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Intracranial Pharmacotherapy and Pain Assays in Rodents
Published on: April 9, 2019
Low dose alpha-2 antagonist paradoxically enhances rat norepinephrine and clonidine analgesia
Brian Milne1, Maaja Sutak, Catherine M Cahill
1Department of Anesthesiology & Perioperative Medicine, Queen's University, Kingston, Ontario, Canada.
Abstract:
Ultralow-dose opioid antagonists prolong opioid antinociception and block tolerance. In this study we determined whether low doses of the α-2 adrenergic receptor (A2-R) antagonist, atipamezole, similarly influenced A2-R-induced antinociception and tolerance. In rats, intrathecal norepinephrine (NE) or clonidine in combination with atipamezole was tested using tail-flick and paw pressure tests. Acute tolerance to NE was induced by serial injections. Low-dose atipamezole significantly prolonged NE and clonidine-induced antinociception. Coadministration of atipamezole with A2-R agonists also prevented loss of agonist potency in the acute tolerance model. This study demonstrates paradoxical effects of low-dose A2-R antagonists augmenting A2-R agonist-induced analgesia.
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