Spinal cord turnover

ACh is widely distributed throughout the brain and parts of the spinal cord (ventral horn and dorsal columns). Whole brain concentrations of lOnmolg" tissue have been reported with highest concentrations in the interpeduncular, caudate and dorsal raphe nuclei. Turnover figures of 0.15-2.0 nmol g min vary with the area studied and the method of measurement, e.g. synthesis of labelled ACh from [ " C]-choline uptake or rundown of ACh after inhibition of choline uptake by hemicholinium. They are all sufficiently high, however, to suggest that in the absence of synthesis depletion could occur within minutes. 

The CSF/serum ratio of albumin during mid-adult life is less than 7 x 10. If the barrier permeability increases (as seen in purulent meningitis), the albumin ratio can increase to values greater than 100 x 10 (barrier breakdown). The albumin ratio is not dependent only on the barrier s permeability, but also on the fluid turnover, which normally is 14% per hour of the total CSF space volume. If turnover decreases, as in the presence of a spinal cord tumor, the albumin ratio can increase to values < 100 X 10-3 (CSF block). 

Kanterman RY, Felder CC, Brenneman DE, Ma AL, Fitzgerald S, Axelrod J. arAdrenergic receptor mediates arachidonic-acid release in spinal-cord neurons independent of inositol phospholipid turnover. J Neurochem 1990 54 1225-1232. 

CSF is secreted by the choroid plexuses, around the cerebral vessels, and along the walls of the ventricles of the brain. It fills the ventricles and cisternae, bathes the spinal cord, and is reabsorbed into the blood through the arachnoid villi. CSF turnover is rapid, exchanging totally about four times per day. More than 80% of CSF protein content originates from plasma by ultrafiltration and pinocytosis the remainder is from intrathecal synthesis. The lowest concentration of total protein and the smallest proportion of the larger protein molecules are in the ventricular fluid as the CSF passes down to the lumbar spine (from which site specimens are usually collected), the protein concentration increases. This difference in concentration at different levels of the CNS is illustrated by the following reference intervalsd ... 

Teichberg, S., Holtzman, E., Crain, S.M. and Peterson, E. (1975) Circulation and turnover of synaptic vesicle membrane in cultured fetal mammalian spinal cord neurons. J. Cell Biol. 67 215-230. 

Several studies indicate that opioids activate serotonergic neurons and increase 5-HT turnover in the spinal cord, " Intrathecal 5-HT produced antinociception in mice (tail flick). 3, Q2e of sero-... 

Small amounts of cholesterol can also be taken up into the nervous system from the blood following injection of C -cholesterol into 15-day-old rabbits. Once incorporated into the brain, C -cholesterol undergoes slow metabolism and is then retained with little apparent turnover for a period of at least 9 months. Spinal cord cholesterol is equally stable meta-bolically (Fig. 5). In the rabbit, as in the chicken, liver, kidney, and plasma cholesterol undergo quite rapid metabolism. In other experiments (Davison et al., 1959a) brains from rabbits, previously injected with 4-C -cholesterol, were separated into gray and white matter. It became apparent that all the turnover of the C -choIesterol was associated with the gray matter, and that there was little if any metabolism of cholesterol incorporated into the white matter. Since white matter is particularly rich in myelin, this suggested that once cholesterol has been incorporated into... 

Giorgi O and Meek J. L. (1984) v-aminobutync acid turnover m rat striatum. Effects of glutamate and kainic add / Neurochem 42, 215-220 Graham L T Jr and Aprison M H (1969) Distribution of some enzymes associated with the metabolism of aspartate, glutamate, y-aminobutyrate, and glutamine in cat spinal cord /. Neurochem 16, 559-566... 

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