Visual Activity In Sd Rats, The Primary Visual Cortex Ii / Iii Neurons The Internal Level Of Plasticity Of Lateral Synaptic Connections

Neuronal activity is important for the formation and maturation of neural circuits in the mammalian nervous system. Very early in development, the basic connections that define these circuits are determined genetically. Refinement of these connections during later development, however, is strongly influenced by neuronal activity. But exactly how activity shapes synaptic connectivity during development, and the precise mechanisms underlying experience-dependent plasticity and refinement of central circuits are still not fully understood.Primary visual cortex is often used to study experience dependent neural plasticity. The formation of normal binocular connections in the visual cortex requires input from eyes during a postnatal critical period that can be delayed by biocular deprivation. Various forms of activity-dependent modifications have been described by studying synaptic plasticity in the visual cortex. The common approach has been to record intracellular or population excitatory postsynaptic potentials in layerⅡ/Ⅲthat are evoked by electrical stimulation at the border of the white matter and layerⅣ. The purpose of the approach is to mimic the visual input.To explore the role of visual experience in experience-dependent critical period, we induced and recorded long-term potentiation(LTP) of pyramidal neurons in layerⅡ/Ⅲthat were evoked at neighboring layerⅡ/Ⅲof visual cortical slices to mimic the connections between neurons within layerⅡ/Ⅲin normal reared rats and lid sutured (LS) rats. We found that both normal reared rats and lid sutured rats can not be induced LTP. We also tested the influence of this tetanic stimulation to vertical input that from layerⅣ. The results showed that normal reared rats induced robust LTP, while visual deprived rats can induce short-term potentiation (STP) but not LTP. It is very similar to the responses that take place before eyes opening when the layerⅡ/Ⅲstimulation also induced STP from vertical input. This indicate that visual deprivation prolongs the time window of vertical input responses. The different effect of visual deprivation on LTP stimulation from two direction indicate that the maturation of inhibitory GABAergic synapses in different input direction may be not synchronous. AMPAR(α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor)mediated mEPSCs and GABAR (γ-aminobutyric acid receptors) mediated mIPSCs are also recorded. Visual deprivation lead to an increase in mEPSCs amplitude but had no influence on frequency and decay kinetics. Differently, visual deprivation lead to a decrease in mIPSCs amplitude and frequency but had no influence on mIPSCs kinetics. This indicated visual deprivation had different effects on the expression of AMPARs and GABARs on neuron surface. Excitatory and inhibitory synaptic currents are regulated in opposite directions by activity blockade (lid suture), and these data suggest that the balance between excitation and inhibition is dynamically regulated by ongoing activity.