This idea was further developed when nicotine was found to BAY 73-4506 supplier reverse the effects of scopolamine on attention in young volunteers.108 The opportunity has thus existed for over 16 years to utilize a model to help screen potential anti-Alzheimer drugs in phase

1. The validity of this model has been widely established109-112 and a wide variety of drugs have been screened. The model is particularly sensitive to anticholinesterases, for example, physostigmine 2 mg subcutaneously has been found to rapidly and completely reverse the impairment produced by scopolamine on all CDR tasks employed, Inhibitors,research,lifescience,medical yet these effects were only temporary and had faded an hour later.113 This mimics the clinical situation perfectly, many early trials showing brief improvements in AD patients during infusions of physostigmine, which faded rapidly on cessation of the infusion. A further trial has confirmed this Inhibitors,research,lifescience,medical rapid but temporary action of physostigmine and has further shown it to be strongly dose-dependent.114 In a further series of studies, velnacrine, an analogue of the anticholinesterase tacrine, was found to produce widespread reversal of the cognitive impairment on CDR tasks produced by scopolamine.113,115,116 The drug was then

administered to AD patients Inhibitors,research,lifescience,medical and improvements were seen on some of the CDR tasks that reversals had been identified in the scopolamine model.115,116 The model is sensitive to a range of compounds, Inhibitors,research,lifescience,medical even those without known cholinergic effects. The classic nootropics aniracetam and piracetam have shown activity in the model,117 as has tenilsetam,118 Inhibitors,research,lifescience,medical though 30H-aniracetam (Ro 15-5986) showed no activity.47,119 The monoamine oxidase inhibitor moclobemide has been shown to reverse the effects of scopolamine,47,119 as has the partial agonist at the strychnine-insensitive glycine site on the NMDA receptor, D-cycloserine, in both young and elderly volunteers.120,121 L-NAME HCl The effects

of the latter compound were particularly interesting as they were limited to the working and episodic memoryeffects of scopolamine. FK960 has shown a widespread ability to reverse the effects of scopolamine.122 Quite a number of compounds have not shown sensitivity in the model, despite performing very well in various animal models, but these have not been released into the public domain. One compound that failed to have any effect on the impairment due to scopolamine was candoxatril, a prodrug of the atriopeptidase inhibitor, candoxatrilat, which increases circulating levels of the peptide hormone atrial natriuretic peptide and inhibits the degradation of endogenous enkephalins.