Ontogeny of central serotonergic neurons in the directly developing frog, Eleutherodactylus coqui |
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Authors: | Ten Eyck Gary R Jermakowicz Walter J Chinn Alison F Summers Cliff H |
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Institution: | (1) Department of Psychology, Biopsychology Area, The University of Michigan, Ann Arbor, MI 48109-1109, USA;(2) Neuroscience Graduate Program, Vanderbilt Brain Institute, Vanderbilt University Medical Center, Nashville, TN 37240, USA;(3) Department of Biology, The University of South Dakota, Vermillion, SD 57069, USA;(4) Department of Biology and Neuroscience Group, Division of Basic Biomedical Sciences, School of Medicine, The University of South Dakota, Vermillion, SD 57069, USA;(5) Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA |
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Abstract: | Embryonic development of the central serotonergic neurons in the directly developing frog, Eleutherodactylus coqui, was determined by using immunocytochemistry. The majority of anuran amphibians (frogs) possess a larval stage (tadpole)
that undergoes metamorphosis, a dramatic post-embryonic event, whereby the tadpole transforms into the adult phenotype. Directly
developing frogs have evolved a derived life-history mode where the tadpole stage has been deleted and embryos develop directly
into the adult bauplan. Embryonic development in E. coqui is classified into 15 stages (TS 1–15; 1 = oviposition / 15 = hatching). Serotonergic immunoreactivity was initially detected
at TS 6 in the raphe nuclei in the developing rhombencephalon. At TS 7, immunopositive perikarya were observed in the paraventricular
organ in the hypothalamus and reticular nuclei in the hindbrain. Development of the serotonergic system was steady and gradual
during mid-embryogenesis. However, starting at TS 13 there was a substantial increase in the number of serotonergic neurons
in the paraventricular, raphe, and reticular nuclei, a large increase in the number of varicose fibers, and a differentiation
of the reticular nuclei in the hindbrain. Consequentially, E. coqui displayed a well-developed central serotonergic system prior to hatching (TS 15). In comparison, the serotonergic system
in metamorphic frogs typically starts to develop earlier but the surge of development that transpires in this system occurs
post-embryonically, during metamorphosis, and not in the latter stages of embryogenesis, as it does in E. coqui. Overall, the serotonergic development in E. coqui is similar to the other vertebrates. |
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Keywords: | 5-Hydroxytryptamine Development Immunocytochemistry Amphibian Direct development |
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