Central administration of yohimbine increases free 3-methoxy-4-hydroxyphenylglycol in the cerebrospinal fluid of the rat.

The effect of the alpha2-antagonist, yohimbine, on cerebrospinal fluid 3-methoxy-4-hydroxyphenylglycol (MHPG), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindolactic acid (5-HIAA) concentrations was studied in vivo. Cerebrospinal fluid was removed at a constant flow rate of 1 microliters/min from the third ventricle of rats and directly analysed by liquid chromatography coupled with electrochemical detection. An intracerebroventricular injection of yohimbine (100 nmol) dramatically increased MHPG levels. These results suggest a functional stimulation of alpha-2 adrenoceptors modulating noradrenergic neurotransmission in vivo.