Effects of electrical stimulation and morphine microinjection into periaqueductal gray on 5-hydroxyindole oxidation current in spinal cord of cats.
1. The effects of electrical stimulation and microinjection of morphine into the periaqueductal gray (PAG) on the 5-hydroxyindole oxidation current (280-300 mV) in laminae I-VI (800-2500 microns) of the spinal cord were examined using in vivo voltammetry in anesthetized cats. 2. Electrical stimulation of the PAG (PAG-S) both enhanced and attenuated the current. PAG-S increased the signal by 13.3 +/- 3.7% (laminae I-II: 800-1200 microns) or 19.0 +/- 3.6% (laminae V-VI: 1700-2500 microns) in comparison to control values. Attenuation by PAG-S decreased the signal by 15.3 +/- 2.6% (laminae I-II) or 13.3 +/- 2.0% (laminae V-VI) of control values. Naloxone antagonized signal enhancement by PAG-S. 3. Morphine (10 micrograms/microliter) microinjected into the PAG significantly increased the height of the signal (laminae I-II: 15.0 +/- 3.4%, laminae V-VI: 12.2 +/- 1.5%). Enhancement by microinjected morphine was antagonized by naloxone. In contrast, microinjected morphine also significantly decreased the signal by 10.4 +/- 2.7% (laminae I-II) and by 10.3 +/- 1.3% (laminae V-VI) of control values. 4. Microinjection of morphine and electrical stimulation of the PAG was observed both to enhance and attenuate the oxidation current of 5-hydroxyindole in the superficial and deeper dorsal horn. PAG may function to regulate the RVM-spinal serotonergic pathway, which modulates the transmission of nociceptive messages at the spinal cord.
Kato
M
M
Department of Pharmacology, Showa College of Pharmaceutical Sciences, Tokyo, Japan.
Taguchi
K
K
Hagiwara
Y
Y
Kubo
T
T
D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D007211:Indoles / Q000378:metabolism*; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009294:Narcotics / Q000008:administration & dosage / Q000494:pharmacology*; D010084:Oxidation-Reduction; D010487:Periaqueductal Gray / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013268:Stimulation, Chemical
D007211:Indoles; D009294:Narcotics; C026785:5-hydroxyindole; D012701:Serotonin; D009020:Morphine