Cd transport in rat brain

The brain distribution of ¹⁰⁹CdCl₂ following administration into either the tail vein, the lateral ventricle or the olfactory bulb was studied to clarify permeability of the brain barrier system to cadmium (Cd) and Cd movement in the cerebrospinal fluid (CSF) and the brain extracellular fluid. One hour after intravenous (i.v.) injection, ¹⁰⁹Cd was largely concentrated in the choroid plexus, and ¹⁰⁹Cd concentration in the major part of the brain parenchyma, except for the circumventricular organs such as the pineal gland and the regions around them, was low. Six days after i.v. injection, ¹⁰⁹Cd concentration in the choroid plexus was still high, and ¹⁰⁹Cd was also detected highly in the pineal gland and small part around the median eminence. ¹⁰⁹Cd concentration in the major part of the brain parenchyma was decreased in parallel with that in the blood. In the case of injection of ¹⁰⁹CdCl₂ into the lateral ventricle, a large portion of ¹⁰⁹Cd was detected in the ventricular system 6 days after injection, and ¹⁰⁹Cd concentration in the major part of the brain parenchyma was less than the detection limit. These results suggest that Cd cannot easily get into the brain and is blocked not only by the blood—brain and the blood—CSF barriers, but also by the ependymal and pial surfaces. In the case of injection of ¹⁰⁹CdCl₂ into the olfactory bulb, a large portion of ¹⁰⁹Cd was detected in the injected area 24 h after injection, and, the next 24 h later, ¹⁰⁹Cd distribution in the brain was not changed appreciably. These results suggest that Cd cannot easily move in the brain extracelular space, and is taken up into the brain parenchyma.