Elsevier

Brain Research

Volume 533, Issue 2, 19 November 1990, Pages 192-195
Brain Research

α-Adrenergic receptor agonists, but not antagonists, alter the tail-flick latency when microinjected into the rostral ventromedial medulla of the lightly anesthetized rat

https://doi.org/10.1016/0006-8993(90)91339-IGet rights and content

Abstract

The present experiments, part of an ongoing study designed to characterise the role norepinephrine (NE) in regulating the activity of putative nociceptive modulatory neurons in the rostral ventromedial medulla (RVM), assessed the effects of α-adrenergic receptor-selective agents on the nociceptive threshold (as measured by the tail-flick withdrawal response on noxious heat). These microinjection studies were carried out in the barbiturate-anesthetized rat, a preparation which is favourable for acute neurophysiological studies. The data obtained demonstrate that, as observed by others in the awake animal, activation ofα2-adrenergic receptors in the RVM produces hypoalgesia. However, unlike in the awake animal, when antagonists selective for either theα1- orα2-adrenergic receptor are microinjected alone into the RVM there is no change in the nociceptive threshold. These data suggest that theα2-adrenergic receptor has a postsynaptic location and that barbiturate anaesthesia suppresses a tonically active or noxious stimulus-activated noradrenergic input to the RVM that is present in the awake animal.

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A preliminary report of these findings was presented at the 1988 Annual Meeting of the Society for Neuroscience.

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