Hypericum polyanthemum cyclohexane extract potentiates behavioral effects and neurodegeneration induced by nigral infusions of 6-hydroxydopamine in rats.

Introduction: Parkinson's Disease (PD) is a progressive neurodegenerative disorder, hallmark of which is loss of nigral dopaminergic neurons. Since a  Hypericum polyanthemum extract inhibits monoamine reuptake and some of its constituents present cytotoxic properties, the aim of this study was to evaluate the effect of this extract in an animal PD model.

Methods: Adult Wistar rats (110 days old) received 6-hydroxydopamine (6-OHDA) infusions into the right medial forebrain bundle. A cyclohexane extract from aerial parts of H. polyanthemum (POL; 90 mg/kg/administration; gavage) was administered in three different regimens. In Regimens 1 and 2, rats received 3 administrations of POL starting 4 or 24 h after 6-OHDA infusion, respectively. In Regimen 3, these administrations were carried out 1 day before any evaluation of ipsilateral rotational activity induced by methylphenidate (MP, 20 mg/kg, i.p.). MP was administered 10, 45, and 85 days after 6-OHDA infusion in all groups. Nigral tyrosine hydroxylase (TH) immunocontent was evaluated 120 days after 6-OHDA infusion in animals submitted to Regimen 2 only. The effect of POL on apomorphine-induced climbing behavior in non-lesioned adult CF1 mice (60 days old) treated with POL was also evaluated.

Results: Regimen 2 increased MP-induced rotational activity and decreased nigral TH levels in 6-OHDA-lesioned rats. Rotational activity was not altered in regimens 1 and 3. In addition, no change in climbing behavior was observed in non-lesioned mice.

Conclusion: Together, these results indicate that, in 6-OHDA-lesioned rats, a cyclohexane  H. polyanthemum extract potentiates neurotoxicity and MP-induced motor asymmetry depending on the time of administration. In the short term, it seems to not act directly on mice dopaminergic receptors.