In vivo elimination of [3H]L-Glu from rat CSF. A. Residual concentration in rat CSF versus time profiles of [3H]L-Glu (closed circle) and [14C]D-mannitol (open square) after intracerebroventricular administration. The solution (10 μL) containing [3H]L-Glu (1.5 μM) and [14C]D-mannitol (18 μM) was administered into the rat lateral ventricle. The solid line was obtained using non-linear least-squares regression analysis. Each point represents the mean ± SEM (n = 3-4). B. Inhibition of [3H]L-Glu elimination from the CSF by simultaneous injection of unlabeled L-Glu (50 mM), D-Asp (25 mM), and kainite (12.5 mM). The concentrations in rat CSF of L-Glu, D-Asp, and kainate were estimated to be 2 mM, 1 mM, and 0.5 mM, respectively. The values, determined 5 min after intracerebroventricular administration, are expressed as the ratio of 3H/14C in the CSF divided by the same ratio in the injectate. Each column represents the mean ± SEM (n = 3-6). **p < 0.01, significantly different from the control.