Chronic exposure to aluminium impairs the glutamate-nitric oxide-cyclic GMP pathway in the rat in vivo Carlos Hermenegildo a , Rosana SaÂez a , Claudio Minoia b , Luigi Manzo b , Vicente Felipo a, * a Instituto de Investigaciones Citologicas, Fundacio Ân Valenciana de Investigaciones Biome Âdicas, Amadeo de Saboya, 4. 46010, Valencia, Spain b Toxicology Unit, University of Pavia and Salvatore Maugeri Foundation Medical Centre, Pavia, Italy Received 12 October 1998; received in revised form 21 December 1998; accepted 4 January 1999 Abstract Aluminium is neurotoxic and is considered a possible etiologic factor in Alzheimer's disease, dialysis syndrome and other neurological disorders. The molecular mechanism of aluminium-induced impairment of neurological functions remains unclear. We showed that aluminium impairs the glutamate-nitric oxide-cGMP pathway in cultured neurons. The aim of this work was to assess by in vivo brain microdialysis whether chronic administration of aluminium in the drinking water (2.5% aluminium sulfate) also impairs the glutamate-nitric oxide-cGMP pathway in the cerebellum of rats in vivo. Chronic exposure to aluminium reduced NMDA-induced increase of extracellular cGMP by ca 50%. The increase in extracellular cGMP induced by the nitric oxide generating agent S-nitroso-N-acetylpenicillamine was higher (240%) in rats treated with aluminium than in controls. Immunoblotting experiments showed that aluminium reduced the cerebellar content of calmodulin and nitric oxide synthase by 34 and 15%, respectively. Basal activity of soluble guanylate cyclase was decreased by 66% in aluminium-treated rats, while the activity after stimulation with S-nitroso-N-acetylpenicillamine was similar to controls. Basal cGMP in the cerebellar extracellular space was decreased by 50% in aluminium-treated rats. These results indicate that chronic exposure to aluminium reduces the basal activity of guanylate cylcase and impairs the glutamate-nitric oxide-cGMP pathway in the animal in vivo. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction Humans are exposed to aluminium (Al), the third most abundant element in the Earth's crust, from var- ious therapeutic treatments (especially antacids) and environmental sources, such as cookware, cans, some foods and drinking water. Al is present in small amounts in mammalian tissues, and is toxic when more than trace amounts enter the body. It is known that Al is neurotoxic (Boegman and Bates, 1984; Jope and Johnson, 1992), and it is considered a causative factor in the development of several neurological dis- orders, including dialysis syndrome (Alfrey et al., 1976), amyotrophic lateral sclerosis (Gadjusek and Salazar, 1982; Perl et al., 1982) and Alzheimer's (Good et al., 1992; Lukiw, 1997; Perl and Brody, 1980), and Parkinson's diseases (Hirsch et al., 1991). The molecular mechanism of Al neurotoxicity has not been clari®ed, but some reports suggest that Al interferes with glutamatergic neurotransmission (Platt et al., 1994; Provan and Yokel, 1992). We have recently shown that Al impairs the neur- onal glutamate (Glu)-nitric oxide (NO)-cyclic GMP pathway in primary cultures of cerebellar neurons (Cucarella et al., 1998). Activation of ionotropic (mainly NMDA) glutamate receptors leads to increased intracellular Ca 2+ , which, after binding to Neurochemistry International 34 (1999) 245±253 0197-0186/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0197-0186(99)00010-8 * Corresponding author. Tel.: +349 6 3391250; fax: +349 6 3601453. E-mail address: vfelipo@ochoa.®b.es (V. Felipo) Abbreviations: Al, aluminium; BSA, bovine serum albumin; Glu, glutamate; IBMX, isobutylmethylxanthine; NMDA, N-methyl-D- aspartate; NO, nitric oxide; SNAP, S-nitroso-N-acetylpenicillamine.