Lumbar intrathecal catheterization in rats targeting the cerebral cortex: a drug delivery method and validation

Abstract Intrathecal (IT) drug delivery is a critical technique for bypassing the blood-brain and blood-spinal cord barriers in preclinical CNS research. However, conventional rat catheterization methods suffer from high rates of neurologic complications, poor reliability, and unverified dosing due to epidural reflux and inconsistent supraspinal distribution. Our objective was to develop and validate an improved method for lumbar IT catheterization in rats that ensures distribution to the brain and to confirm supraspinal pharmacodynamic target engagement. We describe a refined microsurgical technique using dural puncture under direct visual control at the L6-S1 interlaminar space, a site chosen for its anatomical safety margin. The method uses a small-bore (0.33 mm OD) polyurethane (PU) catheter to minimize durotomy size, air-bubble tracking to compensate for catheter dead volume, and epidural sealing with Surgifoam ® to minimize reflux. Visualization using Evans Blue dye confirmed complete neuraxial distribution from a single 30 µL lumbar bolus injection, with dye reaching the ventral/dorsal brain cisterns. Pharmacodynamic validation of cortical exposure was achieved using an S6 kinase 1 (S6K1) inhibitor. Lumbar IT administration over a period of 6 hours via a pump resulted in significant supraspinal S6K1 engagement, demonstrated by a reproducible reduction in S6 phosphorylation in the cerebral cortex. Highlights Method for lumbar intrathecal catheterization in rats under direct visual control, using basic surgical tools CNS distribution validated by Evans Blue dye reaching ventral and dorsal brain Pharmacodynamic confirmation of supraspinal target engagement following lumbar intrathecal delivery of a small molecule kinase inhibitor Serves as a faithful preclinical model for therapeutics intended for clinical intrathecal administration Provides a screening route for early-stage compounds not yet optimized for CNS penetrance, supporting efficacy testing prior to medicinal chemistry investment