Silver nanoparticles (AgNP) are widely used for their antibacterial properties. Incorporation of AgNP into food-related products and health supplements represents a potential route for oral exposure to AgNP; however, the effects of such exposure on the gastrointestinal system are mostly unknown. This study evaluated changes in the populations of intestinal-microbiota and intestinal-mucosal gene expression in Sprague-Dawley rats (both male and female) that were gavaged orally with discrete sizes of AgNP (10, 75 and 110 nm) and silver acetate. Doses of AgNP (9, 18 and 36 mg/kg body weight/day) and silver acetate (100, 200 and 400 mg/kg body weight/day) were divided and administered to rats twice daily (∼10 h apart) for 13 weeks. The results indicate that AgNP prompted size- and dose-dependent changes to ileal-mucosal microbial populations, as well as, intestinal gene expression and induced an apparent shift in the gut microbiota toward greater proportions of Gram-negative bacteria. DNA-based analyses revealed that exposure to 10 nm AgNP and low-dose silver acetate caused a decrease in populations of Firmicutes phyla, along with a decrease in the Lactobacillus genus. Analysis of host gene expression demonstrated that smaller sizes and lower doses of AgNP exposure prompted the decreased expression of important immunomodulatory genes, including MUC3, TLR2, TLR4, GPR43 and FOXP3. Gender-specific effects to AgNP exposure were more prominent for the gut-associated immune responses. These results indicate that the oral exposure to AgNP alter mucosa-associated microbiota and modulate the gut-associated immune response and the overall homeostasis of the intestinal tract.

Objectives: To define the role of magnetic resonance imaging (MRI) and intraoperative electrophysiological recording in targeting the subthalamic nucleus (STN) in Parkinson's disease and to determine accuracy of electrode placement. Patients and methods: We implanted 54 electrodes into the STN in 27 patients. Target planning was done by coordinate guidelines and visualising the STN on MRI and defined in relation to the mid-point of the AC-PC line. Intraoperative microelectrode recording was used. We adjusted electrode positions for placement in the centre of the STN electrical activity and verified this on postoperative MRI in 16 cases, which were fused to the preoperative images to measure actual error in electrode placement in the three axes.Results: Based on coordinate calculation and MRI localisation, the mean of the target was 11.5 mm lateral, 2.5 mm posterior and 4.1 mm inferior to the mid-point of the AC-PC line. Fifty good electrophysiological recordings of the STN (average length 4.65 mm) were achieved and target point adjusted in 90% of lead placements. The mean of the final target after electrophysiological correction was 11.7 mm lateral, 2.1 mm posterior, and 3.8 mm inferior to the mid-point. The distance from the centre of the electrode artefact to the final target used after electrophysiological recording on the fused images was 0.48 mm, 0.69 mm, and 2.9 mm in the x, y, and z axes, respectively. No postoperative MRI related complication was observed. Conclusion: Both direct visualisation of the STN on MRI and intraoperative electrophysiological recording are important in defining the best target. Individual variations exist in the location of the STN target. Fewer tracks were required to define STN activity on the side operated first. Our current stereotactic method of electrode placement is relatively accurate.

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