Neonatal overfeeding disrupts pituitary ghrelin signalling in female rats long-term; Implications for the stress response.

The hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress are exacerbated in adult female but not male rats made obese due to overfeeding in early life. Ghrelin, traditionally known for its role in energy homeostasis, has been recently recognised for its role in coordinating the HPA responses to stress, particularly by acting directly at the anterior pituitary where the growth hormone secretagogue receptor (GHSR), the receptor for acyl ghrelin, is abundantly expressed. We therefore hypothesised that neonatal overfeeding in female rats would compromise pituitary responsiveness to ghrelin, contributing to a hyperactive central stress responsiveness. Unlike in males where hypothalamic ghrelin signalling is compromised by neonatal overfeeding, there was no effect of early life diet on circulating ghrelin or hypothalamic ghrelin signalling in females, indicating hypothalamic feeding and metabolic ghrelin circuitry remains intact. However, neonatal overfeeding did lead to long-term alterations in the pituitary ghrelin system. The neonatally overfed females had increased neonatal and reduced adult expression of GHSR and ghrelin-O-acyl transferase (GOAT) in the pituitary as well as reduced pituitary responsiveness to exogenous acyl ghrelin-induced adrenocorticotropic hormone (ACTH) release in vitro. These data suggest that neonatal overfeeding dysregulates pituitary ghrelin signalling long-term in females, potentially accounting for the hyper-responsive HPA axis in these animals. These findings have implications for how females may respond to stress throughout life, suggesting the way ghrelin modifies the stress response at the level of the pituitary may be less efficient in the neonatally overfed

Primer details for qRT-PCR.

<p>Primer details for qRT-PCR.</p

Effects of neonatal overfeeding on the neonatal ghrelin system.

<p>A) neonatal body weight, postnatal day (P) 12; n = 6 CL, 5 SL. B-D) serum ghrelin concentrations in control (CL) and neonatally overfed (SL) rats at P7 and P14; n = 8 for all groups. E) hypothalamic growth hormone secretagogue receptor (<i>Ghsr</i>) mRNA expression and F) ghrelin O-acyl transferase (GOAT; <i>Mboat4</i>); n = 8 CL P7, SL P7, CL P14, 7 SL P14. Data are mean + SEM. * <i>p</i> < 0.05. There was a significant main effect of age on acyl and total ghrelin, but no <i>post hoc</i> group differences in this measure. <i>Post hoc</i> differences between the groups are indicated by joining lines and *.</p

Effects of neonatal overfeeding on pro-opiomelanocortin (<i>Pomc</i>) and Growth hormone (<i>Gh</i>) mRNA expression in the adult pituitary.

<p>A) Adult pituitary pro-opiomelanocortin (<i>Pomc</i>); n = 8 CL, 6 SL, and B) growth hormone (<i>Gh</i>) mRNA expression; n = 6 CL, 7 SL. Data are mean + SEM.</p

Effects of neonatal overfeeding on the ghrelin system long-term.

<p>A) adult serum ghrelin concentrations. B) hypothalamic growth hormone secretagogue receptor (<i>Ghsr</i>) and C) ghrelin O-acyl transferase (GOAT; <i>Mboat4</i>) mRNA expression; n = 6 CL, 8 SL for A-C. D) adult body weight n = 6 for all groups. Data are mean + SEM. * <i>p</i> < 0.05. T-test differences between the groups are indicated by joining lines and *.</p

Effects of neonatal overfeeding on the neonatal response to ghrelin.

<p>A) Neuronal activation in response to an i.p. ghrelin injection in the arcuate nucleus (ARC) (n = 6 CL Saline, SL Saline, CL AG, CL DAG, 5 SL AG, 7 SL DAG) and B) paraventricular nucleus of the hypothalamus (PVN) (n = 6 CL Saline, SL Saline, CL AG, SL AG, CL DAG, 7 SL DAG). C) Photomicrographs of the PVN. Scale bar = 100 μm. Data are mean + SEM. * <i>p</i> < 0.05. <i>Post hoc</i> differences between the groups are indicated by joining lines and *.</p

Primer details for qRT-PCR.

<p>Primer details for qRT-PCR.</p

Effects of neonatal overfeeding on the ghrelin pituitary signalling long-term.

<p>A) Neonatal pituitary growth hormone secretagogue receptor (<i>Ghsr</i>); n = 8 CL P7, CL P14, 7 SL P7, 6 SL P14, and B) pituitary ghrelin O-acyl transferase (GOAT; <i>Mboat4</i>) mRNA expression; n = 7 CL P7, SL P7, CL P14, 6 SL P14. C) Adult pituitary <i>Ghsr</i> and D) pituitary <i>Mboat4</i> mRNA expression in control (CL) and neonatally overfed (SL) rats; n = 6 CL, 8 SL. Data are mean + SEM. * <i>p</i> < 0.05. <i>Post hoc</i> and t-test differences between the groups are indicated by joining lines and *.</p