Developing insects repeatedly shed their cuticle by means of a stereotyped behavior called ecdysis, thought to be initiated by the brain peptide eclosion hormone. Here an ecdysis-triggering hormone, Mas-ETH, is described from the tobacco hornworm Manduca sexta. Mas-ETH contains 26 amino acids and is produced by a segmentally distributed endocrine system of epitracheal glands (EGs). The EGs undergo a marked reduction in volume, appearance, and immunohistochemical staining during ecdysis, at which time Mas-ETH is found in the hemolymph. Injection of EGs extract or synthetic Mas-ETH into pharate larvae, pupae, or adults initiates preecdysis within 2 to 10 minutes, followed by ecdysis. Sensitivity to injected Mas-ETH appears much earlier before ecdysis and occurs with shorter latency than that reported for eclosion hormone. The isolated central nervous system responds to Mas-ETH, but not to eclosion hormone, with patterned motor bursting corresponding to in vivo preecdysis and ecdysis. Mas-ETH may be an immediate blood-borne trigger for ecdysis through a direct action on the nervous system.
"In this study, analysis of the test insect fed with C. microphylla extracts, revealed a developmental disruption in which the insects died (between 10 and 25 ppm) during pharate conditions after initiation of molting (the apolysis step), without completion of morphogenesis . During a molt, ecdysteroid levels first rise to stimulate onset of apolysis and cuticle synthesis, but then must fall to facilitate the release of eclosion hormone (EH) (Truman et al., 1983; 2002) and the ecdysis-triggering hormone (ETH) (Zitnan et al., 1996, 1999). These last substances act in concert to trigger insect ecdysis during the final stages of the molt. "
"peptide modulation of behavior. In the moth Manduca, ETH (and the cosynthesized P-ETH peptide) derives from endocrine cells associated with trachea and elicits coordinated behavior by directly activating diverse neural targets (Zitnan et al., 1996). To discover the cellular basis for this precise modulatory mechanisms, Kim et al. (2006a) identified the receptors specifically tuned to ETH—these GPCRs are most closely related to receptors for mammalian neuromedins and TRH (Hewes and Taghert, 2001; Park et al., 2003). "
[Show abstract][Hide abstract] ABSTRACT: Neuropeptides modulate neural circuits controlling adaptive animal behaviors and physiological processes, such as feeding/metabolism, reproductive behaviors, circadian rhythms, central pattern generation, and sensorimotor integration. Invertebrate model systems have enabled detailed experimental analysis using combined genetic, behavioral, and physiological approaches. Here we review selected examples of neuropeptide modulation in crustaceans, mollusks, insects, and nematodes, with a particular emphasis on the genetic model organisms Drosophila melanogaster and Caenorhabditis elegans, where remarkable progress has been made. On the basis of this survey, we provide several integrating conceptual principles for understanding how neuropeptides modulate circuit function, and also propose that continued progress in this area requires increased emphasis on the development of richer, more sophisticated behavioral paradigms.
"Instead, neurosecretory cells that send axons to a release site are located mainly in the pars intercerebralis, but some are also located in the pars lateralis or tritocerebrum, in the suboesophageal and/or ventral ganglia. Non-neuronal Inka cells that produce the releasing hormone ecdysis-triggering hormone (ETH) are located on the surface of insect tracheae . The gut is also a site of synthesis and release (into the hemolymph) of some brain-gut peptides. "
[Show abstract][Hide abstract] ABSTRACT: Vertebrate releasing hormones include gonadotropin releasing hormone (GnRH), growth hormone releasing hormone (GHRH), corticotropin releasing hormone (CRF), and thyrotropin-releasing hormone (TRH). They are synthesized in the hypothalamus and stimulate the release of pituitary hormones. Here we review the knowledge on hormone releasing systems in the protostomian lineage. We address the question: do insects have peptides that may be phylogenetically related to an ancestral GnRH, GHRH, TRH, and CRF? Such endocrine archeology has become possible thanks to the growing list of fully sequenced genomes as well as to the continuously improving bioinformatic tool set. It has recently been shown that the ecdysozoan (nematodes and arthropods) adipokinetic hormones (AKHs), the lophotrochozoan (annelids and mollusks) GnRHs as well as the protochordate GnRHs are structurally related. The adipokinetic hormone precursor-related peptides (APRPs), in locusts encoded by the same gene that contains the AKH-coding region, have been forwarded as the structural counterpart of GHRH of vertebrates. CRF is relatively well conserved in insects, in which it functions as a diuretic hormone. Members of TRH-receptor family seem to have been conserved in some arthropods, but other elements of the thyroid hormone signaling system are not. A challenging idea is that in insects the functions of the thyroid hormones were taken over by juvenile hormone (JH). Our reconstruction suggests that, perhaps, the ancestral releasing hormone precursors played a role in controlling energy metabolism and water balance, and that releasing hormone functions as present in extant vertebrates were probably secondarily acquired.
General and Comparative Endocrinology 03/2012; 177(1):18-27. DOI:10.1016/j.ygcen.2012.02.002 · 2.47 Impact Factor
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