Figure 1.

μ-Opioid receptor activation disrupts gamma oscillations and long-range synchrony. (a) Schematic of a hippocampal slice illustrating the sites of stimulation/recording in area CA1. (b) Posttetanic gamma oscillations evoked simultaneously at two sites demonstrate rhythmicity (frequency = 52 ± 2 Hz, n = 6, from autocorrelograms) and synchrony (phase lag/lead = 1.0 ± 0.6 ms, n = 6, from cross-correlograms) in control slices (bi). Morphine, added to the slice bathing medium, causes a concentration-dependent disruption of rhythmicity with multiple autocorrelation peaks seen at concentrations above 20 μM. Synchrony between sites is also detrimentally affected at these concentrations with a significant increase in phase lag to 4.6 ± 0.7 ms at 50 μM (P < 0.05) (bii and biii). Bath application of 10–20 μM cyprodime (a selective μ-receptor antagonist) reversed the effects of 50–100 μM morphine on rhythmicity and synchrony (biv). The above effects of morphine were mimicked by 2 μM β-endorphin (bv). Scale bars equal 5 mV and 300 ms.