Development of ventilatory chemoreflexes in Coturnix quail chicks

Area of Science:

• Comparative Physiology
• Developmental Biology
• Respiratory Control

Background:

• Respiratory control system development in birds is poorly understood compared to mammals.
• Understanding avian respiratory development offers insights into comparative physiology and evolutionary biology.

Purpose of the Study:

• To investigate the developmental changes in respiratory control in Coturnix quail chicks.
• To compare the hypoxic ventilatory response (HVR) and hypercapnic ventilatory response (HCVR) across different posthatching ages.

Main Methods:

• Ventilation and metabolic rates were measured in quail chicks exposed to normoxia, hypoxia (11% O2), and hypercapnia (4% CO2).
• Measurements were taken at three key developmental stages: 0-1, 3-4, and 6-7 days posthatching (dph).

Main Results:

• Mass-specific ventilation and metabolic rate increased from 0-1 to 3-4 dph, then decreased by 6-7 dph.
• The HVR magnitude increased with age, transitioning from a biphasic response (initial increase followed by decline) in younger chicks to a sustained response in older chicks.
• The hypercapnic ventilatory response (HCVR) was sustained across all ages but decreased in magnitude with age. Hypoxic hypometabolism was observed but did not explain the biphasic HVR.

Conclusions:

• Coturnix quail chicks exhibit developmental patterns in ventilatory chemoreflexes similar to newborn mammals.
• Key similarities include age-dependent increases in HVR, a shift from biphasic to sustained HVR, and decreasing HCVR.
• Further research is needed to determine if homologous mechanisms underlie these developmental changes in birds and mammals.