Use of cryostat sections from snap-frozen nervous tissue for combining stereological estimates with histological, cellular, or molecular analyses on adjacent sections

Basic quantitative morphological methods applied to the central nervous system

Generating numbers has become an almost inevitable task associated with studies of the morphology of the nervous system. Numbers serve a desire for clarity and objectivity in the presentation of results and are a prerequisite for the statistical evaluation of experimental outcomes. Clarity, objectivity, and statistics make demands on the quality of the numbers that are not met by many methods. This review provides a refresher of problems associated with generating numbers that describe the nervous system in terms of the volumes, surfaces, lengths, and numbers of its components. An important aim is to provide comprehensible descriptions of the methods that address these problems. Collectively known as design‐based stereology, these methods share two features critical to their application. First, they are firmly based in mathematics and its proofs. Second and critically underemphasized, an understanding of their mathematical background is not necessary for their informed and productive application. Understanding and applying estimators of volume, surface, length or number does not require more of an organizational mastermind than an immunohistochemical protocol. And when it comes to calculations, square roots are the gravest challenges to overcome. Sampling strategies that are combined with stereological probes are efficient and allow a rational assessment if the numbers that have been generated are “good enough.” Much may be unfamiliar, but very little is difficult. These methods can no longer be scapegoats for discrepant results but faithfully produce numbers on the material that is assessed. They also faithfully reflect problems that associated with the histological material and the anatomically informed decisions needed to generate numbers that are not only valid in theory. It is within reach to generate practically useful numbers that must integrate with qualitative knowledge to understand the function of neural systems.

Effects of Umbilical Cord Occlusion in Late Gestation on the Ovine Fetal Brain and Retina

OBJECTIVE

Previous studies on the effects of umbilical cord occlusion (UCO) on the fetal brain have focused on short-term alterations, and in most cases have used only subjective techniques to evaluate brain injury. Our aim was to assess quantitatively the persistent consequences of UCO on the developing brain; we also examined the retina.

METHODS

We subjected fetal sheep to a single episode of UCO at 126 days of gestation (term approximately 147 days) to induce at least 10 minutes of isoelectric fetal electrocorticogram (ECoG).

RESULTS

UCO resulted in fetal asphyxia and transient mild alterations in fetal mean arterial pressure (MAP). UCO did not result in significant injury to the developing brain or retina when assessed 15 days after the insult. There was no change in the endogenous expression of brain-derived neurotrophic factor (BDNF) protein in the hippocampus, nor was there a significant loss of CA1 hippocampal pyramidal cells. However, this insult did result in subtle neuropathologic alterations in the brain, including a reduction in the weight of the cerebral hemispheres, an increase in the areal density of cerebellar Purkinje cells, and enlarged perivascular spaces around blood vessels and inflammatory cells in the cerebral white matter. UCO did not affect the thickness of the central or peripheral retina or the numbers of retinal dopaminergic, cholinergic, and nitrergic amacrine cells.

CONCLUSIONS

Thus, while 10 minutes of UCO did not result in overt injury to the fetal brain or retina, the observed changes in the fetal brain suggest altered growth of neural processes, which may contribute to neurologic deficits postnatally or to increased vulnerability of the brain to later insults during either the remainder of gestation or after birth.

A novel approach for integrative studies on neurodegenerative diseases in human brains

Despite a massive research effort to elucidate Alzheimer's disease (AD) in recent decades, effective treatment remains elusive. This failure may relate to an oversimplification of the pathogenic processes underlying AD and also lack of understanding of AD progression during its long latent stages. Although evidence shows that the two specific neuropathological hallmarks in AD (neuronal loss and protein accumulation), which are opposite in nature, do not progress in parallel, the great majority of studies have focused on only one of these aspects. Furthermore, research focusing on single structures is likely to render an incomplete picture of AD pathogenesis because as AD involves complete brain networks, potential compensatory mechanisms within the network may ameliorate impairment of the system to a certain extent. Here, we describe an approach for enabling integrative analysis of the dual-nature lesions, simultaneously, in all components of one of the brain networks most vulnerable to AD. This approach is based on significant development of methods previously described mainly by our group that were optimized and complemented for this study. It combines unbiased stereology with immunohistochemistry and immunofluorescence, making use of advanced graphics computing for three-dimensional (3D) volume reconstructions. Although this study was performed in human brainstem and focused in AD, it may be applied to the study of any neurological disease characterized by dual-nature lesions, in humans and animal models. This approach does not require a high level of investment in new equipment and a significant number of specimens can be processed and analyzed within a funding cycle.

Spiral and vestibular ganglion estimates in archival temporal bones obtained by design based stereology and Abercrombie methods

The objective of this study was to make direct comparisons of the estimates of spiral and vestibular neuronal number in human archival temporal bone specimens using design-based stereology with those using the assumption-based Abercrombie method. Archival human temporal bone specimens from subjects ranging in age from 16 to 80 years old were used. The number of spiral and vestibular ganglia neurons within the counting areas was estimated using the stereology-optical disector technique and compared with estimates obtained using the assumption-based Abercrombie method on the same specimens. Using the optical disector method, there was an average of 41,480 (coefficient of variation=0.12) spiral ganglia neurons and 28,930 (coefficient of variation=0.15) vestibular ganglia neurons. The mean coefficient of error was 0.076 for the spiral ganglion estimates, and 0.091 for the vestibular ganglion estimates. Using the Abercrombie correction method of two-dimensional analysis, an average of 23,110 (coefficient of variation of 0.08) spiral ganglia neurons, and 16,225 vestibular ganglia neurons (coefficient of variation of 0.15) was obtained. We found that there was a large disparity between the estimates with a significant 44% underestimation of the spiral and vestibular ganglion counts obtained using the Abercrombie method when compared with estimates using the optical disector method.

Histological asymmetry of the human recurrent laryngeal nerve

Histological studies of the human recurrent laryngeal nerves (RLNs) have described differences in fiber length and thickness between the right and left RLNs. This asymmetry is probably involved in the different times of arrival of the stimuli to the laryngeal musculature controlled by each nerve. Histological and structural differences between the right and left RLNs could explain the synchronicity of laryngeal musculature contraction despite the differing nerve lengths. The purpose of this investigation was to shed some light on this paradigm by obtaining estimates of some morphometric parameters, such as intraperineural area, intraperineural perimeter, fiber area, fiber perimeter, fiber density (number of fibers/mm(2)), and total number of fibers in the right and left RLN of humans. Thus, the right and left RLNs were studied in a total sample of eight human specimens obtained from necropsies. The nerves were analyzed using histology, and the morphometric parameters were measured using Image Pro Plus Software 4.1 (Media Cybernetics, Silver Spring, MD, USA). No statistical differences between the two RLNs were observed in the intraperineural area, intraperineural perimeter, density (number of fibers/mm(2)), and total number of fibers. However, the area and perimeter of fibers of the right RLN were statistically larger when compared with those of the left RLN--21% and 11%, respectively. In conclusion, we show that in humans, the area and perimeter of the right RLN are larger than those of the left RLN. This morphological finding is probably related to the different time of arrival of the stimulus to the laryngeal musculature.

Total number and volume of Von Economo neurons in the cerebral cortex of cetaceans

Von Economo neurons (VENs) are a type of large, layer V spindle-shaped neurons that were previously described in humans, great apes, elephants, and some large-brained cetaceans. Here we report the presence of Von Economo neurons in the anterior cingulate (ACC), anterior insular (AI), and frontopolar (FP) cortices of small odontocetes, including the bottlenose dolphin (Tursiops truncatus), the Risso's dolphin (Grampus griseus), and the beluga whale (Delphinapterus leucas). The total number and volume of VENs and the volume of neighboring layer V pyramidal neurons and layer VI fusiform neurons were obtained by using a design-based stereologic approach. Two humpback whale (Megaptera novaeangliae) brains were investigated for comparative purposes as representatives of the suborder Mysticeti. Our results show that the distribution of VENs in these cetacean species is comparable to that reported in humans, great apes, and elephants. The number of VENs in these cetaceans is also comparable to data available from great apes, and stereologic estimates indicate that VEN volume follows in these cetacean species a pattern similar to that in hominids, the VENs being larger than neighboring layer V pyramidal cells and conspicuously larger than fusiform neurons of layer VI. The fact that VENs are found in species representative of both cetacean suborders in addition to hominids and elephants suggests that these particular neurons have appeared convergently in phylogenetically unrelated groups of mammals possibly under the influence of comparable selective pressures that influenced specifically the evolution of cortical domains involved in complex cognitive and social/emotional processes.

Quantitative assessment of relative changes of immunohistochemical staining by light microscopy in specified anatomical regions

Despite the advent of ever newer microscopic techniques for the study of the distribution of macromolecules in biological tissues, the enzyme-based immunohistochemical (IHC) methods are still used widely and routinely. However, the acquisition of reliable conclusions from the pattern of the reaction products of IHC procedures is hindered by the regular need for subjective judgments, in view of frequent inconsistencies in staining intensity from section to section or in repeated experiments. Consequently, when numerical comparisons are required, light microscopic morphological descriptions are commonly supplemented with analytical data (e.g. from Western blot analyses); however, these cannot be directly associated with accurate structural information and can easily be contaminated with data from outside the region of interest. Alternatively, to eliminate the more or less subjective evaluation of the results of IHC staining, procedures should be developed that correct for the variability of staining through the use of objective criteria. This paper describes a simple procedure, based on digital image analysis methods and the use of an internal reference area on the analyzed sections, that reduces the operator input and hence subjectivity, and makes the relative changes in IHC staining intensity in different experiments comparable. The reference area is situated at a position of the section that is not affected by the experimental treatment, or a disease condition, and that can therefore be used to specify the baseline of the IHC staining. Another source of staining variability is the internal heterogeneity of the object to be characterized, which means that identical fields can never be analyzed. To compensate for this variability, details are given of a systematic random sampling paradigm, which provides simple numerical data describing the extent and strength of IHC staining throughout the entire volume to be characterized. In this integrated approach, the figures are derived by pooling relative IHC staining intensities from all sections of the series from a particular animal. The procedure (1) eliminates the problem arising from the personal assessment of the significance of the IHC staining intensity, (2) does not depend on the precise dissection of the tissue on a gross scale and (3) considerably reduces the consequences of limited, arbitrary sampling of the region of interest for IHC analysis. The quantification procedure is illustrated by data from an experiment in which inflammatory reactions in the murine spinal cord, measured as microglial activation, were followed by IHC after the lesion of the sciatic nerve.

Effect of gestational ethanol exposure on parvalbumin and calretinin expressing hippocampal neurons in a chick model of fetal alcohol syndrome

Fetal alcohol syndrome (FAS), a condition occurring in some children of mothers who have consumed alcohol during pregnancy, is characterized by physical deformities and learning and memory deficits. The chick hippocampus, whose functions are controlled by interneurons expressing calcium-binding proteins parvalbumin (PV) and calretinin (CR), is involved in learning and memory mechanisms. Effects on growth and development and hippocampal morphology were studied in chick embryos exposed to 5% and 10% ethanol volume/volume (vol/vol) for 2 or 8 days of gestation. There was a significant dose-dependent reduction (P<.05) in body weight and mean number per section of PV and CR expressing hippocampal neurons in ethanol-exposed chicks, without alterations in neuronal nuclear size or hippocampal volume, compared appropriate controls. Moreover, when chicks exposed to 5% ethanol for 2 and 8 days of gestation were compared, no significant differences were found in body parameters or neuronal counts. Similarly, exposure to 10% ethanol did not induce any significant changes in chicks exposed for 2 or 8 gestational days. Thus, these results suggest that gestational ethanol exposure induces a reduction in the mean number per section of PV and CR expressing hippocampal neurons, and could be a possible mechanism responsible for learning and memory disorders in FAS.

Exposure to Altered Gravity During Specific Developmental Periods Differentially Affects Growth, Development, the Cerebellum and Motor Functions in Male and Female Rats

We previously reported that perinatal exposure to hypergravity affects cerebellar structure and motor coordination in rat neonates. In the present study, we explored the hypothesis that neonatal cerebellar structure and motor coordination may be particularly vulnerable to the effects of hypergravity during specific developmental stages. To test this hypothesis, we compared neurodevelopment, motor behavior and cerebellar structure in rat neonates exposed to 1.65 G on a 24-ft centrifuge during discrete periods of time: the 2(nd) week of pregnancy [gestational day (G) 8 through G15; group A], the 3(rd) week of pregnancy (G15 through birth on G22/G23; group B), the 1(st) week of nursing [birth through postnatal day (P) 6; group C], the 2(nd) and 3(rd) weeks of nursing (P6 through P21; group D), the combined 2(nd) and 3(rd) weeks of pregnancy and nursing (G8 through P21; group E) and stationary control (SC) neonates (group F). Prenatal exposure to hypergravity resulted in intrauterine growth retardation as reflected by a decrease in the number of pups in a litter and lower average mass at birth. Exposure to hypergravity immediately after birth impaired the righting response on P3, while the startle response in both males and females was most affected by exposure during the 2(nd) and 3(rd) weeks after birth. Hypergravity exposure also impaired motor functions, as evidenced by poorer performance on a rotarod; while both males and females exposed to hypergravity during the 2(nd) and 3(rd) weeks after birth performed poorly on P21, male neonates were most dramatically affected by exposure to hypergravity during the second week of gestation, when the duration of their recorded stay on the rotarod was one half that of SC males. Cerebellar mass was most reduced by later postnatal exposure. Thus, for the developing rat cerebellum, the postnatal period that overlaps the brain growth spurt is the most vulnerable to hypergravity. However, male motor behavior is also affected by midpregnancy exposure to hypergravity, suggesting discrete and sexually dimorphic windows of vulnerability of the developing central nervous system to environmental perturbations.

Two distinct events, section compression and loss of particles (“lost caps”), contribute toz-axis distortion and bias in optical disector counting

Deformation of tissue sections in the z-axis can bias optical disector counting. When samples of particle densities are not representative for the entire tissue section, significant bias of estimated numbers can result. To assess the occurrence, prevalence, extent, sequence of events, and causes of z-axis distortion, the distribution of neuronal nucleoli in thick paraffin and vibratome sections was determined in chicken, rodent, and human brain tissues. When positions of neuronal nucleoli were measured in the z-axis, nucleoli were more frequent at the surfaces (bottom and top) of tissue sections than in the core. This nonlinear z-axis distribution was not lab-, equipment-, or investigator-specific, and was independent of age, fixation quality, coverslipping medium, or paraffin melting temperature, but in paraffin sections, was highly correlated with the tilt of the knife (cutting) angle. Manipulation of subsequent tissue processing steps revealed that two events contribute to z-axis distortion. Initially, a higher density of particles results at surfaces after sectioning, apparently due to section compression. Subsequently, particles can be lost to varying degrees from surfaces during floating or staining and dehydration, resulting in "lost caps." These results may explain different degrees of z-axis distortion between different types of sections and different labs, and reinforce the importance of checking z-axis distributions as a "quality control" prior to selection of guard zones in optical disector counting. Indirect approaches to assess section quality, such as resectioning in a perpendicular plane, yield additional artifacts, and should be replaced by a direct quantitative measurement of z-axis distribution of particles.

Perinatal exposure to polychlorinated biphenyls differentially affects cerebellar development and motor functions in male and female rat neonates

Perinatal exposure to polychlorinated biphenyls (PCBs) interacts with genetics and impacts the course of the central nervous system (CNS) development in both humans and animals. To test the hypothesis that the neurobehavioral impairments, and specifically motor dysfunctions following perinatal PCB exposure in rats are associated with changes in a specific brain region, the cerebellum, we compared neurodevelopment, motor behavior, cerebellar structure, and protein expression in rat neonates exposed to the PCB mixture Aroclor 1254 (A1254, 10.0 mg/kg/day) from gestational day 11 until postnatal day (P) 21 with that of controls. Body mass of PCB-exposed pups was not affected at birth, but was significantly lower than that of controls between birth and weaning; by P21 the difference was greater in females than in males. A1254 exposure delayed ear unfolding and impaired performance on the following behavioral tests: (1) righting response on P3-P6; (2) negative geotaxis on P5-P7; (3) startle response on P10-P12; and (4) a rotorod on P12, with PCB-male pups more severely affected than female. Changes in the behavior of PCB pups were associated with changes in cerebellar structure and protein expression. Cerebellar mass was more reduced in PCB-male than PCB-female pups. Analysis of selected cerebellar proteins revealed an increase in GFAP expression, greater in male than in female, and a decrease in L1 expression in both sexes. These results suggest that PCB exposure affects behavior and cerebellar development differently in male and female rat neonates, with greater effects in males. Further studies of neonatal PCB exposure will establish whether the environmental pollutants can contribute to the sex-related preponderance of certain neuropsychiatric disorders.

Design-based stereology in neuroscience

Quantitative morphology of the CNS has recently undergone major developments. In particular, several new approaches, known as design-based stereologic methods, have become available and have been successfully applied to neuromorphological research. However, much confusion and uncertainty remains about the meaning, implications, and advantages of these design-based stereologic methods. The objective of this review is to provide some clarification. It does not comprise a full description of all stereologic methods available. Rather, it is written by users for users, provides the reader with a guided tour through the relevant literature. It has been the experience of the authors that most neuroscientists potentially interested in design-based stereology need to analyze volumes of brain regions, numbers of cells (neurons, glial cells) within these brain regions, mean volumes (nuclear, perikaryal) of these cells, length densities of linear biological structures such as vessels and nerve fibers within brain regions, and the cytoarchitecture of brain regions (i.e. the spatial distribution of cells within a region of interest). Therefore, a comprehensive introduction to design-based stereologic methods for estimating these parameters is provided. It is demonstrated that results obtained with design-based stereology are representative for the entire brain region of interest, and are independent of the size, shape, spatial orientation, and spatial distribution of the cells to be investigated. Also, it is shown that bias (i.e. systematic error) in results obtained with design-based stereology can be limited to a minimum, and that it is possible to assess the variability of these results. These characteristics establish the advantages of design-based stereologic methods in quantitative neuromorphology.

Prenatal protracted irradiation at very low dose rate induces severe neuronal loss in rat hippocampus and cerebellum

Prenatal irradiation is known to damage the developing brain. However, little is known about the consequences of very low dose rate prenatal protracted irradiation over several days on neuron numbers in the offspring brain, and on volumes of the corresponding brain regions. Pregnant Wistar rats were exposed either to a protracted gamma irradiation from embryonic day (E) 13 to E16 (0.7 mGy/min; total cumulative dose approximately 3 Gy) or were sham-irradiated. Thirty months old male and female offspring were then analyzed for alterations in hippocampal and cerebellar morphology. Using design-based stereology and the analysis of sets of sections systematically and randomly sampled to span the entire brain region of interest, a statistically significant decrease in numbers of hippocampal pyramidal and granule cells as well as of cerebellar Purkinje and granule cells (approximately 50%) was found in male and female irradiated offspring. The volumes of these brain regions were comparably altered. The analysis of only a "representative" section per animal yielded mostly non-significant trends. Evaluation of neuron densities showed no differences between prenatally irradiated and sham-irradiated offspring. Most importantly, very low dose rate prenatal protracted gamma irradiation did not result in the same morphologic alterations in the offspring brain as previously observed after prenatal single irradiation such as derangement of the laminar structure of pyramidal cells within the hippocampus or malformation of cerebellar lobules.

Hippocampal mossy fibre terminal field size is differentially affected in a rat model of risk-taking behaviour

Individual differences in novelty-induced exploratory activity identify rats which can serve as a model of human sensation-seeking, risk-taking behaviour. Experimentally naïve rats, when exposed to mild stress of a novel environment, exhibit variability in their exploratory activity. Some rats display high rates of locomotor reactivity to novelty (high responders (HR)), and others display low rates (low responders (LR)). The LRHR phenotype is a reliable predictor of drug-taking behaviour and is linked to differences in hippocampal glucocorticoid receptor mRNA expression. In this study, we investigated whether the LRHR phenotype is associated with differences in the quantitative morphology of the hippocampal field CA3, dentate gyrus molecular layer, granule cell layer and mossy fibres. LRs and HRs showed no significant differences in the volumes of CA3 and dentate molecular layer volume or the number of dentate granule cells. However, LRs had a significantly larger suprapyramidal mossy fibre terminal field volume when compared to HRs. The infrapyramidal mossy fibres did not differ between phenotypes. Also, we found a LRHR phenotype-independent significant negative correlation between molecular layer volume per granule cell and the total number of granule cells. These findings implicate the SP-MF in vulnerability for risk-taking behaviour, and we propose that LR and HR hippocampi may differ in the way novelty information is processed.

A stereological approach to human cortical architecture: identification and delineation of cortical areas

Stereology offers a variety of procedures to analyze quantitatively the regional and laminar organization in cytoarchitectonically defined areas of the human cerebral cortex. Conventional anatomical atlases are of little help in localizing specific cortical areas, since most of them are based on a single brain and use highly observer-dependent criteria for the delineation of cortical areas. In consequence, numerous cortical maps exist which greatly differ with respect to number, position, size and extent of cortical areas. We describe a novel algorithm-based procedure for the delineation of cortical areas, which exploits the automated estimation of volume densities of cortical cell bodies. Spatial sampling of the laminar pattern is performed with density profiles, followed by multivariate analysis of the profiles' shape, which locates the cytoarchitectonic borders between neighboring cortical areas at sites where the laminar pattern changes significantly. The borders are then mapped to a human brain atlas system comprising tools for three dimensional reconstruction, visualization and morphometric analysis. A sample of brains with labeled cortical areas is warped into the reference brain of the atlas system in order to generate a population map of the cortical areas, which describes the intersubject variability in spatial conformation of cortical areas. These population maps provide a novel tool for the interpretation of images obtained with functional imaging techniques.