Neuropeptides in interneurons of the insect brain

Abstract

A large number of neuropeptides has been identified in the brain of insects. At least 35 neuropeptide precursor genes have been characterized in Drosophila melanogaster, some of which encode multiple peptides. Additional neuropeptides have been found in other insect species. With a few notable exceptions, most of the neuropeptides have been demonstrated in brain interneurons of various types. The products of each neuropeptide precursor seem to be co-expressed, and each precursor displays a unique neuronal distribution pattern. Commonly, each type of neuropeptide is localized to a relatively small number of neurons. We describe the distribution of neuropeptides in brain interneurons of a few well-studied insect species. Emphasis has been placed upon interneurons innervating specific brain areas, such as the optic lobes, accessory medulla, antennal lobes, central body, and mushroom bodies. The functional roles of some neuropeptides and their receptors have been investigated in D. melanogaster by molecular genetics techniques. In addition, behavioral and electrophysiological assays have addressed neuropeptide functions in the cockroach Leucophaea maderae. Thus, the involvement of brain neuropeptides in circadian clock function, olfactory processing, various aspects of feeding behavior, and learning and memory are highlighted in this review. Studies so far indicate that neuropeptides can play a multitude of functional roles in the brain and that even single neuropeptides are likely to be multifunctional.

Mas‐allatotropin in the developing antennal lobe of the sphinx moth Manduca sexta: Distribution, time course, developmental regulation, and colocalization with other neuropeptides

“…In general, corelease is thought to enhance the repertoire of synaptic interactions within a neuronal network (for a review see Nusbaum et al, 2001). In the AL, neuropeptides might operate as cotransmitters of GABA (c-aminobutyric acid), the principle transmitter of LNs , but the function of cotransmission has so far not been studied in the AL or in general within the insect brain (Nässel and Homberg, 2006).…”

“…In insects, a few studies on the role of neuropeptides revealed important functions in the brain, e.g. regulation of the insect molt (Truman, 1996b;Mesce and Fahrbach, 2002;Ewer, 2005), regulation of circadian control, and regulation of various aspects of feeding behavior (for a recent review see Nässel and Homberg, 2006).…”

“…Since then, allatotropins (-TARGFamides) have been shown to be a highly conserved insect neuropeptide family (for reviews see Elekonich and Horodyski, 2003;Homberg et al, 2004;Nässel and Homberg, 2006). In M. sexta, the fall armyworm Spodoptera frugiperda, and the Eri silkworm Samia cynthia ricini, the allatotropin gene is expressed as at least three mRNAs that differ by alternative splicing.…”

Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha

“…This neuropeptide family is widely distributed among invertebrates and vertebrates and an increasing amount of literature on the structural diversity and neurohormonal action of invertebrate FaRPs and other peptides, e.g. in Coelenterata (review Grimmelikhuijzen et al 1992), Plathelminthes (review Fairweather and Halton 1991;Choi et al 1996), Mollusca (review Muneoka and Kobayashi 1992), and Arthropoda (Keller 1992;Gaus et al 1993;Groome 1993;Nässel 1993;Homberg 1994;Nässel and Homberg 2006) highlights a growing appreciation of the importance of these substances. So far, the evidence for the presence of FaRPs in Chaetognatha stems from immunocytochemical experiments only (Bone et al 1987;Goto et al 1992;Harzsch and Müller 2007) but the sequences of the FaRPs present in this clade are still unknown.…”

Global and local modulatory supply to the mushroom bodies of the moth Spodoptera littoralis

“…A-type allatostatins are a family of neuroactive peptides found in many insects (Nässel and Homberg, 2006). Their suggested functions include roles in the control of gut peristalsis, heart rate, circadian rhythms, and production of juvenile hormone (Hernández-Martínez et al, 2005;Duve et al, 1999Duve et al, , 2000.…”