Hypothesis

Age‑related deterioration of hypothalamic autonomic nuclei and vagal efferent output reduces acetylcholine‑dependent signaling to the gut vasculature, leading to mesenteric arterial stiffening, elastin fragmentation, and systemic propagation of vascular aging.

Mechanistic Rationale

Central autonomic circuits regulate gut blood flow via cholinergic motor neurons that release acetylcholine onto intestinal smooth muscle and endothelial cells (, 2026)【4】. In aging, hypothalamic NF‑κB activation diminishes parasympathetic tone【5】, while vagal efferent fibers show dystrophic loss【3】. Acetylcholine normally suppresses NF‑κB in vascular endothelium and stimulates elastin‑preserving pathways through muscarinic M3 receptors. Loss of this tonic inhibition permits chronic low‑grade inflammation, oxidative stress, and matrix metalloproteinase activation in the mesenteric artery wall, accelerating calcification and stiffening. Stiff mesenteric vasculature elevates pulse pressure transmitted to the portal system, impairing nutrient flux and gut barrier integrity, which then feeds back to aggravate brain inflammation via afferent vagal signals—a vicious loop that inverts the typical gut‑→‑brain causality.

Testable Predictions

1. Old mice with selective chemogenetic activation of hypothalamic parasympathetic nuclei will exhibit restored vagal efferent firing, increased intestinal acetylcholine levels, and reduced mesenteric arterial stiffness compared with age‑matched controls.
2. Pharmacological blockade of muscarinic M3 receptors in the gut will abolish the protective effects of central autonomic activation, confirming the gut‑vascular mediator.
3. Rescue of mesenteric elastin content (by histology or ex vivo tensile testing) will correlate with improved systemic pulse wave velocity and preserved cognitive performance in aging mice.
4. Conversely, induced vagal efferent loss in young animals will recapitulate mesenteric stiffening and accelerate systemic aging markers without alterations in microbiota composition.

Experimental Design

• Subjects: C57BL/6 mice aged 6 mo (young) and 24 mo (old).
• Interventions:
  • Chemogenetic (DREADD) activation of hypothalamic paraventricular nucleus cholinergic neurons using CNO.
  • Gut‑specific M3 antagonist (telenzepine) administered via oral gavage.
  • Control groups receive vehicle or inert DREADD ligand.
• Readouts:
  • In vivo vagal efferent activity (electrophysiology).
  • Mesenteric acetylcholine concentration (microdialysis).
  • Arterial stiffness (pulse wave velocity, ultrasound).
  • Histologic elastin integrity (Verhoeff‑Van Gieson) and calcification (Alizarin Red).
  • Systemic biomarkers: plasma IL‑6, TNF‑α, pulse pressure.
  • Cognitive assay: Morris water maze.
• Analysis: Two‑way ANOVA (age × treatment) with post‑hoc Tukey; significance set at p<0.05.

If central autonomic restoration normalizes gut vascular mechanics and delays systemic aging, the hypothesis will be supported. Failure to improve mesenteric stiffness despite increased vagal efferent tone would falsify the proposed neurovascular‑first mechanism.