THE EFFECTS OF BARBITURATES ON PARTIALLY ISOLATED REGIONS OF THE CENTRAL NERVOUS SYSTEM

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Abstract
In 52 cats in which the left frontal lobe (including the motor cortex) or the whole cerebral hemisphere had been removed 3 months to 2 years previously, sodium pentobarbital (i.v., 1.0-2.0 mg/kg) caused weakness and in-co-ordination in the decentralized limbs. Larger quantities of pentobarbital (3.0-8.0 mg/kg)made the animals unable to stand ("standing test") for 13.0 [plus or minus] 1.8 minutes while 25 control cats exhibited this effect for 5.6 [plus or minus] 1.5 minutes. Using the "standing test" as a criterion the median effective dose of pentobarbital was found to be 1.7 mg/kg for the operated group and 3.7 mg/kg for the controls, the difference being statistically significant. Sodium pheno-barbital had similar effects. Injected (i.m.) 1 hour before pentylene-tetrazol (10 mgAg) in 21 operated and 19 control cats, pentobarbital (1.0-6.0 mgAg) reduced the incidence and severity of convulsions in the operated cats to a greater extent than in the controls, as judged by a conversion of the clonic-tonic-clonic fits into purely clonic seizures. In 23 spinal cats in which the spinal cord was semisected 9 to 39 days previously, the excitability of the motoneurones was tested by means of intraaortal injections of acetylcholine (ACh, 0.03-3 mgAg). Small quantities of pentobarbital occasionally augmented the responses to ACh whereas larger quantities of pentobarbital (0.3-11.0 mgAg) or pheno-barbital (0.7-6.0 mgAg) had a depressant effect, both actions being more marked on the semisected side. The significance of these findings is discussed.