Collateral sprouting of insect motorneurons.

Area of Science:

• Neurobiology
• Muscle Physiology
• Insect Motor Control

Background:

• The extensor tibiae muscle in Teleogryllus oceanicus crickets receives innervation from two distinct excitatory axons: a fast axon and a slow axon.
• These axons originate from different nerve roots and innervate specific regions of the muscle fibers, with some fibers receiving dual innervation.

Purpose of the Study:

• To investigate the plasticity of motor neuron innervation fields in a partially denervated insect muscle.
• To determine the rate and mechanism of innervation field expansion by intact motor neurons.

Main Methods:

• Surgical sectioning of nerve roots (nerve 5 for the fast axon, nerve 3 for the slow axon) to induce partial denervation.
• Observation of muscle fiber innervation patterns and motor neuron axon field expansion over time.
• Assessment of axon regeneration and its effect on the expanded innervation field.

Main Results:

• Partial denervation led to the expansion of the innervation field of the intact motor neuron.
• The slow axon's innervation field expanded linearly at a rate of 20-40 micrometers per day.
• This expansion persisted even after the regeneration of the denervated fast axon.

Conclusions:

• The intact slow motor neuron axon exhibits plasticity by expanding its innervation territory in response to partial denervation.
• Collateral sprouting of slow axon terminals is the likely mechanism driving this observed expansion.
• This finding provides insights into the adaptive capabilities of motor neuron systems.