Interactions between U-50,488H and σ receptor antagonists: EEG, EEG power spectral and behavioral correlates

I.v. administration of U-50,488H after i.v. saline pretreatment produced occasional high-voltage EEG slow-wave bursts that were associated with relatively small increases in spectral power in the 2.5–7.5 Hz band as a spectral peak and with behavioral incidents of sedation, ataxia, ptosis, straub tail, hunching of the back, and backing-up. After pretreatment with the σ antagonists rimcazole and DuPont Merck S-7389-4, U-50,488H administration produced significantly larger increases in absolute EEG spectral power, both over the 1–50 Hz range and in the 2.5–5.0 and 5.0–7.5 Hz bands, than after saline pretreatment; rimcazole pretreatment eliminated U-50,488H-induced incidents of ataxia, ptosis, hunching of the back and backing-up. In summary, effects of U-50,488H on EEG, EEG power spectra and behavior may reflect interactions between κ opioid and σ (non-opioid) receptor-effector systems.