TETANUS-INDUCED POTENTIATION OF INHIBITORY POSTSYNAPTIC POTENTIALS INHIPPOCAMPAL CA1 NEURONS

In the present study, tetanus-induced potentiation of inhibitory posts ynaptic potentials (IPSPs). previously described by our laboratory, wa s further investigated in guinea pig hippocampal CA1 neurons. Tetanic stimulation of the stratum radiatum induced a long-term potentiation o f the excitatory postsynaptic potential and a potentiation of the gamm a-aminobutyric acid A (GABA(A)) receptor mediated fast IPSP without en hancing the GABA(B) receptor-mediated slow IPSP. During the potentiati on, IPSPs evoked by stimulation of the alveus were unaffected. When sl ices were superfused with DL-2-amino-5-phosphonovaleric acid (an N-met hyl-D-aspartate, NMDA, antagonist) and 6-cyano-7-nitroquinoxaline-2,3- dione (a non-NMDA glutamate antagonist), the potentiation of the monos ynaptic fast IPSP could still be induced and maintained, suggesting th at polysynaptic influences were unnecessary for this process. Finally, since the potentiation was observed in CA1 neurons in which BAPTA or K-252b was injected, this form of plasticity does not appear to be dep endent on a rise in intracellular [Ca2+] or protein kinase C (PKC) act ivity. These results indicate that tetanic stimulation of the stratum radiatum induces a potentiation of GABAergic fast IPSPs in CA1 neurons . The potentiation may be localized to the GABAergic synapse on CA1 ne urons.