Brain and Pituitary Response to Vaccination in Gilthead Seabream (Sparus aurata L.).

X H Liu,F E Reyes-López,J M Mancera,L Tort,A R Khansari,Y G Zhang,G Martínez-Rodríguez,M Teles

doi:10.3389/fphys.2019.00717

Abstract

Vaccination is a widely used therapeutical strategy in aquaculture, but whether vaccination elicits stress responses in the central neuroendocrine system and enhances the crosstalk between the immune and endocrine systems in the brain or pituitary after vaccination is unclear. To answer this question two experiments using two different vaccine exposure routes, i.e., bath or intraperitoneal (i.p.) injection, were carried out on gilthead seabream (Sparus aurata L.). In the first one, the stress responses of fish subjected to waterborne Vibrio anguillarum bacterin were compared with responses after air exposure or their combination. In the second experiment, fish were subjected to an intraperitoneal injection of Lactococcus garvieae bacterin and we assessed the central stress response and also whether or not a significant immune response was induced in brain and pituitary. In both experiments, blood, brain and pituitary tissues were collected at 1, 6, and 24 h post stress for plasma hormone determination and gene expression analysis, respectively. Results indicated that bath vaccination induced a decreased central stress response compared to air exposure which stimulated both brain and pituitary stress genes. In the second experiment, injection vaccination kept unchanged plasma stress hormones except cortisol that raised at 6 and 24 h. In agreement, non-significant or slight changes on the transcription of stress-related genes were recorded, including the hormone genes of the hypothalamic pituitary interrenal (HPI) axis and other stress markers such as hsp70, hsp90, and mt genes in either brain or pituitary. Significant changes were observed, however, in crhbp and gr. In this second experiment the immune genes il1β, cox2, and lys, showed a strong expression in both brain and pituitary after vaccination, notably il1β which showed more than 10 fold raise. Overall, vaccination procedures, although showing a cortisol response, did not induce other major stress response in brain or pituitary, regardless the administration route. Other than main changes, the alteration of crhbp and gr suggests that these genes could play a relevant role in the feedback regulation of HPI axis after vaccination. In addition, from the results obtained in this work, it is also demonstrated that the immune system maintains a high activity in both brain and pituitary after vaccine injection.

Highlights

Stress is defined as a state of real or perceived challenge for homeostasis that induces a response consisting in an array of biological reactions to compensate for the consequences of the threat created by the stressor (Tort and Teles, 2011; Schreck and Tort, 2016)
The dynamics of the vaccine plus air exposure was similar to that observed after air exposure, the recovery took place later on, indicating that the air exposure stressor was predominant in the cortisol response
In terms of plasma hormones, it seems that fish would not perceive vaccines as primary stressors stimulating the hierarchical activation of hypothalamic pituitary interrenal (HPI) axis, it would indirectly activate cortisol release in the case of vaccine injection linked to the air exposition period during the injection procedure

Summary

Introduction

Stress is defined as a state of real or perceived challenge for homeostasis that induces a response consisting in an array of biological reactions to compensate for the consequences of the threat created by the stressor (Tort and Teles, 2011; Schreck and Tort, 2016). The release of ACTH into the bloodstream and interaction with the receptors of interrenal tissue, will subsequently induce cortisol release (Gorissen and Flik, 2016). Assuming that brain and pituitary are the hierarchical onset organs of the stress reaction (Cerdá-Reverter and Canosa, 2009), other central interactions have been shown to occur at brain and pituitary level, the cortisol feed-back interaction via GR (Gorissen and Flik, 2016)

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