John C. Hedreen

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part II. Standardization of the neuropathologic assessment of Alzheimer's disease

The Neuropathology Task Force of the Consortium to Establish a Registry for Alzheimers Disease (CERAD) has developed a practical and standardized neuropathology protocol for the postmortem assessment of dementia and control subjects. The protocol provides neuropathologic definitions of such terms as “definite Alzheimers disease” (AD), “probable AD,” “possible AD,” and “normal brain” to indicate levels of diagnostic certainty, reduce subjective interpretation, and assure common language. To pretest the protocol, neuropathologists from 15 participating centers entered information on autopsy brains from 142 demented patients clinically diagnosed as probable AD and on eight nondemented patients. Eighty-four percent of the dementia cases fulfilled CERAD neuropathologic criteria for definite AD. As increasingly large numbers of prospectively studied dementia and control subjects are autopsied, the CERAD neuropathology protocol will help to refine diagnostic criteria, assess overlapping pathology, and lead to a better understanding of early subclinical changes of AD and normal aging.

Widespread expression of Huntington's disease gene (IT15) protein product

Huntingtons Disease (HD) is caused by expansion of a CAG repeat within a putative open reading frame of a recently identified gene, IT15. We have examined the expression of the genes protein product using antibodies developed against the N-terminus and an internal epitope. Both antisera recognize a 350 kDa protein, the predicted size, indicating that the CAG repeat is translated into polyglutamine. The HD protein product is widely expressed, most highly in neurons in the brain. There is no enrichment in the striatum, the site of greatest pathology in HD. Within neurons, the protein is diminished in nuclei and mitochondria and is present in the soluble cytoplasmic compartment, as well as loosely associated with membranes or cytoskeleton, in cell bodies, dendrites, and axons. It is concentrated in nerve terminals, including terminals within the caudate and putamen. Thus, the normal HD gene product may be involved in common intracellular functions, and possibly in regulation of nerve terminal function. The product of the expanded allele is expressed, consistent with a gain of function mechanism for HD at the protein level.

A modified histochemical technique to visualize acetylcholinesterase-containing axons

An improved histochemical method for light microscopic demonstration of acetylcholinesterase (AChE) has been developed. Axonal, dendritic, and perikaryal staining are well delineated, both in areas of low AChE content, such as cerebral cortex, and in areas of high AChE content, such as neostriatum. Axonal staining, including arborizations, stands out against a clear background devoid of diffuse reaction product.

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part X. Neuropathology Confirmation of the Clinical Diagnosis of Alzheimer's Disease

Article abstract-This report summarizes the neuropathologic findings in the first 106 autopsies of CERAD (Consortium to Establish a Registry for Alzheimers Disease) dementia patients diagnosed clinically as having Alzheimers disease (AD). In 92 (87%) of the 106 cases, neuropathologists confirmed Alzheimers disease (AD) as the primary dementing illness. Coexistent Parkinsons disease (PD) changes were present in 19 (21%) and vascular lesions of varying nature and size in 26 (28%) of these 92 AD cases. The 14 cases in which AD was not interpreted as the primary dementing illness can be divided into four major subgroups based on their neuropathology findings: PD and related pathology (n = 5), hippocampal sclerosis (n = 3), miscellaneous neurodegenerative and other disorders (n = 3), and no significant changes (n = 3). Despite the relatively high level of clinical diagnostic accuracy, further refinement of assessment batteries may facilitate distinction of non-AD dementias from AD. NEUROLOGY 1995;45: 461-466

Early Loss of Neostriatal Striosome Neurons in Huntington's Disease

During the first years of symptomatic Huntingtons disease (HD), no readily apparent pathology is seen in the neostriatum at autopsy. To investigate the pathological correlates of chorea and other early clinical signs, we examined the evolution of neuronal loss and accompanying astrocytosis in neostriatal tissue from autopsy cases of early HD. We found scattered islands of astrocytosis and neuronal loss that were present before the previously described ventrally progressive wave of generalized neuronal loss. Histological demonstration of these islands, which are apparently specific to HD, is very helpful in the pathological differential diagnosis of this disease. Immunocytochemical stains for glial fibrillary acidic protein and for markers of the neostriatal striosome-matrix system showed that these islands correspond to the striosome compartment. Striosomal neuronal loss was present throughout the dorsoventral extent of the caudate nucleus and putamen during the early phase of symptomatic disease, and this loss extended to the most ventral region of the nucleus accumbens in later stages. Analysis of the functional circuitry of the basal ganglia suggests that early degeneration of striosomal neurons may produce hyperactivity of the nigrostriatal dopaminergic pathway, causing chorea and other early clinical manifestations of HD.

Huntington's disease gene (IT15) is widely expressed in human and rat tissues

Huntingtons Disease (HD) is notable for selective neuronal vulnerability in the basal ganglia and cerebral cortex. We have investigated in human and rodent tissues the expression of the gene (IT15) whose mutation causes HD. IT15 is widely expressed, with highest levels of expression in brain, but also in lung, testis, ovary, and other tissues. Within the brain, expression is widespread with a neuronal pattern and is not enriched in the basal ganglia. Expression of IT15 is not reduced in the brain of HD patients when corrected for actin (though it is slightly decreased in the striatum when uncorrected, consistent with neuronal loss). Thus, the widespread distribution of IT15 expression does not correspond with the restricted distribution of neuropathologic changes in HD. We suggest that pathophysiology may relate to abnormal cell type-specific protein interactions of the HD protein.

Neuronal loss in layers V and VI of cerebral cortex in Huntington's disease.

Neuronal loss in the cerebral cortex in Huntingtons disease (HD) has not been well documented, nor has its laminar pattern been definitively established. We therefore counted neurons in individual cortical laminae in the dorsal frontal cortex of 5 HD and 5 control autopsy brains. Significant neuronal loss (to 57% of control, P = 0.002) was found in layer VI of HD brains. These cells project principally to the thalamus, the claustrum and other regions of cerebral cortex; thus their loss is unlikely to be the result of retrograde degeneration secondary to striatal pathology. Layer V neurons were also decreased (to 71% of control, P = 0.034). Degeneration of cerebral cortical neurons may be at least partly responsible for some of the non-choreic symptoms of HD, such as dementia, irritability, apathy, and depression.

Parkinson's disease: Loss of ineurons from the ventral tegmental area contralateral to therapeutic surgical lesions

Decreased numbers of pigmented neurons of the dopaminer-gic nigrostriatal system are the most striking pathology in the brains of individuals with Parkinsons disease (PD), but it is clear that neurons in the locus ceruleus, vagal nuclei, and nucleus basalis of Meynert are also affected in this disease. Because neurochemical evidence suggested that the mesolimbic dopaminergic system originating in the ventral tegmental area (VTA) may also be involved, the present study was designed to evaluate the mesolimbic dopamine system in PD by counting pigmented neurons in the VTA contralateral to therapeutic lesions placed in the basal ganglia or thalamus. In PD, VTA neurons were depleted to 36 to 55% of control values. Moreover, the VTA showed excessive free pigment, a marker for death of pigmented neurons. These changes may be important in disorders of movement or mentation occurring in PD.

Topography of the Magnocellular Basal Forebrain System in Human Brain

In primates, the large neurons in the nucleus basalis of Meynert (nbM), nucleus of the diagonal band of Broca (dbB), and medial septum are part of a cholinergic system with direct projections to amygdala, hippocampus, and cortex. Recent evidence indicates that neurons of this system selectively degenerate in individuals with Alzheimers disease (AD) and suggests that degeneration of these cells contributes to the loss of presynaptic cortical cholingergic markers which occurs in these patients. The present report describes the topographical distribution of these large, intensely basophilic, basal forebrain neurons in human brain. Rostrally, neurons of this magnocellular system are present in the medial septum and the dorsal and ventral parts of the nucleus of the dbB. The largest number occur in the nbM, which is situated in the substantia innominata below the globus pallidus. Caudally, large nbM-type neurons are found along the ventral and lateral edges of the globus pallidus. Neurons of this type are also encountered in the white matter below the putamen and nucleus accumbens, at the edges of the anterior commissure, in the white matter laminae of the globus pallidus and within and at the medial edge of the genu of the interal capsule. Directions for dissection of this system in human brain are given in an Appendix.

Neuronal degeneration in rat brain induced by 6-hydroxydopamine; a histological and biochemical study

Abstract 6-OHDA injected into the cerebrospinal fluid of the rat causes a fall in brain NE and DA levels, accompanied by degeneration of neuronal perikarya in SN and in adjacent VTA and lateral tegmentum, and terminal degeneration in CP, NAcc and OT demonstrable by the Nauta-Gygax and Fink-Heimer silver methods. NE levels fell to 5% of normal 14 days after a high dose (200 μg + 400 μg) of 6-OHDA, and DA levels to 17%. Even the more moderate declines in catecholamine levels following 200 μg 6-OHDA were accompanied by florid argyrophilic neuronal degeneration. The location of the terminal degeneration is very similar to that of DA-containing terminals identified by use of the histofluorescence method for monoamines. The location of degenerating cell bodies in SN closely corresponds to that of perikarya found by the histofluorescence method to contain dopamine, but the distribution in tegmentum and VTA is more restricted. Occasional cell bodies were seen to degenerate in the locus coeruleus and a few other areas after high doses of 6-OHDA. A group of degenerating axons of unusual appearance was found, probably afferent to NAcc and OT. No degeneration was seen in areas in which NE-containing terminals have been reported, despite reports of electron microscopic evidence of bouton degeneration in such areas elicited by 6-OHDA, and despite the severe decline in brain NE content in the higher-dose group. Nor was any change seen in the infundibular nucleus and median eminence, regions in which DA-containing neurons have been reported. Electrolytic SN lesions cause dense terminal degeneration in CP indistinguishable from that caused by 6-OHDA injection into the CSF. Only sparse terminal degeneration appeared in CP if electrolytic SN lesions were placed in rats that had received 6-OHDA several weeks prior to surgery. Large SN lesions in such pretreated animals induce a tendency to turn in circles away from the lesioned side.