Transportation Stress Increases Fos Immunoreactivity in the Paraventricular Nucleus, but Not in the Nucleus of the Hippocampal Commissure in the Pekin Duck, Anas platyrhynchos domesticus

Abstract

Commercial poultry undergo transportation during their life, and the effects of transportation can negatively impact poultry production and welfare. In order to maintain physiological homeostasis, the hypothalamic−pituitary−adrenal axis (HPA) works to respond to stressors. Previous studies by others have shown contradictory effects of transportation on corticosterone release. However, recent studies from our lab and by others have shown that cortisol may also be an important hormone in the avian HPA. The purpose of our current study was to determine the effects of transportation stress on the stimulation of brain nuclei that regulate the HPA in birds, and on glucocorticoid (GC) secretion. To test this hypothesis, we collected blood and brain samples from developer drakes and hens (N = 10 per sex/time point): 24 h prior to transportation, immediately after transportation, 24 h after transportation, and 1 week after transportation. Serum GC levels and fos immunocytochemistry (ICC) within the nucleus of the hippocampal commissure (NHpC) and paraventricular nucleus (PVN) were measured. Data were analyzed using a two-way ANOVA. Post hoc analysis was completed using a Fisher’s PLSD with a p < 0.05 considered significant. We observed a sex difference (p < 0.05) in both corticosterone and cortisol secretion in Pekin ducks, although neither GC showed a significant increase in secretion associated with transportation. However, we did observe a significant (p < 0.05) increase in fos-like immunoreactivity for 24 h in the PVN, but not in the NHpC. Further studies are required to determine the specific role that GCs play in the avian stress response and the short-term stressors that could have long-term physiological effects on birds.

Keywords: corticosterone; cortisol; nucleus of hippocampal commissure; paraventricular nucleus; sex difference.

Figure 1

Serum glucocorticoids in ducks following transportation stress. Sex differences were observed in that hens showed significantly greater levels of both circulating corticosterone (A) and cortisol (B) compared to drakes. Transportation elicited a non-significant increase in both glucocorticoids. The lack of significant increase may likely be due to the timing of blood sampling relative to the perceived onset of stress. * = p < 0.05.

Figure 2

Fos-ir in the NHpC and PVN associated with transportation. A significant increase in the number of fos-ir was observed at Transportation in the PVN (B) but not in the NHpC (A) that lasted through the Transportation + 24 h sample time. Further, a significant sex difference was observed in that hens showed a greater number of fos-ir in the PVN compared to drakes at Transportation and Transportation + 24 h. Asterisks indicate differences from controls of the same sex where, ** = p < 0.01, *** = p < 0.001. Differences between sexes at same time points, p = 0.0036.

Figure 3

Representative photomicrographs of fos-ir. Top row: no differences in fos-ir were observed in the NHpC at any time point assessed. Bottom row: the number of fos-ir nuclei in the PVN increased with Transportation and continued to show increased numbers for 24 h before returning to Pre-transport levels. Arrows = fos-ir nuclei. AC = anterior commissure. 3v = third ventricle. Bar = 100 μm. Arrows point to representative fos-ir.