RESUMO
Nanosecond electric pulse (nsEP) exposure generates an array of physiological effects. The extent of these effects is impacted by whether the nsEP is a unipolar (UP) or bipolar (BP) exposure. A 600 ns pulse can generate 71% more YO-PRO-1 uptake compared to a 600 ns + 600 ns pulse exposure. This observation is termed "bipolar cancellation" (BPC) because despite the BP nsEP consisting of an additional 600 ns pulse, it generates reduced membrane perturbation. BPC is achieved by varying pulse amplitudes, and symmetrical and asymmetric pulse widths. The effect appears to reverse by increasing the interphase interval between symmetric BP pulses, suggesting membrane recovery is a BPC factor. To date, the impact of the interphase interval between asymmetrical BP and other BPC-inducing symmetrical BP nsEPs has not been fully explored. Additionally, interpulse intervals beyond 50 µs have not been explored to understand the impact of time between the BP nsEP phases. Here, we surveyed different interphase intervals among symmetrical and asymmetrical BP nsEPs to monitor their impact on BPC of YO-PRO-1 uptake. We identified that a 10 microsecond (ms) interphase interval within a symmetrical 600 ns + 600 ns, and 900 ns + 900 ns pulse can resolve BPC. Furthermore, the interphase interval to resolve asymmetric BPC from a 300 ns + 900 ns pulse versus 600 ns pulse exposure is greater (<10 ms) compared to symmetrical BP nsEPs. From these findings, we extended on our conceptual model that BPC is balanced by localized charging and discharging events across the membrane. Bioelectromagnetics. 39:441-450, 2018. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.
Assuntos
Membrana Celular/metabolismo , Estimulação Elétrica/métodos , Animais , Benzoxazóis/farmacocinética , Células CHO , Permeabilidade da Membrana Celular , Cricetulus , Corantes Fluorescentes/farmacocinética , Microscopia Confocal , Compostos de Quinolínio/farmacocinética , Fatores de TempoRESUMO
Dendritic spines are fine neuronal processes where spatially restricted input can induce activity-dependent changes in one spine, while leaving neighboring spines unmodified. Morphological spine plasticity is critical for synaptic transmission and is thought to underlie processes like learning and memory. Significantly, defects in dendritic spine stability and morphology are common pathogenic features found in several neurodevelopmental and neuropsychiatric disorders. The remodeling of spines relies on proteins that modulate the underlying cytoskeleton, which is primarily composed of filamentous (F)-actin. The Rho-GTPase Rac1 is a major regulator of F-actin and is essential for the development and plasticity of dendrites and spines. However, the key molecules and mechanisms that regulate Rac1-dependent pathways at spines and synapses are not well understood. We have identified the Rac1-GTPase activating protein, α2-chimaerin, as a critical negative regulator of Rac1 in hippocampal neurons. The loss of α2-chimaerin significantly increases the levels of active Rac1 and induces the formation of aberrant polymorphic dendritic spines. Further, disruption of α2-chimaerin signaling simplifies dendritic arbor complexity and increases the presence of dendritic spines that appear poly-innervated. Our data suggests that α2-chimaerin serves as a "brake" to constrain Rac1-dependent signaling to ensure that the mature morphology of spines is maintained in response to network activity.
Assuntos
Quimerina 1/metabolismo , Espinhas Dendríticas/metabolismo , Neurogênese , Citoesqueleto de Actina/metabolismo , Animais , Células Cultivadas , Quimerina 1/genética , Espinhas Dendríticas/fisiologia , Hipocampo/citologia , Hipocampo/metabolismo , Potenciação de Longa Duração , Camundongos , Camundongos Endogâmicos C57BL , Neuropeptídeos/metabolismo , Proteínas rac1 de Ligação ao GTP/metabolismoRESUMO
Under most circumstances, GABA activates chloride-selective channels and thereby inhibits neuronal activity. Here, we identify a GABA receptor in the nematode Caenorhabditis elegans that conducts cations and is therefore excitatory. Expression in Xenopus oocytes demonstrates that LGC-35 is a homopentameric cation-selective receptor of the cys-loop family exclusively activated by GABA. Phylogenetic analysis suggests that LGC-35 evolved from GABA-A receptors, but the pore-forming domain contains novel molecular determinants that confer cation selectivity. LGC-35 is expressed in muscles and directly mediates sphincter muscle contraction in the defecation cycle in hermaphrodites, and spicule eversion during mating in the male. In the locomotory circuit, GABA release directly activates chloride channels on the muscle to cause muscle relaxation. However, GABA spillover at these synapses activates LGC-35 on acetylcholine motor neurons, which in turn cause muscles to contract, presumably to drive wave propagation along the body. These studies demonstrate that both direct and indirect excitatory GABA signaling plays important roles in regulating neuronal circuit function and behavior in C. elegans.
Assuntos
Proteínas de Caenorhabditis elegans/fisiologia , Caenorhabditis elegans/fisiologia , Músculos/fisiologia , Receptores de GABA/fisiologia , Transmissão Sináptica/fisiologia , Acetilcolina/fisiologia , Animais , Comportamento Animal , Proteínas de Caenorhabditis elegans/genética , Copulação/fisiologia , Defecação , Masculino , Neurônios Motores/fisiologia , Contração Muscular/fisiologia , Oócitos/efeitos dos fármacos , Receptores de GABA/genética , Comportamento Sexual Animal/fisiologia , Xenopus laevisRESUMO
Changes in brain cholesterol homeostasis are associated with multiple diseases, such as Alzheimer's and Huntington's; however, controversy persists as to whether adult neurons produce their own cholesterol, or if it is outsourced to astrocytes. To address this issue, we analyzed 25 genes most immediately involved in cholesterol homeostasis from in situ data provided by the Allen Brain Mouse Atlas. We compared the relative mRNA expression in the pyramidal and granule layers, populated with neurons, with the rest of the hippocampus which is populated with neuronal processes and glia. Comparing the expression of the individual genes to markers for neurons and astrocytes, we found that cholesterol homeostasis genes are preferentially targeted to neuronal layers. Therefore, changes in gene expression levels might affect neuronal populations directly.
Assuntos
Astrócitos/metabolismo , Colesterol/genética , Colesterol/metabolismo , Hipocampo/citologia , Homeostase/genética , Neurônios/metabolismo , Animais , Apolipoproteína E4/genética , Apolipoproteína E4/metabolismo , Proteína Glial Fibrilar Ácida , Peptídeos e Proteínas de Sinalização Intracelular/genética , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , RNA Mensageiro/metabolismo , Receptores de AMPA/genética , Receptores de AMPA/metabolismo , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismoRESUMO
OBJECTIVE The aims of this study were to determine if the morphological and functional changes induced by neural stem cell (NSC) grafts after transplantation into the rodent spinal cord can be detected using MR diffusion tensor imaging (DTI) and, furthermore, if the DTI-derived mean diffusivity (MD) metric could be a biomarker for cell transplantation in spinal cord injury (SCI). METHODS A spinal contusion was produced at the T-8 vertebral level in 40 Sprague Dawley rats that were separated into 4 groups, including a sham group (injury without NSC injection), NSC control group (injury with saline injection), co-injection control group (injury with Prograf), and the experimental group (injury with NSC and Prograf injection). The NSC injection was completed 1 week after injury into the site of injury and the rats in the experimental group were compared to the rats from the sham, NSC control, and co-injection groups. The DTI index, MD, was assessed in vivo at 2, 5, and 10 weeks and ex vivo at 10 weeks postinjury on a 9.4-T Bruker scanner using a spin-echo imaging sequence. DTI data of the cervical spinal cord from the sham surgery, injury with saline injection, injury with injection of Prograf only, and injury with C17.2 NSC and Prograf injection were examined to evaluate if cellular proliferation induced by intrathoracic C17.2 engraftment was detectable in a noninvasive manner. RESULTS At 5 weeks after injury, the average fractional anisotropy, longitudinal diffusion (LD) and radial diffusion (RD) coefficients, and MD of water (average of the RD and LD eigenvalues in the stem cell line-treated group) increased to an average of 1.44 × 10-3 sec/mm2 in the cervical segments, while the control groups averaged 0.98 × 10-3 s/mm2. Post hoc Tukey's honest significant difference tests demonstrated that the transplanted stem cells had significantly higher MD values than the other groups (p = 0.032 at 5 weeks). In vivo and ex vivo findings at 10 weeks displayed similar results. This statistical difference between the stem cell line and the other groups was maintained at the 10-week postinjury in vivo and ex vivo time points. CONCLUSIONS These results indicate that the DTI-derived MD metric collected from noninvasive imaging techniques may provide useful biomarker indices for transplantation interventions that produce changes in the spinal cord structure and function. Though promising, the results demonstrated here suggest additional work is needed before implementation in a clinical setting.
Assuntos
Imagem de Difusão por Ressonância Magnética , Imagem de Tensor de Difusão , Células-Tronco Neurais/transplante , Traumatismos da Medula Espinal/diagnóstico por imagem , Traumatismos da Medula Espinal/terapia , Transplante de Células-Tronco , Animais , Linhagem Celular , Medula Cervical/diagnóstico por imagem , Medula Cervical/patologia , Imagem de Difusão por Ressonância Magnética/métodos , Imagem de Tensor de Difusão/métodos , Modelos Animais de Doenças , Feminino , Temperatura Alta , Imuno-Histoquímica , Atividade Motora/fisiologia , Células-Tronco Neurais/fisiologia , Percepção da Dor/fisiologia , Distribuição Aleatória , Ratos Sprague-Dawley , Traumatismos da Medula Espinal/patologia , Traumatismos da Medula Espinal/fisiopatologia , Transplante de Células-Tronco/métodos , Vértebras Torácicas/lesões , Fatores de Tempo , Resultado do TratamentoRESUMO
A bipolar (BP) nanosecond electric pulse (nsEP) exposure generates reduced calcium influx compared to a unipolar (UP) nsEP. This attenuated physiological response from a BP nsEP exposure is termed "bipolar cancellation" (BPC). The predominant BP nsEP parameters that induce BPC consist of a positive polarity (↑) front pulse followed by the delivery of a negative polarity (↓) back pulse of equal voltage and width; thereby the duration is twice a UP nsEP exposure. We tested these BPC parameters, and discovered that a BP nsEP with symmetrical pulse widths is not required to generate BPC. For example, our data revealed the physiological response initiated by a ↑900 nsEP exposure can be cancelled by a second pulse that is a third of its duration. However, we observed a complete loss of BPC from a ↑300 nsEP followed by a ↓900 nsEP exposure. Spatiotemporal analysis revealed these asymmetrical BP nsEP exposures generate distinct local YO-PRO®-1 uptake patterns across the plasma membrane. From these findings, we generated a conceptual model that suggests BPC is a phenomenon balanced by localized charging and discharging events across the membrane.