Background: Orthotopic in vivo models for the experimental treatment of malignant gliomas have become indispensable to evaluate the efficacy of novel therapeutic regimens. Recently, a guide screw system was introduced which is implanted into the cranium of small rodents where it facilitates fast, repeated and exactly reproducible intracerebral injections, avoiding time consuming stereotactic procedures. Here we report our experience with this system, and describe several modifications which we introduced to improve its reliability and to simplify its application.
Findings: The most important modification made was the optimization of the guide screw implantation site, which needs to be adapted to the age of the mice. Other improvements were the fixation of the guide screw to the cranium of the mice using a two component adhesive. This avoids the tendency, when daily intratumoural injections are performed over several weeks, for the screw to loosen, making precise injections impossible. The injection procedure, initially described as a free-hand approach, was improved by mounting the syringe to a Greenberg retractor. This provided additional stability and speeded up the process. Applying this modified technique, we were able to achieve reproducible results with regard to engraftment rate, tumour growth, and intratumoural treatment in immunocompromized mice.
Interpretation: We introduced several major and some minor improvements to make working with the guide screw system more reliable, faster and more comfortable. Daily injections over a period of three weeks using this system are feasible and well tolerated by mice.