Differential effects of intracerebrally microinjected enkephalin analogs on centrally versus peripherally induced pain, and evidence for a facial versus lower body analgesic effect.
[D-Ala2]-Met-Enkephalin and [D-Ala2]-Met-Enkephalinamide were microinjected (10-30 microgram) into the midbrain ventrolateral central gray of rats. The opiate analogs produced profound analgesia in left and right facial areas, and on the hot plate test. The tail-flick test showed significant analgesia, but in a significantly smaller amount than that obtained with noxious face heating. All effects were blocked by naloxone pre-treatment. The drugs had no effect on thresholds for defense responses to high (200 Hz) and low (20 Hz) frequency aversive stimulation in midbrain areas associated with pain perception.
D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology; D004558:Electric Stimulation; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000008:administration & dosage / Q000494:pharmacology*; D005145:Face / Q000294:innervation; D007276:Injections, Intraventricular; D008297:Male; D008845:Microinjections; D009270:Naloxone / Q000494:pharmacology; D009619:Nociceptors / Q000187:drug effects; D010146:Pain / Q000503:physiopathology*; D051381:Rats
D004723:Endorphins; D004745:Enkephalins; D009270:Naloxone