Biology subjects

Bhandawat, V.

Publications and source records attributed to Bhandawat, V..

7 recordsLinked to original sources

bioRxiv2025

Behaviors resulting from the activation of single olfactory receptor neuron class depends on multiple second-order neuron types

Animals rely on olfactory cues to guide critical behaviors such as foraging, mate selection, and predator avoidance. Animals discriminate between different odors because each odor binds to a distinct set of olfactory receptor neurons (ORNs). The relationship between the activated ORN class and resulting behavior is an intensely studied problem. Genetic tools in the Drosophila olfactory system make it particularly suitable for understanding this relationship. In this study, we investigate how activity in Or7a-expressing ORNs (Or7a-ORNs) which projects to the DL5 glomerulus, is transformed into aversive behavior. We find that optogenetically activating Or7a-ORNs causes an increase in locomotion speed which results in mild aversion. Surprisingly, silencing the synaptically connected second-order neuron called DL5PN increases the aversion. Silencing DL5PN has no effect on the increase in speed. The increased aversion results from the flies returning to the stimulated area less often. When DL5PN is left intact, flies return more frequently to the stimulated area. Patch-clamp recordings from PNs other than DL5PNs suggest they are activated when Or7a-ORNs are activated. These results suggest that the behavioral effect downstream of a given ORN class is mediated by multiple PN classes. This work advances our understanding of how aversion is encoded and transmitted through early sensory circuits to shape behavior.

neuroscience↗

bioRxiv2025

Passive muscle forces in Drosophila are large but insufficient to support a flys weight

Movement of a limb is shaped by active forces generated by muscle contraction but also by passive forces within individual muscles and joints. In small animals such as insects, the contribution of passive forces to limb movement can match the active forces. However, most measurements of passive forces are limited to the femur-tibia joint in large insects. Here we take advantage of genetic tools in Drosophila to measure passive torques at multiple joints in the flys leg. We genetically inactivate all the motor neurons to assess passive forces. We find that the passive torques are well approximated by a linear spring, i.e., the passive torques linearly increase with angular deviation from the rest angle. The torques are much larger than the gravitational torque due to the leg itself. We estimate that the passive torques are seventy times smaller than necessary to support the weight of the animal. We also inactivated all the motor neurons in a freely standing fly and found that, as predicted from the model, the fly falls when the motor neurons are inactivated. We found that the height at which a fly stands, and, therefore the active forces vary. The flys height affects the time to initiate a fall. The time it takes for the fall is consistent with the active forces decaying with a time constant of [~]100 ms. Thus, although passive forces are strong and will have a large effect on limb kinematics, they are not strong enough to support the weight of the fly.

neuroscience↗

bioRxiv2024

Leg compliance is required to explain the ground reaction force patterns and speed ranges in different gaits

Two simple models - vaulting over stiff legs and rebounding over compliant legs - are employed to describe the mechanics of legged locomotion. It is agreed that compliant legs are necessary for describing running and that legs are compliant while walking. Despite this agreement, stiff legs continue to be employed to model walking under the assumption that the compliance of the leg during walking is high enough to be considered stiff. Here we study gait choice and walk-to-run transition in a biped with compliance and show that the principles underlying gait choice and transition are completely different from stiff legs. Two findings underpin our conclusions: First, at the same speed, step length, and stance duration, multiple gaits that differ in the number of leg contraction cycles are possible. Among them, humans and other animals choose the (normal) gait with M-shaped vertical ground reaction forces (vGRF) not just because of energy considerations but also constraints from forces. Second, the transition from walking to running occurs because of three factors: vGRF minimum at mid-stance characteristic of normal walking, synchronization of horizontal and vertical motions during single support, and velocity redirection during the double support. The insight above required an analytical approximation of the double spring-loaded pendulum (DSLIP) model describing the intricate oscillatory dynamics that relate single and double support phases. Additionally, we also examined DSLIP as a quantitative model for locomotion and conclude that DSLIP speed-range is limited. However, insights gleaned from the analytical treatment of DSLIP are general and will inform the construction of more accurate models of walking.

neuroscience↗

bioRxiv2024

Neurons underlying aggressive actions that are shared by both males and females in Drosophila

Aggression involves both sexually monomorphic and dimorphic actions. How the brain implements these two types of actions is poorly understood. We found that a set of neurons, which we call CL062, previously shown to mediate male aggression also mediate female aggression. These neurons elicit aggression acutely and without the presence of a target. Although the same set of actions is elicited in males and females, the overall behavior is sexually dimorphic. The CL062 neurons do not express fruitless, a gene required for sexual dimorphism in flies, and expressed by most other neurons important for controlling fly aggression. Connectomic analysis suggests that these neurons have limited connections with fruitless expressing neurons that have been shown to be important for aggression, and signal to different descending neurons. Thus, CL062 is part of a monomorphic circuit for aggression that functions parallel to the known dimorphic circuits.

neuroscience↗

bioRxiv2022

Sensorimotor transformation underlying odor-modulated locomotion in walking Drosophila

Most real-world behaviors are performed with incomplete information. Odor-guided locomotion, an ecologically important behavior essential to an animals survival, is an example of such a behavior. Different odors activate different patterns of olfactory receptor neuron (ORN) classes providing information about which odor is present but does not provide any navigational information. In this study, we investigate the sensorimotor transformation that relates ORN activation to locomotion changes in Drosophila by optogenetically activating different combinations of ORN classes and measuring the resulting changes in locomotion. Three features describe this sensorimotor transformation: First, locomotion depends on both the instantaneous firing frequency (f) and its change (df); the two together serve as short-term memory that allows the fly to automatically adapt its motor program to sensory context. Second, the mapping between f-df and locomotor parameters such as speed or curvature is distinct for each pattern of activated ORNs. Finally, the sensorimotor mapping changes with time after odor exposure allowing integration of information over a longer timescale.

neuroscience↗

bioRxiv2018

Kinematic and biomechanical analyses in Drosophila suggests that most legged locomotion in insects can be understood within a single framework.

Despite the fact that all insects have six legs, they display considerable differences in their legged locomotion. Are these differences irreconcilable, or simply different domains of the same system? In this study, we investigate walking in Drosophila. We find that despite the fact that flies walk extremely slowly relative to their size, they predominantly employ an alternating tripod gait, a gait typically associated with high-speed locomotion. The kinematics of their center of mass (CoM) is diametrically opposite to the CoM kinematics observed in insect runners such as cockroach. We resolve this tension between similar gaits, and differing kinematics in slow and high-speed locomotion by showing that the mechanics of a tripod gait naturally reduces to a simple biomechanical model which can support a range of kinematic patterns including both fly-like and cockroach-like patterns. These findings suggest that legged locomotion in different insects might represent different domains of the same system.

neuroscience↗

bioRxiv2018

Statistical structure of locomotion and its modulation by odors

Most behaviors such as making tea are not stereotypical but have an obvious structure. However, analytical methods to objectively extract structure from non-stereotyped behaviors are immature. In this study, we analyze the locomotion of fruit flies and show that this non-stereotyped behavior is well-described by a Hierarchical Hidden Markov Model (HHMM). HHMM shows that a flys locomotion can be decomposed into a small number of locomotor features, and odors modulate locomotion by altering the time a fly spends performing different locomotor features. Importantly, although all flies in our dataset use the same set of locomotor features, individual flies vary considerably in how often they employ a given locomotor feature, and how this usage is modulated by odor. This variation is so large that the behavior of individual flies is best understood as being grouped into at least 3-5 distinct clusters, rather than variations around an average fly.

neuroscience↗