ABSTRACT
This chapter presents a summarized account of studies on exterotrophic neuronal functions which support the idea that axoplasmic transport is an important mediator of trans-synaptic target cell maintenance. The idea that nerve cells exert trophic influences on themselves, as well as on the target cells they innervate, have a long history extending back to the mid-19th century. A classical illustration of neurotrophic influences which exist in the absence of nerve impulse activity is the finding that denervation changes develop sooner if the nerve is cut close to, rather than far from, the innervated structure. Identification of neural substances influencing target cell properties has been approached mainly by attempting artificial replacement of materials which are missing from noninnervated embryonic cells maintained in tissue culture. While in recent years a considerable amount of information has been gathered on the neural regulation of certain skeletal muscle properties, knowledge gained on the molecular mechanisms behind trophic phenomena has been meager.
