Chemoaffinity hypothesis
Encyclopedia
The Chemoaffinity hypothesis states that neuron
s make connections with their targets based on interactions with specific molecular markers and, therefore, that the initial wiring diagram
of an organism is (indirectly) determined by its genotype
. The markers are generated during cellular differentiation
and aid not only with synaptogenesis
, but also act as guidance cues for their respective axon
.
pioneered the inception of the Chemoaffinity Hypothesis following his experiments on the African Clawed Frog
. He removed the eye of a frog and rotated it 180°, Sperry then replaced the eye and the visual nervous system repaired itself. However, the frog now had inverted vision; for example, the subject extended its tongue in the opposite direction to the food source stimulus.
Sperry concluded that each individual optic nerve
and tectal neuron used some form of chemical marker which dictated their connectivity during development. He reasoned that when the eye had been rotated, each optic fiber and each tectal neuron possessed cytochemical labels that uniquely denoted their neuronal type and position and that optic fibers could utilize these labels to selectively navigate to their matching target cell, hence the visuomotor impairment.
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s make connections with their targets based on interactions with specific molecular markers and, therefore, that the initial wiring diagram
Wiring diagram
A wiring diagram is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified shapes, and the power and signal connections between the devices. A wiring diagram usually gives more information about the relative position and...
of an organism is (indirectly) determined by its genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
. The markers are generated during cellular differentiation
Cellular differentiation
In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...
and aid not only with synaptogenesis
Synaptogenesis
Synaptogenesis is the formation of synapses. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development...
, but also act as guidance cues for their respective axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
.
Sperry's experiments
Roger Wolcott SperryRoger Wolcott Sperry
Roger Wolcott Sperry was a neuropsychologist, neurobiologist and Nobel laureate who, together with David Hunter Hubel and Torsten Nils Wiesel, won the 1981 Nobel Prize in Medicine for his work with split-brain research....
pioneered the inception of the Chemoaffinity Hypothesis following his experiments on the African Clawed Frog
African clawed frog
The African clawed frog is a species of South African aquatic frog of the genus Xenopus. Its name is derived from the three short claws on each hind foot, which it uses to tear apart its food...
. He removed the eye of a frog and rotated it 180°, Sperry then replaced the eye and the visual nervous system repaired itself. However, the frog now had inverted vision; for example, the subject extended its tongue in the opposite direction to the food source stimulus.
Sperry concluded that each individual optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
and tectal neuron used some form of chemical marker which dictated their connectivity during development. He reasoned that when the eye had been rotated, each optic fiber and each tectal neuron possessed cytochemical labels that uniquely denoted their neuronal type and position and that optic fibers could utilize these labels to selectively navigate to their matching target cell, hence the visuomotor impairment.