Composition effects on photooxidative membrane destabilization by TiO2 nanoparticles.

Membrane interactions and photooxidative membrane destabilization of titanium dioxide (TiO2) nanoparticles were investigated, focusing on the effects of membrane composition, notably phospholipid headgroup charge and presence of cholesterol. For this, we employed a battery of state-of-the-art methods for studies of bilayers formed by zwitterionic palmitoyloleoylphosphatidylcholine (POPC) containing also polyunsaturated palmitoylarachidonoylphosphocholine (PAPC), as well as its mixtures with anionic palmitoyloleoylphosphatidylglycerol (POPG) and cholesterol. It was found that the TiO2 nanoparticles display close to zero charge at pH 7.4, resulting in aggregation. At pH 3.4, in contrast, the 6 nm TiO2 nanoparticles are well dispersed due to a strongly positive ζ-potential. Mirroring this pH dependence, TiO2 nanoparticles were observed to bind to negatively charged lipid bilayers at pH 3.4, but much less so at pH 7.4. While nanoparticle binding has some destabilizing effect alone, illumination with ultraviolet (UV) light accentuates membrane destabilization, a result of oxidative stress caused by generated reactive oxygen species (ROS). Neutron reflectivity (NR), quartz crystal microbalance (QCM), and small-angle X-ray scattering (SAXS) results all demonstrate that membrane composition strongly influences membrane interactions and photooxidative destabilization of lipid bilayers. In particular, the presence of anionic POPG makes the bilayers more sensitive to oxidative destabilization, whereas a stabilizing effect was observed in the presence of cholesterol. Also, structural aspects of peroxidation were found to depend strongly on membrane composition, notably the presence of anionic phospholipids. The results show that membrane interactions and UV-induced ROS generation act in concert and need to be considered together to understand effects of lipid membrane composition on UV-triggered oxidative destabilization by TiO2 nanoparticles, e.g., in the context of oxidative damage of bacteria and cells.

Perinatal high fat diet increases inhibition of dorsal motor nucleus of the vagus neurons regulating gastric functions.

BACKGROUND: Previous studies suggest an increased inhibition of dorsal motor nucleus of the vagus (DMV) neurons following exposure to a perinatal high fat diet (PNHFD); the underlying neural mechanisms, however, remain unknown. This study assessed the effects of PNHFD on inhibitory synaptic inputs to DMV neurons and the vagally dependent control of gastric tone and motility. METHODS: Whole-cell patch clamp recordings were made from DMV neurons in thin brainstem slices from Sprague-Dawley rats fed either a control diet or HFD (14 or 60% kcal from fat, respectively) from embryonic day 13 onwards; gastric tone and motility were recorded in in vivo anesthetized rats. KEY RESULTS: The non-selective GABAA antagonist, BIC (10 µmol L-1 ), induced comparable inward currents in PNHFD and control DMV neurons, but a larger current in PNHFD neurons at higher concentrations (50 µmol L-1 ). Differences were not apparent in neuronal responses to the phasic GABAA antagonist, gabazine (GBZ), the extrasynaptic GABAA agonist, THIP, the GABA transport blocker, nipecotic acid, or the gliotoxin, fluoroacetate, suggesting that PNHFD altered inhibitory transmission but not GABAA receptor density or function, GABA uptake or glial modulation of synaptic strength. Similarly, the increase in gastric motility and tone following brainstem microinjection of low doses of BIC (1-10 pmoles) and GBZ (0.01-0.1 pmoles) were unchanged in PNHFD rats while higher doses of BIC (25 pmoles) induced a significantly larger increase in gastric tone compared to control. CONCLUSIONS AND INFERENCES: These studies suggest that exposure to PNHFD increases the tonic inhibition of DMV neurons, possibly contributing to dysregulated vagal control of gastric functions.

Human Lipoproteins at Model Cell Membranes: Effect of Lipoprotein Class on Lipid Exchange.

High and low density lipoproteins (HDL and LDL) are thought to play vital roles in the onset and development of atherosclerosis; the biggest killer in the western world. Key issues of initial lipoprotein (LP) interactions at cellular membranes need to be addressed including LP deposition and lipid exchange. Here we present a protocol for monitoring the in situ kinetics of lipoprotein deposition and lipid exchange/removal at model cellular membranes using the non-invasive, surface sensitive methods of neutron reflection and quartz crystal microbalance with dissipation. For neutron reflection, lipid exchange and lipid removal can be distinguished thanks to the combined use of hydrogenated and tail-deuterated lipids. Both HDL and LDL remove lipids from the bilayer and deposit hydrogenated material into the lipid bilayer, however, the extent of removal and exchange depends on LP type. These results support the notion of HDL acting as the 'good' cholesterol, removing lipid material from lipid-loaded cells, whereas LDL acts as the 'bad' cholesterol, depositing lipid material into the vascular wall.

Multilayering of Calcium Aerosol-OT at the Mica/Water Interface Studied with Neutron Reflection: Formation of a Condensed Lamellar Phase at the CMC.

Using specular neutron reflection, the adsorption of sodium and calcium salts of the surfactant bis(2-ethylhexyl) sulfosuccinate (Aerosol-OT or AOT) has been studied at the mica/water interface at concentrations between 0.1 and 2 CMC. The pH dependence of the adsorption was also probed. No evidence of the adsorption of Na(AOT) was found even at the critical micelle concentration (CMC) while the calcium salt was found to adsorb significantly at concentrations of 0.5 CMC and above. This interesting and somewhat unexpected finding demonstrates that counterion identity may be used to tune the adsorption of anionic surfactants on anionic surfaces. At the CMC, three condensed bilayers of Ca(AOT)2 were adsorbed at pH 7 and 9 and four bilayers adsorbed at pH 4. Multilayering at the CMC of Ca(AOT)2 on the mica surface is an unusual feature of this surfactant/surface combination. Only single bilayer adsorption has been observed at other surfaces at the CMC. We suggest this arises from the high charge density of mica which must provide an excellent template for the surfactant.

Complete bilayer adsorption of C16TAB on the surface of mica using neutron reflection.

We present neutron reflection data from an alkylammonium surfactant (C16TAB) at the mica/water interface. The system is studied in situ in a noninvasive manner and indicates the formation of a complete adsorbed bilayer with little evidence of defects. A detailed analysis suggests that the data are not consistent with some other previously reported adsorbed structures, such as micelles or cylinders.

Diminished vagal tone is a predictive biomarker of necrotizing enterocolitis-risk in preterm infants.

BACKGROUND: Necrotizing enterocolitis (NEC) is an acute neonatal inflammatory disease which may lead to intestinal necrosis, multisystem failure, and death. Currently, NEC is diagnosed by a combination of laboratory and radiographic tests conducted a posteriori i.e., when NEC is already clinically significant. Given the acute onset and rapid progression of NEC, a non-invasive biomarker that allows early detection of patients at risk is required as a matter of urgency. We evaluated whether the high frequency (HF) component of heart rate variability (HRV), a measure of vagal efferent tonic cholinergic activity may be used as a predictive biomarker for NEC-risk before the onset of clinical disease. METHODS: In this prospective study, stable preterm (gestational age 28-35 weeks) infants had HRV power spectra analyzed from surface electrocardiogram waveforms taken at rest on day 5-8 of life. We used regression modeling to determine the utility of HF-HRV in predicting NEC. KEY RESULTS: HF-HRV power was 21.5 ± 2.7 and 3.9 ± 0.81 ms(2) in infants that remained healthy and those that later developed stage 2+ NEC, respectively (p < 0.001). Nine of 70 enrolled infants developed NEC. The ROC discriminated a HF-HRV value of 4.68 ms(2) predictive for developing NEC with a sensitivity and specificity of 89% and 87%, and positive and negative predictive value of 50% and 98%, respectively. With predictive regression modeling, the risk (odds ratio) of developing NEC was 10 per every one SD decrease in HF-HRV. CONCLUSIONS & INFERENCES: Our preliminary data indicate that HF-HRV may serve as a potential, non-invasive predictive biomarker of NEC-risk in NICU infants.

Ghrelin increases vagally mediated gastric activity by central sites of action.

BACKGROUND: Vagally dependent gastric reflexes are mediated through vagal afferent fibers synapsing upon neurons of the nucleus tractus solitarius (NTS) which, in turn modulate the preganglionic parasympathetic dorsal motor nucleus of the vagus (DMV) neurons within the medullary dorsal vagal complex (DVC). The expression and transport of ghrelin receptors has been documented for the afferent vagus nerve, and functional studies have confirmed that vagal pathways are integral to ghrelin-induced stimulation of gastric motility. However, the central actions of ghrelin within the DVC have not been explored fully. METHODS: We assessed the responses to ghrelin in fasted rats using: (i) in vivo measurements of gastric tone and motility following IVth ventricle application or unilateral microinjection of ghrelin into the DVC and (ii) whole cell recordings from gastric-projecting neurons of the DMV. KEY RESULTS: (i) IVth ventricle application or unilateral microinjection of ghrelin into the DVC-elicited contractions of the gastric corpus via excitation of a vagal cholinergic efferent pathway and (ii) ghrelin facilitates excitatory, but not inhibitory, presynaptic transmission to DMV neurons. CONCLUSIONS & INFERENCES: Our data indicate that ghrelin acts centrally by activating excitatory synaptic inputs onto DMV neurons, resulting in increased cholinergic drive by way of vagal motor innervation to the stomach.

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.

Glucose-dependent trafficking of 5-HT3 receptors in rat gastrointestinal vagal afferent neurons.

BACKGROUND: Intestinal glucose induces gastric relaxation via vagally mediated sensory-motor reflexes. Glucose can alter the activity of gastrointestinal (GI) vagal afferent (sensory) neurons directly, via closure of ATP-sensitive potassium channels, and indirectly, via the release of 5-hydroxytryptamine (5-HT) from mucosal enteroendocrine cells. We hypothesized that glucose may also be able to modulate the ability of GI vagal afferent neurons to respond to the released 5-HT, via regulation of neuronal 5-HT(3) receptors. METHODS: Whole-cell patch clamp recordings were made from acutely dissociated GI-projecting vagal afferent neurons exposed to equiosmolar Krebs' solution containing different concentrations of d-glucose (1.25-20 mmol L(-1)) and the response to picospritz application of 5-HT assessed. The distribution of 5-HT(3) receptors in neurons exposed to different glucose concentrations was also assessed immunohistochemically. KEY RESULTS: Increasing or decreasing extracellular d-glucose concentration increased or decreased, respectively, the 5-HT-induced inward current and the proportion of 5-HT(3) receptors associated with the neuronal membrane. These responses were blocked by the Golgi-disrupting agent Brefeldin-A (5 µmol L(-1)) suggesting involvement of a protein-trafficking pathway. Furthermore, l-glucose did not mimic the response of d-glucose implying that metabolic events downstream of neuronal glucose uptake are required to observe the modulation of 5-HT(3) receptor mediated responses. CONCLUSIONS & INFERENCES: These results suggest that, in addition to inducing the release of 5-HT from enterochromaffin cells, glucose may also increase the ability of GI vagal sensory neurons to respond to the released 5-HT, providing a means by which the vagal afferent signal can be amplified or prolonged.

Oxytocin-immunoreactive innervation of identified neurons in the rat dorsal vagal complex.

BACKGROUND: Oxytocin (OXT) has been implicated in reproduction and social interactions and in the control of digestion and blood pressure. OXT-immunoreactive axons occur in the dorsal vagal complex (DVC; nucleus tractus solitarius, NTS, dorsal motor nucleus of the vagus, DMV, and area postrema, AP), which contains neurons that regulate autonomic homeostasis. The aim of the present work is to provide a systematic investigation of the OXT-immunoreactive innervation of dorsal motor nucleus of the vagus (DMV) neurons involved in the control of gastrointestinal (GI) function. METHODS: We studied DMV neurons identified by (i) prior injection of retrograde tracers in the stomach, ileum, or cervical vagus or (ii) induction of c-fos expression by glucoprivation with 2-deoxyglucose. Another subgroup of DMV neurons was identified electrophysiologically by stimulation of the cervical vagus and then juxtacellularly labeled with biotinamide. We used two- or three-color immunoperoxidase labeling for studies at the light microscopic level. KEY RESULTS: Close appositions from OXT-immunoreactive varicosities were found on the cell bodies, dendrites, and axons of DMV neurons that projected to the GI tract and that responded to 2-deoxyglucose and juxtacellularly labeled DMV neurons. Double staining for OXT and choline acetyltransferase revealed that OXT innervation was heavier in the caudal and lateral DMV than in other regions. OXT-immunoreactive varicosities also closely apposed a small subset of tyrosine hydroxylase-immunoreactive NTS and DMV neurons. CONCLUSIONS & INFERENCES: Our results provide the first anatomical evidence for direct OXT-immunoreactive innervation of GI-related neurons in the DMV.

Experimental spinal cord injury in rats diminishes vagally-mediated gastric responses to cholecystokinin-8s.

BACKGROUND: We have shown recently that our model of experimental high-thoracic spinal cord injury (T3-SCI) mirrors the gastrointestinal clinical presentation of neurotrauma patients, whereby T3-SCI animals show diminished gastric emptying and dysmotility. In this study we used cholecystokinin as a model peptide to test the hypothesis that the T3-SCI induced gastroparesis is due, in part, to an impaired vagally-mediated response to gastrointestinal peptides. METHODS: We measured the responses to sulfated cholecystokinin (CCK-8s) in control and T3-SCI (3 or 21 days after injury) rats utilizing: (i) c-fos expression in the nucleus tractus solitarius (NTS) following peripherally administered CCK-8s; (ii) in vivo gastric tone and motility following unilateral microinjection of CCK-8s into the dorsal vagal complex (DVC); and (iii) whole cell recordings of glutamatergic synaptic inputs to NTS neurons. KEY RESULTS: Our results show that: (i) medullary c-fos expression in response to peripheral CCK-8s was significantly lower in T3-SCI rats 3 days after the injury, but recovered to control values at 3 weeks post-SCI, (ii) Unilateral microinjection of CCK-8s in the DVC induced a profound gastric relaxation in control animals, but did not induce any response in T3-SCI rats at both 3 and 21 days after SCI, (iii) Perfusion with CCK-8s increased glutamatergic currents in 55% of NTS neurons from control rats, but failed to induce any response in NTS neurons from T3-SCI rats. CONCLUSIONS & INFERENCES: Our data indicate alterations of vagal responses to CCK-8s in T3-SCI rats that may reflect a generalized impairment of gastric vagal neurocircuitry, leading to a reduction of gastric functions after SCI.

Plasticity of vagal brainstem circuits in the control of gastric function.

BACKGROUND: Sensory information from the viscera, including the gastrointestinal (GI) tract, is transmitted through the afferent vagus via a glutamatergic synapse to neurons of the nucleus tractus solitarius (NTS), which integrate this sensory information to regulate autonomic functions and homeostasis. The integrated response is conveyed to, amongst other nuclei, the preganglionic neurons of the dorsal motor nucleus of the vagus (DMV) using mainly GABA, glutamate and catecholamines as neurotransmitters. Despite being modulated by almost all the neurotransmitters tested so far, the glutamatergic synapse between NTS and DMV does not appear to be tonically active in the control of gastric motility and tone. Conversely, tonic inhibitory GABAergic neurotransmission from the NTS to the DMV appears critical in setting gastric tone and motility, yet, under basal conditions, this synapse appears resistant to modulation. PURPOSE: Here, we review the available evidence suggesting that vagal efferent output to the GI tract is regulated, perhaps even controlled, in an 'on-demand' and efficient manner in response to ever-changing homeostatic conditions. The focus of this review is on the plasticity induced by variations in the levels of second messengers in the brainstem neurons that form vago-vagal reflex circuits. Emphasis is placed upon the modulation of GABAergic transmission to DMV neurons and the modulation of afferent input from the GI tract by neurohormones/neurotransmitters and macronutrients. Derangement of this 'on-demand' organization of brainstem vagal circuits may be one of the factors underlying the pathophysiological changes observed in functional dyspepsia or hyperglycemic gastroparesis.

Protease-activated receptors: novel central role in modulation of gastric functions.

Protease-activated receptors (PARs) are members of a subfamily of G-protein-coupled receptors that regulate diverse cell functions in response to proteolytic cleavage of an anchored peptide domain that acts as a 'tethered' receptor-activating ligand. PAR-1 and PAR-2 in particular are present throughout the gastrointestinal (GI) tract and play prominent roles in the regulation of GI epithelial function, motility, inflammation and nociception. In a recent article in Neurogastroenterology and Motility, Wang et al. demonstrate, for the first time, that PAR-1 and PAR-2 are present on preganglionic parasympathetic neurons within the rat brainstem. As in other cellular systems, proteases such as thrombin and trypsin activate PAR-1 and PAR-2 on neurons of the dorsal motor nucleus of the vagus (DMV), leading to an increase in intracellular calcium levels via signal transduction mechanisms involving activation of phospholipase C and inositol triphosphate (IP3). The authors also report that the level of PAR-1 and PAR-2 transcripts in DMV tissue is increased following experimental colitis, suggesting that inflammatory conditions may modulate neuronal behavior or induce plasticity within central vagal neurocircuits. It seems reasonable to hypothesize, therefore, that the activity and behavior of vagal efferent motoneurons may be modulated directly by local and/or systemic proteases released during inflammation. This, in turn, may contribute to the increased incidence of functional GI disorders, including gastric dysmotility, delayed emptying and gastritis observed in patients with inflammatory bowel diseases.

Modulation of inhibitory neurotransmission in brainstem vagal circuits by NPY and PYY is controlled by cAMP levels.

Pancreatic polypeptides such as neuropeptide Y (NPY) and peptide YY (PYY) exert profound, vagally mediated effects on gastrointestinal (GI) motility. Vagal efferent outflow to the GI tract is determined principally by tonic GABAergic synaptic inputs onto dorsal motor nucleus of the vagus (DMV) neurons, yet neither peptide modulates GABAergic transmission. We showed recently that opioid peptides appear similarly ineffective because of the low resting cAMP levels. Using whole cell recordings from identified DMV neurons, we aimed to correlate the influence of brainstem cAMP levels with the ability of pancreatic polypeptides to modulate GABAergic synaptic transmission. Neither NPY, PYY, nor the Y1 or Y2 receptor selective agonists [Leu,Pro]NPY or NPY(3-36) respectively, inhibited evoked inhibitory postsynaptic current (eIPSC) amplitude unless cAMP levels were elevated by forskolin or 8-bromo-cAMP, by exposure to adenylate cyclase-coupled modulators such as cholecystokinin octapeptide (sulfated) (CCK-8s) or thyrotropin releasing hormone (TRH), or by vagal deafferentation. The inhibition of eIPSC amplitude by [Leu,Pro]NPY or NPY(3-36) was stable for approximately 30 min following the initial increase in cAMP levels. Thereafter, the inhibition declined gradually until the agonists were again ineffective after 60 min. Analysis of spontaneous and miniature currents revealed that such inhibitory effects were due to actions at presynaptic Y1 and Y2 receptors. These results suggest that, similar to opioid peptides, the effects of pancreatic polypeptides on GABAergic transmission depend upon the levels of cAMP within gastric inhibitory vagal circuits.

Ketamine inhibits long-term, but not intermediate-term memory formation in Lymnaea stagnalis.

We investigated the effects of the drug ketamine on procedural intermediate- and long-term memory formation in a well-established operant learning and memory model system, Lymnaea stagnalis. Animals were administered ketamine at discrete time points, ranging from 2 h pre-one-trial training (1TT) to 23 h post-1TT. Our results demonstrated that ketamine causes impairment of procedural memory formation, and that ketamine acts differentially, inhibiting only long-term memory (LTM) formation while having no effect on intermediate-term memory (ITM) formation. Ketamine's ability to inhibit LTM was found not to be due to state dependent learning implying that ketamine's effects are therefore specific to the molecular process involved in procedural LTM formation. Given past data from our laboratory, this suggests that ketamine may be exerting its differential effects by altering the gene transcription processes necessary and specific for LTM formation. Additionally, ketamine was found to have no effect on retrieval when administered 1 h before testing. However, ketamine was able to disrupt LTM formation when administered immediately before 1TT and up to 2 h after 1TT. Our findings suggest a longer period of consolidation after 1TT than previously demonstrated in Lymnaea, during which the procedural long-term memory remains labile and is vulnerable to disruption via amnestic agents, such as ketamine.

Control of protein translation by phosphorylation of the mRNA 5'-cap-binding complex.

Initiation of mRNA translation is a key regulatory step in the control of gene expression. Microarray analysis indicates that total mRNA levels do not always reflect protein levels, since mRNA association with polyribosomes is necessary for protein synthesis. Phosphorylation of translation initiation factors offers a cost-effective and rapid way to adapt to physiological and environmental changes, and there is increasing evidence that many of these factors are subject to multiple regulatory phosphorylation events. The present article focuses on the nature of reversible phosphorylation and the function of the 5'-cap-binding complex in plants.

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.

Melanin concentrating hormone innervation of caudal brainstem areas involved in gastrointestinal functions and energy balance.

Neural signaling by melanin-concentrating hormone and its receptor (SLC-1) has been implicated in the control of energy balance, but due to the wide distribution of melanin-concentrating hormone-containing fibers throughout the neuraxis, its critical sites of action for a particular effect have not been identified. The present study aimed to anatomically and functionally characterize melanin-concentrating hormone innervation of the rat caudal brainstem, as this brain area plays an important role in the neural control of ingestive behavior and autonomic outflow. Using retrograde tracing we demonstrate that a significant proportion (5-15%) of primarily perifornical and far-lateral hypothalamic melanin-concentrating hormone neurons projects to the dorsal vagal complex. In the caudal brainstem, melanin-concentrating hormone-ir axon profiles are distributed densely in most areas including the nucleus of the solitary tract, dorsal motor nucleus of the vagus, and sympathetic premotor areas in the ventral medulla. Close anatomical appositions can be demonstrated between melanin-concentrating hormone-ir axon profiles and tyrosine hydroxylase, GABA, GLP-1, NOS-expressing, and nucleus of the solitary tract neurons activated by gastric nutrient infusion. In medulla slice preparations, bath application of melanin-concentrating hormone inhibited in a concentration-dependent manner the amplitude of excitatory postsynaptic currents evoked by solitary tract stimulation via a pre-synaptic mechanism. Fourth ventricular administration of melanin-concentrating hormone (10 microg) in freely moving rats decreased core body temperature but did not change locomotor activity and food and water intake. We conclude that the rich hypothalamo-medullary melanin-concentrating hormone projections in the rat are mainly inhibitory to nucleus of the solitary tract neurons, but are not involved in the control of food intake. Projections to ventral medullary sites may play a role in the inhibitory effect of melanin-concentrating hormone on energy expenditure.