Effects of l-threo-DOPS, a noradrenaline precursor, on the long-term potentiation in the rat hippocampal mossy fiber-CA3 region

The effects of l-threo-3,4-dihydroxyphenylserine ( l-threo-DOPS), a synthetic precursor of norepinephrine (NE), on the long-term potentiation (LTP) in the hippocampal mossy fiber-CA3 system was examined in urethane-anesthetized rats, the objective being to determine whether or not this drug acts as NE on the LTP. l-threo-DOPS may be effective for treating some type of mental disorders, including dementia. The LTP, induced in CA3 by tetanic stimulation (100 Hz for 1 s) applied to the mossy fiber persisted for more than 4 h. When l-threo-DOPS (50 and 150 μg) was injected into the lateral ventricle 30 min prior to the tetanic stimulation, there were no significant alterations in the LTP. However, in animals treated with reserpine (5 mg/kg i.p.) 24 h before the experiment. LTP was not induced with tetanic stimulation alone yet was obtained when tetanic stimulation was preceded by l-threo-DOPS (50 and 150 μg) applied to the ventricle. The LTP obtained by l-threo-DOPS in the reserpine-treated animal was inhibited by pretreatment with benserazide and was completely blocked by the simultaneous administration of sotalol. These results suggest that NE converted from l-threo-DOPS plays an important role in inducing LTP in the mossy fiber-CA3 system in the animals deficient in catecholamines.