Printed in U.S.A. INCREASED SENSITIVITY TO PENTYLENETETRAZOL AND FLUROTHYL FOLLOWING CORTICAL ABLATIONS IN RATS ’ 2

Alterations in respoilsiveness to convulsant drugs after brain damage have been noted in both the experimental and clinical literature. Pentylenetetrazol is known to induce or increase epileptiform discharge in the EEG of epileptic patients more than in nonepileptic individuals (Cure et al., 1948). This procedure has been used as a diagnostic technique for epileptogenic foci in man. A greater sensitivity to pentyl-enetetrazol was noted in cats tested several weeks or months after unilateral frontal abla-tions or hemidecerebratioiis (Drake et al., 1956). Dandy and Elman (1925) had previ-ously reported that damage to the motor cortex of cats resulted in an increased sensitiv-ity to the convulsant absinthe. However, dam-age to the occipital cortex produced inconclu-sive changes, possibly due to the fact that only three cats were used. Lashley (1935) noted that lesions of the frontal cortex of rats re-suited in deficits in some performance tasks whereas lesions of the rosterior cortex resulted in deficits in brightness discrimination tests. The fiber connections, as well as tile functions, of the two areas of the cortex differ. The frontal area is concerned with motor movements and certain autonomic functions, while the poste-nor cortex is concerned primarily with vision. A quantitative coml)arison of the effects of cortical ablations in each of tilese areas might indicate whether different anatomical and func-tional pathways can induce changes in sensitiv-ity to convulsant drugs. During the course of tile illvestigation with pentylenetetrazoi, certain difficulties arose in connection with the administration of this agent. The low margin of safety between con-vulsant and lethal dosages resulted in tile death of some animals. In others, there was Received for publication October 6, 1964. ‘This study was supported by Public Healt