Bockemühl, T. | Search bioRxiv

bioRxiv2024

Nutritional state-dependent modulation of Insulin-Producing Cells in Drosophila

Insulin plays a key role in metabolic homeostasis across vertebrate and invertebrate species. Drosophila Insulin-Producing Cells (IPCs) are functional analogues to mammalian pancreatic beta cells and release insulin directly into circulation. IPC activity is modulated by nutrient availability, circadian time, and the behavioral state. To investigate the in vivo dynamics of IPC activity in the context of metabolic homeostasis, we quantified effects of nutritional and internal state changes on IPCs using electrophysiological recordings. We found that the nutritional state strongly modulates IPC activity. IPCs became less active with increasing periods of starvation. Refeeding starved flies with glucose or fructose, two nutritive sugars, significantly increased IPC activity, whereas non-nutritive sugar and protein had no effect. In contrast to feeding, glucose perfusion did not affect IPC activity. This was reminiscent of the mammalian incretin effect, in which ingestion of glucose drives higher insulin release than intravenous glucose application. Contrary to IPCs, Diuretic hormone 44-expressing neurons in the pars intercerebralis (DH44PINs), which are anatomically similar to IPCs, responded to glucose perfusion. Functional connectivity experiments demonstrated that glucose-sensing DH44PINs do not affect IPC activity, while other DH44Ns inhibit IPCs. This suggests that populations of autonomously and systemically sugar-sensing neurons work in parallel to maintain metabolic homeostasis. Ultimately, metabolic state changes affect behavior. For example, hungry flies increase their locomotor activity in search of food. In support of this idea, activating IPCs had a small, satiety-like effect on starved flies, resulting in reduced walking activity, whereas activating DH44Ns strongly increased walking activity. Taken together, we show that IPCs and DH44Ns are an integral part of a sophisticated modulatory network that orchestrates glucose homeostasis and adaptive behavior in response to shifts in the metabolic state.

neuroscience↗

bioRxiv2023

Natural variability and individuality of walking behavior in Drosophila

Insects use walking behavior in a large number of contexts, such as exploration, foraging, escape and pursuit, or migration. A lot is known on how nervous systems produce this behavior in general and also how certain parameters vary with regard to walking direction or speed, for instance. An aspect that has not received much attention is if and how walking behavior varies across individuals of a particular species. To address this, we created a large corpus of kinematic walking data of many individuals of the fruit fly Drosophila. We only selected instances of straight walking in a narrow range of walking speeds to minimize the influence of these high-level parameters, aiming to uncover more subtle aspects of variability. Using high-speed videography and automated annotation we captured the positions of the six leg tips for thousands of steps and used principal components analysis to characterize the postural space individuals used during walking. Our analysis shows that the largest part of walking kinematics can be described by five principal components (PCs). Separation of these five PCs into a 2-dimensional and a 3-dimensional subspace was found to divide the description of walking behavior into invariant features shared across individuals and features that relate to the specifics of individuals; the latter features can be regarded as idiosyncrasies. We also demonstrate that this approach can detect the effects of experimental interventions in an unbiased manner and that general aspects of individuality, such as the average width of the individual walking posture, can be described. Summary statementThe kinematics of walking behavior in Drosophila can be decomposed into general aspects of motor output and idiosyncrasies of individual flies.

animal behavior and cognition↗