Long-term suppression of synaptic transmission by tetanization of a singlepyramidal cell in the mouse hippocampus in vitro

1. The consequences of stimulating a single pyramidal cell in the CA1 area of the hippocampus for synaptic transmission in the stratum radiatum were i nvestigated. 2. Tetanic activation of single pyramids caused by depolarizing current inj ection, but not an equal number of distributed action potentials, reduced e xcitatory transmission by 20%, with a delayed onset, for more than 1 h. 3. EPSPs in the tetanized pyramidal cells were increased for equally long p eriods but this was not the cause of the field EPSP reduction. Spontaneous somatic IPSPs were not affected; evoked IPXPs were decreased in the tetaniz ed cell. 4. Paired pulse facilitation of the field EPSPs was unchanged. 5. The field EPSP reduction nias markedly diminished by a knife cut along t he base of pyramidal cells in CA1. 6. The addition of antagonists of GABA, NMDA and metabotropic glutamate rec eptors blocked or diminished the field EPSP slope reduction evoked by intra cellular stimulation. 7. Simultaneous recordings revealed long-lasting excitations of interneuron s located in the outer oriens layer as a result of single pyramid tetanizat ion. 8. Intense firing of small numbers of pyramidal cells can thus persistently inhibit mass transmission through the hippocampus. This effect involves ac tivation of interneurons by glutamate receptors.