Characterization of effects of mean arterial blood pressure induced by cocaine and cocaine methiodide on BOLD signals in rat brain

A total of 45 male Sprague‐Dawley rats were employed to determine whether cocaine or cocaine methiodide (CM) administration can induce a significant increase in mean arterial blood pressure (MABP) in rats, and whether such an increase in MABP can produce a global increase in blood oxygenation level‐dependent (BOLD) contrast in the rat brain detectable by functional magnetic resonance imaging (fMRI). Cocaine methiodide is a quaternary derivative of cocaine that shares the same cardiovascular effects of cocaine, but does not penetrate the blood‐brain barrier (BBB). Experimental results demonstrated that both CM (with doses of 2.5 and 7.5 mg/kg) and cocaine (with doses of 1.25 and 5.0 mg/kg) can induce a significant MABP change (30–80%). It was found that CM can only produce scattered, weak, and transient BOLD signals in a few voxels of the rat brain, and that these MABP‐induced BOLD signals are not dose‐dependent. In contrast, the administration of cocaine induced dose‐dependent biphasic BOLD signals that were consistent with pharmacologically‐induced cerebral vascular constriction and neuronal activity in the mesolimbic systems of the rat brain. The potential confounding factor of the MABP changes had little effect on the interpretation of drug‐induced BOLD signal changes. These results confirm that the BOLD‐weighted fMRI method can be extended to map drug‐induced neuronal activity. Magn Reson Med 49:264–270, 2003. © 2003 Wiley‐Liss, Inc.