Introduction

A vasopressin-like peptide was isolated from the locust Locusta migratoria (Proux et al., 1987). Related peptides have been identified in some other insects species (e. g. Tribolium castaneum and Nasonia vitripennis), but not in Drosophila or other dipteran insects, nor in Bombyx mori or Apis mellifera (Stafflinger et al 2008). The invertebrate forms of vasopressin-like peptides have a well conserved sequence and have been designated inotocins (Stafflinger et al 2008) and are cyclic peptides, due to an internal cystein bridge (Li et al., 2008). The sequence of Tribolium inotocin is CLITNCPRGamide (Li et al., 2008). Inotocin receptors were identified from Tribolium and Nasonia and display strong similarities to inotocin GPCRs from the water flee Daphnia pulex and the snail Lymnaea stagnalis, as well as mouse receptors to oxytocin and vasopressin (Aikins et al., 2008; Stafflinger et al 2008).

Location

Inotocin is expressed in only two neurons in the subesophageal ganglion of locusts and Triboleum with branches arborizing extensively in the brain and ventral nerve cord and vasopressin-like immunoreactivity is also seen in a similar pair of neurons in cockroaches and mantids (Aikins et al., 2008; Davis and Hilderbrand, 1992; Tyrer et al., 1993). The inotocin receptor of Tribolium is expressed mainly within the CNS, and not in renal tubules (Aikins et al., 2008; Stafflinger et al 2008).

Function

In Triboleum inotocin indirectly triggers diuresis (Aikins et al., 2008). Since the receptor appears expressed mainly within the CNS and no branches of the inotocin neurons reside outside the CNS, it was hypothesized that inotocin regulates neurosecretory cells that produce a diuretic hormone.

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Suggested Reviews

References

• Aikins MJ, Schooley DA, Begum K, Detheux M, Beeman RW, Park Y. 2008. Vasopressin-like peptide and its receptor function in an indirect diuretic signalling pathway in the red flour beetle. Insect biochemistry and molecular biology 38(7):740-748.
• Davis NT, Hildebrand JG. 1992. Vasopressin-immunoreactive neurons and neurohemal systems in cockroaches and mantids. The Journal of comparative neurology 320(3):381-393.
• Li B, Predel R, Neupert S, Hauser F, Tanaka Y, Cazzamali G, Williamson M, Arakane Y, Verleyen P, Schoofs L, Schachtner J, Grimmelikhuijzen CJ, Park Y. 2008. Genomics, transcriptomics, and peptidomics of neuropeptides and protein hormones in the red flour beetle Tribolium castaneum. Genome research 18(1):113-122.
• Tyrer NM, Davis NT, Arbas EA, Thompson KS, Bacon JP. 1993. Morphology of the vasopressin-like immunoreactive (VPLI) neurons in many species of grasshopper. The Journal of comparative neurology 329(3):385-401.