The noradrenaline–dopamine interaction in the rat medial prefrontal cortex studied by multi-probe microdialysis

Abstract

Multi-probe microdialysis was used to investigate the interaction between the release of noradrenaline and dopamine in the medial prefrontal cortex. Retrograde microdialysis was used to stimulate or inhibit the activity of the locus coeruleus for a restricted period of time, and the response of extracellular noradrenaline and dopamine in the ipsilateral and contralateral medial prefrontal cortex was recorded with microdialysis probes. Infusion of clonidine into the locus coeruleus (100 μM for 45 min) suppressed noradrenaline release and slightly inhibited dopamine release in the ipsilateral medial prefrontal cortex. Application of carbachol to the locus coeruleus (100 μM for 45 min) stimulated both the noradrenaline and dopamine release in the ipsilateral medial prefrontal cortex. No changes were seen in the contralateral medial prefrontal cortex. In the ipsilateral nucleus accumbens, extracellular noradrenaline levels increased, but dopamine levels remained unchanged. Application to the locus coeruleus (during 10 min) of the glutamate receptor agonists N-methyl- d-aspartate (NMDA) (300 μM) or kainate (100 μM) strongly increased extracellular noradrenaline and dopamine levels in the ipsilateral medial prefrontal cortex. However, in the contralateral probe the release of dopamine (but not of noradrenaline) was also stimulated. Application of carbachol to the locus coeruleus was used as a model to further investigate the presumed noradrenaline–dopamine interaction. In a series of dual-probe experiments, α 1-, α 2-, and β-adrenoceptor antagonists (prazosin, idazoxan, propranolol) or a reuptake-inhibitor (nomifensine) was administered during carbachol stimulation of the locus coeruleus. Prazosin and propranolol were administered systemically in a dose of 3 mg/kg, whereas idazoxan (10 μM) and nomifensine (100 μM) were infused into the medial prefrontal cortex. However, none of these pretreatments modified the effects of the control carbachol-infusions. The results did not identify a receptor-interaction or a common reuptake site that explained the presumed interaction between dopamine and noradrenaline in the medial prefrontal cortex. Therefore, the noradrenaline–dopamine interaction hypothesis could not be confirmed or refuted.