Fish on Prozac: effect of serotonin reuptake inhibitors on cognition in goldfish.

The authors studied the effect of fluoxetine (a specific serotonin reuptake inhibitor--SSRI) on active avoidance learning in fish. In an active, two-way, shuttle-box avoidance task we compared escape and avoidance of shock among fish receiving chronic administration of fluoxetine (Prozac), others receiving a 5-HT(1A) receptor antagonist (WAY 100,635; Sigma, St. Louis, MO) and controls. The receptor-blocked group performed significantly more Avoids than the fluoxetine group, which was lowest in performance, or than controls, which were slightly higher, and not significantly different from, the fluoxetine group. This conforms to results reported in rats. Active avoidance learning may be stimulated by the 5-HT(1A) receptor antagonist. Fluoxetine-treated fish seemed less active in their home tanks than controls or blocker-treated fish. These results suggest that at the dosages used in this experiment, the 5-HT(1A) receptor antagonist WAY 100,635 may have positive effects on cognition in fishes and its action may not necessarily be restricted to blockage of 5 HT reuptake inhibition. It seems that serotonin mechanisms may be highly conserved in vertebrate evolution.