Estimating the number of granule cells in the dentate gyrus with the disector

Purkinje cell-specific deletion of CREB worsens alcohol-induced cerebellar neuronal losses and motor deficits

INTRODUCTION

Exposure to alcohol during pregnancy can kill developing fetal neurons and lead to fetal alcohol spectrum disorder (FASD) in the offspring. However, not all fetuses are equally vulnerable to alcohol toxicity. These differences in vulnerability among individuals are likely due, at least in part, to genetic differences. Some genes encode neuroprotective molecules that act through signaling pathways to protect neurons against alcohol's toxic effects. One signaling pathway that can protect cultured neurons against alcohol-induced cell death in vitro is the cAMP pathway. A goal of this study was to determine whether the cAMP pathway can exert a similar neuroprotective effect against alcohol in vivo. A key molecule within the cAMP pathway is cAMP response element binding protein (CREB). In this study, CREB was specifically disrupted in cerebellar Purkinje cells to study its role in protection of cerebellar neurons against alcohol toxicity.

METHODS

Mice with Purkinje cell-specific knockout of CREB were generated with the Cre-lox system. A 2 × 2 design was used in which Cre-negative and Cre-positive mice received either 0.0 or 2.2 mg/g ethanol by intraperitoneal (i.p.) injection daily over postnatal day (PD) 4-9. Stereological cell counts of cerebellar Purkinje cells and granule cells were performed on PD 10. Motor function was assessed on PD 40 using the rotarod.

RESULTS

Purkinje cell-specific disruption of CREB alone (in the absence of alcohol) induced only a small reduction in Purkinje cell number. However, the loss of CREB function from Purkinje cells greatly increased the vulnerability of Purkinje cells to alcohol-induced cell death. While alcohol killed 20% of Purkinje cells in the Cre-negative (CREB-expressing) mice, alcohol killed 57% of Purkinje cells in the Cre-positive (CREB-nonexpressing) mice. This large loss of Purkinje cells did not lead to similar alcohol-induced losses of granule cells. In the absence of alcohol, lack of CREB function in Purkinje cells had no effect on rotarod performance. However, in the presence of alcohol, disruption of CREB in Purkinje cells substantially worsened rotarod performance.

DISCUSSION

Disruption of a single gene (CREB) in a single neuronal population (Purkinje cells) greatly increases the vulnerability of that cell population to alcohol-induced cell death and worsens alcohol-induced brain dysfunction. The results suggest that the cAMP pathway can protect cells in vivo against alcohol toxicity and underline the importance of genetics in determining the neuropathology and behavioral deficits of FASD.

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.

Regional Patterns of Alcohol-Induced Neuronal Loss Depend on Genetics: Implications for Fetal Alcohol Spectrum Disorder

BACKGROUND

Alcohol exposure during pregnancy can kill developing neurons and lead to fetal alcohol spectrum disorder (FASD). However, affected individuals differ in their regional patterns of alcohol-induced neuropathology. Because neuroprotective genes are expressed in spatially selective ways, their mutation could increase the vulnerability of some brain regions, but not others, to alcohol teratogenicity. The objective of this study was to determine whether a null mutation of neuronal nitric oxide synthase (nNOS) can increase the vulnerability of some brain regions, but not others, to alcohol-induced neuronal losses.

METHODS

Immunohistochemistry identified brain regions in which nNOS is present or absent throughout postnatal development. Mice genetically deficient for nNOS (nNOS^-/- ) and wild-type controls received alcohol (0.0, 2.2, or 4.4 mg/g/d) over postnatal days (PD) 4 to 9. Mice were sacrificed in adulthood (~PD 115), and surviving neurons in the olfactory bulb granular layer and brain stem facial nucleus were quantified stereologically.

RESULTS

nNOS was expressed throughout postnatal development in olfactory bulb granule cells but was never expressed in the facial nucleus. In wild-type mice, alcohol reduced neuronal survival to similar degrees in both cell populations. However, null mutation of nNOS more than doubled alcohol-induced cell death in the olfactory bulb granule cells, while the mutation had no effect on the facial nucleus neurons. As a result, in nNOS^-/- mice, alcohol caused substantially more cell loss in the olfactory bulb than in the facial nucleus.

CONCLUSIONS

Mutation of the nNOS gene substantially increases vulnerability to alcohol-induced cell loss in a brain region where the gene is expressed (olfactory bulb), but not in a separate brain region, where the gene is not expressed (facial nucleus). Thus, differences in genotype may explain why some individuals are vulnerable to FASD, while others are not, and may determine the specific patterns of neuropathology in children with FASD.

Hippocampal mechanisms in impaired spatial learning and memory in male offspring of rats fed a low-protein isocaloric diet in pregnancy and/or lactation

Maternal nutritional challenges during fetal and neonatal development result in developmental programming of multiple offspring organ systems including brain maturation and function. A maternal low-protein diet during pregnancy and lactation impairs associative learning and motivation. We evaluated effects of a maternal low-protein diet during gestation and/or lactation on male offspring spatial learning and hippocampal neural structure. Control mothers (C) ate 20% casein and restricted mothers (R) 10% casein, providing four groups: CC, RR, CR, and RC (first letter pregnancy, second lactation diet). We evaluated the behavior of young adult male offspring around postnatal day 110. Corticosterone and ACTH were measured. Males were tested for 2 days in the Morris water maze (MWM). Stratum lucidum mossy fiber (MF) area, total and spine type in basal dendrites of stratum oriens in the hippocampal CA3 field were measured. Corticosterone and ACTH were higher in RR vs. CC. In the MWM acquisition test CC offspring required two, RC three, and CR seven sessions to learn the maze. RR did not learn in eight trials. In a retention test 24 h later, RR, CR, and RC spent more time locating the platform and performed fewer target zone entries than CC. RR and RC offspring spent less time in the target zone than CC. MF area, total, and thin spines were lower in RR, CR, and RC than CC. Mushroom spines were lower in RR and RC than CC. Stubby spines were higher in RR, CR, and RC than CC. We conclude that maternal low-protein diet impairs spatial acquisition and memory retention in male offspring, and that alterations in hippocampal presynaptic (MF), postsynaptic (spines) elements and higher glucocorticoid levels are potential mechanisms to explain these learning and memory deficits.

Re-evaluating the link between neuropsychiatric disorders and dysregulated adult neurogenesis

People diagnosed with neuropsychiatric disorders such as depression, anxiety, addiction or schizophrenia often have dysregulated memory, mood, pattern separation and/or reward processing. These symptoms are indicative of a disrupted function of the dentate gyrus (DG) subregion of the brain, and they improve with treatment and remission. The dysfunction of the DG is accompanied by structural maladaptations, including dysregulation of adult-generated neurons. An increasing number of studies using modern inducible approaches to manipulate new neurons show that the behavioral symptoms in animal models of neuropsychiatric disorders can be produced or exacerbated by the inhibition of DG neurogenesis. Thus, here we posit that the connection between neuropsychiatric disorders and dysregulated DG neurogenesis is beyond correlation or epiphenomenon, and that the regulation of adult-generated DG neurogenesis merits continued and focused attention in the ongoing effort to develop novel treatments for neuropsychiatric disorders.

Corruption of the dentate gyrus by "dominant" granule cells: Implications for dentate gyrus function in health and disease

The dentate gyrus (DG) and area CA3 of the hippocampus are highly organized lamellar structures which have been implicated in specific cognitive functions such as pattern separation and pattern completion. Here we describe how the anatomical organization and physiology of the DG and CA3 are consistent with structures that perform pattern separation and completion. We then raise a new idea related to the complex circuitry of the DG and CA3 where CA3 pyramidal cell 'backprojections' play a potentially important role in the sparse firing of granule cells (GCs), considered important in pattern separation. We also propose that GC axons, the mossy fibers, already known for their highly specialized structure, have a dynamic function that imparts variance--'mossy fiber variance'--which is important to pattern separation and completion. Computational modeling is used to show that when a subset of GCs become 'dominant,' one consequence is loss of variance in the activity of mossy fiber axons and a reduction in pattern separation and completion in the model. Empirical data are then provided using an example of 'dominant' GCs--subsets of GCs that develop abnormally and have increased excitability. Notably, these abnormal GCs have been identified in animal models of disease where DG-dependent behaviors are impaired. Together these data provide insight into pattern separation and completion, and suggest that behavioral impairment could arise from dominance of a subset of GCs in the DG-CA3 network.

Genetic absence of nNOS worsens fetal alcohol effects in mice. II: microencephaly and neuronal losses

BACKGROUND

Prenatal alcohol exposure can kill developing neurons, leading to microencephaly and mental retardation. However, not all fetuses are equally vulnerable to alcohol's neurotoxic effects. While some fetuses are severely affected and are ultimately diagnosed with fetal alcohol syndrome (FAS), others have no evidence of neuropathology and are behaviorally normal. These widely different outcomes among alcohol-exposed fetuses are likely due, in part, to genetic differences. Some fetuses possess genotypes that make them much more vulnerable than others to alcohol's teratogenic effects. However, to date, only 1 gene has been identified whose mutation can worsen alcohol-induced behavioral deficits in an animal model of FAS. That gene is neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine whether mutation of nNOS can likewise worsen alcohol-induced microencephaly and lead to permanent neuronal deficits.

METHODS

Wild-type and nNOS(-/-) mice received alcohol (0.0, 2.2, or 4.4 mg/g) daily over postnatal days (PDs) 4 to 9. Beginning on PD 85, the mice underwent a series of behavioral tests; the results of which are reported in the companion paper. The brains were then weighed, and stereological cell counts were performed on the cerebral cortex and hippocampal formation, which are the brain regions that mediate the aforementioned behavioral tasks.

RESULTS

Alcohol caused dose-dependent microencephaly, but only in the nNOS(-/-) mice and not in wild-type mice. Alcohol-induced neuronal losses were more severe in the nNOS(-/-) mice than in the wild-type mice in all of the brain regions examined, including the cerebral cortex, hippocampal CA3 subregion, hippocampal CA1 subregion, and dentate gyrus.

CONCLUSIONS

Targeted mutation of the nNOS gene increases the vulnerability of the developing brain to alcohol-induced growth restriction and neuronal losses. This increased neuropathology is associated with worsened behavioral dysfunction. The results demonstrate the critical importance of genotype in determining the outcome of developmental alcohol exposure.

Synaptic alterations in the rTg4510 mouse model of tauopathy

Synapse loss, rather than the hallmark amyloid-β (Aβ) plaques or tau-filled neurofibrillary tangles (NFT), is considered the most predictive pathological feature associated with cognitive status in the Alzheimer's disease (AD) brain. The role of Aβ in synapse loss is well established, but despite data linking tau to synaptic function, the role of tau in synapse loss remains largely undetermined. Here we test the hypothesis that human mutant P301L tau overexpression in a mouse model (rTg4510) will lead to age-dependent synaptic loss and dysfunction. Using array tomography and two methods of quantification (automated, threshold-based counting and a manual stereology-based technique) we demonstrate that overall synapse density is maintained in the neuropil, implicating synapse loss commensurate with the cortical atrophy known to occur in this model. Multiphoton in vivo imaging reveals close to 30% loss of apical dendritic spines of individual pyramidal neurons, suggesting these cells may be particularly vulnerable to tau-induced degeneration. Postmortem, we confirm the presence of tau in dendritic spines of rTg4510-YFP mouse brain by array tomography. These data implicate tau-induced loss of a subset of synapses that may be accompanied by compensatory increases in other synaptic subtypes, thereby preserving overall synapse density. Biochemical fractionation of synaptosomes from rTg4510 brain demonstrates a significant decrease in expression of several synaptic proteins, suggesting a functional deficit of remaining synapses in the rTg4510 brain. Together, these data show morphological and biochemical synaptic consequences in response to tau overexpression in the rTg4510 mouse model.

Effect of 17ß-estradiol on zinc content of hippocampal mossy fibers in ovariectomized adult rats

Sex hormones such as estrogen (17ß-estradiol) may modulate the zinc content of the hippocampus during the female estrous cycle. The mossy fiber system is highly plastic in the adult brain and is influenced by multiple factors including learning, memory, and stress. However, whether 17ß-estradiol is able to modulate the morphological plasticity of the mossy fibers throughout the estrous cycle remains unknown. Ovariectomized (Ovx) female 70- to 90-day-old Sprague-Dawley rats without or with estrogen supplement (OvxE) were compared with control rats in three stages of the estrous cycle: diestrus, proestrus, and estrus. The brain tissue from each of the five groups was processed with Timm's silver sulfide technique using the Image J program to measure the mossy fiber area in the stratum lucidum of CA3. Total zinc in the hippocampus was measured using Graphite Furnace Atomic Absorption Spectrophotometry. Two additional (Ovx and OvxE) groups were examined in spatial learning and memory tasks using the Morris water maze. Similar increases in total zinc content and mossy fiber area were observed. The mossy fiber area decreased by 26 ± 2 % (difference ± SEM percentages) in Ovx and 23 ± 4 % in estrus as compared to the proestrus group and by 18 ± 2 % in Ovx compared to OvxE. Additionally, only the OvxE group learned and remembered the task. These results suggest that estradiol has a significant effect on zinc content in hippocampal CA3 during the proestrus stage of the estrous cycle and is associated with correct performance in learning and memory.

The appropriateness of unbiased optical fractionators to assess cell proliferation in the adult hippocampus

Optical fractionators have dominated the field of neural cell counting for two decades. These unbiased stereological techniques are often used for the quantification of hippocampal cell proliferation in neurogenesis experiments. However, the heterogeneous distribution of labeled cells, especially in the form of clusters, confounds the application of these techniques. A critical evaluation of the applicability of the optical fractionator suggests that absolute counting achieves higher efficiency in the quantification of cell proliferation than unbiased estimations.

Impact of environmental enrichment on neurogenesis in the dentate gyrus during the early postnatal period

Accumulating evidence shows that environmental enrichment increases neurogenesis in the adult hippocampal dentate gyrus. The goal of the current study was to examine the effect of environmental enrichment on hippocampal neurogenesis during early life stages. We used as an animal model the guinea pig, a precocious rodent that is early independent from maternal care. Animals were assigned to either a standard (control) or an enriched environment a few days after birth (P5-P6). Between P14 and P17 animals received one daily bromodeoxyuridine (BrdU) injection, to label dividing cells, and were sacrificed either on P18, to evaluate cell proliferation or on P45, to evaluate cell survival and differentiation. In 18-day old enriched animals, there was a larger number of BrdU-positive cells compared to that found in controls. At P45, enriched animals had more surviving cells and more cells with a neuronal phenotype than controls. Unbiased stereology revealed that enriched animals had more granule cells (+37% at P18 and +31% at P45). Results show that environmental enrichment in the early postnatal period notably increases cell proliferation and survival, with a large increase in the number of neurons forming the granule cell layer. The impact of environmental enrichment in the early postnatal period emphasizes the relevance of extrinsic factors in the modulation of neurogenesis during critical time windows of hippocampal development.

Three-dimensional relationships between perisynaptic astroglia and human hippocampal synapses

Perisynaptic astroglia are critical for normal synaptic development and function. Little is known, however, about perisynaptic astroglia in the human hippocampus. When mesial temporal lobe epilepsy (MTLE) is refractory to medication, surgical removal is required for seizure quiescence. To investigate perisynaptic astroglia in human hippocampus, we recovered slices for several hours in vitro from three surgical specimens and then quickly fixed them to achieve high-quality ultrastructure. Histological samples from each case were found to have mesial temporal sclerosis with Blumcke Type 1a (mild, moderate) or 1b (severe) pathology. Quantitative analysis through serial section transmission electron microscopy in CA1 stratum radiatum revealed more synapses in the mild (10/10 microm(3)) than the moderate (5/10 microm(3)) or severe (1/10 microm(3)) cases. Normal spines occurred in mild and moderate cases, but a few multisynaptic spines were all that remained in the severe case. Like adult rat hippocampus, perisynaptic astroglial processes were preferentially associated with larger synapses in the mild and moderate cases, but rarely penetrated the cluster of axonal boutons surrounding multisynaptic spines. Synapse perimeters were only partially surrounded by astroglial processes such that all synapses had some access to substances in the extracellular space, similar to adult rat hippocampus. Junctions between astroglial processes were observed more frequently in moderate than mild case, but were obscured by densely packed intermediate filaments in astroglial processes of the severe case. These findings suggest that perisynaptic astroglial processes associate with synapses in human hippocampus in a manner similar to model systems and are disrupted by severe MTLE pathology.

Septo-temporal gradients of neurogenesis and activity in 13-month-old rats

Recent studies suggest that hippocampal function is partially dissociable along its septo-temporal axis: the septal hippocampus is more critical for spatial processing, while the temporal hippocampus may be more important for non-spatial-related behavior. In young adults, water maze training specifically activates new neurons in the temporal hippocampus, but it is unknown whether subregional differences are maintained in older animals, which have reduced neurogenesis levels. We therefore examined gradients of activity-related Fos expression and neurogenesis in 13-month-old rats and found that neurogenesis occurs relatively evenly throughout the dentate gyrus. Water maze experience significantly increased Fos expression in the suprapyramidal blade and Fos was highest in the septal pole of the dentate gyrus whether the animal learned a platform location, swam in the absence of a platform or remained in their cage. No Fos+ young neurons were found using typical markers of immature neurons. However, Fos expression in the subgranular zone, where adult-born neurons predominate, was disproportionally high in the temporal dentate gyrus. These findings indicate that adult-born neurons in the temporal hippocampus are preferentially activated compared with older neurons.

Stereological estimation of gap junction surface area per neuron in the developing nervous system of the invertebrate Mesocestoides corti

As a major morphological feature in establishing the form of the nervous system, it is recognized that neurons are initially overproduced, then naturally occurring cell death reduces the neuron number to the functional requirement. However, the mechanisms controlling the selective elimination of certain neurons during a general phase of cell death are not fully understood. One event that seems to be pivotal is the establishment of neural connections, the degree of which may be influential regarding the fate of specific neurons. However, little quantitative evidence is available to either support or refute this theory. In this current study, a Stereological measurement of gap junction per neuron was carried out within the invertebrate model system of the tapeworm metacestode Mesocestoides corti, which has previously been shown to overproduce neurons during the asexual reproduction stage of its life-cycle. Novel Stereological estimation methods with ‘ vertical sections’ indicated that prior to asexual division the cerebral ganglion possessed approximately 268 neurons, each with a gap junction surface area of 250 μm2. As division progressed, the neuron number increased to approximately 700, while the total surface area of gap junction remained statistically unchanged. As a result the surface area of gap junction per neuron decreased to 106 μm2, less than half that in the undividing stage. These results provide the first non-biased quantitative data regarding changes in the mean surface area of gap junction per neuron in a developing cerebral ganglion.

A single exposure to alcohol during brain development induces microencephaly and neuronal losses in genetically susceptible mice, but not in wild type mice

Maternal alcohol abuse during pregnancy can damage the fetal brain and lead to fetal alcohol syndrome (FAS). Despite public warnings discouraging alcohol use during pregnancy, many pregnant women continue to drink intermittently because they do not believe that occasional exposures to alcohol can be harmful to a fetus. However, because of genetic differences, some fetuses are much more susceptible than others to alcohol-induced brain injury. Thus, a relatively low quantity of alcohol that may be innocuous to most fetuses could damage a genetically susceptible fetus. Neuronal nitric oxide synthase (nNOS) can protect developing mouse neurons against alcohol toxicity by synthesizing neuroprotective nitric oxide. This study examined whether a single exposure to alcohol, which causes no evident injury in wild type mice, can damage the brains of mice genetically deficient for nNOS (nNOS-/- mice). Wild type and nNOS-/- mice received intraperitoneal injections of alcohol (0.0, 2.2, or 4.4mg/g body weight) either as a single dose on postnatal day (PD) 4 or as repeated daily doses over PD4-9. Brain volumes and neuronal numbers within the hippocampus and cerebral cortex were determined on PD10. Alcohol exposure on PD4-9 restricted brain growth and caused neuronal death in both strains of mice, but the severity of microencephaly and neuronal loss were more severe in the nNOS-/- mice than in wild type. The 4.4 mg/g alcohol dose administered on PD4 alone caused significant neuronal loss and microencephaly in the nNOS-/- mice, while this same dose caused no evident injury in the wild type mice. Thus, during development, a single exposure to alcohol can injure a genetically vulnerable brain, while it leaves a wild type brain unaffected. Since the genes that confer alcohol resistance and vulnerability in developing humans are unknown, any particular human fetus is potentially vulnerable. Thus, women should be counseled to consume no alcohol during pregnancy.

Neocortical and hippocampal neuron and glial cell numbers in the rhesus monkey

The rhesus monkey is widely used as an experimental animal model in the study of brain function and disease. While previous quantitative studies have provided knowledge of regional numbers, little is known of the total neocortical neuron and glial cell numbers in this species. The aim of this study is to establish quantitative norms. We use the optical fractionator and Cavalieri principle to examine the right hemisphere of eight young rhesus monkeys taken from the control group of an ongoing study. Applying these methods to agar-embedded and vibratome-sectioned tissue, we generate estimates of cell numbers and regional volumes of neocortical and hippocampal regions with coefficients of variance (CV) around 10%. The mean unilateral neocortical neuron number is 1.35 x 10(9) (CV +/- 0.10) and the mean unilateral neocortical glial cell number is 0.78 x 10(9) (CV +/- 0.17). Mean unilateral neocortical volume is found to be 8.5 (CV +/- 0.10) cm(3) after processing, or 19 cm(3) when correcting for shrinkage. The neuron/glia ratio is 1.77. The neurons are distributed with 18% in the frontal cortex, 57% in the temporal and parietal cortices, and 25% in the occipital cortex. In the hippocampal subregions, we found unilateral neuron number of 1.72 x 10(6) (CV +/- 0.13) and glial number of 2.25 x 10(6) (CV +/- 0.17) in CA1, and 0.80 x 10(6) (CV +/- 0.27) neurons and 1.05 x 10(6) (CV +/- 0.26) glial cells in CA2-3. Comparisons with related studies show quantitative variation, but also variations in methods and applications. The results are phylogenetically consistent, apart from the neuron/glia ratio, which is remarkably higher than what is found in other species.

Design-based estimation of neuronal number and individual neuronal volume in the rat hippocampus

Tools recently developed in stereology were employed for unbiased estimation of the neuronal number and volume in three major subdivisions of rat hippocampus (dentate granular, CA1 and CA3 pyramidal layers). The optical fractionator is used extensively in quantitative studies of the hippocampus; however, the classical optical fractionator design may be affected by tissue deformation in the z-axis of the section. In this study, we applied an improved optical fractionator design to estimate total number of neurons on 100 microm thick vibratome sections that had been deformed, in the z-dimension, during histological processing. For estimating cell number, it is necessary to randomize only the location of section planes. But, in the local stereological methods, like cell volume estimation, the orientation of sections must also be randomized. We present a detailed application of a method for making vertical sections from the hippocampus. The volume of hippocampal neurons was estimated using the rotator principle on 40 microm thick plastic vertical uniform random sections and corrected for tissue shrinkage. Application of the proposed new design should result in more accurate estimates of neuron number and neuronal volumes in tissue sections affected by homogenous non-uniform shrinkage.

Severe alcohol-induced neuronal deficits in the hippocampus and neocortex of neonatal mice genetically deficient for neuronal nitric oxide synthase (nNOS)

Alcohol can severely damage the developing brain, and neuronal loss is a critical component of this injury. Thus, identification of molecular factors that ameliorate alcohol-induced neuronal loss is of great importance. Previous in vitro work has demonstrated that nitric oxide (NO) protects neurons against alcohol toxicity. We tested the hypothesis that neonatal mice carrying a null mutation for neuronal nitric oxide synthase (nNOS), the enzyme that synthesizes NO in neurons, have an increased vulnerability to alcohol-induced neuronal loss in the neocortex and hippocampus. Wildtype mice and nNOS-/- mice received ethanol (0.0, 2.2, 3.3, or 4.4 g/kg) daily over postnatal days (P) 4-9 and were sacrificed on P10. The number of hippocampal CA1 and CA3 pyramidal cells, dentate gyrus granule cells, and neocortical neurons were determined using stereological methods. Alcohol pharmacokinetics did not differ between wildtype and nNOS-/- strains. Alcohol induced dose-dependent reductions in all four neuronal populations, and the losses were substantially more severe in the nNOS-/- mice than in wildtype. Furthermore, the threshold dose of alcohol to induce cell death was lower in the nNOS-/- mice than in the wildtype mice for all neuronal populations. While nNOS deficiency worsened alcohol-induced neuronal losses, the magnitude of this exacerbation varied among brain regions and depended on alcohol dose. These results demonstrate that nNOS deficiency decreases the ability of developing neurons in vivo to survive the toxic effects of alcohol and strengthen the hypothesis that NO exerts a neuroprotective effect against alcohol toxicity in the developing brain.

Use of frozen sections to determine neuronal number in the murine hippocampus and neocortex using the optical disector and optical fractionator

Stereology is an important technique for the quantification of neurons in subregions of the central nervous system. A commonly used method of stereology relies upon embedment of tissue in glycol methacrylates to allow production of sections that are resistant to shrinkage in thickness. However, the use of glycol methacrylates for stereology has several disadvantages, including severe constraints on the size of tissue that can be processed and the long duration of time often required for infiltration. We describe a novel method of stereology utilizing tissue sections cut in the frozen state. This new methodology relies upon the staining of sections as free-floating sections and upon the mounting of these sections onto slides with a water-based mounting media. Sections cut in the frozen state and processed by these methods undergo little or no shrinkage in thickness and are ideal for stereological cell counts utilizing either the optical disector or optical fractionator methods of stereology. We demonstrate that frozen sections can be utilized to estimate neuronal number with high degrees of precision and with low coefficients of error. Because large tissue blocks can be cut as frozen sections, this method expands the range of tissues that can be processed efficiently for stereology and readily allows quantification of neurons from multiple brain regions from the same tissue sections. We applied this new methodology to estimate neuronal numbers in the neocortex and hippocampus of 10-day-old mice. The method was useful for estimation of both large, sparsely packed cell populations, such as the neocortex, and small, densely packed cells, such as the dentate gyrus granule cells. Thus, frozen section methodology offers many potential advantages over the use of glycol methacrylate embedment for stereology. These advantages include expansion of the size of tissue blocks that can be processed, reduction in expended time and costs, and ability to quantify multiple brain regions from a single set of sections.

Hierarchical model of the population dynamics of hippocampal dentate granule cells

A hierarchical modeling approach is used as the basis for a mathematical representation of the population activity of hippocampal dentate granule cells. Using neural field equations, the variation in time and space of dentate granule cell activity is derived from the summed synaptic potential and summed action potential responses of a population of granule cells evoked by monosynaptic excitatory input from entorhinal cortical afferents. In this formulation of the problem, we have considered a two-level hierarchy: the synapses of entorhinal cortical axons define the first level of organization, and dentate granule cells, which include these synapses, define the second, higher level of organization. The model is specified by two state field variables, for membrane potential and for synaptic efficacy, respectively, with both evolving according to different time scales. The two state field variables introduce new parameters, physiological and anatomical, which characterize the dentate from the point of view of neuronal and synaptic populations: (1) a set of geometrical constraints corresponding to the morphological properties of granule cells and anatomical characteristics of entorhinal-dentate connections; and (2) a set of neuronal parameters corresponding to physiological mechanisms. Assuming no interaction between granule cells, i.e., neither ephaptic nor synaptic coupling, the model is shown to be mathematically tractable and allows solution of the field equations leading to the determination of activity. This treatment leads to the definition of two state variables, volume of stimulated synapses and firing time, which describe observed activity. Numerical simulations are used to investigate the populational characterization of the dentate by individual parameters: (1) the relationship between the conditions of stimulation of active perforant path fibers, e.g., stimulating intensity, and activity in the granule cell layer; and (2) the influence of geometry on the generation of activity, i.e., the influence of neuron density and synaptic density-connectivity. As an example application of the model, the granule cell population spike is reconstructed and compared with experimental data.

Neurogenesis may relate to some but not all types of hippocampal-dependent learning

The hippocampal formation generates new neurons throughout adulthood. Recent studies indicate that these cells possess the morphology and physiological properties of more established neurons. However, the function of adult generated neurons is still a matter of debate. We previously demonstrated that certain forms of associative learning can enhance the survival of new neurons and a reduction in neurogenesis coincides with impaired learning of the hippocampal-dependent task of trace eyeblink conditioning. Using the toxin methylazoxymethanol acetate (MAM) for proliferating cells, we tested whether reduction of neurogenesis affected learning and performance associated with different hippocampal dependent tasks: spatial navigation learning in a Morris water maze, fear responses to context and an explicit cue after training with a trace fear paradigm. We also examined exploratory behavior in an elevated plus maze. Rats were injected with MAM (7 mg/kg) or saline for 14 days, concurrent with BrdU, to label new neurons on days 10, 12, and 14. After treatment, groups of rats were tested in the various tasks. A significant reduction in new neurons in the adult hippocampus was associated with impaired performance in some tasks, but not with others. Specifically, treatment with the antimitotic agent reduced the amount of fear acquired after exposure to a trace fear conditioning paradigm but did not affect contextual fear conditioning or spatial navigation learning in the Morris water maze. Nor did MAM treatment affect exploration in the elevated plus maze. These results combined with previous ones suggest that neurogenesis may be associated with the formation of some but not all types of hippocampal-dependent memories.

Neurons in the hilus region of the rat hippocampus are depleted in number by exposure to alcohol during early postnatal life

We have previously shown that exposing rats to a relatively high dose of ethanol during early postnatal life resulted in a deficit in spatial learning ability. This ability is controlled, at least in part, by the hippocampal formation. The purpose of the present study was to determine whether exposure of rats to ethanol during early postnatal life affected the number of specific neurons in the hippocampus. Wistar rats were exposed to a relatively high daily dose of ethanol between postnatal days 10 and 15 by placing them for 3 h each day in a chamber containing ethanol vapor. The blood ethanol concentration was about 430 mg/dl at the end of the exposure period. Groups of ethanol-treated (ET) rats, separation controls (SC), and mother-reared controls (MRC) were anesthetized and killed at 16 days of age by perfusion with phosphate-buffered glutaraldehyde (2.5%). The Cavalieri principle was used to determine the volume of various subdivisions of the hippocampal formation (CA1, CA2+CA3, hilus, and granule cell layer), and the physical disector method was used to estimate the numerical densities of neurons within each subdivision. The total number of neurons was calculated by multiplying estimates of the numerical density with the volume. There were, on average, about 441,000 granule cells in the granule cell layer and 153,000 to 177,000 pyramidal cells in both the CA1 and CA2+CA3 regions in all three treatment groups. In the hilus region, ET rats had about 27,000 neuronal cells. This was significantly fewer than the average of 38,000 such neurons estimated to be present in both MRC and SC animals. Thus, neurons in the hilus region may be particularly vulnerable to the effects of a high dose of ethanol exposure during early postnatal life.

Enhanced neurogenesis in the rodent hippocampus following traumatic brain injury

Recent studies have shown that neurogenesis in the dentate gyrus of the rodent hippocampus continues throughout life. Several physiological and pathological conditions have been reported to alter the rate of progenitor cell division resulting in the increased production of mature granule neurons. Excitotoxic and mechanical lesions of the granule cell layer also stimulate the proliferation of precursor cells suggesting that the death of pre-existing granule neurons may act as a trigger for enhanced neurogenesis. Hippocampal pyramidal neurons, and to a lesser extent granule neurons, have been reported to die as a result of traumatic brain injury in rodents. To determine if the proliferation of precursor cells is enhanced as a result of brain injury in rodents, newly divided cells were labeled with the thymidine analog, bromodeoxyuridine (BrdU). Traumatic brain injury increased the production of BrdU-labeled cells in the dentate gyrus with a maximal rate observed at 3 days post-injury. These cells, a proportion of which co-localize with the immature neuronal marker TOAD-64, implanted themselves into the granule cell layer where they accumulated over time. When examined 1 month post-injury, the majority of BrdU-labeled cells co-labeled with the mature neuronal marker calbindin. These findings show that traumatic brain injury increases neurogenesis in the granule cell layer and suggests that these new cells may contribute to the function of the hippocampus.

The combined retrograde transport and unbiased stereological study of the claustrocortical connections in the rabbit

The quantitative analysis of the claustrocortical connections in the rabbit, labeled with the fluorescent retrograde tracer Fluoro-Gold (FG), was conducted by means of unbiased stereology. The FG was injected into selected regions of the motor, somatosensory, auditory and visual cortices and then a comparison of the various claustrocortical projections was carried out. This was achieved by comparing (1) the numerical densities of projecting neurones for each claustral projection zone and (2) the distribution of the labeled neurones throughout the rostro-caudal extent of the claustrum. No significant differences between the numerical densities of labeled neurones in the various projection zones are reported. The motor and primary somatosensory projections dominated in the anterior and central parts of the claustrum, whereas the secondary somatosensory, auditory and visual projections--in the posterior part. The difference in the distributions was significant (p < 0.001). Summarizing, the cortical projections in the claustrum, although varying topographically, do not reveal a quantitative differentiation. This may speak in favour of the integrative and modulating function of this structure in relationship to the neocortex.

Quantitative analysis of GABAergic neurons in the mouse hippocampus, with optical disector using confocal laser scanning microscope

The numerical densities (NDs) of glutamic acid decarboxylase (GAD) 67 immunoreactive (IR) neurons in the mouse hippocampus were estimated according to the optical disector method using a confocal laser scanning microscope (CLSM), and the cell sizes of disector-counted neurons were measured. Particularly, we focused on the dorsoventral differences of the NDs and cell sizes in individual subdivisions and layers. The NDs of GAD67-IR neurons were larger at the ventral level than at the dorsal level in most subdivisions and layers, except in the stratum pyramidale (SP) of the CA1 region and stratum radiatum (SR) of the CA3 region. In the whole hippocampus, the ND of GAD67-IR neurons was 5.7+/-0.2x103/mm3 at the dorsal level, and 7.3+/-0.3x103/mm3 at the ventral level. The laminar differences showed that the NDs of GAD67-IR neurons in the principal cell layers were generally larger than those in the dendritic layers in each subdivision. The ND of GAD67-IR neurons was largest in the SP of the CA1 region at the dorsal level (13.5+/-0.9x103/mm3), and smallest in the molecular layer (ML) of the dentate gyrus (DG) at the dorsal level (1.7+/-0.2x103/mm3). The mean cell sizes of GAD67-IR neurons also showed prominent dorsoventral and laminar differences. In the CA3 region, the mean cell size of GAD67-IR neurons was smaller at the dorsal level than at the ventral level, while in the DG, it was larger at the dorsal level than at the ventral level. On the other hand, the mean cell size of GAD67-IR neurons in the CA1 region showed no significant dorsoventral difference. In the whole hippocampus, the mean cell size of GAD67-IR neurons was slightly smaller at the dorsal level (somatic profile area 149.2+/-2.5 microm2) than at the ventral level (154.2+/-2.9 microm2). The laminar differences showed that the mean cell sizes of GAD67-IR neurons in the principal cell layers were generally larger than those in the dendritic layers in each subdivision. The mean cell size of GAD67-IR neurons was largest in the SP of the CA3 region at the ventral level (180.7+/-8.7 microm2), and smallest in the stratum lacunosum-moleculare (SLM) of the CA3 region at the dorsal level (115.9+/-7.9 microm2). The cell size distributions in individual layers revealed that GAD67-IR neurons were roughly classified into two subgroups. The composition of these subgroups suggested the heterogeneity of GAD67-IR neurons in the mouse hippocampus in view of cell size

Research uses of neuropathological data

The study of relationships between neuropathological characteristics and behavioral, structural, chemical, and molecular variables offers immense promise for understanding the basic pathophysiology of Alzheimer's disease. This position paper examines the need for standardized procedures and quantitation if neuropathological data are to be optimally useful among laboratories investigating the biology of Alzheimer's disease. These requirements include standardized fixation, embedding, sectioning, staining, brain regions and sampling methods. In addition, the definition of the structures to be quantified, such as plaque type(s), needs to be rigorously specified. Unbiased stereological methods for quantification should be used. These needs for optimal research utility exceed the needs and practicality for diagnostic purposes, suggesting a two-tiered approach to the neuropathology of Alzheimer's disease: diagnostic and research.

Suppression of age-related changes in mouse hippocampal CA3 nerve cells by a free radical scavenger

This study was designed to evaluate the relationship between oxygen free radicals and age-related morphological changes in hippocampal nerve cells using K-7259 (N,N' bis[4-(3,4,5-trimethoxyphenyl)butyl] homopiperazine dihydrochloride), a known neuro-protective agent. A chemiluminescence assay has shown that this agent is a potent free radical scavenger with an IC50 of 1.6 x 10(-5)M. Mice fed diets containing 10, 20, 40 mg/kg/day of K-7259, for periods ranging from 25 to 40 or 50 weeks of age were used as test groups, and 10-, 20-, 30-, 40-, and 50-week-old mice fed a standard diet were used as controls. We measured the number and area of pyramidal nerve cells within a defined frame in the hippocampal CA3 field using an image analyzer and the density of nerve cells by the disector method. These values decreased gradually in controls as expected, and the number and area yielded a significant difference between control mice at the ages of 10 and 30 weeks. As compared with the corresponding controls, all test groups had greater cell numbers (statistical significance at 40 weeks in the 40 mg/kg/day group) and density, while cell areas were greater in all but a 10 mg/kg/day group (statistical significance at 50 weeks). In summary, the free radical scavenger K-7259 forestalled an age-related decrease in the number and size of hippocampal CA3 nerve cells, thus suggesting that free radicals play an important role in the cellular morphological changes which appear with age.

Connection matrix of the hippocampal formation: I. The dentate gyrus

The hippocampal formation presents a special opportunity for realistic neural modeling since its structure, connectivity, and physiology are better understood than that of other cortical components. A review of the quantitative neuroanatomy of the rodent dentate gyrus (DG) is presented in the context of the development of a computational model of its connectivity. The DG is a three-layered folded sheet of neural tissue. This sheet is represented as a rectangle, having a surface area of 37 mm2 and a septotemporal length of 12 mm. Points, representing cell somata, are distributed in the model rectangle in a roughly uniform fashion. Synaptic connectivity is generated by assigning each presynaptic cell a spatial zone representing its axonal arbor. For each postsynaptic cell, a list of potential presynaptic cells is compiled, based on which arbor zones the given postsynaptic cell falls within. An appropriate number of presynaptic inputs are then selected at random. The principal cells of the DG, the granule cells, are represented in the model, as are non-principal cells, including basket cells, chandelier cells, mossy cells, and GABAergic peptidergic polymorphic (GPP) cells. The neurons of layer II of the entorhinal cortex are included also. The DG receives its main extrinsic input from these cells via the perforant path. The basket cells, chandelier cells, and GPP cells receive perforant path and granule cell input and exert both feedforward and feedback inhibition onto the granule cells. Mossy cells receive converging input from granule cells and send their output back primarily to distant septotemporal levels, where they contact both granule cells and non-principal cells. To permit numerical simulations, the model must be scaled down while preserving its anatomical structure. A variety of methods for doing this exist. Hippocampal allometry provides valuable clues in this regard.

Response of striatal astrocytes to neuronal deafferentation: an immunocytochemical and ultrastructural study

This ultrastructural and light microscopic immunocytochemical study describes the time course of anatomical changes that occur in striatal astrocytes in response to neuronal deafferentation in young adult rats and the coordinate distribution of two astrocytic proteins involved in reactive synaptogenesis, glial fibrillary acidic protein and clusterin. We found that following a unilateral lesion of the cerebral cortex, striatal astrocytes undergo a rapid ultrastructural transformation from a protoplasmic to a reactive type of astroglia and are the primary cells involved in the removal of degenerating axon terminals, but not axons of passage, from the neuropil. In addition, at 10 and 27 days postlesion, processes of reactive astrocytes are also seen to occupy vacant postsynaptic spines after degenerating presynaptic terminals are removed, suggesting that they may also participate in the reinnervation of the deafferented neurons. By immunocytochemistry, reactive astrocytes were characterized by a significant increase in the intensity of glial fibrillary acidic protein staining beginning at three days postlesion and lasting for at least 27 days postlesion. Reactive astrocytes were characterized by cellular hypertrophy and an increase in the density of immunoreactive processes distributed throughout the deafferented striatum. However, our analysis of astrocyte cell number found no evidence of astrocyte proliferation in response to the deafferentation lesion. Although previous in situ hybridization studies have reported elevated clusterin messenger RNA in reactive astrocytes after decortication, clusterin immunoreactivity was not seen in the cell soma of reactive astrocytes but was distributed as punctate deposits, ranging from 1 to 2 microns in diameter, within the neuropil of the deafferented striatum. At 10 days postlesion, the distribution of clusterin staining appeared as large aggregates of immunoreactive deposits adjacent to neurons. However, by 27 days postlesion, the aggregates of clusterin reaction product were replaced by a fine scattering of individual punctate deposits distributed evenly over the dorsal part of the deafferented striatum. These data support the notion that reactive astrocytes serve multiple, time-dependent roles in response to brain injury and are involved in both the removal of degenerative debris from the lesion site as well as in reforming the synaptic circuitry of the damaged brain. Our data suggest that, in response to decortication, reactive astrocytes are the primary cells responsible for removing degenerating axon terminals, but not axons of passage, from the deafferented striatum and that the coordinate increase in glial fibrillary acidic protein may serve to stabilize the extension of reactive astrocytic processes during phagocytosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of chronic alcohol consumption and withdrawal on the somatostatin-immunoreactive neurons of the rat hippocampal dentate hilus

Previous studies have demonstrated that the dentate granule and the CA3 pyramidal cells of the rat hippocampal formation are neuronal populations vulnerable to the toxic effects of ethanol. It also has been shown that the resulting alterations do not end after withdrawal from ethanol. As the neurons in the dentate hilus are heavily interconnected with the dentate granule cells, the authors decided to examine the fate of the hilar neurons after chronic alcohol consumption and withdrawal, inasmuch as the hilar somatostatin-immunoreactive (SS-I) neurons were found to be sensitive to cerebral ischemia and to seizures. The following groups of adult rats were studied: (1) alcohol-fed for 6 and 12 months; (2) alcohol-fed for 6 months and then switched to water for a further 6 months; (3) pair-fed controls; and (4) controls fed ad libitum. The authors determined the numerical density of hilar neurons and the number of its SS-I subpopulation. These were found to be significantly reduced in both the alcohol-fed and withdrawal groups when compared with the respective age-matched controls. The consequent loss of the integrative action of the hilar neurons, including the SS-Is, could explain some of the alcohol-related functional deficits as well as their persistence after withdrawal.

Numerical data on neocortical neurons in adult rat, with special reference to the GABA population

The disector method was used to estimate the numerical density of neurons (number per unit volume) and their actual number per column (number under a given area of pial surface), in the occipital (monocular segment of the primary visual area, Oc1M), the parietal (somatosensory barrelfield area, Par1) and the frontal cortex (primary motor area, Fr1) of adult rat. Values were first obtained for all neurons in each layer, and then for GABA neurons as identified with postembedding immunocytochemistry on semithin sections. The numerical density of neurons in the frontal cortex (34,000/mm3) was significantly lower than in the two other neocortical areas (occipital: 52,000; parietal: 48,000/mm3). The GABA population showed a similar difference and consequently represented an equivalent proportion of total (15%) in the three cortical areas. Across layers, there was an alternate distribution of low and high density of neurons from layers II-III to VI in the three cortical areas, with the highest density in layer IV of the two sensory areas. The laminar changes in density of the GABA neurons were not as pronounced as those of the overall population. Consequently, the layers with the highest overall neuronal densities tended to have a lower proportion of GABA neurons and vice versa. There were more neurons under 1 mm2 of surface in the parietal (90,000) than the occipital or the frontal cortex (71,000), which was also true of the GABA neurons. The greater number of neurons per column in the parietal cortex was mostly imputable to layer IV, the main recipient of thalamic axons.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of recent advances in stereology for quantifying neural structure

The science of stereology has undergone a revolution over the past decade with the introduction of design-based (assumption- or model-free) methods which are highly efficient and generally unbiased. No other morphometric approach currently offers these twin benefits. Stereology is ideal for extrapolating 3-D structural quantities (real volumes, surface areas, lengths and numbers) from simple counts made on 2-D slice images. The images may take various forms (e.g. physical or optical sections, MRI slices, CT scans) but they must be sampled so as to be random in orientation and/or position if valid estimates are to be made. All the recent developments in stereology are applicable to problems in neuromorphometry. This review provides an account of major developments and the state of the art, emphasizes the importance of properly randomized sampling and identifies some applications to neural structure at different levels of organization. These include the counting and sizing of synapses, neurites, cells and whole brains.

Effects of hypothyroidism upon the granular layer of the dentate gyrus in male and female adult rats: a morphometric study

The effects of hypothyroidism upon the structure of the central nervous system of adult rats are poorly understood in spite of evidence that the mature brain is vulnerable to this condition. Existing developmental studies show that the morphological changes induced by thyroid hormone deficiency are related to alterations in neurogenesis. We studied the granular layer of the dentate gyrus under different experimental conditions of hypothyroidism, because in rodents the neurogenesis of the granule cells continues during adulthood. The following groups of rats were analysed: 1) control; 2) hypothyroid from day 0 until day 180 (hypothyroid group); 3) hypothyroid until day 30 and henceforth maintained euthyroid (recovery group); and 4) hypothyroid since day 30 (adult hypothyroid group). Groups of 6 male rats and 6 female rats were analysed separately. The volume of the dentate gyrus granular layer and the numerical density of its neurons were evaluated, so we were able to estimate the total number of granule cells. Because in the experimental groups the volume of the granular layer and the numerical density of its neurons were reduced, the total number of granule cells was decreased. In the hypothyroid and recovery groups the alterations were identical and more striking than in the adult hypothyroid groups. The total number of granule cells displayed sexual differences in all groups studied except in the hypothyroid groups. The present results support the view that thyroid hormone deficiency interferes with the process of cell acquisition by reducing neuronal proliferation and that it also leads to increased cell death. These events underlie the irreversible morphological changes observed in the brain of hypothyroid rats, either during development or at maturity. The referred structural alterations are probably related to the functional deficits observed in this condition.

Unbiased stereological estimation of the total number of neurons in thesubdivisions of the rat hippocampus using the optical fractionator

A stereological method for obtaining estimates of the total number of neurons in five major subdivisions of the rat hippocampus is described. The new method, the optical fractionator, combines two recent developments in stereology: a three-dimensional probe for counting neuronal nuclei, the optical disector, and a systematic uniform sampling scheme, the fractionator. The optical disector results in unbiased estimates of neuron number, i.e., estimates that are free of assumptions about neuron size and shape, are unaffected by lost caps and overprojection, and approach the true number of neurons in an unlimited manner as the number of samples is increased. The fractionator involves sampling a known fraction of a structural component. In the case of neuron number, a zero dimensional quantity, it provides estimates that are unaffected by shrinkage before, during, and after processing of the tissue. Because the fractionator involves systematic sampling, it also results in highly efficient estimates. Typically only 100-200 neurons must be counted in an animal to obtain a precision that is compatible with experimental studies. The methodology is compared with those used in earlier works involving estimates of neuron number in the rat hippocampus and a number of new stereological methods that have particular relevance to the quantitative study of the structure of the nervous system are briefly described in an appendix.

Accurate prediction of Purkinje cell number from cerebellar weight can be achieved with the fractionator

Purkinje cell nucleoli are used as counting units in order to obtain unbiased (fractionator) estimates of the number, N, of Purkinje neurons in adult mammalian cerebella of known weight, W. Regression analysis is then employed to establish the nature of the relationship between logN and logW. The linear regression equation defines an allometric relation that is employed to predict number in cerebella of known weight from other mammals. Predicted numbers are tested against empirical estimates. For 19 cerebella ranging in weight from 0.2 g (rat) to 113 g (human), the allometric relation between Purkinje cell number and organ weight was determined. By using this relation, the mean complement in three rabbit cerebella (average weight, 0.87 g) is predicted to be 0.63 million. This figure is confirmed by fractionator estimates made on the same three brains. The cat cerebellum should contain about 1.5-2.0 million Purkinje cells. An estimate of 1.2-1.3 million cells is to be found in the literature. Including rabbit cerebella in a refined equation yields the following relation: N = 686000W(0.695). With this refined equation, further predictions are made about the numbers likely to be found in the cerebella of the dog, goat, pig, ox, and horse. The numbers predicted for these animals must await experimental verification, but they are entirely consistent with previous suggestions that neuronal packing densities decrease with increasing brain size.

Stereology: a method for analyzing images

This review deals with notions of shape, sizes, numbers, densities and orientation in space, all basic concepts in stereology. With the initiation by Delesse in 1847, but mainly since the beginning of the XXth century, many stereological methods have been published allowing us to relate two-dimensional measurements easily obtainable on flat histological images with three-dimensional characteristics of the structure analysed. Looking at these methods, the neurobiologist, generally impermeable to concepts of sampling, statistical bias, efficiency, cost of effort and distribution-free, is discountenanced and continues old laboratory usages and customs. Furthermore, for the last ten years, the advent of a plethora of new powerful tools, considered as assumption-free and more efficient than the previous ones, increase the risk proportionately the disarray of the potential user. The purpose of this review is to present synthetically all traditional and actual aspects of stereology in order to guide the reader in the labyrinth of this speciality. The necessarily short exposition is compensated by many references to which the beginner or the initiated can refer.

The supraoptic nucleus in hypothyroid and undernourished rats: an experimental morphometric study

The supraoptic nuclei of both male and female 30-day-old rats rendered hypothyroid by daily subcutaneous injection of propylthiouracil were studied and the results were compared with age- and sex-matched rats fed ad libitum (control rats) and with undernourished rats. Morphometric methods were used to evaluate the volume of the supraoptic nucleus and the areal and numerical densities of its neurons. These parameters allowed us to estimate the total number of neurons of this nucleus. In addition, the mean cross-sectioned area and mean nuclear diameter of the same neurons were also evaluated. The volume of the supraoptic nucleus was reduced both in hypothyroid and undernourished animals when compared with normal controls. The areal and numerical densities of neurons from the former groups were increased and the volume density of the neuropil was reduced. As a consequence, the total number of neurons was found to be identical in all groups studied. Furthermore, the mean nuclear diameters and cross-sectioned areas of the supraoptic neurons were similar in all groups. The volumetric differences and the increased packing found were always more marked for hypothyroid than for undernourished rats. Differences were not detected between male and female groups. The present results support the view that the increased cell packing in hypothyroid animals depends upon a reduction in the neuropil of the nucleus, as has been described under similar conditions in other central nervous system areas displaying identical patterns of neurogenesis. In addition, it was found that the effects of undernourishment cannot be discriminated from those dependent on neonatal hypothyroidism.

Unbiased stereological estimation of the number of neurons in the human hippocampus

The total numbers of neurons in five subdivisions of human hippocampi were estimated using unbiased stereological principles and systematic sampling techniques. The method addresses the problems associated with the results and conclusions of previous quantitative studies, virtually all of which have been based on biased estimates of neuron densities. For each subdivision, the total number of neurons was calculated as the product of the estimate of the volume of the neuron-containing layers and the estimate of the numerical density of neurons in the layers. Each hippocampus was cut into 3-mm-thick slabs, transverse to the rostrocaudal axis. One 70-micron-thick section from each slab was used in the analysis. The volumes of the layers containing neurons in five major subdivisions of the hippocampus (granule cell layer, hilus, CA3-2, CA1, and subiculum) were estimated with point-counting techniques after delineation of the layers on each section. The numerical densities of neurons in each subdivision were estimated on the same sections with optical disectors. The sampling used in both estimates was performed systematically in all three dimensions. In an example of five hippocampi, the mean numbers of neurons (CV = SD/mean) in the different subdivisions were as follows: granule cells 15 X 10(6) (0.28), hilus 2.0 X 10(6) (0.16), CA3-2 2.7 X 10(6) (0.22), CA1 16 X 10(6) (0.32), subiculum 4.5 X 10(6) (0.19). The stereological measurements contributed approximately 25% of the observed variance. Among the five subjects there was a significant inverse relationship between age (which ranged from 47 to 85 years) and the total number of neurons in CA1 (which ranged from 24 to 11 X 10(6)). An optimized sampling scheme for studies of the number of neurons in the human hippocampus has been designed on the basis of an analysis of variance of the estimates at different levels of the sampling scheme. Counting neurons in the five subdivisions of the human hippocampus with the optimized sampling scheme takes less than 4 hours.