Does naloxone have functional significant activity on medial thalamic neurons? Microiontophoretical study

Local administration (microiontophoretically) of naloxone was tested in 57 parafascicularis thalamic (PF) neurons of morphine-naive and morphine-dependent rats. In morphine-naive rats microiontophoretic applications of naloxone induced changes in 52% of the PF neurons. Reduction in neuronal activity was observed in the majority of them; this reduction phenomena exhibited dose response characteristics, i.e., each incremental naloxone dose caused further decrease of the neuronal discharges. In morphine-dependent animals, 64% of the PF neurons were affected. The changes seen after naloxone were mainly increases of electrical discharges (i.e. the opposite effects obtained in morphine-naive animals).