Hiromi Yuasa

1. In isolated cortical slabs, intracellular recording was performed. The average membrane potential of impaled cells was -30 mV with a S. D. of ±7.0 mV. In these cells there were spontaneous postsynaptic potentials or synaptic noise, which were mostly solitary PSPs. The frequency of PSPs amounted to about 40% of that of the intact visual cortex.2. Spontaneous IPSPs appeared more frequently in an isolated slab than in, an intact cortex. Inhibitory as well as excitatory interneurons were found in isolated cortical slabs.3. By application of tetrodotoxin in an intact cortex, the spontaneous PSPs, disappeared within first 20 minutes, while in this period the membrane potential was largely depolarized.4. Epicortical stimulation of an isolated cortex produces a long lasting IPSP as in an intact cortex. The mean latency of IPSPs was 2.8 msec with or without a preceding spike. No IPSP was elicited earlier than 1.7 msec. It was concluded that the intracortically produced IPSP was caused bi-synaptically by an inhibitory interneuron which might be connected with recurrent collaterals of cortical pyramidal cells.