Myoinhibitory peptides in the central complex of the locust Schistocerca gregaria and colocalization with locustatachykinin‐related peptides

Abstract

The central complex in the brain of insects provides a neural network for sensorimotor processing that is essential for spatial navigation and locomotion and plays a role in sleep control. Studies on the neurochemical architecture of the central complex have been performed especially in the fruit fly Drosophila melangoaster and the desert locust, Schistocerca gregaria. In several insect species, myoinhibitory peptides (MIPs) are involved in circadian control and sleep‐wake regulation. To identify neurons that might underlie these functions, we investigated the distribution of MIPs in the central complex of the locust. In silico transcript analysis suggests the presence of eight different MIPs in the desert locust. Through immunolabeling, we identified five systems of central‐complex neurons that express MIP‐like peptides. Two systems constitute columnar neurons of the protocerebral bridge and the lower division of the central body, while the other three systems are columnar neurons (two systems) and tangential neurons (one system) of the upper division of the central body. The innervation pattern and cell count of two systems of columnar neurons revealed the existence of 18 instead of 16 columns of the protocerebral bridge. Immunostaining of preparations containing intracellularly stained single cells allowed us to further specify subtypes of labeled columnar neurons. Double‐label experiments showed that three systems of MIP‐immunostained columnar neurons are also locustatachykinin‐immunoreactive. No colocalization was found with serotonin immunostaining. The data provide novel insights into the architecture of the locust central complex and suggest that MIPs play a prominent role within the central‐complex network.

Neuroarchitecture of the central complex in the Madeira cockroach Rhyparobia maderae: Pontine and columnar neuronal cell types

“…Further insights into the layering of the CBL and CBU require the analysis of individually labeled tangential neurons, planned in an upcoming study on the cockroach CX. As shown here, the PB of the cockroach is composed of nine slices per hemisphere in unison with the PB of the bumblebee Bombus terrestris (Sayre et al., 2021), the fly D. melanogaster (Lin et al., 2013; Wolff et al., 2015), and the desert locust S. gregaria (Hensgen et al., 2022). As in the fly and bee, the innermost columns 1 apparently lack CL2, CPU4, and CPU5 neurons, resulting in systems of eight bilateral pairs of these neurons across the cockroach PB.…”

“…Table 1), kindly obtained from Dr. Hans Agricola (University of Jena, Germany), was biotinylated as described by Vitzthum and Homberg (1998). Staining with the biotinylated and nonbiotinylated antiserum resulted in identical staining patterns on brain sections from the desert locust (Hensgen et al, 2022;Vitzthum & Homberg, 1998).…”

Comparative morphology of serotonin‐immunoreactive neurons innervating the central complex in the brain of dicondylian insects

“…In both cases, the serotonin phenotypes of these columnar neurons likely represent apomorphic characters in dragonflies and locusts. Interestingly, the CL1c neurons in the dragonflies consist of 18 individual neurons, like the CL1a and CL1b neurons in the locust (Hensgen et al., 2022) as well as their counterparts, the EPG neurons of Drosophila suggesting that the 18‐fold columnar organization of the PB is not a derived character of flies (Wolff et al., 2015) but is rooted deep in the phylogeny of hexapods. Of all insect species studied so far, locusts show the richest composition of serotonin‐labeled cell types innervating the CX.…”

Integration of optic flow into the sky compass network in the brain of the desert locust

“…It consists of the protocerebral bridge (PB), the lower (CBL) and upper (CBU) division of the central body, also termed ellipsoid- and fan-shaped body, and a pair of layered noduli (NO), and is associated with learning, memory and, importantly, spatial orientation (Pfeiffer and Homberg, 2014). The PB and the CBL are subdivided into series of 16 or 18 columns that are connected across the brain midline in a precise topographic manner (Pfeiffer and Homberg, 2014; Hulse et al, 2021; Hensgen et al, 2022).…”

“…The PB and the CBL are subdivided into series of 16 or 18 columns that are connected across the brain midline in a precise topographic manner (Pfeiffer and Homberg, 2014;Hulse et al, 2021;Hensgen et al, 2022).…”