General Summary

Abstract

The regenerative properties of central noradrenaline (NA), dopamine (DA) and indolamine (IA) neurons in the adult rat brain have been studied using irides implanted in various brain sites as targets. 1. The iris transplants were readily revascularized from the brain vessels, and there was a high degree of survival. The recirculation started already at day one, was well developed at day five, and was fully developed after 2–3 weeks. The cerebral implant received its blood supply from the pial vessels as well as directly from the brain parenchyma. It is concluded that the brain is an excellent transplantation site. 2. The vital parts of the transplanted hides (usually almost the entire iris) exert striking attracting and organizing influences on the regrowing sprouts of lesioned central monoamine neurons, and it seems that this is due both to an attraction of the growing, sprouts across the necrosis, and to a stimulation of the growth and arborization of new fibres within the transplant. 3. In the caudal diencephalon the transplanted iris is invaded by regenerating sprouts from lesioned central NA and DA axons. The sprouting NA fibres-primarily originating from the locus coeruleus axons in the dorsal tegmental bundle-expand rapidly over the entire iris, and within 3 to 4 weeks they form plexuses that much resemble the normal autonomic ground plexus of the normal iris. This reinnervation pattern was partly found to be permanent. The sprouting central DA fibres-originating from the MFB-grow abundantly into the iris at the site of contact with the MFB, but in contrast with the NA fibres they remain restricted to an area of the iris close to the ingrowth site. 4.