1
|
Sombke A, Stemme T. Serotonergic neurons in the ventral nerve cord of Chilopoda - a mandibulate pattern of individually identifiable neurons. ZOOLOGICAL LETTERS 2017; 3:9. [PMID: 28690866 PMCID: PMC5496589 DOI: 10.1186/s40851-017-0070-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 06/21/2017] [Indexed: 05/28/2023]
Abstract
BACKGROUND Given the numerous hypotheses concerning arthropod phylogeny, independent data are needed to supplement knowledge based on traditional external morphology and modern molecular sequence information. One promising approach involves comparisons of the structure and development of the nervous system. Along these lines, the morphology of serotonin-immunoreactive neurons in the ventral nerve cord has been investigated in numerous tetraconate taxa (Crustacea and Hexapoda). It has been shown that these neurons can be identified individually due to their comparably low number, characteristic soma position, and neurite morphology, thus making it possible to establish homologies at the single cell level. Within Chilopoda (centipedes), detailed analyses of major branching patterns of serotonin-immunoreactive neurons are missing, but are crucial for developing meaningful conclusions on the homology of single cells. RESULTS In the present study, we re-investigated the distribution and projection patterns of serotonin-immunoreactive neurons in the ventral nerve cord of three centipede species: Scutigera coleoptrata, Lithobius forficatus, and Scolopendra oraniensis. The centipede serotonergic system in the ventral nerve cord contains defined groups of individually identifiable neurons. An anterior and two posterior immunoreactive neurons per hemiganglion with contralateral projections, a pair of ipsilateral projecting lateral neurons (an autapomorphic character for Chilopoda), as well as a postero-lateral group of an unclear number of cells are present in the ground pattern of Chilopoda. CONCLUSIONS Comparisons to the patterns of serotonin-immunoreactive neurons of tetraconate taxa support the homology of anterior and posterior neurons. Our results thus support a sister group relationship of Myriapoda and Tetraconata and, further, a mandibulate ground pattern of individually identifiable serotonin-immunoreactive neurons in the ventral nerve cord. Medial neurons are not considered to be part of the tetraconate ground pattern, but could favor the 'Miracrustacea hypothesis', uniting Remipedia, Cephalocarida, and Hexapoda.
Collapse
Affiliation(s)
- Andy Sombke
- University of Greifswald, Zoological Institute and Museum, Cytology and Evolutionary Biology, Soldmannstrasse 23, 17487 Greifswald, Germany
| | - Torben Stemme
- Division of Cell Biology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173 Hannover, Germany
- Current address: University of Ulm, Institute for Neurobiology, Helmholtzstraße 10/1, 89081 Ulm, Germany
| |
Collapse
|
2
|
Stemme T, Stern M, Bicker G. Serotonin-containing neurons in basal insects: In search of ground patterns among tetraconata. J Comp Neurol 2017; 525:79-115. [PMID: 27203729 DOI: 10.1002/cne.24043] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Revised: 05/17/2016] [Accepted: 05/18/2016] [Indexed: 11/08/2022]
Abstract
The ventral nerve cord of Tetraconata contains a comparably low number of serotonin-immunoreactive neurons, facilitating individual identification of cells and their characteristic neurite morphology. This offers the rather unique possibility of establishing homologies at the single cell level. Because phylogenetic relationships within Tetraconata are still discussed controversially, comparisons of individually identifiable neurons can help to unravel these issues. Serotonin immunoreactivity has been investigated in numerous tetraconate taxa, leading to reconstructions of hypothetical ground patterns for major lineages. However, detailed descriptions of basal insects are still missing, but are crucial for meaningful evolutionary considerations. We investigated the morphology of individually identifiable serotonin-immunoreactive neurons in the ventral nerve cord of Zygentoma (Thermobia domestica, Lepisma saccharina, Atelura formicaria) and Archaeognatha (Machilis germanica, Dilta hibernica). To improve immunocytochemical resolution, we also performed preincubation experiments with 5-hydroxy-L-tryptophan and serotonin. Additionally, we checked for immunolabeling of tryptophan hydroxylase, an enzyme associated with the synthesis of serotonin. Besides the generally identified groups of anterolateral, medial, and posterolateral neurons within each ganglion of the ventral nerve cord, we identified several other immunoreactive cells, which seem to have no correspondence in other tetraconates. Furthermore, we show that not all immunoreactive neurons produce serotonin, but have the capability for serotonin uptake. Comparisons with the patterns of serotonin-containing neurons in major tetraconate taxa suggest a close phylogenetic relationship of Remipedia, Cephalocarida, and Hexapoda, supporting the Miracrustacea hypothesis. J. Comp. Neurol., 2016. © 2016 Wiley Periodicals, Inc. J. Comp. Neurol. 525:79-115, 2017. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Torben Stemme
- University of Veterinary Medicine Hannover, Division of Cell Biology, D-30173, Hannover, Germany
| | - Michael Stern
- University of Veterinary Medicine Hannover, Division of Cell Biology, D-30173, Hannover, Germany
| | - Gerd Bicker
- University of Veterinary Medicine Hannover, Division of Cell Biology, D-30173, Hannover, Germany
| |
Collapse
|
3
|
Stegner ME, Brenneis G, Richter S. The ventral nerve cord in Cephalocarida (Crustacea): New insights into the ground pattern of Tetraconata. J Morphol 2013; 275:269-94. [DOI: 10.1002/jmor.20213] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Revised: 08/28/2013] [Accepted: 09/06/2013] [Indexed: 11/08/2022]
Affiliation(s)
- Martin E.J. Stegner
- Universität Rostock, Institut für Biowissenschaften, Allgemeine und Spezielle Zoologie, Universitätsplatz 2; 18055 Rostock Mecklenburg-Vorpommern Germany
| | - Georg Brenneis
- Universität Rostock, Institut für Biowissenschaften, Allgemeine und Spezielle Zoologie, Universitätsplatz 2; 18055 Rostock Mecklenburg-Vorpommern Germany
| | - Stefan Richter
- Universität Rostock, Institut für Biowissenschaften, Allgemeine und Spezielle Zoologie, Universitätsplatz 2; 18055 Rostock Mecklenburg-Vorpommern Germany
| |
Collapse
|
4
|
Serotonin-immunoreactive neurons in scorpion pectine neuropils: similarities to insect and crustacean primary olfactory centres? ZOOLOGY 2012; 115:151-9. [PMID: 22445574 DOI: 10.1016/j.zool.2011.10.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2011] [Revised: 10/17/2011] [Accepted: 10/20/2011] [Indexed: 11/23/2022]
Abstract
The pectines of scorpions are a single pair of mechano- and chemosensory appendages located ventrally behind the most posterior pair of walking legs. They are used for probing the substrate in behaviours such as prey tracking and courtship. The sensory afferents on the pectines supply large segmental neuropils with a conspicuous glomerular structure. The pectine neuropils thus bear similarities to insect and crustacean deutocerebral chemosensory centres associated with the antennae, but they also possess idiosyncratic features. One characteristic property of many insect and decapod crustacean olfactory neuropils is their innervation by single, or very few, large serotonergic (inter-) neurons. This feature, among others, has been proposed to support homology of the olfactory lobes in the two arthropod groups. A possible serotonergic innervation of the scorpion pectine neuropils has not yet been studied, despite its apparent diagnostic and functional importance. We thus examined serotonin-immunoreactivity in the pectine neuropils of Androctonus australis and Pandinus imperator. Both scorpion species yielded similar results. The periphery of the neuropil and the matrix between the glomeruli are supplied by a dense network of serotonin-immunoreactive (5-HT-ir) arborisations and varicosities, while the glomeruli themselves are mostly free of 5-HT-ir fibres. The 5-HT-ir supply of the pectine neuropils has two origins. The first is a pair of neurons on each body side, up to 30 μm in diameter and thus slightly larger than the surrounding somata. These cell bodies are and associated with the neuromeres of the genital and pectine segments. The situation is reminiscent of the 5-HT supply of insect and crustacean olfactory and antennal neuropils. The second 5-HT innervation of the pectine neuropils is from a group of some 10-20 ipsilateral neuronal somata of slightly smaller size (15-20 μm). These are part of a much larger 5-HT-ir group comprising 70-90 somata. The whole group is located more anteriorly than the single soma mentioned above, and associated with the neuromere of the last (4th) walking leg. When compared to data from other arthropods, our findings may suggest that glomerular organisation is an ancestral feature of primary chemosensory centres innervated by arthropod appendages. This idea needs further scrutiny, although supporting evidence may have been overlooked previously, due to the small size of chemosensory neuropils in walking legs and in reduced segmental appendages.
Collapse
|
5
|
Fritsch M, Richter S. The formation of the nervous system during larval development in Triops cancriformis (Bosc) (crustacea, Branchiopoda): An immunohistochemical survey. J Morphol 2010; 271:1457-81. [DOI: 10.1002/jmor.10892] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
6
|
Koza A, Wilhelm M, Hiripi L, Elekes K, Csoknya M. Embryogenesis of the serotonergic system in the earthwormEisenia fetida (Annelida, Oligochaeta): Immunohistochemical and biochemical studies. J Comp Neurol 2006; 497:451-67. [PMID: 16736470 DOI: 10.1002/cne.21008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Organization of the serotonergic system and changes of the serotonin (5-HT) content were studied during the embryogenesis of the earthworm Eisenia fetida, using immunocytochemistry and HPLC. A gradual emergence of 5-HT immunoreactive (IR) cells and their axon projections in the several ganglia of the central (CNS) and peripheral nervous system are described in the context of a staged time-scale of development. The first 5-HT-IR neurons appear in the subesophageal ganglion at an early embryonic stage (E2), followed by neurons in some rostrally located ventral ganglia. In the cerebral ganglion, 5-HT-IR cells can be detected only from stage E5. The number of labeled cells in each ganglion of the embryo increases until hatching, when it is still considerably lower than that observed in adults. This shows that the development of the 5-HTergic system is far from complete by the end of embryogenesis. Organization of 5-HT-IR innervation of the body wall starts by stages E3 to E4. In the stomatogastric nervous system the first 5-HT-IR fibers can be detected by stage E5. By stage E9 5-HT immunopositive neurons can be observed in both the stomatogastric ganglia and the enteric plexus. Both 5-HT levels and the numbers of the labeled cells show a significant increase before hatching, which indicate a functional maturation of the 5-HTergic system. Based on the early appearance of 5-HT, we suppose that it may play a regulatory role in both the gangliogenesis and the maturation of peripheral functions necessary during postembryonic life.
Collapse
Affiliation(s)
- Anna Koza
- MTA-PTE Adaptation Biology Research Group, University of Pécs, Pécs, Hungary
| | | | | | | | | |
Collapse
|
7
|
Morita A, Niimi T, Yamashita O. Physiological differentiation of DH-PBAN-producing neurosecretory cells in the silkworm embryo. JOURNAL OF INSECT PHYSIOLOGY 2003; 49:1093-1102. [PMID: 14624881 DOI: 10.1016/j.jinsphys.2003.08.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Embryonic diapause of the silkworm, Bombyx mori, is induced by a neuropeptide hormone, the diapause hormone (DH), which is secreted from a limited number of neurosecretory cells in the subesophageal ganglion (SG) at the maternal generation. We examined the developmental fate of the hormone-producing cell (DH-pheromone biosynthesis activating neuropeptide [PBAN]-producing cell) in the embryonic stage at the level of gene expression and cell biology. The DH-PBAN gene expression started at the histogenesis stage and gradually increased toward hatching. DH is an amidated peptide belonging to FXPRLamide family. The immunoreactive somata against anti FXPRLamide antiserum were found in the SG from blastokinesis. Immunoreactive neural processes with varicosites were also found on the corpus cardiacum and the corpus allatum. The implantation of a part of a developing embryo including the SG into the pupae with the SG removed induced diapause eggs in the progeny. These results were obtained from eggs incubated under diapause-averting conditions as well as diapause-inducing conditions. Thus, a neurosecretory system responsible for biosynthesis of FXPRLamide neuropeptides is established as early as histogenesis, although the system to regulate the secretion of neuropeptide hormones has not been fully formed by that time.
Collapse
Affiliation(s)
- Akihiro Morita
- Laboratory of Entomoresources, Graduate School of Bioagricultural Sciences, Nagoya University, 464-8601, Chikusa Nagoya, Japan.
| | | | | |
Collapse
|
8
|
Harzsch S. Evolution of identified arthropod neurons: the serotonergic system in relation to engrailed-expressing cells in the embryonic ventral nerve cord of the american lobster homarus americanus milne edwards, 1873 (malacostraca, pleocyemata, homarida). Dev Biol 2003; 258:44-56. [PMID: 12781681 DOI: 10.1016/s0012-1606(03)00113-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
One of the long-standing questions in zoology is that on the phylogenetic relationships within the Arthropoda. Comparative studies on structure and development of the nervous system can contribute important arguments to this discussion. In the present report, the arrangement of serotonin- and engrailed-expressing cells was examined in the embryonic ventral nerve cord of the American lobster Homarus americanus Milne Edwards, 1873 (Malacostraca, Pleocyemata, Homarida), and the spatial relationship of these two cell classes was explored by a double-labelling approach. The goal of this study was to determine whether the lobster serotonergic neurons are homologous to similar cells present in representatives of the Hexapoda and other Arthropoda. The results indicate that, in fact, these neurons in the lobster ventral nerve cord have corresponding counterparts in many other mandibulate taxa. Based on the finding of these homologies, the arrangement of serotonergic neurons in a model trunk ganglion of the mandibulate ground pattern was reconstructed as comprising an anterior and a posterior pair of serotonergic neurons per hemiganglion, each cell with both an ipsilateral and a contralateral neurite. Starting from this ground pattern, the evolutionary diversification of this class of neurons within the Mandibulata is discussed.
Collapse
Affiliation(s)
- Steffen Harzsch
- Universität Ulm, Sektion Biosystematische Dokumentation and Abteilung Neurobiologie, Helmholtzstrasse 20, 89081 Ulm, Germany.
| |
Collapse
|
9
|
Abstract
Analysis of the serotonin immunoreactive neurons in the central brain of the beetle Tenebrio molitor during postembryonic development shows that the basic structural characteristics of larval brain resemble those of the adult. Most, if not all, serotonin immunoreactive central brain neurons persist with metamorphosis. Their fate can be followed during development. GABA immunoreactivity occurs in about 360 neurons assembled in ten different clusters of somata in the larval midbrain. During metamorphosis no additional clusters are formed. However, the number of immunoreactive neurons increases to 450. Their morphological analysis is restricted to location of the somata and the distribution of arborizations within neuropil areas. Metamorphic transition of glomerular sub-units in the antennal lobes as well as ellipsoid body development can be followed by GABA immunohistochemistry. Furthermore, the study of these transitions proved useful in displaying changes during metamorphic pattern formation induced by sublethal application of the pyrethroid insecticide fenvalerate.
Collapse
Affiliation(s)
- R Wegerhoff
- Institute of Biochemistry, University of Kiel, Germany.
| |
Collapse
|
10
|
Schachtner J, Klaassen L, Truman JW. Metamorphic control of cyclic guanosine monophosphate expression in the nervous system of the tobacco hornworm, Manduca sexta. J Comp Neurol 1998; 396:238-52. [PMID: 9634145 DOI: 10.1002/(sici)1096-9861(19980629)396:2<238::aid-cne8>3.0.co;2-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
During metamorphosis of Manduca sexta, defined sets of neurons show a dramatic accumulation of cyclic guanosine monophosphate (cGMP). Although many of these cells show low but detectable levels of cGMP during specific developmental windows, these levels are enhanced dramatically during dissection of the central nervous system (CNS). The ability of these neurons to show this induced cGMP expression depends on the developmental stage. Larvae do not show this capacity but it appears during the transition from the larval to the pupal stage. There are two different classes of response: the early expressing neurons start to show a cGMP response at the beginning of the prepupal stage while the late expressing cGMP neurons start at different times during the pupal-adult transition. The former set includes larval neurons that will likely be remodeled during metamorphosis, and a number of them are serotonergic. The late-expressing group also includes some larval cells, but most are adult-specific neurons. At least for one adult-specific cluster, the antennal lobe neurons, the cGMP expression parallels the maturation phase of these cells.
Collapse
Affiliation(s)
- J Schachtner
- Department of Biology, Neurobiology, Philipps-Universität Marburg, Germany
| | | | | |
Collapse
|
11
|
Mesce KA, Klukas KA, Brelje TC. Improvements for the anatomical characterization of insect neurons in whole mount: the use of cyanine-derived fluorophores and laser scanning confocal microscopy. Cell Tissue Res 1993; 271:381-97. [PMID: 8472298 DOI: 10.1007/bf02913721] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The optical sectioning capability of the laser scanning confocal microscope was utilized to image dye-filled neurons within whole-mounted insect ganglia. Specific pterothoracic interneurons, in the moth Manduca sexta, were retrogradely filled with Neurobiotin and subsequently visualized with a monoclonal anti-biotin conjugated with one of the following fluorophores: fluorescein, and the newly developed cyanines, Cy3.18 (Cy3) and Cy5.18 (Cy5). Overall, the Cy5 fluorophore was best suited for imaging insect neurons within ganglia. This new methodology allowed us to identify and characterize morphologically a collection of descending multisegmental interneurons with large or small diameter somata. A variety of larger molecular weight (10,000 daltons) tracers was also used to examine the possibility of nonselective filling of neurons with Neurobiotin, possibly through gap junctions. We also investigated the usefulness of Cy3 and Cy5 as fluorophores for transmitter immunostaining of neurons in whole mount. Neurons immunoreactive for serotonin and the neuropeptides, FMRFamide and SCPB, were imaged in the brain and the pterothoracic ganglion. The central projections of some of these immunoreactive neurons were imaged in their entirety.
Collapse
Affiliation(s)
- K A Mesce
- Department of Entomology, University of Minnesota, St. Paul 55108
| | | | | |
Collapse
|
12
|
Sivasubramanian P. Serotonin-immunoreactive neurons in the ventral nerve cord of the larva of the Eastern spruce budworm, Choristoneura fumiferana. ACTA ACUST UNITED AC 1992; 101:513-8. [PMID: 1354127 DOI: 10.1016/0742-8413(92)90079-m] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
1. Using indirect immunofluorescent method, the distribution of serotonin immunoreactivity was examined in the ventral nerve cord of the larva of the Eastern spruce budworm, Choristoneura fumiferana. 2. There were two pairs of serially homologous serotonin immunoreactive neurons per ganglion. 3. The subesophageal ganglion which develops from the fusion of three neuromeres had accordingly, six pairs of immunoreactive neurons. 4. The neurons were positioned ventrolaterally at the posterior end of the ganglia and distributed in a bilaterally symmetrical fashion. 5. The axonal processes from serotonin-immunoreactive neurons projected to the contralateral side of the hemiganglion through a ventral commissure and formed an extensive network of fibers on the dorsal side of each ganglion.
Collapse
Affiliation(s)
- P Sivasubramanian
- Department of Biology, University of New Brunswick, Fredericton, Canada
| |
Collapse
|
13
|
5-Hydroxytryptamine metabolism in the damselfly, Ischnura graellsii, in relation to sex and larval-adult period. Neurochem Int 1991; 18:199-205. [DOI: 10.1016/0197-0186(91)90186-h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/1990] [Accepted: 05/09/1990] [Indexed: 11/18/2022]
|
14
|
Homberg U, Hildebrand JG. Serotonin immunoreactivity in the optic lobes of the sphinx moth Manduca sexta and colocalization with FMRFamide and SCPB immunoreactivity. J Comp Neurol 1989; 288:243-53. [PMID: 2677065 DOI: 10.1002/cne.902880204] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In the optic lobes (OLs) of the sphinx moth Manduca sexta, 300-350 neurons per hemisphere are immunoreactive with an antiserotonin antiserum. Two groups of weakly serotonin-immunoreactive cells (OL1) appear to be amacrine cells of the medulla, whereas more intensely immunoreactive cells (OL2) are probably centrifugal neurons that innervate the lobula, medulla, and lamina, as well as the superior protocerebrum. At least one other OL2 cell is a local optic-lobe interneuron with arborizations in the dorsal medulla and lobula. The serotonin-immunoreactive cells are also immunoreactive with an antiserum against Drosophila melanogaster DOPA decarboxylase. All OL2 cells, but not the OL1 cells, are furthermore immunoreactive with an anti-FMRFamide antiserum and an anti-SCPB antiserum. This suggests that neuropeptides related or identical to FMRFamide and SCPB are localized and may serve as cotransmitters with serotonin in OL2 optic-lobe interneurons.
Collapse
Affiliation(s)
- U Homberg
- Arizona Research Laboratories, University of Arizona, Tucson 85721
| | | |
Collapse
|
15
|
Granger NA, Homberg U, Henderson P, Towle A, Lauder JM. Serotonin-immunoreactive neurons in the brain of Manduca sexta during larval development and larval-pupal metamorphosis. Int J Dev Neurosci 1989; 7:55-72. [PMID: 2711869 DOI: 10.1016/0736-5748(89)90044-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The developing serotonergic system of the tobacco hornworm, Manduca sexta, has been studied immunocytochemically in whole mount preparations of brain-retrocerebral complexes. The distribution of serotonin-immunoreactive cell bodies, fibers and terminal fields has been analysed during larval and larval-pupal development using a specific rabbit antiserum against serotonin-hemocyanin conjugates. The serotonergic system was conserved from the fourth to the fifth larval stadium, with minimal changes occurring until the onset of pupal development. At this time, alterations in the distribution of serotonin-immunoreactive cells and processes were observed, including the apparent disappearance of some cell bodies and terminals. Nevertheless, the overall appearance of this system in the pupal brain was not significantly different from that in the larva. The larval pattern was characterized by eight bilateral groups of cell bodies which sent thick bridges of fibers across the midline, a feature strikingly similar to the serotonergic system in vertebrate embryos. In addition, three bilateral immunoreactive fields of arborization were observed around and ventral to these cell groups, together with regions of serotonin immunoreactivity in the medial and lateral protocerebral lobes. The central body, larval antennal centers, larval accessory lobes, and the tritocerebrum were also immunoreactive. Fibrous networks of serotonergic processes were usually observed around nerves emanating from the brain, including the connectives from the brain to the corpus cardiacum and corpus allatum. Smaller varicosities were observed in the interior of these neurohemal and glandular organs, and a network of 5-HT fibers was occasionally found around the corpus cardiacum and corpus allatum. The possible relationship of serotonin to cerebral neuroendocrine functions during the postembryonic development of M. sexta is discussed.
Collapse
Affiliation(s)
- N A Granger
- Department of Cell Biology and Anatomy, University of North Carolina School of Medicine, Chapel Hill 27514
| | | | | | | | | |
Collapse
|