Figure 2.
Postsynaptic injection of heparin, an inhibitor of IP3 receptors, disrupts 5-HT-dependent facilitation of the sensorimotor synapse in culture. A, Representative EPSPs for three of the experimental groups: 5-HT control, 5-HT/heparin, and test-alone/heparin. Trial times correspond to those indicated on the abscissa of the graph in B. B, Mean normalized amplitude of the EPSPs in the four experimental groups: synapses in the 5-HT control group (n = 7); synapses treated with 5-HT after heparin had been injected into the motor neuron (5-HT/heparin; n = 5); synapses that received the test stimuli but were not treated with 5-HT (test-alone; n = 6); synapses that received the test stimuli together with postsynaptic heparin (test-alone/heparin; n = 5). A repeated-measures ANOVA on the data from the 5-HT treatment period (10-15 min trials) indicated that there was a significant main effect for experimental treatment (F(2,20) = 34.76; p < 0.0001). The mean normalized EPSPs for the 10 min trial were 344 ± 44% in the 5-HT control group, 225 ± 23% in the 5-HT/heparin group, and 80 ± 6% in the combined test-alone group (n = 11). The mean normalized EPSPs for the 15 min trial were 331 ± 43% in the 5-HT control group, 186 ± 19% in the 5-HT/heparin group, and 68 ± 4% in the combined test-alone group. SNK post hoc tests indicated that the EPSPs in the 5-HT control group were significantly greater than those in the other two experimental groups during the 5-HT treatment period (p < 0.05 for each test) and that the EPSPs in the 5-HT/heparin group were significantly greater than those in the combined test-alone group during 5-HT treatment (p < 0.05). A repeated-measures ANOVA on the data from the period after washout of 5-HT (20-55 min trials) revealed that there was a highly significant main effect for experimental treatment during this period (F(2,20) = 21.78; p < 0.0001). SNK post hoc tests showed that the mean value for the EPSPs after drug washout was significantly greater for the 5-HT control group than those for the other two experimental groups (p < 0.05 for each test). The difference between the EPSP data for the 5-HT/heparin and combined test-alone groups during this period, however, was not significant. The asterisks indicate significant differences between the 5-HT control and 5-HT/heparin data, the # symbol indicates the significant difference between the 5-HT/heparin and test-alone data, and the crosses indicate significant differences between the 5-HT control and the test-alone data. Error bars represent SEM. Interstimulus interval, 5 min.