Figure 2. Correlation between mitochondrial movements and synaptic potentiation. Upper panel: Mitochondrial density (M.D.) is the number of mitochondria per micrometer measured because the diameter of nerve branches at the NMJ presynaptic terminal appears to be constant. The density is presented in terms of length rather than volume. M.D. of the control-potentiated terminal (•) is compared with the section-matching contralateral unpotentiated terminal (). Density increase indicates a net increase of mitochondrial flow toward the synapse. Data points are means ± SD (n = 8 terminals). There is no significant difference before 10 min (P = 0.13–0.21). Significant difference between unpotentiated and potentiated synapses is detected after 10 min (P < 0.001). Lower panel: Evoked synaptic potentials (EJPs) were measured and plotted. The M.D. and EJP measurements under rotenone (1 µmol l^–1) are shown () with the bar (———) indicating the application of rotenone via suction electrode from 5 min until 10 min for both panels. Significant differences were detected between control and potentiated EJP amplitude at 14 min (P < 0.001) and 22 min (P < 0.001). The dashed lines indicate the timing between potentiation occurrence and mitochondrial density increase, comparing control synapses to neurofibromin expression synapses. Neurofibromin enhanced the delivery of mitochondria to the synaptic terminals, demonstrated as a significant elevation of mitochondrial density during tetanic stimulation, correlated with an increased EJP in the hsNF1/+ synapses () at 9, 11, 14, and 22 min compared to both the unpotentiated (P < 0.001) and control potentiated synapses (P < 0.01 at 9 and 11 min, P < 0.02 for at 14 and 22 min). Stimulation: 1 ms, 2x threshold, 10 Hz; begins at 7 min, ends at 23 min. Data collected each minute.