c-fos Expression in the forebrain and brainstem of White Leghorn hens following osmotic and cardiovascular challenges

Abstract

In chickens, hyperosmolality and hemorrhage increase hypothalamic vasotocin (AVT) gene expression and stimulate the secretion of AVT from the posterior pituitary gland. In this study, c-fos expression was used to identify areas in the forebrain and brainstem of the domestic chicken that are activated following acute osmotic stress and hemorrhage-induced hypotension. Conscious hens were osmotically stimulated by administering a single intraperitoneal injection of 3 M NaCl (5 ml/kg). Urethane-anesthetized hens were bled to a mean systemic arterial pressure of 80-90 mm Hg and maintained at this blood pressure for 1 h with additional bleedings as required. In both studies, the expression of c-fos was determined in control and experimental birds by using Northern blot analysis and in situ hybridization analysis. Osmotic stress and hemorrhage-induced hypotension increased c-fos expression in the same brain regions. Prominent structures in the forebrain that expressed c-fos mRNA following acute osmotic stress and hemorrhage-induced hypotension included the supraoptic nucleus and paraventricular nucleus and nuclei within the hypothalamus that are anterior and ventral to the third ventricle. In the chicken, this region includes the organum subseptale, the o. vasculosum laminae terminalis, and the nucleus septalis medialis. In the brainstem, following either injection of 3 M NaCl or hemorrhageinduced hypotension, increased c-fos expression was observed in the nucleus of the solitary tract, parabrachial nucleus, area postrema, and locus ceruleus. Thus, the chicken central nervous system appears to use shared neuronal circuitry to stimulate hypothalamic AVT release in response to disturbances in body fluid composi-tion and decreases in either systemic blood pressure or volume.

Telencephalic regulation of the HPA axis in birds

“…The avian PVN is activated during acute stress ( Berk and Butler, 1981 ; Nagarajan et al, 2014 ). It responds to all different kinds of stressors, both psychological ( Calisi et al, 2008 ; Goodson and Evans, 2004 ) and physiological (heat stress, infection, osmotic; Calefi et al, 2016 ; Jaccoby et al, 1999 ), and activity levels (both baseline and stress-induced) can be sensitive to season ( Calisi et al, 2008 ). Restraint stress leads to the activation of parvocellular AVT neurons in the core PVN ( Nagarajan et al, 2014 ).…”

“…The exact cell types activated depend on the stressor (e.g. magnocellular AVT + neurons respond to osmotic stress; Jaccoby et al, 1999 ) or behavioural context, such as copulation and male-male aggression ( Xie et al, 2010 ). Many papers do not investigate which exact cell types are activated, but only report that they are located in the PVN.…”

“…In birds, PVN also receives input from the LC, the NTS, and possibly from the Raphe Nuclei ( Korf, 1984 ). The HPA response to osmotic stressors is regulated by putative inputs to the PVN from the Subseptal Organ (SSO; equivalent to the mammalian SFO) and the Vascular Organ of the Lamina Terminalis (OVLT), both known to be involved in osmoregulation ( Atoji and Wild, 2004 ; Jaccoby et al, 1999 ; Korf, 1984 ; Montagnese et al, 2004 ). Both SSO and OVLT also respond to a psychogenic stressor (acute restraint), with some evidence that the OVLT is more involved in psychogenic stress than the SSO ( Aman et al, 2016 ).…”

“…In birds as well, LHy has reciprocal connections with the PVN and is known to have an inhibitory effect on at least some parts of the PVN (definitely the magnocellular part, and maybe some of the parvocellular part as well) ( Felix and Roesch, 1984 ; Korf, 1984 ), but we currently do not know if this affects the CRH + neurons or the parvocellular AVT component that release their peptides into the median eminence. We do know, however, that LHy is activated during acute and chronic restraint stress in chickens ( Nagarajan et al, 2014 ), and not during osmotic or haemorrhagic stress ( Jaccoby et al, 1999 ). In at least one species, the LHy has also been shown to express GR and MR ( Dickens et al, 2011 ).…”

“…This activation in song sparrows mostly involves non-CRH + neurons ( Goodson and Evans, 2004 ). It also responds to osmotic and haemorrhagic stress in chickens ( Jaccoby et al, 1999 ). BSTL, at least in songbirds, has been shown to contain GR, but not MR ( Senft et al, 2016 ; Shahbazi et al, 2011 ).…”