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Objective To investigate the electrophysiological properties of layer Ⅱ/Ⅲ pyramidal neurons of the early postnatal stage rat visual cortex.Methods By using the whole cell patch-clamp recording technique combined with direct visualization of cells,we studied the passive and active electrophysiological properties as well as firing properties of layer Ⅱ/Ⅲ pyramidal neurons in acute rat visual cortical slices.Results Resting membrane potential,input resistance,membrane capacitance and membrane time constant of pyramidal neurons at postnatal days 11-13(P 11-13) were(-56.6?1.8)mV,(185.4?2.7)M?,(77.9?2.2)pF and(16.9?2.4)ms,respectively.Action potential amplitude and duration were(97.7?2.7)mV and(2.3?0.1)ms,respectively.Threshold potential was(-31.8?1.2)mV and afterdepolarizing potential was(-65.3?1.1)mV.When presented with long depolarizing current pulse of constant amplitude,most of the neurons exhibited pronounced adaptation of spike frequency.The steady-state firing frequency was(30.4?9.4)% of the first interval firing frequency.Conclusion The electrophysiological properties of layer Ⅱ/Ⅲ pyramidal neurons of the early postnatal stage rat visual cortex are not fully mature.Most of the neurons display regular firing patterns,but the degree of firing frequency adaptation is relatively small.
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Objective To study the changes of field potentials (FPs) during development and after long-term potentiation (LTP) induction in rat visual cortical slices. Methods Field potentials recorded from layer Ⅱ/Ⅲ induced by layer Ⅳ in the rat visual cortical slices were examined. The developing changes of FPs from postnatal days 8-13,15-21 and 29-35 were observed. Amplitudes, peak latencies and slopes of FPs before and after LTP induction were compared. Results Field potentials changed with the development, and the stimulating threshold at p15-21 was lower than that of the other two groups. The increase of FP amplitude was positively correlated with increase of its slope. The shortening of FP latency was positively correlated with the difference between changes of slope and amplitude. Conclusion Developing changes of field potentials reflect the development of visual cortex. The changes of FP slope follow the changes of its amplitude and latency, and thereby the slope is a proper parameter used as an index to evaluate LTP in visual cortex.
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Long-term potentiation is an important form of synaptic plasticity and a cellular model for study of learning and memory. Long-lasting long-term potentiation is also a cellular model used in the research of long-term memory. The transformation from silent synapses to the functional ones is probably the important mechanism for the LTP maintenance. After induction, the LTP could be reversed by the physiological or artificial stimulations. Owing to the reversibility of LTP and its input-specific characteristics, it is reasonable to interfere specifically the addiction memory with particular deep brain electrical stimulation without damaging the brain functions.
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Objective To compare the different effects of different titanic parameters on the expression of long-term potentiation (LTP) and to determine the optimal patterns of tetanizing stimulation in hippocampal CA1 area in adult male rats. Methods Four tetanic parameters of 100Hz were used in the experiment. Tetanus 1 was a short burst of stimulus composed of 60 pulses, which were divided into 5 sets, each set including 4-pulses-bursts. The inter-burst intervals are lengthened gradually, 1s, 5s, 30s, 10min in sequence. Tetanus 2 was a long burst of stimulus composed of 300 pulses in all, each burst including 20 pulses. The inter-burst interval is 2s, and tetanus 3 is also a short burst of stimulus composed of 15 bursts, each burst including 4 pulses. The inter-burst interval is 2s and tetanus 4 is a single train of burst composed of 60 pulses. The field excitatory post-synaptic potentials (fEPSPs) in hippocampal CA1 area were evoked by stimulating the Schaffer collateral fibers in the stratum radiatum and the expressions of LTP induced by the four parameters were evaluated. Results The amplitude and incidence of LTP induced by tetanus 1 were higher than those induced by the other three parameters. There was no statistical significance between the responses induced by the other three parameters. Both tetanus 1 and tetanus 3 could lead to long-lasting-LTP (LL-LTP, over 3h). Conclusion A high frequency stimulus with 200ms-inter-burst interval (theta frequency) is better in the induction of LTP in hippocampal CA1 area. A short burst of stimulus with 100Hz can evoke the expression of LL-LTP in hippocampal CA1 area.
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Objective To study the effects of gamma-aminobutyric acid (GABA) on the induction of long-term potentiation (LTP) in developing rat visual cortical slices. Methods Field potentials recorded from layer Ⅱ/Ⅲ induced by layer Ⅳ stimulation in rat visual cortical slices were examined. LTP was induced by tetanus in the slices on the postnatal 2, 3 and 5-week rats. The LTP incidences and the effects of GABA on them in different developmental stages were compared. Results LTP incidence at postnatal week 5 was significantly lower than that in other two groups. GABA A receptor antagonist picrotoxin could reverse this tendency, but had no effects on the LTP induction at the early postnatal age. Conclusion In visual cortex, GABA has inhibitory effects on the LTP induction only after the end of critical period and has no any facilitatory effects on the LTP induction before the developmental critical period.