Biology subjects

Giez, C.

Publications and source records attributed to Giez, C..

7 recordsLinked to original sources

bioRxiv2025

Cross-species comparative connectomics reveals the evolution of an olfactory circuit

Animal behavioural diversity ultimately stems from variation in neural circuitry, yet how central neural circuits evolve remains poorly understood. Studies of neural circuit evolution often focus on a few elements within a network. However, addressing fundamental questions in evolutionary neuroscience, such as whether some elements are more evolvable than others, requires a more global and unbiased approach. Here, we used synapse-level comparative connectomics to examine how an entire olfactory circuit evolves. We compared the full antennal lobe connectome of the larvae of two closely related Drosophila species, D. melanogaster and D. erecta, which differ in their ecological niches and odour-driven behaviours. We found that evolutionary change is unevenly distributed across the network. Some features, including neuron types, neuron numbers and interneuron-to-interneuron connectivity, are highly conserved. These conserved elements delineate a core circuit blueprint presumably required for fundamental olfactory processing. Superimposed on this scaffold, we find rewiring changes that mirror each species ecologies, including a systematic shift in the excitation-to-inhibition balance in the feedforward pathways. We further show that some neurons have changed more than others, and that even within individual neurons some synaptic elements remain conserved while others display major species-specific changes, suggesting evolutionary hot-spots within the circuit. Our findings reveal constrained and adaptable elements within olfactory networks, and establish a framework for identifying general principles in the evolution of neural circuits underlying behaviour.

neuroscience↗

bioRxiv2024

Assembly of a functional neuronal circuit in embryos of an ancestral metazoan is influenced by environmental signals including the microbiome

Understanding how neural populations evolve to give rise to behavior is a major goal in neuroscience. However, the complexity of the nervous system in most invertebrates and vertebrates complicates the deciphering of underlying fundamental processes. Here, we explore the self-assembly of neural circuits in Hydra, an organism with a simple nervous system but no centralized information processing, to improve the understanding of nervous system evolution. The N4 neuronal circuit in embryos develops through activity-driven self-assembly, where neurons in distinct regions increase connectivity and synchronization. Gap junctions and vesicle-mediated communication between neuronal and non-neuronal cells drive rapid assembly, with the embryos prospective oral region exhibiting the highest neuronal density. An artificial electrical circuit-based model demonstrates dynamic increases in synchronization over time, along with predictions for selective dynamic adaptions of connections. Environmental factors, like temperature and an absent microbiome, modify neural architecture, suggesting the existence of a certain plasticity in neural development. We propose that these fundamental features originated in the last common bilaterian ancestor, supporting the hypothesis that the basic architecture of the nervous system is universal.

neuroscience↗

bioRxiv2024

A functional network model for body column neural connectivity in Hydra

Hydra is a non-senescent animal with a relatively small number of cell types and overall low structural complexity, but a surprisingly rich behavioral repertoire. The main drivers of Hydra s behavior are neurons that are arranged in two nerve nets comprising several distinct neuronal populations. Among these populations is the ectodermal nerve net N3 which is located throughout the animal. It has been shown that N3 is necessary and sufficient for the complex behavior of somersaulting and is also involved in Hydra feeding behavior. Despite being a behavioral jack-of-all-trades, there is insufficient knowledge on the coupling structure of neurons in N3, its connectome, and its role in activity propagation and function. We construct a model connectome for the part of N3 located on the body column. Using experimental data on the placement of neuronal somata and the spatial dimensions of the body column, we show that a generative network model combining non-random placement of neuronal somata and the preferred orientation of primary neurites yields good agreement with experimentally observed distributions of connection distances, connection angles, and the number of primary neurites per neuron. Having validated the N3 connectome model in this fashion, we place a simple excitable dynamical model on each node of the body column network and show that it generates directed, short-lived, fast propagating patterns of activity. In addition, by slightly changing the parameters of the dynamical model, the same structural network can also generate persistent activity. Finally, we use a neuromorphic circuit based on the Morris-Lecar model to show that the same structural connectome can, in addition to through-conductance with biologically plausible time scales, also host a dynamical pattern related to the complex behavioral pattern of somersaulting. We speculate that such different dynamical regimes act as dynamical substrates for the different functional roles of N3, allowing Hydra to exhibit behavioral complexity with a relatively simple nervous system that does not possess modules or hubs.

neuroscience↗

bioRxiv2023

The internal metabolic state controls behavior in Hydra through an interplay of enteric and central nervous system-like neuron populations

Hunger and satiety can have an influence on decision making, sensory processing, and motor behavior by altering the internal state of the brain. This process necessitates the integration of peripheral sensory stimuli into the central nervous system. Interestingly, even organisms without a brain, such as the Cnidaria, exhibit feeding dependent behavioral changes. The underlying mechanisms, however, remain unclear. In this study, we demonstrate that neuronal activity in two distinct neuronal populations, the ectodermal N3 neurons and the endodermal N4 neurons in Hydra, an ancestral metazoan animal with a diffuse nerve net spread throughout the body with no signs of centralization, are responsible for feeding dependent behavioral changes. Specifically, endodermal N4 neurons are essential for food intake and digestive functions, similar to the enteric nervous system, while the N3 population influences and inhibits other motor related behaviors, comparable to the central nervous system. This fascinating observation provides a new insight into the evolution and the complexity of a simple non-centralized nervous system.

neuroscience↗

bioRxiv2023

Microbes as part of ancestral neuronal circuits: Bacterial produced signals affect neurons controlling eating behavior in Hydra

Although recent studies indicate the impact of microbes on the central nervous systems and behavior, it remains unclear how the relationship between the functionality of the nervous system, behavior and the microbiota arise. We studied the eating behavior of Hydra, a host that has a simple nervous system and a low-complexity microbiota. To identify the neuronal subpopulations involved, we used a subpopulation specific cell ablation system and calcium imaging. The role of the microbiota was uncovered by reducing the diversity of the natural microbiota. Here, we demonstrate that different neuronal subpopulations are functioning together to control the eating behavior. The microbiota participates in control of the eating behavior since germ-free or mono-colonized animals have drastic difficulties in mouth opening. This was restored by adding a full complement of the microbiota. In summary, we provide a mechanistic explanation of how the eating behavior is controlled in Hydra and how microbes can affect the neuronal circuit. Highlights- Multiple neuronal modules and their networks control complex behavior in an animal lacking a central nervous system. - Its associated microbes participate in these neuronal circuits and influence the eating behavior. - Disorganization of the microbiota negatively impacts this eating behavior. - Glutamate participates in an evolutionary ancient interkingdom language.

animal behavior and cognition↗

bioRxiv2022

Spontaneous body wall contractions stabilize the fluid microenvironment that shapes host-microbe associations

The freshwater polyp Hydra is a popular biological model system; however, we still do not understand one of its most salient behaviours, the generation of spontaneous body wall contractions. Here, by applying experimental fluid dynamics analysis and mathematical modelling, we provide functional evidence that spontaneous contractions of body walls enhance the transport of chemical compounds from and to the tissue surface where symbiotic bacteria reside. Experimentally, a reduction in the frequency of spontaneous body wall contractions is associated with a changed composition of the colonizing microbiota. Together, our findings suggest that spontaneous body wall contractions create an important fluid transport mechanism that (1) may shape and stabilize specific host-microbe associations and (2) create fluid microhabitats that may modulate the spatial distribution of the colonizing microbes. This mechanism may be more broadly applicable to animal-microbe interactions since research has shown that rhythmic spontaneous contractions in the gastrointestinal tracts are essential for maintaining normal microbiota.

biophysics↗

bioRxiv2019

Prototypical pacemaker neurons are immunocompetent cells

Pacemaker neurons exert control over neuronal circuit function by their intrinsic ability to generate rhythmic bursts of action potential. Recent work has identified rhythmic gut contractions in human, mice and hydra to be dependent on both neurons and the resident microbiota. However, little is known about the evolutionary origin of these neurons and their interaction with microbes. In this study, we identified and functionally characterized prototypical ANO/SCN/TRPM ion channel expressing pacemaker cells in the basal metazoan Hydra by using a combination of single-cell transcriptomics, immunochemistry, and functional experiments. Unexpectedly, these prototypical pacemaker neurons express a rich set of immune-related genes mediating their interaction with the microbial environment. Functional experiments validated a model of the evolutionary emergence of pacemaker cells as neurons using components of innate immunity to interact with the microbial environment and ion channels to generate rhythmic contractions.

developmental biology↗