Differential effects of desipramine on direct- and sensory-evoked noradrenaline release in thalamic locus coeruleus terminals.

The effects of desipramine on sensory-evoked (sciatic nerve stimulation) activation of locus coeruleus neurones were investigated in vivo by using treated carbon-fibre electrodes in conjunction with either differential normal pulse voltammetry or differential pulse amperometry. Firstly, the amplitude of the sensory-evoked increase in extracellular noradrenaline, monitored in thalamic locus coeruleus terminals, was not modified by desipramine (10 mg/kg), whereas that evoked by direct activation of locus coeruleus neurones was greatly increased: +143% for dorsal noradrenergic bundle stimulation and +761% for glutamate ejection in the locus coeruleus. Secondly, desipramine administered at the same dose significantly reduced (-48%) the activation of locus coeruleus neurones (monitored at the somato-dendritic level) evoked by prolonged sciatic nerve stimulation. Our results indicate that acute treatment with desipramine does not potentiate overall noradrenergic transmission by locus coeruleus neurones during sensory stimulation.