Provision of brain-derived neurotrophic factor via anterograde transport from the eye preserves the physiological responses of axotomized geniculate neurons

The neurotrophic factors of the nerve growth factor family (neurotrophins) have been shown to promote neuronal survival after brain injury and in various models of neurodegenerative conditions. However, it has not been determined whether neurotrophin treatment results in the maintenance of function of the rescued cells. Here we have used the retrograde degeneration of geniculate neurons as a model system to evaluate neuronal rescue and sparing of function after administration of brain-derived neurotrophic factor (BDNF). Death of geniculate neurons was induced by a visual cortex lesion in adult rats, and exogenous BDNF was delivered to the axotomized geniculate cells via anterograde transport after injection into the eye. By microelectrode recordings from the geniculate in vivo we have measured several physiological parameters such as contrast threshold, spatial resolution (visual acuity), signal-to-noise ratio, temporal resolution, and response latency. In control lesioned animals we found that geniculate cell dysfunction precedes the onset of neuronal death, indicating that an assessment of neuronal number per se is not predictive of functional performance. The administration of BDNF resulted in a highly significant cell-saving effect up to 2 weeks after the cortical damage and maintained nearly normal physiological responses in the geniculate. This preservation of function in adult axotomized neurons suggests possible therapeutic applications of BDNF.