Developmental malformations in Huntington disease: neuropathologic evidence of focal neuronal migration defects in a subset of adult brains.

Neuropathologic hallmarks of Huntington Disease (HD) include the progressive neurodegeneration of the striatum and the presence of Huntingtin (HTT) aggregates that result from abnormal polyQ expansion of the HTT gene. Whether the pathogenic trinucleotide repeat expansion of the HTT gene causes neurodevelopmental abnormalities has garnered attention in both murine and human studies; however, documentation of discrete malformations in autopsy brains of HD individuals has yet to be described. We retrospectively searched the New York Brain Bank (discovery cohort) and an independent cohort (validation cohort) to determine whether developmental malformations are more frequently detected in HD versus non-HD brains and to document their neuropathologic features. One-hundred and thirty HD and 1600 non-HD whole brains were included in the discovery cohort and 720 HD and 1989 non-HD half brains were assessed in the validation cohort. Cases with developmental malformations were found at 6.4-8.2 times greater frequency in HD than in non-HD brains (discovery cohort: OR 8.68, 95% CI 3.48-21.63, P=4.8 × 10-5; validation cohort: OR 6.50, 95% CI 1.83-23.17, P=0.0050). Periventricular nodular heterotopias (PNH) were the most frequent malformations and contained HTT and p62 aggregates analogous to the cortex, whereas cortical malformations with immature neuronal populations did not harbor such inclusions. HD individuals with malformations had heterozygous HTT CAG expansions between 40 and 52 repeats, were more frequently women, and all were asymmetric and focal, aside from one midline hypothalamic hamartoma. Using two independent brain bank cohorts, this large neuropathologic series demonstrates an increased occurrence of developmental malformations in HD brains. Since pathogenic HTT gene expansion is associated with genomic instability, one possible explanation is that neuronal precursors are more susceptible to somatic mutation of genes involved in cortical migration. Our findings further support emerging evidence that pathogenic trinucleotide repeat expansions of the HTT gene may impact neurodevelopment.

Bone morphogenetic proteins promote astroglial lineage commitment by mammalian subventricular zone progenitor cells.

The epigenetic signals that regulate lineage development in the embryonic mammalian brain are poorly understood. Here we demonstrate that a specific subclass of the transforming growth factor beta superfamily, the bone morphogenetic proteins (BMPs), cause the selective, dose-dependent elaboration of the astroglial lineage from murine embryonic subventricular zone (SVZ) multipotent progenitor cells. The astroglial inductive effect is characterized by enhanced morphological complexity and expression of glial fibrillary acidic protein, with concurrent suppression of neuronal and oligodendroglial cell fates. SVZ progenitor cells express transcripts for the appropriate BMP-specific type I and II receptor subunits and selective BMP ligands, suggesting the presence of paracrine or autocrine developmental signaling pathways (or both). These observations suggest that the BMPs have a selective role in determining the cell fate of SVZ multipotent progenitor cells or their more developmentally restricted progeny.

Mechanisms underlying neural cell death in neurodegenerative diseases: alterations of a developmentally-mediated cellular rheostat.

Genes associated with neurodegenerative diseases are normally expressed throughout neural development and are essential for the elaboration and maintenance of neuronal subpopulations. Disease-causing mutations can compromise defined subsets of these neural specification events in subtle ways that initially lead to impairments in the cellular homeostasis of evolving regional neuronal subpopulations, and adult-onset cell death from normally non-lethal environmental stressors. Neurodegenerative diseases may, therefore, represent an emerging class of developmental disorders characterized by novel biological responses to subthreshold neurodevelopmental abnormalities that impair targeted neuronal biosynthetic pathways without causing obvious developmental deficits. This developmental model of pathogenesis predicts that it will soon be possible to identify these dysfunctional pathways prior to the occurrence of irreversible cellular injury, and to successfully intervene using innovative neuroprotective and neural regenerative strategies.

Hematolymphopoietic and inflammatory cytokines in neural development.

It is now clear that cytokines traditionally viewed as immune modulators participate in inflammatory responses within the adult nervous system. However, in the developing nervous system hematolymphopoietic cytokines also play a role unrelated to neural-immune interactions. Instead, many of these factors subserve primary regulatory functions related both to the morphogenesis and to the cellular maturation of the central and peripheral nervous systems. This article focuses specifically on cytokine actions in neural development.

Bone morphogenetic proteins in the nervous system.

Bone morphogenetic proteins (BMPs) are a rapidly expanding subclass of the transforming growth factor superfamily. BMP ligands and receptor subunits are present throughout neural development within discrete regions of the embryonic brain and within neural crest-derived pre- and post-migratory zones. BMPs initially inhibit the formation of neuroectoderm during gastrulation while, within the neural tube, they act as gradient morphogens to promote the differentiation of dorsal cell types and intermediate cell types throughout co-operative signaling. In the peripheral nervous system, BMPs act as instructive signals for neuronal lineage commitment and promote graded stages of neuronal differentiation. By contrast, within the CNS, these same factors promote astroglial lineage elaboration from embryonic subventricular zone progenitor cells, with concurrent suppression of the neuronal or oligodendroglial lineages, or both. In addition, BMPs act on more lineage-restricted embryonic CNS progenitor cells to promote regional neuronal survival and cellular differentiation. Furthermore, these versatile cytokines induce selective apoptosis of discrete rhombencephalic neural crest-associated cellular populations. These observations suggest that the BMPs exhibit a broad range of cellular and context-specific effects during multiple stages of neural development.

Developmental mechanisms in the pathogenesis of neurodegenerative diseases.

Cellular genes that are mutated in neurodegenerative diseases code for proteins that are expressed throughout neural development. Genetic analysis suggests that these genes are essential for a broad range of normal neurodevelopmental processes. The proteins they code for interact with numerous other cellular proteins that are components of signaling pathways involved in patterning of the neural tube and in regional specification of neuronal subtypes. Further, pathogenetic mutations of these genes can cause progressive, sublethal alterations in the cellular homeostasis of evolving regional neuronal subpopulations, culminating in late-onset cell death. Therefore, as a consequence of the disease mutations, targeted cell populations may retain molecular traces of abnormal interactions with disease-associated proteins by exhibiting changes in a spectrum of normal cellular functions and enhanced vulnerability to a host of environmental stressors. These observations suggest that the normal functions of these disease-associated proteins are to ensure the fidelity and integration of developmental events associated with the progressive elaboration of neuronal subtypes as well as the maintenance of mature neuronal populations during adult life. The ability to identify alterations within vulnerable neuronal precursors present in pre-symptomatic individuals prior to the onset of irrevocable cellular injury may help foster the development of effective therapeutic interventions using evolving pharmacologic, gene and stem cell technologies.

Multiple roles of bone morphogenetic protein signaling in the regulation of cortical cell number and phenotype.

Members of the bone morphogenetic protein (BMP) family have been implicated in multiple aspects of neural development in both the CNS and peripheral nervous system. BMP ligands and receptors, as well as the BMP antagonist noggin, are expressed in the developing cerebral cortex, making the BMPs likely candidates for regulating cortical development. To define the role of these factors in the developing cerebral cortex, we examined the effects of BMP2 and BMP4 on cortical cells in vitro. Cells were cultured from embryonic day 13 (E13) and E16 rat cerebral cortex in the absence or presence of different concentrations of fibroblast growth factor 2, a known regulator of cortical cell proliferation and differentiation. At E13, the BMPs promoted cell death and inhibited proliferation of cortical ventricular zone cells, resulting in the generation of fewer neurons and no glia. At E16, the effects of the BMPs were more complex. Concentrations of BMP2 in the range of 1-10 ng/ml promoted neuronal and astroglial differentiation and inhibited oligodendroglial differentiation, whereas 100 ng/ml BMP2 promoted cell death and inhibited proliferation. Addition of the BMP antagonist noggin promoted oligodendrogliogenesis in vitro, demonstrating that endogenous BMP signaling influences the differentiation of cortical cells in vitro. The distribution of BMP2 and noggin within the developing cortex suggests that local concentrations of ligands and antagonists define gradients of BMP signaling during corticogenesis. Together, these results support the hypothesis that the BMPs and their antagonist noggin co-regulate cortical cell fate and morphogenesis.

Functional properties of channels formed by the neuronal gap junction protein connexin36.

The expression and functional properties of connexin36 (Cx36) were examined in two communication-deficient cell lines (N2A-neuroblastoma and PC-12 cells) transfected with Cx36 and in hippocampal neurons that express the connexin endogenously. Transfected cells expressed the expected 2.9 kb Cx36 transcript and Cx36 immunoreactivity, whereas nontransfected cells were devoid of Cx36. The relationship between steady-state junctional conductance (g(j)) and transjunctional voltage was well described by a two-state Boltzmann equation. The half-inactivation voltage (V(0)), the ratio of minimal to maximal g(j) (g(min)/g(max)), and the equivalent gating charge were +/- 75 mV, 0.55, and 1.75, respectively, indicating that Cx36 exhibits very low voltage sensitivity. Conductance of single Cx36 channels measured with patch pipettes containing 130 mM CsCl was 10-15 pS (n = 15 cell pairs); despite this low unitary conductance, Cx36 channels were permeable to the dye Lucifer yellow. Hippocampal neurons expressed Cx36 both in vivo and in culture. The electrophysiological properties of channels in cultured hippocampal neurons were similar to those of the channels expressed by the transfected cell lines, and the neuronal channels were similarly permeable to Lucifer yellow. The unique combination of weak voltage sensitivity, small unitary conductance, and permeation by anions as large as second messenger molecules endows Cx36 gap junction channels with properties well suited for mediating flexible electrical and biochemical interactions between neurons.

Reversible rostral basilar artery syndrome.

We prospectively studied 34 patients with clinical and radiologic evidence of rostral basilar artery syndrome, a vaso-occlusive disorder, who had uniformly excellent short-term functional recovery, in marked contrast to the classic syndrome. All patients displayed important neurobehavioral disturbances, including an acute confusional state, necessitating medical consultation. The composite group had minimal hypertension, significant arrhythmias in the young, and no history of vertebrobasilar insufficiency. Unsuspected cases of idiopathic orthostatic hypotension, as well as cardiac arrhythmias in the elderly, were discovered. A vascular cause was not considered in 79% of those presenting for emergency evaluation and prevented proper acute diagnostic evaluation in 88%. Recognition of this potentially reversible cerebrovascular syndrome may prevent hazardous diagnostic and therapeutic interventions.

Postnatal cerebral cortical multipotent progenitors: regulatory mechanisms and potential role in the development of novel neural regenerative strategies.

In the developing postnatal cerebral cortex, protracted generation of glia and neurons occurs and precise matching of local cell types is needed for the functional organization of regional microdomains characteristic of complex CNS tissues. Recent studies have suggested that multipotent progenitors play an important role in neural lineage elaboration during neurogenesis and gliogenesis after migration from paramedian generative zones. The presence of a separate reservoir of cerebral cortical multipotent cells under strict local environmental regulation would provide an appropriate mechanism for terminal developmental sculpting and for reconstitution of regional cellular pools after injury. We have isolated distinct pools of EGF- and bFGF-responsive multipotent progenitors from the postnatal mammalian cerebral cortex independent of the subventricular zone. These progenitor populations are under tight environmental regulation by specific hierarchies of cytokine subclasses that program the progressive elaboration of intermediate lineage-restricted progenitors and differentiated type I and II astrocytes, myelinating oligodendrocytes and neuronal subtypes that express specific neuromodulatory proteins. Neural lineage development from these cortical multipotent progenitors is a graded developmental process involving sequential induction of specific cytokine receptors, acquisition of factor responsiveness and complex lineage interdependence. The cortical multipotent progenitor pathways program the elaboration of neural lineage species with distinct cellular response properties when compared with analogous species derived from subventricular zone progenitors, indicating that the cortical multipotent cells contribute to the establishment of lineage diversity within the developing cortical cortex. In addition, the cortical multipotent cells generate dynamic intermediate progenitor pools that utilize temporally-coded environmental cues to alter neural fate decisions. These cumulative observations suggest that postnatal cerebral cortical multipotent cells represent a novel set of progenitor pathways necessary for normal mammalian cortical maturation, and may have important implications for our understanding of a wide variety of neuropathological conditions and for the development of more effective regenerative strategies to combat these pervasive neurological disorders.

The neuro-ophthalmologic spectrum of the rostral basilar artery syndrome.

A broad range of neuro-ophthalmologic signs occurs with the rostral basilar artery syndrome (RBAS) and transient ischemia or infarction of the midbrain, thalamus, hypothalamus, paramedian diencephalon, and posterior temporal and occipital lobes. The pattern of affected neuroanatomic regions results in diverse patterns of interrelated functional disabilities in the areas of vertical gaze, nystagmus, oculomotor function, pupillary reactivity, visual fields, color vision, and visual illusions. With increasing recognition of more clinically benign forms of RBAS, it has become apparent that the vascular syndrome is often improperly diagnosed and may be associated with remediable occult medical disorders. To facilitate the acquisition of accurate diagnostic and therapeutic information, neuro-ophthalmologic signs were prospectively assessed in 61 patients with RBAS. The clinicoanatomic correlates of these diverse ocular manifestations are presented.

Late-onset acid maltase deficiency. Detection of patients and heterozygotes by urinary enzyme assay.

Daily urinary excretion of acid maltase (12.78 +/- 2.10 units/24 hr/mg of creatinine, in 11 normal adults) was significantly decreased in ten patients with late-onset acid maltase deficiency (1.33 +/- 0.16 units/24 hr; P less than .001) and 11 heterozygotes (3.27 +/- 0.62 units/24 hr; P less than .001). Maximal inhibition of urinary acid maltase activity by antibodies against human placental enzyme was 53% in controls, 30% in heterozygotes, and virtually absent in patients. Investigation of pH curves and enzyme inhibition by antibodies confirmed the presence in the kidney of an immunologically distinct "extra" maltase enzyme active at acid pH. Whether acid maltase in normal urine originates in the kidney or cells of the lower urinary tract, the enzyme defect seems to be expressed in these cells in late-onset acid maltase deficiency.

Progenitor cell biology: implications for neural regeneration.

A few brief years ago, damage to the central nervous system was generally perceived to be irreparable, and loss of neurons was largely viewed as an irreversible process. However, major advances in the study of neural progenitor cells have altered these perceptions, and rational approaches to the repair of the damaged nervous system using transplanted progenitor cells now seem feasible. This review will discuss the basic biology of neural progenitor cells, the mechanisms regulating the generation of neurons and glia from these cells, and the techniques that are available for preparing such cells for transplantation into the nervous system. The potential uses for these cells in treating neurologic disease will then be reviewed, and the theoretical and technical problems that may be encountered will be discussed.

Atypical psychosis with disseminated subpial demyelination.

A 34-year-old woman experienced three episodes of an atypical psychosis, characterized by confusion, agitation, delusional thinking, paranoid ideation, and auditory hallucinations, during the 14 months prior to her death. Findings of gross examination of the brain and spinal cord were unremarkable. Histologic examination revealed scattered subpial foci of demyelination throughout the brain stem, with involvement of the hippocampal formation bilaterally. Although occasional active lesions at early stages of development were noted, most lesions were gliotic and therefore quiescent. This case and one similar example of disseminated subpial demyelination found in the literature probably represent an unusual variant of multiple sclerosis.

Residual acid maltase activity in late-onset acid maltase deficiency.

Residual acid maltase activity was found by a sensitive fluorometric assay in muscle biopsies from 15 patients with late-onset acid maltase deficiency (mean, 6.91 percent; range, 2.4 to 12.2) but not in biopsy or autopsy muscle from three patients with the infantile form. Electrophoresis, kinetic characteristics, and subcellular fractionation indicated that the residual activity was lysosomal acid maltase and not a contaminating isozyme of neutral maltase. There was no correlation between the amount of residual acid maltase activity and the severity of the clinical picture or glycogen accumulation. The presence of acid maltase activity in muscle, liver, and, to a greater extent, leukocytes in late-onset but not infantile acid maltase deficiency and the failure of the two disease forms to occur in the same family suggest that they are genetically distinct.

The rostral basilar artery syndrome: diagnosis, etiology, prognosis.

Vascular occlusive disease of the rostral basilar artery (RBAS) causes a myriad of clinical signs and symptoms reflecting rostral brainstem-diencephalic and posterior hemispheric dysfunction. To help define the clinical profile, we prospectively studied 61 patients with clinical/neuroimaging evidence of RBAS during a 7-year period. Fourteen patients mirrored classic descriptions: severe visual, oculomotor and behavioral signs without prominent motoric dysfunction, uniformly poor prognosis, and intimate association with hypertension and prior episodes of vertebrobasilar ischemia (VBI). In contrast, 47 individuals had a reversible syndrome with excellent short-term functional recoveries, and were distinguished by a lower frequency and severity of hypertension, a greater incidence of arrhythmias in the young, and no history of VBI. All patients had important neurobehavioral abnormalities including an invariable acute confusional state. Diagnosis required the integrated assessment of neurobehavioral, ophthalmologic, and imaging tests. The clinical syndrome is more common and etiologically diverse than previously reported and is frequently unrecognized in the young and elderly who present with acute confusion.

Reduced somatostatin-like immunoreactivity in cerebral cortex in nonfamilial dysphasic dementia.

A nonfamilial syndrome is described in two middle-aged men who presented with progressive aphasia without incipient signs of cognitive impairment. In each case, 2 years elapsed before progressive functional decline or behavioral disabilities supervened. Radiologic studies documented asymmetric left cerebral atrophy that was progressive. The structure of the language disintegration was distinctive and not like that in Alzheimer's disease. Pathologic studies performed at postmortem examination of one patient documented asymmetric cerebral atrophy with nonspecific histopathologic changes. Biochemical studies revealed normal tissue levels of choline acetyltransferase activity, but reduced somatostatin-like immunoreactivity. Since cerebral somatostatin is largely present in intrinsic cortical neurons, while cholinergic innervation is largely derived from the basal forebrain, these findings suggest that nonfamilial dysphasic dementia may be an example of a distinct class of dementia due to intrinsic cortical degeneration, with sparing of the basal forebrain.

Primary medullary hypertensive hemorrhage.

A 33-year-old man with untreated hypertension had sudden onset of signs and symptoms suggestive of a dorsal lateral medullary syndrome. He died after 27 days. Postmortem studies revealed intramedullary hemorrhage with extension into the fourth ventricle and hypertensive cardiovascular disease.

Hemispatial and directional performance biases in motor neglect.

Motivationally responsive motor deficits may occur in isolation or as part of more general neglect syndromes. We describe three patients with two discrete syndromes of isolated motor neglect, differentiated primarily by their performance in motor tasks enacted within or toward the contralesional hemispace. The lesions in our patients likely disrupted attentional interactions with two separable sensorimotor processing subsystems. Physiologic data support the existence of a parietal-lateral premotor circuit that processes information encoded in spatial coordinates referenced to the extrapersonal environment and of a basal ganglionic-mesial premotor circuit that processes information mostly encoded in egocentric skeletomotor coordinates. The correlation of ischemic lesions resulting in hemispatial and directional biases in motor neglect with disruption of known physiologic subsystems may provide the basis for rational cognitive rehabilitation of these higher-order motor deficits. These observations are supported by recent PET studies that document the presence of specific attentional-motoric interactions within discrete processing components of a distributed sensorimotor attentional network.

Clinico-pathologic studies in dementia: nondemented subjects with pathologically confirmed Alzheimer's disease.

We compared neuropsychological findings in 28 longitudinally evaluated elderly subjects with their postmortem neuropathology, including senile plaque and neurofibrillary tangle counts from standardized sections. Nine of the subjects were not demented when evaluated just prior to their death. Numerous cortical senile plaques and other changes of Alzheimer's disease (AD) occurred in six of nine nondemented old-old subjects. Five of these six subjects had shown decline on yearly neuropsychological tests but their cognitive impairment was too mild to meet clinical criteria for dementia. Whereas cortical senile plaque count did not distinguish well between demented and nondemented subjects, every subject with numerous cortical neurofibrillary tangles was demented. The nondemented subjects with Alzheimer pathology may have had "preclinical" AD, or numerous cortical plaques may occur in some elderly subjects who would never develop clinical dementia.