The gatekeepers of growth: The neural roles and regulation of growth hormone-releasing hormone neurons

Abstract

The neuroendocrine control of growth is mediated by the hypothalamic–pituitary–somatic (HPS) axis. This involves the hypothalamic release of growth hormone-releasing hormone (GHRH), which stimulates the pituitary secretion of growth hormone (GH). GH subsequently promotes growth both directly and indirectly by stimulating insulin-like growth factor 1 (IGF1) release from the liver. While extensive research has focused on the actions and mechanisms of GH and IGF1, comparatively little attention has been given to how GHRH neurons themselves are regulated. This review aims to provide insight into how GHRH neurons are controlled, emphasizing their intrinsic electrophysiological properties and the broader brain circuitry involved in detecting physiological signals such as hormonal and metabolic status. Central to this regulation is the balance of excitatory and inhibitory inputs that generate the pulsatile secretion pattern essential for growth regulation. Somatostatin (SST) provides critical inhibitory control over both GH secretion and GHRH neuronal activity. Feedback from peripheral hormones and integration of environmental and metabolic cues can further shape GHRH neuron function. Developmental, sex-dependent, and species-specific variations in GHRH neuron regulation are also discussed, highlighting important avenues for future research. This review offers a neuroendocrine perspective on growth regulation, with important implications for understanding the brain's role in regulating growth and development.