Ocular Nerve Growth Factor (NGF) and NGF Eye Drop Application as Paradigms to Investigate NGF Neuroprotective and Reparative Actions

The eye is a central nervous system structure that is uniquely accessible to local treatment. Through the ocular surface it is possible to access the retina, optic nerve, and brain. Animal models of retina degeneration or optic nerve crush could thus serve as tools to investigate whether and how factors, which are anterogradely or retrogradely transported through the optic nerve, might contribute to activate neuroprotection, and eventually regeneration. Among these factors, nerve growth factor (NGF) plays a crucial role during development of the visual system, as well as during the entire life span, and in pathological conditions. The ability of NGF to exert survival and trophic actions on retina and brain cells when applied intraocularly, and topically as eye drops is critically reviewed here, together with the effects of ocular neurotrophins on neuronal pathways influencing body rhythm, cognitions, and behavioural functions. The latest data from animal models and humans are presented and the mechanism of action of ocularly administered NGF is discussed. NGF eye drops is proposed as an experimental strategy to investigate the role and cellular targets of neurotrophins in the mechanism(s) underlying neurodegeneration/regeneration, and their involvement in the regulation of neurological and behavioural dysfunctions.