Elsevier

Neuroscience

Volume 126, Issue 4, 2004, Pages 879-887
Neuroscience

Upregulation of endothelial nitric oxide synthase maintains nitric oxide production in the cerebellum of thioacetamide cirrhotic rats

https://doi.org/10.1016/j.neuroscience.2004.04.010Get rights and content

Abstract

This study examines the expression and cellular distribution pattern of nitric oxide synthase (NOS) isoforms, nitrotyrosine-derived complexes, and the nitric oxide (NO) production in the cerebellum of rats with cirrhosis induced by thioacetamide (TAA). The results showed local changes in the tissue distribution pattern of the NOS isoforms and nitrated proteins in the cerebellum of these animals. Particularly, eNOS immunoreactivity in perivascular glial cells of the white matter was detected only in TAA-treated animals. In addition, although neither neuronal NOS (nNOS) nor inducible NOS (iNOS) cerebellar protein levels appeared to be affected, the endothelial NOS (eNOS) isoform significantly increased its expression, and NO production slightly augmented in TAA-treated rats. These NOS/NO changes may contribute differently to the evolution of the hepatic disease either by maintaining the guanosine monophosphate–NO signal transduction pathways and the physiological cerebellar functions or by inducing oxidative stress and cell damage. This model gives rise to the hypothesis that the upregulation of the eNOS maintains the physiological production of NO, while the iNOS is silenced and the nNOS remains unchanged. The differential NOS-distribution and expression pattern may be one of the mechanisms involved to balance cerebellar NO production in order to minimize TAA toxic injury. These data help elucidate the role of the NOS/NO system in the development and progress of hepatic encephalopathy associated with TAA cirrhosis.

Section snippets

Animals and cirrhotic experimental model

A total of 20 adult (200–250 g; 4-month-old) male Wistar rats were kept under standard conditions of light and temperature and allowed ad libitum access to a commercial rat chow. Half of these animals were given TAA in the drinking water (300 mg/ml for 97 days) to trigger hepatic cirrhosis (Torres et al., 1998), while the other half served as controls. To verify that the cirrhotic process and the neuronal injury characteristic of hepatogenic encephalopathy (Sarhan et al., 1993, Peeling et al.,

NOS isoform immunocytochemistry

Immunoreactivity (IR) of nNOS (nNOS-IR) in the cerebellar cortex is presented in Fig. 1A, B. Both control (Fig. 1A) and TAA-cirrhotic rats (Fig. 1B) showed nNOS-IR stellate and basket cells; however, basket-cell bodies and their processes surrounding Purkinje cell showed higher IR in TAA-cirrhotic than in control rats (insert in Fig. 1B). In addition, in the molecular layer the stellate-cell population appeared to have not only high IR but also a greater number of nNOS-IR cells in the TAA

Discussion

The results presented here reveal slight changes in the tissue and cellular distribution pattern of the nNOS, iNOS and nitrated proteins in the cerebellum of rats with TAA-induced cirrhosis. In addition, cirrhotic animals showed strong eNOS IR and NADPH-diaphorase activity in perivascular glial cells. Moreover, although neither nNOS nor iNOS cerebellar protein levels appeared to be significantly affected, the eNOS isoform augmented its expression and a trend of increased NO production took

Acknowledgements

This work was supported by Dirección General de Investigación Científica y Técnica (PM98-0126-CO2-02) and Junta de Andalucía (CVI-0184). Santos Blanco is a FPDeI grant holder from Junta de Andalucía. We thank Mr. David Nesbitt for his help in the manuscript preparation.

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