Melatonin, a hormone monitorable in vivo by voltammetry

• Published in: Analyst (London) Vol. 119; no. 10; pp. 2193 - 2197
• Main Authors: CRESPI, F, RATTI, E, TRIST, D. G
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.10.1994
• Subjects: Analysis of Variance; Animals; Biological and medical sciences; Brain - drug effects; Brain - metabolism; Brain Chemistry; Butyrates - pharmacology; Butyric Acid; Electrochemistry - instrumentation; Electrochemistry - methods; Fundamental and applied biological sciences. Psychology; General aspects. Models. Methods; Hydroxyindoleacetic Acid - metabolism; Male; Melatonin - analysis; Melatonin - metabolism; Oxidation-Reduction; Pineal Gland - drug effects; Pineal Gland - metabolism; Rats; Rats, Sprague-Dawley; Sensitivity and Specificity; Tryptophan - metabolism; Tryptophan - pharmacology; Vertebrates: nervous system and sense organs; Suprachiasmatic nucleus; Endocrine gland; Rat; Aminoacid derivative hormone; Rodentia; Differential impulse voltamperometry; Pineal body; Hypothalamus; Melatonine; In vivo; Vertebrata; Mammalia; Biosensor; Measurement method; Quantitative analysis
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/AN9941902193

Melatonin, an indoleamine hormone synthesized in the pinealocytes, is electroactive at the surface of pre-treated carbon fibre microelectrodes (mCFE) in vitro when using differential-pulse voltammetry (DPV), at the specific oxidation potential of approximately +570 mV. In vivo DPV experiments have then been performed in melatonergic regions such as the pineal gland or the suprachiasmatic nucleus (SCH) of anaesthetized adult male rats. These experiments indicated the feasibility of simultaneous measurements of the indolaminergic peak 3, which occurred at approximately +280 mV, due mainly to the oxidation of extracellular 5-hydroxyindoleacetic acid (5HIAA), and a signal at approximately +580 mV which we called peak M. Pharmacological in vivo experiments performed in anaesthetized rats prepared for DPV analysis with the mCFE implanted into the pineal gland or the SCH indicated that intravenous or intra-cerebral injections of exogenous melatonin (5 mg kg-1 or 2 micrograms microliter-1, n = 3, respectively) were followed by a selective and significant increase of in vivo peak M. Other in vivo experiments with anaesthetized rats prepared for DPV analysis with the mCFE into the SCH showed that tryptophan [TRY, 30 mg kg-1 intravenous (i.v.), n = 3] and n-acetyl serotonin (nA-5HT, 5 mg kg-1 i.v., n = 3), both precursors of melatonin, were responsible for a transient but significant increase in the size of peak M (approximately 320% or 126% of control levels within 10 min or 20 min, respectively).