An air pressure system for the injection of tracer substances into the brain

A system for injecting traces and other substances into the brain through glass micropipettes using mechanically or electromechanically regulated air pressure as the driving force is described. The system has a number of advantages over currently used devices including: accurate ejection of a wide range of volumes (2 nl to several microliters); the capability to inject all currently utilized tracers; and, the direct visualization of the volume of solution injected. This system has proven reliable for a number of tract tracing experiments ranging from the injection of tracers into deep structures of the monkey brain to injecting small quantities of tracers into the brains of fetal rats.