SYNAPTIC INHIBITION REGULATES ASSOCIATIVE INTERACTIONS BETWEEN AFFERENTS DURING THE INDUCTION OF LONG-TERM POTENTIATION AND DEPRESSION

The induction of long-term potentiation and depression depends upon as sociative interactions between synapses that converge on individual de ndrites. The distance over which these associative interactions occur is limited. The present study evaluates whether this limitation is reg ulated by synaptic inhibition. We evaluated the associative interactio ns between two inputs that terminate on different proximo-distal locat ions along the dendrites of dentate granule cells in the presence of t he gamma-aminobutyric acid (GABA) antagonist bicuculline methiodide. L ocal blockade of GABAergic inhibition enhanced associative interaction s between nonoverlapping inputs, compared to within-animal control sit es, where inhibitory transmission was intact. The results suggest that synaptic inhibition limits interactions between excitatory synapses b y creating current shunts that limit the spread of depolarization with in the dendritic tree.