Date of Graduation

5-2020

Document Type

Thesis

Degree Name

Master of Science in Poultry Science (MS)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Kuenzel, Wayne J.

Committee Member

Rhoads, Douglas D.

Second Committee Member

Bottje, Walter G.

Third Committee Member

Dridi, Sami

Keywords

Birds; Corticotropin Releasing Hormone; HPA; HPT; Neuroendocrine; Stress

Abstract

The hypothalamo-pituitary-adrenal (HPA) axis is the regulatory system for the neuroendocrine stress response within vertebrates. Within the HPA axis corticotropin releasing hormone (CRH) is a major regulator and driving hormone. A structure named the nucleus of the hippocampal commissure (NHpC) has been found to contain CRH neurons and also these neurons respond to early food deprivation stress significantly prior to the paraventricular nucleus (PVN), the major driving nucleus of the classic neuroendocrine HPA axis. The objective of this study was to perform a knock down of the NHpC via electrolytic lesioning, thus eliminating a significant portion of its population of CRH neurons. An experiment was designed to determine whether the elimination of CRH neurons within the NHpC would have a significant effect on HPA function following exposure of broiler chicks to food deprivation (FD). Male chicks (BW 300-350g, 10-14 d) were used in this experiment and split into 3 groups: 1) Sham surgical controls without FD (SHAM), 2) Sham surgical birds with 2h FD stress (SHAM+FD), and 3) Birds subjected to electrolytic lesioning and 2h FD (LES+FD). Blood, brain and anterior pituitary (APit) were sampled promptly from each bird at 2h of FD for the LES+FD and SHAM+FD groups and intermittently for SHAM CON birds. RT-PCR was performed for gene expression within the NHpC, PVN and anterior pituitary (APit) and a radioimmunoassay was performed to determine plasma corticosterone (CORT) concentrations. All RT-PCR data were analyzed with the Tukey Kramer HSD test and all CORT data were analyzed using one-way ANOVA. Electrolytic lesioning of the NHpC significantly reduced plasma CORT in the LES+FD group compared to intact levels in the SHAM+FD group. Decreased CORT occurred concurrently with decreased amounts of CRH mRNA within the NHpC of the LES + FD group. Supporting this, Proopiomelanocortin heteronuclear RNA (POMC hnRNA) within the APit was significantly downregulated. Interestingly, PVN CRH levels were found to be significantly decreased in the LES+FD group of birds with no lesioning of the PVN itself. Results suggest a possible neural connection from the NHpC to the PVN exists, resulting in down regulation of CRH expression in the PVN. Corticotropin releasing hormone receptor 2 (CRHR2) was found to be significantly downregulated within the PVN and APit in the LES+FD group of birds. Thyroid stimulating hormone beta (TSHβ) was also downregulated along with CRHR2 in the PVN and APit suggesting that CRHR2 expression within the PVN could be an important part of the hypothalamo-pituitary-thyroid (HPT) axis. In conclusion, lesioning the NHpC had a significant effect on the HPA axis. CRH neurons within the NHpC and/or PVN had a significant effect on the HPA and/or HPT axes.

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