Intracerebroventricular self-injection of morphine in response to pain in the rat.
Rats were chronically implanted with a lateral cerebral ventricular guide cannula. After recovery they were trained to self-inject morphine sulfate. A week after this training period, self-injection behavior was studied during nociceptive stimulation. In response to a nociceptive stimulation rats increased their intracerebroventricular self-administration of morphine. This effect is specific for morphine since under identical conditions rats did not increase NaCl administration. Naloxone pretreatment inhibits self-administration of morphine in 5 rats. However, two rats increased morphine self-intake. These results show that rats can directly perceive a decrease of pain sensation induced by the morphine self-administration. This experimental situation is therefore similar to the therapeutic situation in humans, in which the criterion of efficacy of an analgesic is a reduction of the conscious pain sensation. Experimental self-administration during painful stimulation might therefore be used for preclinical evaluation of the efficacy of an analgesic drug.
D000818:Animals; D004305:Dose-Response Relationship, Drug; D007276:Injections, Intraventricular; D009020:Morphine / Q000008:administration & dosage*; D009619:Nociceptors / Q000187:drug effects; D051381:Rats; D012640:Seizures / Q000139:chemically induced; D012646:Self Administration; D012684:Sensory Thresholds
D009020:Morphine