Effects of clonidine on morphine withdrawal signs in the rat.

The influence of clonidine on the naloxone-induced withdrawal signs, escape attempts and precipitated shakes, was studied in morphine-dependent rats. Clonidine injected i.p. or intraventricularly (i. vent.) inhibited precipitated shakes and potentiated escape attempts induced by naloxone in morphine-dependent rats. Under pentobarbital anesthesia, precipitated shakes and ice water-induced wet shakes were inhibited by clonidine and norepinephrine. Clonidine injected i. vent. reduced body temperatures in morphine-dependent rats but not in placebo pellet-implanted rats. We suggest that clonidine modulates morphine withdrawal signs by potentiating the behavior associated with heat dissipation (escape attempts) and inhibiting the behavior associated with heat gain mechanisms (precipitated shakes). These effects may occur via stimulation of central noradrenergic mechanisms.