Organization of descending neurons in the brain of the desert locust

Abstract

In most animals, multiple external and internal signals are integrated by the brain, transformed and, finally, transmitted as commands to motor centers. In insects, the central complex is a motor control center in the brain, involved in decision-making and goal-directed navigation. In desert locusts, it encodes celestial cues in a compass-like fashion indicating a role in sky-compass navigation. While several descending brain neurons (DBNs) including two neurons transmitting sky compass signals have been identified in the locust, a complete analysis of DBNs and their relationship to the central complex is still lacking. As a basis for further studies, we used Neurobiotin tracer injections into a neck connective to map the organization of DBNs in the brain. Cell counts revealed a maximum of 324 bilateral pairs of DBNs with somata distributed in 14 ipsilateral and nine contralateral groups. These neurons invaded most brain neuropils, especially the posterior slope, posterior and ventro-lateral protocerebrum, the antennal mechanosensory and motor center, but less densely the lateral accessory lobes that are targeted by central-complex outputs. No arborizations were found in the central complex and only few processes in the mushroom body, antennal lobe, lobula, medulla, and superior protocerebrum. Double label experiments provide evidence for the presence of GABA, dopamine, tyramine, but not serotonin, in small sets of DBNs.The data show that some DBNs may be targeted directly by central-complex outputs, but many others are likely only indirectly influenced by central-complex networks, in addition to input from multiple other brain areas.

Mosaic evolution of a learning and memory circuit in Heliconiini butterflies

“…GABA is a prominent neurotransmitter and one of three found in MBONs [14]. There is a strong overlap between GABA and GAD antibodies as reported elsewhere [73], and western blot analysis identified bands consistent with GAD subunits [74]. Additionally, conserved labelling across arthropods has been identified [75], while GABA itself is highly conserved [76] giving confidence that GAD is an accurate marker for GABA-ergic neurons.…”

Anatomical organization of the cerebrum of the praying mantis Hierodula membranacea

“…In the mantis, a subdivision, like in the cockroach, dung beetles, and locust (Althaus et al., 2022; Immonen et al., 2017; von Hadeln et al., 2018), was not obvious. The PS is a major target of motion‐sensitive projection neurons from the ME and LOX signaling ego motion (Namiki, Dickinson, et al., 2018; Paulk et al., 2008, 2009; Ryu et al., 2022; Strausfeld, 1976; Strausfeld & Bassemir, 1985a, 1985b; Suver et al., 2016) and is innervated by numerous descending and ascending neurons (Okada et al., 2003; Ryu et al., 2022; Staudacher, 1998; Staudacher et al., 2023; Strausfeld, 1976). In addition, the PS receives input from numerous brain areas including the LAL, as reported in the silk moth ( Bombyx mori ), where these neurons seem to be involved in motor control for pheromone processing (Namiki, Wada, et al., 2018).…”

“…Direct input from Johnston's organ to the VLP was also found in ants (Grob et al., 2021). In desert locusts, the PLP and PVLP receive massive input from ascending neurons providing auditory and cercal wind‐sensory input (Staudacher et al., 2023). The glomerular organization of the PVLP and PLP in D. melanogaster is largely based on a visual feature map provided by parallel projections of lobula columnar neurons signaling various aspects of moving objects (Aptekar et al., 2015; Klapoetke et al., 2022; Wu et al., 2016).…”

“…Direct input from Johnston's organ to the VLP was also found in ants (Grob et al, 2021). In desert locusts, the PLP and PVLP receive massive input from ascending neurons providing auditory and cercal wind-sensory input (Staudacher et al, 2023).…”