Interaction of nicotine with morphine potency in .

Aims: Many studies have been carried out about the interaction between nicotine and morphine in higher animals. Although previous behavioral and pharmacological evidence indicated the presence of opioid system in protozoa, there is no available data about nicotine effect on the potency of morphine in eukaryotic unicellular organisms such as protozoa. Hence, this work aims to investigate the interaction of nicotine with morphine in the protozoan .

Main Methods: According to our innovative model, the movement behavior of was investigated with a numerical scale using the Sedgewick-Rafter counting chamber at the field of view of 4X light microscope objective lens, such that the difference in number of Paramecia cells at definite moments after injection of drugs/substances was considered as a criterion for the behavioral response of .

Key Findings: Results indicated the variations of morphine potency at the dose of 2 μg morphine accompanied by different doses of nicotine in so that the highest aggregation of Paramecia cells occurred at the dose of 2 μg morphine + 4 μg nicotine.

Significance: This confirmed that in eukaryotic unicellular organisms such as , nicotine can reinforce the morphine potency in a dose-dependent manner.