Several works have suggested a potential role for nitric oxide in alcohol-seeking behavior and we have recently shown that the specific blockade of the expression of the neuronal nitric oxide synthase (NOS1) decreases rat ethanol intake. Our previous results have also shown that chronic ethanol exposure has differential effect on the brain NOS activity depending on rat brain area. In the present study, we examine the effects of chronic administration of ethanol on the NOS1-mRNA levels measured with the competitive reverse transcriptase-polymerase chain reaction technique. Chronic administration of ethanol differentially regulated NOS1-mRNA levels depending on rat brain area. Chronic ethanol exposure had no effect on the NOS1-mRNA levels in frontal cortex, but decreased the NOS1-mRNA levels in hippocampus (P<0.01, 39% decrease) and induced a strong increase in striatum (P<0.01, 92% increase). These effects of ethanol were not affected by 7-nitro indazole (25 mg/kg, i.p. daily for 1 week) treatment. These data further support that NOS1 is regulated by chronic exposure to ethanol and that these effects are related to modifications of mRNA levels.