Fluorescence imaging of lymphatic outflow of cerebrospinal fluid in mice

摘要

Cerebrospinal fluid (CSF) is known to be reabsorbed by the lymphatic vessels and drain into the lymph nodes (LNs) through peripheral lymphatic vessels. In the peripheral lymphatics, the contractile pumping action of lymphangions mediates lymph drainage; yet it is unknown whether lymphatic vessels draining cranial and spinal CSF show similar function. Herein, we used non-invasive near-infrared fluorescence imaging (NIRFI) to image (i) indocyanine green (ICG) distribution along the neuraxis and (ii) routes of ICG-laden CSF outflow into the lymphatics following intrathecal lumbar administration. For intrathecal injection, a 31-gauge needle was inserted between L5 and L6 vertebrae and a tail flick response was referenced as indication of correct position of the needle into the intradural space. Imaging agents were injected immediately after a tail flick. A volume of 10 to 30μl of 645μM of ICG was injected. We demonstrate lymphatic contractile function in peripheral lymphatics draining from the nasal lymphatics to the mandibular LNs. In addition, we observed afferent sciatic lymphatic vessels, which also show contractile activity and transport spinal CSF into the sciatic LNs. NIRFI could be used as a tool to probe CSF pathology including neurological disorders by imaging CSF outflow dynamics to lymphatics.