Duplacortina , Comportamento Exploratório/efeitos dos fármacos , Comportamento Exploratório/fisiologia , Feminino , Hipocampo/efeitos dos fármacos , Hipocampo/crescimento & desenvolvimento , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Aprendizagem em Labirinto/fisiologia , Proteínas Associadas aos Microtúbulos/metabolismo , Neurogênese/efeitos dos fármacos , Neurogênese/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/patologia , Neurônios/fisiologia , Neuropeptídeos/metabolismo , Tamanho do Órgão , Gravidez , Células Piramidais/efeitos dos fármacos , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/patologia , Células Piramidais/fisiologia , Ratos WistarRESUMO
There is recent evidence of continuing development throughout adolescence in two neural areas involved in emotion and cognition, the basolateral amygdala (BLN) and the medial prefrontal cortex (mPFC). Previous research from our laboratory has demonstrated a cellular loss in both of these brain regions in rats between postnatal day (P) 35 and 90. This study investigates dendritic changes in pyramidal neurons of the BLN and Layer 5 of the mPFC at P20 (juvenile), 35 (puberty), and 90 (adulthood) in hooded rats of both sexes. Dendritic branching and dendritic spines were quantified in Golgi-Cox impregnated tissue. Between P20 and 35, dendritic length and complexity, as well as the density of dendritic spines, increased in both structures. Between P35 and 90, dendritic spines in the mPFC neurons significantly decreased in both sexes, while a loss of basilar dendrites was only detected in females. In the BLN, there was an increase in the number of branches between P35 and 90 without an increase in the total length of the dendritic tree. BLN spine density also remained stable during this period. These results show that the dendritic tree grows prior to puberty while dendritic remodeling and pruning occurs after puberty in both of these neural areas. This late development may lead to susceptibilities to psychopathologies and addictions that often develop at this time.
Assuntos
Tonsila do Cerebelo/crescimento & desenvolvimento , Espinhas Dendríticas , Córtex Pré-Frontal/crescimento & desenvolvimento , Tonsila do Cerebelo/citologia , Animais , Feminino , Masculino , Córtex Pré-Frontal/citologia , Células Piramidais/citologia , Células Piramidais/crescimento & desenvolvimento , Ratos , Ratos Long-Evans , Fatores SexuaisRESUMO
Proper distribution of axonal mitochondria is critical for multiple neuronal functions. To understand the underlying mechanisms for population behavior, quantitative characterisation of elemental dynamics on multiple time scales is required. Here we investigated the stability and transport of axonal mitochondria using live-cell imaging of cultured mouse hippocampal neurons. We first characterised the long-term stability of stationary mitochondria. At a given moment, about 10% of the mitochondria were in a state of transport and the remaining 90% were stationary. Among these stationary mitochondria, 40% of them remained in the same position over several days. The rest of the mitochondria transited to mobile state stochastically and this process could be detected and quantitatively analysed by time-lapse imaging with intervals of 30 min. The stability of axonal mitochondria increased from 2 to 3 weeks in culture, was decreased by tetrodotoxin treatment, and was higher near synapses. Stationary mitochondria should be generated by pause of moving mitochondria and subsequent stabilisation. Therefore, we next analysed pause events of moving mitochondria by repetitive imaging at 0.3 Hz. We found that the probability of transient pause increased with field stimulation, decreased with tetrodotoxin treatment, and was higher near synapses. Finally, by combining parameters obtained from time-lapse imaging with different time scales, we could estimate transition rates between different mitochondrial states. The analyses suggested specific developmental regulation in the probability of paused mitochondria to transit into stationary state. These findings indicate that multiple mitochondrial behaviors, especially those regulated by neuronal activity and synapse location, determine their distribution in the axon.
Assuntos
Axônios/metabolismo , Mitocôndrias/metabolismo , Dinâmica Mitocondrial , Células Piramidais/metabolismo , Sinapses , Animais , Células Cultivadas , Camundongos , Células Piramidais/citologia , Células Piramidais/crescimento & desenvolvimentoRESUMO
Hippocampal neurons play a critical role in learning and memory; however, the effects of environmental mechanical forces on neurite extension and associated underlying mechanisms are largely unexplored, possibly due to difficulties in maintaining central nervous system neurons. Neuron adhesion, neurite length, and mechanotransduction are mainly influenced by the extracellular matrix (ECM), which is often associated with structural scaffolding. In this study, we investigated the relationship between substrate stiffness and hippocampal neurite outgrowth by controlling the ratios of polydimethylsiloxane (PDMS) base to curing agent to create substrates of varying stiffness. Immunostaining results demonstrated that hippocampal neurons have longer neurite elongation in 35:1 PDMS substrate compared those grown on 15:1 PDMS, indicating that soft substrates provide a more optimal stiffness for hippocampal neurons. Additionally, we discovered that pPKCα expression was higher in the 15:1 and 35:1 PDMS groups than in the poly-L-lysine-coated glass group. However, when we used a fibronectin (FN) coating, we found that pFAKy397 and pFAKy925 expression were higher in glass group than in the 15:1 or 35: 1 PDMS groups, but pPKCα and pERK1/2 expression were higher in the 35:1 PDMS group than in the glass group. These results support the hypothesis that environmental stiffness influences hippocampal neurite outgrowth and underlying signaling pathways.
Assuntos
Hipocampo/citologia , Hipocampo/metabolismo , Neuritos/metabolismo , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/metabolismo , Animais , Proteína-Tirosina Quinases de Adesão Focal/metabolismo , Camundongos , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Cultura Primária de Células , Proteína Quinase C-alfa/metabolismoRESUMO
Schizophrenia is a neurodevelopmental disorder whose clinical features include impairments in perception, cognition and motivation. These impairments reflect alterations in neuronal circuitry within and across multiple brain regions that are due, at least in part, to deficits in dendritic spines, the site of most excitatory synaptic connections. Dendritic spine alterations have been identified in multiple brain regions in schizophrenia, but are best characterized in layer 3 of the neocortex, where pyramidal cell spine density is lower. These spine deficits appear to arise during development, and thus are likely the result of disturbances in the molecular mechanisms that underlie spine formation, pruning, and/or maintenance. Each of these mechanisms may provide insight into novel therapeutic targets for preventing or repairing the alterations in neural circuitry that mediate the debilitating symptoms of schizophrenia.
Assuntos
Espinhas Dendríticas/patologia , Neocórtex/patologia , Esquizofrenia/patologia , Humanos , Neocórtex/crescimento & desenvolvimento , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/patologiaRESUMO
The neuron-specific K-Cl cotransporter, KCC2, is highly expressed in the vicinity of excitatory synapses in pyramidal neurons, and recent in vitro data suggest that this protein plays a role in the development of dendritic spines. The in vivo relevance of these observations is, however, unknown. Using in utero electroporation combined with post hoc iontophoretic injection of Lucifer Yellow, we show that premature expression of KCC2 induces a highly significant and permanent increase in dendritic spine density of layer 2/3 pyramidal neurons in the somatosensory cortex. Whole-cell recordings revealed that this increased spine density is correlated with an enhanced spontaneous excitatory activity in KCC2-transfected neurons. Precocious expression of the N-terminal deleted form of KCC2, which lacks the chloride transporter function, also increased spine density. In contrast, no effect on spine density was observed following in utero electroporation of a point mutant of KCC2 (KCC2-C568A) where both the cotransporter function and the interaction with the cytoskeleton are disrupted. Transfection of the C-terminal domain of KCC2, a region involved in the interaction with the dendritic cytoskeleton, also increased spine density. Collectively, these results demonstrate a role for KCC2 in excitatory synaptogenesis in vivo through a mechanism that is independent of its ion transport function.
Assuntos
Espinhas Dendríticas/metabolismo , Neurogênese/fisiologia , Células Piramidais/crescimento & desenvolvimento , Células Piramidais/metabolismo , Simportadores/metabolismo , Animais , Eletroporação , Imuno-Histoquímica , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Córtex Somatossensorial/crescimento & desenvolvimento , Córtex Somatossensorial/metabolismo , Transfecção , Cotransportadores de K e Cl-RESUMO
Accumulating evidence suggests that global depletion of adult hippocampal neurogenesis influences its function and that the timing of the depletion affects the deficits. However, the behavioral roles of adult-born neurons during their establishment of projections to CA3 pyramidal neurons remain largely unknown. We used a combination of retroviral and optogenetic approaches to birth date and reversibly control a group of adult-born neurons in adult mice. Adult-born neurons formed functional synapses on CA3 pyramidal neurons as early as 2 weeks after birth, and this projection to the CA3 area became stable by 4 weeks in age. Newborn neurons at this age were more plastic than neurons at other stages. Notably, we found that reversibly silencing this cohort of ~4-week-old cells after training, but not cells of other ages, substantially disrupted retrieval of hippocampal memory. Our results identify a restricted time window for adult-born neurons essential in hippocampal memory retrieval.