chemoaffinity hypothesis
{{short description|Theory that neurons initially form connections based on molecular markers}}
In neuroscience, the chemoaffinity hypothesis states that neurons make connections with their targets based on interactions with specific molecular markers{{cite web|title=BIO254:Chemoaffinity|url=http://openwetware.org/wiki/BIO254:Chemoaffinity|publisher=OpenWetWare|accessdate=1 September 2011}}{{unreliable source?|date=September 2011}} 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.
Sperry's experiments
Roger Wolcott Sperry pioneered the inception of the chemoaffinity hypothesis following his 1960s experiments on the African clawed frog.{{cite journal |journal= Neuropsychologia |year=1998 |volume=36 |issue=10 |pmid= 9845045 |pages=957–980 |title= Roger Sperry and his Chemoaffinity Hypothesis |author= Ronald L. Meyer |doi=10.1016/S0028-3932(98)00052-9 |s2cid=5665287 }} He would remove the eye of a frog and reinsert it rotated upside-down—the visual nervous system would eventually repair itself,{{cite journal|last=Ferry|first=Gorgina|title=The nervous system repairs to the network|journal=New Scientist|date=10 June 1989|issue=1668|url=https://www.newscientist.com/article/mg12216687.200-the-nervous-system-repairs-to-the-network.html|accessdate=1 September 2011}}{{subscription required}} and the frog would exhibit inverted vision. In other words, the initial eye orientation is reversed such that the dorsal part of the eye becomes the ventral side, and the ventral side becomes the dorsal side; when a food source was put above the frog, the frog would extend its tongue downwards.{{cite journal |journal= The Journal of Experimental Zoology |year=1943 |volume=92 |issue=3 |pages=263–279 |title= Effect of 180 Degree Rotation of the Retinal Field on Visuomotor Coordination |author= Roger W. Sperry |doi=10.1002/jez.1400920303|bibcode=1943JEZ....92..263S }} In follow-up experiments, the eye was detached and rotated 180° like before, but additionally the optic nerve was cut—the results were identical.{{citation needed|date=December 2011}}
Sperry hypothesized that each individual optic nerve and tectal neuron used some form of chemical marker to dictate the connectivity during development. Sperry reasoned that when the eye had been rotated, each optic fiber and tectal neuron possessed cytochemical labels that uniquely denoted their type and position, and thus optic fibers utilize these labels to selectively navigate to their matching target cell via a sort-of chemotaxis.
See also
References
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