Simultaneous determination of cholecystokinin, dopamine, glutamate and aspartate in cortex and striatum of the rat using in vivo microdialysis.

Extracellular levels of cholecystokinin (CCK), dopamine (DA), glutamate (Glu) and aspartate (Asp) were simultaneously monitored in the frontoparietal cortex and the striatum of halothane-anaesthetized rats using in vivo microdialysis. Under basal conditions, cortical and striatal CCK levels were 3.11 ± 0.39 pM and 2.76 ± 0.15 pM, respectively. Local KCl (10(-1) M) and bicuculline (10(-4) M) co-application in cortex or striatum increased the CCK levels 18-fold and 26-fold, respectively. The DA level in striatum was 3.78 ± 0.28 nM and the local perfusion with KCl + bicuculline led to a 45-fold increase. The cortical and striatal outputs of Glu were of the order of 2 · 10(-6) M and Asp levels were around 6 · 10(-7) M. Local stimulation with KCl (10(-1) M) and bicuculline (10(-4) M) caused a small increase (2 fold) in cortical and striatal levels of Glu and Asp. The addition of KCl (10(-1) M) and bicuculline (10(-4) M) to the cortical perfusion medium did not modify CCK, DA or Glu concentrations in striatum. These results demonstrate that CCK, DA, Glu and Asp may be simultaneously monitored in vivo and support the idea that their extracellular levels recovered in the microdialysis perfusates could be derived from neuronal pools.