sentence: Microiontophoretic applications of E transmitter glutamate and I transmitter γ - aminobutyric acid ( GABA ) at the apical dendrite induce rapid membrane depolarizations and hyperpolarizations , respectively , with kinetics similar to those of natural excitatory postsynaptic potentials ( EPSPs ) and inhibitory postsynaptic potentials ( IPSPs ) elicited by extracellular electrical stimulation in the CA1 region , respectively ( Fig. 1B ) ( 21 ) .