Nicotine induces long-lasting potentiation in the dentate gyrus of nicotine-primed rats

A challenge dose of nicotine (0.4 mg kg −1 s.c.) produced a long-lasting potentiation (LLP) of field EPSPs evoked in the dentate gyrus by stimulation of the medial perforant path of urethane-anaesthetized rats primed four weeks previously with seven daily injections of nicotine (0.8 mg kg −1 s.c.). The same dose of nicotine did not alter EPSPs evoked in rats primed with saline vehicle. Systemic injection of either mecamylamine or propranolol, 30 min before nicotine challenge, prevented induction of LLP without affecting baseline EPSPs but neither drug affected LLP when given after it was established. Since the nicotine-priming regime is known to increase tyrosine hydroxylase activity and hippocampal noradrenaline release in response to nicotine challenge, the results suggest that systemic injection of nicotine released sufficient noradrenaline in nicotine-primed rats to induce a β-adrenoceptor-mediated LLP.