Depotentiation in the dentate gyrus of freely moving rats is modulated by D1/D5 dopamine receptors

Hippocampal depotentiation comprises a reversal of tetanization-induced long term potentiation (LTP) which occurs following low-frequency stimulation. In the CA1 region, it has been reported that agonist activation of D1/D5 dopamine receptors enhances LTP expression and inhibits depotentiation. The role of these receptors in synaptic plasticity in the dentate gyrus (DG) has not been characterized. This study therefore investigated the role of D1/D5 receptors in LTP and depotentiation in the DG of freely moving rats. Male Wistar rats underwent chronic implantation of a recording electrode in the DG granule cell layer, a bipolar stimulating electrode in the medial perforant path and a cannula in the ipsilateral cerebral ventricle (to enable drug administration). The D1/D5 agonist Chloro PB dose-dependently inhibited depotentation in the DG. This effect was prevented by the D1/D5 antagonist SCH 23390. Neither D1/D5 agonist nor antagonist had an effect on LTP expression or basal synaptic transmission. These results highlight differences between D1/D5 receptor-involvement in LTP and depotentiation in the CA1 region and DG, and indicate that whereas D1/D5 receptor activation may not he a critical factor in LTP induction in the DG, a differential role for these receptors in the expression of depotentiation, in this hippocampal subfield, may exist.