Microcapillary specifically designed for pressure microinjections of very low volumes

Tracer micronjections are very widely used in brain mapping research. While administration of small quantities/volumes of tracers can easily be achieved through iontophoresis, in the case of pressure injections the volume of the substances injected are much more difficult to control. Instead of using different variables like hydrodynamic conductance, pressure pulses, pressure-temperature-dependent protocols to quantify very small volumes in the nanoliter range out of a higher volume, within the confines of the present study a novel microcapillary design is presented. This microcapillary contains exactly the volume of tracer one intends to inject, therefore the danger of flooding large brain areas or the risk of tracer leakage to neighbouring nuclei are completely eliminated, and in the same time this design assures that very small and circumscribed areas can be labeled and their connections mapped, thus making the experiments more specific. In combination with high precision stereotaxic measurements these small volumes of tracers can yield well targeted and very discrete injection sites that make possible the mapping of individual nuclear subdivisions or delicate nuclei in the brain.