Inhibitory potentials in neurons of the deep layers of the in vitro neocortical slice

Neocortical neurons in slices of the rat sensorimotor region maintained in vitro generate postsynaptic potentials (PSPs) in response to focal extracellular stimulation. These PSPs are mainly depolarizing at the resting membrane potential (Vm) but a sequence of depolarizing-hyperpolarizing potentials is often disclosed by depolarizing the Vm. The stimulus-induced hyperpolarization can last up to 1000 ms and show two components: the early one (peak latency 10-20 ms), is inverted by diffusion of Cl- into the cell; the late one is diminished by augmenting [K+]o. The membrane conductance is increased throughout the stimulus-induced hyperpolarization, mainly during the first 10-60 ms. A decrease in excitability results from both the hyperpolarizing trend and the conductance increase. The latter is more effective in decreasing depolarizing than hyperpolarizing pulses of current injected intracellularly.