Nerve growth factor-induced stimulation of dorsal root ganglion/spinal cord co-grafts in oculo: enhanced survival and growth of CGRP-immunoreactive sensory neurons

Intraocular co-grafts of rat fetal spinal cord and dorsal root ganglia were used to examine the enhanced survival, growth, and differentiation of sens ory neurons by nerve growth factor. E14 lumbar spinal segments were implant ed into the anterior eye chamber of capsaicin-pretreated rats. Two weeks la ter, an E14 dorsal root ganglion was implanted beside the spinal cord graft . Nerve growth factor or vehicle was injected weekly for 4 weeks into the a nterior eye chamber. Go-grafts were examined weekly and, at 6 weeks, proces sed for calcitonin gene-related peptide (CGRP) immunofluorescence. No diffe rences in overall size were determined for the grafts. Go-grafts treated wi th nerve growth factor contained many more CGRP neurons (19.4 cells/20 mu m ) that were significantly larger (mean 764 mu m(2)) than neurons from contr ol co-grafts (8.6 cells/20 mu m; mean 373 mu m(2)). In co-grafts treated wi th nerve growth factor, CGRP-immunoreactive fibers were extensive in the do rsal root ganglion, adjacent iris, and spinal cord compared to control co-g rafts. A few CGRP-positive motoneurons were observed in the spinal cord, bu t no differences in number or size of motoneurons were found. The current r eport demonstrates that spinal cord and dorsal root ganglia can be co-graft ed in oculo for long periods of time. Many dorsal root ganglion neurons sur vive and send peripheral processes into the iris and central processes into the spinal cord under the influence of exogenous nerve growth factor. The intraocular graft paradigm can be of use to further examine the role of neu rotrophic factors in regulating or modulating dorsal root ganglion and spin al cord neurons.