Nerve cell loss in the thalamic mediodorsal nucleus in Huntington's disease. II. Optimization of a stereological estimation procedure

Pathoarchitectonics of the cerebral cortex in chorea-acanthocytosis and Huntington's disease

AIMS

Quantitative estimation of cortical neurone loss in cases with chorea-acanthocytosis (ChAc) and its impact on laminar composition.

METHODS

We used unbiased stereological tools to estimate the degree of cortical pathology in serial gallocyanin-stained brain sections through the complete hemispheres of three subjects with genetically verified ChAc and a range of disease durations. We compared these results with our previous data of five Huntington's disease (HD) and five control cases. Pathoarchitectonic changes were exemplarily documented in TE1 of a 61-year-old female HD-, a 60-year-old female control case, and ChAc3.

RESULTS

Macroscopically, the cortical volume of our ChAc cases (ChAc1-3) remained close to normal. However, the average number of neurones was reduced by 46% in ChAc and by 33% in HD (P = 0.03 for ChAc & HD vs. controls; P = 0.64 for ChAc vs. HD). Terminal HD cases featured selective laminar neurone loss with pallor of layers III, V and VIa, a high density of small, pale, closely packed radial fibres in deep cortical layers VI and V, shrinkage, and chromophilia of subcortical white matter. In ChAc, pronounced diffuse astrogliosis blurred the laminar borders, thus masking the complete and partial loss of pyramidal cells in layer IIIc and of neurones in layers III, V and VI.

CONCLUSION

ChAc is a neurodegenerative disease with distinct cortical neurodegeneration. The hypertrophy of the peripheral neuropil space of minicolumns with coarse vertical striation was characteristic of ChAc. The role of astroglia in the pathogenesis of this disorder remains to be elucidated.

Comparing glutamatergic neuron population in the mediodorsal thalamic nucleus of genetic absence epilepsy rats from strasbourg (GAERS) and normal control Wistar rats

An imbalance between GABAergic inhibition and glutamatergic excitation is suspected to play a role in the genesis of epileptic processes. In the present study we quantified the number of glutamate+ve neurons in the mediodorsal thalamic nucleus (MD) of genetic absence epilepsy rats from Strasbourg (GAERS) and compared these with values for normal Wistar rats. The MD thalamic nucleus was removed from each animal and the glutamatergic neurons were labelled using light-microscopy glutamate immunohistochemistry. The disector method was used to quantify the glutamate+ve neurons in the MD thalamic nucleus of GAERS and Wistar rats. The data were statistically analyzed. In the Wistar animals glutamate+ve neurons formed 89% and in GAERS 92.3% of the total neurons in 1000μm³ of MD thalamic nucleus. In GAERS glutamate+ve neurons showed statistically significant increase in the MD thalamic nucleus compared to Wistar animals. In Wistar animals the glutamate-ve neurons formed 11% and in GAERS 7.7% of the total neurons in 1000μm³ of MD thalamic. No significant difference was observed in glutamate-ve neurons between the two strains. The average diameter of glutamate+ve neurons showed no significance, while glutamate-ve neurons were significant between the two strains. The results of the present study, on genetic absence epilepsy model, GAERS, confirms the role of MD thalamic nucleus in chemically induced absence epilepsy.

Three-dimensional and stereological characterization of the human substantia nigra during aging

The human brain undergoes non-uniform changes during aging. The substantia nigra (SN), the source of major dopaminergic pathways in the brain, is particularly vulnerable to changes in the progression of several age-related neurodegenerative diseases. To establish normative data for high-resolution imaging, and to further clinical and anatomical studies we analyzed SNs from 15 subjects aged 50-91 cognitively normal human subjects without signs of parkinsonism. Complete brains or brainstems with substantia nigra were formalin-fixed, celloidin-mounted, serially cut and Nissl-stained. The shapes of all SNs investigated were reconstructed using fast, high-resolution computer-assisted 3D reconstruction software. We found a negative correlation between age and SN volume (p = 0.04, rho = -0.53), with great variability in neuronal numbers and density across participants. The 3D reconstructions revealed SN inter- and intra-individual variability. Furthermore, we observed that human SN is a neuronal reticulum, rather than a group of isolated neuronal islands. Caution is required when using SN volume as a surrogate for SN status in individual subjects. The use of multimodal sequences including those for fiber tracts may enhance the value of imaging as a diagnostic tool to assess SN in vivo. Further studies with a larger sample size are needed for understanding the structure-function interaction of human SN.

Motor afferents from the cerebellum, zona incerta and substantia nigra to the mediodorsal thalamic nucleus in the rat

The mediodorsal (MD) thalamic nucleus provides information from subcortical structures to the prefrontal cortex. The human MD thalamic nucleus has been implicated in a great variety of different clinical conditions and normal functions ranging from schizophrenia, Parkinsonism and epilepsy to many cognitive functions. In the rat the MD thalamic nucleus is divided into three cytoarchitectonic sectors whereas in the primates it is divided into two; medial one-third (magnocellular) and lateral two-thirds further the lateral sector is divided into pars parvocellularis pars multiformis, pars fasciculosa and pars caudalis. In this study we used a retrograde tracer, fluoro-gold (FG) to evaluate some of the afferents reaching the lateral sector of the MD (MDl) thalamic nucleus. The results of the present study have shown that MDl receives afferent connections from the lateral cerebellar nucleus (dentate nucleus), substantia nigra pars reticulata (SNR) and zona incerta (ZI). Subsequent to FG injections into the MDl, labeled cells were observed mainly bilaterally but were sparser on the contralateral side than ipsilaterally from each of the three structures listed. All three afferents showed a topographical organization. The labeled neurons were localized at the dorsomedial aspect of the lateral cerebellar nucleus, the dorsoventral aspect of the SNR and in the dorsal sector of the ZI. The lateral cerebellar nucleus reached the MDl via the superior cerebellar peduncle. No other deep cerebellar nuclei showed labeled cells. There were no labeled cells in the substantia nigra pars compacta (SNC). Although the three regions identified here are recognized as having motor functions, the connections to MD suggest that their outputs also play a role in cognitive or other higher cortical functions.

Huntington's Disease (HD): Neurodegeneration of Brodmann's Primary Visual Area 17 (BA17)

Huntington's disease (HD), an autosomal dominantly inherited polyglutamine or CAG repeat disease along with somatomotor, oculomotor, psychiatric and cognitive symptoms, presents clinically with impairments of elementary and complex visual functions as well as altered visual-evoked potentials (VEPs). Previous volumetric and pathoanatomical post-mortem investigations pointed to an involvement of Brodmann's primary visual area 17 (BA17) in HD. Because the involvement of BA17 could be interpreted as an early onset brain neurodegeneration, we further characterized this potential primary cortical site of HD-related neurodegeneration neuropathologically and performed an unbiased estimation of the absolute nerve cell number in thick gallocyanin-stained frontoparallel tissue sections through the striate area of seven control individuals and seven HD patients using Cavalieri's principle for volume and the optical disector for nerve and glial cell density estimations. This investigation showed a reduction of the estimated absolute nerve cell number of BA17 in the HD patients (71,044,037 ± 12,740,515 nerve cells) of 32% in comparison with the control individuals (104,075,067 ± 9,424,491 nerve cells) (Mann-Whitney U-test; P < 0.001). Additional pathoanatomical studies showed that nerve cell loss was most prominent in the outer pyramidal layer III, the inner granular layers IVa and IVc as well as in the multiform layer VI of BA17 of the HD patients. Our neuropathological results in BA17 confirm and extend previous post-mortem, biochemical and in vivo neuroradiological HD findings and offer suitable explanations for the elementary and complex visual dysfunctions, as well as for the altered VEP observed in HD patients.

Mouse Models of Huntington's Disease

In this review, we explore the similarities and differences in the behavioural neurobiology found in the mouse models of Huntington's disease (HD) and the human disease state. The review is organised with a comparative focus on the functional domains of motor control, cognition and behavioural disturbance (akin to psychiatric disturbance in people) and how our knowledge of the underlying physiological changes that are manifest in the HD mouse lines correspond to those seen in the HD clinical population. The review is framed in terms of functional circuitry and neurotransmitter systems and how abnormalities in these systems impact on the behavioural readouts across the mouse lines and how these may correspond to the deficits observed in people. In addition, interpretational issues associated with the data from animal studies are discussed.

Estimation of numerical density and mean synaptic height in chick hippocampus 24 and 48 hours after passive avoidance training

The effects of passive avoidance learning on synaptic morphology and number in the dorsolateral hippocampus of chick were investigated at 24 and 48 h after training. Chicks of both sexes were used. The numerical density of synapses and mean synaptic height were determined using design-based quantitative electron microscopic techniques. Our results suggest that after training there is a significant increase in synaptic density in the dorsolateral hippocampus of chicks at both 24 and 48 h, and also that the mean synaptic height was significantly different between trained and control groups. The increase in synaptic density was due to shaft (type II) synapses. It is known that during synaptogenesis, shaft synapses are formed first and are then converted to spine synapses. The only hemispheric asymmetry was found in the 24 h water-trained (W-trained) males where the numerical density of spine synapses was significantly higher in the left hippocampus. No significant differences due to gender in either numerical synaptic density or synapse height were observed at either 24 and 48 h. Comparison of the 24 h with 48 h groups showed an increase in shaft synaptic density over time in the W-trained groups, and an increased density of both shaft and spine synapses with time in methylanthranilate-trained (MeA-trained) chicks. These results demonstrate that the dorsolateral hippocampus of the chick shows synaptic changes at both 24 and 48 h after training and implicates this region in the long-term memory process.

Computer experiments to determine whether over- or under-counting necessarily affects the determination of difference in cell number between experimental groups

Computer cell counting experiments were performed in order to examine the consequences of over- or under-counting. The three-dimensional reaggregate culture laboratory environment for cell counting was used as a model for computer simulation. The laboratory environment for aggregate and cell sizes, numbers and spatial placement in gelatin blocks was mimicked in the computer setup. However, in the computer, cell counting was set to be either ideally unbiased, or deliberately biased in regard to over- or under-counting so as to compare eventual results when using the various cell counting methods. It was found that there was no effect of the cell counting methods used in determining whether there was a significant difference in cell number between two experimental groups. In addition, it was found that under the conditions of these simulations, the optical dissector method behaved similarly, on the average, as the ideal method of counting cell centers and in both of those cases, the average ratio between actual cell number in a flask and estimated number was close to 1.00.

Celloidin mounting (embedding without infiltration) - a new, simple and reliable method for producing serial sections of high thickness through complete human brains and its application to stereological and immunohistochemical investigations

Celloidin mounting (embedding without infiltration) of the human central nervous system (CNS) proved to be superior to gelatin embedding for the production of serial sections ranging in thickness from 220 to 500 microm. After gallocyanin-staining, a comprehensive neuroanatomical as well as neuropathological survey of the human brain is possible, including diagnosis of Alzheimer's disease. Details of a fractionator analysis of the total striatal neuron number are described and the possible quantitative analysis of parallel immunohistochemically stained sections is discussed.

Recommendations for straightforward and rigorous methods of counting neurons based on a computer simulation approach

Any investigation of the total number of neurons in a given brain region must first address the following questions. What is the best method for estimating the total number of neurons? What are the validity and the expected precision of the obtained data? What precision must the estimates attain with respect to the scientific question? In the present study, these questions were addressed using a computer simulation. Virtual brain regions with various spatial distributions of virtual neurons were modeled. The total numbers of virtual neurons in the modeled brain regions were repeatedly estimated by simulation of modern design-based stereology, either by using the 'fractionator' method or by the established method based on the product of estimated neuron density and estimated volume of the reference space. We show that estimates of total numbers of neurons obtained using the fractionator are from a statistical and economical standpoint more efficient than corresponding estimates obtained using the density/volume procedure. Furthermore, the use of two simple prediction methods (one for homogeneous and the other for clustered neuron distributions) permits satisfactory predictions about the variation of presumably any estimates of total numbers of neurons obtained using the fractionator. Finally, we show that assessing the reliability of estimates of mean total neuronal numbers using the ratio between the mean of the squared coefficients of error of the estimates and the squared coefficient of variation of the estimated total neuronal numbers, a frequently employed method in stereological studies, is neither useful nor informative. The present results may constitute a new set of recommendations for the rigorous usage of design-based stereology. In particular, we strongly recommend counting considerably more neurons than is currently done in the literature when estimating total neuronal numbers using design-based stereology.

Subnucleus-specific loss of neurons in medial thalamus of schizophrenics

The hypoactivity of dorsolateral prefrontal cortex in schizophrenics is well known. One cause of this hypoactivity may be defective corticocortical or thalamocortical connections. Recent imaging studies of the thalamus suggest reductions in volume of the whole thalamus and reduced activity in the medial group of thalamic nuclei, which may indicate loss of functional input to the cortex. Using stereological techniques in six pairs of individually matched brains from schizophrenics and controls, we measured the volumes and obtained estimates of the number of neurons in the three subnuclei (parvocellular, pc; densocellular, dc; magnocellular, mc) of the mediodorsal nucleus (MD) and from the ventral posterior medial nucleus. There was a significant reduction in total neuron number in MD as a whole but this neuron loss was largely restricted to MDpc and MDdc [-30.9 and -24.5%, respectively (P </= 0.01)]. MDmc and the control ventral posterior medial nucleus showed no significant changes in cell number. Because the subnuclei of MD have different connections and project to different areas of the frontal cortex, the specific loss of neurons in MDpc and MDdc has implications for the functional defects observed in schizophrenia.

More cerebellar granule cells following prenatal low-dose X-irradiation

It was the aim of this study to estimating and comparing the total number of granule and Purkinje cells in the cerebellum of 180-day-old mice following a prenatal low-dose X-irradiation (50 cGy) at day 13 of gestation. Using the optical fractionator we found an expected, significant decrease of the total number of Purkinje cells (-21.1%; P=0.041) and a surprising, significant increase of the total number of granule cells (+23.1%; P=0.026) if comparing prenatally irradiated with sham-irradiated mice. The possible molecular basis of these seemingly paradoxical results is discussed.

Stereological quantification of carboxyfluorescein-labeled rat lung metastasis: a new method for the assessment of natural killer cell activity and tumor adhesion in vivo and in situ

The function of natural killer (NK) cells is often studied by assessing in vitro levels of NK cell mediated lysis of target cells, or by assessing in vivo levels of lung tumor cell retention or metastatic colonization of intravenously injected tumor cells. However, these methods do not permit direct quantification and visualization of NK cells and their targets in vivo and in situ. Here, a new approach is described to visualize effector-to-target interactions as well as to estimate total numbers of targets in the lung, in vivo and in situ. MADB106 tumor cells were vitally labeled using carboxyfluorescein (CFSE) and intravenously (i.v.) injected into Fischer 344 rats (10(6) cells/rat). This mammary adenocarcinoma derived cell line is syngeneic to the inbred Fischer 344 rat and highly sensitive to NK cell activity in vivo. Effector-to-target interactions were visualized by immunostaining. Using the optical fractionator method, total numbers of CFSE-labeled MADB106 tumor cells were estimated in the left lung of the animals 5 min after tumor inoculation. To further demonstrate the usefulness of this approach in reflecting in vivo processes, rats were inoculated with MADB106 cells and simultaneously with a single i.v. bolus of either 1 microg/kg adrenaline or saline. Both lungs were removed 5 min later. Adrenaline caused a significant 80% reduction in the total number of lung CFSE-labeled MADB106 tumor cells, suggesting a rapid modulation of metastasis by stress hormones. This new approach facilitates the monitoring of effector-to-target interactions and the quantification of immune cell function or tumor adhesion in vivo and in situ.

Facts and fictions regarding post-natal neurogenesis in the developing human cerebral cortex

In a recent paper (Shankle et al., 1998a), post-natal neurogenesis in the human cerebral cortex was discussed. Based on re-calculations of morphometric data from the literature, the authors concluded an average 1.1% monthly increase in post-natal cortical neuron number between post-natal months 15-72. The present paper makes clear by discussing four main assumptions done by Shankle et al., i.e. shrinkage of the tissue, morphometric features of the neurons under study, conversion of cell densities per area to number per unit volume and estimation of coefficients of variation, that their final conclusion about an increase in neuron number is unsound. Furthermore, five points are discussed here that Shankle et al. had mentioned in order to demonstrate that the pulse thymidine labeling method is less reliable than some have assumed. The present paper refute these assumptions point by point. Thus, the Shankle et al. paper does not provide scientifically valid evidence of a post-natal neurogenesis in the developing human cerebral cortex.

Neuron loss in the mouse hippocampus following prenatal injection of tritiated thymidine or saline

To investigate possible effects of injections of tritiated thymidine ([3H]dThd) into pregnant mice or the injection procedure itself on the proliferation of neuronal precursor cells in the fetuses, pregnant mice received intraperitoneal injections of either [3H]dThd or saline on embryonic days 12, 14, and 19, while their offspring remained untreated. A second group of dams was not injected but their male offspring received a subcutaneous injection of again either [3H]dThd or saline on postnatal day 10. Then total numbers of hippocampal pyramidal cells (areas CA1 to CA3) and granular cells (dentate gyrus) were determined stereologically for 20-day-old as well as for 80-day-old male pups. No significant differences were found for the mean total number of pyramidal cells between the investigated groups of pups. However, the mean total number of granular cells was significantly reduced in those groups in which the dams had received an intraperitoneal injection, irrespective of whether [3H]dThd or saline was injected. This revives the repeated warning in the literature to consider the effect of the injection procedure on the developing brain when interpreting possible effects of agents administered during pregnancy.