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The normal microbiota plays a key role in the health of host, but little is known of how the fish immune system recognizes and responds to indigenous bacteria/probiotics. Our previous studies have showed that heat-inactivated indigenous Bacillus pumilus SE5 activate the TLR2 signaling pathways and modulate the intestinal microbiota in grouper (Epinephelus coioides), suggesting microbial-associated molecular patterns (MAMPs) involved. In this study, whole cell wall (CW) and two possible MAMPs, peptidoglycan (PG) and lipoteichoic acid (LTA) have been extracted from B. pumilus SE5 and their effects on intestinal immune related genes expression and microbiota were evaluated in a 60 days feeding trial. Significantly elevated expression of TLR1, TLR2, TLR5 and MyD88 was observed in fish fed the CW, PG and LTA containing diets, and the highest expression was observed in groups PG and LTA. At the same time, significantly upregulated expression of antimicrobial effectors, such as antimicrobial peptides (epinecidin-1, hepcidin-1 and β-defensin), C-type Lectin and IgM was observed in fish fed PG and LTA containing diets. This induced activation of intestinal immunity was consistent with the microbiota data showing that CW, PG and LTA originated from SE5 modulated the overall structure of intestinal microbiota, and the relative abundance of potentially pathogenic Vibrio decreased significantly while beneficial Lactobacillus increased significantly in fish fed PG and LTA. In conclusion, both the PG and LTA originated from B. pumilus SE5 could activate TLRs/MyD88 signaling and expression of wide-ranging antibacterial effectors, and therefore shape the intestinal microbiota in grouper., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

p38 mitogen-activated protein kinase (MAPK) is an important protein which plays a key role in regulating the innate immunity, so exploring its molecular characterization is helpful in understanding the resistance against microbial infections in cultured fish. Here, a full-length cDNA of p38 MAPK was cloned from liver of blunt snout bream (Megalobrama amblycephala) which covered 2419 bp with an open reading frame of 1086 bp encoding 361 amino acids. p38 MAPK contained the characteristic structures of Thr-Gly-Tyr (TGY) motif and substrate binding site Ala-Thr-Arg-Trp (ATRW), which are conserved in MAPK family. To investigate p38 MAPK functions, two in vivo experiments were carried out to examine its expression following ammonia exposure and bacterial challenge. Also, an in vitro experiment was conducted to assess the role of p38 MAPK in inflammation of primary hepatocytes induced by lipopolysaccharide (LPS). The results showed the ubiquitous expression of p38 MAPK in all the tested tissues with varying levels. p38 MAPK mRNA expression was significantly up-regulated by ammonia stress and Aeromonas hydrophila challenge, and altered in a time-dependent manner. Moreover, the results indicated that the inflammatory response induced by LPS in hepatocytes is p38 MAPK dependent as knockdown of p38 MAPK using siRNA technology depressed the expression of IL-1β and IL-6. The findings in this study showed that p38 MAPK has anti-stress property, and plays key role in protection against bacterial infection and inflammation in blunt snout bream., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This study was conducted to investigate the effects of fructooligosaccharide (FOS) and Bacillus licheniformis (B. licheniformis) and their interaction on innate immunity, antioxidant capability and disease resistance of triangular bream Megalobrama terminalis (average initial weight 30.5 ± 0.5 g). Nine experimental diets were formulated to contain three FOS levels (0, 0.3% and 0.6%) and three B. licheniformis levels (0, 1 × 10(7), 5 × 10(7) CFU g(-1)) according to a 3 × 3 factorial design. At the end of the 8-week feeding trial, fish were challenged by Aeromonas hydrophila (A. hydrophila) and survival rate was recorded for the next 7 days. The results showed that leucocyte counts, alternative complement activity as well as total serum protein and globulin contents all increased significantly (P < 0.05) as dietary B. licheniformis levels increased from 0 to 1 × 10(7) CFU g(-1), while little difference (P > 0.05) was observed in these parameters in terms of dietary FOS levels. Both plasma alkaline phosphatase and phenoloxidase activities were significantly (P < 0.05) affected only by dietary FOS levels with the highest values observed in fish fed 0.6 and 0.3% FOS, respectively. Both immunoglobulin M content and liver superoxide dismutase (SOD) activity were significantly affected (P > 0.05) by both FOS and B. licheniformis. Liver catalase, glutathione peroxidase as well as plasma SOD activities of fish fed 1 × 10(7) CFU g(-1)B. licheniformis were all significantly (P < 0.05) higher than that of the other groups, whereas the opposite was true for malondialdehyde content. After A. hydrophila challenge, survival rate was not affected (P > 0.05) by either FOS levels or B. licheniformis contents, whereas a significant (P < 0.05) interaction between these two substances was observed with the highest value observed in fish fed 0.3% FOS and 1 × 10(7) CFU g(-1)B. licheniformis. The results of this study indicated that dietary FOS and B. licheniformis could significantly enhance the innate immunity and antioxidant capability of triangular bream, as well as improve its disease resistance. The best combination of these two prebiotics and/or probiotics was 0.3% FOS and 1 × 10(7) CFU g(-1)B. licheniformis., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This study aimed to evaluate the effects of dietary carbohydrate/lipid (CHO:L) ratios on stress, liver oxidative status and non-specific immune responses of fingerling blunt snout bream. Fish were fed six isonitrogenous and isoenergetic diets containing various CHO:L ratios for 10 weeks. After the feeding trial, fish were challenged by Aeromonas hydrophila and survival rate was recorded for the next 10 days. The lowest plasma cortisol, lactate, aspartate aminotransferase and alanine aminotransferase were all observed in fish fed a CHO:L ratio of 5.64. They were significantly (P < 0.05) lower than those of fish offered the lowest CHO:L ratio, but showed little difference (P > 0.05) with those of fish fed the highest CHO:L ratio. This also held true for liver catalase and glutathione peroxidase activities, whereas the opposite was true for liver reduced glutathione contents, plasma lysozyme and alternative complement (ACH50) activities. Contrary to leucocyte counts, plasma glucose levels, liver malondialdehyde contents, blood haemoglobin contents and erythrocyte numbers all increased significantly (P < 0.05) with decreasing dietary CHO:L ratios. The highest plasma total protein and globulin content both observed in fish fed a CHO:L ratio of 2.45 was significantly (P < 0.01) higher than that of fish offered the lowest CHO:L ratio, but showed no statistical difference (P > 0.05) with that of the other groups. After challenge, fish fed the lowest CHO:L ratio obtained significantly (P < 0.05) low survival rate. However, survival rate showed little difference (P > 0.05) as dietary CHO:L ratios ranged from 3.67 to 24.20. The results of this study indicated that high dietary lipid may cause metabolic stress of fingerling blunt snout bream, as might consequently lead to the elevated liver oxidation rates, impaired liver function, depressed immunity and reduced resistance to A. hydrophila infection of this species, whereas the opposite was true for carbohydrate enriched diets., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Effects of rolipram, a selective inhibitor of phosphodiesterases (PDE) IV, on induction of action potential bursts were studied pharmacologically on the RP4 central neuron of the giant African snail (Achatina fulica Ferussac). Oscillations of membrane potential bursts were elicited by rolipram and forskolin. The bursts of potential elicited by rolipram were not inhibited after administration with (a) calcium-free solution, (b) high-magnesium solution (30 mM) or (c) U73122. However, the bursts of potential elicited by rolipram were inhibited by pretreatment with KT-5720 (10 microM). Voltage-clamp studies revealed that rolipram decreased the total inward current and steady-state outward currents of the RP4 neuron. The negative slope resistance (NSR) was not detectable in control or rolipram treated RP4 neurons. TEA elicited action potential bursts and an NSR at membrane potential between -50 mV and -30 mV. It is suggested that the bursts of potential elicited by rolipram were not due to (1) synaptic effects of neurotransmitters; (2) NSR of steady-state I-V curve; (3) phospholipase activity of the neuron. The rolipram-elicited bursts of potential were dependent on the phosphodiesterases inhibitory activity and the cAMP signaling pathway in the neuron.