Title: In vivo voltammetric detection of DOPAC and 5HIAA in the brain of unanesthetized rats.
Abstract: Voltammetric technique has been recently developed and successfully applied to the in vivo detection of catecholamines (CA), indoleamines and their metabolites. We reported previously that CA released from the substantia nigra of anesthetized rats could be detected with an implanted carbon-fiber electrode (Jpn. J. Pharmacol., 32, Suppl., 72p, 1982). In the present study, we found that 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5HIAA) could be simultaneously measured using a new type of carbon-fiber electrode (diameter : 7 μm, length : 200 μm). Differential pulse voltammetry recordings were carried out at 15-min intervals in the nucleus caudatus (CD) of unanesthetized Wistar rats. The voltammograms had two peaks; Peak 1 appeared at the in vitro potential (+0.12V) of dopamine (DA) and DOPAC, while peak 2 coincided with the in vitro potential (+0.27V) of 5-hydroxy-tryptamine (5-HT) and 5HÍAA. Micro-infusions of DA or DOPAC and 5-HT or 5HIAA into the CD selectively increased peak 1 and peak 2, respectively. Peak 1 from regions known to be densely innervated by DA neurons was larger than that from other regions. A relatively large peak 2 was seen in the nucleus dorsalis raphes and the pineal body. Also, peak 1 increased after injection of haloperidol (0.5mg/kg, i.p.) or γ-butyrolactone (700mg/kg, i.p.) and decreased after amphetamine (2mg/kg, i.p.) or pargyline (75mg/kg, i.p.) treatment. Peak 2 increased after 5-hydroxytryptophan (10mg/kg, i.p.) or probenecid (200mg/kg, i.p.), but decreased after pargyline (75mg/kg, i.p.) treatment. These results suggest that the two signals, peaks 1 and 2, might reflect the levels of extraneuronal DOPAC and 5HIAA, respectively.