Endogenous release of neuronal serotonin and 5-hydroxyindoleacetic acid in the caudate-putamen of the rat as revealed by intracerebral dialysis coupled to high-performance liquid chromatography with fluorimetric detection.
Extracellular levels of endogenous serotonin (5-HT) and its major metabolite, 5-hydroxyindoleacetic acid (5-HIAA), were measured in the caudate-putamen of anesthetized and awake rats using intracerebral microdialysis coupled to HPLC with fluorimetric detection. A dialysis probe (of the loop type) was perfused with Ringer solution at 2 microliters/min, and samples collected every 30 or 60 min. Basal indole levels were followed for up to 4 days in both intact and 5,7-dihydroxytryptamine (5,7-DHT) lesioned animals. Immediately after the probe implantation, the striatal 5-HT levels were about 10 times higher than the steady-state levels that were reached after 7-8 h of perfusion. The steady-state baseline levels, which amounted to 22.5 fmol/30 min sampling time, remained stable for 4 days. In 5,7-DHT-denervated animals, the steady-state levels of 5-HT, measured during the second day after probe implantation, were below the limit of detection (less than 10 fmol/60 min). However, during the first 6 h post-implantation, the 5-HT output was as high as in intact animals, which suggests that the high 5-HT levels recovered in association with probe implantation were blood-derived. As a consequence, all other experiments were started after a delay of at least 12 h after implantation of the dialysis probe. In awake, freely moving animals, the steady-state 5-HT levels were about 60% higher than in halothane-anesthetized animals, whereas 5-HIAA was unaffected by anesthesia. KCl (60 and 100 mM) added to the perfusion fluid produced a sharp increase in 5-HT output that was eight-fold at the 60 mM concentration and 21-fold at the 100 mM concentration. In contrast, 5-HIAA output dropped by 43 and 54%, respectively. In 5,7-DHT-lesioned animals, the KCl-evoked (100 mM) release represented less than 5% of the peak values obtained for the intact striata. Omission of Ca2+ from the perfusion fluid resulted in a 70% reduction in baseline 5-HT output, whereas the 5-HIAA levels remained unchanged. High concentrations of tetrodotoxin (TTX) added to the perfusion medium (5-50 microM) resulted in quite variable results. At a lower concentration (1 microM), however, TTX produced a 50% reduction in baseline 5-HT release, whereas the 5-HIAA output remained unchanged. The 5-HT reuptake blocker, indalpine, increased the extracellular levels of 5-HT sixfold when added to the perfusion medium (1 microM), and threefold when given intraperitoneally (5 mg/kg). By contrast, the 5-HIAA level remained unaffected during indalpine infusion.(ABSTRACT TRUNCATED AT 400 WORDS)
Kalén
P
P
Department of Medical Cell Research, University of Lund, Sweden.
Strecker
R E
RE
Rosengren
E
E
Björklund
A
A
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000758:Anesthesia; D000818:Animals; D001921:Brain / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002421:Caudate Nucleus / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003714:Denervation; D003956:Dialysis; D005260:Female; D006221:Halothane; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011699:Putamen / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists; D013779:Tetrodotoxin / Q000494:pharmacology
D010880:Piperidines; D012702:Serotonin Antagonists; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D013779:Tetrodotoxin; D006897:Hydroxyindoleacetic Acid; D011189:Potassium Chloride; D002118:Calcium; D006221:Halothane; C018181:indalpine