The effects of etorphine, fentanyl and morphine on noradrenaline and dopamine concentrations in the striatum of rat.

The effects of etorphine, fentanyl and morphine on noradrenaline and dopamine concentrations in the striatum of rat. Acta Physiol. Pol. 1977, 28 (2): 107--112. Dopamine (DA) concentrations were determined after administration of etorphine (M 99--0.008 mg/kg), fentanyl (0.006 mg/kg) and very high doses of morphine (20.0 mg/kg). DA was chosen as a striatal neurotransmitter playing the main role in the extrapyramidal system. The concentrations of noradrenaline (NA) were determined for comparison. Etorphine in therapeutic doses and morphine in subtoxic doses increased the concentration of DA in striatal neurons. Since, under these conditions, the behavior of animals resembles the symptom complex characteristic of the so-called parkinsonian or postneuroleptic syndrome in which a deficiency of absence of DA has been found in striatum, it might be supposed that the cataleptic action of etorphine and morphine may be due to inhibition of presynaptic striatal structures, with consequent disturbances in DA release from its stores.