Fluctuations in pyramid-pyramid excitatory postsynaptic potentials modified by presynaptic firing pattern and postsynaptic membrane potential using paired intracellular recordings in rat neocortex

Single axon excitatory connections between pairs of neocortical pyramidal neurons were studied using paired intracellular recordings in layers II/III and IV of coronal slices of adult rat somatosensory/motor cortex. Excitatory postsynaptic potentials evoked with different presynaptic firing patterns and at different postsynaptic membrane potentials were compared. Two methods of statistical analysis were used in attempts to determine whether changes in mean excitatory postsynaptic potential amplitude were due to presynaptic or postsynaptic modifications. Analysis of the decrease in mean excitatory postsynaptic potential amplitude associated with increases in presynaptic firing rate were consistent with a change in probability of transmitter release. Paired pulse depression appeared to exhibit both presynaptic and postsynaptic components when the interspike interval was