Viscera Mechanism Of Conditioned Taste Aversion Induced By Physical Exercise In Rats

Conditioned taste aversion (CTA) is a type of associative conditioning that the subject learns to associate a taste with delayed malaise. The correlation of taste and visceral discomfort is a critical factor for this phenomenon. It is now evident that physical exercise induces aversion in rats to the taste paired with the exercise in recent years, which suggests similar role in both physical exercise and gastrointestinal discomfort as unconditioned stimulus(US) might be involved in the development of taste aversion. However, the elucidation of physiological visceral processing underlying CTA induced by physical exercise is still in question. To elucidate the problem, adult male Sprague-Dawley rats were tested in the present experiments. Before or after acquisition of a CTA against sucrose induced by swimming, rats underwent bilateral subdiaphragmatic vagotomy, intraperitoneal (IP) injection of granisetron or ablating the chemosensitive area postrema(AP). We explored the possible role of the vagal afferent nerve and blood-borne visceral stimuli on acquisition and retention of CTA induced by physical exercise and effects of AP lesion on rats taste responses to dilute saccharin solution after acquisition of a CTA.The study found as following:1,Forced swimming with 20 min duration caused relatively strong aversion to the 0.1% saccharin solution consumed before swimming. However the effectiveness of swimming was weaker than LiCl injection as US in inducing conditioned taste aversion, which suggested physical exercise have resulted in weaker visceral malaise.2,CTA could be slowly induced when rats underwent bilateral subdiaphragmatic vagotomy and ablating AP prior to the correlation of taste stimulus and exercise, but significantly attenuated by IP injection of granisetron, which suggested visceral information relayed by afferent fibers of the abdominal vagus nerve and chemosensitive AP only play a part of role in CTA induced by physical exercise. The increased synthesis of 5-hydroxytryptamine induced by swimming in brain may be important in exercise-induced CTA.3,The extinction of CTA that repeated saccharin solution exposure without subsequent physical exercise was accelerated in rats underwent subdiaphragmatic vagotomy and ablating AP after learned CTA. This manifested that integrity structure of vagus nerve and AP is necessary for the retention of CTA. Disorder of autonomic nervous system caused by function deficits of vagus nerve and AP may be the one of reasons that contributed to the acceleration of CTA extinction.4,Compared with sham rats, rats with AP lesion exhibited more total licks and licking bouts, but less bout size and bout duration in the unit time. Although sham and AP lesions rats accepted taste stimulation with delayed swimming as reinforcement procedure after extinction of CTA were known to exhibit a reduction in total licks, rats with AP lesion was less reduction. There were no significant differences between AP lesion and sham rats in variation of licking bouts, bout duration and bout size. The acceleration extinction of CTA and increased quantities of sucrose in rats may be relevant to reduction of inhibitory feedback and rats taste alteration of saccharin intensity and property caused by ablating AP.