The silver nanoparticles induce c-Fos expression in the central nucleus of amygdala that relief the aversive effect of naloxone in the morphine relied animal

Objective(s): Silver nanoparticles (Ag-NPs) that are used daily in care service can enter the body and create free radicals. Despite the toxicity at high concentrations, these particles are non-toxic and useful at low concentrations. Thus, we investigated the effectiveness of nontoxic Ag-NPs to inhibit the avoiding effect of naloxone (NLX) and low level of c-Fos in the testing of morphine-induced conditioned place preference (CPP) in rat. Methods: The animals (weighing 300-350 g) were surgically equipped by cannulae at the CeA (AP= -2.12 mm; L= ±4.1 mm; V= 7.8 mm). The paradigm was done by using a three-stage technique. Morphine (0.5-7.5 mg/kg) was injected subcutaneously (s.c.) in the second stage. NLX (0.4 µg/rat) was microinjected, intra-CeA, 10 min before the test. Ag-NPs (0.01 µg/rat) were injected before the NLX. The saline (1 µL/rat) was injected, intra-CeA, in the control group. c-Fos level was quantified immunohistochemically in rats at the end of the experiments. Results: The CeA and hippocampal cornu ammonis 1 (CA1) of rats that treated by NLX showed low c-Fos protein levels during testing, whereas levels of protein were high in the brains of morphine conditioned rats. Interestingly, both areas (CeA and CA1) showed similar increases in protein levels when the injection of NLX was combined with the Ag-NPs. However, these regions were not significantly different in the single Ag-NPs receiving and control groups. Conclusions: This indicates that the two regions interact with each other when NLX is injected and that in presence of Ag-NPs the protein levels are elevated in the regions.