Impaired cardiorespiratory responses to hypercapnia in neonatal mice lacking PAC1 but not VPAC2 receptors

Cellular mechanisms underlying pituitary adenylate cyclase activating polypeptide-stimulated secretion in the adrenal medulla

The adrenal medulla is a key effector of the sympathetic nervous system in the periphery. Its primary function is to translate variations in sympathetic activity into hormone outputs that modify end organ function throughout the body. These hormones include epinephrine, norepinephrine, and a variety of vasoactive peptides. Hormone secretion occurs when neurotransmitters, delivered by sympathetic nerves, bind to, and activate receptors on adrenomedullary chromaffin cells. In this context, two neurotransmitters of particular importance are acetylcholine (ACh) and pituitary adenylate cyclase activating polypeptide (PACAP). PACAP, discovered initially as a secretagogue in the hypothalamus, is now appreciated to provoke a strong secretory response from chromaffin cells in vitro and in situ. However, the cellular mechanisms underlying PACAP-stimulated secretion are still poorly understood. In the sections below, we will summarize what is known about the actions of PACAP in the adrenal medulla, discuss recent advances that pertain to the PACAP signaling pathway, and highlight areas for future investigation.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Sudden Infant Death Syndrome: A Potential Model for Investigation

Sudden infant death syndrome (SIDS) represents a significant cause of post-neonatal mortality, yet its underlying mechanisms remain unclear. The triple-risk model of SIDS proposes that intrinsic vulnerability, exogenous triggers, and a critical developmental period are required for SIDS to occur. Although case-control studies have identified potential risk factors, no in vivo model fully reflects the complexities observed in human studies. Pituitary adenylate cyclase-activating polypeptide (PACAP), a highly conserved neuropeptide with diverse physiological functions, including metabolic and thermal regulation, cardiovascular adaptation, breathing control, stress responses, sleep-wake regulation and immunohomeostasis, has been subject to early animal studies, which revealed that the absence of PACAP or its specific receptor (PAC1 receptor: PAC1R) correlates with increased neonatal mortality similar to the susceptible period for SIDS in humans. Recent human investigations have further implicated PACAP and PAC1R genes as plausible contributors to the pathomechanism of SIDS. This mini-review comprehensively synthesizes all PACAP-related research from the perspective of SIDS and proposes that PACAP deficiency might offer a promising avenue for studying SIDS.