Influence of postbiotic RG14 and inulin combination on cecal microbiota, organic acid concentration, and cytokine expression in broiler chickens.

This study examined the effects of different combinations of inulin and postbiotics RG14 on growth performance, cecal microbiota, volatile fatty acids (VFA), and ileal cytokine expression in broiler chickens. Two-hundred-and sixteen, one-day-old chicks were allocated into 6 treatment groups, namely, a basal diet (negative control, NC), basal diet + neomycin and oxytetracycline (positive control, PC), T1 = basal diet + 0.15% postbiotic RG14 + 1.0% inulin, T2 = basal diet + 0.3% postbiotic RG14 + 1.0% inulin, T3 = basal diet + 0.45% postbiotic RG14 + 1.0% inulin, and T4 = basal diet + 0.6% postbiotic RG14 + 1.0% inulin, and fed for 6 weeks. The results showed that birds fed T1 and T3 diets had higher (P < 0.05) final body weight and total weight gain than NC and PC birds. A lower (P < 0.05) feed conversion ratio was observed in birds fed T1 and T2 compared with those fed the NC diet. Birds fed PC, T1, T2, and T3 had higher (P < 0.05) cecum total bacteria and Bifidobacteria compared to the NC birds. Diet had no effect on cecum Lactobacilli, Enterococcus and Salmonella. The NC birds had higher (P < 0.05) Enterobacteria and E. coli than other treatments. Concentration of acetic acid was higher in birds fed PC, T1, and T4 compared to the NC birds. However, the concentration of butyric acid, propionic acid, and total VFA did not differ (P > 0.05) among diets. The NC birds had higher (P < 0.05) expression of interferon (IFN) and Lipopolysaccharide-induced tumor necrosis factor-alpha factor (LITAF) gene compared with those fed other diets. The mRNA expression of interluken-6 (IL-6) was up-regulated in birds fed T3 and T4 compared to the NC birds. However, the expression of interluken-8 (IL-8) gene was not influenced by diet. Postbiotic and inulin combinations are potential replacements for antibiotic growth promoters in the poultry industry.

Progression of subcortical atrophy in mild Parkinson's disease and its impact on cognition.

BACKGROUND AND PURPOSE: Mild cognitive impairment (MCI) is associated with pronounced grey matter atrophy in various brain regions. However, the association between atrophy patterns and progression from no cognitive impairment (NCI) to Parkinson's disease (PD)-MCI is not clearly known. We investigated the pattern and progression of atrophy in subcortical structures and its impact on cognition in patients with mild PD. METHODS: Sixty-five patients with mild PD with baseline and longitudinal clinical and neuropsychological assessments, and structural magnetic resonance imaging scans were studied. Movement Disorder Society Task Force criteria were used to classify patients with PD into PD-NCI (n = 54) and PD-MCI (n = 11). Based on progression over time, those who remained without cognitive impairment were classified as PD-stable (n = 42) and those who converted to MCI over 18 months were classified as PD-converters (n = 12). FreeSurfer was used to measure cortical thickness and subcortical volumes at baseline and follow-up. RESULTS: Parkinson's disease-MCI showed baseline thalamus atrophy and progressive atrophy in the thalamus, caudate, presubiculum, cornu ammonis 1 and 2-3, and significant memory and executive dysfunction compared with PD-NCI. PD-converters had greater accumbens atrophy at baseline and progressive atrophy in the thalamus, caudate and accumbens with dysfunctions in memory and executive domains. CONCLUSIONS: Progression of cognitive impairment in non-demented PD is associated with a specific pattern of subcortical atrophy. Findings from this study will allow future studies to investigate in the role of subcortical structures as a biomarker for PD dementia.

Concentration and state dependent reductions in corn oil intakes after glossopharyngeal nerve transections in rats.

Previous studies indicate a role for the glossopharyngeal nerve (GL) in the detection of dietary fats. The present experiments examined the effects of bilateral glossopharyngeal nerve transections (GLx) on the intake of low (4.8%), moderate (16%), and full-fat (100%) corn oil in non-deprived, food-deprived, and water-deprived rats. The rats had access to oils, 0.3 M sucrose, and water in a gustometer that measured number of licks and latency to the first lick during brief access trials. The behavioral measures were used as indices of the amount consumed and the motivation to ingest, respectively. After baseline intakes had stabilized, the rats received GLx or sham transections (Sham) and were then re-tested. Pre and post-surgery responses were compared to determine the impact of GLx on intake and the motivation to ingest. In non-deprived rats, GLx reduced the intake of 4.8% and 16% oils and decreased the motivation to ingest these oils. In food-deprived rats, GLx prevented increases in the ingestion of 4.8% and 16% oils and in the motivation to ingest these oils. In water-deprived rats, GLx reduced the intake of 100% oil and produced a general decrease in the motivation to consume low, moderate, and full-fat emulsions. These results indicate that GL is partially involved in corn oil intake and suggest an interactive effect of oil concentration with homeostatic state.

Dietary putrescine effects on performance parameters, nutrient digestibility, intestinal morphology and tissue polyamine content of broilers fed low protein diet.

This study was carried out to investigate the effects of dietary putrescine (PUT) on broiler's response fed low crude protein (CP) diets. A total of 192 male day old chicks were fed with four dietary treatments including two levels of PUT (0 and 0.03%) and two levels of CP (normal and low) with factorial combinations. Weekly growth performance, nutrient digestibility and intestinal morphology (at the age of 21 days) and liver and intestinal tissue polyamines content were measured. As a result of this study lower dietary CP had a significant (P<0.05) lower body weight gain (BWG) and improved protein efficiency ratio (PER). PUT improved energy efficiency ratio (EER) significantly (P<0.05). Dry matter (DM) digestibility was decreased by lower dietary CP whereas 0.03% PUT significantly (P<0.05) increased it. Low CP caused significant (P<0.05) greater calcium digestibility, while this effect was not found when PUT was added. PUT had no effect on intestine villous height and crypt depth. Polyamine content of intestine and liver was influenced by the age of the birds, while PUT had no effects on them. In conclusion, dietary PUT has beneficial effects on EER in chicks fed CP-deficient diet, indicating possible involvement of PUT in energy metabolism. PUT supplementation did not moderate the reduced BWG of the chicks fed low protein. Intestinal and liver polyamine concentration was mainly affected by dietary CP and age of the birds rather than dietary PUT.

The long-term outcome of HIV-infected patients after intensive care admission.

Long-term outcomes of HIV-infected patients admitted to the intensive care unit (ICU) since the advent of combination antiretroviral therapy (cART) have not been well described. We reviewed the long-term outcomes and clinical follow-up of HIV-infected patients admitted to the Prince of Wales Hospital ICU between 1999 and 2005 by a retrospective medical record review. Mortality was assessed in the ICU, in hospital and in the long-term. Twenty-four HIV-infected male patients underwent 26 ICU admissions. Their ICU and in-hospital mortalities were 33% and 46%, respectively. Higher APACHE (acute physiology and chronic health evaluation) II scores (median 27 versus 12, P < 0.001), lower CD4 cell counts (median 45 versus 335 cells/µL, P = 0.041) and longer hospitalization times prior to ICU admission (median 4 versus 1 day, P = 0.02) were significantly associated with in-hospital mortality. We found 85% of the subjects who survived hospital admission were still alive at a median of 41 months (4 months to 5 years) of follow-up, all of who were functionally independent. HIV-infected patients who survived ICU admission at our institution had good long-term outcomes in the cART era.

Egg production, faecal pH and microbial population, small intestine morphology, and plasma and yolk cholesterol in laying hens given liquid metabolites produced by Lactobacillus plantarum strains.

1. Various dosages of metabolite combinations of the Lactobacillus plantarum RI11, RG14 and RG11 strains (COM456) were used to study the egg production, faecal microflora population, faecal pH, small intestine morphology, and plasma and egg yolk cholesterol in laying hens. 2. A total of 500 Lohmann Brown hens were raised from 19 weeks to 31 weeks of age. The birds were randomly divided into 5 groups and fed on various treatment diets: (i) basal diet without supplementation of metabolites (control); (ii) basal diet supplemented with 0·3% COM456 metabolites; (iii) basal diet supplemented with 0·6% COM456 metabolites; (iv) basal diet supplemented with 0·9% COM456 metabolites; and (v) basal diet supplemented with 1·2% COM456 metabolites. 3. The inclusion of 0·6% liquid metabolite combinations, produced from three L. plantarum strains, demonstrated the best effect in improving the hens' egg production, faecal lactic acid bacteria population, and small intestine villus height, and reducing faecal pH and Enterobacteriaceae population, and plasma and yolk cholesterol concentrations. 4. The metabolites from locally isolated L. plantarum are a possible alternative feed additive in poultry production.

Effects of liquid metabolite combinations produced by Lactobacillus plantarum on growth performance, faeces characteristics, intestinal morphology and diarrhoea incidence in postweaning piglets.

A study was carried out to investigate the effects of feeding liquid metabolite combinations produced by Lactobacillus plantarum strains on growth performance, diarrhoea incidence, faecal pH, microfloral counts, short-chain fatty acids (SCFA) and intestinal villus height and crypt depth of postweaning piglets. A total of 120 piglets (26 days old) were randomly assigned evenly into five treatment groups treated with same basal diet: (1) -ve control (free antibiotic); (2) + ve control (0.03% of chlortetracycline); (3) Com 1 (0.3% metabolite of TL1, RG11 and RI11 strains); (4) Com 2 (0.3% metabolite of TL1, RG14 and RS5 strains); (5) Com 3 (0.3% metabolite of RG11, RG14 and RI11 strains). After 5 weeks, the average daily feed intake was not significantly different (P > 0.05) among the treatments and feed conversion ratio was the highest (P < 0.05) in the -ve control group. In addition, diarrhoea incidence was reduced when piglets were fed with metabolite combinations. Faecal lactic acid bacteria (LAB) counts were significantly higher (P < 0.05) in metabolite treatment groups than in the groups without metabolites. However, the treatment of Com 2 metabolite resulted lower (P < 0.05) faecal pH and Enterobacteriaceae (ENT) than the -ve control group. In contrast, total faecal SCFA of Com 2 were significantly higher (P < 0.05) than the -ve control group. The villus height of duodenum was higher (P < 0.05) in the + ve control and Com 2 groups as compared to -ve control group. The results obtained in this study showed that feeding metabolite combinations could improve growth performance, and increase the population of gut LAB and faecal SCFA of postweaning piglets.

The modulatory effects of rostral ventromedial medulla on air-puff evoked microarousals in rats.

This study tested whether the duration of microarousals from sleep evoked by innocuous air-puff is affected by intra-RVM administration of neurotensin and bicuculline, pharmacological manipulations that affect on and off cell activity. Air-puff evoked microarousal duration was unaffected by 0.05ng neurotensin, but decreased by 502ng neurotensin, and 5 and 50ng bicuculline. These results suggest a putative role for off cells in protecting sleep from interruption by non-noxious stimuli.

Live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 and D4 for protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus).

AIMS: To evaluate a live recombinant Lactococcus lactis vaccine expressing aerolysin genes D1 (Lac-D1ae) and/or D4 (Lac-D4ae) in protection against Aeromonas hydrophila in tilapia (Oreochromis niloticus). METHODS AND RESULTS: The polymerase chain reaction (PCR)-amplified 250- and 750-bp sequences coding for domains D1 and D4 of aerolysin were individually cloned into pNZ8048 and electrotransformed into L. lactis. The recombinant vaccine candidates were then either orally fed or injected intraperitoneally into tilapia. The development of antibodies in sampled fish compared to control groups implied that the recombinant epitopes expressed in L. lactis were able to elicit an immunogenic response in tilapia. Interestingly, the lower doses of both Lac-D1ae and Lac-D4ae gave higher antibody levels over the study period. Fish immunized with Lac-D1ae and Lac-D4ae together showed the highest level of protection, and the mortality was reduced significantly compared to control strains in both modes of vaccination. CONCLUSIONS: The recombinant L. lactis strain expressing D1 and D4 produced aerolysin-specific serum IgM in tilapia. Both D1 and D4 promoted 55-82% relative per cent survival (RPS) against Aeromonas infection through intraperitoneal injection, whereas the RPS following oral feeding of the vaccine was 70-100%. SIGNIFICANCE AND IMPACT OF THE STUDY: The D1 and D4 regions of the aerolysin protein have been successfully identified as immunogenic regions that can elicit antibody production in tilapia and protect against challenge with Aer. hydrophila. A promising oral vaccine using L. lactis harbouring the D1 and D4 regions has been developed to control Aer. hydrophila.

Laboratory test performance in young adults during influenza outbreaks at World Youth Day 2008.

BACKGROUND: The performance of influenza laboratory diagnostics in young adults and in the setting of outbreaks during mass gatherings has not been well studied. OBJECTIVES: We compare the performance of point-of-care tests (POCTs) and immunofluorescence assays (IFAs) with nucleic acid tests (NATs) and viral culture in pilgrims attending influenza clinics established during a large influenza outbreak (World Youth Day, Sydney, Australia, 2008) to assess their performance under the real-life pressures of a mass influenza outbreak. STUDY DESIGN: Patients with an influenza-like illness (ILI) underwent respiratory specimen sampling. Combined deep nares and throat swabs were collected for POCT by trained or untrained clinic staff; type-specific IFA; NAT and viral culture. Laboratory-confirmed influenza occurred if viral culture and/or NAT were positive; the performance of laboratory tests was calculated against this 'gold standard'. RESULTS: A total of 230 samples were collected from 227 patients (median age, 20 years; interquartile range, 18-28 years), with 95 samples (41.3%) having laboratory-confirmed influenza infection (influenza A, 57; influenza B, 38). IFA and POCT sensitivities were 74.5% and 55%, respectively. Four of 51 (8%) culture-positive specimens were negative by NAT, and several errors in influenza virus typing occurred with IFA, POCT and NAT. A non-significant trend towards better POCT performance with increased operator training was demonstrated. CONCLUSION: Different environments, patient populations, operator experience, laboratory access and practicalities associated with performing tests during mass influenza outbreaks may affect performance of influenza-specific laboratory tests.

Analgesia accompanying food consumption requires ingestion of hedonic foods.

Animals eat rather than react to moderate pain. Here, we examined the behavioral, hedonic, and neural requirements for ingestion analgesia in ad libitum fed rats. Noxious heat-evoked withdrawals were similarly suppressed during self-initiated chocolate eating and ingestion of intraorally infused water, sucrose, or saccharin, demonstrating that ingestion analgesia does not require feeding motivation, self-initiated food procurement, sucrose, or calories. Rather, food hedonics is important because neither salt ingestion nor quinine rejection elicited analgesia. During quinine-induced nausea and lipopolysaccharide (LPS)-induced illness, conditions when chocolate eating was presumably less pleasurable, analgesia accompanying chocolate consumption was attenuated, yet analgesia during water ingestion was preserved in LPS-injected rats who showed enhanced palatability for water within this context. The dependence of ingestion analgesia on the positive hedonics of an ingestate was confirmed in rats with a conditioned taste aversion to sucrose: after paired exposure to sucrose and LPS, rats no longer showed analgesia during sucrose ingestion but continued to show analgesia during chocolate consumption. Eating pauses tended to occur less often and for shorter durations in the presence of ingestion analgesia than in its absence. Therefore, we propose that ingestion analgesia functions to defend eating from ending. Muscimol inactivation of the medullary raphe magnus blocked the analgesia normally observed during water ingestion, showing the involvement of brainstem endogenous pain inhibitory mechanisms in ingestion analgesia. Brainstem-mediated defense of the consumption of palatable foods may explain, at least in part, why overeating tasty foods is so irresistible even in the face of opposing cognitive and motivational forces.

Food consumption inhibits pain-related behaviors.

The function of the endogenous analgesia system under natural circumstances has been little explored. Our recent work shows that animals are significantly less responsive to noxious stimulation during slow wave sleep, micturition, and while eating than during quiet wake. The analgesia associated with eating is dependent on activity in the medullary raphe magnus, the final common brain stem region in endogenous analgesia pathways. Eating analgesia does not depend on energy-depletion due to food deprivation. Further, analgesia accompanies chow-eating even though chow has no sucrose, demonstrating that sucrose is not a necessary component of analgesia-evoking ingestates. Since raphe magnus modulates processing of innocuous as well as nociceptive information, the sensory suppression accompanying eating is likely a more general depression of the response to external stimulation. Such a phenomenon would serve animals well under natural conditions where energy-dense food is scarce but has counterproductive effects, possibly contributing to obesity, in modern human society where energy-dense food is readily available.

Effects of feeding metabolite combinations produced by Lactobacillus plantarum on growth performance, faecal microbial population, small intestine villus height and faecal volatile fatty acids in broilers.

1. Four combinations of metabolites produced from strains of Lactobacillus plantarum were used to study the performance of broiler chickens. 2. A total of 432 male Ross broilers were raised from one-day-old to 42 d of age in deep litter pens (12 birds/pen). These birds were divided into 6 groups and fed on different diets: (i) standard maize-soybean-based diet (negative control); (ii) standard maize-soybean-based diet + Neomycin and Oxytetracycline (positive control); (iii) standard maize-soybean-based diet + 0.3% metabolite combination of Lactobacillus plantarum RS5, RI11, RG14 and RG11 strains (com3456); (iv) standard maize-soybean-based diet + 0.3% metabolite combination of L. plantarum TL1, RI11 and RG11 (Com246); (v) standard maize-soybean-based diet + 0.3% metabolite combination of L. plantarum TL1, RG14 and RG11 (Com256) and (vi) standard maize-soybean-based diet + 0.3% metabolite combination of L. plantarum TL1, RS5, RG14 and RG11 (Com2356). 3. Higher final body weight, weight gain, average daily gain and lower feed conversion ratio were found in all 4 treated groups. 4. The addition of a metabolite combination supplementation also increased faecal lactic acid bacteria population, small intestine villus height and faecal volatile fatty acids and faecal Enterobacteriaceae population.

Eating is a protected behavior even in the face of persistent pain in male rats.

Feeding is critical for survival. Yet, patients with chronic pain often lose their appetite and eat less. We previously showed that ad libitum fed male rats continue to feed rather than withdraw from a brief noxious stimulus. This study examined the effects of a sustained noxious stimulus on feeding by testing ad libitum fed male rats for five eating behaviors--latency to eat, time taken to eat each chip, pauses and scanning during eating, and the number of chocolate chips eaten--during the hour following a sham injection or an injection of a low (0.5%) or moderate (1.5%) dose of formalin into the hind paw. Sham-injected rats showed no pain-related behaviors, rats injected with 0.5% formalin showed very few pain-related behaviors, and rats injected with 1.5% formalin showed favoring, lifting and licking of the injured paw with a characteristic biphasic time course. Besides taking less time to commence eating during the first phase of formalin pain, rats injected with either dose of formalin did not differ from sham-injected rats on any of the other eating measures. Rats injected with 0.5% formalin showed no pain behaviors during eating, whereas those given 1.5% formalin typically ate while not exhibiting any pain behaviors but occasionally ate while favoring the paw, rarely while lifting the paw, and never while licking the paw. These results show that eating is a protected activity even in the presence of persistent pain in male rats.

Sensory suppression during feeding.

Feeding is essential for survival, whereas withdrawal and escape reactions are fundamentally protective. These critical behaviors can compete for an animal's resources when an acutely painful stimulus affects the animal during feeding. One solution to the feeding-withdrawal conflict is to optimize feeding by suppressing pain. We examined whether rats continue to feed when challenged with a painful stimulus. During feeding, motor withdrawal responses to noxious paw heat either did not occur or were greatly delayed. To investigate the neural basis of sensory suppression accompanying feeding, we recorded from brainstem pain-modulatory neurons involved in the descending control of pain transmission. During feeding, pain-facilitatory ON cells were inhibited and pain-inhibitory OFF cells were excited. When a nonpainful somatosensory stimulus preactivated ON cells and preinhibited OFF cells, rats interrupted eating to react to painful stimuli. Inactivation of the brainstem region containing ON and OFF cells also blocked pain suppression during eating, demonstrating that brainstem pain-modulatory neurons suppress motor reactions to external stimulation during homeostatic behaviors.

Cell surface display system for Lactococcus lactis: a novel development for oral vaccine.

The food-grade Lactococcus lactis is a potential vector to be used as a live vehicle for the delivery of heterologous proteins for vaccine and pharmaceutical purposes. We constructed a plasmid vector pSVac that harbors a 255-bp single-repeat sequence of the cell wall-binding protein region of the AcmA protein. The recombinant plasmid was transformed into Escherichia coli and expression of the gene fragment was driven by the T7 promoter of the plasmid. SDS-PAGE showed the presence of the putative AcmA' fragment and this was confirmed by Western blot analysis. The protein was isolated and purified using a His-tag affinity column. When mixed with a culture of L. lactis MG1363, ELISA and immunofluorescence assays showed that the cell wall-binding fragment was anchored onto the outer surface of the bacteria. This indicated that the AcmA' repeat unit retained the active site for binding onto the cell wall surface of the L. lactis cells. Stability assays showed that the fusion proteins (AcmA/A1, AcmA/A3) were stably docked onto the surface for at least 5 days. The AcmA' fragment was also shown to be able to strongly bind onto the cell surface of naturally occurring lactococcal strains and Lactobacillus and, with less strength, the cell surface of Bacillus sphericus. The new system designed for cell surface display of recombinant proteins on L. lactis was evaluated for the expression and display of A1 and A3 regions of the VP1 protein of enterovirus 71 (EV71). The A1 and A3 regions of the VP1 protein of EV71 were cloned upstream to the cell wall-binding domains of AcmA protein and successfully expressed as AcmA/A1 and AcmA/A3. Whole-cell ELISA showed the successful display of VP1 protein epitopes of EV71 on the surface of L. lactis. The success of the anchoring system developed in this study for docking the A1 and A3 epitopes of VP1 onto the surface of L. lactis cells opens up the possibilities of peptide and protein display for not only Lactococcus but also for other gram-positive bacteria. This novel way of displaying epitopes on the cell surface of L. lactis and other related organisms should be very useful in the delivery of vaccines and other useful proteins.

Movement-related discharge of ventromedial medullary neurons.

Studies in anesthetized animals implicate nonserotonergic cells in the ventromedial medulla (VMM) in opioid modulation of nociceptive transmission but do not reveal the conditions that engage VMM cells in unanesthetized rats. The few studies of VMM cells in unanesthetized rats show that VMM cells change their discharge across the sleep-wake cycle and during active movements. Since active movements are more likely to occur during waking than sleep, state-related discharge may in fact represent movement-related discharge. In this study, we recorded the discharge of VMM neurons in unanesthetized, drug-free, freely moving rats and examined whether neuronal activity was related to wake/sleep state, to motor activity, or to both factors. Most cells (45/67) were more active during waking states than sleeping states, 1 cell was more active during sleep states, and the remaining 21 cells did not fire preferentially across the sleep-wake cycle. Most wake-active cells (36/45) showed discharge bursts during movement bursts, and 9/11 wake-active cells were excited by noxious heat and innocuous air puff stimulation. In contrast, few state-independent cells (9/21) showed movement-related bursts in discharge. These results suggest that VMM neurons modulate spinal processes during phasic motor activity.

Discharge of raphe magnus ON and OFF cells is predictive of the motor facilitation evoked by repeated laser stimulation.

Medullary raphe magnus (RM) on and off cells are thought to modulate spinal nociception by gating withdrawals evoked by noxious stimulation. To test whether withdrawal initiation is the target of RM modulation, we examined the relationship between on and off cell discharge and motor withdrawal evoked by noxious laser heat in halothane-anesthetized rats. The cellular responses of both cell types began during the 50 msec after onset of the tail flick, peaked within 200 msec, and outlasted the duration of the motor reaction. Thus, it is unlikely that the target of on and off cell modulation is withdrawal initiation; instead, on and off cells may modulate reactions to repeated noxious stimulation. We therefore tested whether laser heat-evoked changes in RM cell discharge were predictive of the modulatory effects of one noxious stimulus on the reaction to a subsequent noxious stimulus. Two pulses of laser heat were presented at interpulse intervals of 0.8, 2.0, or 10.0 sec. The motor withdrawal evoked by the second pulse was significantly enhanced relative to that evoked by the first pulse. The observed motor enhancement depended on supraspinal input because it was not present in spinalized rats. Comparison of the relative changes in motor and cellular activity preceding double laser heat stimulation revealed parallel changes between motor facilitation, decreases in off cell discharge, and increases in on cell discharge. This finding suggests a preparatory role for RM on and off cells in enhancing reactions to a noxious stimulus that closely follows another noxious stimulus.

Brainstem modulation of pain during sleep and waking.

Moderately painful stimuli applied during sleep evoke motor and neural responses indicative of arousal, but seldom cause awakening. Different reactions occur in response to acute pain stimulation across behavioral states; pain reactions are modulated by the activity of serotonergic and non-serotonergic cells in the raphe magnus (RM). Serotonergic RM cells have state-dependent discharge and may inhibit simple motor withdrawal responses during waking. ON and OFF cells are non-serotonergic RM neurons thought to facilitate and inhibit pain, respectively. These cells display reciprocal spontaneous discharge patterns across the sleep-wake cycle, with ON cells most active during waking and OFF cells most active during sleep. We propose that they also play an important role in modulating the alertness evoked by any brief external stimulus, either noxious or innocuous. ON cells may facilitate alertness during waking and OFF cells suppress arousals during sleep. In the presence of chronic pain, both ON and OFF cell discharge appear to increase. The increase in ON cell discharge may contribute to enhancing pain sensitivity and alertness. Future research is needed to understand why sleep is so adversely affected in chronic pain patients, whereas sleep is minimally disrupted, even by acutely painful stimuli, in humans and animals without chronic pain.