Andrade R, Vandermaelen C P, Aghajanian G K
Eur J Pharmacol. 1983 Jul 22;91(2-3):161-9. doi: 10.1016/0014-2999(83)90461-2.
Extracellular single unit recordings in vitro from the locus coeruleus in rat brainstem slices revealed the presence of spontaneously active neurons. These cells fired between 0.1 and 3.0 spikes/s and were inhibited by nM concentrations of morphine and clonidine. Locus coeruleus neurons in slices from animals treated chronically, but not subacutely, with morphine exhibited a significant decrease in sensitivity to morphine. This tolerance appeared to be specific for opiates since no decrease in sensitivity was seen for the alpha 2-adrenoceptor agonist clonidine. However, in contrast to what has been reported in vivo, no signs of dependence (withdrawal activation) were evident in slices from morphine tolerant animals.
