The priming effect on LTP is mediated by D1/D5 receptors. (A) Oral administration of the D1 receptor antagonist SKF 83566 together with nicotine for 7 d blocked the enhancement of LTP in the DG. (Open squares) 7-d SKF 83566+nicotine+cocaine, (closed circles) 7-day nicotine+cocaine. (B) SKF 83566 alone did not alter LTP. (Closed circles) 7-d SKF 83566, (open squares) control. (C) Oral administration of the D1 agonist SKF 38393 together with nicotine prior to cocaine did not further enhance the priming effect on LTP induced by 7-d nicotine/cocaine. (Open squares) 7-d SKF 38393+nicotine+cocaine, (closed circles) 7-d nicotine+cocaine. (D) Oral administration of the D1 agonist SKF 38393 significantly enhanced LTP induced by 1-d nicotine exposure and cocaine. (Open squares) SKF 38393+1-d nicotine+cocaine, (closed circles) 1-d nicotine+cocaine. (E) Oral administration of the D1 agonist SKF 38393 alone did not alter LTP. (Closed circles) SKF 38393, (open squares) control. (F) The protein kinase A (PKA) inhibitor KT5720 blocked the enhancement of LTP induced by 7-d nicotine and cocaine. (Open squares) KT5720+7-d nicotine+cocaine, (closed triangle) KT5720, (closed circles) 7-d nicotine+cocaine.
