Effects of perivagal administration of capsaicin on post-surgical food intake

Improving Milk Yield, Milk Quality, and Follicular Functionality Behavior in Dairy Cows from the Implementation of Microencapsulated Chili Pepper Supplements in Their Diets

The present study evaluates the effect of including microencapsulated hot chili pepper (MHCP) in the diet of crossbred dairy cows on the volume and quality of milk and on ovarian morphofunctionality. Twenty-four crossbred females in their lactating period were used. The cows were divided into two experimental groups, a control (CT) and an MHCP -supplemented group (CP) given 1 g a day per animal of microencapsulated hot chili in concentrate for 42 days. Over seven weeks of daily milk production was measured, and sample milk was collected weekly for composition analysis. Animals were subject to an ovulation synchronization protocol on day 0 (D0), and an intravaginal progesterone (P4) implant, estradiol benzoate, and prostaglandin (PGF2α) were administered. On D8, the P4 implant was removed and PGF2α, equine chorionic gonadotropin, and estradiol cypionate were administered to the animals. The ovarian dynamics were evaluated in B mode and color Doppler. There were significant differences (p < 0.05) in the group X time interaction, the volume of milk produced, and the amount in kg/day of milk components. There was a higher percentage of vascularization in the preovulatory follicle in the CP group (p ≥ 0.10). The findings show that the inclusion of MHCP in the diet of dairy cows does influence their milk production and reproduction.

Capsaicin as a Dietary Additive for Dairy Cows: A Meta-Analysis on Performance, Milk Composition, Digestibility, Rumen Fermentation, and Serum Metabolites

This study aimed to evaluate the effects of dietary supplementation with capsaicin (CAP) on productive performance, milk composition, nutrient digestibility, ruminal fermentation, and serum metabolites of dairy cows using a meta-analytical approach. The database included 13 studies, from which the response variables of interest were obtained. Data were analyzed using a random effects model, and results were expressed as weighted mean differences between treatments supplemented with and without CAP. Dietary supplementation with CAP increased (p < 0.05) dry matter intake, milk yield, feed efficiency, milk fat yield, and milk fat content. However, CAP supplementation did not affect (p > 0.05) milk protein and lactose yield, milk urea nitrogen, or milk somatic cell count. Greater (p < 0.05) apparent digestibility of dry matter and crude protein was observed in response to the dietary inclusion of CAP. Likewise, supplementation with CAP increased (p < 0.05) the rumen concentration of total volatile fatty acids. In contrast, CAP supplementation did not affect (p > 0.05) ruminal pH or the ruminal concentration of ammonia nitrogen, acetate, propionate, and butyrate. In blood serum, CAP supplementation increased (p < 0.05) the glucose concentration and decreased (p < 0.05) the concentration of non-esterified fatty acids. However, CAP supplementation did not affect (p > 0.05) the serum concentration of urea and beta-hydroxybutyrate. In conclusion, capsaicin can be used as a dietary additive to improve the productive performance, milk composition, and nutrient digestibility in dairy cows and, at the same time, improve the ruminal concentration of total volatile fatty acids and serum levels of glucose and non-esterified fatty acids.

Effects of Capsicum Oleoresin Supplementation on Lactation Performance, Plasma Metabolites, and Nutrient Digestibility of Heat Stressed Dairy Cow

The present study investigates the effect of Capsicum oleoresin (CAP) supplementation on the dry matter intake, milk performance, plasma metabolites, and nutrient digestibility of dairy cows during the summer. Thirty-two lactating Holstein dairy cows (n = 32) were randomly divided into four groups. The CAP was dissolved in water and added to the total mixed ration with graded levels of CAP (0, 20, 40, and 80 mg/kg of dry matter). The trial period consisted of seven days for adaptation and thirty days for sampling. Data were analyzed using the MIXED and GLM procedure SAS. The linear and quadratic effects were tested. The milk yield, milk fat, and milk urea nitrogen increased linearly with the dietary addition of CAP (p < 0.05). The dry matter intake increased linearly in the 20CAP group (p < 0.05). Additionally, the 4% fat-corrected milk, energy-corrected milk, milk fat yield, and milk fat to milk protein ratio increased quadratically (p < 0.05), while the rectal temperature decreased quadratically (p < 0.05). Serum total cholesterol and non-esterified fatty acids increased linearly (p < 0.05); glucose and β-hydroxybutyrate tended to increase quadratically with the dietary addition of CAP (p = 0.05). Meanwhile, CAP supplementation did not affect the milk protein yield, blood concentration of triglyceride, insulin, lipopolysaccharide, immunoglobulin G, or heat shock protein 70 expression level (p > 0.05). In addition, nutrient digestibility was comparable among groups (p > 0.05). These findings indicated that CAP supplementation could enhance the lactation performance of dairy cows during the summer.

Effects of pepper extract in suckling lamb feed: Growth performance, metabolism, and oxidative responses

Our objective was to determine whether the inclusion of pepper extract would improve health in suckling lambs, stimulating antioxidant activity, and improving performance. We used Lacaune lambs distributed in four treatments, with four repetitions per treatment and three lambs per repetition: control group (T0) and treatments T1, T2, and T3 that received 200, 400, and 800 mg/kg of pepper extract, respectively. Groups T1 and T2 consumed more significant amounts of silage than group T0, and animals from group T1 consumed more concentrate and, consequently, consumed more solids. The addition of pepper extract enhanced growth performance, with the lowest dose (T1) giving rise to the most significant weight gain, average daily gain, and body weight, compared to T0. Regression analysis showed that the optimum point for pepper extract supplementation was 301.5 mg/kg. The levels of total protein and globulins were significantly higher for animals supplemented with pepper extract (day 28) than the control; the concentrations of albumin and urea increased over time but did not differ significantly among treatments. Serum glucose levels decreased significantly over time; however, the groups supplemented with pepper extract showed higher concentrations than group T0. The hematocrit was significantly higher in groups fed pepper extract; hemoglobin concentrations were also more significant, increasing over time in both groups. The groups that consumed the pepper extract had higher leukocyte counts due to greater lymphocytes and neutrophils. Levels of non-protein thiols increased significantly over time, while lipid peroxidation levels decreased significantly in all groups. The concentrations of reactive oxygen species significantly decreased in the serum of group T3 animals, those fed with pepper extract (day 28), compared to the control. In general, the addition of pepper extract in lamb feed can enhance weight gain, increase antioxidant levels, and stimulate the production of leukocytes and globulins in lambs.

Role of cholecystokinin and oxytocin in slower gastric emptying induced by physical exercise in rats

Vigorous exercise can induce gastrointestinal disorders such decreased gastric emptying pace, while low-intensity exercise can accelerate gastric motility. However, the mechanisms of these effects are still unknown. We investigated the possible neurohumoral mechanisms involved in these phenomena. In sedentary (Sed) and acute exercise (Ex) groups of rats, we assessed the activation of c-Fos in NTS and DVMN and the plasma levels of CCK and OXT. Separate groups received pretreatment with the oxytocin antagonist atosiban (AT), the cholecystokinin antagonist devazepide (DVZ), or the TRPV1 receptor inhibitor capsazepine (CAPZ). AT, DVZ and CAPZ treatments prevented (p<0.05) slower gastric emptying induced by acute exercise. The gene expression of OXT decreased (P<0.05) while that of CCK increased (P<0.05) in the gastric fundus and pylorus of the Ex group, while the plasma levels of OXT rose (p<0.05) and of CCK declined (p<5.05). We also observed activation (p<0.05) of c-Fos-sensitive neurons in the NTS and DVMN of exercised rats. In conclusion, acute exercise slowed gastric emptying by the vagal afferent pathway, which involved activation of CCK1/OXT/TRPV1 sensitivity.

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Relevance of the nucleus of the solitary tract, gelatinous part, in learned preferences induced by intragastric nutrient administration

Food preferences have been investigated in Wistar rats utilizing a learned concurrent flavor preference behavioral procedure. Previous studies have demonstrated that the perivagal administration of neurotoxin capsaicin disrupts the learning of preferences induced by intragastric administration of rewarding nutrients (pre-digested milk). The vagus nerve projects almost exclusively towards the nucleus of the solitary tract (NST), a brain medullary gateway for visceral signals. The objective of this study was to investigate the participation of the lateral portion of the dorsomedial region, the gelatinous subnucleus (SolG), in the learning of a concurrent preference task. Results show that unlike neurologically intact animals, which learn this task correctly, animals lesioned in the gelatinous part of NST manifest a disruption of discrimination learning. Thus, intakes of the flavored stimulus paired with predigested liquid diet and of the flavored stimulus paired with physiological saline were virtually identical. However, SolG- and sham-lesioned groups consumed similar total amounts of both flavors. These findings suggest that SolG, as a relay of the vagus nerve, along with its anatomical projection, the external lateral parabrachial subnucleus (LPBe), may constitute an anatomical axis that is important in the induction of concurrent flavor/side preferences. It also appears to be relevant in other behavioral processes that require rapid processing of information from the upper gastrointestinal tract.

Disruption of re-intake after partial withdrawal of gastric food contents in rats lesioned in the gelatinous part of the nucleus of the solitary tract

Sensory information from the upper gastrointestinal tract is critical in food intake regulation. Signals from different levels of the digestive system are processed to the brain, among other systems, via the vagus nerve, which mainly projects towards the nucleus of the solitary tract (NST). The objective of this study was to analyze the participation of the gelatinous part (SolG) of the NST in short-term food intake. One-third of the stomach food content was withdrawn at 5 min after the end of a meal, and food was then available ad libitum for different time periods. SolG-lesioned and control animals ingested a similar amount of the initial liquid meal, but the former consumed significantly smaller amounts and failed to compensate for the food deficit, whereas the controls re-ingested virtually the same amount as extracted. These data suggest that the SolG, as in the case of related anatomical structures such as the vagus nerve or external lateral parabrachial subnucleus, may be relevant in particular circumstances that require the rapid processing of vagal-related food intake adjustment associated to the upper gastrointestinal tract.

Effects of perineural capsaicin treatment of the abdominal vagus on endotoxin fever and on a non-febrile thermoregulatory event

Following perineural capsaicin pretreatment of the main trunks of the abdominal vagus of rats, the first and the second phases of the polyphasic febrile response to intravenous lipopolysaccharide were unaltered, while the third phase of fever course (peak at 5 h) was attenuated. In rats desensitized by intraperitoneal (i.p.) capsaicin (i.e. abdominal non-systemic desensitization), mainly the first but not the later fever phases were reduced. The postprandial hyperthermia to intragastric injection of BaSO4 suspension was attenuated by either i.p. or perineural capsaicin treatment. It is concluded that, in contrast to the accepted model of postprandial hyperthermia, which is mediated by capsaicin-sensitive fibers of the abdominal vagus, in the early phase of polyphasic fever the vagal afferent nerves appear to play no role. The influence of i.p. capsaicin-desensitization on this initiating fever phase is independent of the vagus, and a capsaicin-induced alteration of endotoxin action in the liver, prior to vagal nerve endings, is more likely. The late febrile phase is probably influenced by efferent vagal fibers, which might be damaged more easily by perineural than i.p. capsaicin treatment.

Vagal afferent-dependent cholecystokinin modulation of visceral pain requires central amygdala NMDA-NR2B receptors in rats

BACKGROUND

Cholecystokinin (CCK), a gut hormone that is released during feeding, exerts gastrointestinal effects in part through vagal pathway. It is reported to be a potential trigger for increased postprandial visceral sensitivity in healthy subjects and, especially in patients with irritable bowel syndrome. NR2B-containing N-methyl-d-aspartate (NMDA) receptors in the central amygdala (CeA) participate in pain modulation. Systemically administered CCK activates the CeA-innervating neurons. Here, we investigated whether CCK modulation of visceral sensitivity is mediated through CeA NMDA-NR2B receptors and whether this modulation involves vagal pathway.

METHODS

We first examined the visceromotor response (VMR) to colorectal distention (CRD) following i.p. injection of CCK octapeptide (CCK-8) in a rat model. Next, the NR2B antagonist ifenprodil and the NR2A antagonist NVP-AAM077 were microinjected into the CeA before systemic CCK injection. NR2B phosphorylation was detected by Western blot. To down-regulate NR2B gene expression, NR2B-specific small interfering RNA (siRNA) was delivered into CeA neurons by electroporation. In addition, the effects of functional deafferentation by perivagal application of capsaicin and pretreatment with the CCK1 receptor antagonist devazepide were investigated.

KEY RESULTS

CCK-8 increased VMR to CRD in a dose-dependent manner. This effect was blunted by intra-CeA administration of ifenprodil (but not NVP-AAM077) and was accompanied by phosphorylation of NR2B subunits in the CeA. CCK failed to increase VMR to CRD in NR2B siRNA-treated rats. Perivagal capsaicin application and pretreatment with devazepide prevented CCK-induced pronociception and CeA NR2B phosphorylation.

CONCLUSIONS & INFERENCES

The pronociception induced by systemic CCK, which is vagal afferent-dependent, requires activation of CeA NMDA-NR2B receptors.

Vagal anandamide signaling via cannabinoid receptor 1 contributes to luminal 5-HT modulation of visceral nociception in rats

Serotonin (5-HT) plays pivotal roles in the pathogenesis of postinfectious irritable bowel syndrome (PI-IBS), and luminal 5-HT time-dependently modulates visceral nociception. We found that duodenal biopsies from PI-IBS patients exhibited increased 5-HT and decreased anandamide levels and that decreased anandamide was associated with abdominal pain severity, indicating a link between 5-HT and endocannabinoid signaling pathways in PI-IBS. To understand this, we investigated the role of endocannabinoids in 5-HT modulation of visceral nociception in a rat model. Acute intraduodenally applied 5-HT attenuated the visceromotor response (VMR) to colorectal distention, and this was reversed by the cannabinoid receptor 1 (CB1) antagonist AM251. Duodenal anandamide (but not 2-arachidonoylglycerol) content was greatly increased after luminal 5-HT treatment. This effect was abrogated by the 5-HT 3 receptor (5-HT3R) antagonist granisetron, which was luminally delivered to preferentially target vagal terminals. Chemical denervation of vagal afferents blocked 5-HT-evoked antinociception and anandamide release. Chronic luminal 5-HT exposure for 5 days increased baseline VMR and VMR post-5-HT (days 4 and 5). Duodenal levels of anandamide and N-acyl-phosphatidylethanolamine-specific phospholipase D (NAPE-PLD, the anandamide-synthesizing enzyme) protein gradually declined from day 1 to 5. The time-dependent effects of 5-HT were abolished by daily granisetron pretreatment. Daily pretreatment with CB1 agonists or anandamide from day 3 attenuated 5-HT-induced hyperalgesia. These data suggest that vagal 5-HT3R-mediated duodenal anandamide release contributes to acute luminal 5-HT-induced antinociception via CB1 signaling, whereas decreased anandamide is associated with hyperalgesia upon chronic 5-HT treatment. Further understanding of peripheral vagal anandamide signaling may provide insights into the mechanisms underlying 5-HT-related IBS.

Effects of afferent and efferent denervation of vagal nerve on endotoxin-induced oxidative stress in rats

This study investigated the role of vagal innervation in oxidative stress after systemic administration of lipopolysaccharide (LPS) endotoxin. Control rats and rats subjected to bilateral subdiaphragmatic vagotomy, perivagal capsaicin application (5 mg/ml) or cholinergic receptor blockade with subcutaneous atropine (1 mg/kg), were intraperitoneally injected with 300 μg/kg of LPS and euthanized 4 h later. Results indicated that; (1) surgical vagotomy and sensory denervation by perivagal capsaicin increased brain oxidative stress and decreased reduced glutathione in basal condition (saline-treated rats) and following endotoxin challenge; (2) oxidative stress decreased after cholinergic blockade with atropine in endotoxemic rats; (3) nitric oxide decreased by abdominal vagotomy, sensory deafferentation and cholinergic blockade after endotoxin injection; (4) liver lipid peroxidation decreased after surgical vagotomy and cholinergic blockade but increased after sensory deafferentation; (5) liver reduced glutathione decreased following vagotomy and sensory denervation in basal state and by cholinergic blockade in basal state and during endotoxemia; (6) nitric oxide increased by vagotomy in basal state and by sensory denervation and cholinergic blockade in basal state and during endotoxemia; (7) liver histological damage increased by subdiaphragmatic vagotomy, sensory denervation or cholinergic blockade. These findings suggest that: (1) sensory fibers (signals from the periphery) running in the vagus nerves are important in maintaining the redox status of the brain; (2) capsaicin vagal sensory nerves are likely to maintain nitric oxide tone in basal conditions; (3) the vagus nerve modulates liver redox status and nitric oxide release, (4) the vagus nerve mediates protective role in the liver with both cholinergic and capsaicin-sensitive mechanisms being involved.

A critical re-evaluation of the specificity of action of perivagal capsaicin

Perivagal application of capsaicin (1% solution) is considered to cause a selective degeneration of vagal afferent C fibres and has been used extensively to examine the site of action of many gastrointestinal (GI) neuropeptides. The actions of both capsaicin and GI neuropeptides may not be restricted to vagal afferent fibres, however, as other non-sensory neurones have displayed sensitivity to capsaicin and brainstem microinjections of these neuropeptides induce GI effects similar to those obtained upon systemic application. The aim of the present study was to test the hypothesis that perivagal capsaicin induces degeneration of vagal efferents controlling GI functions. Experiments were conducted 7-14 days after 30 min unilateral perivagal application of 0.1-1% capsaicin. Immunohistochemical analyses demonstrated that, as following vagotomy, capsaicin induced dendritic degeneration, decreased choline acetyltransferase but increased nitric oxide synthase immunoreactivity in rat dorsal motor nucleus of the vagus (DMV) neurones. Electrophysiological recordings showed a decreased DMV input resistance and excitability due, in part, to the expression of a large conductance calcium-dependent potassium current and the opening of a transient outward potassium window current at resting potential. Furthermore, the number of DMV neurones excited by thyrotrophin-releasing hormone and the gastric motility response to DMV microinjections of TRH were decreased significantly. Our data indicate that perivagal application of capsaicin induced DMV neuronal degeneration and decreased vagal motor responses. Treatment with perivagal capsaicin cannot therefore be considered selective for vagal afferent C fibres and, consequently, care is needed when using perivagal capsaicin to assess the mechanism of action of GI neuropeptides.

Effect of intraperitoneal injection of curcumin on food intake in a goldfish model

Although spice compounds have several pharmacological and biochemical actions such as antioxidant activity, their physiological effects on neuropeptides related to feeding regulation are not well known. The aim of the present study was to identify the pharmacological activities of spice compounds on appetite regulation using a goldfish (Carassius auratus) model with emphasis on the role of neuropeptides. The spice compounds used in this study were curcumin, piperine, and ursolic acid. Goldfish were injected intraperitoneally with test solutions containing each spice or vehicle (including 10% dimethyl sulfoxide in saline), and the changes in food intake were measured every 15 min for 60 min. Among the tested spice compounds, curcumin was found to reduce cumulative food intake and was thus selected for further experiments. Pretreatment with capsaicin, a neurotoxin of afferent nerves, abolished the curcumin-induced decrease of food intake. Curcumin-induced anorexigenic action was also attenuated by intracerebroventricular injection of the corticotropin-releasing hormone (CRH) receptor antagonist α-helical CRH((9-41)). We also examined the expression levels of mRNA for CRH, which is a potent anorexigenic neuropeptide in goldfish, in the diencephalon at 1 h after treatment with curcumin, and found that they were increased. Therefore, the reduction of appetite induced by curcumin treatment in goldfish was suggested to be mediated by the vagal afferent and subsequently through the CRH/CRH receptor pathway.

Capsaicin-sensitive vagal afferents modulate posttranscriptional regulation of the rat Na+/glucose cotransporter SGLT1

INTRODUCTION

the intestinal Na(+)/glucose cotransporter (SGLT1) displays rapid anticipatory diurnal rhythms in mRNA and protein expression. The vagus nerve has been implicated in the entrainment of some transporters. We aimed to clarify the influence of the vagus nerve on the diurnal entrainment pathway for SGLT1 and examine the role of vagal afferent fibers.

METHODS

male Sprague-Dawley rats were randomized to three groups, total subdiaphragmatic vagotomy, selective deafferentation of the vagus with capsaicin, or sham laparotomy. Postoperatively, animals were maintained in a 12-h light-dark cycle with food access limited to night. On the ninth postoperative day, animals were euthanized to harvest jejunal mucosa at 6-h intervals starting at 10 AM. Whole cell SGLT1 protein was measured by semiquantitative densitometry of immunoblots. Sglt1 and regulatory subunit RS1 mRNA was assessed by quantitative PCR. Fluorogold tracer technique was used to confirm adequacy of the vagotomy.

RESULTS

the diurnal rhythm in intestinal SGLT1, with a 5.3-fold increase in Sglt1 mRNA at 4 PM, was preserved in both vagotomy and capsaicin groups. However, the rhythmicity in SGLT1 protein expression (2.3-fold peak at 10 PM; P = 0.041) was abolished following either total vagotomy or deafferentation. Lack of change in RS1 mRNA suggests this is independent of the RS1 regulatory pathway.

CONCLUSION

SGLT1 transcription is independent of the vagus. However, dissociation of the protein rhythm from the underlying mRNA signal by vagotomy suggests the vagus may be involved in posttranscriptional regulation of SGLT1 in an RS1 independent pathway. Disruption following afferent ablation by capsaicin suggests this limb is specifically necessary.

Effects of alfalfa extract, anise, capsicum, and a mixture of cinnamaldehyde and eugenol on ruminal fermentation and protein degradation in beef heifers fed a high-concentrate diet

Four Holstein heifers (360 +/- 22 and 450 +/- 28 kg of BW in Exp. 1 and 2, respectively) fitted with ruminal trocars were used in 4 x 4 Latin square designs to evaluate the effects on ruminal microbial fermentation of the following: Exp. 1, no additive, alfalfa extract (30 g/d, AEX), a mixture of cinnamaldehyde (0.18 g/d) and eugenol (0.09 g/d; CIE1), and AEX and CIE1 in combination; and Exp. 2, no additive, anise oil (2 g/d), capsicum oil (1 g/d), and a mixture of cinnamaldehyde (0.6 g/d) and eugenol (0.3 g/d). Heifers were fed a 90:10 concentrate:barley straw diet (16% CP; 25% NDF) for ad libitum intake. Each period consisted of 15 d for adaptation and 6 d for sampling. On d 16 to 18, DM and water intakes were measured. On d 19 to 21 ruminal contents were sampled at 0, 3, 6, 9, and 12 h after feeding to determine ruminal pH and the concentrations of VFA, L-lactate, large peptides, small peptides plus AA (SPep+AA), and ammonia N. On d 20 and 21, samples of ruminal fluid were collected at 0 and 3 h after feeding to determine protozoal counts. In Exp. 1, CIE1 and AEX decreased (P < 0.05) total DMI, concentrate DMI, and water intake. The increase (P < 0.05) in SPep+AA and the decrease (P < 0.05) in ammonia N when supplementing CIE1 suggest that deamination was inhibited. Treatment AEX increased (P < 0.05) the acetate to propionate ratio, which is less efficient for beef production. Treatment CIE1 increased (P < 0.05) counts of holotrichs. Effects of AEX and CIE1 were not additive for many of the measured metabolites. In Exp. 2, treatments had no effect on ruminal pH, total VFA concentration, and butyrate proportion. The capsicum oil treatment increased (P < 0.05) DMI, water intake, and SPep+AA N concentration and decreased (P < 0.05) acetate proportion, branched-chain VFA concentration, and large peptide N concentration. The cinnamaldehyde (0.6 g/d) and eugenol (0.3 g/d) treatment decreased (P < 0.05) water intake, acetate proportion, branched-chain VFA, L-lactate, and ammonia N concentrations and increased (P < 0.05) propionate proportion and SPep+AA N concentration. The anise oil treatment decreased (P < 0.05) acetate to propionate ratio, branched-chain VFA and ammonia N concentrations, and protozoal counts. The results indicate that at the doses used a mixture of cinnamaldehyde and eugenol, anise oil, and capsicum oil may be useful as modifiers of rumen fermentation in beef production systems.

Invited review: Essential oils as modifiers of rumen microbial fermentation

Microorganisms in the rumen degrade nutrients to produce volatile fatty acids and synthesize microbial protein as an energy and protein supply for the ruminant, respectively. However, this fermentation process has energy (losses of methane) and protein (losses of ammonia N) inefficiencies that may limit production performance and contribute to the release of pollutants to the environment. Antibiotic ionophores have been very successful in reducing these energy and protein losses in the rumen, but the use of antibiotics in animal feeds is facing reduced social acceptance, and their use has been banned in the European Union since January 2006. For this reason, scientists have become interested in evaluating other alternatives to control specific microbial populations to modulate rumen fermentation. Essential oils can interact with microbial cell membranes and inhibit the growth of some gram-positive and gram-negative bacteria. As a result of such inhibition, the addition of some plant extracts to the rumen results in an inhibition of deamination and methanogenesis, resulting in lower ammonia N, methane, and acetate, and in higher propionate and butyrate concentrations. Results have indicated that garlic oil, cinnamaldehyde (the main active component of cinnamon oil), eugenol (the main active component of the clove bud), capsaicin (the active component of hot peppers), and anise oil, among others, may increase propionate production, reduce acetate or methane production, and modify proteolysis, peptidolysis, or deamination in the rumen. However, the effects of some of these essential oils are pH and diet dependent, and their use may be beneficial only under specific conditions and production systems. For example, capsaicin appears to have small effects in high-forage diets, whereas the changes observed in high-concentrate diets (increases in dry matter intake and total VFA, and reduction in the acetateto-propionate ratio and ammonia N concentration) may be beneficial. Because plant extracts may act at different levels in the carbohydrate and protein degradation pathways, their careful selection and combination may provide a useful tool to manipulate rumen microbial fermentation effectively. However, additional research is required to establish the optimal dose in vivo in units of the active component, to consider the potential adaptation of microbial populations to their activities, to examine the presence of residues in the products (milk or meat), and to demonstrate improvements in animal performance.

Vagally mediated, nonparacrine effects of cholecystokinin-8s on rat pancreatic exocrine secretion

Cholecystokinin (CCK) has been proposed to act in a vagally dependent manner to increase pancreatic exocrine secretion via actions exclusively at peripheral vagal afferent fibers. Recent evidence, however, suggests the CCK-8s may also affect brain stem structures directly. We used an in vivo preparation with the aims of 1) investigating whether the actions of intraduodenal casein perfusion to increase pancreatic protein secretion also involved direct actions of CCK at the level of the brain stem and, if so, 2) determining whether, in the absence of vagal afferent inputs, CCK-8s applied to the dorsal vagal complex (DVC) can also modulate pancreatic exocrine secretion (PES). Sprague-Dawley rats (250-400 g) were anesthetized and the common bile-pancreatic duct was cannulated to collect PES. Both vagal deafferentation and pretreatment with the CCK-A antagonist lorglumide on the floor of the fourth ventricle decreased the casein-induced increase in PES output. CCK-8s microinjection (450 pmol) in the DVC significantly increased PES; the increase was larger when CCK-8s was injected in the left side of the DVC. Protein secretion returned to baseline levels within 30 min. Microinjection of CCK-8s increased PES (although to a lower extent) also in rats that underwent complete vagal deafferentation. These data indicate that, as well as activating peripheral vagal afferents, CCK-8s increases pancreatic exocrine secretion via an action in the DVC. Our data suggest that the CCK-8s-induced increases in PES are due mainly to a paracrine effect of CCK; however, a relevant portion of the effects of CCK is due also to an effect of the peptide on brain stem vagal circuits.

Learned flavor preferences induced by intragastric administration of rewarding nutrients: role of capsaicin-sensitive vagal afferent fibers

Learned flavor preferences can be established after intragastric nutrient administration by two different behavioral procedures, concurrent and sequential. In a concurrent procedure, two flavored stimuli are offered separately but at the same time on a daily basis: one stimulus is paired with the simultaneous intragastric administration of partially digested food and the other with physiological saline. In sequential learning, the two stimuli are presented during alternate sessions. Neural mechanisms underlying these learning modalities have yet to be fully elucidated. The aim of this study was to examine the role of vagal afferent fibers in the visceral processing of rewarding nutrients during concurrent (experiment 1) and sequential (experiment 2) flavor preference learning in Wistar rats. For this purpose, capsaicin, a neurotoxin that destroys slightly myelinated or unmyelinated sensory axons, was applied to the subdiaphragmatic region of the esophagus to selectively damage most of the vagal afferent pathways that originate in the gastrointestinal system. Results showed that capsaicin [1 mg of capsaicin dissolved in 1 ml of vehicle (10% Tween 80 in oil)] blocked acquisition of concurrent but not sequential flavor preference learning. These results are interpreted in terms of a dual neurobiological system involved in processing the rewarding effects of intragastrically administered nutrients. The vagus nerve, specifically capsaicin-sensitive vagal afferent fibers, would only be essential in concurrent flavor preference learning, which requires rapid processing of visceral information.

Effects of cholecystokinin-8s in the nucleus tractus solitarius of vagally deafferented rats

We have shown recently that cholecystokinin octapeptide (CCK-8s) increases glutamate release from nerve terminals onto neurons of the nucleus tractus solitarius pars centralis (cNTS). The effects of CCK on gastrointestinal-related functions have, however, been attributed almost exclusively to its paracrine action on vagal afferent fibers. Because it has been reported that systemic or perivagal capsaicin pretreatment abolishes the effects of CCK, the aim of the present work was to investigate the response of cNTS neurons to CCK-8s in vagally deafferented rats. In surgically deafferented rats, intraperitoneal administration of 1 or 3 mug/kg CCK-8s increased c-Fos expression in cNTS neurons (139 and 251% of control, respectively), suggesting that CCK-8s' effects are partially independent of vagal afferent fibers. Using whole cell patch-clamp techniques in thin brain stem slices, we observed that CCK-8s increased the frequency of spontaneous and miniature excitatory postsynaptic currents in 43% of the cNTS neurons via a presynaptic mechanism. In slices from deafferented rats, the percentage of cNTS neurons receiving glutamatergic inputs responding to CCK-8s decreased by approximately 50%, further suggesting that central terminals of vagal afferent fibers are not the sole site for the action of CCK-8s in the brain stem. Taken together, our data suggest that the sites of action of CCK-8s include the brain stem, and in cNTS, the actions of CCK-8s are not restricted to vagal central terminals but that nonvagal synapses are also involved.

Capsaicin-sensitive afferent vagal fibers are involved in concurrent taste aversion learning

Taste aversion learning (TAL) is a type of learning characterized by rejection of a gustatory/flavor stimulus as a consequence of its pairing with visceral discomfort and malaise. TAL can be established in the laboratory by two different behavioral procedures, concurrent or sequential. Neural mechanisms of these learning modalities remain to be elucidated, but several studies have discussed the implication of various anatomical structures, including the vagus nerve. The aim of this study was to examine the role of capsaicin-sensitive vagal afferent fibers in concurrent (Experiment 1) and sequential (Experiment 2) TAL in Wistar rats. Results showed that perivagal administration of capsaicin (1mg of capsaicin dissolved in 1ml of vehicle (10% Tween 80 in oil)) blocked acquisition of concurrent but not sequential TAL. These data support the hypothesis of two different modalities of TAL mediated by distinct neurobiological systems, with vagal nerve participation only being essential in concurrent TAL.

Effects of perivagal administration of capsaicin on food intake in animals after noxious gastric surgery

Previous studies have shown that the perivagal administration of capsaicin induces greater food intake vs. controls at 24 h after the surgery but a similar intake to that of controls at 48 h. The present study aimed to determine whether the nutritive effect observed after perivagal capsaicin administration is due to the interruption of noxious vagal fibers in rats. For this purpose, postsurgical food intake was analyzed in control and capsaicin-treated animals with (Experiment 2) and without (Experiment 1) noxious lesions in the gastric wall. The results of both experiments showed that the food intake of capsaicin-treated animals was greater vs. control animals at 24 h but not at 48 h after the surgery (p<0.025), as previously demonstrated. However, the food intake of the capsaicin-treated lesion animals in Experiment 2, although still greater than that of the control group, was significantly less than the intake of the capsaicin-treated animals in Experiment 1 (p<0.01). Therefore, it appears unlikely that the demonstrated effect is produced by lesion to noxious vagal fibers destroyed by the capsaicin. On the contrary, it is more likely that the vagal afferent pathways are those related to short-term nutrition.

Gastric satiation is volumetric, intestinal satiation is nutritive

Gerry Smith's thoughtful survey in his book Satiation (1998) outlined the established principles of gastric and intestinal satiation and delineated several questions still requiring clarification. Experiments since the time of the review have addressed some of these questions. A synthesis of the principles outlined in the Gerry Smith survey and the subsequent experimental results indicates that the direct controls, or neural feedback signals from the GI tract, that limit meal size consist of gastric volumetric signals and intestinal nutritive signals. The two types of negative feedback synergize in the control of feeding, and both are carried by vagal afferents.