The mutual influence of insulin and environmentally-conditioned central nervous system performance on the regulation of carbohydrate metabolism

Investigating the effects of insulin on carbohydrate metabolism and on the central nervous system (C.N.S.) under conditions of rest and of stress in dogs and in rats, using the conditional reflex method and measuring the nitrogen and phosphate brain metabolites and the blood sugar differences, the author found that cerebral glucose metabolism is dependent upon insulin, and that if glucose supplies are adequate, insulin stimulates C.N.S. performance within 15–20 minutes. The C.N.S. and blood sugar reactivity depend upon the environmental situation: the conditional stimuli for stress increase glycemia. Animals under stress went into shock even though their glycemic levels were relatively high, whereas those at rest did not go into shock or sometimes reacted with slight symptoms of somnolence even at a lower glycemic level. In experimental hyperglycemia the level rises even more during stress, with ensuing coma, especially with larger doses of insulin. An increase of inhibition with reduced learning precedes the glycemic irregularities. Thus, insulin directly influences the central nervous system.