Systemic naloxone enhances cerebral blood flow in anesthetized morphine-dependent rats

Eur J Pharmacol. 2000 Nov 24;408(3):299-304. doi: 10.1016/s0014-2999(00)00794-9.


Laser-Doppler flowmetry was used to study cerebral cortical blood flow responses to morphine and naloxone in morphine-naive and -dependent rats. The experiments were performed in spontaneously breathing anesthetized rats. Morphine (10 mg/kg, i.p.) administration reduced regional cerebral blood flow in control, sham-operated and morphine-dependent rats, but the depressant effect of morphine in morphine-dependent animals was less than that in control and sham-operated groups. While naloxone (0.5 mg/kg, s.c.) had no considerable effect on regional cerebral blood flow in control and sham-operated groups, it increased regional blood flow in morphine dependent ones. The depressant effect of morphine in all groups and the enhancing effect of naloxone in morphine-dependent animals were not seen after local application of lidocaine at the recording site. This study may provide a framework to study the cellular and molecular mechanisms responsible for coupling neuronal electrical activity with regional alterations in blood flow during precipitation of morphine withdrawal.

MeSH terms

  • Anesthesia
  • Anesthetics, Local / pharmacology
  • Animals
  • Brain / blood supply
  • Cerebrovascular Circulation / drug effects*
  • Diarrhea / chemically induced
  • Lidocaine / pharmacology
  • Male
  • Morphine / adverse effects
  • Morphine Dependence / physiopathology*
  • Naloxone / pharmacology*
  • Narcotic Antagonists / pharmacology*
  • Pain / chemically induced
  • Rats
  • Rats, Wistar
  • Substance Withdrawal Syndrome / pathology
  • Substance Withdrawal Syndrome / physiopathology
  • Weight Loss / drug effects


  • Anesthetics, Local
  • Narcotic Antagonists
  • Naloxone
  • Morphine
  • Lidocaine