A volume-distribution analysis of the water soluble contrast medium, meglumine iothalamate, injected into various ventricular and subarachnoid sites was accomplished radiographically in the cat with the aid of a newly designed screw-type cannula having a deadspace of 6 to 8 pl. The cannula is positioned stereotaxically and mounts directly and permanently in the cranium by a single self-tapping insertion maneuver. As little as 100 p1 of solution injected into the anterior horn of the lateral ventricle, or 50 and 20 pl into the third and fourth ventricles, respectively, was visualized immediately in the lateral apertures of the fourth ventricle connecting with the subarachnoid spaces. Injection of 50 pl into the posterior horn of the lateral ventricle delineated the entire ventricle as well as the interventricular foramen. A volume of 12 pl deposited in the base of the third ventricle served to define the hypothalamic cleft and infundihular recess. If rate of injection was not excessive, the solution could be introduced into the third and fourth ventricles without penetrating into the more anterior regions. Radiopaque medium injected into subarachnoid spaces (cisternae ambiens and cerebellomedullaris) did not enter the ventricular system.
1 Supported by N.I.H. grant NB-04456. zpresented as a preliminary report ?t the A@, 1965 meeting of the Federation of American Societies for Experimental Biology (Federation Proc., 24: 399).
3 Available from Kouf Instruments. Tuiunza, Cali-, -fornia.
4 See footnote 3.