a, Cerebellar granule cells were cultured in K25 NB medium supplemented with B27 for one week. At this time, lowering of K+ concentration for 2 days decreased viability and enhanced the expression of group I mGluRs as measured by 100 µM ACPD-stimulated PI hydrolysis (shown as % of basal PI hydrolysis). b, Time course of developing toxicity after medium change from K25+B27 to K5 in the presence and absence of B27. c, The ACPD-stimulated PI hydrolysis, enhanced 24 h after medium change from K25+B27 to K5+B27, is inhibited by the mGlu1 antagonist CPCCOEt (100 µM) but not by the mGlu5 antagonist MPEP (10 µM). Western blots showing that K5+B27 conditions induce a time-dependent increase of mGlu1 (d), but not mGlu5 (e) expression and quantification of these blots after normalization using β-actin (f). Simultaneous removal of B27 accelerates mGlu1 expression as seen on a representative Western blot (g) and quantified after normalization using β-actin (h). All values are means from at least three independent experiments with error bars representing S.E.M. * p<0.05 and **p<0.001 as compared to untreated controls using Student’s t-test.