TY - BOOK

T1 - Central mechanisms underlying variability in the behavioral and neuroendocrine responses to stress in fish

AU - Moltesen, Maria Møller

PY - 2017

Y1 - 2017

N2 - Comparative models have revealed fundamental principles of nervous system functionand organization. Teleost model systems have contributed essentially to ourunderstanding of the evolution of the mechanisms involved in the behavioral andneuroendocrine stress response.The purpose of the stress response is to protect or re-establish homeostasis inresponse to a perceived threat. A suite of neuroendocrine events aiming at enhancingan individual’s survival characterizes it. By filtering relevant sensory inputs andinitiating stress responses, the brain is an essential organ in the regulation of the stressresponse. In mammals, the hippocampus and amygdala in the telencephalon playcentral roles in the process of discriminating sensory inputs that, potentially, willthreaten the homeostasis of an individual. These regions are part of the limbic system,which interacts with the hypothalamic-pituitary-adrenal axis (HPA axis). Thisneuroendocrine stress axis includes corticotropin-releasing factor (CRF), whichregulates the release of adrenocorticotropic hormone (ACTH) from the pituitary. Apeptide is released to the circulation, inducing release of glucocorticoids from theadrenal cortex. The neurotransmitter serotonin (5-hydroxytryptamine; 5-HT) also playsan important role in the neuroendocrine stress response by controlling CRF release inhypothalamus. The transmission of 5-HT and CRF are under feedback control ofglucocorticoids and interact with the stress response by affecting processes in thelimbic system. In fish, the telencephalon contains regions that are functionalhomologues to the mammalian limbic system including amygdala and hippocampus.However, the involvement of this brain region in the regulation of the hypothalamicpituitary-interrenal (HPI) axis, the homologue of the mammalian HPA axis, is still notfully understood.This PhD thesis investigates the role of the teleost telencephalon in regulationof the behavioral and neuroendocrine stress responses. Three studies were conducted:Study I investigated the effect of acute and chronic stress on plasma cortisol,the major glucocorticoid in fish, and if these effects were related to changes inneurochemistry and gene expression in the telencephalon of rainbow trout(Oncorhynchus mykiss). The results showed that chronic stress affected HPI axisreactivity and serotonergic neurochemistry in the telencephalon. Moreover, effects ofacute stress on post stress mRNA levels of the cortisol receptor; the mineralocorticoidreceptor (MR) and the 5-HT receptor (5-HT1A) suggested that these receptors areinvolved in feedback mechanisms of the HPI axis.Study II investigated if contrasting stress coping styles was reflected intelencephalic neurochemistry and gene expression in juvenile Gilthead seabream(Sparus aurata). The results showed that contrasting stress coping styles werereflected in differences in telencephalic serotonergic neurochemistry, independently ofHPI axis reactivity.Study III investigated if different behavioral responses to hypoxia in rainbowtrout strains with contrasting stress coping styles were linked to differences inactivation patterns in telencephalon and cognition. Neuronal activity in response tohypoxia stress, quantified by expression of the immediate early gene c-fos, revealedthe engagement of distinct brain regions with limbic functions in the telencephalon.Moreover, differences in a conditioned-place-avoidance (CPA) test together with strainspecific activation in Dm, an amygdaloid region, suggest that the telencephalon isinvolved in cognitive process underlying contrasting stress coping styles.It is concluded that both individuality in the behavioral stress response andeffects of chronic stress are reflected in 5-HT-ergic turnover in the telencephalon.Moreover, different activation patterns in the telencephalon during hypoxia in fishwith contrasting stress coping styles further supports this brain region’s involvement inregulation of the behavioral and neuroendocrine stress responses. This is furthersupported by changes in post stress mRNA levels of MR and 5-HT1A, suggesting thattelencephalon is involved in feedback regulation of the HPI axis.

AB - Comparative models have revealed fundamental principles of nervous system functionand organization. Teleost model systems have contributed essentially to ourunderstanding of the evolution of the mechanisms involved in the behavioral andneuroendocrine stress response.The purpose of the stress response is to protect or re-establish homeostasis inresponse to a perceived threat. A suite of neuroendocrine events aiming at enhancingan individual’s survival characterizes it. By filtering relevant sensory inputs andinitiating stress responses, the brain is an essential organ in the regulation of the stressresponse. In mammals, the hippocampus and amygdala in the telencephalon playcentral roles in the process of discriminating sensory inputs that, potentially, willthreaten the homeostasis of an individual. These regions are part of the limbic system,which interacts with the hypothalamic-pituitary-adrenal axis (HPA axis). Thisneuroendocrine stress axis includes corticotropin-releasing factor (CRF), whichregulates the release of adrenocorticotropic hormone (ACTH) from the pituitary. Apeptide is released to the circulation, inducing release of glucocorticoids from theadrenal cortex. The neurotransmitter serotonin (5-hydroxytryptamine; 5-HT) also playsan important role in the neuroendocrine stress response by controlling CRF release inhypothalamus. The transmission of 5-HT and CRF are under feedback control ofglucocorticoids and interact with the stress response by affecting processes in thelimbic system. In fish, the telencephalon contains regions that are functionalhomologues to the mammalian limbic system including amygdala and hippocampus.However, the involvement of this brain region in the regulation of the hypothalamicpituitary-interrenal (HPI) axis, the homologue of the mammalian HPA axis, is still notfully understood.This PhD thesis investigates the role of the teleost telencephalon in regulationof the behavioral and neuroendocrine stress responses. Three studies were conducted:Study I investigated the effect of acute and chronic stress on plasma cortisol,the major glucocorticoid in fish, and if these effects were related to changes inneurochemistry and gene expression in the telencephalon of rainbow trout(Oncorhynchus mykiss). The results showed that chronic stress affected HPI axisreactivity and serotonergic neurochemistry in the telencephalon. Moreover, effects ofacute stress on post stress mRNA levels of the cortisol receptor; the mineralocorticoidreceptor (MR) and the 5-HT receptor (5-HT1A) suggested that these receptors areinvolved in feedback mechanisms of the HPI axis.Study II investigated if contrasting stress coping styles was reflected intelencephalic neurochemistry and gene expression in juvenile Gilthead seabream(Sparus aurata). The results showed that contrasting stress coping styles werereflected in differences in telencephalic serotonergic neurochemistry, independently ofHPI axis reactivity.Study III investigated if different behavioral responses to hypoxia in rainbowtrout strains with contrasting stress coping styles were linked to differences inactivation patterns in telencephalon and cognition. Neuronal activity in response tohypoxia stress, quantified by expression of the immediate early gene c-fos, revealedthe engagement of distinct brain regions with limbic functions in the telencephalon.Moreover, differences in a conditioned-place-avoidance (CPA) test together with strainspecific activation in Dm, an amygdaloid region, suggest that the telencephalon isinvolved in cognitive process underlying contrasting stress coping styles.It is concluded that both individuality in the behavioral stress response andeffects of chronic stress are reflected in 5-HT-ergic turnover in the telencephalon.Moreover, different activation patterns in the telencephalon during hypoxia in fishwith contrasting stress coping styles further supports this brain region’s involvement inregulation of the behavioral and neuroendocrine stress responses. This is furthersupported by changes in post stress mRNA levels of MR and 5-HT1A, suggesting thattelencephalon is involved in feedback regulation of the HPI axis.

UR - https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122565229805763

M3 - Ph.D. thesis

BT - Central mechanisms underlying variability in the behavioral and neuroendocrine responses to stress in fish

PB - Department of Biology, Faculty of Science, University of Copenhagen

ER -