Evidence that ventilatory rhythmogenesis in the frog involves two distinct neuronal oscillators

Area of Science:

• Neuroscience
• Comparative Physiology
• Respiratory Physiology

Background:

• Amphibians utilize distinct buccal and lung ventilation mechanisms.
• The neural control and coordination of these ventilatory behaviors remain largely uncharacterized.

Purpose of the Study:

• To identify specific brainstem regions responsible for generating and coordinating buccal and lung ventilation in Rana catesbeiana.
• To investigate the neural circuitry underlying amphibian respiratory control.

Main Methods:

• Microinjection of AMPA (glutamate agonist) into isolated postmetamorphic brains to identify excitatory loci.
• Microinjection of GABA (inhibitory neurotransmitter) to assess the role of identified loci.
• Brainstem transection to evaluate the independence of rhythmogenic sites.

Main Results:

• Two rhythmogenic sites were identified: a caudal site (near CN X) influencing buccal bursts and a rostral site (between CN VIII and IX) affecting both buccal and lung bursts.
• Inhibiting the caudal site suppressed buccal rhythm, while inhibiting the rostral site abolished lung bursts.
• Both rostral and caudal brainstem sections maintained rhythmogenesis after transection, indicating distinct oscillators.

Conclusions:

• The amphibian respiratory network comprises at least two interacting oscillators: one for buccal ventilation and one for lung inflation.
• These findings provide a model for studying coupled oscillators in vertebrate respiratory systems.