Chemoaffinity hypothesis

The Chemoaffinity hypothesis states that neurons make connections with their targets based on interactions with specific molecular markers^[1] 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.^[1]

Sperry's experiments

Roger Wolcott Sperry pioneered the inception of the Chemoaffinity Hypothesis following his experiments on the African Clawed Frog.^[2] He removed the eye of a frog and rotated it 180°, Sperry then replaced the eye and the visual nervous system repaired itself.^[3] However, the frog now had inverted vision; for example, the subject extended its tongue in the opposite direction to the food source stimulus.^[4]

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.^[2]

See also

• Neural development

References

1. ^ ^{a b} "BIO254:Chemoaffinity". OpenWetWare. http://openwetware.org/wiki/BIO254:Chemoaffinity. Retrieved 1 September 2011. ^{[unreliable source?]}
2. ^ ^{a b} Ronald L. Meyer (1998). "Roger Sperry and his Chemoaffinity Hypothesis". Neuropsychologia 36 (10): 957–980. doi:10.1016/S0028-3932(98)00052-9. PMID 9845045. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0D-3V7S6N6-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=9b889f47fd1cf9a5c398cc8592bc816b. 
3. ^ Ferry, Gorgina (10 June 1989). "The nervous system repairs to the network". NewScientist (1668). http://www.newscientist.com/article/mg12216687.200-the-nervous-system-repairs-to-the-network.html. Retrieved 1 September 2011. (subscription required)
4. ^ Roger W. Sperry (1943). "Effect of 180 Degree Rotation of the Retinal Field on Visuomotor Coordination" (PDF). The Journal of Experimental Zoology 92 (3): 263–279. doi:10.1002/jez.1400920303. http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc49212/nrcc49212.pdf. Retrieved 2009-09-01.