A double constriction micropipette for the quantitative injection of tracer substance

A glass, double constriction injector micropipette ('micropet') has been designed to overcome problems associated with commercial microliter syringes. These problems include: inconsistent volume delivery, inability to view tracer during filling or injection, and the relatively large size of the needle supplied. 'Micropets' of different volumes are easily made from inexpensive, commercially available Drummond 100 microliter glass tubes (bores) fitted with teflon plungers. Tracer substances may be viewed in the bores during filling and injection and the needle tip can be pulled as small as 50 micrometers. For deep stereotactic injection, a long triple constriction 'micropet' has also been devised. The 'micropet' is based in principle on the commercial Lang-Levy double constriction micropipettes and these are used for radiometric calibration of the 'micropets'. Thus the 'micropet' accuracy is a reflection of these commercial micropipettes, and is approximately +/- 0.5%. Precision is also on the order of +/- 0.5% as determined by radioassay. When combined with an oil-filled, variable-speed microdrive the injector 'micropet' provides a highly controlled and precise system for the accurate delivery of tracer substance important for quantitative neuroanatomical investigations.