Bcl-2 immunoreactive cells with immature neuronal phenotype exist in the nonepileptic adult human brain

Structural plasticity in the entorhinal and perirhinal cortices following hippocampal lesions in rhesus monkeys

Immature neurons expressing the Bcl2 protein are present in various regions of the mammalian brain, including the amygdala and the entorhinal and perirhinal cortices. Their functional role is unknown but we have previously shown that neonatal and adult hippocampal lesions increase their differentiation in the monkey amygdala. Here, we assessed whether hippocampal lesions similarly affect immature neurons in the entorhinal and perirhinal cortices. Since Bcl2-positive cells were found mainly in areas Eo, Er, and Elr of the entorhinal cortex and in layer II of the perirhinal cortex, we also used Nissl-stained sections to determine the number and soma size of immature and mature neurons in layer III of area Er and layer II of area 36 of the perirhinal cortex. We found different structural changes in these regions following hippocampal lesions, which were influenced by the time of the lesion. In neonate-lesioned monkeys, the number of immature neurons in the entorhinal and perirhinal cortices was generally higher than in controls. The number of mature neurons was also higher in layer III of area Er of neonate-lesioned monkeys but no differences were found in layer II of area 36. In adult-lesioned monkeys, the number of immature neurons in the entorhinal cortex was lower than in controls but did not differ from controls in the perirhinal cortex. The number of mature neurons in layer III of area Er did not differ from controls, but the number of small, mature neurons in layer II of area 36 was lower than in controls. In sum, hippocampal lesions impacted populations of mature and immature neurons in discrete regions and layers of the entorhinal and perirhinal cortices, which are interconnected with the amygdala and provide major cortical inputs to the hippocampus. These structural changes may contribute to some functional recovery following hippocampal injury in an age-dependent manner.

Reorganization in the macaque interoceptive-allostatic network following anterior cingulate cortex damage

Accumulating evidence indicates that the adult brain is capable of significant structural change following damage-a capacity once thought to be largely limited to developing brains. To date, most existing research on adult plasticity has focused on how exteroceptive sensorimotor networks compensate for damage to preserve function. Interoceptive networks-those that represent and process sensory information about the body's internal state-are now recognized to be critical for a wide range of physiological and psychological functions from basic energy regulation to maintaining a sense of self, but the extent to which these networks remain plastic in adulthood has not been established. In this report, we used detailed histological analyses to pinpoint precise changes to gray matter volume in the interoceptive-allostatic network in adult rhesus monkeys (Macaca mulatta) who received neurotoxic lesions of the anterior cingulate cortex (ACC) and neurologically intact control monkeys. Relative to controls, monkeys with ACC lesions had significant and selective unilateral expansion of the ventral anterior insula and significant relative bilateral expansion of the lateral nucleus of the amygdala. This work demonstrates the capacity for neuroplasticity in the interoceptive-allostatic network which, given that changes included expansion rather than atrophy, is likely to represent an adaptive response following damage.

Doublecortin-Expressing Neurons in Human Cerebral Cortex Layer II and Amygdala from Infancy to 100 Years Old

A cohort of morphologically heterogenous doublecortin immunoreactive (DCX +) "immature neurons" has been identified in the cerebral cortex largely around layer II and the amygdala largely in the paralaminar nucleus (PLN) among various mammals. To gain a wide spatiotemporal view on these neurons in humans, we examined layer II and amygdalar DCX + neurons in the brains of infants to 100-year-old individuals. Layer II DCX + neurons occurred throughout the cerebrum in the infants/toddlers, mainly in the temporal lobe in the adolescents and adults, and only in the temporal cortex surrounding the amygdala in the elderly. Amygdalar DCX + neurons occurred in all age groups, localized primarily to the PLN, and reduced in number with age. The small-sized DCX + neurons were unipolar or bipolar, and formed migratory chains extending tangentially, obliquely, and inwardly in layers I-III in the cortex, and from the PLN to other nuclei in the amygdala. Morphologically mature-looking neurons had a relatively larger soma and weaker DCX reactivity. In contrast to the above, DCX + neurons in the hippocampal dentate gyrus were only detected in the infant cases in parallelly processed cerebral sections. The present study reveals a broader regional distribution of the cortical layer II DCX + neurons than previously documented in human cerebrum, especially during childhood and adolescence, while both layer II and amygdalar DCX + neurons persist in the temporal lobe lifelong. Layer II and amygdalar DCX + neurons may serve as an essential immature neuronal system to support functional network plasticity in human cerebrum in an age/region-dependent manner.

Autism spectrum disorders pathogenesis: Toward a comprehensive model based on neuroanatomic and neurodevelopment considerations

Autism spectrum disorder (ASD) involves alterations in neural connectivity affecting cortical network organization and excitation to inhibition ratio. It is characterized by an early increase in brain volume mediated by abnormal cortical overgrowth patterns and by increases in size, spine density, and neuron population in the amygdala and surrounding nuclei. Neuronal expansion is followed by a rapid decline from adolescence to middle age. Since no known neurobiological mechanism in human postnatal life is capable of generating large excesses of frontocortical neurons, this likely occurs due to a dysregulation of layer formation and layer-specific neuronal migration during key early stages of prenatal cerebral cortex development. This leads to the dysregulation of post-natal synaptic pruning and results in a huge variety of forms and degrees of signal-over-noise discrimination losses, accounting for ASD clinical heterogeneities, including autonomic nervous system abnormalities and comorbidities. We postulate that sudden changes in environmental conditions linked to serotonin/kynurenine supply to the developing fetus, throughout the critical GW7 - GW20 (Gestational Week) developmental window, are likely to promote ASD pathogenesis during fetal brain development. This appears to be driven by discrete alterations in differentiation and patterning mechanisms arising from in utero RNA editing, favoring vulnerability outcomes over plasticity outcomes. This paper attempts to provide a comprehensive model of the pathogenesis and progression of ASD neurodevelopmental disorders.

Immature excitatory neurons in the amygdala come of age during puberty

The human amygdala is critical for emotional learning, valence coding, and complex social interactions, all of which mature throughout childhood, puberty, and adolescence. Across these ages, the amygdala paralaminar nucleus (PL) undergoes significant structural changes including increased numbers of mature neurons. The PL contains a large population of immature excitatory neurons at birth, some of which may continue to be born from local progenitors. These progenitors disappear rapidly in infancy, but the immature neurons persist throughout childhood and adolescent ages, indicating that they develop on a protracted timeline. Many of these late-maturing neurons settle locally within the PL, though a small subset appear to migrate into neighboring amygdala subnuclei. Despite its prominent growth during postnatal life and possible contributions to multiple amygdala circuits, the function of the PL remains unknown. PL maturation occurs predominately during late childhood and into puberty when sex hormone levels change. Sex hormones can promote developmental processes such as neuron migration, dendritic outgrowth, and synaptic plasticity, which appear to be ongoing in late-maturing PL neurons. Collectively, we describe how the growth of late-maturing neurons occurs in the right time and place to be relevant for amygdala functions and neuropsychiatric conditions.

Doublecortin-Expressing Neurons in Chinese Tree Shrew Forebrain Exhibit Mixed Rodent and Primate-Like Topographic Characteristics

Doublecortin (DCX) is transiently expressed in new-born neurons in the subventricular zone (SVZ) and subgranular zone (SGZ) related to adult neurogenesis in the olfactory bulb (OB) and hippocampal formation. DCX immunoreactive (DCX+) immature neurons also occur in the cerebral cortex primarily over layer II and the amygdala around the paralaminar nucleus (PLN) in various mammals, with interspecies differences pointing to phylogenic variation. The tree shrews (Tupaia belangeri) are phylogenetically closer to primates than to rodents. Little is known about DCX+ neurons in the brain of this species. In the present study, we characterized DCX immunoreactivity (IR) in the forebrain of Chinese tree shrews aged from 2 months- to 6 years-old (n = 18). DCX+ cells were present in the OB, SVZ, SGZ, the piriform cortex over layer II, and the amygdala around the PLN. The numerical densities of DCX+ neurons were reduced in all above neuroanatomical regions with age, particularly dramatic in the DG in the 5–6 years-old animals. Thus, DCX+ neurons are present in the two established neurogenic sites (SVZ and SGZ) in the Chinese tree shrew as seen in other mammals. DCX+ cortical neurons in this animal exhibit a topographic pattern comparable to that in mice and rats, while these immature neurons are also present in the amygdala, concentrating around the PLN as seen in primates and some nonprimate mammals.

Life and Death of Immature Neurons in the Juvenile and Adult Primate Amygdala

In recent years, a large population of immature neurons has been documented in the paralaminar nucleus of the primate amygdala. A substantial fraction of these immature neurons differentiate into mature neurons during postnatal development or following selective lesion of the hippocampus. Notwithstanding a growing number of studies on the origin and fate of these immature neurons, fundamental questions about the life and death of these neurons remain. Here, we briefly summarize what is currently known about the immature neurons present in the primate ventral amygdala during development and in adulthood, as well as following selective hippocampal lesions. We provide evidence confirming that the distribution of immature neurons extends to the anterior portions of the entorhinal cortex and layer II of the perirhinal cortex. We also provide novel arguments derived from stereological estimates of the number of mature and immature neurons, which support the view that the migration of immature neurons from the lateral ventricle accompanies neuronal maturation in the primate amygdala at all ages. Finally, we propose and discuss the hypothesis that increased migration and maturation of neurons in the amygdala following hippocampal dysfunction may be linked to behavioral alterations associated with certain neurodevelopmental disorders.

Development of the Entorhinal Cortex Occurs via Parallel Lamination During Neurogenesis

The entorhinal cortex (EC) is the spatial processing center of the brain and structurally is an interface between the three layered paleocortex and six layered neocortex, known as the periarchicortex. Limited studies indicate peculiarities in the formation of the EC such as early emergence of cells in layers (L) II and late deposition of LIII, as well as divergence in the timing of maturation of cell types in the superficial layers. In this study, we examine developmental events in the entorhinal cortex using an understudied model in neuroanatomy and development, the pig and supplement the research with BrdU labeling in the developing mouse EC. We determine the pig serves as an excellent anatomical model for studying human neurogenesis, given its long gestational length, presence of a moderate sized outer subventricular zone and early cessation of neurogenesis during gestation. Immunohistochemistry identified prominent clusters of OLIG2+ oligoprogenitor-like cells in the superficial layers of the lateral EC (LEC) that are sparser in the medial EC (MEC). These are first detected in the subplate during the early second trimester. MRI analyses reveal an acceleration of EC growth at the end of the second trimester. BrdU labeling of the developing MEC, shows the deeper layers form first and prior to the superficial layers, but the LV/VI emerges in parallel and the LII/III emerges later, but also in parallel. We coin this lamination pattern parallel lamination. The early born Reln+ stellate cells in the superficial layers express the classic LV marker, Bcl11b (Ctip2) and arise from a common progenitor that forms the late deep layer LV neurons. In summary, we characterize the developing EC in a novel animal model and outline in detail the formation of the EC. We further provide insight into how the periarchicortex forms in the brain, which differs remarkably to the inside-out lamination of the neocortex.

Neuron numbers increase in the human amygdala from birth to adulthood, but not in autism

Remarkably little is known about the postnatal cellular development of the human amygdala. It plays a central role in mediating emotional behavior and has an unusually protracted development well into adulthood, increasing in size by 40% from youth to adulthood. Variation from this typical neurodevelopmental trajectory could have profound implications on normal emotional development. We report the results of a stereological analysis of the number of neurons in amygdala nuclei of 52 human brains ranging from 2 to 48 years of age [24 neurotypical and 28 autism spectrum disorder (ASD)]. In neurotypical development, the number of mature neurons in the basal and accessory basal nuclei increases from childhood to adulthood, coinciding with a decrease of immature neurons within the paralaminar nucleus. Individuals with ASD, in contrast, show an initial excess of amygdala neurons during childhood, followed by a reduction in adulthood across nuclei. We propose that there is a long-term contribution of mature neurons from the paralaminar nucleus to other nuclei of the neurotypical human amygdala and that this growth trajectory may be altered in ASD, potentially underlying the volumetric changes detected in ASD and other neurodevelopmental or neuropsychiatric disorders.

Hamartia in hippocampal sclerosis-associated mesial temporal lobe epilepsy

Hamartia are small collections of rounded glioneuronal cells that are thought to be due to aberrant cell migration. Their presence has been recognized in association with mesial temporal lobe epilepsy; their prevalence among cases of hippocampal sclerosis (HS) and any potential association with patient demographics and outcomes is unknown. This study examines hamartia in a series of 292 patients with pathologically confirmed HS. Medical records were reviewed for pertinent patient clinical information (follow-up mean 5years). Hamartia were identified in 96 cases (33%) and were seen primarily in the amygdala (n=88) and less commonly in the hippocampus (n=10) and temporal lobe (n=4). A statistically significant relationship was found between the presence of hamartia and male gender, younger age of seizure onset, and history of childhood febrile seizures and developmental delay. It is unclear if these associations represent a real association or are a result of the underlying pathologies related to chronic epilepsy. At follow-up, there were no significant differences between patients who had hamartia and those who lacked this finding. Hamartia were observed in all subtypes of HS and there was a significant difference found in subtype distribution as well as proportion of cases between subtypes, but no association with any specific subtype overall. The presence of hamartia was not associated with the coexistence of focal cortical dysplasia or any specific histologic pattern of dysplasia. Hamartia are a common concomitant finding in HS and indicates evidence of aberrant cell migration in the hippocampal and parahippocampal regions in these patients.

Selective lesion of the hippocampus increases the differentiation of immature neurons in the monkey amygdala

A large population of immature neurons is present in the ventromedial portion of the adult primate amygdala, a region that receives substantial direct projections from the hippocampal formation. Here, we show the effects of neonatal (n = 8) and adult (n = 6) hippocampal lesions on the populations of mature and immature neurons in the paralaminar, lateral, and basal nuclei of the adult monkey amygdala. Compared with unoperated controls (n = 7), the number of mature neurons was about 70% higher in the paralaminar nucleus of neonate- and adult-lesioned monkeys, and 40% higher in the lateral and basal nuclei of neonate-lesioned monkeys. The number of immature neurons in the paralaminar nucleus was 40% higher in neonate-lesioned monkeys and 30% lower in adult-lesioned monkeys. Similar changes in neuron numbers were also found in two monkeys with nonexperimental, selective, bilateral hippocampal damage. These changes in neuron numbers following hippocampal lesions appear to reflect the differentiation of immature neurons present in the paralaminar nucleus. After adult lesions, the differentiation of immature neurons was essentially restricted to the paralaminar nucleus and was associated with a decrease in the population of immature neurons. In contrast, after neonatal lesions, the differentiation of immature neurons involved the paralaminar, lateral, and basal nuclei. It was associated with an increase in the population of immature neurons in the paralaminar nucleus. Such lesion-induced neuronal plasticity sheds new light on potential mechanisms that may facilitate functional recovery following focal brain injury.

Maternal deprivation alters expression of neural maturation gene tbr1 in the amygdala paralaminar nucleus in infant female macaques

Early parental loss is associated with social-emotional dysregulation and amygdala physiologic changes. Previously, we examined whole amygdala gene expression in infant monkeys exposed to early maternal deprivation. Here, we focus on an amygdala region with immature neurons at birth: the paralaminar nucleus (PL). We hypothesized that 1) the normal infant PL is enriched in a subset of neural maturation (NM) genes compared to a nearby amygdala subregion; and 2) maternal deprivation would downregulate expression of NM transcripts (mRNA). mRNAs for bcl2, doublecortin, neuroD1, and tbr1-genes expressed in post-mitotic neurons-were enriched in the normal PL. Maternal deprivation at either 1 week or 1 month of age resulted in PL-specific downregulation of tbr1-a transcription factor necessary for directing neuroblasts to a glutamatergic phenotype. tbr1 expression also correlated with typical social behaviors. We conclude that maternal deprivation influences glutamatergic neuronal development in the PL, possibly influencing circuits mediating social learning.

Hippocampal asymmetry and sudden unexpected death in infancy: a case report

The differential diagnosis of known entities associated with sudden unexpected death in infancy is ever expanding. Here we report the case of a 10-month-old infant boy whose clinical presentation mimicked that of the sudden infant death syndrome (SIDS). This presentation included the typical features of SIDS: sleep-related death; prone position upon discovery; and minor illness within 2 days of death. Nevertheless, neuropathologic examination revealed striking hippocampal asymmetry and microdysgenesis similar to that reported previously by us in toddlers with sleep-related sudden death. Hippocampal maldevelopment in the setting of sudden death in infants and toddlers is analogous to sudden unexpected death in epilepsy associated with temporal lobe pathology, and suggests a possible role for seizures in the terminal events leading to sudden death. This report serves to alert pediatric and forensic pathologists to hippocampal asymmetry and microdysgenesis in the differential diagnosis of sudden infant death mimicking SIDS.

Postnatal development of the amygdala: A stereological study in macaque monkeys

Abnormal development of the amygdala has been linked to several neurodevelopmental disorders, including schizophrenia and autism. However, the postnatal development of the amygdala is not easily explored at the cellular level in humans. Here we performed a stereological analysis of the macaque monkey amygdala in order to characterize the cellular changes underlying its normal structural development in primates. The lateral, basal, and accessory basal nuclei exhibited the same developmental pattern, with a large increase in volume between birth and 3 months of age, followed by slower growth continuing beyond 1 year of age. In contrast, the medial nucleus was near adult size at birth. At birth, the volume of the central nucleus was half of the adult value; this nucleus exhibited significant growth even after 1 year of age. Neither neuronal soma size, nor neuron or astrocyte numbers changed during postnatal development. In contrast, oligodendrocyte numbers increased substantially, in parallel with an increase in amygdala volume, after 3 months of age. At birth, the paralaminar nucleus contained a large pool of immature neurons that gradually developed into mature neurons, leading to a late increase in the volume of this nucleus. Our findings revealed that distinct amygdala nuclei exhibit different developmental profiles and that the amygdala is not fully mature for some time postnatally. We identified different periods during which pathogenic factors might lead to the abnormal development of distinct amygdala circuits, which may contribute to different human neurodevelopmental disorders associated with alterations of amygdala structure and functions.

Revisiting the hippocampal-amygdala pathway in primates: association with immature-appearing neurons

Elucidation of the 'fear circuit' has opened exciting avenues for understanding and treating human anxiety disorders. However, the translation of rodent to human studies, and vice versa, depends on understanding the homology in relevant circuits across species. Although abundant evidence indicates that the hippocampal-amygdala circuit mediates contextual fear learning, previous studies indicate that this pathway is more restricted in primates than in rodents. Moreover, cellular components of the amygdala differ across species. The paralaminar nucleus (PL) of the amygdala, a structure that is closely associated with the basal nucleus, is one example, having no clear homologue in rodents. In both human and nonhuman primates, the PL contains a subpopulation of immature-appearing neurons, which merge into the corticoamygdaloid transition area (CTA). To understand whether immature-appearing neurons are positioned to participate in fear circuitry, we first mapped the hippocampal-amygdala projection in the monkey. We then determined whether immature-appearing neurons were targets of this path. Retrograde results show that the hippocampal inputs to the amygdala originate in uncal region (CA1') and the rostral prosubiculum, consistent with earlier studies. The amygdalohippocampal area, ventral basal nucleus, the medial paralaminar nucleus, and its confluence with the CTA are the main targets of this projection. Immature neurons are prominent in the PL and CTA, and are overlapped by anterogradely labeled fibers from CA1', particularly in the medial PL and CTA. Hippocampal inputs to the amygdala are more focused in higher primates compared to rodents, supporting previous anatomic studies and recent data from human functional imaging studies of contextual fear. At the cellular level, a hippocampal interaction with immature neurons in the amygdala suggests a novel substrate for cellular plasticity, with implications for mechanisms underlying contextual learning and emotional memory processes.

Stereological analysis of neuron, glial and endothelial cell numbers in the human amygdaloid complex

Cell number alterations in the amygdaloid complex (AC) might coincide with neurological and psychiatric pathologies with anxiety imbalances as well as with changes in brain functionality during aging. This stereological study focused on estimating, in samples from 7 control individuals aged 20 to 75 years old, the number and density of neurons, glia and endothelial cells in the entire AC and in its 5 nuclear groups (including the basolateral (BL), corticomedial and central groups), 5 nuclei and 13 nuclear subdivisions. The volume and total cell number in these territories were determined on Nissl-stained sections with the Cavalieri principle and the optical fractionator. The AC mean volume was 956 mm³ and mean cell numbers (x10⁶) were: 15.3 neurons, 60 glial cells and 16.8 endothelial cells. The numbers of endothelial cells and neurons were similar in each AC region and were one fourth the number of glial cells. Analysis of the influence of the individuals’ age at death on volume, cell number and density in each of these 24 AC regions suggested that aging does not affect regional size or the amount of glial cells, but that neuron and endothelial cell numbers respectively tended to decrease and increase in territories such as AC or BL. These accurate stereological measures of volume and total cell numbers and densities in the AC of control individuals could serve as appropriate reference values to evaluate subtle alterations in this structure in pathological conditions.

Where and what is the paralaminar nucleus? A review on a unique and frequently overlooked area of the primate amygdala

The primate amygdala is composed of multiple subnuclei that play distinct roles in amygdala function. While some nuclei have been areas of focused investigation, others remain virtually unknown. One of the more obscure regions of the amygdala is the paralaminar nucleus (PL). The PL in humans and non-human primates is relatively expanded compared to lower species. Long considered to be part of the basal nucleus, the PL has several interesting features that make it unique. These features include a dense concentration of small cells, high concentrations of receptors for corticotropin releasing hormone and benzodiazepines, and dense innervation of serotonergic fibers. More recently, high concentrations of immature-appearing cells have been noted in the primate PL, suggesting special mechanisms of neural plasticity. Following a brief overview of amygdala structure and function, this review will provide an introduction to the history, embryology, anatomical connectivity, immunohistochemical and cytoarchitectural properties of the PL. Our conclusion is that the PL is a unique subregion of the amygdala that may yield important clues about the normal growth and function of the amygdala, particularly in higher species.

Brain tumors in adults with medically intractable epilepsy

Much of the literature on tumors arising in the setting of chronic epilepsy focuses on children. This study reviewed 1 institution's 141-patient experience with tumors in adults arising in this clinical setting. The majority of tumors (71.6%) arose in the temporal lobe. The most common tumor types encountered included ganglioglioma (n = 38), low-grade fibrillary astrocytoma (n = 24), and low-grade oligodendroglioma (n = 22). Coexistent focal cortical dysplasia (type IA) was identified in 15 cases (10.6%). The largest group of tumors in adults were World Health Organization (WHO) grade II neoplasms compared with WHO grade I tumors in children. Gangliogliomas are the most commonly encountered neoplasms. Coexistent focal cortical dysplasia may be observed in a significant minority of tumors, suggesting a possible developmental origin for some of these neoplasms.

A developmental neurobiological model of motivated behavior: anatomy, connectivity and ontogeny of the triadic nodes

Adolescence is the transition period that prepares individuals for fulfilling their role as adults. Most conspicuous in this transition period is the peak level of risk-taking behaviors that characterize adolescent motivated behavior. Significant neural remodeling contributes to this change. This review focuses on the functional neuroanatomy underlying motivated behavior, and how ontogenic changes can explain the typical behavioral patterns in adolescence. To help model these changes and provide testable hypotheses, a neural systems-based theory is presented. In short, the Triadic Model proposes that motivated behavior is governed by a carefully orchestrated articulation among three systems, approach, avoidance and regulatory. These three systems map to distinct, but overlapping, neural circuits, whose representatives are the striatum, the amygdala and the medial prefrontal cortex. Each of these system-representatives will be described from a functional anatomy perspective that includes a review of their connectivity and what is known of their ontogenic changes.

Class III beta-tubulin is constitutively coexpressed with glial fibrillary acidic protein and nestin in midgestational human fetal astrocytes: implications for phenotypic identity

Class III beta-tubulin isotype (betaIII-tubulin) is widely regarded as a neuronal marker in developmental neurobiology and stem cell research. To test the specificity of this marker protein, we determined its expression and distribution in primary cultures of glial fibrillary acidic protein (GFAP)-expressing astrocytes isolated from the cerebral hemispheres of 2 human fetuses at 18 to 20 weeks of gestation. Cells were maintained as monolayer cultures for 1 to 21 days without differentiation induction. By immunofluorescence microscopy, coexpression of betaIII-tubulin and GFAP was detected in cells at all time points but in spatially distinct patterns. The numbers of GFAP+ cells gradually decreased from Days 1 to 21 in vitro, whereas betaIII-tubulin immunoreactivity was present in 100% of cells at all time points. beta-III-tubulin mRNA and protein expression were demonstrated in cultured cells by reverse-transcriptase-polymerase chain reaction and immunoblotting, respectively. Glial fibrillary acidic protein+/beta-III-tubulin-positive cells coexpressed nestin and vimentin but lacked neurofilament proteins, CD133, and glutamate-aspartate transporter. Weak cytoplasmic staining was detected with antibodies against microtubule-associated protein 2 isoforms. Confocal microscopy, performed on autopsy brain samples of human fetuses at 16 to 20 gestational weeks, revealed widespread colocalization of GFAP and betaIII-tubulin in cells of the ventricular/subventricular zones and the cortical plate. Our results indicate that in the midgestational human brain, betaIII-tubulin is not neuron specific because it is constitutively expressed in GFAP+/nestin+ presumptive fetal astrocytes.

Sudden death in toddlers associated with developmental abnormalities of the hippocampus: a report of five cases

Sudden unexplained death in childhood (SUDC) is the sudden death of a child older than 1 year of age that remains unexplained after review of the clinical history, circumstances of death, and autopsy with appropriate ancillary testing. We report here 5 cases of SUDC in toddlers that we believe define a new entity associated with hippocampal anomalies at autopsy. All of the toddlers died unexpectedly during the night, apparently during sleep. Within 48 hours before death, 2 toddlers had fever, 3 had a minor upper respiratory tract infection, and 3 experienced minor head trauma. There was a history of febrile seizures in 2 (40%) and a family history of febrile seizures in 2 (40%). Hippocampal findings included external asymmetry and 2 or more microdysgenetic features. The incidence of certain microdysgenetic features was substantially increased in the temporal lobes of these 5 cases compared with the temporal lobes of 39 (control) toddlers with the causes of death established at autopsy (P < 0.01). We propose that these 5 cases define a potential subset of SUDC whose sudden death is caused by an unwitnessed seizure arising during sleep in the anomalous hippocampus and producing cardiopulmonary arrest. Precipitating factors may be fever, infection, and/or minor head trauma. Suggested risk factors are a history of febrile seizures and/or a family history of febrile seizures. Future studies are needed to confirm these initial findings and to define the putative links between sudden death, hippocampal anomalies, and febrile seizures in toddlers.

Distribution of serotonin transporter labeled fibers in amygdaloid subregions: implications for mood disorders

BACKGROUND

The serotonin transporter 5-HTT mediates responses to serotonin reuptake inhibitors (SSRIs), a mainstay treatment in mood disorders. The amygdala, a key emotional processing center, has functional abnormalities in mood disorders, which resolve following successful SSRI treatment. To better understand the effects of SSRIs in mood disorders, we examined the distribution of 5-HTT labeled fibers relative to specific nuclear groups in the amygdala.

METHODS

Immunocytochemical techniques were used to chart 5-HTT labeled fibers in the amygdala in coronal sections through the brain of six adult Macaques. Nissl staining was used to define nuclear groups in the amygdala.

RESULTS

The serotonin transporter 5-HTT is distributed heterogeneously in the primate amygdala, with the lateral subdivision of the central nucleus, intercalated cell islands, amygdalohippocampal area, and the paralaminar nucleus showing the heaviest concentrations.

CONCLUSIONS

5HTT-labeled fibers are very densely concentrated in output regions of the amygdala. High concentrations of 5-HTT-positive fibers in the central nucleus indicate that tight regulation of serotonin is critical in modulating fear responses mediated by this nucleus. High concentrations of 5-HTT-labeled fibers in the intercalated islands and parvicellular basal nucleus/paralaminar nucleus, which contain immature -appearing neurons, suggest a potential trophic role for serotonin in these subregions.

Expression of Bcl-2 and Bax protein in normal pineal gland in children and young adult

The Bcl family contains both pro and antiapoptotic proteins participating in the regulation of neuronal cell death in several pathological conditions. However, very little is known about physiological profiles of Bcl-2/Bax expression in normal brain. In this study, we examined expression profile of Bcl-2 and Bax proteins in normal pineal gland in children. The material for analysis was obtained by biopsy of pineal parenchyma during surgery of pineal cysts. All specimens were labeled immunohistochemically and analyzed by means of confocal laser scanning microscope. We found only few Bcl-2 expressing (0.7%) and no Bax-immunopositive (0.0%) pinealocytes. Bcl-2-positive cells were mature neurons, neither young ones nor glia.

Losing neurons: selective vulnerability and mesial temporal sclerosis

Mesial temporal sclerosis (MTS) is found in about two-thirds of patients with refractory temporal lobe epilepsy (TLE), and surgical removal of the sclerotic structures eliminates seizures in the majority of cases undergoing surgical resection. Although multiple factors have been implicated in the genesis of MTS, it is still unclear why some individuals are more likely to develop hippocampal sclerosis than others. Epileptologists have proposed that there must be at least two factors involved-an initial precipitating injury (IPI), such as a prolonged febrile seizure, CNS infection, or head trauma, and a second factor that increases vulnerability to neuronal injury. This has been termed the "two-hit hypothesis." Three of the many factors that could possibly heighten susceptibility to neuronal injury and MTS are discussed here. These are microdysgenesis, hippocampal dysgenesis, prior seizures, and genetic predisposition. We conclude that there is currently no compelling evidence to support a role for microdysgenesis in MTS. Hippocampal dysgenesis, on the other hand, may account for febrile seizures and possibly MTS in a small subpopulation of patients with TLE. Additional larger studies are needed to confirm these findings. Experimental evidence indicates that an epileptogenic hippocampus can result from prolonged febrile seizures in infant rats, even though these seizures do not cause MTS in the rat. It is not known if this pathophysiological sequence occurs in humans. Lastly, there appears to be a strong genetic component that predisposes some individuals to MTS, regardless of whether they experience an IPI.

Bcl-2 immunoreactive neurons are differentially distributed in subregions of the amygdala and hippocampus of the adult macaque

The amygdala and hippocampus are key limbic structures of the temporal lobe, and are implicated in the pathology of mood disorders. Bcl-2, an intracellular protein, has recently been identified in the primate amygdala and hippocampus, and is now recognized as an intracellular target of mood stabilizing drugs. However, there are few data on the cellular phenotypes of bcl-2-expressing cells, or their distribution in specific subregions of the amygdala and hippocampus. We used a number of histochemical markers to define specific subregions of the primate amygdala and hippocampus, and examined phenotype-specific distributions of bcl-2 immunoreactive cells within each subregion. Immature-appearing bcl-2 labeled neurons, which co-contain class III beta-tubulin immunoreactivity, are found in distinct subregions in each structure. In the amygdala, bcl-2 positive neurons with an immature morphology are densely distributed in the paralaminar nucleus and intercalated cell islands, the parvicellular basal nucleus, and the ventral periamygdaloid cortex and amygdalohippocampal area. In the hippocampus, immature-appearing bcl-2-labeled cells are confined to the polymorph layer (subgranular zone), and base of the granule cell layer in the dentate gyrus. Well-differentiated neurons also express bcl-2. In the amygdala, labeled cells with mature phenotypes are concentrated in the parvicellular basal nucleus, the accessory basal nucleus, and the periamygdaloid cortex. The medial nucleus and central extended amygdala also contain many well-differentiated bcl-2 positive cells. In the hippocampus, the dentate gyrus and Ammon's horn contain many bcl-2 immunoreactive nonpyramidal cells. These are preferentially distributed in the rostral hippocampus. CA3 and CA2 contain relatively higher concentrations of bcl-2-labeled cells than CA1 and the subiculum. Bcl-2 is thus important in intrinsic circuitry of the hippocampus, and in amygdaloid subregions modulated by the hippocampus. In addition, the extended amygdala, a key amygdaloid output, is richly endowed with bcl-2 positive cells. This distribution suggests a role for bcl-2 in circuits mediating emotional learning and memory which may be targets of mood stabilizing drugs.

Class III beta-tubulin isotype: a key cytoskeletal protein at the crossroads of developmental neurobiology and tumor neuropathology

The expression of the cytoskeletal protein class III beta-tubulin isotype is reviewed in the context of human central nervous system development and neoplasia. Compared to systemic organs and tissues, class III beta-tubulin is abundant in the brain, where it is prominently expressed during fetal and postnatal development. As exemplified in cerebellar neurogenesis, the distribution of class III beta-tubulin is neuron associated, exhibiting different temporospatial gradients in the neuronal progeny of the external granule layer versus the neuroepithelial germinal matrix of the velum medullare. However, transient expression of this protein is also present in the telencephalic subventricular zones comprising putative neuronal and/or glial precursor cells. This temporospatially restricted, potentially non-neuronal expression of class III beta-tubulin may have implications in the accurate identification of presumptive neurons derived from transplanted embryonic stem cells. In the adult central nervous system, the distribution of class III beta-tubulin is almost exclusively neuron specific. Altered patterns of expression are noted in brain tumors. In "embryonal"-type neuronal/neuroblastic tumors of the central nervous system, such as the medulloblastomas, class III beta-tubulin expression is associated with neuronal differentiation and decreased cell proliferation. In contrast, the expression of class III beta-tubulin in gliomas is associated with an ascending grade of histologic malignancy and with correspondingly high proliferative indices. Thus, class III beta-tubulin expression in neuronal or neuroblastic tumors is differentiation dependent, whereas in glial tumors, it is aberrant and/or represents "dedifferentiation" associated with the acquisition of glial progenitor-like phenotype(s). From a diagnostic perspective, the detection of class III beta-tubulin immunostaining in neoplastic cells should not be construed as categorical evidence of divergent neuronal differentiation in tumors, which are otherwise phenotypically glial. Because class III beta-tubulin is present in neoplastic but not in normal differentiated glial cells, the elucidation of molecular mechanisms responsible for the altered expression of this isotype may provide critical insights into the dynamics of the microtubule cytoskeleton in the growth and progression of gliomas.

Microdysgenesis in mesial temporal lobe epilepsy: A clinicopathological study

The interrelationship of mesial temporal lobe epilepsy (MTLE), hippocampal sclerosis, and febrile convulsions still remains an enigma. Additional microscopical cortical dysplasia or microdysgenesis has been suggested as pre-existent susceptibility factor rendering the affected brain vulnerable to the development of MTLE after initial precipitating injuries such as febrile convulsions. Twenty-four MTLE cases with histopathologically definite hippocampal sclerosis were examined for clearly defined features of microdysgenesis and further signs of neocortical dysplasia. Although unequivocal signs of dysplasia were absent, 29.2% of cases showed cortical neuronal clustering, 25.0% showed perivascular clustering, and 20.8% showed increased white matter neurons. The features of microdysgenesis studied here were not linked with each other and were not related to initial precipitating injuries, positive family history, or any other clinical parameter. Their suggested fundamental role as dysplastic factor within development of hippocampal sclerosis and MTLE is not confirmed.

Ammon's horn sclerosis: a maldevelopmental disorder associated with temporal lobe epilepsy

Ammon's horn sclerosis (AHS) is the major neuropathological substrate in patients with temporal lobe epilepsy (TLE). Histopathological hallmarks include segmental loss of pyramidal neurons, granule cell dispersion and reactive gliosis. Pathogenetic mechanisms underlying this distinct hippocampal pathology have not yet been identified and it remains to be resolved whether AHS represents the cause or the consequence of chronic seizure activity and pharmacoresistant TLE. Whereas the clinical history indicates an early onset in most patients, ie, occurrence of febrile seizures at a young age, surgical treatment is usually carried out at an end stage of the disease. It has, therefore, been difficult to analyse the sequential development of hippocampal pathology in TLE patients. Recent molecular neuropathological studies focusing on developmental aspects of hippocampal organization revealed 2 intriguing findings in AHS specimens: i) The persistence of Cajal-Retzius cells in AHS patients points towards an early insult and an altered Reelin signaling pathway and ii) increased neurogenesis in and abnormal architectural organization of the dentate granule cell layer can be observed in young patients with early hippocampal seizure onset. These findings would be compatible with a model that involves a neurodevelopmental component in the formation of AHS. Its association with a lowered seizure threshold and an increased susceptibility for segmental cell loss in the hippocampus during the long course of the disease may constitute additional elements in a pathogenic cascade.

Cortical dysgenesis and epilepsy

Cortical dysgenesis (CD) describes a wide spectrum of brain anomalies that involve abnormal development of the cerebral cortex. There is a strong association between CD and epilepsy, and it comprises a significant proportion of children and adults whose epilepsy cannot be controlled with medications. There has been intense effort to define the relationship between CD and epilepsy so that more effective therapies can be devised. These efforts have ranged from detailed study of people with CD and epilepsy from a clinical standpoint to single-cell analysis of mRNA expression and postsynaptic receptor function. Animal models have also been developed to mimic certain aspects of CD in a situation when quantitative, controlled, and interventional experiments can be performed that would not be possible in a clinical setting. This review will give an overview of human CD syndromes and their causes, when possible, and describe some specific abnormalities in dysplastic cortex that may underlie its epileptogenic potential. It will also review several animal models of CD that have been studied mechanistically from the standpoint of epileptogenesis. In conclusion, some general trends will be proposed based on human and animal studies to encapsulate our current understanding of CD and how it causes epilepsy.

Localization of the neuronal class III beta-tubulin in oligodendrogliomas: comparison with Ki-67 proliferative index and 1p/19q status

The class III beta-tubulin isotype (betaIII) is widely regarded as a neuronal marker in development and neoplasia. Whereas the expression of betaIII in neuronal/neuroblastic tumors is differentiation-dependent, the aberrant expression of this cytoskeletal protein in astrocytomas is associated with an ascending gradient of malignancy. To test the generality of this observation we have compared the immunoreactivity (IR) profiles of the betaIII isotype with the Ki-67 nuclear antigen proliferative index in 41 archival, surgically excised oligodendrogliomas (32 classical [WHO grade II] and 9 anaplastic [WHO grade III]). Seventeen of 41 tumors were examined by quantitative microsatellite analysis for loss of 1p and/or 19q. Minimal deletion regions were defined on 1p (D1S468, D1S214) and 19q (D19S408, D19S867). Three of 10 classical oligodendrogliomas had combined 1p/19q loss, while 2 exhibited loss of either 1p or 19q. Three of 7 anaplastic tumors had combined 1p/19q loss. BetaIII IR was present in all tumors, but was significantly greater in the anaplastic (median labeling index [MLI] 61%, interquartile range [IQR] 55%-64%) as compared with the classical variants (MLI, 19%, IQR, 11-36%) (p < 0.0001). A highly significant relationship was found to exist between betaIII and Ki-67 LIs (betaIII, p < 0.0001 and Ki-67, p < 0.0001. r = 0.809). BetaIII localization delineated hitherto understated unipolar or bipolar tumor phenotypes with growth cones and leading cell processes resembling migrating oligodendrocyte progenitor cells. Codistribution of betaIII and GFAP IR was present in "gliofibrillary" tumor areas. Synaptophysin IR was detected in rare tumor cells (mean LI, 0.7%), and only in 4/41 samples (10%), denoting a lack of relationship between betaIII and synaptophysin expression. No significant differences in betaIII LIs were observed in tumors with 1p and/or 19q loss as compared to those with 1p/19q intact status. Increased betaIII IR in oligodendrogliomas is associated with an ascending degree of malignancy and thus is a potentially useful tumor marker. However, the significance of high betaIII LIs in low-grade oligodendrogliomas with respect to prognostic and predictive value requires further evaluation. Class III beta-tubulin expression in oligodendrogliomas should not be construed as a priori evidence of divergent neuronal differentiation.