PTX-induced hyperexcitability affects dendritic shape and GABAergic synapse density but not synapse distribution...

Area of Science:

• Neuroscience
• Developmental Biology
• Insect Physiology

Background:

• Insect metamorphosis involves significant remodeling of the nervous system, including motoneurons.
• Postembryonic development of adult motor behaviors is linked to changes in neuronal structure and function.

Purpose of the Study:

• To investigate the impact of increased neuronal activity on dendritic architecture and synaptic input distribution in the flight motoneuron 5 (MN5) of Manduca sexta.
• To determine if enhanced excitability influences synaptic targeting and overall motoneuron development during pupal stages.

Main Methods:

• Systemic administration of picrotoxin (PTX), a chloride channel blocker, during early pupal development.
• Electrophysiological recordings from motoneurons to assess membrane properties and excitability.
• Quantitative three-dimensional reconstruction of MN5 dendritic trees and analysis of GABAergic input distribution.

Main Results:

• Systemic PTX injections increased pupal reflex responsiveness without impairing overall development.
• Adult MN5 neurons exhibited dendritic overgrowth and reduced density of GABAergic inputs following PTX treatment.
• Sub-dendritic distribution patterns of GABAergic terminals remained unchanged, suggesting activity-independent targeting.

Conclusions:

• Increased neuronal excitability during postembryonic development can lead to dendritic overgrowth and decreased inhibitory input in motoneurons.
• Activity-independent mechanisms likely regulate the precise sub-dendritic targeting of synapses.
• While neuronal changes did not abolish flight, they impaired maximum flight performance in Manduca sexta.