Table 1.

Effects of morphine on fast inhibitory oscillations are mediated by μ-opioid receptors

Parameter	Control	Morphine (100 μM)	Morphine + cyp	Morphine + nal	Morphine + nor-BNI
Maximum frequency, Hz	38 (36–41)	77 (65–84)*	42 (38–50)†	84 (69–85)	72 (68–90)
Amplitude, nA	0.22 (0.19–0.26)	0.09 (0.06–0.14)*	0.18 (0.16–0.22)†	0.07 (0.06–0.12)	0.10 (0.08–0.15)
τD, ms	11 (10–12)	10 (9–11)	10 (9–12)	11 (10–12)	10 (9–10)

The following opiate antagonists were used to verify the effects of morphine on μ-opioid receptors: cyp, cyprodime [(−)-N-(cyclopropylmethyl)-4,14-dimethoxymorphinan-6-one, μ receptor, 1–10 μM], nal, naltrindole [17-(cyclopropylmethyl)-6,7-dehydro-4,5α-epoxy-3,14-dihydroxy-6,7-2′,3′-indolomorphinan, δ receptor, 2–20 μM], nor-BNI, nor-binaltorphimine [17,17′-(dicyclopropylmethyl)-6,6′,7,7′,6,6′-imino-7,7′-binorphinan-3,4′,14,14′-tetrol, κ receptor, 10 μM]. Drugs were added to the perfusion solution to assess their ability to antagonize the effects of 100 μM morphine. Frequency, amplitude, and decay time constant (τ_D) were measured for each IPSC within a rhythmic train observed in pyramidal cells. All IPSC oscillation data are expressed as the median (interquartile range, in parentheses, n = 4 to 7 animals). Statistical comparisons were made by using nonparametric analysis of variance where appropriate with a minimum of five replicates per slice and concentration of morphine with or without drug. ∗, IPSC parameters significantly different between morphine and control groups (P < 0.05);  

^†, IPSC parameters significantly different between morphine alone and morphine plus opioid antagonist (P < 0.05).