Development of respiratory rhythms in perinatal chick embryos

The CAM Model-Q&A with Experts

The chick chorioallantoic membrane (CAM), as an extraembryonic tissue layer generated by the fusion of the chorion with the vascularized allantoic membrane, is easily accessible for manipulation. Indeed, grafting tumor cells on the CAM lets xenografts/ovografts develop in a few days for further investigations. Thus, the CAM model represents an alternative test system that is a simple, fast, and low-cost tool to study tumor growth, drug response, or angiogenesis in vivo. Recently, a new era for the CAM model in immune-oncology-based drug discovery has been opened up. Although there are many advantages offering extraordinary and unique applications in cancer research, it has also disadvantages and limitations. This review will discuss the pros and cons with experts in the field.

A Method for Recording Chick Embryo Electrocardiogram Using the IX-TA 220 Electrocardiogram Recording System

1. In developmental embryology in chickens, the cardiovascular system is the first to become functional, the first heart muscular contraction (beat) happens as early as 33 h of incubation of a developmental journey that takes 21 d.2. An electrocardiogram (ECG) recording system (IX-TA 220) has been used to record the ECG of various species. The following trial describes the use of such a system for recording electrical tracing of the developing heart in chick embryos on d 19 of embryonic development with the electrodes piercing the eggshell in specific locations to a depth of about 2 mm. The recorded ECG offers an opportunity to measure or calculate ECG parameters like those measured/calculated in humans.3. The use of anaesthesia substantially reduced embryo motion, but may have a transient tachycardia effect on heart rate.4. This is the first time such a system has been successfully used for measuring heart electrical activities in chick embryos and provides a broader research opportunity in chicken embryo cardio-physiology.

Research Note: The effects of chick pipping location on broiler live performance

The objective of this study was to determine the effects of chick pipping location on live broiler performance. A total of 1,350 hatching eggs were collected from a commercial flock of Ross 308 at 38 wk of age. Eggs were incubated with either their large end up (LEU) or small end up (SEU). After transfer on d 19, the air cell area of each fertile egg was marked with a marker pen on the egg surface with a candling light and monitored every 6 h during the hatching period to accurately determine the location of the pip hole. Chicks were classified into 3 groups: 1) egg position LEU and pipped through the air cell (LAC); 2) egg position SEU and pipped through the air cell (SAC); and 3) egg position SEU and pipped through the small end of the egg, not through the air cell (SSE). Individual BW was recorded at placement and at 7, 21, and 35 d of age. Feed consumption was also determined at 7, 21, and 35 d of age. The feed conversion ratio (FCR) was calculated on a pen basis for the same time periods. Mortality was recorded twice a day, and percent mortality was calculated throughout the study. The European production efficiency index (EPEI) was also calculated.

All chicks that hatched from LEU eggs emerged from the egg at the region of the air cell; however, only 10.3% of chicks from the SEU position hatched through air cells. Pipping location greatly affected the hatch time. Chicks pipped through the air cell location hatched earlier than the chicks pipped without using air cell (P < 0.001). The initial BW at placement was higher in the LAC and SAC groups than in the SSE group (P < 0.001). This BW difference was still evident in the subsequent growing period, and the chicks that pipped the SSE exhibited a lower (P = 0.059) BW at 35 d. Additionally, the SSE group had a poorer FCR and numerically higher mortality than the other two groups at 35 d. Overall, the EPEI values in the LAC and SAC groups were higher than that in the SSE group at 35 d (P < 0.001). We concluded that broiler performance was negatively affected when the chicks pipped and hatched without using air cells.

Maturation of Breathing-Related Inhibitory Neurotransmission in the Medulla Oblongata of the Embryonic and Perinatal Zebra Finch (Taeniopygia guttata)

The medullary portion of the embryonic zebra finch hindbrain was isolated and superfused with physiologically relevant artificial cerebral spinal fluid. This in vitro preparation produced uninterrupted rhythmic episodes of neural activity via cranial nerve IX (glossopharyngeal) from embryonic day 4 (E4) through hatching on E14. Cranial nerve IX carries motor activity to the glottis during the inspiratory phase of breathing, and we focused on the role of synaptic inhibition during the embryonic and perinatal maturation of this branchiomotor outflow. We show that spontaneous neural activity (SNA) is first observed on E4 and temporally transforms as the embryo ages. To start, SNA is dependent on the excitatory actions of GABA_A and glycine. As the embryo continues to develop, GABAergic and glycinergic neurotransmission take on a modulatory role, albeit an excitatory one, through E10. After that, data show that GABAergic and glycinergic neurotransmission switches to a phenotype consistent with inhibition, coincident with the onset of functional breathing. We also report that the inhibitory action of GABAergic and glycinergic receptor gating is not necessary for the spontaneous generation of branchiomotor motor rhythms in these birds near hatching. This is the first report focusing on the development of central breathing-related inhibitory neurotransmission in birds during the entire period of embryogenesis.

Expression pattern of heme oxygenase 1 gene and hypoxic adaptation in chicken embryos

Heme oxygenase 1 (HO-1), a rate-limiting enzyme of heme catabolism, has a crucial role of cytoprotective functions under hypoxia. The objective of the present study was to investigate potential differences in protective effect of HO-1 gene on chicken (Gallus gallus) embryo lung during late incubation. At embryonic day (D) D16, D18, D19, and D20 of incubation, the expression of HO-1 in the lungs of chicken embryos (Tibet and Shouguang chickens) incubated in normoxic (21% O2) and hypoxic (13% O2) conditions was measured. SNPs were screened within 5'-flanking region and coding regions with PCR-sequencing and the genotype of the SNPs was determined with PCR-RFLP in Tibet, Chahua and Shouguang chicken populations. In conclusion, the Tibet chicken had higher HO-1 expression on D19 under hypoxic incubation and had two SNPs with different frequency distributions from other chicken breeds, which might be a way that the Tibet chicken had hereditary adaptation to hypoxia during embryonic development.

Embryonic development of endoderm in chicken (Gallus gallus domesticus)

The poultry industry is a sector of agribusiness which represents an important role in the country's agricultural exports. Therefore, the study about embryogenesis of the domestic chicken (Gallus gallus domesticus) has a great economic importance. The aim of this study was to evaluate embryonic development of the endoderm in chicken (Gallus gallus domesticus). Forty fertilized eggs of domestic chickens, starting from the 1st day of gestation and so on until the 19 days of the incubation were collected from the Granja São José (Amparo, SP, Brazil). Embryos and fetus were fixed in 10% formaldehyde solution, identified, weighed, measured, and subjected to light and scanning electron microscopy. The endoderm originates the internal lining epithelium of the digestive, immune, respiratory systems, and the organs can be visualized from the second day (48 h) when the liver is formed. The formation of the digestive system was complete in the 12th day. Respiratory system organs begin at the fourth day as a disorganized tissue and undifferentiated. Their complete differentiation was observed at the 10 days of incubation, however, until the 19 days the syrinx was not observed. The formation of immune system at 10th day was observed with observation of the spleen, thymus, and cloacal bursa. The study of the organogenesis of the chicken based on germ layers is very complex and underexplored, and the study of chicken embryology is very important due the economic importance and growth of the use of this animal model studies such as genetic studies.

Metabolic and ventilatory sensitivity to hypoxia in avian embryos

The article discusses the establishment of pulmonary ventilation (V˙E) in the avian embryo, the metabolic and V˙E sensitivity to hypoxia and the effects of sustained embryonic hypoxia on the hatchling's V˙E chemosensitivity. Throughout embryogenesis, hypometabolism is the common response to hypoxia, with no compensation by anaerobic energy supply. It originates primarily from the depression in body growth and, later in development, from the depression of thermogenesis. The V˙E responses to acute hypoxia or hypercapnia are clearly detectable during the internal pipping phase; their magnitude rapidly increases in the first postnatal day. Sustained prenatal hypoxia diminishes the V˙E chemosensitivity of the hatchling and reduces the hypometabolic response to an acute hypoxic episode. The former most likely originates from a disturbance in the normal development of the carotid bodies, the latter from the central action of hypoxia on thermogenesis. The avian embryo is a model suitable for the studies of the development of respiratory control and offers an alternative to mammalian models for investigations on the short- and long-term effects of prenatal hypoxia.

Simultaneous measurements of instantaneous heart rate and breathing activity in newly hatched chicks

1. Among three types of fluctuations of instantaneous heart rate (IHR) found previously in newly hatched chicks, a high frequency oscillation with a mean frequency of about 0.7 Hz (Type I) appeared to be concurrent with breathing (Moriya et al., Comparative Biochemistry and Physiology, 124A: 461-468, 1999). 2. In order to confirm that Type I HR fluctuation is respiratory sinus arrhythmia (RSA), breathing activity was measured by a condenser microphone, simultaneously with IHR. 3. The microphone detected pressure changes caused by breathing (acoustorespirogram, ARG) and also unexpectedly movement, probably twitch, of hatchlings. 4. Simultaneous measurements of IHR and ARG demonstrated that oscillatory frequency of Type I HR fluctuation coincided with breathing frequency and IHR increased with inspiration, confirming that Type I HR oscillation is RSA. 5. In addition, large transient HR accelerations (Type III HR fluctuation) simultaneously occurred with movement or twitch of the hatchlings, suggesting that Type III HR fluctuation and movement of hatchlings have the same origin, probably sympathetic nerve function.

Expression of growth hormone and its receptor in the lungs of embryonic chicks

The lung is well established as being a postnatal target site for growth hormone (GH) action, since pathophysiological states of GH excess and deficiency are both associated with impaired pulmonary function. Pituitary GH is therefore probably involved in normal lung growth or development, although perinatal lung development occurs prior to the differentiation of pituitary somatotrophs and the ontogeny of pituitary GH secretion. The lung itself may, however, be a site of GH production during prenatal development, since a specific GH-response gene (a marker of GH activity) is expressed in the lungs of early chick embryos, in which GH immunoreactivity is widespread in many other peripheral tissues. We have assessed this possibility in embryonic chicks. A 690-bp cDNA, identical in size and nucleotide sequence to the full-length pituitary GH transcript, was amplified by reverse transcription/polymerase chain reaction from total RNA extracted from the lungs of embryos at 11, 13, 15, and 18 days of the 21-day incubation period. This transcript was localized by in situ hybridization to mesenchymal and epithelial cells of the developing lungs, in which specific GH immunoreactivity was similarly located. Intense GH immunoreactivity was also present after embryonic day 15 (ED15) in the smooth muscle surrounding blood vessels in the lung and surrounding the bronchioles. Lung GH immunoreactivity was primarily associated with a 15-kDa protein, rather than the 26-kDa protein in the pituitary gland. After the onset of pituitary GH secretion (at ED17), GH mRNA was barely detectable in the lungs of ED20 embryos, at the start of lung breathing. GH immunoreactivity was, however, still present in some cells in the lungs of ED20 embryos. GH-receptor mRNA and immunoreactivity were also widespread and abundant within the embryonic lung. Lung GH may thus have autocrine or paracrine roles in lung development or in pulmonary function prior to the ontogeny of the pituitary gland and the appearance of GH in peripheral plasma.

Cardiac rhythms of late pre-pipped and pipped chick embryos exposed to altered oxygen environments

During the final stages of embryonic development in chickens, diffusive gas exchange through the chorioallantoic membrane (CAM) is progressively replaced by pulmonary respiration that begins with internal pipping (IP) of the CAM. Late chick embryos going through the transition from CAM respiration to pulmonary respiration were exposed to hyperoxic (100% O(2)) and hypoxic (10% O(2)/N(2)) environments for 2-h and the responses of baseline heart rate (HR), and HR fluctuation patterns were investigated. 16- and 18-day-old (referred to as 18-d) embryos and 20-d externally pipped (EP) embryos were examined as pre-pipped embryos and pipped embryos, respectively. 19-d embryos were divided into two groups: embryos that had not yet internally pipped (Pre-IP embryos) and embryos that had internally pipped (IP embryos). IP was identified by detecting the breathing signal with a condenser microphone attached hermetically on the eggshell (i.e. acoustorespirogram) on day 19 of incubation. In the hyperoxic environment, HR baseline of pre-pipped embryos remained unchanged and that of pipped embryos was depressed. In the hypoxic environment, HR baseline of 16-d pre-pipped embryos was depressed and that of pipped (IP and EP) embryos elevated. These different responses in pipped embryos might be partially attributed to increased cholinergic input from the vagus nerve in hyperoxia and increased adrenergic response in hypoxia. While hyperoxia did not induce marked modification of instantaneous heart rate (IHR) fluctuation patterns, hypoxia tended to augment transient decelerations of IHR in late pre-pipped embryos and markedly depressed HR fluctuations in pipped embryos.

Selective effects of light exposure on distribution of motility in the chick embryo at E18

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.

Cardiac rhythms in prenatal and perinatal emu embryos

Emu eggs weigh approximately 600 g and have an incubation duration (ID) of approximately 50 days. The egg mass is approximately 10-fold heavier than the chicken egg and the ID is approximately 2.5-fold longer. Daily changes in mean heart rate (MHR) of emu embryos were previously determined, but further measurement was needed to investigate the species-specific behavior of cardiac rhythm for comparison with other species. In the present study, we continuously measured the electrocardiogram of emu embryos while maintaining adequate gas exchange through the eggshell and determined instantaneous heart rate (IHR) during the last 2-7 days of incubation until hatching or death. The MHR over 1-min intervals was calculated from IHR data in order to present continuous developmental patterns of heart rate (HR) in a single graph and 24-h recordings of HR in a single panel, showing the HR trend over a prolonged period. However, neither circadian nor ultradian rhythms of HR were shown in these figures or by power spectrum analysis. The IHR distinctively fluctuated and the fluctuations were mainly comprised of three patterns of irregular HR accelerations in embryos that hatched. Respiratory sinus arrhythmia also occurred in perinatal embryos. During the final stages of the perinatal period, short-term, repeated, large accelerations of IHR appeared, which signaled imminent hatching and has been reported for chick embryos. IHR fluctuations in embryos that failed to hatch tended to become inactive towards death.