Drainage of cerebral interstitial fluid into deep cervical lymph of the rabbit

Lymph from the jugular lymph trunks of anesthetized rabbits has been continuously collected and radioiodinated albumin (RISA) therein estimated after microinjection of 1 microliter of 131I-albumin into the caudate nucleus, after single intraventricular injections, and during intraventricular infusions. Comparison of lymph at 7 and 25 h after intracerebral microinjection with efflux of radioactivity from whole brain suggests that about 50% of cleared radioactivity goes through lymph. Concentrations, normalized to cerebrospinal fluid (CSF), were much higher in lymph and retropharyngeal nodes after brain injection than after CSF injection or infusion. Also after brain injection, lymph and nodes contained more activity on injected side in contrast to lack of laterality after CSF administration. Calculation suggests that less than 30% of RISA cleared from brain can do so via a pool of well-mixed CSF. Analysis of tissues is compatible with much RISA draining by bulk flow via cerebral perivascular spaces plus passage from subarachnoid space of olfactory lobes into submucous spaces of nose and thus to lymph.