Creation and validation of 3D-printed head molds for stereotaxic injections of neonatal mouse brains

Background: An increasing number of rodent model systems use injection of DNA or viral constructs in the neonatal brain. However, approaches for reliable positioning and stereotaxic injection at this developmental stage are limited, typically relying on handheld positioning or molds that must be re-aligned for use in a given laboratory. New method: A complete protocol and open-source software pipeline for generating 3D-printed head molds derived from a CT scan of a neonatal mouse head cast, together with a universal adapter that can be placed on a standard stereotaxic stage. Results: A series of test injections with adenovirus encoding red fluorescent protein, or Fluorogold, were conducted using original clay molds and newly generated 3D printed molds. Several metrics were used to compare spread and localization of targeted injections. Comparison with existing methods: The new method of head mold generation gave comparable results to the field standard, but also allowed the rapid generation of additional copies of each head mold with standardized positioning of the head each time. Conclusions: This 3D printing pipeline can be used to efficiently develop a series of head molds with standardized injection coordinates across multiple laboratories. More broadly, this pipeline can easily be adapted to other perinatal ages or species.