Mu and kappa opioid modulation of olfactory bulb evoked potentials.

Modulatory influences of the mu opioid agonist morphine and the kappa opioid agonist U-50, 488H on field-evoked potentials from the main olfactory bulb (MOB) in response to stimulation of the olfactory nerve were studied. Topically administered morphine upon the MOB dorsal surface produced a noloxone-sensitive depression of the late component of the response without modifying the early one, while topical administration of U-50, 488H suppressed both the early and the late components. Naloxone did not antagonize U-50, 488 effects. Results indicate that mu and kappa opioid agonists can interfere with sensory transmission at the level of second-order neurons of the olfactory pathway, the mitral and/or tufted cells.