SYNAPSE SPECIFICITY OF LONG-TERM POTENTIATION BREAKS DOWN AT SHORT DISTANCES

Long-term potentiation (LTP), the long-lasting increase in synaptic tr ansmission, has been proposed to be a cellular mechanism essential for learning and memory, neuronal development, and circuit reorganization . In the original theoretical(1) and experimental(2) work it was assum ed that only synapses that had experienced concurrent pre- and postsyn aptic activity are subject to synaptic modification. It has since been shown, however, that LTP is also expressed in synapses on neighbourin g neurons that have not undergone the induction procedure(3-5). Yet, i t is still believed that this spread of LTP is limited to adjacent pos tsynaptic cells, and does not occur for synapses on neighbouring input fibres(2,6,7). However, for technical reasons, tests for 'input speci ficity' were always done for synapses relatively far apart. Here we ha ve used a new local superfusion technique, which allowed us to assess the synaptic specificity of LTP with a spatial resolution of similar t o 30 mu m. Our results indicate that there is no input specificity at a distance of less than 70 mu m. Synapses in close proximity to a site of potentiation are also potentiated regardless of their own history of activation, whereas synapses far away show no potentiation.