N-oleoyl-dopamine decreases muscle rigidity induced by reserpine in rats

N-oleoyl-dopamine (OLDA), a product of condensation of oleic acid and dopamine (DA), is a bioactive compound that crosses the blood-brain barrier after systemic administration. The possibility arises that OLDA could have a potential role in treating DA-related disorders, such as Parkinsons disease (PD). In the present study we seek to determine whether OLDA would affect muscle tone and akinesia in two rat models of PD: the reserpine-evoked muscle rigidity and the reserpine- and haloperidol-induced catalepsy. We found that OLDA (20 mg/kg) significantly decreased muscle rigidity induced by reserpine (2.5 mg/kg), measured as an increased mechanical muscle resistance (MMG) in response to a passive extension and flexion of a rat hind limb at the ankle joint. Moreover, OLDA potently decreased the reserpine-enhanced tonic and reflex electromyographic (EMG) activities recorded before and during the movement, respectively. A lower dose of OLDA (10 mg/kg) failed to have appreciable effects. The reference compound L-DOPA (25 mg/kg) also attenuated the reserpine-increased MMG and EMG activities; the effects were, however, observed much later and were less prominent than those characteristic of OLDA. In contrast to the effects on muscle tone, OLDA (20 and 40 mg/kg) did not influence catalepsy induced by either reserpine (1.25 mg/kg) or haloperidol (0.5 mg/kg). In conclusion, the study demonstrates a novel biological action of N-oleoyl-dopamine consisting of lowering the reserpine-induced muscle rigidity. However, the lack of influence on akinesia suggests that the compound has myorelaxant rather than anti-Parkinsonian properties.