Intranasal delivery of siRNA to the olfactory bulbs of mice via the olfactory nerve pathway.

Adopting RNAi technology for targeted manipulation of gene expression in the central nervous system (CNS) will require delivery of RNAi constructs to the CNS followed by cellular transfection and induction of the RNAi machinery. Significant strides have been made in enhancing RNAi transfection and tailoring knockdown toward specific gene targets, however, delivery of the RNAi constructs to the CNS remains a significant challenge. One possible solution for targeting siRNA to the CNS is intranasal administration, which noninvasively delivers a variety of compounds to the CNS. The current study examined delivery of fluorescently labeled siRNA from the nasal cavity to the olfactory bulbs via the olfactory nerve pathway. siRNA was observed along the length of the olfactory nerve bundles, from the olfactory mucosa of the nasal cavity to the anterior regions of the olfactory bulbs. In the olfactory mucosa, labeled siRNA was found within the olfactory epithelium, Bowman's glands, and associated with blood vessels and bundles of olfactory nerves. In the olfactory bulbs, siRNA was observed in the olfactory nerve, glomerular and mitral cell layers. These results demonstrate a role of the olfactory nerve pathway in targeting siRNA to the olfactory bulbs. Additional investigations will be required to assess the distribution of intranasal siRNA to additional regions of the brain and explore the capacity of the delivered siRNA to silence gene expression in the CNS.