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

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 interfere with the aversive effect of naloxone (NLX) and low expression of c-Fos during testing of morphine-induced conditioned place preference (CPP) in rats.

The Wistar rats (weighing 300-350 g) were cannulated bilaterally by stereotaxic apparatus for the CeA (AP= –2.12 mm; L= ±4.1 mm; V= 7.8 mm). CPP was conducted via a three-phase unbiased procedure. Morphine (0.5-7.5 mg/kg) was injected subcutaneously (sc) during the conditioning phase. NLX (0.4 µg/rat) was given, intra-CeA, 10 min before the test. Ag-NPs (0.01 µg/rat) was administered prior to the antagonist. The control group received saline (1 µL/rat, intra-CeA). c-Fos expression was quantified immunohistochemically in rats subsequent the injections:

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.

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.