# Research timeline and gaps: Glymphatic Clearance Hypothesis

Selected publication milestones, not an exhaustive history or discovery priority claim.

**2012 — Tracer and AQP4 experiments establish a restricted perivascular transport mechanism.** [Original PMID22896675](https://pubmed.ncbi.nlm.nih.gov/22896675/).

**2013 — Sleep-state experiments associate larger interstitial space with increased clearance in mice.** [Original PMID24136970](https://pubmed.ncbi.nlm.nih.gov/24136970/).

**2017 — Direct diffusion and AQP4-independent measurements challenge uniform parenchymal convection.** [Original PMID28826498](https://pubmed.ncbi.nlm.nih.gov/28826498/).

**2018 — Human isotope kinetics distinguishes amyloid production from fractional clearance.** [Original PMID29220873](https://pubmed.ncbi.nlm.nih.gov/29220873/).

**2022 — AQP4 loss worsens pathology in a mutant-tau mouse model.** [Original PMID35212707](https://pubmed.ncbi.nlm.nih.gov/35212707/).

**2024 — Small-dye experiments report reduced clearance during sleep and anesthesia.** [Original PMID38741022](https://pubmed.ncbi.nlm.nih.gov/38741022/).

**2025 — Noradrenergic oscillations link sleep microarchitecture to fluid transport.** [Original PMID39788123](https://pubmed.ncbi.nlm.nih.gov/39788123/).

**2026 — Endogenous neuronal protein tracing resolves compartment-specific exit routes.** [Original PMID42214342](https://pubmed.ncbi.nlm.nih.gov/42214342/).

## Research gaps

Influx, redistribution, degradation and net export need independent mass-balance measurements.

Opposite sleep results require matched injection recovery, solute size, compartment and physiological state.

AQP4 affects water homeostasis and cell function beyond the proposed route.

Human device/model estimates need held-out orthogonal clearance validation; plasma changes alone do not identify the route.

A clearance-specific human disease-trajectory intervention and directionally valid genetic instrument remain unverified.

## Boundary experiment

Prospectively register a selective adult pathway manipulation in a predefined aging/neurodegeneration setting, measure endogenous-solute production and net export with independent methods, and follow neuronal/functional trajectory. Match circadian timing, natural sleep, vascular dynamics and delivery pressure; add mediator rescue or epistasis before translating the physiological target to a human clinical trial.