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Serotonin immunoreactivity in the nervous system of the free‐swimming larvae and sessile adult females of Stephanoceros fimbriatus (Rotifera: Gnesiotrocha)
Author(s) -
Hochberg Adele,
Hochberg Rick
Publication year - 2015
Publication title -
invertebrate biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.486
H-Index - 42
eISSN - 1744-7410
pISSN - 1077-8306
DOI - 10.1111/ivb.12102
Subject(s) - metamorphosis , biology , anatomy , nervous system , serotonergic , larva , neurite , infundibulum , serotonin , neuroscience , ecology , receptor , in vitro , biochemistry
Unlike most rotifers (Rotifera), which are planktonic and direct developers, many gnesiotrochan rotifers (Monogononta: Gnesiotrocha) are sessile and have indirect development. Few details exist on larval metamorphosis in most gnesiotrochans, and considering the drastic transformation that takes place at metamorphosis—the replacement of the ciliated corona with a new head that bears ciliated tentacles (the infundibulum)—it is perhaps surprising that there are limited data on the process. Here, we document part of this metamorphosis by examining the presence and distribution of neurons with serotonin immunoreactivity in the nervous system of both planktonic larvae and sessile adult females. Using antibodies against serotonin combined with confocal laser‐scanning microscopy ( CLSM ) and 3D reconstruction software, we mapped the immunoreactive cell bodies and neurites in both life stages and found that relatively few changes occurred during metamorphosis. The larvae possessed a total of eight perikarya with serotonergic immunoreactivity (5 HT ‐ IR ) in the brain, with at least two pairs of perikarya outside the brain in the region of the corona. Cells with 5 HT ‐ IR in the brain innervated the larval corona and also sent neurites to the trunk via the nerve cords. During metamorphosis, the corona was replaced by the infundibulum, which emerged from the larval mouth to become the new functional head. This change led to a posterior displacement of the brain and also involved the loss of 5 HT ‐ IR in the lateral brain perikarya and the gain of two perikarya with 5 HT ‐ IR in the anterior brain region. The innervation of the anterior end was retained in the adult; neurites that extended anteriorly to the mouth of the larva formed a distinct neural ring that encircled the infundibulum after metamorphosis. Significantly, there was no innervation of the infundibular tentacles by neurites with 5 HT ‐ IR , which suggests that ciliary control is unlikely to be modulated by serotonin within the tentacles themselves.