Studies Of Mechanism Of The Effect Of CCK On Gastrointestinal Tract Sensation Afferent Function On Peripheral And Center In Rats

AIM:To study the effect of cholecystokinin on gastrointestinal tract sensation afferent impulse.Method:Gastric distention - induced changes of afferent discharge of subdiaphragmatic vagus nerve was recorded in 86 Wistar rats. We investigated the effect of ectogenous and endogenous CCK on auto-discharges of vagus nerve and gastric distention induced-discharges as well as the effect of different volume of distention to vagal discharge by intravenous injection of different dosage of CCK (0.03,0.06,0.12μg/kg), duodenal infusion of Casein to evoke the excretion of CCK. The projection of the gastrointestinal tract sensation afferent impulses in the nucleus of solitary tract was also observed and the effect of changes in vagal afferent impulse to vegetative nervous system was investigated by HRV.Result:1. Gastric distention had obvious effect on the afferent impulse of vagus nerve. In the range of 0.5 ~ 5 ml, the auto-discharges of vagus afferent nerve were increased gradually with increasing distention volume step by step. When the distention volume was 3ml or more, the auto-discharges were achieved the maximum (p < 0.05). 2. Different dosage of CCK had different effect on vagus afferent discharges: CCK of low dose had no significant effect (p < 0.05); middle dose significantly enhanced vagal discharge immediately after injection; high dose showed a quick effect which lasted for a long time (p < 0.05). 3. Duodenal infusion of Casein had obvious effect on auto-discharge of vagus nerve. Afferent discharge increased markedly 5 minute after infusion and the effect lasted in the observed 1 hour (p < 0.05). Duodenal infusion of Casein had no significant effect on gastric distention-induced vagal discharge (p > 0.05). 4.The effect of CCK + SEC on vagal afferent impulse: the auto-discharge of vagus nerve was increased immediately after intravenous injection of high dose CCK while high dose CCK plus secretin could reverse the effect (p < 0.05). 5. The projection of gastrointestinal tract sensation afferent impulses in the nucleus of solitary tract: in the 21 rats, 125 neurons were recorded. 13 of the total neurons were gastric distention related, among which 10 were excitatory ones (the proportion is 76.9%). 15 of the total were subdiaphragmatic vagus nerve stimulation related, among which 12 were inhibitory ones (the proportion is 80%). 33 of the total were cervical vagus nerve stimulation related, among which 22 were excitatory ones (the proportion is 67%). In the vagus nerve (subdiaphragmatic and cervical vagus nerve) stimulation related neurons, 12 were related to both. 6. The effect of CCK on HRV spectrum parameters: CCK of low dose caused tachycardia and decreased vagal tension, while CCK of middle and high dose had no significant effect on heart rate.Results were expressed as mean ± SE. Statistical significance was assessed by using the one-way ANOVA with SPSS software, and data were regarded as significant at a p value of < 0.05.Conclusion: CCK has excitatory effect on auto-discharge of vagus afferent nerve.CCK has inhibitory effect on gastric mechanism receptors, which were fast (rapid) adaptation receptors. Secretin can inhibit CCK induced auto-discharge increase of vagus afferent nerve.CCK can affect heart rate by vagus nerve.CCK is important in modulation sensation afferent impulse of gastrointestinal tract.