Morphine, naloxone and the responses of medial thalamic neurones of the cat.

Administered electrophoretically morphine depressed the firing of medial thalamic neurones. This effect was not antagonized by naloxone which itself was a depressant. A long lasting increase in sensitivity to L-glutamate followed ejection of both morphine and naloxone. Intravenous morphine, 0.5-1.5 mg/kg, had inconstant effects on spontaneous firing that evoked by electrical stimulation of the forepaws but in 7 of 10 experiments reduced the sensitivity of neurones to L-glutamate. This effect was reversed in all cases by intravenous naloxone, 0.3 mg/kg