Science and Education Publishing American Journal of Infectious Diseases and Microbiology 1 1 2013 02 28 Paramecium caudatum Avoids from Naloxone 21 25 EN Manizheh KARAMI Department.of Biology, Faculty of Basic Sciences, Shahed University, Tehran, Iran Seyedeh Samaneh MOEZZI Bahram KAZEMI Seyed Sajad SHAHROKHI AJIDM2013114 10.12691/ajidm-1-1-4 2013 01 13 2013 01 23 2013 02 28 Protozoa aggregate to or avoid from chemical substances. We aimed to show the significance of nitric oxide (NO) in the performance of the eukaryotes to misuse drug exposure. The micro-organism Paramecium caudatum was collected from natural sources and properly isolated by repeatedly sub-cultivation in hay infusion. Number of cells per 1ml of pure medium culture was counted using Sedgwick-Rafter cell chamber. Doses of naloxone (0.05-0.4¦Ìg/¦Ìl) solely or jointly with the NO agents were infused into the chamber. Cell response was recorded after drug infusion with intervals (0-180 sec). Negative control received distilled water (1¦Ìl) instead of naloxone (legend 0). Along with, the Ca channels or cGMP pathway was banded to discuss the mechanism. According to the results, the Paramecia showed negative chemo-taxis to the naloxone, the response which is comparable with signs of withdrawal from abused drugs. This response was potentiated by activation of NO system, but, reversed after usage of the system blocker. The inhibition of Ca channels or cGMP signaling pathway markedly enhanced the avoidance. In conclusion, this study may clearly contribute the signal molecule NO in the dependence of the eukaryotes on sedative misuse drugs.