Antinociceptive effects of the stereoisomers of nicotine given intrathecally in spinal rats

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Abstract
Spinalized rats received an intrathecal injection of either (−)-nicotine or (+)-nicotine in order to study the stereoselectivity of antinociception. Pain threshold was measured using the tail-flick test. Both stereoisomers had antinociceptive effects, but (−)-nicotine was up to 970 times more potent, depending on test conditions. The antinociceptive action of (−)-nicotine was antagonized by mecamylamine and yohimbine but not by naloxone and atropine. The findings show that spinal mechanisms are highly stereoselective toward nicotine, and suggest that primarily nicotinergic andalpha-adrenergic receptors are involved in its central antinociceptive effects.