Characterization of the in vivo release of dopamine as recorded by different types of intracerebral microdialysis probes.
Microdialysis of dopamine was performed in the striatum with four different microdialysis cannulas: a trans-cerebral probe, a U-shaped probe, a I-shaped probe and a commercially available I-shaped probe (Carnegie). The commercial cannula was studied with as well as without a guide cannula. The effect of infusion of tetrodotoxin (TTX) or calcium free-Ringer solution on the dialysate content of dopamine released was determined 2 h after implantation (day 1) as well as 24 h after implantation (day 2). Two hours after implantation, all cannulas displayed a certain amount of TTX-independent overflow of dopamine. The best results were obtained with the I-shaped cannula: already 2 h after implantation of the probe, about 85% of the release of dopamine was TTX-dependent. In case of the trans-cerebral cannula and the Carnegie cannula (implanted without guide in anesthetized rats), 70-75% of the output of dopamine was TTX-dependent. When the Carnegie cannula was implanted with a guide cannula, only 45% of the dopamine output was TTX-dependent. The responses to calcium-free perfusion were much more variable. Dopamine output in I-shaped and the U-shaped probes was virtually insensitive to calcium-free perfusion in acute experiments. Twenty-four hours after implantation of the probes, the calcium- and TTX-dependency was much more pronounced. All types of cannulas studied now sampled dopamine that was completely TTX-dependent. Calcium-free perfusion caused a reproducible disappearance of dopamine from the dialysates to 30% of controls, in all cannulas studied. When the removable Carnegie cannula was re-implanted 24 h after its first implantation, 91% of the dopamine overflow was TTX-sensitive. These results confirm earlier conclusions that microdialysis experiments should be carried out at least 24 h after implantation of the probe.
University Centre for Pharmacy, Department of Medicinal Chemistry, University of Groningen, The Netherlands.
M
M
Santiago
B H
BH
Westerink
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001923:Brain Chemistry; D002118:Calcium / Q000502:physiology; D002404:Catheterization; D002851:Chromatography, High Pressure Liquid; D003342:Corpus Striatum / Q000737:chemistry / Q000378:metabolism*; D003956:Dialysis; D004298:Dopamine / Q000032:analysis / Q000378:metabolism*; D006719:Homovanillic Acid / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D051381:Rats; D013779:Tetrodotoxin / Q000494:pharmacology
D015102:3,4-Dihydroxyphenylacetic Acid; D013779:Tetrodotoxin; D006897:Hydroxyindoleacetic Acid; D002118:Calcium; D004298:Dopamine; D006719:Homovanillic Acid