BEULIG,, A.*; FOWLER,, J.; New College of Florida; New College of Florida: Serotonin and avoidance learning in goldfish

Serotonin (5-HT) has been implicated in clinical phenomena such as depression, and stress as well as general activity. The development of specific serotonin re-uptake inhibitors (SSRI�s)such as fluoxetine (Prozac)effective in the treatment of clinical depression was a significant achievement. However, diversity of serotonergic function remains to be completely characterised and phylogenetic history of serotonergic mechanisms is not yet well-understood. Studies on rats have shown a negative relationship between serotonergic activity and active avoidance learning suggesting a role in cognition. We sought to investigate this in a phylogenetically lower group, the fish. We assigned groups of 15 goldfish (Carassius auratus) to each of three treatments: fluoxetine; a 5HT-1_A receptor antagonist (WAY 100,635); and a sham control. Drugs were added to aquarium water and levels of fluoxetine were maintained at 81&mug/L and WAY 100,635 at 16&mug/L during the experiment. Subjects were trained in a two-way shuttle-box avoidance task, 15 trials per day for 13 days. A two-way ANOVA showed that WAY-treated subjects performed significantly more avoidance responses (p=.0079) than Prozac-treated or control subjects. It is suggested that normal or exogenously elevated serotonin levels have an inhibitory effect on spontaneous activity in fish in concordance with results in rats. This may have had a negative effect on the rate of acquisition of avoidance responding of control groups and fluoxetine-treated groups compared with 5HT-1_A receptor blocker-treated group. The latter may, therefore, have been more susceptible to the acquisition of the shuttling response. It is also suggested that serotonergic mechanisms may be highly conserved in the vertebrates and that fish may be useful model systems for the study of these mechanisms.