. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 182 J. M. COUPER AND E. M. LEISE Fluoxetine Induces Metamorphosis o 100 10 S-l i 60 4-J (U e 40 u lM OJ 20 n = 100 n=100 n=60 n = 80. FlOb FlOi 5HTb fluox Figure -I. lO"*1 M fluoxetine injections (fluox) induced 61^ meta- morphosis. Statistical analysis comparing I0~" M fluoxetine injections with FIO injections showed a highly significant effect (x'onn = ). The fluoxetine treatment was not significantly different from the 5HTh condition (x; = ; accept H,,). Discussion To partially test the hypothesis that
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 182 J. M. COUPER AND E. M. LEISE Fluoxetine Induces Metamorphosis o 100 10 S-l i 60 4-J (U e 40 u lM OJ 20 n = 100 n=100 n=60 n = 80. FlOb FlOi 5HTb fluox Figure -I. lO"*1 M fluoxetine injections (fluox) induced 61^ meta- morphosis. Statistical analysis comparing I0~" M fluoxetine injections with FIO injections showed a highly significant effect (x'onn = ). The fluoxetine treatment was not significantly different from the 5HTh condition (x; = ; accept H,,). Discussion To partially test the hypothesis that serotonin and se- rotonergic neurons are directly involved in metamor- phosis, behaviorally relevant amounts of 5-HT were in- jected into competent Ilyunasxa larvae. Injections in- duced a high level of metamorphosis, suggesting that serotonin may be normally released as a neurotransmit- ter during metamorphosis. Because metamorphosis was considered to have occurred only if the loss of the velum and development to the juvenile state were completed within the experimental period, percentages of meta- morphosis reported in this study may be somewhat less than those of other authors. Even with these more rigor- ous criteria, the results of our injection experiments were nonetheless significant. Many compounds can be oxidized by seawater, losing or changing potency and thus acting in unexpected ways within larvae (Pires and Hadfield, 1991). Metamorphosis in response to bath-applied 5-HT could reflect the activ- ity of this neurotransmitter within the larval nervous sys- tem or the activity of some unidentified oxidized product of this compound. Direct injection of 5-HT into the hemolymph eliminates the confounding factor inherent in bath-application studies, although it does not elimi- nate the possibility that serotonin is metabolized within larvae and that it is some metabolite, rather than seroto- nin, that was active during our experiments. Still, these experiments allow us to
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