Innervation of peripheral tissue grafts by locus coeruleus in oculo: Only partial correspondence with degree of sympathetic innervation

The locus coeruleus (LC) area from fetuses was homologously an bilaterally grafted to the sympathetically denervated anterior eye chamber of adult rats. After 6 weeks, when the noradrenaline (NA) neurons of the LC grafts had produced a halo of NA fibers on the host iris and had stopped growing, various peripheral tissues were placed in the eye chamber in contact with the LC graft.Using Falck-Hillarp fluorescence histochemistry we found that grafts ofvas deferens andsmall intestine retained a fairly normal histological appearance and received numerous LC fibers with an organotypical distribution but with somewhat lower density than the sympathetic adrenergic innervation in situ.Pineal grafts became richly supplied with LC fibers.Submaxillary salivary glands became innervated by the LC grafts whereassublingual salivary glands did not. The difference mimicks the fate of such grafts when reinnervated by normal sympathetic adrenergic nerves in oculo. Adultauricle grafts as well as embryonicwhole hearts showed good histological survival in oculo but neither of them received any fluorescent fibers from the mature LC grafts. The embryonic heart grafts were beating.Fetal iris grafts did not increase their size in the eye but received a limited number of LC fibers. Bothfetal andadult Harderian gland grafts remained totally devoid of LC fibers in oculo.We conclude that several different sympathetically innervated glandular and muscular tissue grafts can elicit a growth response in the NA neurons of LC upon direct contact. The two sympathetically non-innervated tissues examined (sublingual and Harderian gland) did not become innervated. However, also heart tissue, which is normally sympathetically innervated, was not invaded by LC fibers, suggesting that other and/or additional factors than the sympathetic status of the target grafts regulate ingrowth of LC fibers.