RESUMO
The aim of the present study was to evaluate the effect of rosiglitazone (RSG) or pioglitazone (POG) on the synaptic plasticity, neuronal apoptosis, brain-derived neurotrophic factor (BDNF), and nitric oxide (NO) metabolites in the hippocampus of juvenile hypothyroid rats. The animals were divided into four groups: control; propylthiouracil (PTU), 0.05% dose in drinking water for 42 days; PTU-POG; and PTU-RSG. The POG (20 mg/kg) and the RSG (4 mg/kg) were administered by IP injection. We conducted longterm potentiation (LTP) in the cornu ammonis 1 area of the hippocampus using highfrequency stimulation of the Schaffer collateral pathway. Then, the hippocampal tissues were collected to determine BDNF and NO levels and the degree of apoptosis. PTU administration decreased the slope (10-90%) and amplitude of the fEPSPs compared to control. Injection of RSG or POG increased the slope, slope (10-90%), and amplitude of the fEPSP in the PTUPOG or PTURSG groups compared to the PTU group. TUNELpositive neurons and NO metabolites in the hippocampus of the PTU group were higher than those of the control group. RSG or POG increased BDNF content in PTU-POG or PTU-RSG groups. Treatment of the rats with POG or RSG decreased apoptotic neurons and NO metabolites in the hippocampus of PTU-POG or PTU-RSG groups, respectively, compared to the PTU group. This study's results revealed that POG or RSG normalized LTP impairment, neuronal apoptosis, and improved BDNF content in the hippocampal tissue of juvenile hypothyroid rats.
Assuntos
Apoptose , Fator Neurotrófico Derivado do Encéfalo , Hipocampo , Hipotireoidismo , Potenciação de Longa Duração , PPAR gama , Ratos Wistar , Rosiglitazona , Animais , Apoptose/efeitos dos fármacos , Hipotireoidismo/tratamento farmacológico , Hipotireoidismo/induzido quimicamente , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Masculino , Rosiglitazona/farmacologia , Potenciação de Longa Duração/efeitos dos fármacos , PPAR gama/agonistas , PPAR gama/metabolismo , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Tiazolidinedionas/farmacologia , Pioglitazona/farmacologia , Ratos , Propiltiouracila/farmacologia , Modelos Animais de Doenças , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Óxido Nítrico/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismoRESUMO
The medial prefrontal cortex (mPFC) plays a pivotal role in regulating working memory, executive function, and self-regulatory behaviors. Dysfunction in the mPFC circuits is a characteristic feature of several neuropsychiatric disorders including schizophrenia, depression, and post-traumatic stress disorder. Chronic stress (CS) is widely recognized as a major triggering factor for the onset of these disorders. Although evidence suggests synaptic dysfunction in mPFC circuits following CS exposure, it remains unclear how different neuronal populations in the infralimbic (IL) and prelimbic (PL) cortices are affected in terms of synaptic inhibition/excitation balance (I/E ratio). Here, using neuroproteomic analysis and whole-cell patch-clamp recordings in pyramidal neurons (PNs) and parvalbumin (PV) interneurons within the PL and IL cortices, we examined the synaptic changes after 21â d of chronic unpredictable stress, in male mice. Our results reveal distinct impacts of CS on PL and IL PNs, resulting in an increased I/E ratio in both subregions but through different mechanisms: CS increases inhibitory synaptic drive in the PL while decreasing excitatory synaptic drive in the IL. Notably, the I/E ratio and excitatory and inhibitory synaptic drive of PV interneurons remained unaffected in both PL and IL circuits following CS exposure. These findings offer novel mechanistic insights into the influence of CS on mPFC circuits and support the hypothesis of stress-induced mPFC hypofunction.
Assuntos
Interneurônios , Camundongos Endogâmicos C57BL , Parvalbuminas , Córtex Pré-Frontal , Células Piramidais , Estresse Psicológico , Animais , Interneurônios/fisiologia , Interneurônios/metabolismo , Células Piramidais/fisiologia , Masculino , Estresse Psicológico/fisiopatologia , Parvalbuminas/metabolismo , Inibição Neural/fisiologia , Camundongos , Técnicas de Patch-Clamp , Potenciais Pós-Sinápticos Excitadores/fisiologia , Sinapses/fisiologia , Potenciais Pós-Sinápticos Inibidores/fisiologiaRESUMO
Hyperexcitability of motor neurons and spinal cord motor circuitry has been widely reported in the early stages of Amyotrophic Lateral Sclerosis (ALS). Changes in the relative amount of excitatory to inhibitory inputs onto a neuron (E:I synaptic ratio), possibly through a developmental shift in synapse formation in favour of excitatory transmission, could underlie pathological hyperexcitability. Given that astrocytes play a major role in early synaptogenesis and are implicated in ALS pathogenesis, their potential contribution to disease mechanisms involving synaptic imbalances and subsequent hyperexcitability is also of great interest. In order to assess E:I ratios in ALS, we utilised a novel primary spinal neuron / astrocyte co-culture system, derived from neonatal mice, in which synapses are formed in vitro. Using multiple ALS mouse models we found that no combination of astrocyte or neuron genotype produced alterations in E:I synaptic ratios assessed using pre- and post-synaptic anatomical markers. Similarly, we observed that ephrin-B1, a major contact-dependent astrocytic synaptogenic protein, was not differentially expressed by ALS primary astrocytes. Further to this, analysis of E:I ratios across the entire grey matter of the lumbar spinal cord in young (post-natal day 16-19) ALS mice revealed no differences versus controls. Finally, analysis in co-cultures of human iPSC-derived motor neurons and astrocytes harbouring the pathogenic C9orf72 hexanucleotide repeat expansion showed no evidence of a bias toward excitatory versus inhibitory synapse formation. We therefore conclude, utilising multiple ALS models, that we do not observe significant changes in the relative abundance of excitatory versus inhibitory synapses as would be expected if imbalances in synaptic inputs contribute to early hyperexcitability.
Assuntos
Esclerose Lateral Amiotrófica , Astrócitos , Técnicas de Cocultura , Modelos Animais de Doenças , Neurônios Motores , Medula Espinal , Sinapses , Esclerose Lateral Amiotrófica/patologia , Esclerose Lateral Amiotrófica/fisiopatologia , Esclerose Lateral Amiotrófica/metabolismo , Esclerose Lateral Amiotrófica/genética , Animais , Astrócitos/metabolismo , Astrócitos/patologia , Camundongos , Sinapses/metabolismo , Sinapses/fisiologia , Neurônios Motores/metabolismo , Neurônios Motores/patologia , Neurônios Motores/fisiologia , Medula Espinal/metabolismo , Medula Espinal/patologia , Humanos , Potenciais Pós-Sinápticos Excitadores , Camundongos Transgênicos , Células Cultivadas , Transmissão SinápticaRESUMO
The convergence of conditioned and unconditioned stimuli (CS and US) into the lateral amygdala (LA) serves as a substrate for an adequate fear response in vivo. This well-known Pavlovian paradigm modulates the synaptic plasticity of neurons, as can be proved by the long-term potentiation (LTP) phenomenon in vitro. Although there is an increasing body of evidence for the existence of LTP in the amygdala, only a few studies were able to show a reliable long-term depression (LTD) of excitation in this structure. We have used coronal brain slices and conducted patch-clamp recordings in pyramidal neurons of the lateral amygdala (LA). After obtaining a stable baseline excitatory postsynaptic current (EPSC) response at a holding potential of -70 mV, we employed a paired-pulse paradigm at 1 Hz at the same membrane potential and could observe a reliable LTD. The different durations of stimulation (ranging between 1.5-24 min) were tested first in the same neuron, but the intensity was kept constant. The latter paradigm resulted in a step-wise LTD with a gradually increasing magnitude under these conditions.
Assuntos
Tonsila do Cerebelo , Potenciais Pós-Sinápticos Excitadores , Depressão Sináptica de Longo Prazo , Técnicas de Patch-Clamp , Depressão Sináptica de Longo Prazo/fisiologia , Animais , Potenciais Pós-Sinápticos Excitadores/fisiologia , Tonsila do Cerebelo/fisiologia , Masculino , Células Piramidais/fisiologia , Estimulação Elétrica , Ratos , Ratos Wistar , Córtex Cerebral/fisiologia , Vias Neurais/fisiologia , Técnicas In VitroRESUMO
Chronic ethanol exposure produces neuroadaptations in the medial prefrontal cortex (mPFC) that are thought to facilitate maladaptive behaviors that interfere with recovery from alcohol use disorder. Despite evidence that different cortico-subcortical projections play distinct roles in behavior, few studies have examined the physiological effects of chronic ethanol at the circuit level. The rostromedial tegmental nucleus (RMTg) is functionally altered by chronic ethanol exposure. Our recent work identified dense input from the mPFC to the RMTg, yet the effects of chronic ethanol exposure on this circuitry is unknown. In the current study, we examined physiological changes after chronic ethanol exposure in prelimbic (PL) and infralimbic (IL) mPFC neurons projecting to the RMTg. Adult male Long-Evans rats were injected with fluorescent retrobeads into the RMTg and rendered dependent using a 14-day chronic intermittent ethanol (CIE) vapor exposure paradigm. Whole-cell patch-clamp electrophysiological recordings were performed in fluorescently-labeled (RMTg-projecting) and -unlabeled (projection-undefined) layer 5 pyramidal neurons 7-10 days following ethanol exposure. CIE exposure significantly increased intrinsic excitability as well as spontaneous excitatory and inhibitory postsynaptic currents (sE/IPSCs) in RMTg-projecting IL neurons. In contrast, no lasting changes in excitability were observed in RMTg-projecting PL neurons, although a CIE-induced reduction in excitability was observed in projection-undefined PL neurons. CIE exposure also increased the frequency of sEPSCs in RMTg-projecting PL neurons. These data uncover novel subregion- and circuit-specific neuroadaptations in the mPFC following chronic ethanol exposure and reveal that the IL mPFC-RMTg projection is uniquely vulnerable to long-lasting effects of chronic ethanol exposure. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".
Assuntos
Etanol , Córtex Pré-Frontal , Ratos Long-Evans , Animais , Etanol/farmacologia , Etanol/administração & dosagem , Masculino , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/fisiologia , Ratos , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Depressores do Sistema Nervoso Central/farmacologia , Adaptação Fisiológica/efeitos dos fármacos , Adaptação Fisiológica/fisiologia , Vias Neurais/efeitos dos fármacos , Técnicas de Patch-Clamp , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/fisiologiaRESUMO
The processing of synaptic signals in somatodendritic compartments determines neuronal computation. Although the amplification of excitatory signals by local voltage-dependent cation channels has been extensively studied, their spatiotemporal dynamics in elaborate dendritic branches remain obscure owing to technical limitations. Using fluorescent voltage imaging throughout dendritic arborizations in hippocampal pyramidal neurons, we demonstrate a unique chloride ion (Cl-)-dependent remote computation mechanism in the distal branches. Excitatory postsynaptic potentials triggered by local laser photolysis of caged glutamate spread along dendrites, with gradual amplification toward the distal end while attenuation toward the soma. Tour de force subcellular patch-clamp recordings from thin branches complemented by biophysical model simulations revealed that the asymmetric augmentation of excitation relies on tetrodotoxin-resistant sodium ion (Na+) channels and Cl- conductance accompanied by a more hyperpolarized dendritic resting potential. Together, this study reveals the cooperative voltage-dependent actions of cation and anion conductance for dendritic supralinear computation, which can locally decode the spatiotemporal context of synaptic inputs.
Assuntos
Cloretos , Dendritos , Potenciais Pós-Sinápticos Excitadores , Dendritos/fisiologia , Dendritos/metabolismo , Animais , Potenciais Pós-Sinápticos Excitadores/fisiologia , Cloretos/metabolismo , Células Piramidais/fisiologia , Células Piramidais/metabolismo , Ratos , Técnicas de Patch-Clamp , Hipocampo/fisiologia , Hipocampo/metabolismo , Sinapses/fisiologia , Sinapses/metabolismoRESUMO
Adolescent inhibition of thalamocortical projections from postnatal days P20 to 50 leads to long-lasting deficits in prefrontal cortex function and cognition in the adult mouse. While this suggests a role of thalamic activity in prefrontal cortex maturation, it is unclear how inhibition of these projections affects prefrontal circuitry during adolescence. Here, we used chemogenetic tools to inhibit thalamoprefrontal projections in male/female mice from P20 to P35 and measured synaptic inputs to prefrontal pyramidal neurons by layer (either II/III or V/VI) and projection target (mediodorsal thalamus (MD), nucleus accumbens (NAc), or callosal prefrontal projections) 24â h later using slice physiology. We found a decrease in the frequency of excitatory and inhibitory currents in layer II/III NAc and layer V/VI MD-projecting neurons while layer V/VI NAc-projecting neurons showed an increase in the amplitude of excitatory and inhibitory currents. Regarding cortical projections, the frequency of inhibitory but not excitatory currents was enhanced in contralateral mPFC-projecting neurons. Notably, despite these complex changes in individual levels of excitation and inhibition, the overall balance between excitation and inhibition in each cell was only altered in the contralateral mPFC projections. This finding suggests homeostatic regulation occurs within subcortically but not intracortical callosal-projecting neurons. Increased inhibition of intraprefrontal connectivity may therefore be particularly important for prefrontal cortex circuit maturation. Finally, we observed cognitive deficits in the adult mouse using this narrowed window of thalamocortical inhibition.
Assuntos
Inibição Neural , Vias Neurais , Córtex Pré-Frontal , Tálamo , Animais , Córtex Pré-Frontal/fisiologia , Vias Neurais/fisiologia , Masculino , Feminino , Camundongos , Inibição Neural/fisiologia , Tálamo/fisiologia , Camundongos Endogâmicos C57BL , Núcleo Accumbens/fisiologia , Células Piramidais/fisiologia , Potenciais Pós-Sinápticos Inibidores/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologiaRESUMO
Collagen VI (Col-VI) is an extracellular matrix protein primarily known for its bridging role in connective tissues that has been suggested to play a neuroprotective role. In the present study we report increased mRNA and protein expression of Col-VI in the hippocampus and cortex at a late stage of epileptogenesis in a post-status epilepticus (SE) model of epilepsy and in brain tissue from patients with epilepsy. We further present a novel finding that exposure of mouse hippocampal slices to Col-VI augments paired-pulse facilitation in Schaffer collateral-CA1 excitatory synapses indicating decreased release probability of glutamate. In line with this finding, lack of Col-VI expression in the knock-out mice show paired-pulse depression in these synapses, suggesting increased release probability of glutamate. In addition, we observed dynamic changes in Col-VI blood plasma levels in rats after Kainate-induced SE, and increased levels of Col-VI mRNA and protein in autopsy or postmortem brain of humans suffering from epilepsy. Thus, our data indicate that elevated levels of ColVI following seizures leads to attenuated glutamatergic transmission, ultimately resulting in less overall network excitability. Presumably, increased Col-VI may act as part of endogenous compensatory mechanism against enhanced excitability during epileptogenic processes in the hippocampus, and could be further investigated as a potential functional biomarker of epileptogenesis, and/or a novel target for therapeutic intervention.
Assuntos
Colágeno Tipo VI , Camundongos Knockout , Convulsões , Transmissão Sináptica , Animais , Humanos , Masculino , Camundongos , Ratos , Colágeno Tipo VI/metabolismo , Colágeno Tipo VI/genética , Modelos Animais de Doenças , Potenciais Pós-Sinápticos Excitadores/fisiologia , Hipocampo/metabolismo , Ácido Caínico/toxicidade , Camundongos Endogâmicos C57BL , Ratos Sprague-Dawley , Convulsões/metabolismo , Convulsões/fisiopatologia , Convulsões/induzido quimicamente , Transmissão Sináptica/fisiologiaRESUMO
Estrogens are believed to modulate cognitive functions in part through the modulation of synaptic transmission in the cortex and hippocampus. Administration of 17ß-estradiol (E2) can rapidly enhance excitatory synaptic transmission in the hippocampus and facilitate excitatory synaptic transmission in rat lateral entorhinal cortex via activation of the G protein-coupled estrogen receptor-1 (GPER1). To assess the mechanisms through which GPER1 activation facilitates synaptic transmission, we assessed the effects of acute 10 nM E2 administration on pharmacologically isolated evoked excitatory and inhibitory synaptic currents in layer II/III entorhinal neurons. Female Long-Evans rats were ovariectomized between postnatal day (PD) 63 and 74 and implanted with a subdermal E2 capsule to maintain continuous low levels of E2. Electrophysiological recordings were obtained between 7 and 20 days after ovariectomy. Application of E2 for 20 min did not significantly affect AMPA or NMDA receptor-mediated excitatory synaptic currents. However, GABA receptor-mediated inhibitory synaptic currents (IPSCs) were markedly reduced by E2 and returned towards baseline levels during the 20-min washout period. The inhibition of GABA-mediated IPSCs was blocked in the presence of the GPER1 receptor antagonist G15. GPER1 can modulate protein kinase A (PKA), but blocking PKA with intracellular KT5720 did not prevent the E2-induced reduction in IPSCs. GPER1 can also stimulate extracellular signal-regulated kinase (ERK), a negative modulator of GABAA receptors, and blocking activation of ERK with PD90859 prevented the E2-induced reduction of IPSCs. E2 can therefore result in a rapid GPER1 and ERK signaling-mediated reduction in GABA-mediated IPSCs. This provides a novel mechanism through which E2 can rapidly modulate synaptic excitability in entorhinal layer II/III neurons and may also contribute to E2 and ERK-dependent alterations in synaptic transmission in other brain areas.
Assuntos
Córtex Entorrinal , Estradiol , MAP Quinases Reguladas por Sinal Extracelular , Neurônios , Ratos Long-Evans , Receptores Acoplados a Proteínas G , Animais , Córtex Entorrinal/efeitos dos fármacos , Córtex Entorrinal/fisiologia , Receptores Acoplados a Proteínas G/metabolismo , Estradiol/farmacologia , Feminino , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Ratos , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Receptores de Estrogênio/metabolismo , Ovariectomia , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Técnicas de Patch-Clamp , Estrogênios/farmacologia , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/antagonistas & inibidoresRESUMO
Theory predicts that nonlinear summation of synaptic potentials within dendrites allows neurons to perform linearly non-separable computations (LNSCs). Using Boolean analysis approaches, we predicted that both supralinear and sublinear synaptic summation could allow single neurons to implement a type of LNSC, the feature binding problem (FBP), which does not require inhibition contrary to the exclusive-or function (XOR). Notably, sublinear dendritic operations enable LNSCs when scattered synaptic activation generates increased somatic spike output. However, experimental demonstrations of scatter-sensitive neuronal computations have not yet been described. Using glutamate uncaging onto cerebellar molecular layer interneurons, we show that scattered synaptic-like activation of dendrites evoked larger compound EPSPs than clustered synaptic activation, generating a higher output spiking probability. Moreover, we also demonstrate that single interneurons can indeed implement the FBP. Using a biophysical model to explore the conditions in which a neuron might be expected to implement the FBP, we establish that sublinear summation is necessary but not sufficient. Other parameters such as the relative sublinearity, the EPSP size, depolarization amplitude relative to action potential threshold, and voltage fluctuations all influence whether the FBP can be performed. Since sublinear synaptic summation is a property of passive dendrites, we expect that many different neuron types can implement LNSCs.
Assuntos
Dendritos , Interneurônios , Modelos Neurológicos , Dendritos/fisiologia , Animais , Interneurônios/fisiologia , Potenciais de Ação/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Sinapses/fisiologia , Cerebelo/fisiologia , Cerebelo/citologia , Neurônios/fisiologia , CamundongosRESUMO
Ribbon synapses between inner hair cells (IHCs) and type I spiral ganglion neurons (SGNs) in the inner ear are damaged by noise trauma and with aging, causing "synaptopathy" and hearing loss. Cocultures of neonatal denervated organs of Corti and newly introduced SGNs have been developed to find strategies for improving IHC synapse regeneration, but evidence of the physiological normality of regenerated synapses is missing. This study utilizes IHC optogenetic stimulation and SGN recordings, showing that, when P3-5 denervated organs of Corti are cocultured with SGNs, newly formed IHC/SGN synapses are indeed functional, exhibiting glutamatergic excitatory postsynaptic currents. When using older organs of Corti at P10-11, synaptic activity probed by deconvolution showed more mature release properties, closer to the specialized mode of IHC synaptic transmission crucial for coding the sound signal. This functional assessment of newly formed IHC synapses developed here, provides a powerful tool for testing approaches to improve synapse regeneration.
Assuntos
Gânglio Espiral da Cóclea , Sinapses , Animais , Gânglio Espiral da Cóclea/citologia , Gânglio Espiral da Cóclea/fisiologia , Sinapses/fisiologia , Camundongos , Células Ciliadas Auditivas Internas/fisiologia , Células Ciliadas Auditivas Internas/metabolismo , Transmissão Sináptica/fisiologia , Neurônios/fisiologia , Neurônios/metabolismo , Regeneração/fisiologia , Células Ciliadas Auditivas/fisiologia , Técnicas de Cocultura/métodos , Optogenética/métodos , Regeneração Nervosa/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Órgão Espiral/fisiologia , Órgão Espiral/citologia , Órgão Espiral/metabolismoRESUMO
BACKGROUND: The transition from childhood to adulthood, or adolescence, a developmental stage, is characterized by psychosocial and biological changes. The nucleus accumbens (NAc), a striatal brain region composed of the core (NAcC) and shell (NAcSh), has been linked to risk-taking behavior and implicated in reward seeking and evaluation. Most neurons in the NAc are medium spiny neurons (MSNs) that express dopamine D1 receptors (D1R +) and/or dopamine D2 receptors (D2R +). Changes in dopaminergic and glutamatergic systems occur during adolescence and converge in the NAc. While there are previous investigations into sex differences in membrane excitability and synaptic glutamate transmission in both subdivisions of the NAc, to our knowledge, none have specified NAcSh D1R + MSNs from mice during pre- and mid-adolescence. METHODS: Sagittal brain slices containing the NAc were prepared from B6.Cg-Tg(Drd1a-tdTomato)6Calak/J mice of both sexes from postnatal days 21-25 and 35-47, representing pre- and mid-adolescence, respectively. Whole-cell electrophysiology recordings were collected from NAcSh D1R + MSNs in the form of membrane-voltage responses to current injections, to assess membrane properties and action potential waveform characteristics, and spontaneous excitatory postsynaptic currents (sEPSCs) to assess glutamatergic synaptic activity. RESULTS: Relative to pre-adolescent males, pre-adolescent female NAcSh D1R + MSNs exhibited a less hyperpolarized resting membrane potential, increased input resistance, and smaller action potential afterhyperpolarization amplitudes. During mid-adolescence, decreased input resistance and a shorter action potential duration in females were the only sex differences observed. CONCLUSIONS: Taken together, our results indicate that NAcSh D1R + MSNs in mice exhibit sex differences in membrane properties and AP waveform during pre-adolescence that are overall indicative of increased cellular excitability in females and are suggestive of possible sex differences in glycine receptors, inwardly-rectifying potassium channels, and large conductance voltage-gated potassium channels. These differences do not appear to persist into mid-adolescence, when sex was observed to affect input resistance oppositely to that of pre-adolescence and AP waveform in a manner suggestive of differences in voltage-gated potassium channels.
Adolescence marks a period of substantial changes in both the mind and body, where alterations in the brain's structure can influence behavior. One change in behavior exhibited by many adolescents is an increased tendency to take risks, particularly in males. While taking risks can result in positive outcomes, like learning new skills, it can also lead to reckless behaviors that may result in negative outcomes. The nucleus accumbens, a brain region tied to risk-taking and reward perception, is not well-studied during the transition from childhood to adulthood, particularly in terms of sex differences. To fill this gap in understanding, this study examined a specific type of brain cell in the nucleus accumbens of pre- and mid-adolescent male and female mice. We measured the electrical properties of these cells and assessed how they responded to manipulation of their electrical state. We also measured how much and how often excitatory electrical information is sent to these cells from other brain regions. Our results suggest that in pre-adolescent females, these brain cells are more excited by manipulations of their electrical state and that these brain cells in mid-adolescent males may take longer to communicate information to other brain regions than in similarly aged females. Understanding these intricacies of brain cell communication sheds light on potential sex-specific vulnerabilities during the transition from childhood to adulthood.
Assuntos
Neurônios , Núcleo Accumbens , Receptores de Dopamina D1 , Caracteres Sexuais , Animais , Receptores de Dopamina D1/metabolismo , Núcleo Accumbens/metabolismo , Núcleo Accumbens/fisiologia , Núcleo Accumbens/citologia , Feminino , Masculino , Neurônios/metabolismo , Neurônios/fisiologia , Camundongos , Potenciais da Membrana , Camundongos Endogâmicos C57BL , Potenciais Pós-Sinápticos Excitadores , Camundongos TransgênicosRESUMO
N-methyl-D-aspartate receptors (NMDARs) play a significant role in developing several central nervous system (CNS) disorders. Currently, memantine, used for treating Alzheimer's disease, and ketamine, known for its anesthetic and antidepressant properties, are two clinically used NMDAR open-channel blockers. However, despite extensive research into NMDAR modulators, many have shown either harmful side effects or inadequate effectiveness. For instance, dizocilpine (MK-801) is recognized for its powerful psychomimetic effects due to its high-affinity and nearly irreversible inhibition of the GluN1/GluN2 NMDAR subtypes. Unlike ketamine, memantine and MK-801 also act through a unique, low-affinity "membrane-to-channel inhibition" (MCI). We aimed to develop an open-channel blocker based on MK-801 with distinct inhibitory characteristics from memantine and MK-801. Our novel compound, K2060, demonstrated effective voltage-dependent inhibition in the micromolar range at key NMDAR subtypes, GluN1/GluN2A and GluN1/GluN2B, even in the presence of Mg2+. K2060 showed reversible inhibitory dynamics and a partially trapping open-channel blocking mechanism with a significantly stronger MCI than memantine. Using hippocampal slices, 30⯵M K2060 inhibited excitatory postsynaptic currents in CA1 hippocampal neurons by â¼51â¯%, outperforming 30⯵M memantine (â¼21â¯% inhibition). K2060 exhibited No Observed Adverse Effect Level (NOAEL) of 15â¯mg/kg upon intraperitoneal administration in mice. Administering K2060 at a 10â¯mg/kg dosage resulted in brain concentrations of approximately 2⯵M, with peak concentrations (Tmax) achieved within 15â¯minutes. Finally, applying K2060 with trimedoxime and atropine in mice exposed to tabun improved treatment outcomes. These results underscore K2060's potential as a therapeutic agent for CNS disorders linked to NMDAR dysfunction.
Assuntos
Maleato de Dizocilpina , Receptores de N-Metil-D-Aspartato , Animais , Maleato de Dizocilpina/farmacologia , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/metabolismo , Camundongos , Masculino , Antagonistas de Aminoácidos Excitatórios/farmacologia , Humanos , Memantina/farmacologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Camundongos Endogâmicos C57BL , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismoRESUMO
The anterior cingulate cortex (ACC) is a key cortical region for pain perception and emotion. Different forms of synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD), have been reported in the ACC. Synaptic tagging of LTP plays an important role in hippocampus-related associative memory. In this study, we demonstrate that synaptic tagging of LTD is detected in the ACC of adult male and female mice. This form of tagged LTD requires the activation of metabotropic glutamate receptor subtype 1 (mGluR1). The induction of tagged LTD is time-related with the strongest tagged LTD appearing when the interval between two independent stimuli is 30â min. Inhibitors of mGluR1 blocked the induction of tagged LTD; however, blocking N-methyl-d-aspartate receptors did not affect the induction of tagged LTD. Nimodipine, an inhibitor of L-type voltage-gated calcium channels, also blocked tagged LTD. In an animal model of amputation, we found that tagged LTD was either reduced or completely blocked. Together with our previous report of tagged LTP in the ACC, this study strongly suggests that excitatory synapses in the adult ACC are highly plastic. The biphasic tagging of synaptic transmission provides a new form of heterosynaptic plasticity in the ACC which has functional and pathophysiological significance in phantom pain.
Assuntos
Giro do Cíngulo , Depressão Sináptica de Longo Prazo , Camundongos Endogâmicos C57BL , Animais , Giro do Cíngulo/fisiologia , Giro do Cíngulo/efeitos dos fármacos , Camundongos , Depressão Sináptica de Longo Prazo/fisiologia , Depressão Sináptica de Longo Prazo/efeitos dos fármacos , Masculino , Feminino , Sinapses/fisiologia , Sinapses/efeitos dos fármacos , Receptores de Glutamato Metabotrópico/metabolismo , Receptores de Glutamato Metabotrópico/antagonistas & inibidores , Potenciais Pós-Sinápticos Excitadores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacosRESUMO
Birth stress is a risk factor for psychiatric disorders and associated with exaggerated release of the stress hormone arginine vasopressin (AVP) into circulation and in the brain. In perinatal hippocampus, AVP activates GABAergic interneurons which leads to suppression of spontaneous network events and suggests a protective function of AVP on cortical networks during birth. However, the role of AVP in developing subcortical networks is not known. Here we tested the effect of AVP on the dorsal raphe nucleus (DRN) 5-hydroxytryptamine (5-HT, serotonin) system in male and female neonatal rats, since early 5-HT homeostasis is critical for the development of cortical brain regions and emotional behaviors. We show that AVP is strongly excitatory in neonatal DRN: it increases excitatory synaptic inputs of 5-HT neurons via V1A receptors in vitro and promotes their action potential firing through a combination of its effect on glutamatergic synaptic transmission and a direct effect on the excitability of these neurons. Furthermore, we identified two major firing patterns of neonatal 5-HT neurons in vivo, tonic regular firing and low frequency oscillations of regular spike trains and confirmed that these neurons are also activated by AVP in vivo. Finally, we show that the sparse vasopressinergic innervation in neonatal DRN originates exclusively from cell groups in medial amygdala and bed nucleus of stria terminalis. Hyperactivation of the neonatal 5-HT system by AVP during birth stress may impact its own functional development and affect the maturation of cortical target regions, which may increase the risk for psychiatric conditions later on.
Assuntos
Animais Recém-Nascidos , Arginina Vasopressina , Núcleo Dorsal da Rafe , Neurônios Serotoninérgicos , Animais , Arginina Vasopressina/metabolismo , Arginina Vasopressina/farmacologia , Feminino , Neurônios Serotoninérgicos/efeitos dos fármacos , Neurônios Serotoninérgicos/fisiologia , Masculino , Núcleo Dorsal da Rafe/efeitos dos fármacos , Núcleo Dorsal da Rafe/metabolismo , Núcleo Dorsal da Rafe/fisiologia , Ratos , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Ratos Sprague-Dawley , Serotonina/metabolismo , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Receptores de Vasopressinas/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologiaRESUMO
N-Methyl-d-aspartate receptors (NMDARs), encoded by GRIN genes, are ionotropic glutamate receptors playing a critical role in synaptic transmission, plasticity, and synapse development. Genome sequence analyses have identified variants in GRIN genes in patients with neurodevelopmental disorders, but the underlying disease mechanisms are not well understood. Here, we have created and evaluated a transgenic mouse line carrying a missense variant Grin2bL825V , corresponding to a de novo GRIN2B variant encoding GluN2B(L825V) found in a patient with intellectual disability (ID) and autism spectrum disorder (ASD). We used HEK293T cells expressing recombinant receptors and primary hippocampal neurons prepared from heterozygous Grin2bL825V/+ (L825V/+) and wild-type (WT) Grin2b+/+ (+/+) male and female mice to assess the functional impact of the variant. Whole-cell NMDAR currents were reduced in neurons from L825V/+ compared with +/+ mice. The peak amplitude of NMDAR-mediated evoked excitatory postsynaptic currents (NMDAR-eEPSCs) was unchanged, but NMDAR-eEPSCs in L825V/+ neurons had faster deactivation compared with +/+ neurons and were less sensitive to a GluN2B-selective antagonist ifenprodil. Together, these results suggest a decreased functional contribution of GluN2B subunits to synaptic NMDAR currents in hippocampal neurons from L825V/+ mice. The analysis of the GluN2B(L825V) subunit surface expression and synaptic localization revealed no differences compared with WT GluN2B. Behavioral testing of mice of both sexes demonstrated hypoactivity, anxiety, and impaired sensorimotor gating in the L825V/+ strain, particularly affecting males, as well as cognitive symptoms. The heterozygous L825V/+ mouse offers a clinically relevant model of GRIN2B-related ID/ASD, and our results suggest synaptic-level functional changes that may contribute to neurodevelopmental pathology.
Assuntos
Camundongos Transgênicos , Transtornos do Neurodesenvolvimento , Receptores de N-Metil-D-Aspartato , Animais , Receptores de N-Metil-D-Aspartato/genética , Receptores de N-Metil-D-Aspartato/metabolismo , Feminino , Camundongos , Masculino , Humanos , Transtornos do Neurodesenvolvimento/genética , Transtornos do Neurodesenvolvimento/fisiopatologia , Transtornos do Neurodesenvolvimento/metabolismo , Células HEK293 , Hipocampo/metabolismo , Potenciais Pós-Sinápticos Excitadores/fisiologia , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Mutação de Sentido IncorretoRESUMO
Glutamatergic synapses exhibit significant molecular diversity, but circuit-specific mechanisms that underlie synaptic regulation are not well characterized. Prior reports show that Rho-guanine nucleotide exchange factor (RhoGEF) Tiam1 regulates perforant pathâdentate gyrus granule neuron synapses. In the present study, we report Tiam1's homolog Tiam2 is implicated in glutamatergic neurotransmission in CA1 pyramidal neurons. We find that Tiam2 regulates evoked excitatory glutamatergic currents via a postsynaptic mechanism mediated by the catalytic Dbl-homology domain. Overall, we present evidence for RhoGEF Tiam2's role in glutamatergic synapse function at Schaffer collateralâCA1 pyramidal neuron synapses.
Assuntos
Região CA1 Hipocampal , Potenciais Pós-Sinápticos Excitadores , Ácido Glutâmico , Fatores de Troca do Nucleotídeo Guanina , Células Piramidais , Transmissão Sináptica , Animais , Feminino , Masculino , Camundongos , Região CA1 Hipocampal/fisiologia , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/metabolismo , Potenciais Pós-Sinápticos Excitadores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Ácido Glutâmico/metabolismo , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Camundongos Endogâmicos C57BL , Células Piramidais/fisiologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/metabolismo , Sinapses/fisiologia , Sinapses/efeitos dos fármacos , Sinapses/metabolismo , Transmissão Sináptica/fisiologia , Transmissão Sináptica/efeitos dos fármacos , Fatores de Troca de Nucleotídeo Guanina RhoRESUMO
The mechanisms utilized by neurons to regulate the efficacy of phasic and tonic inhibition and their impacts on synaptic plasticity and behavior are incompletely understood. Cleft lip and palate transmembrane protein 1 (Clptm1) is a membrane-spanning protein that interacts with multiple γ-aminobutyric acid type A receptor (GABAAR) subunits, trapping them in the endoplasmic reticulum and Golgi network. Overexpression and knock-down studies suggest that Clptm1 modulates GABAAR-mediated phasic inhibition and tonic inhibition as well as activity-induced inhibitory synaptic homeostasis in cultured hippocampal neurons. To investigate the role of Clptm1 in the modulation of GABAARs in vivo, we generated Clptm1 knock-out (KO) mice. Here, we show that genetic KO of Clptm1 elevated phasic and tonic inhibitory transmission in both male and female heterozygous mice. Although basal excitatory synaptic transmission was not affected, Clptm1 haploinsufficiency significantly blocked high-frequency stimulation-induced long-term potentiation (LTP) in hippocampal CA3âCA1 synapses. In the hippocampus-dependent contextual fear-conditioning behavior task, both male and female Clptm1 heterozygous KO mice exhibited impairment in contextual fear memory. In addition, LTP and contextual fear memory were rescued by application of L-655,708, a negative allosteric modulator of the extrasynaptic GABAAR α5 subunit. These results suggest that haploinsufficiency of Clptm1 contributes to cognitive deficits through altered synaptic transmission and plasticity by elevation of inhibitory neurotransmission, with tonic inhibition playing a major role.
Assuntos
Haploinsuficiência , Proteínas de Membrana , Camundongos Knockout , Plasticidade Neuronal , Receptores de GABA-A , Transmissão Sináptica , Animais , Camundongos , Masculino , Receptores de GABA-A/genética , Receptores de GABA-A/metabolismo , Feminino , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Transmissão Sináptica/fisiologia , Plasticidade Neuronal/fisiologia , Plasticidade Neuronal/genética , Camundongos Endogâmicos C57BL , Potenciais Pós-Sinápticos Excitadores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciação de Longa Duração/fisiologia , Potenciação de Longa Duração/genética , Hipocampo/metabolismo , Transtornos da Memória/genética , Transtornos da Memória/metabolismo , Transtornos da Memória/fisiopatologia , Medo/fisiologia , Potenciais Pós-Sinápticos Inibidores/fisiologia , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Memória/fisiologia , Inibição Neural/fisiologiaRESUMO
In the rodent whisker system, active sensing and sensorimotor integration are mediated in part by the dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1). However, understanding these dynamic interactions requires knowledge about the synapses and how specific neurons respond to their input. Here, we combined optogenetics, retrograde labeling, and electrophysiology to characterize the synaptic connections between M1 and layer 5 (L5) intratelencephalic (IT) and pyramidal tract (PT) neurons in S1 of mice (both sexes). We found that M1 synapses onto IT cells displayed modest short-term depression, whereas synapses onto PT neurons showed robust short-term facilitation. Despite M1 inputs to IT cells depressing, their slower kinetics resulted in summation and a response that increased during short trains. In contrast, summation was minimal in PT neurons due to the fast time course of their M1 responses. The functional consequences of this reduced summation, however, were outweighed by the strong facilitation at these M1 synapses, resulting in larger response amplitudes in PT neurons than IT cells during repetitive stimulation. To understand the impact of facilitating M1 inputs on PT output, we paired trains of inputs with single backpropagating action potentials, finding that repetitive M1 activation increased the probability of bursts in PT cells without impacting the time dependence of this coupling. Thus, there are two parallel but dynamically distinct systems of M1 synaptic excitation in L5 of S1, each defined by the short-term dynamics of its synapses, the class of postsynaptic neurons, and how the neurons respond to those inputs.
Assuntos
Córtex Motor , Optogenética , Córtex Somatossensorial , Animais , Córtex Somatossensorial/fisiologia , Córtex Motor/fisiologia , Masculino , Feminino , Vias Neurais/fisiologia , Sinapses/fisiologia , Camundongos , Neurônios/fisiologia , Camundongos Endogâmicos C57BL , Vibrissas/fisiologia , Tratos Piramidais/fisiologia , Camundongos Transgênicos , Potenciais Pós-Sinápticos Excitadores/fisiologiaRESUMO
Neurons receive correlated levels of excitation and inhibition, a feature that is important for proper brain function. However, how this relationship between excitatory and inhibitory inputs is established during the dynamic period of circuit wiring remains unexplored. Using multiple techniques, including in utero electroporation, electron microscopy, and electrophysiology, we reveal a tight correlation in the distribution of excitatory and inhibitory synapses along the dendrites of developing CA1 hippocampal neurons. This correlation was present within short dendritic stretches (<20 µm) and, surprisingly, was most pronounced during early development, sharply declining with maturity. The tight matching between excitation and inhibition was unexpected, as inhibitory synapses lacked an active zone when formed and exhibited compromised evoked release. We propose that inhibitory synapses form as a stabilizing scaffold to counterbalance growing excitation levels. This relationship diminishes over time, suggesting a critical role for a subcellular balance in early neuronal function and circuit formation.