Effect of chronic drug treatment on acute c-Fos response. Western blot analysis was used to measure the acute pseudoephedrine induced c-Fos expression in striatum (n = 4) and nucleus accumbens (n = 3) of rats chronically treated with pseudoephedrine (8 day treatment of pseudoephedrine twice a day with an increasing dose at 25, 30, 35, 40 mg/kg i.p., on day 1, 2, 3 and 4–8 respectively, rats were killed 1.5 h after 40 mg/kg, i.p pseudoephedrine injection on day 9). The data (quantification of bands from western blots) is expressed as percentage of c-Fos value of control animals injected with saline. (A value of 100% indicates no difference from control) Values are mean ± S.E.M. 'a' indicates significantly different from control and chronic; 'b' indicates significantly different from acute with p < 0.05.