Effects of relative humidity on dry-aged beef quality.

This study was conducted to evaluate the effects of relative humidity (RH) on moisture loss and flavor in dry-aged beef. Sixteen strip loins were assigned to one of the four aging treatments: vacuum (WET), dry-aging at 50% RH, dry-aging at 70% RH, or dry-aging at 85% RH and aged for 42 days at 2 °C. Loins were evaluated for evaporation loss, trim loss, tenderness, sensory, and microbiological characteristics. Results show that lower RH results in accelerated moisture loss during the first 3 days of the aging process without significantly affecting the total amount of moisture loss. Pseudomonadales dominated the aerobically dry-aged loins while Enterobacteriales was the most abundant in the wet-aged samples. Dry-aged samples had increased content of free amino acids in the cooked meat juice compared to the wet-aged counterpart. Dry aging at 50% RH tended to associate with more desirable flavor notes.

Salmonella Biofilm Formation under Fluidic Shear Stress on Different Surface Materials.

This study characterized biofilm formation of various Salmonella strains on common processing plant surface materials (stainless steel, concrete, rubber, polyethylene) under static and fluidic shear stress conditions. Surface-coupons were immersed in well-plates containing 1 mL of Salmonella (6 log CFU/mL) and incubated aerobically for 48 h at 37 °C in static or shear stress conditions. Biofilm density was determined using crystal violet assay, and biofilm cells were enumerated by plating on tryptic soy agar plates. Biofilms were visualized using scanning electron microscopy. Data were analyzed by SAS 9.4 at a significance level of 0.05. A surface-incubation condition interaction was observed for biofilm density (p < 0.001). On stainless steel, the OD600 was higher under shear stress than static incubation; whereas, on polyethylene, the OD600 was higher under static condition. Enumeration revealed surface-incubation condition (p = 0.024) and surface-strain (p < 0.001) interactions. Among all surface-incubation condition combinations, the biofilm cells were highest on polyethylene under fluidic shear stress (6.4 log/coupon; p < 0.001). Biofilms of S. Kentucky on polyethylene had the highest number of cells (7.80 log/coupon) compared to all other strain-surface combinations (p < 0.001). Electron microscopy revealed morphological and extracellular matrix differences between surfaces. Results indicate that Salmonella biofilm formation is influenced by serotype, surface, and fluidic shear stress.

Roles of Aerotolerance, Biofilm Formation, and Viable but Non-Culturable State in the Survival of Campylobacter jejuni in Poultry Processing Environments.

Campylobacter jejuni is one of the most common causes of foodborne human gastroenteritis in the developed world. This bacterium colonizes in the ceca of chickens, spreads throughout the poultry production chain, and contaminates poultry products. Despite numerous on farm intervention strategies and developments in post-harvest antimicrobial treatments, C. jejuni is frequently detected on broiler meat products. This indicates that C. jejuni is evolving over time to overcome the stresses/interventions that are present throughout poultry production and processing. The development of aerotolerance has been reported to be a major survival strategy used by C. jejuni in high oxygen environments. Recent studies have indicated that C. jejuni can enter a viable but non-culturable (VBNC) state or develop biofilm in response to environmental stressors such as refrigeration and freezing stress and aerobic stress. This review provides an overview of different stressors that C. jejuni are exposed to throughout the poultry production chain and the genotypic and phenotypic survival mechanisms, with special attention to aerotolerance, biofilm formation, and development of the VBNC state.

The Prevalence of Salmonella and Campylobacter on Broiler Meat at Different Stages of Commercial Poultry Processing.

In poultry processing, Salmonella and Campylobacter contaminations are major food safety concerns. Peracetic acid (PAA) is an antimicrobial commonly used in commercial poultry processing to reduce pathogen prevalence so as to meet the USDA-FSIS performance standards. The objective of this study was to determine the prevalence of Salmonella and Campylobacter on broiler meat in various steps of commercial poultry processing in plants that use PAA. Post-pick, pre-chill, post-chill, and drumstick chicken samples were collected from three processing plants and mechanically deboned meat (MDM) was collected from two of the three plants. Each plant was sampled thrice, and 10 samples were collected from each processing step during each visit. Among the 420 samples, 79 were contaminated with Salmonella and 155 were contaminated with Campylobacter. Salmonella and Campylobacter contamination on the post-pick samples averaged 32.2%. Significant reductions in Salmonella and Campylobacter were observed in pre-chill to post-chill samples, where the prevalence was reduced from 34% and 64.4% to nondetectable limits and 1.1%, respectively (p < 0.001). Salmonella and Campylobacter remained undetectable on the drumstick samples in all three processing plants. However, the prevalence of Salmonella and Campylobacter on MDM was similar to the post-pick prevalence, which suggests substantial cross-contamination from post-chill to MDM.

Spoilage Bacteria Counts on Broiler Meat at Different Stages of Commercial Poultry Processing Plants That Use Peracetic Acid.

In poultry processing, spoilage microbes are persistent microorganisms, which affect the quality of broiler meat. Peracetic acid (PAA) is the most common antimicrobial used by commercial processing plants, which can reduce the prevalence of these microbes. The goal of this study was to determine the concentrations of aerobic bacteria, coliforms, lactic acid bacteria, and Pseudomonas on broiler meat in processing plants that use peracetic acid in various concentrations as the primary antimicrobial. Samples were collected from three processing plants at five processing steps: post-pick (defeathering), pre-chill, post-chill, mechanically deboned meat (MDM), and drumsticks. Samples were rinsed in buffered peptone water for bacteria isolation. Over six log CFU/sample of aerobic plate counts (APC), lactic acid bacteria, and coliforms were detected on post-pick samples. All spoilage bacteria were reduced to nondetectable levels on post-chill samples (p < 0.001). However, the presence of all bacteria on mechanically deboned meat (MDM) samples indicated varying degrees of cross contamination from post-chill and MDM samples. These results suggest PAA effectively reduces spoilage microbes in chilling applications irrespective of differences in PAA concentrations. However, due to the levels of spoilage microbes detected in MDM, it may be worth investigating the potential interventions for this stage of processing.

Oxidative stress biomarkers and free amino acid concentrations in the blood plasma of moderately exercised horses indicate adaptive response to prolonged exercise training.

Oxidative stress caused by routine physical stressors may negatively impact the performance of equine athletes; thus, the present study identifies oxidative biomarkers in the blood plasma of exercising horses. Stock-type horses were subject to a standardized moderate-intensity exercise protocol 3 times per week for 8 wk. Exercise protocol followed NRC guidelines consisting of 30% walk, 55% trot, and 15% canter, with a target heart rate (HR) of 90 BPM. Blood plasma was collected in wk 1, 2, 7, and 8 immediately before and 0, 30, 60, and 90 min after exercise and analyzed for total antioxidant capacity (TAC), thiobarbituric acid reactive substance (TBARS), glutathione peroxidase activity (GPx), and superoxide dismutase activity (SOD). Data were analyzed as repeated measures with wk, d, time, and their interactions as fixed effects. The TAC on day 2 (0.40 mM Trolox) was 7.5% greater than on day 3 (P = 0.013). There were wk × d × time interactions for SOD, TBARS, and GPx (P < 0.001). The TBARS remained at pre-exercise baseline (d-1 wk-1; 2.7 µM malondialdehyde) for most collection times within weeks 1, 7, and 8 (P ≥ 0.058); however, TBARS increased by 0.24 to 0.41 µM on day 2 of week 2 post-exercise (P < 0.001) and remained similarly elevated on day 3 pre- and immediately post-exercise (P < 0.001). The GPx similarly remained at baseline (172.6 µM/min; P ≥ 0.621) but increased by 48.18 to 83.4 µM/min at most collection times on days 1 and 2 of week 2 (P ≤ 0.023). The SOD remained at baseline (167.2 U/ mL; P ≥ 0.055) until increasing by 11.28 to 15.61 U/mL at 30 min post-exercise on day 1, week 1 and at most collection times on day 3, week 8 (P ≤ 0.043). Amino acids with antioxidant properties such as Met, Tyr, and Trp drastically decreased from weeks 2 to 8 (P < 0.001). Met and Tyr also decreased from -60 to 90 min (P < 0.047), whereas there was no time effect on Trp concentration (P = 0.841). The current study indicates the time-dependent nature of oxidative stress concerning persistent stressors such as exercise.

Performance horses are subjected to numerous stressors. These stressors may subsequently impact their overall performance. The present study measured oxidative stress biomarkers in the blood of exercising horses. Horses were moderately exercised over an 8-wk period and blood plasma was collected to measure total antioxidant capacity (TAC), thiobarbituric acid reactive substance (TBARS), glutathione peroxidase activity (GPx), and superoxide dismutase activity (SOD). Amino acid concentration was also evaluated. The TAC was greater on day 2 vs. day 3. The TBARS remained at pre-exercise (baseline) at most times except for increasing on day 2 of week 2 post-exercise. The GPx also remained at baseline for most times but increased on days 1 and 2 of week 2. The SOD remained at baseline until increasing at 30 min post-exercise on day 1, week 1 and at most collection times on day 3, week 8. Amino acids with antioxidant properties drastically decreased from weeks 2 to 8. Horses are exposed to a variety of physical stressors on a regular basis that may produce similar effects in the equine stress response. Understanding the response in the equine athlete when exposed to new stressors is crucial in determining how to prevent oxidative damage in future athletes.

Prevalence and Molecular Characteristics of Avian Pathogenic Escherichia coli in "No Antibiotics Ever" Broiler Farms.

Avian pathogenic Escherichia coli (APEC) causes significant economic and welfare concerns to the broiler industry. For several decades, prophylactic supplementation of antimicrobial growth promoters was the primary method to control APEC; however, the recent shift to no antibiotics ever (NAE) production has increased colibacillosis incidence. The objectives of this study were to determine the influence of season, flock age, and sample type on the prevalence and virulence of E. coli and to identify the serogroups and antimicrobial susceptibility of virulent and nonvirulent E. coli in NAE broiler farms. Litter, feces, cloacal swabs, and tracheal swabs were collected from 4 NAE farms during spring and summer seasons, and E. coli was isolated and confirmed by PCR. Confirmed E. coli isolates were tested for 5 APEC-virulence-associated genes (VAGs) using quantitative PCR (qPCR). Further, E. coli isolates with all five VAGs (100 isolates) and E. coli isolates without any VAGs (87 isolates) were screened against 11 antimicrobials through Kirby-Bauer disk diffusion assay, and their serogroups were tested using PCR. Data were analyzed using the GLIMMIX procedure of SAS 9.4, and statistical significance was determined at a P value of ≤0.05. Overall, the prevalence of E. coli was not affected by season, flock age, or sample type. However, the prevalence of all tested VAGs decreased from spring to summer (P ≤ 0.002). The frequency of resistance was highest for tetracycline, and serogroups O8 (31%) and O78 (11%) were most frequent in virulent E. coli. In conclusion, there is a high prevalence of virulent E. coli in NAE farms, especially in the spring season. IMPORTANCE Avian pathogenic Escherichia coli causes one of the most detrimental bacterial diseases to the United States poultry industry, colibacillosis. Colibacillosis leads to decreased performance, early mortality, and subsequent production loss. Previously, colibacillosis was largely mitigated by the use of antimicrobial growth promoters. Due to concerns about antimicrobial resistance, the use of these promoters has been largely removed from the broiler industry. With recent shifts in the poultry industry to NAE broiler production, there is an increase in bacterial disease and mortality. We do not know how this shift to NAE affects APEC prevalence within broiler farms. Therefore, in the current study, we attempted to assess the prevalence and virulence of E. coli within an antibiotic-free broiler environment, assessed antimicrobial susceptibility, and identified the serogroups of virulent and nonvirulent E. coli.

Research Note: Prevalence and molecular characteristics of Clostridium perfringens in "no antibiotics ever" broiler farms.

Clostridium perfringens (C. perfringens) is the etiological agent of necrotic enteritis and gangrenous dermatitis; 2 diseases that cause significant economic and welfare concerns to the broiler industry. Previously, Clostridium-related diseases were managed with the use of antimicrobial growth promoters fed to broilers that improved gut health and performance. The recent shift to no antibiotics ever (NAE) production has increased the incidence of Clostridium-related diseases. The objective of this study was to identify C. perfringens prevalence and toxinotypes in NAE farms. Samples of litter, feces, and cloacal swabs were collected from 4 NAE broiler farms in the summer of 2019, on d 28 and d 56 of one flock cycle. A total of 734 presumptive isolates were obtained from 192 samples collected in the study. Irrespective of the age of flock and sample type, all 192 samples contained at least one colony presumptively identified as C. perfringens on Perfringens agar plate with morphology as a single, round colony with opaque ring and black center. All isolates were further screened using PCR for confirmation, toxinotyping, and identification of virulence-associated genes. Only 9 isolates among the 734 presumptive isolates were confirmed as C. perfringens and all confirmed isolates were toxinotype A with variation in presence of netB, cpb2, and tpeL. More extensive studies are required to assess the prevalence and virulence of C. perfringens in NAE farms.

Advancing Semen Evaluation Using Lipidomics.

Developing a deeper understanding of biological components of sperm is essential to improving cryopreservation techniques and reproductive technologies. To fully ascertain the functional determinants of fertility, lipidomic methods have come to the forefront. Lipidomics is the study of the lipid profile (lipidome) within a cell, tissue, or organism and provides a quantitative analysis of the lipid content in that sample. Sperm cells are composed of various lipids, each with their unique contribution to the overall function of the cell. Lipidomics has already been used to find new and exciting information regarding the fatty acid content of sperm cells from different species. While the applications of lipidomics are rapidly evolving, gaps in the knowledge base remain unresolved. Current limitations of lipidomics studies include the number of available samples to analyze and the total amount of cells within those samples needed to detect changes in the lipid profiles across different subjects. The information obtained through lipidomics research is essential to systems and cellular biology. This review provides a concise analysis of the most recent developments in lipidomic research. This scientific resource is important because these developments can be used to not only combat the reproductive challenges faced when using cryopreserved semen and artificial reproductive technologies in livestock such as cattle, but also other mammals, such as humans or endangered species.

Lipidomic markers of sperm cryotolerance in cattle.

The objective of the current study was to determine the fatty acid composition of sperm from Holstein bulls with different freezability (Good and Poor; n = 12). Fatty acids were extracted from frozen sperm in 1:2 (v/v) chloroform-methanol solvent, fractionated into neutral and polar fractions, and composition determined by gas chromatography-mass spectrometry. Thirty-four fatty acids were quantified and their concentrations and percentages within each lipid fraction were calculated. Overall, saturated fatty acids (SFA) were predominant, accounting for 71 to 80% of fatty acids in neutral and polar lipid factions. There were marked differences in fatty acid composition between the lipid fractions (P < 0.001). The branched chain fatty acid (BCFA) concentration (15 to 18 µg) was almost twice as much as polyunsaturated fatty acids (PUFA) concentration found in the polar lipid fraction (8 to 9 µg; P < 0.001). Sperm with different freezability phenotypes only had a few differences in 22:0, 18:1 cis 9, and 14:0 13-methyl fatty acids (P ≤ 0.011). These results are significant because they reveal key understandings of fatty acid composition of sperm membrane and lay a foundation for the manipulation of membrane integrity, fluidity, and stability to advance the assisted reproductive technologies.

Avian Pathogenic Escherichia coli and Clostridium perfringens: Challenges in No Antibiotics Ever Broiler Production and Potential Solutions.

United States is the largest producer and the second largest exporter of broiler meat in the world. In the US, broiler production is largely converting to antibiotic-free programs which has caused an increase in morbidity and mortality within broiler farms. Escherichia coli and Clostridium perfringens are two important pathogenic bacteria readily found in the broiler environment and result in annual billion-dollar losses from colibacillosis, gangrenous dermatitis, and necrotic enteritis. The broiler industry is in search of non-antibiotic alternatives including novel vaccines, prebiotics, probiotics, and housing management strategies to mitigate production losses due to these diseases. This review provides an overview of the broiler industry and antibiotic free production, current challenges, and emerging research on antibiotic alternatives to reduce pathogenic microbial presence and improve bird health.

Application of natural antioxidant extract from guava leaves (Psidium guajava L.) in fresh pork sausage.

The current study was conducted to determine the antioxidant efficacy of guava leaf extract (3000 to 6000 ppm on fat basis) in fresh pork sausage, compared with negative control (CON) and 200 ppm butylated hydroxytoluene (BHT), for 0, 1, 4, 7, 10, and 14 d at 4 °C. The extract provided a total antioxidant capacity of 1505 µmol trolox equivalence/g. From d 4, the extract at 5000 and 6000 ppm provided greater (P < .05) antioxidant capacity than the CON and was either similar (P > .05) or greater (P < .05) than BHT. From d 4, the sausage formulated with 4000 to 6000 ppm of guava leaf extract had less conjugated dienes, lower peroxide and acidic values, less thiobarbituric reactive substances value, and better color (P < .05) than the CON and did not differ from BHT (P > .05). Guava leaf extract at 4000 ppm or greater is effective in preventing oxidation in fresh pork sausage.

Oxylipin concentrations in bovine corpora lutea during maternal recognition of pregnancy.

The objective was to determine the effects of pregnancy status on oxylipin profiles and eicosanoid metabolizing enzymes and in corpora lutea (CL) or endometrial (caruncle; CAR and intercaruncle; IC) tissues. Angus crossed cattle were synchronized with the CO-Synch protocol and artificially inseminated (AI). Sixteen days after AI, cattle were euthanized, and reproductive tracts collected from 6 non-pregnant and 6 pregnant cows. Oxylipin profiles and concentrations of progesterone (P4) were obtained from CL tissues. The activity of cytochrome P450 1A (CYP1A) and UDP-glucuronosyltransferase (UGT) enzymes were determined using specific luminogenic substrates. Data were analyzed using the MIXED procedure of SAS, and the model included pregnancy status. Corpora lutea of pregnant cattle contained greater (P < 0.05) concentrations of 9,10-DiHODE, 15,16-DiHODE, and 9,10-DiHOME. These oxylipins have been observed to increase cellular proliferation and vasodilation. Activity of CYP1A in the CL and UGT in CAR and IC was not different (P > 0.05) between pregnant and non-pregnant cattle. In the CL, activity of UGT was decreased (P < 0.05) in pregnant vs. non-pregnant cattle. The decrease in CL UGT activity during pregnancy indicates alterations in local hormone metabolism, while no differences in CL weight nor amount of P4 in CL were different between pregnant and non-pregnant cattle. Moreover, the increase in specific concentrations of oxylipins in the CL may indicate a novel pathway of steroid and eicosanoid metabolism during maternal recognition of pregnancy.

Effects of feeding endophyte-infected tall fescue seeds to stocker Angus steers on retail quality attributes of beef strip steaks.

The objective of this study was to determine the effects of feeding endophyte-infected tall fescue seeds to Angus steers during the stocker phase on the quality attributes of beef strip steaks during retail display. Endophyte-infected tall fescue seeds had no effect on steak surface lean color, myoglobin forms, proximate composition, thiobarbituric acid reactive substances, aerobic plate count, pH, activity of superoxide dismutase and metmyoglobin reductase, shear force, and sensory attributes (P ≥ 0.087). However, lightness, redness, oxymyoglobin percentage, and MRA decreased from 45.01, 32.60, 67.61%, and 9.54 µM/min/g, respectively, on d 0 to 40.11, 21.83, 48.95%, and 2.30 µM/min/g, respectively, on d 7 (P ≤ 0.001). Thiobarbituric acid reactive substances were increased by 30% by d 5 (P = 0.015) and APC was increased by 0.5 log CFU/g by d 7 (P ≤ 0.012).

Technological characteristics of pre- and post-rigor deboned beef mixtures from Holstein steers and quality attributes of cooked beef sausage.

The objective of this study was to determine the effects of deboning time (pre- and post-rigor), processing steps (grinding - GB; salting - SB; batter formulation - BB), and storage time on the quality of raw beef mixtures and vacuum-packaged cooked sausage, produced using a commercial formulation with 0.25% phosphate. The pH was greater in pre-rigor GB and SB than in post-rigor GB and SB (P < .001). However, deboning time had no effect on metmyoglobin reducing activity, cooking loss, and color of raw beef mixtures. Protein solubility of pre-rigor beef mixtures (124.26 mg/kg) was greater than that of post-rigor beef (113.93 mg/kg; P = .071). TBARS were increased in BB but decreased during vacuum storage of cooked sausage (P ≤ .018). Except for chewiness and saltiness being 52.9 N-mm and 0.3 points greater in post-rigor sausage (P = .040 and 0.054, respectively), texture profile analysis and trained panelists detected no difference in texture between pre- and post-rigor sausage.

Effect of deboning time on the growth of Salmonella, E. coli, aerobic, and lactic acid bacteria during beef sausage processing and storage.

The objective of the current study was to determine the effects of deboning time, three steps of sausage processing (grinding, salting, and batter formulation), and storage time (of raw materials and cooked sausage) on the growth (log CFU/g) of aerobic bacteria, lactic acid bacteria, and inoculated Salmonella and E. coli. Beef deboning time did not influence bacterial counts (P≥0.138). However, salting of raw ground beef resulted in a 0.4-log reduction in both aerobic plate count (APC) and Salmonella (P≤0.001). Lactic acid bacteria were increased from non-detectable concentration (0.54 log) on d 0 to 3.8 log on d 120 of vacuum storage (P≤0.019). Salmonella counts were increased (P<0.001) over storage time (3.2 to 3.3 log CFU/g from d 0 to 10). Results indicated that salting and batter formulation had a greater impact on bacterial counts than rigor state of raw beef.

Mercaptoacetate blocks fatty acid-induced GLP-1 secretion in male rats by directly antagonizing GPR40 fatty acid receptors.

Mercaptoacetate (MA) is an orexigenic agent reported to block fatty acid (FA) oxidation. Recently, however, we reported evidence from isolated nodose ganglion neurons that MA antagonizes the G protein-coupled long- and medium-chain FA receptor GPR40. GPR40 mediates FA-induced secretion of the satietogenic incretin peptide glucagon-like peptide 1 (GLP-1), by enteroendocrine L cells, as well as FA-induced enhancement of glucose-stimulated insulin secretion. Our results in cultured nodose neurons suggest that MA would also block GPR40 in enteroendocrine cells controlling GLP-1 secretion. If so, this would suggest an alternative mechanism by which MA increases food intake. We tested the hypothesis that MA blocks FA-induced GLP-1 secretion in vitro using cultured STC-1 cells (a murine enteroendocrine cell line) and in vivo in adult male rats. In vitro, MA blocked the increase in both cytosolic Ca(2+)and GLP-1 release stimulated by FAs and also reduced (but less effectively) the response of STC-1 cells to grifolic acid, a partial agonist of the GPR120 FA receptor. In vivo, MA reduced GLP-1 secretion following olive oil gavage while also increasing glucose and decreasing insulin levels. The carnitine palmatoyltransferase 1 antagonist etomoxir did not alter these responses. Results indicate that MA's actions, including its orexigenic effect, are mediated by GPR40 (and possibly GPR120) receptor antagonism and not by blockade of fat oxidation, as previously believed. Analysis of MA's interaction with GPR40 may facilitate understanding of the multiple functions of this receptor and the manner in which FAs participate in the control of hunger and satiety.

Stimulation of feeding by three different glucose-sensing mechanisms requires hindbrain catecholamine neurons.

Previous work has shown that hindbrain catecholamine neurons are required components of the brain's glucoregulatory circuitry. However, the mechanisms and circuitry underlying their glucoregulatory functions are poorly understood. Here we examined three drugs, glucosamine (GcA), phloridzin (Phl) and 5-thio-d-glucose (5TG), that stimulate food intake but interfere in different ways with cellular glucose utilization or transport. We examined feeding and blood glucose responses to each drug in male rats previously injected into the hypothalamic paraventricular nucleus with anti-dopamine-ß-hydroxylase conjugated to saporin (DSAP), a retrogradely transported immunotoxin that selectively lesions noradrenergic and adrenergic neurons, or with unconjugated saporin (SAP) control. Our major findings were 1) that GcA, Phl, and 5TG all stimulated feeding in SAP controls whether injected into the lateral or fourth ventricle (LV or 4V), 2) that each drug's potency was similar for both LV and 4V injections, 3) that neither LV or 4V injection of these drugs evoked feeding in DSAP-lesioned rats, and 4) that only 5TG, which blocks glycolysis, stimulated a blood glucose response. The antagonist of the MEK/ERK signaling cascade, U0126, attenuated GcA-induced feeding, but not Phl- or 5TG-induced feeding. Thus GcA, Phl, and 5TG, although differing in mechanism and possibly activating different neural populations, stimulate feeding in a catecholamine-dependent manner. Although results do not exclude the possibility that catecholamine neurons possess glucose-sensing mechanisms responsive to all of these agents, currently available evidence favors the possibility that the feeding effects result from convergent neural circuits in which catecholamine neurons are a required component.

Hindbrain catecholamine neurons control rapid switching of metabolic substrate use during glucoprivation in male rats.

Using the retrogradely transported immunotoxin, antidopamine ß-hydroxylase-saporin (DSAP), we showed previously that hindbrain catecholamine neurons innervating corticotropin-releasing hormone neurons in the paraventricular nucleus of the hypothalamus are required for glucoprivation-induced corticosterone secretion. Here, we examine the metabolic consequences of the DSAP lesion in male rats using indirect calorimetry. Rats injected into the paraventricular nucleus of the hypothalamus with DSAP or saporin (SAP) control did not differ in energy expenditure or locomotor activity under any test condition. However, DSAP rats had a persistently higher respiratory exchange ratio (RER) than SAPs under basal conditions. Systemic 2-deoxy-D-glucose did not alter RER in DSAP rats but rapidly decreased RER in SAP controls, indicating that this DSAP lesion impairs the ability to switch rapidly from carbohydrate to fat metabolism in response to glucoprivic challenge. In SAP controls, 2-deoxy-D-glucose-induced decrease in RER was abolished by adrenalectomy but not adrenal denervation. Furthermore, dexamethasone, a synthetic glucocorticoid, decreased RER in both SAP and DSAP rats. Thus, rapid switching of metabolic substrate use during glucoprivation appears to be due to impairment of the catecholamine-mediated increase in corticosterone secretion. Sustained elevation of basal RER in DSAP rats indicates that catecholamine neurons also influence metabolic functions that conserve glucose under basal conditions.

Leptin-sensitive neurons in the arcuate nucleus integrate activity and temperature circadian rhythms and anticipatory responses to food restriction.

Previously, we investigated the role of neuropeptide Y and leptin-sensitive networks in the mediobasal hypothalamus in sleep and feeding and found profound homeostatic and circadian deficits with an intact suprachiasmatic nucleus. We propose that the arcuate nuclei (Arc) are required for the integration of homeostatic circadian systems, including temperature and activity. We tested this hypothesis using saporin toxin conjugated to leptin (Lep-SAP) injected into Arc in rats. Lep-SAP rats became obese and hyperphagic and progressed through a dynamic phase to a static phase of growth. Circadian rhythms were examined over 49 days during the static phase. Rats were maintained on a 12:12-h light-dark (LD) schedule for 13 days and, thereafter, maintained in continuous dark (DD). After the first 13 days of DD, food was restricted to 4 h/day for 10 days. We found that the activity of Lep-SAP rats was arrhythmic in DD, but that food anticipatory activity was, nevertheless, entrainable to the restricted feeding schedule, and the entrained rhythm persisted during the subsequent 3-day fast in DD. Thus, for activity, the circuitry for the light-entrainable oscillator, but not for the food-entrainable oscillator, was disabled by the Arc lesion. In contrast, temperature remained rhythmic in DD in the Lep-SAP rats and did not entrain to restricted feeding. We conclude that the leptin-sensitive network that includes the Arc is required for entrainment of activity by photic cues and entrainment of temperature by food, but is not required for entrainment of activity by food or temperature by photic cues.