Striatal adenosine levels measured 'in vivo' by microdialysis in rats with unilateral dopamine denervation

Adenosine, inosine, hypoxanthine and guanosine were measured in perfusates collected from the right and left striatum of halothane-anaesthetized naive and 6-hydroxydopamine-denervated rats by using microdialysis. Samples were taken under basal and KCl-stimulated conditions. Dopamine, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were simultaneously measured. Purines and monoamines were assayed by HPLC-UV and HPLC-EC respectively. In naive rats, basal adenosine (1 microM), inosine (2 microM), hypoxanthine (4 microM), guanosine (0.5 microM) and dopamine (DA, 0.02 microM) levels (corrected by using the in vitro % recovery of each probe) were increased by the inclusion of 100 mM of KCl into the perfusion medium (2.5-, 3-, 3.5-, 1.5- and 30-fold, respectively, while DOPAC (6 microM), HVA (5 microM) and 5-HIAA (3 microM) levels were (72%, 68% and 45% respectively). DA was strongly diminished in the denervated striatum, but when detectable, could be increased (1- to 12-fold) by KCl stimulation. Adenosine, inosine, hypoxanthine and guanosine were, however, largely unaffected by the DA denervation and could be enhanced by KCl stimulation (2-, 3-, 4- and 1.5-fold respectively). The present results indicate that: (1) as in the case for DA, there is a pool of striatal adenosine which is releasable by high concentrations of extracellular K+; however, (2) this pool of adenosine seems not to be significantly modified by mesencephalic dopamine deafferentation.