Evoked changes in 5-hydroxytryptamine and norepinephrine release: in vivo dialysis of the rat dorsal horn

Basal 5-hydroxytryptamine (5HT) and norepinephrine (NE) concentrations were measured in samples collected by in vivo dialysis of the rat dorsal horn. Infusion of KCl, glutamate, and NE by means of the dialysis probe increased NE, but decreased 5HT extracellular concentrations. In contrast, electrical stimulation of the nucleus raphe magnus increased the recovery of both NE and 5HT. These findings suggest differential regulation of noradrenergic and serotonergic nerve terminals modulating nociceptive neurotransmission within the dorsal horn.