Effect of Chronic Methanol Administration on Amino Acids and Monoamines in Retina, Optic Nerve, and Brain of the Rat A. Gonza ´lez-Quevedo,* F. Obrego ´n,† M. Urbina,† T. Rousso ´,* and L. Lima† ,1 †Laboratorio de Neuroquı ´mica, Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela; and *Instituto de Neurologı ´a y Neurocirugı ´a, Ciudad de la Habana, Cuba Received January 28, 2002; accepted June 26, 2002 Effect of Chronic Methanol Administration on Amino Acids and Monoamines in Retina, Optic Nerve, and Brain of the Rat. Gonza ´lez-Quevedo, A., Obrego ´n, F., Urbina, M., Rousso ´, T., and Lima, L. (2002). Toxicol. Appl. Pharmacol. 185, 77– 84. The clinical and electroretinographic features of chronic meth- anol intoxication are scarce, and neurotransmitterstudies have not been conducted. In addition, most of the studies in the field include results after acute administration. In the present work, a chronic methanol intoxication scheme (2 g/kg/day ip for 2 weeks) was carried out in Sprague–Dawley rats previously depleted of folates with methotrexate. Taurine (2%) in drinking water was also administered in two groups of animals. Blood formate levels were increased in methotrexate–methanol-treated animals with respect to controls (0.98  0.09 and 0.30  0.03 mM, respectively). Amino acids and monoamines were determined in plasma and in retina, optic nerve, hippocampus, and posterior cortex by HPLC with fluorescence or electrochemical detection. The main finding was an increased aspartate content in the optic nerve in metho- trexate methanol-treated animals. Methanol alone increased glu- tamate, aspartate, glutamine, taurine, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid levels in the hippocampus and 5-hy- droxytryptamine in the retina. Taurine administration had no significant effect on changes induced by methanol treatment. We concluded that chronic methanol administration produced accumulation of aspartate, an excitotoxic amino acid, in the optic nerve. These findings contribute to the understanding of methanol neurotoxicity and might indicate a relationship between chronic methanol consumption and the development of optic neuropathies. © 2002 Elsevier Science (USA) Key Words: amino acids; methanol toxicity; monoamines; neu- rotransmitters; optic nerve; retina; taurine. Methanol (MeOH) toxicity has been widely studied since it has been recognized as a serious neurotoxin in humans (Mc- Martin et al., 1980). The clinical features of acute MeOH poisoning in man have been amply documented, and include formic acidemia, metabolic acidosis, visual toxicity, coma, and even death (Ingemansson, 1984). It is well known that the nervous system, and specifically the visual system, has in- creased susceptibility for MeOH intoxication (Wallace et al., 1997; Sadun, 1998). In mammalian species, MeOH is metabolized to formalde- hyde in the liver and, by subsequent oxidative steps, formic acid and carbon dioxide are formed (Makar and Tephly, 1977). The metabolism of formate to carbon dioxide is mediated through a tetrahydrofolate-dependent pathway (Eells et al., 1982), and formic acid has been identified as the metabolite responsible for the toxic effects of MeOH (McMartin et al., 1980; Eells et al., 1996). Nonprimate models, in which formate oxidation is inhibited, have been used in order to study the mechanisms underlying MeOH intoxication, thus allowing formate to accumulate to toxic concentrations following MeOH administration. This has been achieved through depleting folates by administering fo- late-deficient diets (Lee et al., 1994a,b) or chemicals that interfere with tetrahydrofolate regeneration such as nitrous oxide (Eells et al., 1982; Eells, 1991; Murray et al., 1991; Eastman et al., 1991) or methotrexate (MTX) (Barford et al., 1980; Dorman et al., 1994; Schalinske and Steele, 1996). MTX, a dehydrofolate analog, selectively inhibits formate ox- idation, binding dehydrofolate reductase, thereby inhibiting the reduction of folate to dehydrofolate and then to tetrahydrofo- late (Eastman et al., 1991), and consequently depleting the animal’s folate stores (Schalinske and Steele, 1996). During the last two decades electrophysiological and histo- logical studies have been the main tools employed for studying the effects of acute MeOH toxicity (Eells, 1991; Gamer and Lee, 1994). Despite the fact that the retinal neurotransmitter systems are one of the best studied in the central nervous system (CNS) (Kalloniatis and Tomisich, 1999), to our knowl- edge no studies have been conducted to clarify the role of different neurotransmitter systems in the physiopathology of MeOH intoxication. On the other hand, while abundant information is available conceming the pathogenic mechanisms of acute MeOH toxic- ity in humans and animal models, the effects of chronic low- level exposure to MeOH have been poorly investigated with the exception of some chronic inhalation studies (Lee et al., 1991, 1994a,b; Poon et al., 1994) and a chronic experiment 1 To whom correspondence should be addressed. Toxicology and Applied Pharmacology 185, 77– 84 (2002) doi:10.1006/taap.2002.9477 77 0041-008X/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved.