The Activities of Butyrylcholinesterase and Carbonic Anhydrase, the Rate of Anaerobic Glycolysts, and the Question of a Constant Density of Glial Cells in Cerebral Cortices of Various Mammalian Species From Mouse to Whale

Abstract

Abstract— The question of a constant density of glial cells in mammalian cerebral cortex regardless of species was examined by surveying the cortical activities of two enzymes primarily localized to dial cells. The cortical activity of butyrylcholinesterase (EC 3.1.1.8) was essentially constant at a rate of approx. 0.1 μmol of butyrylthiocholine hydrolysed min‐1 g‐1 over the range of species from rat (brain wt., 1.6 g) to fin whale and sperm whale (brain wt., 6800 and 7800 g, respectively). Over the same range the activity of cortical acetylcholinesterase, a neuronal enzyme, decreases by a factor of 7. Thus, butyrylcholinesterase ranged from < 2 per cent (in small rodent brains) to approximately 10 per cent (in whale brain) of the cortical acetylcholinesterase activity. The cortical activity of carbonic anhydrase (EC 4.2.1.1) was constant at a rate of 6.2 (± 0.25) μmol of CO2 evolved min‐1 g‐1 over the range of species from guinea‐pig (brain wt., 4.75 g) to fin whale (brain wt., 6800 g). These data obtained by assaying the dehydration reaction were confirmed by limited assays of the esterase activity of the enzyme (with p‐nitrophenylacetate as substrate) and agreed with limited, previously reported data for the hydration reaction. Thus, the circumstantial evidence strongly favoured a relative constancy of cortical glial cell density regardless of species. The rates of anaerobic glycolysis in the cerebral cortex of various species were also investigated. For six species from mouse (brain wt., 0.4 g) to beef (brain wt., 380 g) cortical anaerobic glycolysis varied only slightly in the range of 50–62 μmol of CO2 evolved h‐1 g‐l, whereas cortical oxygen consumption for the same range of species decreased by a factor of 3. Previously frozen samples of beef cortex glycolysed at 35 per Cent of the rate of fresh (unfrozen) samples. Since identical rates were obtained for previously frozen samples of fin whale cerebral cortex, we concluded that the relative constancy of cortical anaerobic glycolysis could be extended to the range from mouse to whale and that this aspect of cortical metabolism is probably primarily glial in localization. Some implications of the latter conclusion for the proposed role of astrocytes as modulators of neuronal activity have been discussed.

A Neurological Comparative Study of the Harp Seal (Pagophilus groenlandicus) and Harbor Porpoise (Phocoena phocoena) Brain

“…The slope of the regression line (Fig. 3) corresponds to what was found by Tower and Young (1973) when comparing brain weight with glial cell/neuron ratio between different mammals. The average glial cell/neuron ratio for the harbor porpoise and for the harp seal was 2.3/1 and 2.8/ 1, respectively.…”

A quantitative, theoretical framework for understanding mammalian sleep

“…If power given to repair per nucleotide or per codon is constant because of the limited spatial access to these domains, then it follows that power given to repair per DNA content is constant. For mammals, DNA content and glial cell size are roughly invariant, but brain neuronal cell size appears to vary as M b 1/4 (43)(44)(45)(46)(47). Consequently, within this scenario, power given to repair per unit volume, P R , would still be a constant for glial cells but would decrease as M b Ϫ1/4 for neuronal cells.…”

The Cortical Ischaemic Penumbra Associated with Occlusion of the Middle Cerebral Artery in the Cat: 1. Topography of Changes in Blood Flow, Potassium Ion Activity, and EEG

“…Tamura and his colleagues suggested that neuronal packing density may be one factor causing species variations in flow threshold for the occur rence of brain damage. It is of interest, but may be coincidental, that the species ranking for flow threshold which now emerges (baboon-cat-rat) is similar to that for glial/neuronal ratio (Tower and Young, 1973). Further caution in the pursuit of this line of argument is necessary since the flow data on which the comparison is based were obtained by different methods (hydrogen clearance and au toradiography).…”