PRESYNAPTIC LONG-TERM CHANGES IN EXCITABILITY OF THE CORTICOSTRIATAL PATHWAY

WE employed measurements of striatal terminal excitability to monitor the presynaptic effects of tetanic stimulation of corticostriatal fibers. Cortical tetanic stimulation (CTS) initiated a long-lasting decrease in terminal excitability. With higher current CTS, a transient increase in excitability preceded the decrease. However, a long-term increase was induced (1) by a second tetanus applied during the brief elevation in excitability initiated by a previous CTS or (2) when dopamine and GABA transmission were disrupted. A long-term increase also occurred following tetanic stimulation of the striatal terminal field (STS). The direction of the long-lasting change in excitability may depend on the level of polarization of the membrane. These presynaptic mechanisms could be important for the long-term selective modification of striatal synaptic transmission.