Revisiting the two rhythm generators for respiration in lampreys

Area of Science:

• Neuroscience
• Comparative Physiology
• Respiratory Control

Background:

• Lamprey respiration exhibits distinct fast and slow rhythms.
• Previous studies proposed conflicting locations for the fast respiratory rhythm generator.
• The neural circuitry for the slow respiratory rhythm remains less understood.

Purpose of the Study:

• To anatomically and physiologically characterize the brainstem regions generating fast and slow respiratory rhythms in lampreys.
• To resolve conflicting data regarding the location of the fast rhythm generator.
• To identify and localize neurons involved in the slow respiratory rhythm generation.

Main Methods:

• Anatomical lesion studies and physiological recordings were used to re-examine the fast rhythm generator's location.
• Unilateral injections of anatomical tracers were combined with stimulation experiments to map the slow rhythm generator.
• Electrical and chemical stimulation, along with Substance P injections, were employed to assess the function of identified neuronal populations.

Main Results:

• The fast respiratory rhythm generator was confirmed to be located rostro-lateral to the trigeminal motor nucleus.
• A distributed population of neurons in the caudal hindbrain's lateral tegmentum was identified as the slow rhythm generator.
• Stimulation of these caudal neurons initiated slow rhythm bursts, while inactivation abolished it; Substance P accelerated the slow rhythm.

Conclusions:

• The fast respiratory rhythm generator in lampreys is primarily situated rostro-lateral to the trigeminal motor nucleus.
• The slow respiratory rhythm generator is distributed within the lateral tegmentum of the caudal hindbrain.
• This study clarifies the neural substrates underlying dual respiratory rhythm generation in lampreys.