Olfactory Memory but not Odor Learning/Discrimination Is Correlated with Residual GluR-B Levels in Hippocampus and Forebrain of GluR-BΔFB Mice
(A) The olfactory memory performance for 18 GluR-BΔFB (red) and 11 littermate control (black) mice is given as mean (thick lines ± SEM) and as individual performance in open circles and triangles. Arrows with numbers (#) indicate those mice used in experiments (B–C). Data were combined from Figure 2 (open symbols) and an additional experiment with nine GluR-BΔFB and two littermate controls (shaded symbols).
(B and C) Residual GluR-B levels as detected by anti-GluR-B immunofluorescence in hippocampus, amygdala, piriform cortex, and olfactory bulb of one control (#1) and two GluR-BΔFB (#2 and #3) coronal mouse brain sections (B) and by immunoblot analysis from hippocampal (Hip), cortical forebrain (FB), and olfactory bulb (OB) protein extracts of control (#4) and GluR-BΔFB mice (#5, #6, #7, and #8) probed with antibodies detecting GluR-B and β-actin as an internal loading control (C). Scale bars: 200 μm (first panel), 100 μm (other panels).
(D) From ten GluR-BΔFB mice, the individual odor learning/discrimination and olfactory memory performance was determined together with the relative GluR-B levels in immunoblots of hippocampal, forebrain, and olfactory bulb protein extracts. Memory performance (top panels) and discrimination capability (bottom panels; discrimination index is measured for the last 100 trials of the mixture discrimination task as indicated by the arrow in Figure 2C) were plotted against GluR-B levels. Memory was tightly correlated to GluR-B protein level in hippocampus (R2 = 0.72; p < 0.003) and cortical forebrain (R2 = 0.62; p < 0.006) and only weakly in the olfactory bulb (R2 = 0.48; p = 0.03). No measure of learning/discrimination (discrimination index for last 100 mixture trials [D], slopes of trend lines, average discrimination index, average sampling pattern differences, correct performance, etc. [not shown]) displayed any correlation (R2 < 0.3).