Neuronal mechanisms of respiratory pattern generation are evolutionary conserved

Area of Science:

• Neuroscience
• Respiratory Physiology
• Comparative Biology

Background:

• The paratrigeminal respiratory group (pTRG) in lampreys is implicated in respiratory rhythm generation.
• Detailed characterization of the pTRG's connectivity and neurochemical properties is lacking.

Purpose of the Study:

• To precisely localize the pTRG in lampreys.
• To identify the neurochemical markers and connectivity of the pTRG.
• To elucidate the role of the pTRG in respiratory pattern generation.

Main Methods:

• Isolated brainstem preparations from adult lampreys.
• Microinjections of pharmacological agents (lidocaine, muscimol, glutamate agonists/antagonists, substance P, nicotine) into the pTRG.
• Retrograde labeling and neurochemical staining (immunoreactivity for substance P, cholinergic markers, α-bungarotoxin binding sites).

Main Results:

• pTRG neurons projecting to the vagal motoneuronal pool were localized in the rostral rhombencephalon.
• Inhibition of pTRG activity abolished respiratory activity, while agonists enhanced it, confirming its critical role.
• pTRG neurons are glutamatergic, influenced by substance P and cholinergic inputs, and express nicotinic receptors.
• Substance P and nicotine restored respiratory activity during induced apnea.

Conclusions:

• The pTRG is a critical site for respiratory rhythm generation in lampreys.
• The pTRG shares functional similarities with the mammalian pre-Bötzinger complex.
• Fundamental mechanisms of respiratory rhythmogenesis are evolutionarily conserved.