Effects of narcotics, including morphine, on visual evoked potential in rats.
The side effects of narcotics, including morphine, on the visual system are still unclear; therefore, the present study was undertaken to examine the effects of narcotics on the visual system at each antinociceptive dose by using the evoked potential (VEP) in rats. Morphine (2 or 5 mg/kg) caused a significant increase in the amplitude of early and late VEP components (P(1)-N(1), N(1)-P(2), P(3)-N(3) and N(3)-P(4)). Fentanyl (0.02 mg/kg) also showed a significant increase in the amplitude of late VEP components (P(3)-N(3), N(3)-P(4)). The effects of morphine and fentanyl on VEP components were antagonized by naloxone (1 mg/kg). On the other hand, (+/-)-pentazocine (20 mg/kg) reduced the amplitude of the late VEP component (N(3)-P(4)), and this effect was not antagonized by naloxone. Butorphanol showed no significant changes in early and late VEP components. In conclusion, morphine stimulated the retino-geniculate-cortex pathway and the thalamus-cortical circuit through the opioid receptors, and fentanyl stimulated the thalamus-cortical circuit through the opioid receptors. It can therefore be assumed that VEP is a useful tool for examining the side effects of drugs, including narcotics, on the visual system.
Kuroda
Ken
K
Department of Medicinal Pharmacology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
Fujiwara
Akinori
A
Takeda
Yasuhiro
Y
Kamei
Chiaki
C
D000818:Animals; D005074:Evoked Potentials, Visual / Q000187:drug effects*; D008027:Light; D008297:Male; D009020:Morphine / Q000009:adverse effects* / Q000037:antagonists & inhibitors; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000009:adverse effects*; D009799:Ocular Physiological Phenomena / Q000187:drug effects / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology
D009292:Narcotic Antagonists; D009294:Narcotics; D009270:Naloxone; D009020:Morphine