Split-brain Cats Prepared by Radiosurgery

Summary

Cats with their optic chiasma and commissural system disconnected along the mid-saggital plane are of special value in central nervous system research. The feasibility of producing such split-brain cats with heavy-particle radiation was attempted. Focused, 910 MeV helium ion particles from the Berkeley cyclotron were restricted to a blade-like beam that was oriented to pass between the cerebral hemispheres. Because of their superior non-scattering property, helium particles retained their sharply-defined beam even after passage through brain tissue along the cat's longitudinal fissure. The efficiency of helium ions in blocking interhemispheric transfer was tested using electrophysiologic techniques. The corpus callosum was permanently implanted with pairs of wire electrodes in the genu and splenium on either side of the interhemispheric fissure. The time–dose relationship to abolish electrically-initiated transcallosal action potentials (TCAP) was investigated. The post-irradiation interval to inhibit TCAP was an inverse function of the logarithm of the absorbed dose above 10 krads of helium ion radiation. TCAP could be selectively inhibited either in the region of the genu, or the splenium. Transmission of the entire corpus callosum could be blocked by a 2 × 25·4 mm helium ion beam. When the corpus callosum absorbed less than 10 krads of helium ions, TCAP were not abolished. A very fine helium ion beam, 0·5 × 25·4 mm, was not successful in halting TCAP, even though the corpus callosum absorbed 50 krads of radiation. The radiovulnerability of the small-calibre nerve fibres (1 µ and less) that constitute the corpus callosum is discussed.