Molecules secreted from target and non-target tissues promote and repel sympathetic fiber distribution in vitro.

By using an in vitro assay system detecting the ability of nerve terminals to recognize the test molecules, I found that sympathetic fibers distributed densely on substrates coated with the particulate (adheron) fractions of growth conditioned medium from expansor secundariorum (target tissue), but did not on substrates coated with those from skeletal muscle (non-target). This result suggests that adheron particles are involved in the haptotactic process of specific sympathetic innervation on the target tissue.