Study On The Relationship Between Fasting And Mechano-sensitivity Of Intestinal Mesenteric Afferent Nerve Fibers

The enteric nervous system?ENS?integrates various sensory signals to maintain the normal physiological function of the intestine,and diet is one of the most important factors affecting the chemical stimulation environment of intestinal lumen and intestinal wall.Numerous studies have shown that ENS contains a wide variety of neurons,including chemical and mechanical stimulation neurons that respond to specific dietary conditions,whose signals are primarily transmitted by related neurotransmitters and receptors.The existence and lack of nutrients in the intestinal tract will have a long-term impact on the survival of neurons,excitability and expression of neurotransmitters,and ultimately affect the structure and function of the intestinal tract.Clinically it can result from anorexia,selfimposed food restriction,and serious conditions in which food ingestion is hampered or patients mainly receive parenteral nutrition.Based on the previous studies of our group on the morphological and biomechanical remodeling of the intestinal tract in fasting rats,the response of mesenteric afferent nerve discharge to mechanical stimulation was studied by the establishment of fasting model combined with biomechanical and histomorphological studies.It is helpful to understand the pathogenesis of digestive diseases related to anorexia and so on.Moreover,to explore the effects of pressure overload on the mechanical sensitivity of isolated jejunum mesenteric afferent in normal and fasting rats,in this study,the distension pattern of sustained high pressure was designed,and the correlation between intestinal histomorphology and the changes in mechanosensitivity of jejunal mesenteric nerve was further explored.The results of this study will provide theoretical basis for solving diseases related to jejunal pressure overload.The main research contents and conclusions of this thesis are as follows:?1?Refeeding reverses fasting-induced remodeling of afferent nerve activity in rat jejunum.This study aimed to characterize the effect of fasting and refeeding on mechanosensitivity in mesenteric afferent nerves in isolated Sprague Dawley?SD?rat jejunum.The rats were randomly divided into three groups.A control group fed ad libitum,a group fasted for 1 week and a group refed 1 week after 1 week fasting were studied.Jejunal segments were used for electrophysiological,histomorphological and mechanical studies.Mesenteric afferent nerve firing was recorded during a ramp distension up to 40mmHg luminal pressure.The results showed that fasting induced intestinal histomorphometric remodeling,which was reversed by refeeding.Multiunit afferent recordings were separated into low-threshold?LT?and wide-dynamic-range?WDR?single unit activity.Jejunal deformation?strain?,bowel distension load?stress?and firing frequency of mesenteric afferent nerve bundles?spike rate increase ratio?SRIR??were compared among groups.The firing frequency increased with distension in all groups.SRIR was largest in the Fasting group?P<0.05?.Compared to the Control group,fasting increased afferent activity in whole nerve bundles and WDR units at high degrees of distensions?P<0.05 at pressure 40 mmHg;P<0.05 at strain 1.2;P<0.01 at stress 8kPa?.Refeeding reversed the fasting-induced afferent hypersensitivity and the shift between receptor subtypes.In conclusion,refeeding reversed fasting-induced remodeling.?2?Pressure overload changes mechanosensitivity of rat jejunal afferent nerve in a stress-dependent way.This study aimed to characterize the effect of overload on mechanosensitivity in mesenteric afferent nerves of isolated jejunum in normal and fasted Sprague Dawley?SD?rats.The rats were randomly divided into two groups.The Control group was fed ad libitum whereas food was restricted for 1 week in the Fasting group.Mesenteric whole afferent nerve firing of jejunal segment was recorded during three distensions,i.e.,a ramp distension up to 80 cmH₂O luminal pressure?D1?following by a sustained distension to120 cmH₂O?D2?for 2 minutes.The third ramp distension was to 80 cmH₂O?D3?.Intestinal deformation?strain?,distension load?stress?and SRIR were compared at 20cmH₂O,40 cmH₂O and maximum pressure levels among the distensions and groups.SRIR increased as function of pressure in all distensions.SRIR and stress changes showed the same pattern in all distensions.As function of maximum pressure level during distension,the biggest SRIR and stress were evident in the fast high distension?0.05>P>0.001?.The SRIR and stress were largest for all distensions in the Fasting group compared to the Control group?P<0.01,P<0.001?.SRIR decreased as function of pressure in D3 compared with that in D1 both in control?P<0.05?and fasting rats?P<0.01?.LT significantly higher in D3 than in D1 for Control group?P<0.05?,and total single units and LT significantly lower in Fasting group than in Control group at D3?P<0.05?.Furthermore,strong association was found between SRIR with stress?R=0.633,P<0.001?.In conclusion,sustained overload decreased afferent mechanosensitivity in a stress-dependent way.Pressure overload caused more decrease in afferent mechanosensitivity in fasting rats.Fasting shifts LT to WDR and high pressure shifts WDR to LT in response to mechanical stimulation.?3?Relationship between morphological and histological remodeling of jejunum in fasting rats and hypersensitivity of afferent nerve to mechanical stimulation.This study aimed to further explore the relationship between the jejunal histomorphological changes due to fasting and the hypersensitivity of the mesenteric afferent nerve to mechanical stimulation.For histological analysis,HE,Nissl and Masson staining were performed.For afferent activity,SRIR at the first distension to 20 cmH₂O,40 cmH₂O and 60 cmH₂O in the distension protocol was obtained from previous chapter where the relevant parameters of preserved jejunum samples in the previous chapter were analyzed.The association between main histological factors and SRIR were analyzed by using single linear regression analysis.The results showed that the fasting significantly reduced most morphometry parameters including opening angle and residual strain of jejunum?0.05>P>0.001?.Histological staining showed that the volume of nerve cells decreased in both muscle and submucosal layers,but the number of nerve cells increased and the particle density of Nissl bodies in nerve cells was not significantly different?P>0.05?.The collagen fiber arrangement in the submucosa of fasting group was relatively dense,and the percentage of submucosal collagen fiber components in fasting group was significantly higher than that in control group?P<0.001?.Under a certain pressure,SRIR was negatively correlated with the thickness of jejunal wall,circumferential muscle layer and outer residual strain,and positively correlated with inner residual strain and the number of intermuscular and submucosal nerve cells.Moreover,under a certain pressure,stress was positively correlated with SRIR,but negatively correlated with jejunal wall thickness.In conclusion,the histomorphological remodeling of the jejunum in fasting rats was significantly correlated with hypersensitivity of afferent nerve to mechanical stimulation.The results of this study enriched the research contents of biomechanical characteristics of digestive tract,histomorphological remodeling and neuro electrophysiology,and provided theoretical basis for further research on the pathogenesis of self-imposed food restriction,anorexia and obesity as well as the clinical diseases related to jejunal pressure overload.