Regional differences in the expression of corticostriatal synaptic plasticity.

Field recordings of responses to activation of corticostriatal afferents were made in coronally sectioned rat brain slices. Each recording site was categorized according to its medial to lateral and rostral to caudal position to investigate anatomical differences in synaptic plasticity. Individual responses were highly variable exhibiting extremes of tetanus induced depression and potentiation. Consequently, averaging masked the capacity of these synapses to express long-term forms of plasticity. Block of GABA(A) inhibition and elimination of dopaminergic input with 6-hydroxydopamine lesions both acted to increase the expression of potentiation, but again considerable variability was observed. Separation of recordings into medial and lateral groups revealed clear anatomical trends which contributed to the variability observed in the total sample. Paired-pulse, post-tetanic and long-term potentiation was greater in medial than in lateral groups in normal artificial cerebral spinal fluid. Similar tendencies were seen after block of GABA(A) receptors with bicuculline. 6-Hydroxydopamine lesions in combination with bicuculline treatment reduced medial to lateral differences. Factoring in medial to lateral trends revealed block of GABA(A) receptor mediated inhibition had its greatest effect on medial corticostriatal responses and 6-hydroxydopamine lesions had their greatest effect on lateral responses. From these data we suggest anatomical variation in striatal circuitry may underlie regional differences in synaptic plasticity evoked by corticostriatal activation.