Biology subjects

Hobbiss, A. F.

Publications and source records attributed to Hobbiss, A. F..

4 recordsLinked to original sources

bioRxiv2024

Covert muscle activity reveals dynamic freezing states and prepares the animal for action

When an animal detects a threat it must make a split-second choice between fight, flight or freezing (1-3). During freezing, skeletal muscles sustain tension to maintain rigid, sometimes atypical postures, for many minutes at a time (4). Meanwhile the animal must dynamically assess its surroundings to plan future actions and ready its body for movement. The interplay between the neural and somatic systems during freezing remains poorly understood. Here we show that freezing Drosophila melanogaster display a striking novel pattern of leg muscle activation unique to immobility, a rhythmic pulsing in the distal tibia. The muscle, which we show to be a previously undescribed leg accessory heart, displays multiple activity modes and ramps up to movement onset, implying a preparation for movement. The frequency of pulsing is dynamically modulated as the fly integrates external threat or safety cues, and artificially increasing pulse frequency leads to freezing breaks, indicating a causal role in the decision to move. Through the identification of a new Drosophila cardiac organ, this study provides a window into the multiple states which can underlie freezing behaviour, and the physiological changes which the body undergoes to ready the animal to move.

neuroscience↗

bioRxiv2022

Sustained spinal motor activity triggered by direct mechanosensory stimulation in adult Drosophila melanogaster

Most vertebrates and invertebrates such as Drosophila melanogaster are able to move in complex environments due to their ability to integrate sensory information along with motor commands. Mechanosensory structures exist along each leg to assist in motor coordination by transmitting external cues or proprioceptive information to motor centers in the central nervous system. Nevertheless, how different mechanosensory structures engage these locomotor centers and their underlying circuits remains poorly understood. Here, we tested the role of mechanosensory structures in movement initiation by optogenetically stimulating specific classes of leg sensory structures. We found that stimulation of leg Mechanosensory Bristles (MsB) and femoral Chordotonal Organ (ChO) is sufficient to initiate forward movement in immobile animals. While the stimulation of the ChO required brain centers to induce forward movement, unexpectedly, brief stimulation of leg MsB triggered sustained cyclic motor activity dependent only on circuits within the Ventral Nerve Cord (VNC). The duration of the MsB-induced movement was dependent on the number of excited cells and specific to leg afferents, since stimulation of MsB in other segments lead to different motor outcomes. MsB-mediated movement lacked inter and intra-leg coordination, but preserved antagonistic muscle activity within joints. Our data shows that sensory stimulation can act in combination with descending commands in order to elicit a faster response to mechanical stimulation. In addition, it sheds light on the ability of specific sensory circuits to modulate motor control, including initiation of movement, presenting a new system to better understand how different levels of coordination are controlled by VNC and central brain locomotor circuits. Significance StatementSensory feedback is critical to allow smooth and stable locomotion. Proprioceptors interact directly with pre-motor centers optimizing and sustaining coordinated movement. However, initiation of moment is considered to be triggered by higher-order centers in the brain. Here we took advantage of the genetic toolkit provided by the fruit fly Drosophila melanogaster to optogenetically activate different classes of leg sensory cells in immobile animals. We found that leg mechanosensory bristles can specifically trigger sustained leg activity independently of higher-order centers as headless flies could sustain prolonged leg movement upon mechanosensory stimulation. Moreover, while this sensory-evoked movement lacks intra- and inter-leg coordination, it still preserved basic antagonistic muscle activity. These findings suggest a parallel mechanism to trigger fast movement upon sensory stimulation. In addition, it provides a new model for movement initiation and a point-of-entry to define pre-motor circuits.

neuroscience↗

bioRxiv2020

SpineS: An interactive time-series analysis software for dendritic spines

Live fluorescence imaging has shown the dynamic nature of dendritic spines, with changes in shape occurring both during development and in response to activity. The structure of a dendritic spine positively correlates with its functional efficacy. Learning and memory studies have shown that great deal of the information stored by a neuron is contained in the synapses. High precision tracking of synaptic structures can give hints about the dynamic nature of memory and help us to understand how memories evolve both in biological and artificial neural networks. Experiments that aim to investigate the dynamics behind the structural changes of dendritic spines require the collection and analysis of large time-series datasets. In this paper, we present an open-source software called SpineS for the automatic longitudinal structural analysis of dendritic spines with additional features for manual intervention to ensure optimal analysis. Our extensive experimental analyses on multiple datasets demonstrate that SpineS can achieve a high-level performance on samples collected both by two-photon and confocal imaging systems.

neuroscience↗

bioRxiv2018

Homeostatic plasticity scales dendritic spine volumes and changes the threshold and specificity of Hebbian plasticity

Information is encoded within neural networks through synaptic weight changes. Synaptic learning rules involve a combination of rapid Hebbian plasticity with slower homeostatic synaptic plasticity (HSP) that regulates neuronal activity through global synaptic scaling. While Hebbian plasticity has been extensively investigated, much less is known about HSP. Here we investigate the structural and functional consequences of HSP at dendritic spines of mouse hippocampal neurons. We find that prolonged activity blockade induces spine growth, paralleling synaptic strength increases. Following activity blockade, glutamate uncaging-mediated long-term potentiation at single spines leads to size-dependent structural plasticity: smaller spines undergo robust growth, while larger spines remain unchanged. Moreover, we find that neighboring spines in the vicinity of the stimulated spine exhibit volume changes following HSP, indicating that plasticity has spread across a group of synapses. Overall, these findings demonstrate that Hebbian and homeostatic plasticity shape neural connectivity through coordinated structural plasticity of clustered inputs.

neuroscience↗