Long-term facilitation of excitatory synaptic transmission in single motor cortical neurones of the cat produced by repetitive pairing of synaptic potentials and action potentials following intracellular stimulation.

The effects of postsynaptic firing activity on excitatory postsynaptic potentials (EPSPs) were studied in the motor cortex of anaesthetized cats. Postsynaptic firing was induced by 1-5 nA cathodal current pulses via the recording intracellular microelectrode, while EPSPs were elicited by thalamic, callosal, pyramidal tract and somatosensory stimuli. In 102 cells, EPSP-spike stimulus pairs were applied with 0.2-1/sec frequency and 10-100 msec interstimulus intervals. In 42 neurones, reversible facilitation of paired EPSPs appeared lasting from 4 to 47 min. The synaptic facilitation in most cases was accompanied by membrane depolarization and an increase in input resistance. The effectiveness of current induced action potentials upon test EPSPs provided evidence for the postsynaptic localization of plastic changes occurring in conditioning experiments.