NEURONAL LOSS IN THE HIPPOCAMPUS IN HUNTINGTONS-DISEASE - A COMPARISON WITH HIV-INFECTION

The hippocampus is usually affected in primary dementias and the patho logical changes may be severe. Knowledge of hippocampal pathology in H IV infection and Huntington's disease (HD), however, is extremely limi ted. A stereological technique (the optical ''disector'') has been use d to assess neuronal populations in four areas of the hippocampus in 1 1 patients with HIV infection and in nine patients with HD. The HIV pa tients died without opportunistic infections or neoplasms affecting th e brain; they had HIV encephalitis or minimal changes. The HD cases we re all clinically diagnosed, had a positive family history and showed the characteristic lesions in the caudate nucleus. The neuronal counts were compared with those in nine controls. In the granule cell layer of the dentate, CA3 and CA4, there was no significant difference in th e neuronal numerical density between the three groups. A striking diff erence between the HIV and HD groups was seen in the CA1 region. The n euronal numerical density in the CA1 area was significantly lower in t he HD patients than in either the HIV patients or the controls (mean ( SD) 37.5 (5.0); 70.1 (13.4); 57.9 (15.4) x 10(3) per mm3, p < 0.001 (S tudents' t test)). This difference represents a neuronal loss of 35%. In all four hippocampal areas the neuronal density was higher in the H IV group than in the controls but the differences were not significant and can-be explained by the higher average age of the control group. These findings contribute to the understanding of the mechanism of dem entia in both AIDS and in Huntington's disease.