Effects of leptin on cat intestinal motility

Novel insights into the pathogenic impact of diabetes on the gastrointestinal tract

Type 2 and type 1 diabetes are common endocrine disorders with a progressively increasing incidence worldwide. These chronic, systemic diseases have multiorgan implications, and the whole gastrointestinal (GI) tract represents a frequent target in terms of symptom appearance and interdependent pathophysiological mechanisms. Metabolic alterations linked with diabetic complications, neuropathy and disrupted hormone homeostasis can lead to upper and/or lower GI symptoms in up to 75% of diabetic patients, with multifactorial involvement of the oesophagus, stomach, upper and lower intestine, and of the gallbladder. On the other hand, altered gastrointestinal motility and/or secretions are able to affect glucose and lipid homeostasis in the short and long term. Finally, diabetes has been linked with increased cancer risk at different levels of the GI tract. The presence of GI symptoms and a comprehensive assessment of GI function should be carefully considered in the management of diabetic patients to avoid further complications and to ameliorate the quality of life. Additionally, the presence of gastrointestinal dysfunction should be adequately managed to improve metabolic homeostasis, the efficacy of antidiabetic treatments and secondary prevention strategies.

Use of intestine-related biomarkers for detecting intestinal epithelial damage in neonatal calves with diarrhea

OBJECTIVE

To evaluate the usefulness of intestinal biomarkers in determining the presence of intestinal epithelial damage in neonatal calves with diarrhea caused by 4 etiologic agents.

ANIMALS

40 neonatal calves that were healthy (n = 10) or had diarrhea (30).

PROCEDURES

The study was a cross-sectional study. Results of hematologic analyses and serum concentrations of intestinal fatty acid-binding protein (I-FABP), liver fatty acid-binding protein (L-FABP), trefoil factor 3 (TFF-3), Claudin-3 (CLDN-3), γ-enteric smooth muscle actin (ACTG2), intestinal alkaline phosphatase (IAP), interleukin-8 (IL-8), platelet-activating factor (PAF), and leptin (LP) were compared among calves grouped according to whether they were healthy (control group; G-1) or had diarrhea caused by K99 Escherichia coli (G-2; n = 10), bovine rota- or coronavirus (G-3; 5 each), or Cryptosporidium spp (G-4; 10).

RESULTS

Across the 3 time points at which blood samples were obtained and evaluated, the groups of calves with diarrhea generally had markedly higher mean serum concentrations of L-FABP, TFF-3, IAP, IL-8, and LP, compared with the control group. In addition, G-2 also consistently had markedly higher mean serum concentrations of I-FAB and ACTG2 and lower mean serum concentrations of CLDN-3, compared with the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that degree of intestinal epithelial damage differed among calves grouped by the etiologic agent of diarrhea and that such damage might have been more severe in calves with diarrhea caused by K99 E coli. Additionally, our results indicated that serum concentrations of I-FABP, L-FABP, TFF-3, IAP, IL-8, ACTG2, LP, and CLDN-3 were useful biomarkers of intestinal epithelial damage in calves of the present study.

Adipocytes-released Peptides Involved in the Control of Gastrointestinal Motility

The present review focuses on adipocytes-released peptides known to be involved in the control of gastrointestinal motility, acting both centrally and peripherally. Thus, four peptides have been taken into account: leptin, adiponectin, nesfatin-1, and apelin. The discussion of the related physiological or pathophysiological roles, based on the most recent findings, is intended to underlie the close interactions among adipose tissue, central nervous system, and gastrointestinal tract. The better understanding of this complex network, as gastrointestinal motor responses represent peripheral signals involved in the regulation of food intake through the gut-brain axis, may also furnish a cue for the development of either novel therapeutic approaches in the treatment of obesity and eating disorders or potential diagnostic tools.

The Food Contaminant Mycotoxin Deoxynivalenol Inhibits the Swallowing Reflex in Anaesthetized Rats

Deoxynivalenol (DON), one of the most abundant mycotoxins found on cereals, is known to be implicated in acute and chronic illnesses in both humans and animals. Among the symptoms, anorexia, reduction of weight gain and decreased nutrition efficiency were described, but the mechanisms underlying these effects on feeding behavior are not yet totally understood. Swallowing is a major motor component of ingestive behavior which allows the propulsion of the alimentary bolus from the mouth to the esophagus. To better understand DON effects on ingestive behaviour, we have studied its effects on rhythmic swallowing in the rat, after intravenous and central administration. Repetitive electrical stimulation of the superior laryngeal nerve or of the tractus solitarius, induces rhythmic swallowing that can be recorded using electromyographic electrodes inserted in sublingual muscles. Here we provide the first demonstration that, after intravenous and central administration, DON strongly inhibits the swallowing reflex with a short latency and in a dose dependent manner. Moreover, using c-Fos staining, a strong neuronal activation was observed in the solitary tract nucleus which contains the central pattern generator of swallowing and in the area postrema after DON intravenous injection. Our data show that DON modifies swallowing and interferes with central neuronal networks dedicated to food intake regulation.

Digestive function of the stomach

The core function of the human stomach is as an aid to digestion. The four key components of gastric digestive function are its function as a reservoir, acid secretion, enzyme secretion and its role in gastrointestinal motility. The reservoir capacity of the stomach allows it to increase its volume significantly while internal pressure increases only slightly. Acid secretion is a very important non-immunological defence against invading pathogens as well as being an important mechanism for vertebrates to have more complex diets. Stimulation of acid secretion involves the translocation of H+/K+-ATPases to the apical membrane of the parietal cell. The stomach is also an important endocrine organ producing an array of peptide hormones important for both enteric and non-enteric physiology including ghrelin and leptin. In addition to the reservoir function, the stomach also plays an important motility role as a pump, which anatomically is provided by the distal two thirds of the corpus, the antrum and the pylorus. This article examines those four functions and the role that they play in normal physiologic function and examines how they may play a role in pathologic states.

Effects of tumor necrosis factor α on leptin-sensitive intestinal vagal mechanoreceptors in the cat

The involvement of tumour necrosis factor α (TNF-α) in inflammatory bowel disease (IBD) has been established, and anti-TNF-α has been suggested as a therapeutic approach for the treatment of these pathologies. We studied the effects of TNF-α on leptin-sensitive intestinal vagal units to determine whether TNF-α exerts its effects through the intestinal vagal mechanoreceptors and to investigate its interactions with substances regulating food intake. The activity of intestinal vagal mechanoreceptors was recorded via microelectrodes implanted into the nodose ganglion in anesthetized cats. TNF-α (1 μg, i.a.) increased the discharge frequency of leptin-activated units (type 1 units; P < 0.05) and had no effect on the discharge frequency of leptin-inhibited units (type 2 units). When TNF-α was administered 20 min after sulfated cholecystokinin-8 (CCK), its excitatory effects on type 1 units were significantly enhanced (P < 0.0001) and type 2 units were significantly (P < 0.05) activated. Pre-treatment with Il-1ra (250 μg, i.a.) blocked the excitatory effects of TNF-α on type 1 units whereas the excitatory effects of TNF-α administration after CCK treatment on type 2 units were not modified. The activation of leptin-sensitive units by TNF-α may explain, at least in part, the weight loss observed in IBD.

Leptin modulates enteric neurotransmission in the rat proximal colon: an in vitro study

Leptin has been shown to modulate gastrointestinal functions including nutrient absorption, growth, and inflammation and to display complex effects on gut motility. Leptin receptors have also been identified within the enteric nervous system (ENS), which plays a crucial role in digestive functions. Although leptin has recently been shown to activate neurons in the ENS, the precise mechanisms involved are so far unknown. Therefore, the aim of the present study was to determine the effects of leptin on rat proximal colon smooth muscle and enteric neuron activities. The effects of exogenous leptin on tone and on responses to transmural nerve stimulation (TNS) of isolated circular smooth muscle of proximal colon in rats were investigated using an organ bath technique. The effects of a physiological concentration (0.1 μM) of leptin were also studied on tone and TNS-induced relaxation in the presence of atropine, hexamethonium, L-N(G)-nitroarginine methyl ester (L-NAME) and capsazepine. Leptin caused a slight but significant decrease in tone, TNS-induced relaxation and contraction in a concentration-dependent manner in colonic preparations. Cholinergic antagonists abolished the effects of 0.1 μM leptin on TNS-induced relaxation. This concentration of leptin had no further effect on relaxation in the presence of L-NAME. In the presence of capsazepine, leptin had no further effect either on tone or relaxation compared to the drug alone. In conclusion, leptin modulates the activity of enteric inhibitory and excitatory neurons in proximal colon. These effects may be mediated through nitrergic neurons. Intrinsic primary afferent neurons may be involved.

Expression and immunohistochemical detection of leptin-like peptide in the gastrointestinal tract of the South American sea lion (Otaria flavescens) and the bottlenose dolphin (Tursiops truncatus)

This study provides an immunohistochemical approach to the expression of leptin in the gastrointestinal tract of the monogastric South American sea lion (Otaria flavescens), and the poligastric bottlenose dolphin (Tursiops truncatus). The specific organization of the gastrointestinal tract is examined in relation to the neuroendocrine regulation of the gut exerted by leptin. In the South American sea lion some leptin-like-immunoreactive (ir) cells, and endocrine type cells, were found in the pit of gastric mucosal folds and in the epithelium of duodenum as well as numerous neurons were detected in the submucosal and myenteric plexuses of the stomach. In the bottlenose dolphin, many leptin-like-ir cells, and exocrine type cells, were identified in the mucosal layer of the main stomach as well as several neurons and nervous fibers were detected in nervous plexuses of main stomach, pyloric stomach, proximal, and middle intestine. Our data suggest that the distribution of leptin-like peptides is similar in the two species, notwithstanding the different anatomical organization of the gastrointestinal apparatus of South American sea lion and bottlenose dolphin. These findings "suggest" the presence of a basal plan in the regulation of food intake, body weight, energy balance and of the gastrointestinal functions in general also in marine mammals with different and specific feeding habits.

Leptin excites enteric neurons of guinea-pig submucous and myenteric plexus

BACKGROUND

Leptin, one of the most prominent mediators released from adipocytes, influences neuronal activity in the central nervous system. The enteric nervous system (ENS) expresses leptin receptors but consequence of activation of these receptors on enteric neuron activity has not been systematically studied. An adipocyte-ENS axis is suggested by close apposition between enteric nerves and adipocytes. The aim of this study was to investigate the effects of leptin on guinea-pig submucous and myenteric neurons.

METHODS

Using voltage sensitive dye imaging, we recorded neural responses to application of leptin (0.0625 nmol L(-1)) in myenteric and submucous neurons, nicotine (10 μmol L(-1)) served as a reference for neuronal excitation. Mucosal ion secretion and muscle activity were measured in vitro with Ussing and organ bath techniques, respectively.

KEY RESULTS

Leptin induced spike discharge in 13.6% of submucous neurons and in 8.2% of myenteric neurons (1.1 ± 0.9 and 1.2 ± 1.0 Hz, respectively). Although there was an overlap of nicotine and leptin responses, 38.5% of submucous and 25% of myenteric neurons activated by leptin did not respond to nicotine. Leptin did not inhibit ongoing spike discharge or fast excitatory postsynaptic potentials. Leptin (0.0625 nmol L(-1)) did not affect mucosal secretion or muscle activity suggesting a subtle modulatory action of leptin at the level of the ENS.

CONCLUSIONS & INFERENCES

Leptin activates submucous and myenteric neurons indicating relevance for adipocyte-ENS signaling. These results set the basis for further studies to reveal the functional correlate of the neural action of leptin in the ENS.

Intracerebroventricular injection of leptin inhibits gastric emptying but has no effect on intestinal transit in rats

AIM: To investigate whether injection of leptin into the lateral cerebral ventricle has impact on gastrointestinal motility in rats.

METHODS: Fifty-two female Sprague-Dawley rats were randomly divided into two groups: normal control group and leptin group. The leptin group was further divided into three subgroups for detection at 1, 3, and 5 h. For intracerebroventricular infusion, a guide cannula was fixed into the lateral cerebral ventricle one week before the experiment. Under no anesthesia, leptin (3.5 g/L) was injected into the lateral cerebral ventricle through the implanted guide cannula. Equal volume of saline was injected as a control. After the injection, rats were subjected to measurement of the rate of gastric emptying and the rate of intestinal transit.

RESULTS: The rate of gastric emptying decreased more significantly in the three leptin subgroups than in the normal control group (54.7% ± 8.3%, 54.6% ± 9.3%, 57.4% ± 8.9% vs 70.0% ± 6.1%, all P <0.05). However, there is no significant difference in the rate of intestinal transit between the leptin subgroups and normal control group (41.1% ± 4.9%, 49.5% ± 13.6%, 43.6% ± 5.5% vs 43.0% ± 6.3%, all P > 0.05).

CONCLUSION: Intracerebroventricular injection of leptin inhibits gastric emptying but has no effect on intestinal transit in rats.

Diverse roles of leptin in the gastrointestinal tract: modulation of motility, absorption, growth, and inflammation

OBJECTIVE

Leptin was discovered in 1994 as a hormone produced by adipose tissue with a modulatory effect on feeding behavior and weight control. Recently, the stomach has been identified as an important source of leptin and growing evidence has shown diverse functions for leptin in the gastrointestinal tract.

METHODS

Using leptin as a keyword in PubMed, more than 17 000 articles were identified, of which more than 500 articles were related to the role of leptin in the gastrointestinal tract. Available abstracts were reviewed and more than 200 original articles were reviewed in detail.

RESULTS

The available literature demonstrated that leptin can modulate several important functions of the gastrointestinal tract. Leptin interacts with the vagus nerve and cholecystokinin to delay gastric emptying and has a complex effect on motility of the small bowel. Leptin modulates absorption of macronutrients in the gastrointestinal tract differentially in physiologic and pathologic states. In physiologic states, exogenous leptin has been shown to decrease carbohydrate absorption and to increase the absorption of small peptides by the PepT1 di-/tripeptide transporter. In certain pathologic states, leptin has been shown to increase absorption of carbohydrates, proteins, and fat. Leptin has been shown to be upregulated in the colonic mucosa in patients with inflammatory bowel disease. Leptin stimulates gut mucosal cell proliferation and inhibits apoptosis. These functions have led to speculation about the role of leptin in tumorigenesis in the gastrointestinal tract, which is complicated by the multiple immunoregulatory effects of leptin.

CONCLUSION

Leptin is an important modulator of major aspects of gastrointestinal tract functions, independent of its more well-described roles in appetite regulation and obesity.

Colonosphincteric electromyographic responses to sacral root stimulation: evidence for a somatosympathetic reflex

The aim of the present study was to determine the effects of selectively stimulating the afferent fibres running in the dorsal sacral roots (S1, S2, S3) and the somatic (radial and sciatic) nerves on colonic and internal anal sphincter (IAS) electromyographic (EMG) activity in anaesthetized cats to try to understand how sacral nerve stimulation can improve fecal continence in human. Electrically stimulating the afferent fibres present in the sacral dorsal roots and somatic nerves inhibited the colonic spike potential frequency (n = 97) and increased the slow variations in the sphincteric membrane potential (n = 76). These effects were found to have disappeared after administering an alpha-noradrenergic receptor blocker (n = 64) or sectioning the sympathetic efferent fibres innervating these organs (n = 69) suggesting the involvement of the sympathetic system in the effects observed. Moreover, no significant differences were observed between the effects of sacral dorsal root vs somatic nerve stimulation on colonic and sphincteric EMG activity. In conclusion, the data obtained here show that neurostimulation applied to the sacral spinal roots may improve fecal continence by inhibiting colonic activity and enhancing IAS activity via a somatosympathetic reflex.

Modulation of vagal afferent excitation and reduction of food intake by leptin and cholecystokinin

The gut-peptide, cholecystokinin (CCK), reduces food intake by acting at CCK-1 receptors on vagal afferent neurons, whereas the feeding effects of the adipokine hormone, leptin, are associated primarily with its action on receptors (ObRb) in the hypothalamus. Recently, however, ObRb mRNA has been reported in vagal afferent neurons, some of which also express CCK-1 receptor, suggesting that leptin, alone or in cooperation with CCK, might activate vagal afferent neurons, and influence food intake via a vagal route. To evaluate these possibilities we have been examining the cellular and behavioral effects of leptin and CCK on vagal afferent neurons. In cultured vagal afferent neurons leptin and CCK evoked short latency, transient depolarizations, often leading to action potentials, and increases in cytosolic calcium. There was a much higher prevalence of CCK and leptin sensitivity amongst cultured vagal afferent neurons that innervate stomach or duodenum than there was in the overall vagal afferent population. Furthermore, almost all leptin-responsive gastric and duodenal vagal afferents also were sensitive to CCK. Leptin, infused into the upper GI tract arterial supply, reduced meal size, and enhanced satiation evoked by CCK. These results indicate that vagal afferent neurons are activated by leptin, and that this activation is likely to participate in meal termination, perhaps by enhancing vagal sensitivity to CCK. Our findings are consistent with the view that leptin and CCK exert their influence on food intake by accessing multiple neural systems (viscerosensory, motivational, affective and motor) at multiple points along the neuroaxis.

Altered intestinal motility in leptin-deficient obese mice

INTRODUCTION

Leptin is produced by adipocytes and causes satiety by regulating hypothalamic neurotransmission and energy expenditure. Leptin functions through the active long form of its receptor, which is expressed throughout the gastrointestinal tract, including the vagal neurons concerned with small intestinal motility. However, the role of leptin in small intestinal motility is poorly understood. Therefore, we hypothesized that leptin-deficient (Lepob) obese mice would have altered small intestinal response to neurotransmitters and transit time.

MATERIALS AND METHODS

Responses of jejunal and ileal segments from lean control and leptin-deficient obese animals to acetylcholine (ACh) and cholecystokinin (CCK) were determined in an organ bath. In addition, gastric emptying was determined as the amount of gavaged liquid diet remaining in the stomach after 1 h, and intestinal transit time was determined by calculating the geometric center (GC) of passage of a fluorescent-labeled marker.

RESULTS

Leptin deficiency resulted in increased jejunal responses to CCK (P <0.05) and a similar response to ACh compared to lean controls. Also, gastric emptying (97% versus 91%, P <0.001) in obese mice was greater. Overall small intestinal transit (GC) in obese mice was decreased (7.3 versus 8.4, P <0.05) even though proximal transit was increased (5.3 versus 1.5, P <0.06).

CONCLUSIONS

These studies indicate that leptin-deficient (Lepob) obese mice have an increased jejunal response to CCK as well as an increased proximal intestinal transit, but an overall decrease in small intestinal transit.

Leptin increases small intestinal response to cholecystokinin in leptin-deficient obese mice

INTRODUCTION

Leptin receptors are present in the jejunum, ileum, and vagal neurons. Leptin increases duodenal secretion of cholecystokinin (CCK) and acts with CCK on vagal mechanoreceptors in the regulation of small intestinal motility. We have demonstrated that leptin-deficient (Lepob) obese mice have increased jejunal and normal ileal responses to CCK. Therefore, we hypothesized that leptin administration alters small intestinal motility observed in leptin-deficient obese mice.

MATERIALS AND METHODS

Twelve-week-old female leptin-deficient (Lepob) obese mice received either saline (n=12) or 5 microg/g leptin ip (n=12) injections daily. After 4 weeks, jejunal and ileal segments were harvested, mounted in an organ bath, and reacted with acetylcholine (ACh, 10(-5)M) and CCK (10(-8,-7,-6)M). Data were expressed as N/cm2 and compared by ANOVA and Student's t test.

RESULTS

The average body weights in the leptin-treated group were significantly decreased compared to those of the saline-treated group (34 versus 49 g, P <0.01). Jejunal responses to ACh within each group were significantly decreased (P <0.05) when compared to ileal responses. No significant differences in responses to ACh were observed between groups. Jejunal responses to 10(-7,-6)M CCK in the leptin-treated group were significantly greater than those in the saline-treated group. Ileal responses in the leptin group were similarly increased at all CCK concentrations.

CONCLUSIONS

These data suggest that daily leptin administration for 4 weeks in leptin-deficient (Lepob) obese mice increases jejunal and ileal responses to CCK and does not alter responses to ACh. Therefore, we conclude that regulation of small intestinal motility may be influenced by synergistic action of cholecystokinin and leptin.

Effects of psychological stress on small intestinal motility and expression of cholecystokinin and vasoactive intestinal polypeptide in plasma and small intestine in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and expression of cholecystokinin (CCK) and vasoactive intestinal polypeptide (VIP) in plasma and small intestine, and to explore the relationship between small intestinal motor disorders and gastrointestinal hormones under psychological stress.

METHODS: Thirty-six mice were randomly divided into psychological stress group and control group. A mouse model with psychological stress was established by housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. CCK and VIP levels in plasma and small intestine in mice were measured by radioimmunoassay (RIA).

RESULTS: Small intestinal transit was inhibited (52.18±19.15% vs 70.19±17.79%, P<0.01) in mice after psychological stress, compared to the controls. Small intestinal CCK levels in psychological stress mice were significantly lower than those in the control group (0.75±0.53 μg/g vs 1.98±1.17 μg/g, P<0.01), whereas plasma CCK concentrations were not different between the groups. VIP levels in small intestine were significantly higher in psychological stress mice than those in the control group (8.45±1.09 μg/g vs 7.03±2.36 μg/g, P<0.01), while there was no significant difference in plasma VIP levels between the two groups.

CONCLUSION: Psychological stress inhibits the small intestinal transit, probably by down-regulating CCK and up-regulating VIP expression in small intestine.

Cooperative activation of cultured vagal afferent neurons by leptin and cholecystokinin

To test the hypothesis that leptin can directly activate vagal afferent neurons, we used fluorescence imaging to detect acute changes in cytosolic calcium after leptin application to primary cultures of vagal afferent neurons dissociated from adult rat nodose ganglia. We found that approximately 40% of vagal afferent neurons exposed to leptin (40 ng/ml) responded with rapid and reversible increases in cytosolic calcium. These responses were dependent upon extracellular calcium. As previously reported, about 35% of vagal afferents increase cytosolic calcium in response to the gut-peptide cholecystokinin (CCK). A majority (74%) of neurons that responded to CCK also exhibited increases in cytosolic calcium in response to leptin. In addition, synergistic increases in cytosolic calcium were observed when leptin and CCK were applied in combination. These results demonstrate that leptin acts directly on vagal afferent neurons to trigger acute influxes of extracellular calcium. Our results also suggest cooperation between leptin and CCK in the activation of some vagal afferent neurons. Acute activation of vagal afferents by leptin alone and in combination with CCK may contribute to modulation of visceral reflexes and control of food intake.

Small intestinal motility

PURPOSE OF REVIEW

In the past year, many studies were published in which new and relevant information on small intestinal motility in humans and laboratory animals was obtained.

RECENT FINDINGS

Although the reported findings are heterogeneous, some themes appear to be particularly interesting and novel. Among these is the association between disordered small intestinal motility and bacterial overgrowth of the small intestine. Studies in patients with portal hypertension, in patients with chronic renal failure, and in a rat model of experimental acute pancreatitis all point in the same direction. Another topic of particular interest is the relation between duodenal motility and glucose absorption; propagated duodenal pressure wave sequences are positively related to glucose absorption. Finally, many studies addressed the mechanisms involved in the regulation of interdigestive and postprandial small intestinal motility. These confirmed the key role of cholecystokinin and provided new information on the role of orexin A and leptin.

SUMMARY

The new information on intestinal motility gathered in the past year provides a greater insight in the pathophysiology of a number of diseases and will stimulate further studies in laboratory animals and in human subjects.

Effects of interactions between interleukin-1 beta and leptin on cat intestinal vagal mechanoreceptors

In a previous study, we established that leptin acts on chemosensitive intestinal vagal mechanoreceptors and that its excitatory effects are blocked by the endogenous interleukin-1beta receptor antagonist (Il-1ra). To determine how interleukin-1beta (Il-1beta) is involved in the action of leptin, we studied the effects of this drug on the single vagal afferent activities of intestinal mechanoreceptors in anaesthetized cats. For this purpose, the activity of 34 intestinal vagal mechanoreceptors was recorded via glass microelectrodes implanted in the nodose ganglion. Il-1beta (1 microg) administered into the artery irrigating the upper part of the intestine activated both the 16 leptin-activated units (type 1 units; P < 0.01) and the 12 leptin-inhibited units (type 2 units; P < 0.001), but had no effect on the six leptin-insensitive units. Cholecystokinin (CCK, 10 microg) induced an activatory response only in the two types of Il-1beta-sensitive units. When Il-1beta was administered after CCK, its excitatory effects on type 1 units were enhanced, whereas the excitatory effects on type 2 units were abolished. Pre-treatment with Il-1ra (250 microg) blocked all the effects of Il-1beta and the excitatory effects of leptin on type 1 units, whereas it enhanced the inhibitory effects of leptin on type 2 units. It can therefore be concluded that (i) leptin acts on intestinal vagal mechanoreceptors via Il-1beta in the case of the type 1 units and independently of Il-1beta in the case of the type 2 units, and (ii) type 1 and type 2 units belong to two different populations of vagal afferents that transmit different information about ingestion or inflammation to the CNS, depending on the chemical environment.