A simplified method for the measurement of caffeine in plasma and brain: evidence for a cortical-subcortical caffeine concentration differential in brain.

We describe a much simplified high-performance liquid chromatography (HPLC) method for the measurement of caffeine in plasma and brain. A particularly attractive feature of this method is that a simple methanol/water (60:40) mobile phase can be used both for plasma and brain samples. In addition, the method is compatible with solid-phase extraction for plasma samples and conventional brain tissue preparation for biogenic amine analysis with HPLC. Using this method to measure the concentrations of caffeine in plasma and brain of rats which received 10 or 50 mg/kg caffeine injections, we found substantial concentration differences between cortical and subcortical brain tissue. Specifically, at the 10 mg/kg dose, a nearly 2-fold difference between cortex and striatum caffeine concentrations was observed. A shortcoming of many neurobehavioral studies of caffeine effects is the absence of caffeine concentration measurements. The simplicity of the present method for the measurement of caffeine in plasma and brain tissue makes it a practical and feasible procedure to incorporate into neurobehavioral studies designed to elucidate the CNS actions of caffeine.