The centromedian-parafascicular complex represents a nodal point in the neuronal loop comprising striatum--globulus pallidus--thalamus--striatum. Striatal neurone degeneration is a hallmark in Huntington's disease and we were interested in estimating total neurone and glial number in this thalamic nuclear complex. Serial 500-microns-thick gallocyanin-stained frontal sections of the left hemisphere from six cases of Huntington's disease patients (three females, three males) and six age- and sex-matched controls were investigated applying Cavalieri's principle and the optical disector. Mean neurone number in the controls was 646,952 +/- 129,668 cells versus 291,763 +/- 60,122 in Huntington's disease patients (Mann-Whitney U-test, P < 0.001). Total glial cell number (astrocytes, oligodendrocytes, microglia, and unclassifiable glial profiles) was higher in controls with 9,544,191 +/- 3,028,944 versus 6,961,989 +/- 2,241,543 in Huntington's disease patients (Mann-Whitney U-test, P < 0.021). Considerable increase of fibrous astroglia within the centromedian-parafascicular complex could be observed after Gallyas' impregnation. Most probably this cell type enhanced the numerical ratio between glial number and neurone number (glial index: Huntington's disease patients = 24.4 +/- 8.1; controls = 15.0 +/- 5.2; Mann-Whitney U-test, P < 0.013). The neurone number in the centromedian-parafascicular complex correlated negatively, although statistically not significantly, with the striatal neurone number. This lack of correlation between an 80% neuronal loss in the striatum and a 55% neurone loss in the centromedian-parafascicular complex points to viable neuronal circuits connecting the centromedian-parafascicular complex with cortical and subcortical regions that are less affected in Huntington's disease.

The total cortical and striatal neurone and glial numbers were estimated in five cases of Huntington's disease (three males, two females) and five ageand sex-matched control cases. Serial 500-l-lm-thick gallocyanin-stained frontal sections through the left hemisphere were analysed using Cavalieri's principle for volume and the optical disector for cell density estimations. The average cortical neurone number of five controls (mean age 53±13 years, range 36-72 years) was 5.97x 10 9 ±320x 10 6 , the average number of small striatal neurones was 82 X 10 6 ± 15.8 X 10 6 • The left striatum (caudatum, putamen, and accumbens) contained a mean of 273 X 10 6 ±53 X 10 6 glial cells (oligodendrocytes, astrocytes and unc1assifiable glial profiles). The mean cortical neurone number in Huntington's disease patients (mean age 49±14 years, range 36-75 years) was diminished by about 33 % to 3.99x10 9 ±218x10 6 nerve cells (P : : ; : : : : 0.012, MannWhitney V-test). The mean number of small striatal neurones decreased tremendously to 9.72 X 10 6 ±