Noradrenaline release from slices of the thalamus of normal and morphine-dependent rats.

The effect of morphine on potassium-induced stimulation of (3H)-noradrenaline release from slices of the rat thalamus was investigated. The in vitro addition of morphine (10(-6)M) significantly depressed potassium-induced tritium overflow by 42% and this was prevented by the prior addition of naloxone (3 x 10(-6)M) to the medium. The stimulation-evoked overflow of tritium from slices of the thalamus of morphine-dependent rats was not significantly different from normal controls. Addition of naloxone (10(-5)M) 10 min before exposure of the tissues to 20 mM K+ significantly enhanced noradrenaline release from 'dependent' slices. The results suggest that the basic release mechanism may have adapted to the continuous presynaptic inhibition of release by morphine.