Effect of pentobarbital and ether on the spreading cortical depression.

WEAK electrical stimulus applied to A the rabbit’s cerebral cortex causes under certain conditions (I) a depression of the spontaneous electrical activity which spreads with low velocity (3-5 mm/min) over the cortex and lasts from I to 3 min. Several repetitions of the stimulus at intervals of 8-10 min may change this spreading cortical depression into a spreading convulsive pattern (2-5). Both the spreading depression and the spreading convulsive pattern are accompanied by a slow potential change of the cortex (I, 5-S). The cortical surface first turns negative with respect to an indifferent electrode; then the polarity is reversed and the cortex becomes positive. The magnitude of the negative phase of the slow potential is often IO mv or more, while the positive phase is usually smaller. In some instances the negative phase is preceded by a small galvanometer deflection indicating cortical positivity. The total duration of this slow potential change may be 3 min or more. It was shown that the slow potential change travels over the cortex at the same velocity as the depression, preceding the latter by 10-40 set (I). Leao (2) found that Dial and pentobarbital in moderate doses, and light ether narcosis do not abolish the spreading depression. Also moderate doses of pentobarbital (up to 30 mg/kg body weight) do not prevent the convulsive patterns which may replace the depression (9). Barbiturates and volatile narcotics are known to act differently on both the electrocorticogram and the polarization state of nervous tissue (see DISCUSSION). It seemed therefore of interest to investigate more fully the effects of ether and pentobarbital, as representatives of these groups of narcotics,