Timing of nicotine effects on learning in zebrafish.

Nicotine has been shown in many, but not all, studies to improve cognitive function in a number of species including rats, mice, monkeys, and humans. Recently, we have found that nicotine also improves memory in zebrafish. Nicotinic agonists are being developed as novel treatments for Alzheimer's disease and other cognitive impairments. In screening the therapeutic potential of novel nicotinic agonists, it is important to have a rapid assay of cognitive improvement. Zebrafish can help with this effort. We have developed a method of rapidly assessing spatial position discrimination learning in zebrafish in one session of seven trials. We used this method to determine the cognitive effects of nicotine. Nicotine (100 mg/l administered during 3 min of immersion) caused a significant improvement in percent correct performance. This dose was within the effective range we found to improve the choice accuracy performance of zebrafish using the more time-intensive delayed spatial alternation procedure. Interestingly, the positive effect of nicotine was seen at 20-40 min postadministration, but not earlier, and declined at 80 and 160 min posttreatment. At the 40-min postdosing interval, 200 mg/l nicotine was also found to significantly improve choice accuracy. Nicotine-induced accuracy improvement was reversed by the nicotinic antagonist mecamylamine given shortly before testing but not when given concurrently with nicotine. This position discrimination procedure in zebrafish effectively demonstrated the cognitive-enhancing effects of nicotine. This model may be useful in the early screening of novel nicotinic compounds for treatment of cognitive dysfunction.