Fig. 15

μ-ORs modulate short-term dynamics of neuronal output in DH but not in VH. Short-term changes in PS induced by frequency stimulation were obtained under control conditions (open symbols) and during application of fentanyl (filled circles). Two stimulation current intensities were used: suprathreshold (circles) and submaximal (triangles) that caused a PS with amplitude 0.1–0.5 mV and 75% of maximal value respectively. Percent changes are plotted as a function of stimulus number. The bottom right diagrams in the two panels (DH and VH) illustrate the average values of fEPSP changes produced by the 8th–10th stimuli (steady state response) plotted as a function of stimulation frequency. Data shown in the two stimulation intensities (suprathreshold and submaximal) were obtained from (slices/rats): 13/10 and 11/8 in the DH and 7/6 and 8/7 in the VH. Statistically significant drug effects observed on responses evoked by suprathreshold stimulation are denoted by horizontal bars or an asterisk (paired t-test of individual responses along the train, p < 0.05). Bars above and below the data curves denote significant drug effects on responses induced by suprathreshold and submaximal stimulation respectively