A three‐dimensional atlas of the honeybee central complex, associated neuropils and peptidergic layers of the central body

Abstract

The central complex (CX) in the brain of insects is a highly conserved group of midlinespanning neuropils consisting of the upper and lower division of the central body, the protocerebral bridge, and the paired noduli. These neuropils are the substrate for a number of behaviors, most prominently goal-oriented locomotion. Honeybees have been a model organism for sky-compass orientation for more than 70 years, but there is still very limited knowledge about the structure and function of their CX. To advance and facilitate research on this brain area, we created a high-resolution threedimensional atlas of the honeybee's CX and associated neuropils, including the posterior optic tubercles, the bulbs, and the anterior optic tubercles. To this end, we developed a modified version of the iterative shape averaging technique, which allowed us to achieve high volumetric accuracy of the neuropil models. For a finer definition of spatial locations within the central body, we defined layers based on immunostaining against the neuropeptides locustatachykinin, FMRFamide, gastrin/cholecystokinin, and allatostatin and included them into the atlas by elastic registration. Our honeybee CX atlas provides a platform for future neuroanatomical work.

3D atlas of cerebral neuropils with previously unknown demarcations in the honey bee brain

“…In recent years, it has become one of the best studied neuropil groups in insects (Green et al., 2019; Hensgen et al., 2021; Pfeiffer, 2022; Pfeiffer & Homberg, 2014; Seelig & Jayaraman, 2015; Stone et al., 2017). A recent study has mapped the anatomical details of the CX in the honey bee brain (Kaiser et al., 2022). Like in other insects, the CX has four distinct subneuropils in Apis mellifera : the lower (CBL) and upper division (CBU) of the central body, the protocerebral bridge (PB), and the paired noduli (NO) (Figure 2a,b,d,f,g; Kaiser et al., 2022).…”

“…A recent study has mapped the anatomical details of the CX in the honey bee brain (Kaiser et al., 2022). Like in other insects, the CX has four distinct subneuropils in Apis mellifera : the lower (CBL) and upper division (CBU) of the central body, the protocerebral bridge (PB), and the paired noduli (NO) (Figure 2a,b,d,f,g; Kaiser et al., 2022). The CB is enclosed by the PED and the MCA of the two brain hemispheres in the center of the brain.…”

“…The posterior optic tubercle (POTU) is a very small neuropil that is positioned at the posteriormost region of the honey bee brain between the LCA of the MB and the posterior optic commissure ( POC ), embedded in the cell body rind (Figure 4l, Kaiser et al., 2022). The POTUs are attached posterolaterally to the PB (Figure 4j–l).…”

“…Consequently, our present detailed 3D neuropil atlas of the honey bee cerebrum can easily be used in combination with the average shape atlas by Brandt et al. (2005), the high‐resolution average‐shape atlas of the CX (Kaiser et al., 2022), and future high‐resolution maps of individual brain neuropils, neuronal tracts, or individual neurons that have been registered and added to existing atlases in the honey bee.…”

“…For example, the relative size of the optic lobes is small in strongly olfactory‐oriented ant species (Bressan et al., 2014; Groh et al., 2014; Ilieş et al., 2015; Yilmaz et al., 2016). Since major primary sensory neuropils (AL, OL) and integration centers (MB, CX) in the honey bee have been described in detail in other studies (for a most recent 3D reconstruction of the CX, see Kaiser et al., 2022; for a recent review on the MB structure and plasticity, see Groh & Rössler, 2020), we focus the following discussion on the newly demarcated neuropils in the cerebrum.…”