Functional state of corticostriatal synapses determines their expression of short- and long-term plasticity

Relationships between presynaptic function and short- and long-term plastic ity were investigated at adult corticostriatal synapses. Wide variability w as observed in the expression of short- and long-term synaptic plasticity. Intracellular records from 47 cells produced 17 examples of LTD (<90% of co ntrol), 10 examples of no long-term change (between 90-110% of control), an d 20 examples of LTP (>110% of control). Similar variation existed in paire d-pulse and posttetanic plasticities. The variability expressed in all thre e forms of plasticity appears to be related, based on correlations found be tween the paired-pulse ratio (PPR) and tetanus-induced short- (3 min postte tanus) and long-term plasticities (16-20 min posttetanus). These data sugge st that tetanus-induced changes in synaptic strength are related to the int rinsic, preconditioned behavior of synapses. Every cell showing paired-puls e depression also expressed LTD in response to high-frequency activation of its afferents. Those synapses showing paired-pulse potentiation tended to express LTP, although exceptions did exist. Similar relationships were foun d in a parallel analysis of population spikes. PPR also changed in associat ion with the expression of posttetanic and long-term depression. Greater pa ired-pulse potentiation was observed in medial intracellular recordings, bu t no medial to lateral differences were seen in posttetanic plasticities. F ield recordings also showed a medial bias toward paired-pulse and posttetan ic potentiation, but not in long-term plasticity. Block of postsynaptic L-t ype Ca2+ channels with nifedipine eliminated LTD expression, but overall no differences were found between nifedipine and control cells. (C) 2000 Wile y-Liss, Inc.