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

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.