GROWTH OF TRIGEMINAL NEURITES AND INTERACTIONS WITH CORNEAL CELLS IN EMBRYONIC CHICK ORGAN-CULTURES

The investigation of interactions between growing neurites and target cells during the development of the sensible corneal innervation is of crucial importance for understanding certain corneal diseases which a re related to abnormal patterns of innervation. The purpose of the pre sent work was to establish a culture system of cornea and trigeminal n eurons and to examine interactions between these tissues. The response s of neurons derived from explanted embryonic chick trigeminal ganglia to co-explanted slices prepared from embryonic cornea were monitored over several days in culture. The growth of trigeminal fibers, but not of neurites derived from control tissues such as trigeminal mesenceph alic nucleus or ciliary ganglion, was preferentially directed towards the co-cultured corneal slices. The ingrowth of trigeminal axons into the cornea was followed by formation of elaborate axonal terminal bran ches. Individual dissociated trigeminal neurons of pseudo-unipolar or bipolar classes developed their typical morphologies in culture. In co -cultures with corneal slices, they reacted to the corneal co-explant by frequently retracting some branches and forming or elongating other ones, which were predominantly directed towards the target tissue. In addition, the presence of a co-explanted trigeminal ganglion increase d the rate of growth in the dissociated trigeminal neurons. The effect was not additive when cornea was present. Antibodies against nerve gr owth factor (NGF) and the low-affinity p75-NGF receptor (LANGFR) revea led that trigeminal ganglion cells support neuritic growth by secretin g NGF, whereas corneal cells secrete additional factor(s) which act vi a the LANGFR.