The antinociceptive effect of intranigral injection of morphine in ketamine- and halothane-anesthetized rats

Document Type

Article

Publication Date

1-1-1990

Abstract

Previous studies have shown that morphine, injected into the substantia nigra of rats, had an antinociceptive effect on the tail-flick test. However, due to a transient behavioral stimulant effect of morphine, given intranigrally, valid tail-flick latencies cannot be obtained prior to 30 min after the injection into the nigra. In order to examine the effect of morphine (5-20 μg), injected into the nigra, on the nociceptive tail-flick reflex at earlier times, animals were anesthetized with either halothane or ketamine (100 or 150 mg/kg, i.m.). Halothane blocked the analgesic effect of intranigrally administered morphine. However, a dose-related antinociceptive effect of morphine was observed in ketamine-anesthetized rats. This effect was demonstrable at 5 min after the injection into the nigra animals that received the small dose of ketamine. This finding provides further evidence that the substantia nigra plays an important role in opiate-induced antinociception. © 1990.

Publication Source (Journal or Book title)

Neuropharmacology

First Page

771

Last Page

777

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