POSSIBLE FUNCTIONAL-ROLE OF DIADENOSINE POLYPHOSPHATES - NEGATIVE FEEDBACK FOR EXCITATION IN HIPPOCAMPUS

Diadenosine polyphosphates (Ap(4)A and Ap(5)A) are present in secretor y granules of chromaffin cells(8) as well as in the rat brain synaptic terminals.(6) Their contribution to the exocytosis of the total synap tosomal content is considerable, ranging from 7% to 12%. Ap(4)A and Ap (5)A are released from synaptosomes in a Ca2+-dependent manner.(6) The re are indications on the high affinity of diadenosine polyphosphates to P-2 receptors,(5,7) but their action on P-1 receptors remains uncle ar. Here we report that both substances induce a blocking action on ex citatory synaptic transmission in the rat hippocampus. This action is elicited via the A(1) (subclass of P-1) receptors and differs in some respects from the action of adenosine.