Influence of substratum on the retrograde response of the rat superior cervical ganglion in vitro.
To study the role of the substratum on the retrograde response of injured peripheral noradrenergic neurons, embryonic rat superior cervical ganglia were grown in vitro on four different substrata: collagen, poly-D-lysine, fibronectin, or tissue culture plastic. The rate and pattern of neurite outgrowth were determined for a 2-week period following injury with explantation. In addition, changes in the activity of tyrosine hydroxylase, the neurotransmitter enzyme that has been shown to be altered during the retrograde response, was measured. The pattern and rate of neurite outgrowth varied directly with the ability of the neuronal growth cone to adhere to the underlying substratum. On poly-D-lysine and collagen, neurites grew as individual processes with extensive branching, whereas on plastic and fibronectin there was little branching and marked neurite fasciculation. The rate of neurite elongation on poly-D-lysine (0.75 mm/day) was faster than on collagen (.53 mm/day), fibronectin (0.33 mm/day), or plastic (0.15 mm/day). On plastic, neurons of the superior cervical ganglion showed a severe and prolonged retrograde response as characterized by a reversible decrease in tyrosine hydroxylase activity to 28% of control which persisted until the 10th day in culture. In contrast, on collagen, there was a smaller, but still significant, decrease in tyrosine hydroxylase activity to 73% of control which lasted only 5 to 6 days. On poly-D-lysine, there was no measureable change in the activity of that enzyme after injury. These studies provide quantitative evidence showing an important role of the microenvironment, and in particular the extracellular matrix, in determining the ability of neurons to respond successfully to injury.