Influence of chronic stress on the mechanism of the cytotoxic system in common carp (Cyprinus carpio).

Mazal Shimon‐Hophy,Ramy R Avtalion

doi:10.1111/imm.13345

Abstract

Aquaculture conditions expose fish to internal and environmental stressors that increase their susceptibility to morbidity and mortality. The brain accumulates stress signals and processes them according to the intensity, frequency duration and type of stress, recruiting several brain functions to activate the autonomic or limbic system. Triggering the autonomic system causes the rapid release of catecholamines, such as adrenaline and noradrenaline, into circulation from chromaffin cells in the head kidney. Catecholamines trigger blood cells to release proinflammatory and regulatory cytokines to cope with acute stress. Activation of the limbic axis stimulates the dorsolateral and dorsomedial pallium to process emotions, memory, behaviour and the activation of preoptic nucleus‐pituitary gland‐interrenal cells in the head kidney, releasing glucocorticoids, such as cortisol to the bloodstream. Glucocorticoids cause downregulation of various immune system functions depending on the duration, intensity and type of chronic stress. As stress persists, most immune functions, with the exception of cytotoxic functions, overcome these effects and return to homeostasis. The deterioration of cytotoxic functions during chronic stress appears to be responsible for increased morbidity and mortality.

Highlights

Aquaculture conditions are often exposed to various stressors
The results of monitoring the influence of chronic hypoxic stress on immune activity in the common carp peripheral blood leucocytes are shown in Table 1, and these results reveal a downregulation of regulatory (IL-10, TGFb, forkhead box P3 (FoxP3)), proinflammatory (IL-1 β, IL-6 ), and inflammatory (IL-17) functions until the second week of chronic stress
Stress-influenced functions revealed the deterioration of cytotoxic activity and cytokines regulating T helper 1 cell (Th1) proliferation (Table 1), but what about the other leucocytes? Studies of leucocyte levels by fluorescence-activated cell sorting (FACS) and by mRNA levels of cell markers revealed a decrease in the levels of like-B, like-plasma, macrophages and CD4 (Th1) cells (Table 2 and Figure 2) [100]

Summary

Introduction

Aquaculture conditions are often exposed to various stressors. Stressors can be a consequence of elevated rearing densities [1], suboptimal water quality, decreased dissolved oxygen and elevated carbon dioxide (CO2) levels [2,3], thermal fluctuations [4,5], diet [6], presence of enemies and pathogens [7–11], and transportation, sorting, handling and confinement stresses [6,12–14].Stressors were reported to reduce hippocampal (dorsolateral pallium in teleost) volume [15–17] and, as a result, to impact memory and learning [18–20]. Similar to the process with mammals, 5-hydroxytryptamine (5-H T) in teleosts influences hypothalamic CRF release, where the 5-H T receptor type 1A plays a central role in the regulation of the HPI axis [73–76].

Results

Conclusion