Telencephalic regulation of the HPA axis in birds

Abstract

The hypothalamo-pituitary-adrenal (HPA) axis is one of the major output systems of the vertebrate stress response. It controls the release of cortisol or corticosterone from the adrenal gland. These hormones regulate a range of processes throughout the brain and body, with the main function of mobilizing energy reserves to improve coping with a stressful situation. This axis is regulated in response to both physical (e.g., osmotic) and psychological (e.g., social) stressors. In mammals, the telencephalon plays an important role in the regulation of the HPA axis response in particular to psychological stressors, with the amygdala and part of prefrontal cortex stimulating the stress response, and the hippocampus and another part of prefrontal cortex inhibiting the response to return it to baseline. Birds also mount HPA axis responses to psychological stressors, but much less is known about the telencephalic areas that control this response. This review summarizes which telencephalic areas in birds are connected to the HPA axis and are known to respond to stressful situations. The conclusion is that the telencephalic control of the HPA axis is probably an ancient system that dates from before the split between sauropsid and synapsid reptiles, but more research is needed into the functional relationships between the brain areas reviewed in birds if we want to understand the level of this conservation.

Developmental-Based Classification of Enkephalin and Somatostatin Containing Neurons of the Chicken Central Extended Amygdala

“…In chicken, the BSTL has been shown to become active by stress ( Nagarajan et al, 2014 ), similarly to that of mammals ( Davis et al, 2010 ). Moreover, it projects to the paraventricular hypothalamic nucleus ( Atoji et al, 2006 ), being thus able to regulate the hypothalamic-pituitary-adrenal axis ( Smulders, 2021 ), and receives input from a posterior part of the arcopallium (part of the avian pallial amygdala) ( Atoji et al, 2006 ) that is also involved in control of fear behavior ( Saint-Dizier et al, 2009 ). The subpallial amygdalar area interposed between the arcopallium and the BSTL also projects to the BSTL and seems to belong to the same functional network ( Kuenzel et al, 2011 ).…”

Distinct Subdivisions in the Transition Between Telencephalon and Hypothalamus Produce Otp and Sim1 Cells for the Extended Amygdala in Sauropsids

“…The central extended amygdala of mammals plays a key role in triggering and regulating fear and anxiety responses ( Phelps and LeDoux, 2005 ; Davis et al, 2010 ). In birds, the BSTL also plays a role in fear and anxiety ( Nagarajan et al, 2014 ; reviewed by Smulders, 2021 ), but the implication of other parts of the central extended amygdala is unknown. The finding of subsets of glutamatergic cells in the BSTL and the capsular part of the central extended amygdala raises questions on the possible interactions of these glutamatergic cells with the typical GABAergic cells found in this nuclear complex.…”

Evolution and Development of Amygdala Subdivisions: Pallial, Subpallial, and Beyond

“…The medial amygdala and BSTM of sauropsids show patterns of connections similar to those of mammalian EAme, such as inputs from the olfactory/vomerolfactory bulbs [Reiner and Karten, 1985;Martínez-García et al, 1991;Halpern and Martínez-Marcos, 2003] and from olfactory and associative parts of the pallial amygdala [Lanuza et al, 1997[Lanuza et al, , 1998Novejarque et al, 2004; in birds, this includes at least the arcopallium and the pallial part of nucleus taeniae: Cheng et al, 1999;Kröner and Güntürkün, 1999]; in addition, they project to the sexually dimorphic medial preoptic nucleus [Absil et al, 2002], the paraventricular hypothalamic nucleus, and the ventromedial hypothalamus [Bruce and Neary, 1995a;reviewed by Martínez-García et al, 2002, 2008Medina et al, 2017Medina et al, , 2019. Like in mammals, these avian preoptic/hypothalamic nuclei targeted by EAme have similar functions to those of mammals: the medial preoptic nucleus is involved in male sexual behavior [Panzica et al, 1996[Panzica et al, , 2001aBalthazart et al, 2001;Balthazart and Ball, 2007]; the paraventricular hypothalamic nucleus is an integral part of the hypothalamo-pituitary-glandular axes for control of stress, reproduction, metabolism, and homeostasis, and also regulates the autonomic nervous system by descending projections to the brainstem [De Vries and Panzica, 2006;Kuenzel and Jurkevich, 2010;Smulders, 2021;Grassi et al, 2022]; and the ventromedial hypothalamic nucleus is involved in aspects of sexual behavior and food intake [Kuenzel et al, 1999;Cline et al, 2007;Riters and Pawlisch, 2007]. The EAme of non-avian reptiles also projects to similar preoptic and hypothalamic nuclei involved in neuroendocrine control and social behavior [Martínez-García et al, 2008;O'Connell and Hofm...…”