Selective Effects of Light Exposure on Distribution of Motility in the Chick Embryo at E18

Abstract

It is well established that orderly patterns of motor neuron activity, muscle recruitment, and limb movement are generated in chicks during motility by embryonic day (E)9, the midpoint in embryonic development. However, our recent work suggests that some attributes of motility, such as the rhythm of repetitive limb movements and distribution of activity, become less orderly after E9. In this study, we extend these observations by performing continuous force recordings over a 24-h period in ovo at E18 with augmented sampling of synchronized video and electromyogram (EMG) recordings. We report the distribution of three repetitive behaviors, rapid limb movement, respiratory-like movement, and beak clapping, identified in force recordings, and the general distribution of motility. We also test a model recently proposed to account for age-related changes in motility parameters. In the model, we proposed that circadian networks contribute to the age-related changes in distribution of motility. As a first test of this hypothesis, we examine whether light exposure contributes to the variable distribution of motility by comparing motility parameters at E18 for embryos incubated and tested under either a 12-h light/dark cycle or continuous light. Results suggest that exposure to light increases the total amount of activity and hastens the onset of extended respiratory-like movement sequences but does not impact expression of repetitive limb movement or beak clapping at E18. The possible influence of circadian mechanisms on embryonic behavior and insensitivity of repetitive limb movements to light exposure are discussed.

Light Accelerates Morphogenesis and Acquisition of Interlimb Stepping in Chick Embryos

“…However, we could not rule out that early hatching only unmasked locomotor potential established well before hatching [6]. Nonetheless, findings in an earlier study of motor activity at E18 appeared to indicate that light exposure accelerated development of respiratory motor control [5], and the array of physical, physiological and behavioral findings across our studies suggest to us that light exposure during embryogenesis accelerates development of many, if not all, body systems. For these reasons we propose that the greater incidence of bilateral RLMs is evidence that embryos incubated in 24L conditions were neurologically more mature than embryos incubated in 12L and 24D; and embryos incubated in 24D conditions were least mature.…”

“…Embryos incubated in bright light exhibited weight gains of up to 17% after 4½ days of exposure, compared to embryos incubated in darkness [3]. Continuous bright light exposure during embryogenesis also appeared to accelerate development of respiratory motor control [5]. We recently found that light exposure accelerates the development of locomotion in register with the accelerated onset of hatching.…”

Effect of Acute Hypoxia on the Motor Activity and Heart Rate of the 10- and 14-Day Chick Embryo

“…It was earlier shown that many environmental factors, such as temperature, illumination, acoustic stimulation, vibration, etc., may considerably affect the motor activity of the chick embryo in the egg [21][22][23][24][25][26][27][28]. Since oxygen is one of the most important environmental factors affecting both physiological processes and development, our study was focused on the effect of oxygen deficit on embryonic motor activity.…”

“…[5,[21][22][23][24][25][26][27][28]. However, the effects of environmental factors on the embryonic motor activity remain largely unknown.…”

Drift during overground locomotion in newly hatched chicks varies with light exposure during embryogenesis

“…Studies have examined the effects of light exposure in the final days before hatching, providing evidence that light is a salient stimulus capable of influencing vision-mediated behavior (Casey & Lickliter, 1998; Rogers, 1982; Rogers & Bolden, 1991), hemispheric specialization (Casey & Martino, 2000; Casey, 2005; Rogers, 1982), and social behavior (Rogers, 1982). A few studies in domestic chicks have also shown that extended light exposure during embryogenesis can accelerate development of respiratory control (Bradley and Jahng, 2003), interlimb stepping prior to hatching (Ryu & Bradley, 2009; Sindhurakar & Bradley, 2012), and overground locomotion at hatching (Sindhurakar & Bradley, 2010). However, it has yet to be determined if this acceleration in motor development is associated with any immediate or longer term negative behavioral or other biological consequences.…”