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Updated: Mar 14, 2026
Assay for Neural Induction in the Chick Embryo
Published on: February 13, 2009
Activation of state-regulating neurochemical systems in newborn and embryonic chicks
Aimee Chan1, SiHan Li1, Ahn R Lee1
1Department of Psychology, McGill University, Montreal, Quebec H3A 1B1, Canada.
Insights
Neurochemical systems coordinating waking and sleep mature after hatching in chicks. Early embryonic development shows distinct activation patterns for arousal and sleep control networks.
Area of Science:
- Neuroscience
- Developmental Biology
- Sleep Research
Background:
- Coordinated neurochemical system activity defines waking and sleep states in adults.
- The developmental timeline of this coordination remains largely unknown.
Purpose of the Study:
- To investigate the developmental emergence of neurochemical systems regulating waking and sleep in avian embryos and newborns.
- To characterize the maturation of hypocretin/orexin (H/O), serotonergic, noradrenergic, cholinergic, and melanin-concentrating hormone (MCH) systems during development.
Main Methods:
- Utilized cFos expression as a marker for cellular activation in embryonic and newborn chickens.
- Compared cFos expression in specific neuronal populations between waking and sleeping states.
- Analyzed developmental expression patterns across different embryonic days (E12, E16, E20) and post-hatching.
Main Results:
- Newborn chicks mirrored adult mammals, showing higher cFos in waking-active H/O, Dorsal Raphe, Locus Coeruleus, and Ch-LDT/PT neurons compared to sleeping chicks.
- cFos expression correlated between these systems and with waking duration.
- MCH neurons exhibited low, state-independent cFos expression.
- Embryonic H/O neurons activated at E16, while Ch-LDT/PT and MCH neurons showed peak activation at E20.
Conclusions:
- Arousal systems mature rapidly post-hatching in chickens.
- Sleep-control networks, including MCH and cholinergic systems, are active in late-stage avian embryos.
- This study provides insights into the developmental neurobiology of sleep-wake regulation.
Abstract:
Coordinated activity in different sets of widely-projecting neurochemical systems characterize waking (W) and sleep (S). How and when this coordination is achieved during development is not known. We used embryos and newborns of a precocial bird species (chickens) to assess developmental activation in different neurochemical systems using cFos expression, which has been extensively employed to examine cellular activation during S and W in adult mammals. Similarly to adult mammals, newborn awake chicks showed significantly higher cFos expression in W-active hypocretin/orexin (H/O), serotonergic Dorsal Raphe, noradrenergic Locus Coeruleus and cholinergic Laterodorsal and Pedunculopontine Tegmental (Ch-LDT/PT) neurons when compared to sleeping chicks. cFos expression was significantly correlated both between these systems, and with the amount of W. S-active melanin-concentrating hormone (MCH) neurons showed very low cFos expression with no difference between sleeping and awake chicks, possibly due to the very short duration of S episodes. In embryonic chicks, cFos expression was low or absent across all five systems at embryonic day (E) 12. Unexpectedly, a strong activation was seen at E16 in H/O neurons. The highest activation of Ch-LDT/PT (also S-active) and MCH neurons was seen at E20. These data suggest that maturation of arousal systems is achieved soon after hatching, while S-control networks are active in late chick embryos.
