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

Abstract

Honey bees (Apis mellifera) express remarkable social interactions and cognitive capabilities that have been studied extensively. In many cases, behavioral studies were accompanied by neurophysiological and neuroanatomical investigations. While most studies have focused on primary sensory neuropils, such as the optic lobes or antennal lobes, and major integration centers, such as the mushroom bodies or the central complex, many regions of the cerebrum (the central brain without the optic lobes) of the honey bee are only poorly explored so far, both anatomically and physiologically.To promote studies of these brain regions, we used anti-synapsin immunolabeling and neuronal tract tracings followed by confocal imaging and 3D reconstructions to demarcate all neuropils in the honey bee cerebrum and close this gap at the anatomical level.We demarcated 35 neuropils and 25 fiber tracts in the honey bee cerebrum, most of which have counterparts in the fly (Drosophila melanogaster) and other insect species that have been investigated so far at this level of detail. We discuss the role of cerebral neuropils in multisensory integration in the insect brain, emphasize the importance of this brain atlas for comparative studies, and highlight specific architectural features of the honey bee cerebrum.

Anatomical organization of the cerebrum of the praying mantis Hierodula membranacea

“…It lies dorsally on the surface of the CRE (Figure 1). As in the cockroach (Althaus et al., 2022) but in contrast to the AOTU of bees (Habenstein et al., 2023) and locusts (von Hadeln et al., 2018), it is relatively small. Two subunits, a larger upper unit (AOTU‐UU) and a smaller lower unit (AOTU‐LU), are distinguishable (Figure 8g).…”

“…In the fruit fly ( D. melanogaster ), descending neurons convey information from the LAL downstream to regions involved in motor control (Namiki, Dickinson, et al., 2018) that may be similar in the mantis. The microglomerular organization of the BU in the mantis is less prominent than in the honey bee (Habenstein et al., 2023) or fruit fly (Ito et al., 2014), and it appears to be undivided, as in the cockroach (Althaus et al., 2022; Homberg et al., 2018). In contrast, the BU in the desert locust constitutes two spatially separated subunits, a medial and a lateral part (Hensgen, Göthe, et al., 2021; Träger et al., 2008).…”

“…It could be clearly distinguished by its fibrous structure observed in synapsin immunolabeling. In other insects, it may have been considered as part of the SMP (Habenstein et al, 2020(Habenstein et al, , 2023Ito et al, 2014). The SIP, like the SMP and SLP, extends from the anterior to the posterior surface of the brain.…”

“…The ventrolateral neuropils (VLNP; Figure 8e,f bees (Habenstein et al, 2023) and locusts (von Hadeln et al, 2018), it is relatively small. Two subunits, a larger upper unit (AOTU-UU) and a smaller lower unit (AOTU-LU), are distinguishable (Figure 8g).…”

“…Based on the criteria defined by Ito et al. (2014), fully segmented 3D digital brain atlases have been established for the ants Cardiocondyla obscurior (Bressan et al., 2015) and Cataglyphis nodus (Habenstein et al., 2020), the locust Schistocerca gregaria (von Hadeln et al., 2018), the monarch butterfly Danaus plexippus (Heinze & Reppert, 2012), the Bogong moth Agrotis infusa (Adden et al., 2020), the cockroach Rhyparobia maderae (Althaus et al., 2022), the honey bee Apis mellifera (Habenstein et al., 2023), and the dung beetles Scarabaeus lamarcki and Scarabaeus satyrus (Immonen et al., 2017). In contrast to the average standard brains, these detailed atlases are based on an individual immunolabeled brain that was reconstructed in detail.…”