122 H. E. HIMWICH VOL. 4 (1950) 



other barbiturates, exerts a metabolic inhibition which is most marked in the brain 

 and relatively unimportant in other organs^^. Measurements of brain metabolism made 

 on human beings in the second and third stages of pentothal anesthesia disclose a 

 decrease of approximately one-third^^. 



The barbiturates not only employ metabolic deprivation but also act on nerve 

 f unction^^. The latter action may be described as an elevation of the synaptic threshold^^ 

 due perhaps to impeded recovery after impulse propagation^^. Despite these diverse 

 influences it is feasible to follow the events caused by metabolic depression. 



In this brief exposition it is impossible to review the signs of pentothal anesthesia. 

 Instead an explanatory diagram is inserted (Fig. 2). The figure is taken from a paper^^ 

 in which it is suggested that the metabolic inhibition is the cause for certain similarities 

 between barbiturate anesthesia and hypoglycemia or anoxia and especially so for the 

 march of signs down the neuraxis with deepening anethesia. On the other hand the 

 distinguishing characteristics of the anesthesia are attributed to the special effects which 

 the barbiturate exert upon nerve functions. 



Since the progression of the changes in behaviour observed following surgical or 

 pharmacologic intervention seem to depend upon the hierarchy of metabolic rates in 

 the various parts of the brain it is worth while to examine that phenomenon further. 

 A clue as to its origin may be offered by a study of the changes in oxygen intake of the 

 various parts of the brain during early growth. Animals which are born in an immature 

 state, resembling man in that way, are appropriate material for a study of postnatal 

 metabolic changes. The newborn rat, blind, poikilothermic and without righting re- 

 flexes, essentially a bulbospinal animal, can be followed through early growth while the 

 later developed portions of the brain take on their due functions. The birth process marks 

 the passage from intrauterine life to individual independence but does not necessarily 

 represent a definite change in the fundamental patterns of growth and energy production. 



Numerous in vitro studies of oxygen intake reveal a higher rate of metabolism in 

 the adult than in the infant. This was first observed in infant rat brain^", and later 

 confirmed on the dog^^. These results indicate a rapid rise of cerebral metabolism in 

 early life. The metabolic changes are the resultants of the distinctive rates in the discrete 

 parts of the brain. It has been experimentally established that the metabolic rates are 

 not equally affected by growth, but that each area possesses its own pattern of devel- 

 opment. In experiments on the rat^^ and the dog^^ (Fig. 3) it was found that the lower 

 parts of the brain are relatively more active than the higher ones at birth, and as 

 development continues, the wave of metabolism presses forward so that the lower 

 portions of the central nervous system are surpassed by the anatomically higher and 

 phyletically more recently developed regions. The increasing rate of metabolism of the 

 brain as a whole must therefore be attributed chiefly to the increasing rate in the newer 

 parts of the brain during early life. 



Additional evidence for this phyletic sequence can be observed by a study of the 

 anaerobic metabolism. The short period of survival in anoxia observed in the mammal 

 is made possible by the anaerobic production of energy which includes the splitting of 

 carbohydrate to form lactic acid. The cerebral glycolytic rates are slowest in the new- 

 born and increase to a maximum in early life^^, ^^. In order to determine the contribution 

 of each area in the brain making for this changing rate of glycolysis both dogs and cats 

 were employed^* and in several age groups: newborns to one week, three to seven weeks, 

 three months, and adult. In general, the results of the experiments on dogs and cats 

 References p. 125. 



