Cerebrospinal fluid flow extends to peripheral nerves further unifying the nervous system

Area of Science:

• Neuroscience
• Biomedical Engineering

Background:

• Cerebrospinal fluid (CSF) is vital for central nervous system (CNS) homeostasis, nutrient supply, and waste removal.
• The extent of CSF circulation within the peripheral nervous system (PNS) remains incompletely understood.

Purpose of the Study:

• To investigate the distribution and transport of cerebrospinal fluid (CSF) from the CNS to the PNS.
• To determine the size limitations for CSF transport between the CNS and PNS.

Main Methods:

• Infusion of 1.9-nanometer and 15-nanometer gold nanoparticles into the lateral cerebral ventricle of the CNS.
• Tracing nanoparticle distribution within the PNS using advanced imaging techniques.
• Evaluating the ability of systemically administered nanoparticles to cross the blood-brain/nerve barrier.

Main Results:

• 1.9-nanometer gold nanoparticles, similar in size to CSF proteins, successfully transited from the CNS to the PNS via root attachment zones.
• Nanoparticles distributed within the PNS perineurium and endoneurium, reaching distal peripheral nerve axoplasm.
• Larger 15-nanometer nanoparticles were restricted to the CNS, forming "dye-cuffs," indicating size-dependent transport limitations.
• Intravenously administered 1.9-nanometer nanoparticles could not cross the blood-brain or blood-nerve barriers.

Conclusions:

• Cerebrospinal fluid (CSF) actively circulates throughout the peripheral nervous system (PNS), not just the CNS.
• This CNS-PNS CSF pathway has significant implications for understanding nervous system homeostasis.
• The findings open new avenues for neural drug delivery and therapeutic strategies targeting both CNS and PNS disorders.