Mohammed T. Abou-Saleh

Principles and Practice of Geriatric Psychiatry.Editors: Professor John R. M. Copeland, Dr Mohammed T. Abou-Saleh and Professor Dan G. BlazerCopyright & 2002 John Wiley & Sons LtdPrint ISBN 0-471-98197-4 Online ISBN 0-470-84641-08Quantitative Structural Changesin the Ageing BrainBente Pakkenberg, Lisbeth Regeur, Hans Jørgen G. Gundersen*Neurological Research Laboratory, Kommunehospitalet, Copenhagen, and*Stereological Research Laboratory, A˚rhus University, A˚rhus, DenmarkEstimates of the total number of human neocortical cells in bothhemispheres range from 10 to 100 billions (10 9 ), but only twomajor studies describe how to estimate total neuron number.Reduction in the number of cells per unit volume of humancerebral cortex with age has been found in seven distinctneocortical brain regions from newborn to 95 year-old individuals2 . Haug 3 estimated neuron density in 10–20 rows arrangedperpendicular to the pial surface of the cortex in two to four areasper brain, multiplied by the assumed neocortical volume, andfound an average of 15610 9 neurons in the human neocortex.Haug found no decrease in total neuronal number with age andno difference in total numbers between males and females.The three steps in estimating the total neuronal number in anydefined brain region include: (a) delineation and estimation of theregion’s volume; (b) uniform sampling of the complex andirregularly shaped neocortex; and (c) estimation of the neuronalnumerical density.Based on unbiased principles, the Cavalieri method for theestimation of volume using systematic sampling and pointcountingcan be applied to any organ that can be cut intoslices—physically or by means of optical or other scanningdevices—and is independent of size or shape of the organ 4,5 .Inarecent study by Regeur 6 , neocortical volume, cortical thicknessand volume of archicortex, the ventricular system, the central greymatter and white matter were estimated using stereologicalmethods on brains from 28 old females (mean age 81.8 years)with increasing degrees of senile dementia, and brains from 13(mean age 82.7 years) non-demented control females. Brains fromthe demented patients [14 Alzheimer’s disease (AD) cases and 14non-AD cases] had a smaller cortex volume and neocorticalthickness was significantly reduced in the demented patients, withthe highest degree of reduction in the most demented patients, aswere the volumes of archicortex. No statistically significantdifferences were found in the volumes of cortex, white matter,central grey structures, ventricular volume or archicortex betweenthe AD demented cases compared with the non-AD dementedcases. The ventricular volume increased with increasing degree ofdementia, but the difference between the demented group and thecontrol group did not reach statistical significance. Surface areadid not change in the demented patients, and no significantreductions were found in the volumes of white matter or centralgrey matter structures in the demented patients compared withcontrols.In 1984 the dissector method was described, in which threedimensionalparticles (e.g. neurons) are sampled with a constantprobability without regard to size, shape and orientation of theparticles, provided that two requirements are fulfilled: (a) thecomplete set of particle profiles hit by the dissector’s planartransects should be identifiable; (2) the dissector positions areuniformly random in the complete reference region 7 . The methodrelies on the fact that one can, without any other assumptions atall, count a cell nucleus or any defined particle within a definedreference volume if it is present in a relatively thin section but notin the previous member of a pair of adjacent sections. Particles ofarbitrary size and shape can only be sampled with equalprobability using a three-dimensional probe, such as the dissector.Systematically sampling a subset of dissectors from the wide rangepossible in a serially sectioned brain region or central nucleus,taking each with a constant but arbitrary probability, is sufficientfor the estimation of the total particle number or, as in thisinstance, nerve cells (for practical details and analyses of samplingdesign, see refs 5, 8–11). Williams and Rakic 12,13 have applied thesame technique using the three-dimensional counting frame 14,15 toobtain estimates of neuronal numerical densities.A method for uniform sampling in human neocortex combinedwith a modification of the dissector principle, the opticaldissector, has been introduced 16 . With the optical dissector theprocedure is performed in thick rather than thin sections, whichmakes it many times more efficient. Using this method, 94 normalbrains were studied, 32 females and 62 males in age-groups 20–90years 17 . An unbiased estimate of the total number of neurons inthe neocortex was obtained simply by multiplying the Cavalieriestimate of the neocortical reference volume by the numericaldensity obtained with the optical dissector. The number ofneocortical neurons in females was 19.3 billion, and in males 22.8billion, a difference of 16%. The difference in the total number ofneocortical nerve cells over the observed range of 70 years was9.5%, providing an average ‘‘loss’’ of neurons of about 85 000/day. This possible age effect was the same for both sexes. The totalnumber of neocortical neurons in the material varied more than afactor of 2 with a range of 118% (14.7–32.0 billion neurons) (seeFigure 8.1). The natural variability in neuron number of 19%(CV=SD/mean=0.19) in normal Danes thus represents avariance of more than eight times the variance of body height[CV (height)=0.065]: (0.19/0.065) 2 &8.On average, there were 186 million more neurons in the lefthemisphere than in the right and this difference was the same inthe two sexes. Sex differences were found in the total volume, totalsurface and thickness of the neocortex, white matter volume,central grey structure and brain weight. With advanced age,Principles and Practice of Geriatric Psychiatry, 2nd edn. Edited by J. R. M. Copeland, M. T. Abou-Saleh and D. G. Blazer&2002 John Wiley & Sons, Ltd