Learning-induced enhancement of feedback inhibitory synaptic transmission.

Olfactory-discrimination learning results with a series of intrinsic and excitatory synaptic modifications in piriform cortex pyramidal neurons. Here we show that such learning results with long-lasting enhancement of inhibitory synaptic transmission onto proximal dendrites of these pyramidal neurons. Such enhancement is mediated by a strong hyperpolarizing shift in the reversal potential of fast inhibitory postsynaptic potentials (fIPSPs). Moreover, paired-pulse depression of these IPSPs, indicating enhanced GABA release, is also apparent after learning. We suggest that learning is accompanied by long-lasting enhancement of synaptic inhibition onto excitatory neurons, thus compensating for the increase of excitation in these neurons.