ALTERED CONTENT AND MODULATION OF SOLUBLE GUANYLATE CYCLASE IN THE CEREBELLUM OF RATS WITH PORTACAVAL ANASTOMOSIS P. MONFORT, a R. CORBALA è N, a L. MARTINEZ, b J.-C. LO è PEZ-TALAVERA, b J. CO è RDOBA b and V. FELIPO a * a Laboratory of Neurobiology, Instituto de Investigaciones Citologicas, Fundacio ¨ n Valenciana de Investigaciones Biome ¨dicas, Amadeo de Saboya 4, 46010 Valencia, Spain b Servicio de Medicina Interna-Hepatolog| ¨a, Hospital Vall d'Hebron, Barcelona, Spain AbstractöIt is shown that the glutamate^NO^cGMP pathway is impaired in cerebellum of rats with portacaval anas- tomosis in vivo as assessed by in vivo brain microdialysis in freely moving rats. NMDA-induced increase in extracellular cGMP in the cerebellum was signi¢cantly reduced (by 27%) in rats with portacaval anastomosis. Activation of soluble guanylate cyclase by the NO-generating agent S-nitroso-N-acetyl-penicillamine and by the NO-independent activator YC-1 was also signi¢cantly reduced (by 35^40%), indicating that portacaval anastomosis leads to remarkable alterations in the modulation of guanylate cyclase in cerebellum. Moreover, the content of soluble guanylate cyclase was increased ca. two-fold in the cerebellum of rats with portacaval anastomosis. Activation of soluble guanylate cyclase by NO was higher in lymphocytes isolated from rats with portacaval anastomosis (3.3-fold) than in lymphocytes from control rats (2.1-fold). The results reported show that the content and modulation of soluble guanylate cyclase are altered in brain of rats with hepatic failure, resulting in altered function of the glutamate^NO^cGMP pathway in the rat in vivo. This may lead to alterations in cerebral processes such as intercellular communication, circadian rhythms, including the sleep^waking cycle, long-term potentiation, and some forms of learning and memory. ß 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved. Key words: hepatic encephalopathy, hyperammonemia, NMDA receptor, nitric oxide. Chronic liver disease leads to altered cerebral function resulting in a complex neuropsychiatric syndrome called hepatic encephalopathy, which can lead to hepatic coma and death. The molecular bases of the neurological alter- ations found in hepatic encephalopathy are not clearly understood. Hyperammonemia is considered one of the main factors responsible for the neurological alterations found in hepatic encephalopathy. Both hyperammone- mia and hepatic failure alter glutamatergic neurotrans- mission at di¡erent steps (Bosman et al., 1992; Hamberger and Nystro «m, 1984; Knecht et al., 1997; Marcaida et al., 1995; Mena and Cotman, 1985; Moroni et al., 1983; Norenberg et al., 1997; Peterson et al., 1990). Some reviews on the e¡ects of hyperammonemia and liver failure on glutamatergic neurotransmission have recently been published (Albrecht, 1998; Michalak and Knecht, 1997; Min ¬ana et al., 1997). It has been suggested that hepatic encephalopathy may be a con- sequence of altered glutamatergic neurotransmission (Butterworth, 1992). Activation of ionotropic, mainly NMDA, glutamate receptors leads to increased intracellular free calcium which, after binding to calmodulin, activates NO syn- thase, leading to increased production of NO, which in turn activates soluble guanylate cyclase, resulting in increased formation of cGMP. The glutamate^NO^ cGMP pathway (see Fig. 1) modulates important cere- bral processes such as intercellular communication, circadian rhythms, including the sleep^waking cycle, long-term potentiation (LTP), and some forms of learn- ing and memory (Boulton et al., 1995; Ding et al., 1994, 1997; Pape, 1995; Sistiaga et al., 1997). We have recently shown, using a model of hyperam- monemia without hepatic failure, that chronic moderate hyperammonemia in rats, similar to that present in patients with liver cirrhosis, impairs the neuronal gluta- mate^NO^cGMP pathway in the animal in vivo, as deter- mined by in vivo brain microdialysis in freely moving rats (Hermenegildo et al., 1998), resulting in decreased for- mation of cGMP due to altered activation of soluble guanylate cyclase. These results were obtained using a 1119 *Corresponding author. Tel.: +34-96-3391250; fax: +34-96- 3601453. E-mail address : vfelipo@ochoa.¢b.es (V. Felipo). Abbreviations : aCSF, arti¢cial cerebrospinal £uid ; ANOVA, analy- sis of variance ; EDTA, ethylenediaminetetra-acetate ; EGTA, ethylene glycol-bis-(2-amino ethyl-ether)N,N,NP,NP-tetraacetic acid ; HEPES, N-(2-hydroxyethyl)piperazine-NP-(2-ethanesulfonic acid) ; IBMX, isobutylmethyl xanthine ; LTP, long-term poten- tiation; NMDA, N-methyl-D-aspartate ; SDS, sodium dode- cylsulfate; SNAP, S-nitroso-N-acetyl-penicillamine ; YC-1, 3-(5P-hydroxymethyl-2P-furyl)-1-benzyl-indazole. NSC 4973 5-7-01 www.elsevier.com/locate/neuroscience Neuroscience Vol. 104, No. 4, pp. 1119^1125, 2001 ß 2001 IBRO. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved PII:S0306-4522(01)00128-2 0306-4522 / 01 $20.00+0.00