Scientists at a university in the United States have identified a new structure of neurons in the poultry brain that may be the starting point for some stress response signals.
The neurons are located in the hippocampal commissure, a structure located in the septum, a brain regional directly above the hypothalamus.
The team, led by Professor Wayne Kuenzel, a poultry scientist from the University of Arkansas, is investigating the hypothalamo-pituitary-adrenal axis (HPA axis) – one of at least four major neuroendocrine systems regulating vertebrate physiology and behaviour.
Prof Kuenzel said the HPA axis is a complex signalling pathway from the brain to the adrenal glands that controls how chickens respond to stress. The communication flow goes both ways with negative and positive feedbacks.
One common example of poultry stress is transportation as chickens are moved from hatcheries to poultry production houses and then on to food processing plants. Stress during these periods can have negative effects on meat quality.
He added that a better understanding of the stress response pathways could help discover ways to alleviate such physiological stressors, which would in turn improve poultry welfare, health and may enhance meat quality.
The current understanding of stress response is that it all begins in the hypothalamus, an area at the base of the brain, directly above the pituitary gland. The hypothalamus contains a number of small clusters of neurons called neural nuclei that have a variety of functions, Prof Kuenzel said.
One of its most important functions is to link the nervous system to the endocrine system via the pituitary gland. This system is designed to maintain homeostasis – a tendency toward equilibrium among a body’s systems.
In response to stress, the hypothalamus releases corticotropin-releasing hormone, or CRH, that stimulates the anterior pituitary gland, located just beneath the brain, to secrete a hormone called ACTH. It travels via the bloodstream to the adrenal glands, located atop the kidneys, which are then stimulated to secrete corticosterones. These are stress hormones in poultry and other birds that adjust metabolism in a manner that allows the birds to cope with stress.
Research by the team showed that the nucleus of the hippocampal commissure – the NHpC – became active and produced CRH in chickens that were stressed by short-term restriction of food.
These neurons responded prior to the major group of CRH neurons in the HPA axis and researchers believe the newly discovered cluster of neurons may be part of the classical HPA chain of neuroendocrine activity that triggers the birds’ stress response.