Changes in Magnetic Resonance Imaging and Sex Behavior After 6-OHDA Injection in the Medial Preoptic Area

Magnetic resonance imaging (MRI) of the brains of male rats was done before and after destroying the catecholamine (CA) fibers by local application of 6-hydroxydopamine (6-OHDA) in the medial preoptic area (mPOA). The male sexual behavior was also assessed before and after injection of this toxic drug. The administration of 6-OHDA (8 μg) resulted in highly variable lesions, as shown by MRI and confirmed by histological examination. A hyperintense area was visible either on one or on both sides, about 1–3 h after the administration of the drug. Postmortem histofluorescence showed destruction of CA fibers in the mPOA on those sides that showed hyperintense areas in the MRI. No CA fiber destruction was seen in those rats that had shown no change in MRI after 6-OHDA injection. There was a transient reduction in sex drive score in all the 6-OHDA-treated rats. The present findings point out a correlation between the MRI changes and CA fiber destruction, whereas the transient reduction in the sexual behavior was not related to these changes. It is suggested that some biochemical events related to 6-OHDA destruction of CA fibers may have been responsible for the hyperintensity seen in the MRI.