In vivo electrochemical monitoring of serotonin in spinal dorsal horn with Nafion-coated multi-carbon fiber electrodes.

Biosensors sensitive for in vivo monitoring of serotonin (5-HT) in the CNS by differential normal pulse voltammetry were constructed by coating treated multicarbon fiber electrodes (mCFEs) with Nafion (N-mCFE). In vitro sensitivities of mCFE and N-mCFE were compared in solutions ranging from 5 nM to 20 microM of uric acid (UA), 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT. The mCFEs were three to seven times less sensitive for 5-HIAA or UA than for 5-HT. Nafion treatment dramatically decreased sensitivity for 5-HIAA and UA of N-mCFEs (approximately 10(3) times), whereas it remained in the nanomolar range for 5-HT. In vivo, in the dorsal horn of the lumbar spinal cord of anesthetized rats, the monoamine oxidase inhibitor clorgyline (10 mg/kg i.p.) produced a reduction (55 +/- 3% at 180 min) of peak 3 of oxidation current (characteristic of 5-hydroxyindoles) monitored with mCFEs, but with N-mCFEs (in this latter case the peak was termed 3N) peak 3N increased to 135 +/- 5% at 180 min. The 5-HT release-inducer p-chloroamphetamine (PCA; 6 mg/kg i.p.) induced a slight (12 +/- 3% at 150 min) decrease in peak 3 measured with mCFEs, whereas with N-mCFEs PCA induced a rapid increase of peak 3N (137 +/- 6% at 90 min). The xanthine oxidase inhibitor allopurinol (10 mg/kg i.p.) produced a decrease (30 +/- 3% at 180 min) in peak 3 (mCFEs), but peak 3N (N-mCFEs) was not affected (106% at 180 min). After pretreatment with allopurinol, PCA also produced an increase (135 +/- 6% at 90 min) in peak 3N.(ABSTRACT TRUNCATED AT 250 WORDS)