3D‐atlas of the brain of the cockroach Rhyparobia maderae

Abstract

The Madeira cockroach Rhyparobia maderae is a nocturnal insect and a prominent model organism for the study of circadian rhythms. Its master circadian clock, controlling circadian locomotor activity and sleep-wake cycles, is located in the accessory medulla of the optic lobe. For a better understanding of brain regions controlled by the circadian clock and brain organization of this insect in general, we created a three-dimensional (3D) reconstruction of all neuropils of the cerebral ganglia based on anti-synapsin and anti-γ-aminobutyric acid immunolabeling of whole mount brains.Forty-nine major neuropils were identified and three-dimensionally reconstructed.Single-cell dye fills complement the data and provide evidence for distinct subdivisions of certain brain areas. Most neuropils defined in the fruit fly Drosophila melanogaster could be distinguished in the cockroach as well. However, some neuropils identified in the fruit fly do not exist as distinct entities in the cockroach while others are lacking in the fruit fly. In addition to neuropils, major fiber systems, tracts, and commissures were reconstructed and served as important landmarks separating brain areas. Being a nocturnal insect, R. maderae is an important new species to the growing collection of 3D insect brain atlases and only the second hemimetabolous insect, for which a detailed 3D brain atlas is available. This atlas will be highly valuable for an evolutionary comparison of insect brain organization and will greatly facilitate addressing brain areas that are supervised by the circadian clock.

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

“…(2014) and, for brain areas specific to the cockroach, Althaus et al. (2022). Based on immunolabeling with antibodies raised against serotonin, Mas‐AT, and the presynaptic marker synapsin, we performed 3D reconstructions of the subdivisions of the cockroach CX (Figure 1), the internal organization of the CB (Figure 2), and the neuropils of the LX (Figure 3).…”

“…E. Buchner and C. Wegener, University of Würzburg, Germany; RRID: AB_2315425) was raised in mice against parts of the D. melanogaster synaptic vesicle protein SYN1 fused with glutathione‐S‐transferase (Klagges et al., 1996). The antibody labels synaptic neuropil as shown in various insect species including the cockroach R. maderae (Althaus et al., 2022; Wei et al., 2010).…”

“…Labeling is abolished by preadsorption of the diluted antiserum with 100 μg·mL −1 serotonin–BSA conjugate (ImmunoStar, product information sheet). In the brain of R. maderae , immunostaining with this antiserum and a second anti‐serotonin antiserum (Sigma, Cat# S5545, RRID: AB 477522) resulted in identical staining patterns (Althaus et al., 2022).…”

“…In the cockroach Rhyparobia maderae , a model organism for research on circadian rhythms (Homberg et al., 2003; Stengl et al., 2015), the gross organization of the CX has been studied recently (Althaus et al., 2022), but no data are available on its cellular composition. By analyzing the morphology of columnar and pontine neurons of the cockroach CX, we aim to broaden our understanding of the variability and evolution of the navigation network in the insect brain.…”

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

“…Images were obtained from https://insectbraindb.org/ (Heinze et al., 2021), and are based on Althaus et al. (2022). Scale bars = 200 μm (a), 100 μm (b).…”