Central peptidergic ensembles associated with organization of an innate behavior

Abstract

At the end of each developmental stage, insects perform the ecdysis sequence, an innate behavior necessary for shedding the old cuticle. Ecdysis triggering hormones (ETHs) initiate these behaviors through direct actions on the CNS. Here, we identify the ETH receptor (ETHR) gene in the moth Manduca sexta, which encodes two subtypes of GPCR (ETHR-A and ETHR-B). Expression of ETHRs in the CNS coincides precisely with acquisition of CNS sensitivity to ETHs and behavioral competence. ETHR-A occurs in diverse networks of neurons, producing both excitatory and inhibitory neuropeptides, which appear to be downstream signals for behavior regulation. These peptides include allatostatins, crustacean cardioactive peptide (CCAP), calcitonin-like diuretic hormone, CRF-like diuretic hormones (DHs) 41 and 30, eclosion hormone, kinins, myoinhibitory peptides (MIPs), neuropeptide F, and short neuropeptide F. In particular, cells L 3,4 in abdominal ganglia coexpress kinins, DH41, and DH30, which together elicit the fictive preecdysis rhythm. Neurons IN704 in abdominal ganglia coexpress CCAP and MIPs, whose joint actions initiate the ecdysis motor program. ETHR-A also is expressed in brain ventromedial cells, whose release of EH increases excitability in CCAP͞MIP neurons. These findings provide insights into how innate, centrally patterned behaviors can be orchestrated via recruitment of peptide cotransmitter neurons.ecdysis sequence ͉ ecdysis triggering hormone ͉ G protein-coupled receptors ͉ neuropeptide ͉ steroid I nnate behaviors are highly stereotypic and fully functional in the absence of prior experience. Examples include nurturing, nest building, courtship, and escape behaviors as well as certain developmental behaviors such as the ecdysis sequence, necessary for the shedding of old cuticle at the end of each developmental stage in insects. Because the ecdysis sequence is hormonally controlled, it provides unique opportunities to define mechanisms by which chemical messengers assemble and regulate the performance of behaviors (for review, see ref. 1).The ecdysis sequence is initiated through direct actions of bloodborne pre-ecdysis triggering hormone (PETH) and ecdysis triggering hormone (ETH) on the CNS (2, 3). These peptides are released from endocrine Inka cells, which are present throughout the Insecta (4-6). In larval Manduca sexta, the sequence consists of three behavioral phases (3). In the first phase, PETH activates preecdysis I behavior; subsequently, ETH activates preecdysis II and ecdysis behaviors. These behaviors can be elicited by ETH from the isolated CNS in vitro and, hence, are centrally patterned (3, 7).The ecdysis behavioral sequence is repeatedly acquired and lost throughout the life history of insects (3,8). The signaling pathways triggered by PETH and ETH are assembled at the end of each developmental stage through steroid-induced gene expression, which is critical for synthesis of PETH and ETH in Inka cells and sensitivity of the CNS to these peptides. Once ecdysis is performed, CNS sensitivity to ET...

MIPs are ancestral ligands for the sex peptide receptor

“…We used MIP-antibody to detect mature MIP peptides in Aedes as well as in Drosophila. The MIP-antibody we used reportedly visualizes MIPs across diverse insect species, including D. melanogaster, Manduca sexta, B. mori, and Rhipicephalus appendiculatus (13,(25)(26)(27), and staining in these species coincides with the expression of MIP mRNA (13,25,26). We confirmed the strong MIP immunoreactivity in the CNS of both Drosophila and Aedes but could not detect any staining in the male reproductive organs of either species (Fig.…”

“…3). These mutant SP and MIP1 peptides (SP [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] W23A,W32A , MIP1 W2A,W9A ) were completely inactive even in 10 μM concentration (Table 1), suggesting that these residues, and by inference the turn conformations, are critical for SPR activation. Furthermore, an MIP mutant (DmMIP1 3-8A ) carrying Ala-replacements in all residues except the conserved Trp residues retained a strong SPR agonist activity (Table 1).…”

The pheromone biosynthesis activating neuropeptide (PBAN) receptor of Heliothis virescens: Identification, functional expression, and structure–activity relationships of ligand analogs

“…WTA11-CHO cells were transiently transfected with ORFs of HevPBANR-A, -B, or -C [22], whereas CHO-K1 cells were transfected with two plasmid containing ORFs of HevPBANR-C and codon-optimized aequorin as described [12,31]. Procedures used for CHO cell transfection and receptor assay were described previously [12,13,22].…”

Molecular physiology of crustacean and insect neuropeptides

“…59,60,[67][68][69][70] To truly understand the ecdysis behavior we have to examine the raison d'être of the molting process. Insects and crustaceans have a rigid exoskeleton and therefore to accommodate growth they have to periodically shed the exoskeleton and replace it with a new one.…”

“…The new cuticle is elaborated, sclerotized and hardened with the help of another neurohormone, bursicon (a 173 amino acid protein belonging to the cystine knot family of growth factors), which is coexpressed with CCAP in the bilateral ventral neurons in the central nervous system of Drosophila. 59,[67][68][69][70]73) The ecdysis cascade begins with the ventro-median cells (VM cells) secreting the eclosion hormone (EH) in the presence of 20E, which is stored in the proctodeal nerves (proct. nerve) which serves as the neurohemal organ and is released in the absence of 20E (Fig.…”