Physiological responses to central and peripheral injection of polyinosinic-polycytidylic acid in chicks

Zymosan and lipopolysaccharide decrease gene expression of neuronal nitric oxide synthase in peripheral organs in chicks

Nitric oxide (NO) is gaseous bioactive molecule that is synthesized by NO synthase (NOS). Inducible NOS (iNOS) expression occurs in response to pathogenic challenges, resulting in the production of large amounts of NO. However, there is a lack of knowledge regarding neuronal NOS (nNOS) and endothelial NOS (eNOS) in birds during pathogenic challenge. Therefore, the present study was conducted to determine the influence of intraperitoneal (IP) injection of zymosan (cell wall component of yeast) and lipopolysaccharide (LPS, a cell wall component of gram-negative bacteria) on NOS expression in chicks (Gallus gallus). Furthermore, the effect of NOS inhibitors on the corresponding behavioral and physiological parameters was investigated. Zymosan and LPS injections induced iNOS mRNA expression in several organs. Zymosan had no effect on eNOS mRNA expression in the organs investigated, whereas LPS increased its expression in the pancreas. Zymosan and LPS decreased nNOS mRNA expression in the lung, heart, kidney, and pancreas. The decreased nNOS mRNA expression in pancreas was probably associated with the NO from iNOS provided that such effect was reproduced by IP injection of sodium nitroprusside, which is a NO donor. Furthermore, pancreatic nNOS mRNA expression decreased following subcutaneous injection of corticosterone. Furthermore, IP injections of a nonspecific NOS inhibitor, NG-nitro-L-arginine methyl ester, and an nNOS-specific inhibitor, 7-nitroindazole, resulted in the significant decreases in food intake, cloacal temperature, and feed passage via the digestive tract in chicks. Collectively, the current findings imply the decreased nNOS expression because of fungal and bacterial infections, which affects food intake, body temperature, and the digestive function in birds.

Possible role of corticosterone on behavioral, physiological, and immune responses in chicks

Glucocorticoids are one of steroid hormone and have a variety of functions including stress response, carbohydrate metabolism, and modulation of immune system in vertebrates. Corticosterone is the main glucocorticoid in birds, although the precise role of the glucocorticoid during immune challenge is not fully understood. Therefore, the purpose of the present study was to determine if a single subcutaneous injection of corticosterone could affect inflammation-related gene expressions in the spleen and liver of chicks (Gallus gallus). In addition, the effects of corticosterone injection on the food intake, cloacal temperature, formation of conditioned visual aversion, and plasma constituents were also measured. Corticosterone did not affect the food intake or cloacal temperature and did not cause conditioned visual aversion in chicks. The corticosterone injection was associated with a significant decrease in gene expression of several pro-inflammatory cytokines including inducible nitric oxide synthase and cyclooxygenase-2 in the spleen and liver at 1 and 3 h post-injection. Corticosterone increased the plasma glucose and uric acid concentrations and the antioxidant capacity. In summary, the present study suggests that corticosterone is likely not associated with food intake, cloacal temperature or the development of aversive sensation, but suppresses the synthesis of inflammation-associated bioactive molecules and increases the antioxidant capacity in chicks.

Biomolecules Triggering Altered Food Intake during Pathogenic Challenge in Chicks

Food intake is regulated by several complicated synergistic mechanisms that are affected by a variety of internal and external influences. Some of these factors include those that are released from pathogens such as bacteria, fungi, and viruses, and most of these factors are associated with suppression of the chick's food intake. Although chicks are well-known to decrease their food intake when they experience a pathogenic challenge, the mechanisms that mediate this type of satiety are poorly understood. One of the goals of our research group has been to better understand these mechanisms in chicks. We recently provided evidence that pathogen-associated molecular patterns, which are recognized by pattern-recognition receptors such as Toll-like receptors, likely contribute to satiety in chicks that are experiencing a pathogenic challenge. Additionally, we identified several inflammatory cytokines, including interleukin-1β, tumor necrosis factor-like cytokine 1A, prostaglandins, and nitric oxide, that likely contribute to satiety during a pathogenic challenge. This review summarizes the current knowledge on pathogen-induced satiety in chicks mainly accumulated through our recent research. The research will give good information to improve the loss of production during infection in poultry production in the future.

Effect of sodium nitroprusside on feeding behavior, voluntary activity, and cloacal temperature in chicks

Nitric oxide (NO) is a well-known gaseous signaling molecule that is involved in a variety of physiological and pathological processes in vertebrates. The role of NO in physiological responses of birds has been investigated primarily using NOS inhibitors. Therefore, the effect of the absence of NO is well characterized. However, there is little knowledge on the effects of abundant NO in birds, which is the case in birds that have infections. Therefore, the purpose of the present study was to determine if intraperitoneal (IP) and intracerebroventricular (ICV) injections of sodium nitroprusside (SNP), a NO donor, affected feed intake, voluntary activity, cloacal temperature, crop emptying rate, and blood constituents in domesticated chicks (Gallus gallus) as model birds. We found that both IP and ICV injections of SNP significantly decreased feed intake while there was little effect on voluntary activity. Cloacal temperature was temporarily, but significantly, decreased by both types of injection of SNP. Additionally, both IP and ICV injections of SNP significantly decreased the crop emptying rate. The IP injection of SNP significantly increased the plasma concentrations of NO₂/NO₃, which are metabolites of NO, and corticosterone, and decreased the plasma glucose concentrations, while the ICV injection had no effect. The IP injection of SNP also showed the tendency to increase the nitrotyrosine level, to increase superoxide dismutase activity, and to decrease catalase activity in the plasma. These results suggest that under specific situations which produce abundant NO such as infection, NO would induce anorexia, hypothermia, inhibition of feed passage, and activation of the hypothalamus-pituitary-adrenal axis in chicks.

Poly I:C and R848 facilitate nitric oxide production via inducible nitric oxide synthase in chicks

Nitric oxide (NO) is a gaseous bioactive molecule associated with many physiological functions including vasodilation and neurotransmission. NO also plays an important role in immune responses during viral infections in mammals. However, there is a paucity of knowledge regarding the involvement of NO in viral infections in birds. Therefore, the purpose of the present study was to determine if intraperitoneal (IP) injection of poly I:C and R848 (resiquimod), which are analogues of virus component, affects NO production in chicks (Gallus gallus) as a bird model. The involvement of inducible NO synthase (iNOS) in poly I:C- and R848-induced anorexia and corticosterone release was also investigated. These virus analogues significantly increased plasma NO metabolites (NOx) concentrations. IP injection of poly I:C and R848 significantly increased iNOS mRNA expression in several organs including the liver. On the other hand, poly I:C and R848 significantly decreased mRNA expressions of endothelial NOS and neural NOS in several organs, indicating that induction of iNOS might be responsible for increased NOx levels in plasma. This finding was further confirmed by using a selective iNOS inhibitor, S-methylisothiourea sulfate (SMT), which abolished the poly I:C- and R848-induced increase in plasma NOx concentration. In addition, SMT partly attenuated the poly I:C- and R848-induced increase in plasma corticosterone concentration, suggesting that corticosterone release induced by these virus analogues may be partly mediated by iNOS. Collectively, the present results suggest that viral infections facilitate NO production by inducing iNOS. The liver would play an important role in the NO production because the response in iNOS mRNA expression to poly I:C and R848 was remarkable. The present results also suggest that NO is associated with corticosterone release in birds under viral infection.

Role of nitric oxide on zymosan-induced inhibition of crop emptying in chicks

Zymosan, a component of yeast cell walls, reduces feed passage through the digestive tract in chicks (Gallus gallus), although the mechanism mediating this effect is poorly understood. Nitric oxide (NO) is associated with a variety of biological actions including effects on the immune system. In addition, it has been suggested that NO is involved in relaxation of the digestive tract and affects feed passage in mammals. It is therefore possible that NO might be related to zymosan-induced reduction of feed passage in chicks. However, the role of NO on the effect of zymosan feed passage has not been clarified yet. Thus, the purpose of the present study was to investigate whether NO is associated with zymosan-induced alteration of feed passage in chicks. Intraperitoneal (IP) injection of zymosan significantly increased plasma nitrate and nitrite (NOx) concentrations at 6 h after injection. Zymosan-induced elevation of plasma NOx concentration was abolished by co-injection of S-methylisothiourea (SMT), a selective inhibitor for inducible NO synthase (iNOS), indicating that zymosan facilitated the induction of iNOS. Furthermore, because zymosan increased iNOS mRNA expression in the digestive tract, NO is likely associated with the effect of zymosan on the digestive tract. IP injection of NO donors significantly decreased crop emptying rate, suggesting that NO functions as an inhibitor of crop emptying. This result implied that zymosan stimulates NO production by the induction of iNOS in the digestive tract and thereby inhibits crop emptying rate. However, the co-injection of SMT did not attenuate the inhibitory effect of zymosan on crop emptying. The present study provides evidence that some changes in the digestive tract caused by zymosan are mediated by iNOS-induced NO in chicks, but NO does not mediate the effect of zymosan on feed passage through the crop.

Behavioral and physiological responses to peripheral injection of flagellin in chicks

Flagellin (Flg) is a globular protein, found in bacterial flagella, that serves as a pathogen-associated molecular pattern and also serves as a toll-like receptor-5 (TLR5) ligand in vertebrates. Most ligands for TLRs are involved in non-specific effects such as anorexia and hypoactivity in an animal infected by bacteria. However, there is little knowledge on the effects of Flg in birds. Therefore, the purpose of the present study was to determine if intraperitoneal (IP) injection of Flg affects food intake, voluntary activity, cloacal temperature, crop emptying rate, blood constituents, and splenic gene expression of cytokines in chicks (Gallus gallus). The effect of Flg22, an N-terminus fragment of Flg, was also investigated. IP injection of 10 µg Flg significantly increased the splenic gene expression of interleukin-8, interferon-γ (IFN-γ), and tumor necrosis factor-like cytokine-1A, suggesting that Flg activated the innate immune system in chicks. The injection of Flg significantly decreased food intake, voluntary activity, blood glucose concentration, and crop emptying rate, and increased cloacal temperature and plasma concentrations of nitrite, nitrate, and corticosterone. However, the injection of Flg22 only affected the splenic gene expression of IFN-γ, indicating that the full-length of Flg is required for its action. These results suggest that Flg, a ligand for TLR5, is related to non-specific symptoms including anorexia, hypoactivity, increase in body temperature, disturbance of food passage in the digestive tract, and the activation of hypothalamic-pituitary-adrenal axis during bacterial infection in chicks.

Behavioral and physiological responses to intraperitoneal injection of zymosan in chicks

Zymosan is a cell wall component of the yeast Saccharomyces cerevisiae and produces severe inflammatory responses in mammals. When zymosan is peripherally injected in mammals, it induces several behavioral and physiological changes including anorexia and hyperthermia. However, to our knowledge, behavioral and physiological responses to zymosan have not yet been clarified in birds. Therefore, the purpose of the present study was to determine if intraperitoneal injection of zymosan affects food intake, voluntary activity, cloacal temperature, plasma corticosterone (CORT) and glucose concentrations, and splenic gene expression of cytokines in chicks (Gallus gallus). Intraperitoneal injection of zymosan (2.5 mg) significantly decreased food intake, voluntary activity, and plasma glucose concentration, and increased plasma CORT concentration. The injection of 0.5 mg zymosan significantly increased cloacal temperature, while 2.5 mg zymosan had a tendency to increase it. Finally, 2.5 mg zymosan significantly increased the splenic gene expression of interleukin-1β (IL-1β), IL-6, IL-8, interferon-γ, and tumor necrosis factor-like cytokine 1A. The present results suggest that zymosan would be one of components which induces nonspecific symptoms including anorexia, hypoactivity, hyperthermia, and stress responses, under fungus infection in chicks.

Effects of toll-like receptor-7 agonists on feeding behaviour, voluntary activity, cloacal temperature and crop emptying in chicks

1. The purpose of the present study was to determine if an intraperitoneal injection of two toll-like receptor-7 (TLR7) agonists, imiquimod and resiquimod, affect feed intake, voluntary activity, cloacal temperature, crop-emptying rate, plasma corticosterone (CORT) and glucose concentrations, and splenic gene expression of cytokines in chicks (Gallus gallus). 2. Although intraperitoneal injection of 100 µg imiquimod significantly increased splenic gene expression of interleukin-1β (IL-1β), IL-6, IL-8, and interferon-γ (IFN-γ), it did not affect feed intake, voluntary activity, cloacal temperature, crop-emptying rate or plasma constituents. 3. Intraperitoneal injection of 100 µg resiquimod significantly decreased feed intake, voluntary activity, cloacal temperature, crop-emptying rate and increased plasma corticosterone concentrations. 4. Intraperitoneal injection of resiquimod significantly increased splenic gene expression of IL-1β, IL-6, IL-8, IFN-γ, and tumour necrosis factor-like cytokine 1A. 5. The results showed that activation of TLR7 is associated with anorexia, hypoactivity, hypothermia, disturbance of feed passage in the digestive tract and the response to stress in chicks.

Physiological responses to central and peripheral injections of compound 48/80 and histamine in chicks

Mast cells are a type of immune cell widely distributed in the body of vertebrates. Mast cells have many granules that contain several bioactive molecules such as histamine, and these molecules are released through degranulation when the mast cell receives certain stimuli. Because the number of mast cells increases during infection in chickens (Gallus gallus), the activity of mast cells might be related to non-specific symptoms such as anorexia under an infectious condition. Therefore, the purpose of the present study was to investigate whether intraperitoneal (IP) and intracerebroventricular (ICV) injections of compound 48/80, which induces degranulation of mast cells, affects feeding, voluntary activity, cloacal temperature, and the concentrations of plasma corticosterone (CORT) and glucose in chicks. The effect of histamine, which is found in mast cell granules, on these parameters was also investigated. IP injection of compound 48/80 significantly decreased food intake, voluntary activity, and cloacal temperature, and increased plasma CORT concentration in the chicks. While ICV injection of compound 48/80 also decreased food intake, it increased cloacal temperature and plasma glucose concentration. Both IP and ICV injections of histamine significantly decreased food intake, cloacal temperature, and plasma CORT concentration. However, only IP injection of histamine significantly decreased voluntary activity and increased plasma glucose concentration. The results suggest that degranulation of mast cells is related to non-specific symptoms in chicks, although the mechanism seems to be different between peripheral and central tissues. In addition, the effect of peripherally-injected compound 48/80 may be partly mediated by histamine.