RESUMO
There is emerging evidence that hyperpolarization-activated cation (HCN) channels are involved in the development of pathological pain, including allodynia and hyperalgesia. Mice lacking the HCN isoform 2 display reduced heat but unchanged mechanical pain behavior, as recently shown in preclinical models of acute inflammatory pain. However, the impact of HCN2 to chronic pain conditions is less clear and has not been examined so far. In this report, we study the role of HCN2 in the complete Freund's adjuvant inflammation model reflecting chronic pain conditions. We used sensory neuron-specific as well as inducible global HCN2 mutants analyzing pain behavior in persistent inflammation and complemented this by region-specific administration of an HCN channel blocker. Our results demonstrate that the absence of HCN2 in primary sensory neurons reduces tactile hypersensitivity in chronic inflammatory conditions but leaves heat hypersensitivity unaffected. This result is in remarkable contrast to the recently described role of HCN2 in acute inflammatory conditions. We show that chronic inflammation results in an increased expression of HCN2 and causes sensitization in peripheral and spinal terminals of the pain transduction pathway. The contribution of HCN2 to peripheral sensitization mechanisms was further supported by single-fiber recordings from isolated skin-nerve preparations and by conduction velocity measurements of saphenous nerve preparations. Global HCN2 mutants revealed that heat hypersensitivity-unaffected in peripheral HCN2 mutants-was diminished by the additional disruption of central HCN2 channels, suggesting that thermal hyperalgesia under chronic inflammatory conditions is mediated by HCN2 channels beyond primary sensory afferents.
Assuntos
Temperatura Alta/efeitos adversos , Hiperalgesia/genética , Hiperalgesia/patologia , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/fisiologia , Canais de Potássio/fisiologia , Tato/genética , Animais , Células Cultivadas , Inflamação/genética , Inflamação/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Técnicas de Cultura de Órgãos , Estimulação Física/efeitos adversosRESUMO
The molecular and physiological basis of the touch-unresponsive zebrafish mutant fakir has remained elusive. Here we report that the fakir phenotype is caused by a missense mutation in the gene encoding voltage-gated calcium channel 2.1b (CACNA1Ab). Injection of RNA encoding wild-type CaV2.1 restores touch responsiveness in fakir mutants, whereas knockdown of CACNA1Ab via morpholino oligonucleotides recapitulates the fakir mutant phenotype. Fakir mutants display normal current-evoked synaptic communication at the neuromuscular junction but have attenuated touch-evoked activation of motor neurons. NMDA-evoked fictive swimming is not affected by the loss of CaV2.1b, suggesting that this channel is not required for motor pattern generation. These results, coupled with the expression of CACNA1Ab by sensory neurons, suggest that CaV2.1b channel activity is necessary for touch-evoked activation of the locomotor network in zebrafish.
Assuntos
Canais de Cálcio Tipo N/metabolismo , Ativação do Canal Iônico/genética , Tato/genética , Acetilcolina/farmacologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/genética , Vias Aferentes/fisiologia , Animais , Animais Geneticamente Modificados , Bungarotoxinas/metabolismo , Canais de Cálcio Tipo N/genética , Curare/farmacologia , Relação Dose-Resposta a Droga , Embrião não Mamífero , Reação de Fuga/efeitos dos fármacos , Reação de Fuga/fisiologia , Potenciais Evocados/genética , Células HEK293 , Humanos , Ativação do Canal Iônico/efeitos dos fármacos , Leucina/genética , Locomoção/efeitos dos fármacos , Locomoção/genética , Modelos Moleculares , Morfolinas/farmacologia , Atividade Motora/genética , Neurônios Motores/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/fisiologia , Mutagênese Sítio-Dirigida/métodos , Mutação/genética , Mutação de Sentido Incorreto/genética , Rede Nervosa/fisiologia , Antagonistas Nicotínicos/farmacologia , Medula Espinal/citologia , Medula Espinal/fisiologia , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/genética , Tato/fisiologia , Valina/genética , Peixe-Zebra , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismoRESUMO
The neural cell adhesion molecule (NCAM) plays important roles in development of the nervous system and in synaptic plasticity and memory formation in the adult. The present study sought to further investigate the role of NCAM in learning by testing habituation and footshock sensitization learning of the startle response (SR) in NCAM null mutant (NCAM-/-) and wildtype littermate (NCAM+/+) mice. Whereas habituation is a form of non-associative learning, footshock sensitization is induced by rapid contextual fear conditioning. Habituation was tested by repetitive presentation of acoustic and tactile startle stimuli. Although NCAM-/- mice showed differences in sensitivity in both stimulus modalities, habituation learning was intact in NCAM-/- mice, suggesting that NCAM does not play a role in the mechanisms underlying synaptic plasticity in the startle pathway. Footshock sensitization was elicited by presentation of electric footshocks between two series of acoustic stimuli. In contrast to habituation, footshock sensitization learning was attenuated in NCAM-/- mice: the acoustic SR increase after the footshocks was lower in the mutant than in wildtype mice, indicating that NCAM plays an important role in the relevant brain areas, such as amygdala and/or the hippocampus.
Assuntos
Aprendizagem por Associação/fisiologia , Habituação Psicofisiológica/fisiologia , Moléculas de Adesão de Célula Nervosa/fisiologia , Reflexo de Sobressalto/fisiologia , Estimulação Acústica , Animais , Limiar Auditivo/fisiologia , Condicionamento Operante/fisiologia , Feminino , Habituação Psicofisiológica/genética , Audição/genética , Audição/fisiologia , Camundongos , Camundongos Knockout , Moléculas de Adesão de Célula Nervosa/genética , Plasticidade Neuronal/genética , Plasticidade Neuronal/fisiologia , Reflexo de Sobressalto/genética , Tato/genética , Tato/fisiologiaRESUMO
In wild-type Caenorhabditis elegans, six cells develop as receptors for gentle touch. In egl-44 and egl-46 mutants, two other neurons, the FLP cells, express touch receptor-like features. egl-44 and egl-46 also affect the differentiation of other neurons including the HSN neurons, two cells needed for egg laying. egl-44 encodes a member of the transcription enhancer factor family. The product of the egl-46 gene, two Drosophila proteins, and two proteins in human and mice define a new family of zinc finger proteins. Both egl-44 and egl-46 are expressed in FLP and HSN neurons (and other cells); expression of egl-46 is dependent on egl-44 in the FLP cells but not in the HSN cells. Wild-type touch cells express egl-46 but not egl-44. Moreover, ectopic expression of egl-44 in the touch cells prevents touch cell differentiation in an egl-46-dependent manner. The sequences of these genes and their nuclear location as seen with GFP fusions indicate that they repress transcription of touch cell characteristics in the FLP cells.
Assuntos
Caenorhabditis elegans/embriologia , Caenorhabditis elegans/genética , Proteínas de Drosophila , Proteínas de Insetos/genética , Mutação , Tato/genética , Alelos , Sequência de Aminoácidos , Animais , Linhagem da Célula , Clonagem Molecular , DNA Complementar/metabolismo , Drosophila , Elementos Facilitadores Genéticos , Biblioteca Gênica , Genes Reporter , Proteínas de Fluorescência Verde , Humanos , Proteínas Luminescentes/metabolismo , Camundongos , Dados de Sequência Molecular , Neurônios/metabolismo , Fenótipo , RNA Mensageiro/metabolismo , Proteínas Recombinantes de Fusão/metabolismo , Homologia de Sequência de Aminoácidos , Fatores de Transcrição/metabolismo , Transcrição GênicaRESUMO
The startle response and adaptability of the startle response (prepulse inhibition and habituation) have been observed in animals. The studies reported here screened 8 inbred mouse strains to determine whether genetic factors influence these behaviors. Strain differences were found in both the sensitivity to acoustic startle and the magnitude of both the auditory and tactile startle as well as the magnitude of prepulse inhibition (PPI) of both tactile and acoustic startle. Neither the 2 startle responses nor the 2 forms of PPI were significantly correlated with one another, suggesting that different genes regulate these 2 forms of startle and PPI. Acoustic-acoustic PPI was significantly correlated, however, with hippocampal auditory gating (TC ratio) suggesting an overlap in the genes that regulate these 2 forms of sensory gating.