A MICRODIALYSIS STUDY ON STRIATAL DOPAMINE, 5-HT AND METABOLITES IN CONSCIOUS RATS AFTER VARIOUS TREATMENTS - EVIDENCE FOR EXTRAVESICULAR RELEASE OF DOPAMINE

THE effects of death and various treatments that affect the status of nigrastriatal neurones on striatal release of dopamine (DA) and 5-hydr oxytryptamine (5-HT) and their metabolites 3,4-dihydroxyphenylacetic a cid (DOPAC), 3-methoxy-4-hydroxyphenylethylamine (3-MT), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were studied by in vivo microdialysis. In conscious rats, DA and 5-HT levels were very lo w compared with their metabolites except 3-MT which was rarely detecta ble. Upon death by pentobarbitone overdose, there was an immediate sur ge of the DA level reflecting massive release of the neurotransmitter. This increase was accompanied by a significant increase in 3-MT level but not the other two DA metabolites. Post mortem release of 5-HT was also observed but to a much smaller extent than that of DA. The amoun ts of amines released appeared to be proportional to the amine stores. When L-dihydroxy-phenylalanine (DOPA) was administered to reserpinize d rats, the extracellular levels of both DOPAC and HVA increased but n ot that of DA. However, marked release of DA occurred at death in cont rast to reserpinized rats not injected with the precursor. It is evide nt that exogenous L-DOPA is taken up into the dopaminergic nerve endin gs and is converted to releasable extravesicular DA, and that this rel easable DA is released, at least in part, in accordance with neuronal activities.