Uptake of fluorescein isothiocyanate-labelled dextran into the CSF after intranasal and intravenous administration to rats.

With the growing number of patients suffering from central nervous system (CNS) diseases a suitable approach for drug targeting to the brain becomes more and more important. In the present study, the contribution of the nose-CSF pathway to the uptake of the model drug fluorescein isothiocyanate-labelled dextran with a molecular weight of 3.0 kDa (FD3) into the CSF was determined in rats. FD3 was administered intranasally (489 microg/rat) and by intravenous infusion (24.4 microg/ml; 119 microg/rat) in the same set of animals (n=6). Blood samples were taken from the tail vein and CSF was sampled by cisternal puncture using a stereotaxic frame. The contribution of the olfactory pathway to the uptake of FD3 into the CSF was determined by comparing the AUCCSF/AUCplasma ratios after intranasal and after intravenous application of FD3 mimicking the blood levels after intranasal delivery. No significant difference was observed between the AUCCSF/AUCplasma ratios of FD3 after intranasal administration (1.33+/-0.40%) and intravenous infusion (1.03+/-0.56%). This indicates that in rats about 1% of the amount of FD3 in plasma reaches the CSF both after nasal and intravenous administration and that no direct transport of FD3 from the nose-CSF could be found.

Clearance of brain edema and macromolecules through the cortical extracellular space.

The transit routes of fluid and particulate matter through brain tissue remain unclear. The object of this study was to examine the movement of macromolecules through brain tissue to further clarify the clearance pathways of edema proteins as they migrate toward the cortex. For this purpose, albumin solution (20 microliters rat albumin diluted to 65 mg/ml with mock cerebrospinal fluid (CSF)) was intracerebrally infused into the caudate putamen, and the migration through brain tissue as well as through the ultrastructure of the cortical surfaces was explored using an immunocytochemical technique. The authors observed immunoreactive product on the glial limitans and pial lining as well as in the extracellular space of the cortical neuropil at 24 hours postinfusion, confirming that the protein had reached the cortical surface. To confirm the efflux of macromolecules into the subarachnoid CSF, 71,200 D fluorescein isothiocyanate-dextran (FITC-dextran 71,200) was infused; cortical surfaces of brains removed en bloc as well as coronal sections were macroscopically observed under ultraviolet illumination at 15 minutes and 24 hours postinfusion. It was observed that infused FITC-dextran 71,200 mainly localized in the cortical white matter and caudate putamen of the infusion site at 15 minutes postinfusion and by 24 hours was distributed in the entire cortex of the infused hemisphere. However, the dynamics of lower-molecular-weight substances was completely different. The spatial distribution of FITC-dextran 4400 diverged upward toward the cortical surface and spread more extensively than FITC-dextran 71,200. These observations were consistent with a diffusion process as the spread of the tracer was dependent upon molecular size. These studies provide compelling evidence that a process other than bulk flow was involved in the spread of macromolecules through the extracellular space of the normal cortical neuropil to sink into the subarachnoid space. It was concluded that the CSF pathway via the extracellular space of the cortical neuropil is a primary route for clearance of extracellular edema proteins to the subarachnoid space and that diffusion is involved in this process.

Circulation of marker substances in the cerebrospinal fluid of an amphibian, Rana pipiens.

Solutions of fluorescein-labelled dextran or Evans blue-albumin were infused into the lateral cerebral ventricle of Rana pipiens. The subsequent distribution in the cerebrospinal fluid (CSF) was investigated between 2 and 24 h after infusion by freezing and examination of the cut blocks of the head and vertebral column of the stage of a freezing microtome. These marker substances move out of the ventricles into the subarachnoid space at the caudal end of the fourth ventricle and spread rapidly along the subarachnoid space of the spinal cord. The spreading of marker substances is slower into the brain subarachnoid space, When the marker is infused into the subarachnoid space of the forebrain, it becomes distributed throughout the subarachnoid space of the brain and spinal cord but not in the ventricles. Partial clearance of markers from the ventricles takes place within 5 h and total clearance within 8 h. Clearance from the brain and cord subarachnoid space is somewhat slower and can only be detected in experiments lasting 10 h or more. Absorption of the markers from the CSF occurs via the intervertebral foramina of the spinal cord. Fluorescence microscopy of sections of the cord show that the fluorescence leaves the subarachnoid space at the point where the spinal nerves traverse the arachnoid membrane.