Abstract
Eschscholzia californica Cham. (Papaveraceae) is traditionally used by the Indians as a medicinal plant for its anxiolytic, anticonflict, analgesic and sedative properties. The mechanisms of action for the sedative and anxiolytic activities have not been clearly established and so to further investigate the pharmacological profile of E. californica in some painful conditions, a 70% v/v ethanol extract, DERnative=5:1, was tested in rat models of neuropathy induced by chronic constriction injury of the sciatic nerve (CCI), with chemotherapeutic oxaliplatin, and osteoarthritis caused by intrarticular injection of monoiodoacetate. In the CCI model evaluated in the rat paw-pressure test, the examined extract (100 mg kg−1 p.o.) showed an antihyperalgesic effect. Eschscholzia extract, after single injection at a dose of 100–300 mg kg−1 p.o., produced also a statistically significant decrease of pain perception on hyperalgesia induced by oxaliplatin and osteoarthritis, while in the same condition gabapentin did not display any antihyperalgesic effect. Furthermore, in the range of antihyperalgesic doses, the extract was efficacious in the hot-plate (thermal stimulus) and carrageenan tests (inflammatory model) without producing any behavioral impairment, as evaluated by the Irwin test. The analgesic effect exhibited by Eschscholzia extract in the mouse hot-plate test was not antagonized by naloxone, indicating that opioid neurotransmission is not involved in the effect.
The above reported results suggest that a 70% (v/v) ethanol dried extract (DERnative=5:1) of E. californica might represent a promising product for the therapy of acute and chronic pain.