Effect of particle size and weight fraction of SiC on the mechanical, tribological, morphological, and structural properties of Al-5.6Zn-2.2Mg-1.3Cu composites using RSM: fabrication, characterization, and modelling

Stir-casting was employed to create Al-5.6Zn-2.2Mg-1.3Cu composites with particle sizes ranging from 30 to 90 μm and a weight fraction of 5-15 SiC articles. The mechanical and wear properties of the material have been assessed. The wear-behaviour of Al-5.6Zn-2.2Mg-1.3Cu composites was investigated using dry pin-on-disc wear testing. Various loads (20 N-60 N), speeds (2 m/s-6 m/s), and sliding-distances were used in the sliding wear experiments (2000 m-4000 m). In the experimental process, XRD, SEM, and EDX were used to characterize the microstructures and materials of diverse composites. Uniform dispersion of the SiC particles is clearly observed in the SEM image. The micro hardness of SiC particles increases by 13% when the weight percent of SiC particles is increased from 5% to 15%. SiC particles outperform tiny SiC particles in terms of wear-resistance. With increasing load, the particular wear-rate showed an increasing trend (20-60 N). The wear-rate of the composite lowers as the weight percentage reinforcement increases (wt. 5% to wt. 15%), and the wear-rate of the composite increases when the particle-size (30 μm-90 μm) increases. The results demonstrated that composites supplemented with coarse SiC particles outperform tiny SiC particles in terms of wear resistance.

Influence of vagal nerve stimulation on food intake and body weight--results of experimental studies

The paper reviews recent advances in vagal nerve stimulation for the control of food intake and body weight. The vagal nerves are the predominant pathway in the "brain-gut axis" responsible for short term regulation of food intake. Stimulation of afferent vagal traffic attenuates food intake by vagal projections to nucleus tractus solitarius, arcuate nucleus and its convergence's to thalamic center of satiety. A few studies have been published in this field so far. All of them are consistent and show significant decrease in body mass during vagal stimulation. Due to promising results of experimental studies, clinical trials are expected in the near future.

Loss of interstitial cells of Cajal after pulsating electromagnetic field (PEMF) in gastrointestinal tract of the rats

Exposure to the magnetic field has remarkably increased lately due to fast urbanization and widely available magnetic field in diagnosis and treatment. However, biological effects of the magnetic field are not well recognized. The myoelectric activity recorded from the gastrointestinal and urinary systems is generated by specialized electrically active cells called interstitial cells of Cajal (ICCs). Thus it seems rational that ICC have significant vulnerability to physical factors like an electromagnetic field. The aim of this study was to evaluate the influence of pulsating electromagnetic field (PEMF) (frequency 10 kHz, 30ms, 300 muT burst, with frequency 1Hz) on ICCs density in the rat gastrointestinal tract. Rats were divided into two groups (n=32). The first group was exposed to PEMF continuously for 1, 2, 3, and 4 weeks (n = 16), and the second group (n=16) served as a control. Tissue samples of the rat stomach, duodenum and proximal colon were fixed and paraffin embedded. The tangential sections of 5 microm thickness were stained immunohistochemically with anti-c-Kit (sc-168) antibody and visualized finally by DAB as chromogen (brown end product). C-Kit positive branched ICC-like cells were detected under the light microscope, distinguished from the c-kit-negative non-branched smooth muscle cells and from the c-kit positive but non-branched mast cells and quantitatively analyzed by MultiScan computer program. Apoptosis detection was performed with rabbit anti-Bax polyclonal antibody (Calbiochem, Germany) and LSAB 2 visualization system. The surface of c-Kit immunopositive cells decreased after exposure to PEMF in each part of the gastrointestinal tract. Reduced density of ICCs was related to exposure time. The most sensitive to PEMF were ICCs in the fundus of the stomach and in the duodenum, less sensitive were ICCs in the colon and pacemaker areas of the stomach. No marked changes in ICC density in the pyloric part of the stomach were observed. We demonstrate that the PEMF induced apoptosis dependent decrease in ICC expression.

The effects of baclofen on the feeding behaviour and body weight of vagally stimulated rats

It is hypothesised that the GABA(B) receptor agonist baclofen increases or has no effect on food intake, and electrical stimulation of vagal nerves decreases food intake. The aim of this study was to evaluate the effects of baclofen in vagally stimulated rats.

MATERIAL AND METHODS

Thirty two Wistar rats were divided into five groups: group A scheduled for microchip implantation for vagal stimulation, group B for sham operation, group C for microchip implantation and baclofen medication, group D for baclofen medication only and group E for gastric motility evaluation under influence of baclofen. The following parameters were then evaluated: food intake and body mass, gastric motility, leptin, insulin, and glucose serum levels.

RESULTS

In the comparison of groups B and A, daily food intake and body weight gain decreased by 17% (p<0.05) and by 22% (p<0.05), respectively. Baclofen alone (group D) did not significantly change either food intake nor diurnal body weight compared to the controls, but when used in conjunction with the microchip (group C) it did significantly reduce effect of vagal neuromodulation (p<0.05). Furthermore, a significant decrease in leptin and glucose levels was detected in group C: 677 to 165 pg/ml (p<0.05) and 5,93 to 4,88 mmol/l (p<0.05), respectively. The administration of baclofen stimulated significantly gastric motility and elicited irregular motor migrating complex (327+/-200 against control 255+/-52 cmH2O/s).

CONCLUSIONS

These results suggest that microchip vagal neuromodulation through increased vagal afferent activity induces an alteration in the feeding behaviour and decreases nocturnal food intake and body weight. These effects were partially attenuated by baclofen. The data suggests that GABA(B) receptors play an important role in the pathomechanism of attenuation of food intake induced by vagal nerve stimulation.

Encoding meal in integrated vagal afferent discharge

Vagal afferents are integral part of the negative feedback loop induced by constitution and size of food stomach and jejunum. Aim of this study was to assess vagal discharge in response to food and gastric distension in rats. Electrophysiological recordings of vagal afferents in fasted (n=32), fed rats (n=20) and during gastric balloon distension (n=12) were performed. After 60 minutes of fasted nerve recording tube feeding was done. Fasted rats also underwent gastric distension via oesophagus. Vagal afferents discharges were analysed with dual time-amplitude window discriminator. Total vagal afferent discharge in fasted and fed rats revealed 0.3 +/- 0.12 vs 0.56 +/- 0.22 Hz (p<0.05). We observed two distinct discharge patterns: high amplitude low frequency (HALF) and low amplitude high frequency (LAHF). HALF spikes were observed more frequent in fasted than in fed rats (0.05 +/- 0.02 vs. 0.03 +/- 0.016 Hz (p<0.05). Conversely LAHF spikes in fed rats predominated over their occurrence in fasted rats: 0.52 +/- 0.2 vs. 0.25 +/- 0.12 Hz (p<0.05). Left vagal afferents discharge rises with gastric distension of 6, 8 and 10 ml and were: 0.46 +/- 0.22 Hz, 0.65 +/- 0.31 Hz, 0.86 +/- 0.33 Hz (p<0.05) respectively. Similar discharge showed right vagal afferents: 0.41 +/- 0.08 Hz, 0.51 +/- 0.13 Hz and 0.77 +/- 0.27 Hz (p<0.05) for 6, 8 and 10 ml of distension, respectively. We conclude that interdigestive information from gastrointestinal tract is encoded in high amplitude low frequency of spikes pattern in the vagus nerves.

Capasaicin induced deafferentation enhances the effect of electrical vagal nerve stimulation on food intake and body mass

Study was based on hypothesis that electrical stimulation (ES) with parameters obtained from analysis of vagal afferent discharge fed state may fake brain with satiety state. We evaluated effect of denervation of vagal capsaicin-sensitive afferents on food intake and body weight in rats with ES of vagal nerves using microchip (MC). Group A was scheduled to MC implantation, B to sham operation only, C to MC implantation and capsaicin vagal deafferentation, and D to capsaicin denervation only. ES lasted 24 days. MC parameters were 0.05 Hz, 0.1s, 0.55 V. ES of left vagus significantly reduced total food intake as well as the mean daily intake in groups A and C in comparison to control and D group (ANOVA, F=18.55, p=0.0038). Body weight was lower in group A (3462 g) and C (2727 g) then in control (3814 g) and D (3568 g) (F=25.68, p=0.00068). Leptin decreased in C (165 pg/mL) in comparison to A (625 pg/mL), B (677 pg/mL), and D (612 pg/mL) (p<0,05), mainly due to ES (F=7.27, p=0.019). Glucose was decreased in A (F=5.55, p=0.036) - by 11% and by 16% in C group. Proper vagal neuromodulation results in central and peripheral effects causing food intake and body weight downregulation.

Effects of vagal neuromodulation and vagotomy on control of food intake and body weight in rats

Food induced neurohumoral signals are conduced to data processing brain centers mainly as vagal afferent discharge resulting in food intake regulation. The aim of this study was to evaluate effects of vagal nerve neuromodulation in control of food intake with fed-pattern microchip (MC) pacing. Experiments were performed on 60 rats divided on 5 groups: I group 0,05Hz left vagal pacing, II - pacing of both vagal nerves with MC 0,05Hz, III- left vagal MC 0,1Hz pacing, IV - pacing of both vagal nerves with MC 0,1 Hz was performed. In group V left vagal pacing was combined with right side abdominal vagotomy. Body weight and total food intake decreased by 12% and 14% (I), 26% and 30%(II), 8% and 21%(III), 14% and 30%(IV), 38% and 41%(IV), respectively (p<0.05). Effects of both vagal nerves stimulation on final body weight and food intake was significantly more effective than only single nerve MC pacing however most effective was stimulation with 0,1Hz combined with right vagotomy. We conclude that vagal stimulation reduce food intake and body weight by increasing vagal afferent signals. Our results suggest that information in vagal afferents can be modulated resulting in changes of feeding behaviour and body weight.

The role of vagal efferents in regulation of gastric emptying and motility in rats

Nonpharmacologic regulation of gastrointestinal motility may become competitive to actually applied methods in the nearest future. The Aim of this study was to evaluate effect of vagal stimulation on gastric motility and emptying. Experiments were performed on 30 male Wistar rats in vivo. Electrodes (120 um O Cr/Mo Microfil Industries) were placed on right vagal trunk below diaphragm without affecting its integrity. The fistula was implanted in gastric antrum. Stimulation parameters were: 0.3 V; 0.5 Hz, impulse duration--10 msec, time stimulation--5 min. Gastric pressure (balloon, Synectics pressure transducer, Sweden) and gastric emptying (red phenol method) were measured subsequently during and between stimulations.

RESULTS

Stimulation significantly decreased amplitude of gastric contractions about 14% (52.7 +/- +/- 24.5 vs control 66.8 +/- 15.0; p < 0.05) and increased liquid gastric emptying from isotonic solution about 10% (87.35 +/- 4.75 vs control 75.31 +/- 11.24; p < 0.001), hypertonic liquid about 15% (49.05 +/- 12.16 vs control 34.1 +/- 13.68; p < 0.001) and hypotonic liquid about 7% (83.05 +/- 8.8 vs control 76.29 +/- 11.88). The frequency of gastric contractions did not change significantly in Fast Fourier Analysis of the period of stimulations and in control group. CCK concentrations were not significantly different between stimulated and control group (0.3 +/- 0.08 vs control 0.27 +/- 0.06 pmol/L). L-NAME infusion abolished completely acceleration of gastric emptying of isotonic solution (50.38 +/- 12.66 vc control 87.82 +/- 5.49; p < 0.05), hypertonic solution (32.17 +/- 15.09 vs control 51.65 +/- 10.74; p < 0.05) and hypotonic solution (60.42 +/- 12.05 vs control 82.67 +/- 8.06; p < 0.05) during electrical stimulation.

DISCUSSION

In this experiment efferent stimulation of abdominal vagal nerve release neuromediators from afferent and efferent fibers. The main regulator seems to be nitric oxide. These results indicate the effective vagal nerve stimulation affects gastric motility and emptying. It is likely that observed effects reflect integrated response with activating vago-vagal reflexes and neurohumoral factors.

[Effect of chemical sympathectomy on myoelectric activity of the small bowel]

Central and peripheral noradrenergic system modulates myoelectric activity of the small bowel. Aim of this study was to evaluate the role of peripheral noradrenergic system in modulation of slow waves activity. Recordings of slow waves were performed on 20 conscious rats chronically fitted with 2 unipolar electrodes. After controls recording the animals were injected i.p. with 6-hydroxydopamine (6-OHDA--Sigma H8523) and the recording were performed on daily basis through the period of one month.

RESULTS

The increase of frequency slow waves during the first week after 6-OHDA from 0.61 (+/- 0.11) to 0.71 (+/- 0.03), (p. < 0.05), and amplitude from 14468 +/- 11196 to 19128 +/- 5282 (microV)2 (p > 0.05) were observed. Variability in control recording was higher (SD +/- 0.11) than after 6-OHDA (SD 0.03). Next day diarrhoea after 6-OHDA occurred, persisted despite return normal myoelectric activity. Slow waves frequency gradually returns to control value after the fourth week.

CONCLUSION

Peripheral noradrenergic system has a significant effect on the frequency and variability of slow wave and minor role on its amplitude but no on diarrhoea pattern.

[Interstitial cells of Cajal and their pacemaker function]

Interstitial cells of Cajal are known more than 100 years. These cells are proved now as slow wave pacesetters. Ultrastructure and physiologic pacemaker's activity is well described by many authors. Dysfunction of these cells is associated with different pathological states in gastrointestinal tract. Strong relationships between GI motility diseases and qualitative and quantitative changes of ICC are observed. Nowadays most of the gastroenterologists agree that evaluation of these cells should become routine diagnostic procedure. We gave a short review of recent achievements and ideas on interstitial cells of Cajal function in gastroenterology.