Blood-brain barrier permeability and immobilization stress.

The regional capacity of the blood-brain barrier (BBB) has been investigated in rat brain during normal conditions and after acute immobilization (IMO). The BBB function was monitored by fluorescence microscopical localization of systemically administered vital dye (trypan blue) and by studying the ability of the brain capillaries to decarboxylate and trap injected L-DOPA. The results demonstrated clear signs of dye penetration into the parenchyma of certain brain regions (area preoptica, some hypothalamic nuclei, area ventralis tegmenti and ventral part of the pons and medulla oblongata) in addition to the areas known to be 'outside the BBB' (the circumventricular organ). There was an an apparent increase in dye penetration in these regions after IMO, most pronounced in the reticular formation of the brain stem. In the mesencephalic reticular formation ruptures of a substantial number of vessels occurred after IMO leading to massive leakage of dye into surrounding brain parenchyma. The main finding after L-DOPA administration was indications of a more efficient decarboxylation and trapping of L-DOPA in most brain regions after IMO. The findings of dye penetration in certain brain regions, which are known to be involved in autonomic regulation, may reflect possible ways of chemical communication between the circulation and neuronal structures in these regions and/or possibly constitute the basis for inactivation processes for transport of substances outwards from the brain as well as potential loci for adverse effects and development of pathological conditions.