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Mice, with the variety of genotypes they provide, should be particularly useful for studies of growth factors and gene products in regeneration of autonomic pathways such as the vagus nerve. To provide a foundation for examinations of mouse vagal reorganization, two experiments assessed the rate, extent, and accuracy of afferent reinnervation of the stomach after vagotomy and related these patterns to feeding behavior. In experiment 1, the pattern of afferent regrowth into the gut after unilateral truncal vagotomy was characterized by labeling of these afferents with wheat germ agglutinin-horseradish peroxidase and Micro-Ruby. Regenerating neurites had reached and, in some cases, already reinnervated the stomach by 4 wk after axotomy. By 8 wk, regrowth was more extensive, and many fibers had redifferentiated terminals in the smooth muscle. By 16 wk, vagal projections had reached or exceeded normal density in the corpus, density in the forestomach was still reduced, and regrowth in the antrum was minimal. At all time points, not only appropriate terminals, but also growth cones and aberrant endings, were observed. In experiment 2, meal patterns of vagotomized mice were evaluated using a solid diet over the period of regeneration; cholecystokinin suppression of a liquid meal after unilateral and bilateral truncal vagotomies was also evaluated. Unilaterally, as well as bilaterally, vagotomized animals ate smaller and more frequent meals. These disturbed patterns became more pronounced in the first 8 wk after vagotomy, during regeneration. Cholecystokinin inhibition of intake was attenuated by bilateral, but not unilateral, vagotomy. Overall, the spatial and temporal patterns of structural and functional changes observed during regeneration verify that the mouse provides a useful preparation for examining the control of vagal plasticity. satiety; stomach; vagus; visceral afferents; cholecystokinin

The gastrointestinal tract 'tastes' nutrients: evidence from the intestinal taste aversion paradigm. Am J Physiol Regul Integr Comp Physiol 287:R1086-R1100, 2004. First published July 15, 2004; doi:10.1152/ajpregu.00047.2004.--To develop and use a behavioral paradigm for assessments of what nutrient properties are detected by intestinal chemoreceptors, we combined features of the 'electronic esophagus' preparation (Elizalde G and Sclafani A. Physiol Behav 47: 63-77, 1990) and the conditioned taste aversion protocol (Garcia J and Koelling RA. Psychon Sci 4: 123-124, 1966). In four experiments, separate groups of food-deprived rats with gastric (experiments 1-4) or duodenal (experiment 4) catheters were infused with either carbohydrates (maltodextrin) or fats (corn oil) into their stomachs or small intestines, either while they consumed nonnutritive flavored solutions (experiments 1 and 2) or in the absence of any intake (experiments 3 and 4). For some animals, one of the macronutrient infusions was paired with lithium chloride injections shown to support conventional conditioned aversions. After training, in various oral preference test trials, animals were given opportunities to taste and consume the nonnutritive solutions that had served as oropharyngeal conditioned stimuli as well as the nutrients that had been infused intragastrically, with or without poisoning, but never sampled by mouth. As previously established, preferences for the nonnutritive flavors were enhanced by association with intragastric infusions of macronutrients, with carbohydrates producing the greater preference. On first exposure to the two macronutrients for oral consumption, animals reduced their intake of the nutrient that had been previously poisoned when it was infused into the gastrointestinal tract. These results, along with additional controls, suggest that nutrient tastes detected in the intestines can be recognized centrally based on oropharyngeal gustatory stimulation. food preference; duodenum; gustatory; macronutrients; Pavlovian conditioning

An understanding of the events initiating vago-vagal reflexes requires knowledge of mechanisms of transduction by vagal afferents. Such information presumes an understanding of receptor morphology and location. Anatomic studies have recently characterized two types of vagal afferents, both putative mechanoreceptors distributed in gastrointestinal (GI) smooth muscle. These two receptors are highly specialized in that they 1) are morphologically distinct, 2) have different smooth muscle targets, 3) form complexes with dissimilar accessory cells, and 4) vary in their regional distributions throughout the GI tract. By comparison, information on the architecture and regional distributions of other classes of vagal afferents, notably chemoreceptors, has only begun to accumulate. Progress on the study of the two mechanoreceptors, however, illustrates general principles and delineates experimental issues that may apply to other submodalities of vagal afterents. By extension from morphological and physiological observations on the two species of smooth muscle endings, it is reasonable to hypothesize that additional classes of vagal receptors are also differentiated morphologically and that they vary in structure, accessory cells, regional distributions, and other features. A full appreciation of vago-vagal reflexes will require thorough structural and regional analyses of each of the types of vagal receptors within the GI tract. chemoreceptors; mechanoreceptors; transduction; vagus; visceral afferents

Selective vagotomies were performed in groups of rats to determine the contribution of the different branches of the vagus to the detection of gastric volume. Sham operated rats still exhibited volume-dependent suppression of food intake after the infusion of specific saline volumes to the stomach. Vagotomy modified this suppression and the extent of modification was affected by the branches of the vagus severed and spared.

The role of the stomach in controlling food intake was investigated in Sprague-Dawley rats implanted with a gastric catheter and a pyloric cuff. Consumption after meals were recorded in four experiments by the pyloric cuff. There was no relationship between nutrient loading and the control of food intake. Data revealed that gastric volume or gastric distention determined the amount of food consumption.

The effects of intraduodenal infusions of 10 nutrients on the food intake of rats with selective deafferentations of the celiac branches of the vagus nerve were observed to identify the location of the receptors involved in the negative feedback loop that controls food intake. The results show that vagal celiac afferent nerves are involved in the suppression of food intake by preabsorptive detection of certain nutrients.

A surgical method for severing the afferent and efferent vagal rootlets in the rat brain was devised. A dorsal approach to the vagal rhizotomy requires cutting a hole through th occipital bone to expose the vagal rootlets. The method allows observations of the influence of vagal innervation on the gastrointestinal system. It also allows observations of food intake, nutrient absorption and digestion since rats show a complete recovery of normal feeding activities after the surgery.