EXTRACELLULAR CALCIUM IN THE HIPPOCAMPUS OF UNANESTHETIZED RABBITS MONITORED WITH DIALYSIS-PERFUSION

Extracellular levels of Ca2+ in the rabbit hippocampus were investigated in vivo with perfusion-dialysis. A thin semipermeable tubing was implanted and perfused at a constant rate with a Ca2+-free medium. Ca2+ levels in the dialysate were measured with an ion-specific electrode or as radioactivity after labeling of the endogenous pool with 45CaCl2. The system was characterized with model studies. The usefulness of the method is demonstrated for studies of, for example chemically evoked changes in Ca2+ concentrations extracellularly in CNS regions of non-anesthetized, freely moving rabbits. Moreover, measurements of Ca2+ changes are easily correlated with neurotransmitter levels in the same samples.