Growth of locus coeruleus neurons in oculo independent of simultaneously present adrenergic and cholinergic nerves in the iris.

Fetal brain tissue pieces containing locus coeruleus (LC) neurons were grafted to the anterior eye chamber alone or together with other grafts (irides, sympathetic ganglia or additional LC) in the presence of the sympathetic and parasympathetic part of the autonomic ground plexus of the iris. Specimens were analyzed with quantitative fluorescence microscopy and uptake of [3H]metaraminol. LC neurons were shown to grow independently of the simultaneous presence of sympathetic fibers in oculo in the following three experimental situations: 1. Fetal LC grafted to normal eyes, analyzed after cessation of the production of the halo of fluorescent fibres on the host irides. 2. Maturated LC neurons in which growth is reinitiated by addition of an iris transplant which becomes completely innervated. 3. Fetal LC neurons placed on or opposite to iris transplants that in turn were introduced into the eye chamber 1 month before. All LC grafts produced halos of fluorescent fibres on both host irides and iris transplants in a restricted zone. Fetal LC grafts produced fluorescent nerve fibres on host irides independent of the removal of the parasympathetic fibres in the irides. Fetal LC grafts were not significantly inhibited in their fibre production on irides where maturated LC grafts had already formed a halo of densely packed fluorescent fibres. When two fetal LC grafts were introduced simultaneously into the same eye chamber both were able to produce fluorescent fibres together on the host iris. Sympathetic ganglion transplants formed normal looking adrenergic plexuses on host irides that were already carrying LC grafts with halos of fluorescent fibres. In conclusion, the fibre production of LC neurons in oculo is independent of the presence of sympathetic, and probably also parasympathetic, and maturated central NA nerves.