Constance J. D'Amato

Dementia of the Alzheimer's Type: Changes in Hippocampal L‐[3H]Glutamate Binding

Abstract: Glutamate or a related excitatory amino acid is thought to be the major excitatory neurotransmitter of hippocampal afferents, intrinsic neurons, and efferents. We have used an autoradiographic technique to investigate the status of excitatory amino acid receptors in the hippocampal formation of patients dying with dementia of the Alzheimer type (DAT). We examined l‐[3H]glutamate binding to sections from the hippocampal formation of six patients dying of DAT and six patients without DAT and found marked reductions in total [3H]glutamate binding in all regions of hippocampus and adjacent parahippocampal cortex in DAT brains as compared to controls. When subtypes of excitatory amino acid receptors were assayed, it was found that binding to the N‐methyl‐d‐aspartate (NMDA)‐sensitive receptor was reduced by 75–87%, with the greatest loss found in stratum moleculare and stratum pyramidale of CA1. Binding to quisqualate (QA)‐sensitive receptors was reduced by 45–69%. There were smaller reductions (21–46%) in GABAA receptors in DAT cases. Muscarinic cholinergic receptors assayed in adjacent sections of hippocampal formation were unchanged in DAT. Benzodiazepine receptors were reduced significantly only in parahippocampal cortex by 44%. These results suggest that glutamatergic neurotransmission within the hippocampal formation is likely to be severely impaired in Alzheimers disease. Such impairment may account for some of the cognitive decline and memory deficits that characterize DAT.

Widespread Alterations of α-Synuclein in Multiple System Atrophy

Glial cytoplasmic inclusions (GCI) are the hallmark of multiple system atrophy (MSA), a rare movement disorder frequently associated with autonomic dysfunction. In this study of 21 cases of MSA, GCI were consistently immunoreactive for α-synuclein and double-immunostained for ubiquitin and oligodendroglial markers, but not glial fibrillary acidic protein. No statistically significant difference was found in the density of GCI in various brain regions in the two forms of MSA, striatonigral degeneration (SND) and olivopontocerebellar atrophy (OPCA). Postmortem brain samples from 9 cases of MSA were fractionated according to solubility in buffer, Triton-X 100, sodium dodecyl sulfate (SDS), and formic acid, and α-synuclein immunoreactivity was measured in Western blots. Total α-synuclein immunoreactivity was increased in MSA compared to controls, with no statistically significant difference between SND and OPCA. Most of the increase was due to α-synuclein in SDS fractions. In controls this fraction had little or no immunoreactivity. In 7 cases and 4 controls correlations were investigated between quantitative neuropathology and biochemical properties of α-synuclein. Surprisingly, the amount of SDS-soluble α-synuclein correlated poorly with the number of GCI in adjacent sections. Furthermore, areas with few or no GCI unexpectedly had abundant SDS-soluble α-synuclein. These findings provide evidence that modifications of α-synuclein in MSA may be more widespread than obvious histopathology. Moreover, these alterations may constitute a biochemical signature for the synucleinopathies.

Fluoro-deoxyglucose positron emission tomography in diffuse Lewy body disease

We report six demented individuals with pathologically verified diffuse Lewy body disease (DLBD) studied with fluoro-deoxyglucose positron emission tomography (FDG-PET). Three subjects had pure DLBD and three subjects had combined DLBD and Alzheimers disease (DLBD-AD) pathology. FDG-PET revealed evidence of diffuse cerebral hypometabolism in both pure DLBD and DLBD-AD with marked declines in association cortices with relative sparing of subcortical structures and primary somatomotor cortex, a pattern reported previously in AD. Unlike AD, however, these subjects also had hypometabolism in the occipital association cortex and primary visual cortex. These findings indicate the presence of diffuse cortical abnormalities in DLBD and suggest that FDG-PET may be useful in discriminating DLBD from AD antemortem. NEUROLOGY 1996;47: 462-466

Motor-sensory and visual behavior after hemispherectomy in newborn and mature rats

Abstract Immature mammals are widely believed to compensate functionally for nervous system alterations better than adults with comparable disorders. Embryos restitute huge losses, but plasticity, remodeling, or use of alternate mechanisms said to underly compensation in injured infants are not understood. Toward understanding these, the effects of ablating or altering parts of the nervous system in infant and mature rats are being studied. In these experiments one lateral half of the forebrain and diencephalon was largely removed at birth or maturity and the consequences to nervous system structure and motor-sensory and visual behavior were observed. Similarities between animals operated on as adults or infants were loss of tactile placing opposite the ablation, ability to discriminate visual patterns, and gauge variable jumping distances visually. Some subjects performed the visual tasks using the eye opposite the hemispherectomy alone, which was exclusively supplied with uncrossed retinogeniculate fibers. Differences were: loss of tactile placing after operation in infants was delayed until the seventeenth day; stride was impaired in animals operated on as adults but was spared in infant subjects; with appropriate ablations, Fink-Heimer-Nauta stains showed that after hemispherectomy, infants, but not adults, developed a small, uncrossed corticospinal tract. The stride component in locomotion seemed dependent on the corticospinal tract system, and was partially dissociated from the placing reaction essential for locomotion on rough terrain. The possibility was considered that the small remodeled corticospinal tract spared the stride component.

Locating corticospinal neurons by retrograde axonal transport of horseradish peroxidase

Abstract Different views of the location and organization of corticospinal (CS) neurons in the rat have resulted from fiber degeneration studies, electrophysiologically derived somatotopic maps, studies of CS axonal branching, and functional alterations after ablation of parts of the motor-sensory cortex. To locate more precisely CS neurons that projected to different levels of the spinal cord, and to determine whether or not they were arranged somatotopically, we labeled them with horseradish peroxidase (HRP) from their cut spinal axons. These labeled neurons were arranged in a major caudal band about 4.5 mm long and 3 mm wide corresponding principally to areas 3, 4, and 6, and a minor rostral band in the anterior part of area 10. The caudal band also corresponded to electrophysiologically derived somatotopic hindlimb and forelimb motor areas. The most significant finding was that CS neurons labeled from the lumbar spinal cord and from cervical levels were intermixed generally throughout the caudal band, showing virtually no somatotopic anatomic arrangement. The rostral band, which corresponded to mouth parts in somatotopic maps, was an unexpected finding. Calculations based on estimates of the numbers of CS axons at different cord levels indicated that about 10,000 CS neurons in each cortex projected as far as the rostral cervical cord, and about 2000 continued as far as lumbar levels. The HRP method as used was capable of labeling a majority of the calculated numbers of CS neurons, but showed a large variance in the total numbers of neurons labeled. The distributions of the neurons within the domains of the bands was consistent regardless of the numbers labeled.

Loss of hippocampal (3H)TCP binding in Alzheimer's disease

We have previously demonstrated a marked loss in N-methyl-D-aspartate (NMDA) receptors in the hippocampus and cerebral cortex of patients dying with dementia of the Alzheimer type (DAT). In addition, we have found that the dissociative anesthetic N-(1-[2-thienyl]cyclohexyl)3,4-piperidine ([3H]TCP) binds to a site whose regional distribution is highly correlated with that of NMDA receptor sites. We studied the binding of [3H]TCP to sections of hippocampi from 8 controls, 12 patients with DAT and 7 patients with other dementias. [3H]TCP binding was significantly reduced in strata pyramidalia of CA1/CA2, CA3 and subiculum of DAT hippocampal formation compared to that of control. Labelled dissociative anesthetics could potentially be used with positron emission tomography in the diagnosis of DAT.

Normal development and post-traumatic plasticity of corticospinal neurons in rats

Abstract Corticospinal (CS) neurons projecting to the spinal cord in the adult rat, identified by retrograde axonal transport of horseradish peroxidase (HRP), formed a caudal band in areas 3, 4, and 6 and a rostral band in area 10, separated by a gap. In the infant the gap was filled with CS neurons. The problem: What happened to the transient infant neurons as the mantle expanded, and would they persist if other CS neurons were destroyed in infancy? Identification of CS neurons by HRP and measurements of the growth of the mantle and cortical areas 3, 4, and 6 showed that CS neurons were scattered widely in the cortex as well as in the gap and future bands at 2 to 10 days. By about 2 weeks, CS neurons labeled from the cervical cord were limited to the “adult” bands. The greatest mantle expansion postnatally was in the occipital and bregma regions, including the anterior, but not the posterior, part of area 3, 4, and 6. Thus, expansion of the mantle, growth of areas 3, 4, and 6, and axonal growth of transient and permanent CS neurons did not parallel each other closely. When one or both caudal band regions were ablated at 5, 7, or 10 days, the gap CS neurons persisted bilaterally to adult life. No necrosis of layer V neurons was observed between 10 days and 2 weeks. It was assumed that the gap neurons and other extraneous CS neurons generated exploratory axons which normally disappeared, but when caudal band neurons were destroyed the transient axons attempted to fill the pathway.

Stable β-Secretase Activity and Presynaptic Cholinergic Markers During Progressive Central Nervous System Amyloidogenesis in Tg2576 Mice

We examined presynaptic cholinergic markers and beta-secretase activity during progressive central nervous system amyloidogenesis in Tg2576 Alzheimer mice (transgenic for human amyloid precursor protein Swedish mutation; hAPPswe). At 14, 18, and 23 months of age there were no significant differences between wild-type and transgenic mice in four distinct central nervous system cholinergic indices--choline acetyltransferase and acetylcholinesterase activities, and binding to vesicular acetylcholine transporter and Na(+)-dependent high-affinity choline uptake sites. A novel enzyme-linked immunosorbent assay measuring only the secreted human beta-secretase cleavage product (APPsbetaswe) of APPswe also revealed no change with aging in Tg2576 mouse brain. In contrast, transgenic but not wild-type mice exhibited an age-dependent increase in soluble Abeta40 and Abeta42 levels and progressive amyloid deposition in brain. Thus, aging Tg2576 mice exhibited presynaptic cholinergic integrity despite progressively increased soluble Abeta40 and Abeta42 levels and amyloid plaque density in brain. Older Tg2576 mice may best resemble preclinical or early stages of human Alzheimers disease with preserved presynaptic cholinergic innervation. Homeostatic APPsbetaswe levels with aging suggest that progressive amyloid deposition in brain results not from increased beta-secretase cleavage of APP but from impaired Abeta/amyloid clearance mechanisms.

EFFECTS OF LOW LEVELS OF IONIZING RADIATION ON THE DEVELOPING CEREBRAL CORTEX OF THE RAT

THE EFFECTS of low levels of radiation on mammalian development have been little studied in contrast to those following exposures to hundreds of roentgensl-5 whose mechanisms are beginning to be understood.F-ll Various recent reports have made low-level irradiation a matter of interest, and sometimes concern, and they raise questions about mechanisms of action, especially persistent and delayed effects. For example, the incidence of certain skeletal anomalies in a strain of mice disposed to develop them sporadically was increased by exposing them to as little as 25 R during stages of embryonic life when the body axis and early skeleton was being established.12 When mice were exposed to fast neutrons continuously from the time they were conceived until they were adults, at a rate of a little less than 1 rad daily, their growth was impaired and their lifespans shortened more than if the irradiation was begun in adolescence.l3 Children exposed to diagnostic X-rays-even a few roentgenswhen they were fetuses showed a slightly but significantly increased incidence of childhood cancer.14 Retarded development of normal conditioned reflexes, and persistent difficulty in retaining these reflexes, was described in rats exposed to 1 R daily for twenty days during intrauterine life.lG Abnormalities of development at both the cytologic and cytoarchitectural level in the cortex and cerebellum of rats that had been exposed to 20 to 40 R during fetal or newborn stages were reported recently.16 In some of these, there is the problem of whether the consequences were secondary to acute brief injury, analogous to some of the

Low Dose Radiation of the Developing Brain

X-irradiation administered in single doses of 10 to 40 r has a widespread effect on the developing rat brain. It first diminishes the formation of cytoplasmic basophilic material in the nerve cells and inhibits their growth. Single doses of 20 to 40 r cause permanent alterations of individual nerve cells, and interfere with their organization into neuronal assemblies, such as layers of the cerebral cortex.