The guidance of regenerating central axons in the goldfish

A small body of evidence has been amassed which indicates that diffusible substances can play a role in neurite guidance. This evidence has been mainly derived from in vi tro studies of target tissue-influences on neuronal growth, as well as with factors such as nerve growth factor, spinal cord growth factor, and ci l iary ganglion growth and survival factors. In each instance, these factors are diffusible, since they are present in tissue culture medium and exert their effects from a distance. These substances produce one or more of the following effects on neurite growth: I) enhancement of neurite growth, 2) apparent chemotropism, 3) restrict the areas of neurite growth. All of these effects can result in fine or coarse guidance of neurite growth. However, what should be considered is that even though these substances are diffusible, they may exert their actions via neurite and/or growth cone-substratum interactions. Thus even though diffusible substances appear to play a role in neurite guidance, they should be considered in conjunction with possible substratum interactions, or diffusible substance-substratum interactions.