Characterization of a putative SchistoFLRFamide receptor in the CNS of Locusta migratoria

More than two decades of research on insect neuropeptide GPCRs: an overview

This review focuses on the state of the art on neuropeptide receptors in insects. Most of these receptors are G protein-coupled receptors (GPCRs) and are involved in the regulation of virtually all physiological processes during an insect's life. More than 20 years ago a milestone in invertebrate endocrinology was achieved with the characterization of the first insect neuropeptide receptor, i.e., the Drosophila tachykinin-like receptor. However, it took until the release of the Drosophila genome in 2000 that research on neuropeptide receptors boosted. In the last decade a plethora of genomic information of other insect species also became available, leading to a better insight in the functions and evolution of the neuropeptide signaling systems and their intracellular pathways. It became clear that some of these systems are conserved among all insect species, indicating that they fulfill crucial roles in their physiological processes. Meanwhile, other signaling systems seem to be lost in several insect orders or species, suggesting that their actions were superfluous in those insects, or that other neuropeptides have taken over their functions. It is striking that the deorphanization of neuropeptide GPCRs gets much attention, but the subsequent unraveling of the intracellular pathways they elicit, or their physiological functions are often hardly examined. Especially in insects besides Drosophila this information is scarce if not absent. And although great progress made in characterizing neuropeptide signaling systems, even in Drosophila several predicted neuropeptide receptors remain orphan, awaiting for their endogenous ligand to be determined. The present review gives a précis of the insect neuropeptide receptor research of the last two decades. But it has to be emphasized that the work done so far is only the tip of the iceberg and our comprehensive understanding of these important signaling systems will still increase substantially in the coming years.

Rhythmic behaviour and pattern-generating circuits in the locust: key concepts and recent updates

There is growing recognition that rhythmic activity patterns are widespread in our brain and play an important role in all aspects of the functioning of our nervous system, from sensory integration to central processing and motor control. The study of the unique properties that enable central circuits to generate their rhythmic output in the absence of any patterned, sensory or descending, inputs, has been very rewarding in the relatively simple invertebrate preparations. The locust, specifically, is a remarkable example of an organism in which central pattern generator (CPG) networks have been suggested and studied in practically all aspects of their behaviour. Here we present an updated overview of the various rhythmic behaviours in the locust and aspects of their neural control. We focus on the fundamental concepts of multifunctional neuronal circuits, neural centre interactions and neuromodulation of CPG networks. We are certain that the very broad and solid knowledge base of locust rhythmic behaviour and pattern-generating circuits will continue to expand and further contribute to our understanding of the principles behind the functioning of the nervous system and, indeed, the brain.

Central effects of the peptides, SchistoFLRFamide and proctolin, on locust oviduct contraction

We have developed a semi-intact preparation-consisting of an isolated oviduct with abdominal ganglia VII and VIII intact and attached-with which to characterize the effects on oviduct contraction, of peptides that are bath applied to CNS tissues. The work presented here offers a qualitative analysis of the central effects of SchistoFLRFamide and proctolin upon action potentials recorded from the oviducal nerves and upon oviduct contraction. In the process of this, we hope to demonstrate that a previously characterized putative CNS SchistoFLRFamide receptor [Peptides 23 (2002) 765] is a functional receptor.SchistoFLRFamide (10(-6)M), bath applied to abdominal ganglion VII, caused an increase in action potential frequencies recorded from the oviducal nerves, as well as an increase in the frequency of phasic contractions of the oviduct. Although the function of this response is not known, these results further support the possibility that the putative CNS SchistoFLRFamide receptors are functional receptors. Proctolin (10(-6)M), bath applied to abdominal ganglion VIII, altered the rhythmic bursting of action potentials recorded from the oviducal nerve and changed the appearance and cycle duration of neurogenic oviduct contractions.