BLOOD-BRAIN EXCHANGE ROUTES AND DISTRIBUTION OF ZN-65 IN RAT-BRAIN

Zinc is essential for normal development and function of the CNS although much is to be learned about brain Zn homeostasis. In these experiments adult male Wistar rats within the weight range 500-600 g were used. Ventriculo-cisternal perfusion was performed to allow the measurement of Zn-65 fluxes between blood and csf across the choroid plexuses. Blood-brain or blood-cerebrospinal fluid barrier permeability to Zn-65 has been determined by graphical analysis in experiments that lasted between 5 and 180 minutes. Cerebral capillary permeability to Zn-65 was found to be low with a K(in) of about 5 x 10(-4)ml/min/g. Choroid plexus permeability to Zn-65 was about 12 fold greater, although Zn influx to brain via this route was <5% that across cerebral capillaries. The autoradiographic distribution of Zn-65 in brain showed regional variation with lowest levels in white matter and high levels in the dentate gyrus and hippocampus.