PHILANTHOTOXINS BLOCK GLUTAMATERGIC TRANSMISSION IN RAT HIPPOCAMPUS .2. INHIBITION OF SYNAPTIC TRANSMISSION IN THE CA1 REGION

1. Philanthotoxins decrease the amplitude of the population spike (PS), the field excitatory postsynaptic potential (f-EPSP), and the presynaptic volley (PV), as evoked by Shaffer-collateral-commissural inputs to the CA1 pyramidal cells in the rat hippocampus slice. 2. The effects are slow and often not completely reversible. 3. Dideaza-philanthotoxin-12 is, in all experiments, the most active antagonist showing a very poor recovery. 4. Using a twin pulse the percentual decreases of f-EPSP and PV amplitudes are almost identical for the first and second response. However, the first PS is much more affected than the second one, indicating a possible effect on the inhibiting circuit. 5. Philanthotoxins cause a non-competitive inhibition. 6. Besides a possible postsynaptic block and a distinct presynaptic effect (preceding paper) a non-postsynaptic effect (on the PV) is described.