Endogenous nerve growth factor stimulation: effects on auditory pathway neural cells in a mouse model.

OBJECTIVE: In the present study, we investigated whether high-pressure hypotonic saline solution (Hphss) affects the basal level of Nerve Growth Factor (NGF) and expression of receptors in the cochlea, bark earing, retina, and visual cortex. MATERIALS AND METHODS: For this study, we used three weeks old female Sprague Dawley (SD) rats (n = 12). Rats were housed in polypropylene cages and were kept under standard conditions (12 h light:12 h dark cycle) with free access to water and food (Purina chow food). A specific dispenser was employed to deliver sterile hypotonic saline at high pressure (pressing emission level (PEL): 7 g/s; emission time (ET): 0.5 s). Rats were divided into two groups: untreated (n = 6) and treated with Hphss (n = 6), three times per day, for 10 consecutive days. Treatment was performed in both nostrils with 50 µl of Hphss using a microsyringe equipped with a plastic tip. RESULTS: We observed a significant enhancement in the level of NGF in the cochlea and bark earing, but not in the retina and visual cortex. This is likely because the nasolacrimal duct pathway does not appear to have an effect on the retina, and the visual cortex appears to be too far from the cribriform plate to be reached by nasal NGF. CONCLUSIONS: This treatment can significantly protect and/or delay degeneration of cochlear auditory NGF-target cells. It is free from side effects and can be used in chronic diseases for as long as needed. It remains to be investigated whether the effects of short-term therapy are long-lasting, or if the treatment must be repeated.