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Mechanosensory Neurons in the Pharynx Regulate Swallowing Behavior in Drosophila melanogaster


Core Concepts
A group of multi-dendritic mechanosensory neurons in the fly's pharynx (cibarium) are essential for coordinating the rhythmic filling and emptying of the cibarium during swallowing. These neurons interact with the motor circuit to control the swallow process.
Abstract
The study investigates the mechanisms underlying the sensorimotor control of swallowing behavior in the fruit fly Drosophila melanogaster. The key findings are: Mutation of mechanotransduction channel genes nompC, Tmc, or piezo impairs the regular pumping rhythm of the cibarium during feeding. These channels are expressed in a group of multi-dendritic mechanosensory neurons (md-C neurons) that wrap around the cibarium. Inhibition of md-C neurons causes difficulty in cibarium emptying and lower ingestion efficiency, while activation of them leads to higher pump frequency and sometimes difficulty in cibarium filling. md-C neurons form synaptic and functional connections with the motor neurons (MN11 and MN12) that control the muscles driving swallowing. Activation of md-C neurons can stimulate the activity of these motor neurons. The mechanosensory feedback from md-C neurons likely modulates the activity of the central pattern generators (CPGs) that control the rhythmic swallowing behavior, depending on the physical properties of the food. Overall, the study elucidates the role of pharyngeal mechanosensation in regulating the swallowing process and provides insights into the neural circuits underlying this essential feeding behavior in Drosophila.
Stats
Mutation of mechanoreceptor genes nompC, Tmc, or piezo leads to a lower pump frequency during swallowing, mainly by increasing the time required to empty the cibarium. Inhibition of the md-C mechanosensory neurons causes difficulty in cibarium emptying and a significant decrease in food intake rate. Activation of the md-C neurons can induce accelerated swallowing, incomplete cibarium filling, and difficulty in filling.
Quotes
"Inhibition of md-C neurons causes difficulty in cibarium emptying and lower ingestion efficiency, while activation of them leads to higher pump frequency and sometimes difficulty in cibarium filling." "md-C neurons form synaptic and functional connections with the motor neurons (MN11 and MN12) that control the muscles driving swallowing. Activation of md-C neurons can stimulate the activity of these motor neurons." "The mechanosensory feedback from md-C neurons likely modulates the activity of the central pattern generators (CPGs) that control the rhythmic swallowing behavior, depending on the physical properties of the food."

Deeper Inquiries

How do the md-C neurons integrate information from the different mechanotransduction channels (nompC, Tmc, piezo) to provide a coherent sensory representation of the swallowing process?

The md-C neurons integrate information from the different mechanotransduction channels by co-expressing nompC, Tmc, and piezo genes. These channels play distinct roles in the sensory representation of the swallowing process. NompC is involved in the initiation of swallowing, while Tmc and piezo control the driving strength of swallowing. The information from these channels is likely integrated in the md-C neurons to provide a comprehensive sensory representation of the mechanical force exerted during the expansion and contraction of the cibarium. This integration allows the md-C neurons to sense the filling and emptying of the cibarium and coordinate the rhythmic pumping required for efficient food ingestion.

What are the potential mechanisms by which the md-C neurons inhibit the activity of the swallowing CPGs under certain conditions, such as during the filling of the cibarium?

The md-C neurons may inhibit the activity of the swallowing Central Pattern Generators (CPGs) during the filling of the cibarium through a feedback mechanism. When the expansion of the cibarium is sensed by the md-C neurons, they may relay inhibitory signals to the CPGs to regulate the rhythm of swallowing. This feedback mechanism could involve the release of neurotransmitters or neuropeptides that modulate the activity of the CPGs controlling the swallow. Additionally, the md-C neurons may interact with inhibitory interneurons to regulate the activity of the CPGs, ensuring coordinated and efficient swallowing behavior. By inhibiting the CPGs during specific phases of the swallowing process, the md-C neurons contribute to the precise control of food ingestion.

Could the principles of sensorimotor integration underlying swallowing control in Drosophila be applicable to the regulation of other rhythmic feeding behaviors across different species?

The principles of sensorimotor integration underlying swallowing control in Drosophila could be applicable to the regulation of other rhythmic feeding behaviors across different species. The coordination between mechanosensory neurons like the md-C neurons and motor neurons controlling feeding muscles is essential for efficient food ingestion. This integration of sensory feedback with motor output is a fundamental aspect of feeding behavior in many organisms. By understanding how mechanosensory neurons regulate the activity of motor circuits during feeding, we can gain insights into the neural basis of feeding control in various species. The principles of sensorimotor integration elucidated in Drosophila could serve as a model for studying and understanding rhythmic feeding behaviors in other organisms, providing valuable insights into the neural mechanisms underlying feeding control.
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