The objective of this study was to investigate under controlled conditions the effects of fentanyl on the rat locus coeruleus catechol oxidation current. Using differential normal pulse voltammetry combined with electrochemically treated carbon fiber electrodes to measure the catechol oxidation current, catecholamine metabolism can be reliably monitored. Male Sprague–Dawley rats weighing 500–600 g had carbon fiber electrodes implanted into the locus coeruleus under halothane – O2 – air anesthesia with controlled ventilation and muscle relaxation. Experiments consisted of four groups of rats given the following treatments: (A) saline (n = 6); (B) fentanyl, 10 μg∙kg−1 i.v. (n = 6); (C) naloxone, 800 μg∙kg−1 i.v. followed 2 min later by fentanyl, 10 μg∙kg−1 (n = 5); (D) clonidine, 200 μg∙kg−1 i.p. (n = 6). There was no significant change in the catechol oxidation current following saline. Fentanyl produced a significant (ANOVA, p < 0.05) decrease in the catechol oxidation current (maximum 32 min postinjection was 75.8 ± 4.6% of baseline). This decrease was prevented by a prior injection of naloxone. Clonidine produced a significant decrease in catechol oxidation current (maximum 40 min postinjection was 54.1 ± 7.0% of baseline). Systolic blood pressure was significantly decreased following clonidine and there were no significant changes in arterial blood gases throughout the experiments. The α2-adrenergic agonist clonidine and the opioid fentanyl produced a decrease in locus coeruleus catechol oxidation current measured by in vivo voltammetry, which monitors catecholamine turnover.Key words: catecholamine, clonidine, fentanyl, opiates, locus coeruleus, in vivo voltammetry.
Locus Coeruleus, Noradrenaline, and Behavior: Network Effect, Network Effects?
