Effect Of Conditioned Taste Aversion On Vagusnerve Afferent Discharge And C-fos Expression In The Brain Of The Rat

When the consumption of novel flavored food is followed by visceral malaise, such as queasiness, diarrhea, bellyache and so on, animals will decrease or avoid ingesting the food with the same gustatory feature on the subsequent exposures. This type of behavioral change is defined as conditioned taste aversion(CTA). CTA associates taste of the food with the visceral signals. It is an important acquired adaptive behaviour, which may prevents animals from ingesting the harmful food again. Visceral malaise is introduced into the brain by vagusnerve(â…©), then vagusnerve regulates intestinal motivity functions again.Many data indicated that visceral malaise affects on the expression of c-fos supposing subdiaphragmatic vagotomy. But little is known about expression of c-fos in brain induced by the taste after CTA and vagotomy below diaphragm. As for the interation between CTA and vagotomy, and whether different taste information influence on afferent discharge of vagusnerve or not. It is not clear. However there has been no report available about them. To elucidate this problem, the experiment was designed using adult male Sprague-Dawley rats as materials. SD rats were trained to establish CTA by the intraoral infusion of 0.2mol/L sucrose paired with intraperitoneal injection of 0.15mol/L LiCl, and the work is repeated six times. This thesis was composed of two parts:in the first part, the discharge of vagal gastirc branch by electrophysiology technique. in the second part, the brain of the rats were took out and immunohistochemical staining technique was used after cutting bilateral vagal gastric branches.Results:1. Discharge integral value of vagal afferent gastirc branch of CTA group were more than control group by the surose and quine stimulation that is before stimulation ,immediately, 30, 60 min after stimulation. 2. Discharge integral value of vagal gastric branch by the surose stimulation had no difference from that by quine stimulation that in before stimulation, immediately, 30, 60min after stimulation in control rats. But in CTA rats, integral value by quine stimulation is more than by surose's just 60 min after stimulation.3. All of the rats still showed strong aversion for sucrose after intraoral infusion of sucrose paired with intraperitoneal injection of LiCl and cutting bilateral vagal gastric branches.4. The FOS-like immunoreactice(FLI) induced by the taste stimuli distributed extensively in the rat brain, such as central nucleus of the amygdala(CeA), area postrema(AP), solitary tract nucleus(Sol), parabrachial nucleus(PBN), bed nucleus of stria terminalis(BST) and so on.5. The number of FLI neurons of bed nucleus of stria terminalis(BSTV), hypothalamic paraventricular(Pa), paraventricular thalamic nucleus(PV), external lateral subnucleus(els) had no significant differences in the group of CTA-vagotomy ,CTA-sham ,Control-vagotomy and Control-sham .6. Sucrose induced more c-fos expression in raphe pallidus nucleus(RPa) of CTA group than that of control group.7. The numbers of FLI neurons in medial part of solitary tract nucleus(SolM) and central lateral subnucleus (cls) of CTA group were more than those of control group. But in control group, vagotomy group had more FLI neurons than sham group in SolM and cls.Conclusions:1. Discharge integral value of vagal gastirc branch of CTA group were more than control group in the electrophysiology experiment. It suggested that CTA group increased vagal afferent activity because the stomach and intestinal motivity function changed.2. Seven days later showed: rats had strong aversion for surose after vagotomy, it suggested that the retention of CTA was independent of vagal afferent.3. The extensive distribution of FLI neurons in CeA, AP, Sol, PBN, BST, and so on, indicated that the areas mentioned above may play an important role in the acquisition of CTA and sense of the stomache and intestine.4. The number of FLI neurons in BSTV,Pa,PV and els had no significant difference in the group of CTA-vagotomy, CTA-sham, Control-vagotomy, Control-sham, suggests that the plasticity change induced by central nervous system is activated by conditioned stimulus solely. But FLI neurons in RPa had difference in group of CTA and control, and CTA group induced more c-fos expression. There were no interaction between the CTA and vagotomy. These results indicats that RPa is related to form of CTA.5. Expression of FLI neurons of SolM and cls of Control-vagotomy group were more than that of control-sham group. So was that of CTA.These suggest CTA and vagotomy has similar effects on FLI expression, also suggest vagotomy is similar to toxic stimulation on inducing internal malaise.