The Involvement of D1 and D2 Dopamine Receptors in the Restoration Effect of Left Frontal Anodal, but not Cathodal, tDCS on Streptozocin-Induced Amnesia

Transcranial direct current stimulation (tDCS) is a non-invasive method that improves learning and memory. In this study, the effect of tDCS on streptozotocin (STZ) induced amnesia in the presence or absence of SCH23390 (D1 dopamine receptor antagonist) and sulpiride (dopamine D2 receptor antagonist) has been investigated in male Wistar rats. Passive avoidance memory, locomotor activity and pain perception have been assessed by step-through, open-field and hot-plate instruments, respectively. Anodal and cathodal tDCS were exerted on the left frontal cortex with an intensity of 0.2 milliamps for 20 minutes twice a day in 2 successive days. Our study showed that STZ at doses of 30 and 60 mg/ml/kg caused amnesia, while they did not alter locomotor activity and a higher dose of STZ induced analgesia 14 days after injection. SCH23390 (0.001 mg/mL/kg) and sulpiride (0.1 mg/mL/kg) did not alter memory formation by themselves and amnesia induced by STZ (30 and 60 mg/mL/kg), while SCH23390 restored the analgesia induced by STZ (60 mg/mL/kg). Moreover, left frontal anodal and cathodal tDCS restored memory impairment induced by STZ (30 and 60 mg/mL/kg). Also, SCH23390 and sulpiride could prohibit the anodic stimulating effect on memory impairment induced by a dose of 60 mg/ml/kg, but they did not hinder the effect of the cathodal stimulation on this phenomenon. The study showed that D1 and D2 dopamine receptors are involved in the restoration effect of left frontal anodal- but not cathodal-tDCS in STZ-induced amnesia.