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.