Central nervous regulation of the hypothalamic-pituitary-adrenal axis and its impact on fertility, immunity, metabolism and animal welfare – a review

Abstract

The paper reviews mechanisms of neuronal control of the hypothalamic-pituitary-adrenal (HPA) axis with a view on its impact on performance and welfare. The limbic hippocampal and amygdaloid input to the paraventricular hypothalamic nucleus constitutes the basic intracerebral axis by which emotional stimuli affect the stress response. This axis is the backbone of the HPA feedback loop where hippocampus and amygdala are plastic elements and add the ability of experience dependent adaptation and (emotional) learning. As a result large individual differences of the stress response may occur. The system mutually interacts with the immune system and with hypothalamic cell groups which control metabolism and fertility, explaining the influence of stress on these performance parameters. It is concluded that for the reliable assessment of emotional welfare in (farm-) animals a multitude of physiological and behavioral measures are needed which take into account the highly crosslinked nature of the system. Key Words: HPA axis, regulation, brain, performance, animal welfare Zusammenfassung Titel der Arbeit: Zentralnervöse Regulation der Hypothalamus-Hypophysen-Nebennierenrindenachse und ihr Einfluss auf Fruchtbarkeit, Immunstatus, Metabolismus und Wohlbefinden -eine Übersicht Es werden Mechanismen der neuronalen Kontrolle der Hypothalamus-Hypophysen-Nebennierenrinden-(HPA-) Achse beschrieben und ihre Einflüsse auf Leistungs-und Befindlichkeitsparameter beleuchtet. Die limbischen Hirnzentren Hippocampus und Amygdala bilden mit ihren Signalen zum paraventrikulären hypothalamischen Nukleus das Rückgrat der intrazerebralen Achse, über die psychische Reize die Stressantwort steuern. Hippocampus und Amygdala sind dabei plastische Elemente, die erfahrungsabhängig physiologische und Verhaltensanpassungen (Lernen) beeinflussen. Als Ergebnis können große individuelle Unterschiede der Stressantwort auftreten. Das System interagiert mit dem Immunsystem und hypothalamischen Neuronenverbänden, die den Metabolismus und die Fruchtbarkeit steuern, wodurch die Wirkung von Stress auf diese Leistungsparameter erklärt werden kann. Die Eigenschaften des Gesamtsystems führen zu der Schlussfolgerung, dass für die zuverlässige Einschätzung des psychisch-emotionalen Wohlbefindens bei (Nutz-) Tieren mehrere physiologische und Verhaltensparameter benötigt werden, die die hochgradig vernetzte Regulation berücksichtigen.Schlüsselwörter: HPA-Achse, Regulation, Gehirn, Leistung, Wohlbefinden Biological function of HPA activity in stressThe aim of this paper is to give the reader an overview of the current understanding of the complex regulation of the hypothalamic-pituitary-adrenal (HPA) axis with its impact on health, fertility, metabolism, and behavioral adaptation. This is, obviously, of particular interest in farm animals where performance and welfare are considerably interfering with (emotional) stress and the resulting coping attempts. Every environment where animals live is to some degree unpredictable. Although some aspects may be quite regular a...

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