1 8 1 8 HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY III 



table 2. Distribution of Enzymes in Rat Brain* 



* Data from references (i, 2, 5, 7, 8, 17, 80, 99). 



f Intracellular fractions obtained through differential centrifugation. 



content and oxidative activity of various nerve libers 

 of the central and peripheral nervous system (un- 

 published observations). With regard to glia, in- 

 formation regarding mitochondrial concentration and 

 distribution is almost completely lacking. Oligo- 

 dendroglia have high oxidative activity (100), while 

 the metabolic activity of astrocytes and microglia can 

 only be inferred from studies on white matter. In 

 addition to being the primary source of energy 

 production, the mitochondria accumulate man) 



important neurohumoral agents, such as epinephrine 



norepinephrine (unpublished observations), 

 histamine (21) and 5-hydroxytryptamine (unpub- 

 lished observations). Both the nature and sitmilicance 

 of the binding of these agents are entirely unknown, 

 although, in view of the potent pharmacological 

 effeel "i these agents on smooth muscle, one might 

 M peel ilnii possible relationship to mitochondrial 

 physiology. Furthermore, the facl thai neurohumoral 

 transmission has been established ai the nerve 

 endings 1 (o), where mitochondria are especially 

 concentrated, points to an importanl relationship 

 between mitochondria and such agents. Oxidative 



phosphorylation itself, however, does not appear to 

 depend upon the presence of (he neurohumoral agents 

 within mitochondria (unpublished observations). 

 The recent finding that the pulsatile activity of 

 oligodendroglia is influenced by 5-hydroxytryptamine 

 is suggestive of the role of this neurohumor in the 

 regulation of secretion or fluid transport ( 1 2 1 |. 



From studies with mammalian nerve and glia cells 

 grown in tissue cultures, it appears that not only is 

 the oxidative and glycolytic activity of microglia and 

 oligodendroglia of considerable magnitude, the Q n 

 varying from 1 j to jo (2), but in the case ol certain 

 enzymes, such .is cytochrome oxidase, succinic and 

 malic dehydrogenases, and adenosinetriphosphatase, 

 the activity of glia is about one half to two thirds 

 that of neurons (unpublished observations). It is, 

 however, difficult at present 10 compare quantitatively 

 the metabolic activity of eelU grown in tissue culture 

 with the parent iclU in their natural environment, .1 

 problem confronting all in vitro work insofar as 

 normally present physical and chemical regulatory 

 factors are eliminated or interfered with in disrupted 



tissues 



