RESUMO
The firing properties of small neurons (with diameters of soma less than 25 µm) were investigated using patch-clamp technique in whole-cell configuration in primary culture of trigeminal ganglia (TG) of postnatal rats. TG neurons were divided into three groups according to their firing responses to long-lasting depolarizing pulses: adaptive neurons (AN) characterized by a strongly adaptive responses; tonic neurons (TN) characterized by a multiple tonic firing; neurons with a delay before initiation of AP generation, namely, NDG. AN, TN and NDG also differed in AP electrophysiological and pharmacological characteristics. TN was distinguished by responses to hyperpolarization and the greatest value of input resistance. TN, AN and NDG were characterized by different active properties (amplitude of action potential and afterhyperpolarization, reobase, threshold). Each group of neurons was characterized by heterogeneity of AP duration and of frequency properties for TN. The application of tetrodotoxin (TTX) (250 nM) resulted in full or partial inhibition of AP generation and some neurons had TTX insensitive firing responses. Neurons that were not affected by TTX had markedly longer AP. TTX had no effect on electrical activity of some AN and NDG. Based on sensitivity to TTX and their electrophysiological properties, AN and NDG seem to be C-fiber nococeptors.
Assuntos
Potenciais de Ação/fisiologia , Neurônios/classificação , Neurônios/fisiologia , Gânglio Trigeminal/fisiologia , Potenciais de Ação/efeitos dos fármacos , Animais , Animais Recém-Nascidos , Feminino , Masculino , Neurônios/citologia , Neurônios/efeitos dos fármacos , Técnicas de Patch-Clamp , Cultura Primária de Células , Ratos , Ratos Wistar , Bloqueadores dos Canais de Sódio/farmacologia , Canais de Sódio/metabolismo , Tetrodotoxina/farmacologia , Fatores de Tempo , Gânglio Trigeminal/citologia , Gânglio Trigeminal/efeitos dos fármacosRESUMO
In this study we conducted a series of experiments to characterize the effect and define the mechanisms of hypoxia on synaptic transmission between retinal ganglion cells and superior colliculus (SC) neurons. Application of hypoxic solution leads to a long lasting potentiation (LTP) NMDA-mediated synaptic transmission. Analysis of the oxygen deficiency effect on the spontaneous and miniature postsynaptic currents (sPSC and mPSC respectively) revealed an increase in the frequency of their occurrence and the appearance of the second peak in the mPSC histogram distribution. The assessment of quantum and binomial parameters reflects the complex pre- and postsynaptic changes during the potentiation, independent of the release probability. Most likely this LTP can be caused by an increase in the total number of active synapses. Glutamatergic synaptic transmission mediated by non-NMDA activation receptor-channel complexes, responded to application of deoxygenated solution by the brief depression, which is the result of presynaptic dysfunction and associates with decrease in release probability and number of active zones. GABAergic synaptic transmission mediated by activation GABA(A)-receptor-channel complexes, responded to hypoxic action by long term depression (LTD). Analysis of sPSC and mPSC showed a significant decrease in the frequency of their occurrence and significant (P = 0.05) decrease in the quantum over a period of oxygen deficiency. In general, the effect of hypoxia-induced LTD of GABAergic synaptic transmission is based on complex changes of presynaptic (independent on the release probability) and postsynaptic (reduction sensitivity of receptors in postsynaptic membrane) mechanisms.
Assuntos
Neurônios/efeitos dos fármacos , Oxigênio/farmacologia , Células Ganglionares da Retina/efeitos dos fármacos , Colículos Superiores/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Animais , Hipóxia Celular , Técnicas de Cocultura , Expressão Gênica , Potenciação de Longa Duração/efeitos dos fármacos , Potenciação de Longa Duração/fisiologia , Depressão Sináptica de Longo Prazo/efeitos dos fármacos , Depressão Sináptica de Longo Prazo/fisiologia , Potenciais Pós-Sinápticos em Miniatura/efeitos dos fármacos , Potenciais Pós-Sinápticos em Miniatura/fisiologia , Neurônios/citologia , Neurônios/fisiologia , Ratos , Receptores de GABA-A/genética , Receptores de GABA-A/metabolismo , Receptores de N-Metil-D-Aspartato/genética , Receptores de N-Metil-D-Aspartato/metabolismo , Células Ganglionares da Retina/citologia , Células Ganglionares da Retina/fisiologia , Colículos Superiores/citologia , Colículos Superiores/fisiologia , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Transmissão Sináptica/fisiologiaRESUMO
The alpha subunit composition of nicotinic acetylcholine receptors (nAChRs) expressed in the neurons of intracardiac ganglia of the rat was investigated using monoclonal and polyclonal antibodies against alpha3, alpha4, alpha5 and alpha7 nAChR subunits. The acetylcholine-induced membrane potentials in the neurons of the subepicardial plexus isolated from the left atrium of the heart were studied by intracellular recording performed in the presence of subunit-specific nAChR-blocking antibodies applied either separately or in various combinations. It was found that intracardiac ganglia neurons express alpha3alpha5; alpha7; alpha7(alpha5) and alpha4-containing nAChRs. The neurons were heterogeneous as to the nAChR subtypes expressed that possibly indicated their functional differences.
