Hindbrain Similarities: Humans And Chickens

The human hindbrain and a chicken's hindbrain share some similarities. For example, neural stem cells from chick embryonic hindbrains have been found to recapitulate hindbrain development in culture, exhibiting similar properties to neurospheres from different CNS origins. Additionally, both the human and avian telencephalon are organised into two distinct hemispheres, with lateralization of functions such as vision, auditory, and olfactory processing. While there are some similarities, it is important to note that the external morphology of the chicken brain, including the hindbrain, can vary between different breeds, such as the crested Padovana chicken, which exhibits unique skull characteristics.

Hindbrain cells in human and chicken embryos contain NSCs that develop into neurospheres

The human brain and the avian brain share some similarities. Both are organised into two distinct hemispheres, with one hemisphere dominating certain functions. The avian telencephalon, for instance, is dominated by a large pallium, which corresponds to the mammalian cerebral cortex and is responsible for cognitive functions.

Chickens, along with rats and mice, are commonly used in research aimed at understanding the human brain, particularly early brain development, because scientists have easier access. The Rhombomeres area of the brain stem, for example, is home to the Hox genes, which are responsible for foetal development and control things like breathing and heart rate.

In recent studies, researchers have identified a population of neural stem cells (NSCs) in the chick embryonic hindbrain. These NSCs reside in specialised domains in-between rhombomeres, termed hindbrain boundaries. They express Sox2, nestin, and GFAP, which are typical NSC markers, and contribute amplifying progenitors and differentiating neurons to adjacent domains.

These NSCs from the chick embryonic hindbrain have been found to form neurospheres in vitro. These neurospheres have been shown to self-renew, aggregate, divide, connect, and differentiate into distinct lineages, as well as retain their regional identity.

Similarly, hindbrain cells isolated from mice embryo (E12) or human embryos (E35–E60) were found to contain NSCs that give rise to stereotypic neurospheres in culture. These neurospheres preserved hindbrain-specific markers such as particular Hox genes and the neurotransmitter 5-hydroxytryptamine, which is exclusive to hindbrain serotonergic neurons. Thus, the findings suggest that hindbrain cells in human and chicken embryos contain NSCs that develop into neurospheres.

The human and chicken telencephalon is organised into two distinct hemispheres

The human hindbrain and a chicken's hindbrain share some similarities. Hindbrain cells isolated from chicken embryos have been found to contain neural stem cells (NSCs) that give rise to neurospheres in culture, similar to those found in mice and human embryos. These neurospheres preserved hindbrain-specific markers such as Hox genes, which are responsible for foetal development and control functions like breathing and heart rate. This discovery strengthens the potential of using the chicken embryonic system to study specific NSC subpopulations.

Additionally, the avian telencephalon, which includes the chicken's telencephalon, shares organizational similarities with its human counterpart. Both are divided into two distinct hemispheres, with lateralization of functions. In chickens, the left hemisphere dominates tasks that require separating important stimuli from distractions, while the right hemisphere is more easily distracted but excels in fear and escape responses. This lateralization allows chickens to simultaneously search for food (a left-hemisphere task) and remain vigilant for predators (a right-hemisphere task).

The telencephalon in birds is dominated by a large pallium, which corresponds to the mammalian cerebral cortex and is responsible for cognitive functions. The pallium is composed of structures like the hyperpallium, nidopallium, mesopallium, and archipallium, which are associated with perception, learning, and cognition. This challenges the old notion that mammals think with their neocortex while birds rely solely on their basal ganglia.

While the hindbrains of humans and chickens share some similarities at the cellular level, particularly in the presence of NSCs and Hox genes, the overall brain structure and organization of functions between the two species differ. In chickens with cranial protuberances, the forebrain and hindbrain appear more separated, giving the brain an hourglass shape. This morphological variation is not typically observed in humans and may impact the overall shape and arrangement of the brain.

In summary, while there are some shared features in the hindbrains of humans and chickens, particularly at the cellular level, the overall organization and structure of their brains differ. The chicken's telencephalon, like the human telencephalon, is divided into two distinct hemispheres, but the lateralization of functions and the specific structures within the pallium differ between the two species. These differences highlight the unique adaptations and cognitive abilities that have evolved in both humans and chickens.

The human cerebral cortex is larger, but the brains of mammals and birds are similar

The human cerebral cortex is larger than a chicken's, but the brains of mammals and birds share many similarities. The avian telencephalon, like its human counterpart, is organised into two distinct hemispheres, with each hemisphere dominating certain functions. The left hemisphere of the brain, for instance, dominates activities that require the separation of important stimuli from distracting ones, while the right hemisphere is more easily distracted and has a broad attention span. It also dominates fear and escape responses. This lateralization of the brain is also observed in humans, where the right and left hemispheres divide up some tasks rather than duplicating the work.

The avian brain also has a pallium, which corresponds to the mammalian cerebral cortex and is responsible for the cognitive functions of birds. The pallium is made up of several major structures, including the hyperpallium, a dorsal bulge found only in birds, and the nidopallium, mesopallium, and archipallium. The avian pallium has been found to support cognitive abilities similar to, and in some cases more advanced than, those of many mammals. This challenges the old dichotomy that mammals think with their neocortex while birds act on instincts rooted in their basal ganglia.

The similarities between the brains of mammals and birds make chickens a useful model for understanding human brains, particularly in the study of early brain development. For example, the hindbrain of a chicken embryo has been found to contain neural stem cells (NSCs) that give rise to neurospheres in culture, preserving hindbrain-specific markers such as Hox genes and the neurotransmitter 5-hydroxytryptamine. Hox genes are responsible for foetal development and control things like breathing and heart rate.

Additionally, the external morphology of the brain in certain chicken breeds, such as the Crested Padovana chicken, differs from that of other chicken breeds. In these breeds, the forebrain and the hindbrain appear more separated from each other, giving the brain an hourglass shape.

The forebrain and hindbrain are more separated in crested Padovana chickens

The brain of a chicken is remarkably similar to the brains of mammals and other birds. The avian telencephalon, for example, is organised into two distinct hemispheres, much like its human counterpart.

However, the crested Padovana chicken (Gallus gallus f.d.) is a unique breed with a distinctive skull shape. The external morphology of its brain is different from that of other chicken breeds. The forebrain and the hindbrain are more separated from each other, and the cerebral hemispheres are extruded into the anterodorsal region of the skull, giving the brain the shape of an hourglass. This morphological curiosity may be due to the fact that the feather crest of the WCP is placed on a bony protuberance of frontal bones, which is not always completely calcified.

This unusual skull shape is observed in both black-coloured and chamois-coloured Padovana chickens. Black-coloured Padovana chickens have a distinct bony protuberance, while chamois-coloured Padovana chickens have a similar-sized crest but with less conspicuous cranial protuberances.

The crested Padovana chicken is a breed with a long history of pure breeding. Its unique skull and brain morphology make it an interesting subject for research into neuroanatomical evolution, brain-skull integration, and skull and brain deformities. By studying chickens with cerebral elongation, scientists may gain a better understanding of skull and brain dysplasia and cerebral hernia development.

Additionally, the crested Padovana chicken provides a promising comparative system for investigating the emergence of novel brain and skull morphologies. The differences in the morphology of the Padovana chicken's brain compared to other chicken breeds may be due to the presence of the cranial protuberance. Padovana chickens without a cranial protuberance do not show the same level of separation between the forebrain and hindbrain.

The avian brain stem contains Hox genes, which are responsible for foetal development

The avian brain stem contains Hox genes, which play a crucial role in foetal development. This region, located just anterior to the spinal cord, is small yet highly significant functionally. Hox genes are responsible for specifying the hindbrain territory and regulating its properties in vertebrates. During embryonic development, the vertebrate hindbrain undergoes segmentation, dividing the neuroepithelium into compartments or rhombomeres along the anteroposterior (AP) axis. This early cellular partitioning is essential for establishing the initial neuronal organization and diversification.

The Hox genes in the avian brain stem are specifically involved in controlling vital functions such as breathing and heart rate. They also contribute to the formation of the axial skeleton and the musculature of the trunk. In chickens (Gallus gallus), the median extended amygdala, which is part of the avian brain, plays a role in male sexual behaviour. Additionally, the avian telencephalon, similar to humans, is organised into two distinct hemispheres, with lateralised functions such as song learning, vision, and auditory processing.

Research on chicken brains has provided valuable insights into early brain development due to their accessibility and similarities to mammalian and human brains. The crested Padovana chicken (Gallus gallus f.d.), for example, exhibits unique skull morphology, with a distinct bony protuberance. This physical characteristic results in a more pronounced separation between the forebrain and the hindbrain, giving the brain an hourglass shape.

Hox genes have been extensively studied in Drosophila, where they are associated with the visible segmentation of the embryo and the establishment of regionalised neuronal identity. These genes are highly conserved in evolution, playing similar roles in the brain development of vertebrates, including chickens. Abnormalities in Hox gene expression during development can lead to issues such as anterior displacement of the otic vesicles, expansion of the anterior hindbrain, and spinal cord anomalies.

Understanding the expression patterns and functions of Hox genes in the avian brain stem provides valuable insights into the complex process of brain development and the underlying genetic mechanisms that govern it. By studying avian models, researchers can gain a better understanding of human brain development and various disorders associated with Hox genes.

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