DIFFERENTIAL-EFFECTS OF DESIPRAMINE ON DIRECT-EVOKED AND SENSORY-EVOKED NORADRENALINE RELEASE IN THALAMIC LOCUS-CERULEUS TERMINALS

The effects of desipramine on sensory-evoked (sciatic nerve stimulatio n) activation of locus coeruleus neurones were investigated in vivo by using treated carbon-fibre electrodes in conjunction with either diff erential normal pulse voltammetry or differential pulse amperometry. F irstly, the amplitude of the sensory-evoked increase in extracellular noradrenaline, monitored in thalamic locus coeruleus terminals, was no t modified by desipramine (10 mg/kg), whereas that evoked by direct ac tivation of locus coeruleus neurones was greatly increased: +143% for dorsal noradrenergic bundle stimulation and +761% for glutamate ejecti on in the locus coeruleus. Secondly, desipramine administered at the s ame dose significantly reduced (-48%) the activation of locus coeruleu s neurones (monitored at the somato-dendritic level) evoked by prolong ed sciatic nerve stimulation. Our results indicate that acute treatmen t with desipramine does not potentiate overall noradrenergic transmiss ion by locus coeruleus neurones during sensory stimulation.