Is nasal delivery a viable option for trophic factor delivery to the brain?

Neurotrophic factors have great potential as neuroprotective drugs for Parkinson's disease but their delivery from the blood to the brain is poor, necessitating neurosurgical strategies to achieve therapeutic levels at brain sites.  Intranasal administration has been suggested as a non-invasive alternative to bypass the blood-brain barrier and directly target brain sites by mechanisms that are still unclear.  Is nasal application a viable option for delivery of neurotrophic factors to the brain?"