Figure 4.

Recovery of the inhibitory effect of ME (3.2 μM, 1 min) following two successive administrations of β‐FNA (300 nM, 15 min). (A) Symbols represent the mean ± SEM of the percentage of ME‐induced inhibitory effect. The horizontal axis represents the time after the end of β‐FNA (300 nM, 15 min) application, whereas the vertical axis indicates the inhibitory effect of ME (3.2 μM, 1 min) expressed as a percentage of its initial FR. The lines of the figure represent the theoretical curve constructed from the average of the recovery kinetic parameters that define the functional turnover of μ receptors. Note that the recovery of the inhibitory effects of ME after the first β‐FNA application is significantly higher than that of the inhibitory effects of ME achieved after the second antagonist perfusion (n = 5; *P < 0.05; Student's paired t‐test). (B) Representative example of FR recording of LC neuron showing the recovery of the inhibitory effect of ME (3.2 μM, 1 min) after two successive administrations of β‐FNA (300 nM, 15 min). Vertical lines represent the number of spikes recorded every 10 s and the horizontal bars the period of drug application. Note that the inhibitory effect of ME is almost blocked 15 min after both β‐FNA administrations. The inhibitory effect of ME completely recovers to the control effect within 120 min after the first β‐FNA administration but not after the second β‐FNA application.