Depressant and excitant effects of intraspinal microinjections of morphine and methionine-enkephalin in the cat.
The effects of intraspinal microinjectins of morphine (10 microgram) and methionine-enkephalin (Met-enkephalin) (5 microgram) on the C-fiber and polysynaptic reflexes in the acute decerebrate low spinal cat were investigated. Microinjected into the dorsal horn, morphine and Met-enkephalin depressed the nociceptive C-fiber reflex (CFR) without altering the short latency polysynaptic reflex. Microinjected into the ventral horn, morphine and Met-enkephalin facilitated the C-fiber and polysynaptic reflexes. Pretreatment of the cats with intravenous naltrexone (2 mg/kg) antagonized the depressant effects produced by dorsal horn intraspinal microinjections of morphine and Met-enkephalin. The excitant effects of ventral horn microinjections of morphine were not antagonized by naltrexone (2 mg/kg). These results support a hypothesis that the analgesic effects of morphine at the spinal cord level are due to interactions with opiate receptors in the dorsal horn.
D000818:Animals; D002415:Cats; D004723:Endorphins / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D005727:Ganglia, Spinal / Q000187:drug effects; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009046:Motor Neurons / Q000187:drug effects; D009271:Naltrexone / Q000494:pharmacology; D009412:Nerve Fibers / Q000187:drug effects; D009619:Nociceptors / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects*; D013569:Synapses / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects
D004723:Endorphins; D004745:Enkephalins; D009271:Naltrexone; D009020:Morphine