Fig. 7.

The polyamine spermine selectively inhibits apical spine responses. A: depolarization from −80 to +40 mV increased the PPR of apical (left) but not basal (right) spines, as can be seen in the inverted and scaled response at −80 mV shown in gray superimposed on the response at +40 mV. Summary graph indicates that apical spine, but not basal spine, PPRs were increased by depolarization. B: responses to pairs of photostimuli at an apical spine are shown before (black) and after (gray) bath application of 50 μM spermine (left). Spermine reduced the amplitude of the 1st response and increased the PPR, as seen most clearly after scaling the responses so that the amplitudes of the 2 1st responses are the same (right). Summary graph indicates that apical spine, but not basal spine, phEPSC amplitudes were significantly depressed by spermine and that only the PPR of apical spine phEPSCs was affected by spermine (n = 8 apical and 5 basal spines). *P < 0.05; **P < 0.01; paired t-tests.