Local inhibition of uptake transporters augments stress-induced increases in serotonin in the rat central amygdala.

Organic cation transporter 3 (OCT3) is a corticosterone-sensitive, low-affinity, high-capacity transporter. This transporter functions, in part, to clear monoamines, including serotonin (5-HT), from the extracellular space. The central nucleus of the amygdala (CeA) is an important structure controlling fear- and anxiety-related behaviors. The CeA has reciprocal connections with brainstem nuclei containing monoaminergic systems, including serotonergic systems arising from the dorsal raphe nucleus, which are thought to play an important role in modulation of CeA-mediated behavioral responses. Organic cation transporter 3 (OCT3) is expressed in the CeA, but little is known about the role of OCT3 within the CeA in modulating serotonergic signaling. We hypothesized that inhibition of OCT3-mediated transport in the CeA during restraint stress would increase extracellular 5-HT. In Experiment 1, rats received unilateral reverse dialysis of either corticosterone or normetanephrine, which interfere with OCT3-mediated transport, into the CeA under home cage control conditions. In Experiment 2, rats received unilateral reverse dialysis of corticosterone, normetanephrine, or vehicle into the CeA, while undergoing a 40-min period of restraint stress. Infusion of these drugs had no effect on extracellular concentrations of 5-HT during home cage control conditions, but, in contrast, markedly increased extracellular concentrations of 5-HT during restraint stress, relative to vehicle-treated controls. These findings suggest a role for OCT3 in the CeA in control of serotonergic signaling during stressful conditions.