Locus coeruleus: fibre growth regulation in oculo.

Locus coeruleus (LC) neurons from fetal and young rats survived homotransplantation to the anterior eye chamber. The outgrowth of LC fibres on sympathetically denervated host irides could be quantified precisely using Falck-Hillarp fluorescence histochemistry and [3H]metaraminol uptake. Fetal LC neurons survive better than postnatal ones and produced fibres for one month in oculo: by then )0-50% of the area of the host iris was innervated. After intraocular maturation of the CNS graft the fibre amount on the iris remained constant. Introduction of an iris graft contacting a mature LC graft immediately stimulated the LC to a complete (100%) reinnervation of the iris graft without any change of the restricted innervated area already formed on the host iris. The outgrowth of LC fibres on irides was not influenced by the presence or absence of sympathetic or parasympathetic nerves or by nerve growth factor or its antiserum. We conclude that an iris transplant offers a specific growth stimulus for the LC graft and that this stimulus is not present in the normal host iris. The nature of this stimulus is unknown but may involve the sensory denervation of the iris graft.