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Muscle grafts as entries for blood-borne proteins into the extracellular space of the brain.

Nuchal muscle autografts of two different sizes were transplanted into rat brain parenchyma (intraparenchymal, 1.5 X 1.5 X 1 mm) and onto the surface of the brain stem (intraventricular, 2 X 2 X 1 and 1.5 X 1.5 X 1 mm). The vasculature of the transplants retained its permeability to proteins. Exogenous, intravenously injected horseradish peroxidase (HRP) and endogenous immunoglobulins (IgG) crossed the vessels of the grafts to enter the surrounding brain tissue 1 and 3 months after transplantation. HRP infiltrated about 0.46 to 4.6 mm into the extracellular spaces around the grafts 60 minutes after its intravenous injection. The penetration of HRP depended on the size and age of the graft. Infiltration was greater in 1-month-old rats with slightly larger intraventricular grafts than in those with smaller grafts. There was a tendency for the penetration of HRP to be greater from 1-month-old grafts than from 3-month-old grafts, but the difference was not statistically significant, except for the horizontal vector of spread in the intraparenchymal group. Although endogenous IgG infiltrated the surrounding brain tissue, its penetration was very limited in comparison with that of HRP. The results suggest that muscle grafts could be used as a readily available and accessible means of circumventing the blood-brain barrier selectively and focally.