Glial cell line-derived neurotrophic factor was first described as a trophic factor for developing dopamine neurons. However, it has been shown that glial cell line-derived neurotrophic factor messenger RNA is also expressed in several areas of the developing brain and spinal cord, suggesting that it may have additional roles in the nervous system. Intraocular transplantation of neural tissue provides a unique method to examine in vivo effects of trophic factors. We have therefore studied the effects of glial cell line-derived neurotrophic factor on spinal cord survival and development following grafting to the anterior chamber of the eye of adult rats. We used spinal cord tissue from fetal stages (embryonic days 14 and 18) and postnatal days 1 and 14 as donors. The spinal cord tissue was allotransplanted to the anterior eye chamber of Sprague-Dawley host rats after incubation in buffered saline containing 100 micrograms glial cell line-derived neurotrophic factor/ml or 100 micrograms cytochrome C/ml. One group of postnatal day 1 spinal cord grafts was also treated with concentrations of 20 and 10 micrograms glial cell line-derived neurotrophic factor/ml. In all cases, 5 microliters of the same solution was injected into the anterior eye chamber on postgrafting days 5, 10, 15 and 20 (total amounts 0.5, 0.1 and 0.05 microgram/eye/injection, respectively). We found that all glial cell line-derived neurotrophic factor-treated spinal cord grafts grew more than controls. The effect of glial cell line-derived neurotrophic factor was most prominent in grafts from newborn rats. In these grafts we found a dose-dependent effect of glial cell line-derived neurotrophic factor on growth. Moreover, grafts treated with the highest dose (0.5 microgram) grew to sizes exceeding the initial size at transplantation. In these transplants we also found greater numbers of large neurons compared to controls. Glial fibrillary acidic protein immunoreactivity, in contrast, showed increased gliosis in controls. Similar results were found with syngeneic spinal cord postnatal day 1 grafts in Fisher hosts. Spinal cord tissue grafts from two-week-old rats treated with the highest glial cell line-derived neurotrophic factor dose every fifth day, through day 35 postgrafting, responded with increased growth and less necrotic tissue compared with controls; however, we could not detect neurofilament immunoreactivity in these transplants. Taken together, these results suggest that glial cell line-derived neurotrophic factor may be a potent trophic factor for neurons in the spinal cord and in spinal cord transplants. Of particular importance is that glial cell line-derived neurotrophic factor treatment can be used to obtain survival of postnatal spinal cord tissue, that would otherwise show minimal or no survival. Thus, glial cell line-derived neurotrophic factor allows successful transplantation of more mature spinal cord tissue, which may have important implications for both basic and clinical neuroscience.