| Abstract: | alpha 2-Agonist clonidine has been used for several years in the detoxification of opiate-addicts since it reduces withdrawal symptoms in man although craving for narcotic is not well suppressed. In the present work the potential "anticraving" properties of another alpha 2-agonist guanfacine were studied in rats trained to self-administer morphine. In the special series of experiments the influence of guanfacine on behavioral manifestation of morphine withdrawal in rats was studied. Analgesic action of guanfacine was evaluated by tail-flick procedure. It was shown that guanfacine (2-4 mg/kg, i.p.) essentially inhibited the morphine intravenous self-administration in a dose-dependent manner. These findings can be interpreted as reduction of morphine's positive reinforcing properties by guanfacine and point out on the possibility to prevent morphine abuse by guanfacine. Analgesic effect of guanfacine in tail-flick test was revealed in doses of 1-8 mg/kg, i.p. (50-100% increase in latency of nociceptive reaction, p < 0.05, Student's t-test). In the other experiments the morphine dependence was induced by i.p. injections of this drug during 5 day period with gradually elevated doses from 5 up to 25 mg/kg. Morphine discontinuation and injection of naloxone (0.5 mg/kg, i.p.) on day 6 induced the behavioral symptoms of abstinence ("wet dog shakes" and jumping). Guanfacine (4 mg/kg, i.p., immediately after naloxone) significantly increased the number of jumps and locomotions (p < 0.05), while increase in "wet dog shakes" was not statistically significant. The potentiation of morphine-withdrawal jumping by guanfacine was antagonized by iohimbine and prazosine in doses of 1 mg/kg, i.p. In the same conditions both prazosine and iohimbine removed "wet dog shakes." The results suggest that the potentiation effect of guanfacine on morphine-withdrawal jumping in rats can be mediated through alpha 1- and alpha 2-adrenoreceptors. Nonspecific interaction between prazosine and mentioned effect of guanfacine (which can be resulted from potentiation of blood pressure fall and of motor deficit) cannot be excluded. |
