RESUMEN
Exploring the transition from inter-ictal to ictal epileptiform discharges (IDs) and how GABA receptor-mediated action affects the onset of IDs will enrich our understanding of epileptogenesis and epilepsy treatment. We used Mg-free artificial cerebrospinal fluid (ACSF) to induce epileptiform discharges in juvenile mouse hippocampal slices and used a micro-electrode array to record the discharges. After the slices were exposed to Mg-free ACSF for 10 min-20 min, synchronous recurrent seizure-like events were recorded across the slices, and each event evolved from inter-ictal epileptiform discharges (IIDs) to pre-ictal epileptiform discharges (PIDs), and then to IDs. During the transition from IIDs to PIDs, the duration of discharges increased and the inter-discharge interval decreased. After adding 3 μmol/L of the GABA receptor agonist muscimol, PIDs and IDs disappeared, and IIDs remained. Further, the application of 10 μmol/L muscimol abolished all the epileptiform discharges. When the GABA receptor antagonist bicuculline was applied at 10 μmol/L, IIDs and PIDs disappeared, and IDs remained at decreased intervals. These results indicated that there are dynamic changes in the hippocampal network preceding the onset of IDs, and GABA receptor activity suppresses the transition from IIDs to IDs in juvenile mouse hippocampus.
Asunto(s)
Animales , Masculino , Ratones , Animales Recién Nacidos , Bicuculina , Farmacología , Modelos Animales de Enfermedad , Epilepsia , Patología , Agonistas de Receptores de GABA-A , Farmacología , Antagonistas de Receptores de GABA-A , Usos Terapéuticos , Hipocampo , Metabolismo , Técnicas In Vitro , Magnesio , Metabolismo , Farmacología , Potenciales de la Membrana , Ratones Endogámicos C57BL , Muscimol , Farmacología , Red Nerviosa , Receptores de GABA-A , MetabolismoRESUMEN
In vertebrate visual system, retina is the first stage for visual information processing. Retinal ganglion cells are the only output neurons of the retina, and their firing activities are dependent on visual stimuli. Retinal ganglion cells can effectively encode visual information via various manners, such as firing rate, temporal structure of spike trains, and concerted activity, etc. Adaptation is one of the basic characteristics of the nervous system, which enables retinal neurons to encode stimuli under a wide variety of natural conditions with limited range in their output. This article reviews the recent studies focused on the coding properties and adaptation of retinal ganglion cells. Relevant issues about dynamical adjustment of coding strategies of retinal ganglion cells in response to different visual stimulation, as well as physiological property and function of adaptation are discussed.
Asunto(s)
Estimulación Luminosa , Retina , Células Ganglionares de la RetinaRESUMEN
Correlated firings among neurons have been extensively investigated; however, previous studies on retinal ganglion cell (RGC) population activities were mainly based on analyzing the correlated activities between the entire spike trains. In the present study, the correlation properties were explored based on burst-like activities and solitary spikes separately. The results indicate that: (1) burst-like activities were more correlated with other neurons' activities; (2) burst-like spikes correlated with their neighboring neurons represented a smaller receptive field than that of correlated solitary spikes. These results suggest that correlated burst-like spikes should be more efficient in signal transmission, and could encode more detailed spatial information.
Asunto(s)
Animales , Potenciales de Acción , Simulación por Computador , Oscuridad , Electrofisiología , Técnicas In Vitro , Luz , Técnicas de Placa-Clamp , Sumación de Potenciales Postsinápticos , Rana catesbeiana , Fisiología , Cirugía General , Retina , Fisiología , Células Ganglionares de la Retina , Fisiología , Neuronas Retinianas , Fisiología , Transducción de SeñalRESUMEN
To investigate the spatiotemporal properties of epileptiform activity in vitro, 400 microm-thick transverse hippocampal slices were prepared from juvenile rat and planar multi-electrode array (MEA) containing 60 electrodes was used to record the electrical activity induced by bath application of high potassium artificial cerebrospinal fluid (ACSF) on slices. Following successful induction of epileptiform bursts, phenobarbital sodium was applied to test for its inhibitory effects on bursting activity in different regions of slice. Region-specific characteristics of epileptiform activity and anticonvulsant actions of phenobarbital sodium in the hippocampal network were determined by comparing the population activity obtained from MEA. The results showed that: (1) 15 min after high-K+ ACSF application, rhythmic and synchronous epileptiform bursts could be detected from all CA sub-regions. Quantitative analysis indicates that the firing patterns of different CA sub-regions were not statistically different (P>0.05). However, no bursting activity was recorded from granular cells in dentate gyrus, only sparse spikes were observed, with frequency significantly lower than that in CA regions (P<0.05). (2) The high-K+-induced bursting activity could last for more than 40 min with stable bursting activities. (3) Bath application of 60 micromol/L phenobarbital sodium inhibited the bursting activities on hippocampal slice. Bursting activities in CA3c and CA1 were firstly suppressed. 10 min after the phenobarbital sodium application, strong bursting activities persisted only in some of pyramidal cells in CA3a and CA3b. These results show that MEA could be applied for studying the spatial and temporal properties of epileptiform activity in vitro, as well as the region-specific effects of anti-epileptic drugs.
Asunto(s)
Animales , Masculino , Ratas , Potenciales de Acción , Fisiología , Electrodos , Electroencefalografía , Fenómenos Electrofisiológicos , Fisiología , Epilepsia , Hipocampo , Técnicas In Vitro , Ratas Sprague-Dawley , Procesamiento de Señales Asistido por ComputadorRESUMEN
In the present study, the modulatory effect of AMPA receptors on gamma-aminobutyric acid (GABA) transporter current was investigated on enzymatically isolated horizontal cells of carp retina. The GABA transporter current elicited by 1 mmol/L GABA was decreased immediately after pre-application of AMPA (30 mumol/L or 3 mmol/L) for 50 s. Application of 10 mmol/L BAPTA in intracellular solution inhibited the suppression effect of AMPA on GABA transporter current. The suppression effect induced by co-application of 3 mmol/L AMPA and 3 mmol/L NMDA was similar to that of 3 mmol/L AMPA or 3 mmol/L NMDA alone. These results suggest that the activation of AMPA receptors inhibits GABA transporter-mediated current by affecting intracellular Ca(2+) processes in the retinal horizontal cells, which is identical with the modulatory effect of NMDA receptors on GABA transporters.
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Animales , Carpas , Ácido Egtácico , Farmacología , Proteínas Transportadoras de GABA en la Membrana Plasmática , Metabolismo , Receptores Ionotrópicos de Glutamato , Metabolismo , Células Horizontales de la Retina , Metabolismo , Ácido gamma-Aminobutírico , FarmacologíaRESUMEN
In the present study, the correlated activities of adjacent ganglion cells of transient subtype in response to full-field white light stimulation were investigated in the chicken retina. Pharmacological studies and cross-correlation analysis demonstrated that application of the GABA(A) receptor antagonist bicuculline (BIC) significantly down-regulated the correlation strength while increasing the firing activities. Meanwhile, application of the GABA(A) receptor agonist muscimol (MUS) potentiated the correlated activities while decreasing the firing rates. However, application of the GABA(C) receptor antagonist (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) did not have a consistent influence on either the firing rates or the correlation strength. These results suggest that in the chicken retina, correlated activities among neighborhood transient ganglion cells can be increased while firing activities are reduced with the activation of GABA(A) receptors. The GABA(A)-receptor-mediated inhibitory pathway may be critical for improving the efficiency of visual information transmission.
Asunto(s)
Animales , Ratones , Potenciales de Acción , Bicuculina , Farmacología , Antagonistas de Receptores de GABA-A , Farmacología , Muscimol , Farmacología , Ácidos Fosfínicos , Farmacología , Piridinas , Farmacología , Receptores de GABA-A , Metabolismo , Retina , Fisiología , Células Ganglionares de la Retina , Fisiología , Ácido gamma-AminobutíricoRESUMEN
It was previously found that the efficacy of synaptic transmission between retinal cone systems and luminosity-type horizontal cells (LHCs) was activity-dependent. Repetitive activation of red-cone pathway increased the LHCos hyperpolarizing response to red light, and the response enhancement was reversible. In this study, intracellular recording and pharmacological method were applied to investigate the mechanism(s) underlying red-flickering-induced response enhancement. Lowering intracellular Ca(2+) in the LHC by intracellular injection of Ca(2+) chelator EGTA prevented the development of red-flickering-induced response enhancement, which implicates the importance of postsynaptic calcium signal. The response enhancement could also be eliminated by a potent antagonist of Ca(2+)-permeable AMPA receptor (CP-AMPAR), which suggests the possibility that Ca(2+) influx via glutamate-gated calcium channels is related to the changes of [Ca(2+)](i). Furthermore, the administration of ryanodine or caffeine also attenuated the phenomenon, which gives evidence that the local calcium signal caused by intracellular calcium-induced calcium release (CICR) may be involved. Taken together, our data implicate that postsynaptic CICR and CP-AMPAR are related to the activity-dependent response enhancement.